Material mixture for a fiber optic measuring system for temperature measurement, fiber optic measuring system for temperature measurement, and methods for temperature measurement using the fiber optic measuring system

Abstract

The present invention relates to a material mixture for an optical fiber measurement system for temperature measurement. The material mixture comprises at least one thermoresponsive polymer, at least one viscosity enhancer, and at least one solvent, wherein the at least one solvent is selected from the group consisting of water, methanol, ethanol, propanol, butanol, butyl acetate, chloroform, ionic liquids, and mixtures thereof. The at least one viscosity enhancer is at least one polymer soluble in the at least one solvent, which has a number-average molar mass M w of at least 200 kg / mol. In addition, the present invention relates to an optical fiber measurement system for temperature measurement and a method for temperature measurement using the optical fiber measurement system.

Description

[0001] The present invention relates to a substance mixture for a fiber-optic measuring system for temperature measurement. The substance mixture comprises at least one thermoresponsive polymer, at least one viscosity increaser, and at least one solvent, wherein the at least one solvent is selected from the group consisting of water, methanol, ethanol, propanol, butanol, butyl acetate, chloroform, ionic liquids, and mixtures thereof. The at least one viscosity increaser is at least one polymer soluble in the at least one solvent and having a mass-average molar mass M w of at least 200 kg / mol. Furthermore, the present invention relates to a fiber optic measuring system for temperature measurement and a method for temperature measurement using the fiber optic measuring system.

[0002] Thermoresponsive polymer solutions, such as those described in DE 10 2015 100 097 A1, are suitable as a measuring medium for fiber optic measuring systems or sensors for temperature measurement because they exhibit temperature-dependent turbidity within a temperature range dependent on the polymer structure, polymer concentration, solvent, and several other parameters. This results in the optical transmission values ​​of the mixture and the temperature being proportional to each other. However, this temperature-dependent turbidity, on which the measuring principle is based, does not remain constant over time because the separated polymer phase forms macroscopic aggregates over time, which then precipitate. This significantly limits their practical usability.

[0003] Due to this limitation, other measurement principles for fiber optic temperature sensors have been preferred so far, but these have certain disadvantages, as described below. Phaser-Bragg-Grating:

[0004] One variant uses a fiber Bragg grating (FBG) as the sensor element. This FBG is permanently embedded in an optical fiber. Light in a narrow wavelength range is reflected by this grating, with the center wavelength being referred to as the Bragg wavelength and representing the actual measured value. With a length of a few millimeters, the FBG can be regarded as a point sensor. The Bragg wavelength is temperature-dependent, thus the FBG can be used as a temperature sensor. The sensitive element is relatively expensive due to the manufacturing process. Since a spectral measurement is usually performed, the measuring device also represents a significant cost factor. With precise – but expensive – measuring devices, a high spectral resolution of up to 1 pm is achieved. With a temperature sensitivity of the FBG of approximately 10 pm / K, a resolution of 0.1 K can be achieved.The disadvantage, besides the cost, is their increased weight and larger size compared to simpler FBG measuring devices. More compact, lighter, and less expensive measuring devices are available, but these devices have significantly lower resolution. GaAs element:

[0005] Fiber optic temperature sensors are also used, which use a GaAs semiconductor as a temperature-sensitive element. The semiconductor element is attached to the end of an optical fiber and serves as a point sensor at this point. The GaAs semiconductor has a temperature-dependent band edge (GaAs becomes transparent from approximately 850 nm). A change in temperature results in a shift that is usually recorded spectrally. With semiconductor-based fiber optic temperature sensors, the measurement uncertainty is approximately ± 0.2 K, which is greater than with sensors based on thermoresponsive polymer solutions. Another disadvantage is the high cost. The measuring device usually records the optical spectrum, which requires relatively expensive measurement technology. Furthermore, the use of an optical spectrometer results in a relatively large measuring device. Fluorescence:

[0006] In another variant, fluorescent material is applied to the end of an optical fiber. With this point sensor, the material is excited by light, and the decay time of the fluorescent material is measured. This decay time depends on the temperature, and the optical signal is recorded with time resolution. The measurement system equipped with a fluorescent sensor element provides a cost-effective measurement technology due to the simple measurement method. However, the disadvantage is the relatively large measurement uncertainty of approximately ± 0.5 K. DTS:

[0007] In addition to the point sensors mentioned above, the fiber itself can also be used as a temperature-sensitive element. By exploiting Raman scattering in an optical fiber, temperature measurements can be performed along the entire fiber length. Raman spectroscopy captures Raman scattering with spatial resolution, enabling distributed temperature measurements along the optical fiber. Currently available Raman measurement technology is expensive and requires very large and correspondingly heavy devices. Furthermore, Raman sensors achieve a spatial resolution of approximately 1 m, which is unsuitable for targeted temperature measurements in many cases. Furthermore, the measurement uncertainty is ± 0.5 K, which also often does not meet requirements.

[0008] Based on this, it was the object of the present invention to provide a substance mixture containing at least one thermoresponsive polymer and at least one solvent, which has improved stability.

[0009] This object is solved with respect to a substance mixture having the features of claim 1, with respect to an optical fiber measuring system having the features of claim 10, and with respect to a method for temperature measurement having the features of claim 14. The respective dependent patent claims represent advantageous developments.

[0010] According to the invention, a substance mixture for a fiber-optic measuring system for temperature measurement (or for a fiber-optic temperature sensor) is thus specified, which mixture comprises at least one thermoresponsive polymer, at least one viscosity increaser, and at least one solvent. The at least one solvent is selected from the group consisting of water, methanol, ethanol, propanol, preferably n-propanol, butanol, preferably n-butanol, butyl acetate, preferably n-butyl acetate, chloroform (CHCl 3 ), ionic liquids and mixtures thereof. According to the invention, the at least one viscosity increaser is at least one polymer which is soluble in the at least one solvent (and different from the at least one thermoresponsive polymer) and which has a mass-average molar mass M w of at least 200 kg / mol. The mass-average molar mass M w can be determined, for example, using gel permeation chromatography (GPC).

[0011] The substance mixture according to the invention can also be referred to as a thermoresponsive mixture or as a thermoresponsive polymer solution.

[0012] Thermoresponsive polymers are polymers whose physical properties, such as solubility, change with temperature. Due to the presence of at least one thermoresponsive polymer, the mixture exhibits temperature-dependent turbidity and can thus, in principle, be used for a fiber optic temperature measurement system.

[0013] Within the scope of the present invention, it was surprisingly found that certain solvent-containing thermoresponsive polymer solutions, ie mixtures of substances comprising at least one thermoresponsive polymer and at least one specific solvent, can be stabilized by increasing the viscosity of the solution by adding at least one viscosity increaser in the form of at least one polymer having a mass-average molecular weight M wof at least 200 kg / mol. In this case, the at least one viscosity increaser prevents or at least significantly reduces any continuation of the aggregate formation or even precipitation of the separated polymer phase. As a consequence, the turbidity of the solution remains constant over a long period of time at a constant temperature, thus ensuring the possibility of reliable measurement not only in short time intervals, but also over a longer period of time. Consequently, the substance mixture according to the invention has improved stability. It is therefore better suited for fiber-optic temperature measurement than previous substance mixtures without viscosity increasers. In particular, the substance mixture according to the invention thus enables precise and inexpensive fiber-optic temperature measurement with high reliability even over long periods of time.

[0014] The at least one viscosity increaser is at least one polymer which is soluble in the at least one solvent and which has a mass-average molecular weight M wof at least 200 kg / mol. This at least one polymer (acting as a viscosity increaser) can be regarded as soluble in the at least one solvent if it can be dissolved essentially completely in the at least one solvent at a temperature of 20 °C, preferably at any temperature in the temperature range from 5 °C to 60 °C, particularly preferably regardless of the temperature (i.e. at any temperature at which the at least one solvent is liquid), with a concentration of (at least) 1 g / l (i.e. 1 g of the at least one polymer in 1 liter of the at least one solvent). “Essentially completely” can be understood to mean that at least 95% by weight, preferably at least 97% by weight, particularly preferably at least 99% by weight, very particularly preferably at least 99.5% by weight, of the at least one polymer (based on the total weight of the at least one polymer) dissolves in the at least one solvent.

[0015] The at least one viscosity increaser may also be referred to as at least one thickener.

[0016] Preferably, the at least one solvent is selected from the group consisting of water, methanol, ethanol, propanol, preferably n-propanol, butanol, preferably n-butanol, butyl acetate, preferably n-butyl acetate, chloroform, ionic liquids, mixtures of chloroform and methanol, mixtures of (different) ionic liquids, and mixtures of water and methanol, wherein preferably the ionic liquids each comprise or consist of at least one cation and at least one anion (or are constituted thereof), - wherein the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphosphonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or - the at least one anion is selected from the group consisting of bis(trifluoromethanesulfone)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof.

[0017] Particularly preferably, the at least one solvent is water, at least one ionic liquid or a mixture of water and at least one ionic liquid, wherein preferably the at least one ionic liquid comprises or consists of at least one cation and at least one anion (or is constituted thereof), - wherein the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphosphonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or - the at least one anion is selected from the group consisting of bis(trifluoromethanesulfone)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof.

[0018] The chemical composition of the substance mixture according to the invention can be determined, for example, by means of NMR spectroscopy and / or IR spectroscopy, optionally with additional use of GPC (gel permeation chromatography) and HPLC (high performance liquid chromatography), if possible coupled with MS (mass spectrometry).

[0019] A preferred embodiment of the substance mixture according to the invention is characterized in that the mass-average molecular weight M w of the at least one polymer soluble in at least one solvent - at least 300 kg / mol, preferably at least 400 kg / mol, particularly preferably at least 500 kg / mol, very particularly preferably at least 600 kg / mol, in particular at least 700 kg / mol, for example at least 800 kg / mol, and / or - at most 20,000 kg / mol, preferably at most 6,000 kg / mol, particularly preferably at most 3,000 kg / mol, very particularly preferably at most 2,000 kg / mol, in particular at most 1,500 kg / mol, for example at most 1,000 kg / mol.

[0020] The mass-average molar mass M w can be determined, for example, using gel permeation chromatography (GPC).

[0021] According to a further preferred embodiment of the substance mixture according to the invention, the number-average molar mass M w of the at least one polymer soluble in the at least one solvent is in the range from 200 kg / mol to 20000 kg / mol, preferably from 300 kg / mol to 6000 kg / mol, particularly preferably from 500 kg / mol to 3000 kg / mol, very particularly preferably from 700 kg / mol to 2200 kg / mol, in particular from 800 kg / mol to 1800 kg / mol, for example from 900 kg / mol to 1500 kg / mol. The number-average molar mass M w can be determined, for example, by means of gel permeation chromatography (GPC).

[0022] In general, for the present invention, the number-average molar mass M wof the at least one polymer (used as at least one viscosity enhancer) soluble in the at least one solvent (and different from the at least one thermoresponsive polymer), for example by means of gel permeation chromatography (GPC). The eluent used may be, for example, 0.1 mol·l -1 NaNO 3 in water + 10 ppm sodium azide (NaN 3 ) or water (or ultrapure water) + 10 ppm sodium azide (NaN 3 ) or 0.07 mol·l -1 N / a 2 HPO 4 in water + 10 ppm NaN 3 , pH 7.4. The concentration (of the at least one polymer soluble in the at least one solvent) in the eluent can be, for example, 5 mg·ml -1 The flow rate can be e.g. 1.0 ml·min -1The columns that can be used are, for example: 2 x ShodexOHpak SB806 MHQ or PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm). The molecular weight can be determined, for example, via static light scattering. Alternatively (i.e., if the molecular weight is not determined via static light scattering), calibration can be carried out, for example, using PEG standards, pullulan standards (MP 0.342 - 710 g mol -1 ) or via poly(diallyldimethylammonium chloride) standards.

[0023] However, other conditions may also be used to determine the mass-average molar mass M w by GPC. For example, for mixtures based on non-aqueous solvents, it may also be necessary to determine the mass-average molar mass M wGPC requires the use of non-aqueous eluents, such as chloroform. In these cases, column combinations other than those mentioned above can be used. The exact conditions for GPC generally depend on the polymer being investigated, whose mass-average molecular weight M w should be determined.

[0024] In principle, suitable conditions for determining the mass-average molar mass M w using GPC within the scope of his expertise.

[0025] For example, gel permeation chromatography can be used to determine the mass-average molecular weight M w of the at least one polymer (used as at least one viscosity increaser) soluble in the at least one solvent (and different from the at least one thermoresponsive polymer) - be carried out in accordance with the following conditions: Eluent: 0.1 mol·l -1 NaNO 3in water + sodium azide; concentration of the polymer (at least one soluble in at least one solvent) in the eluent: 5 mg·ml -1 ; Flow rate: 1.0 ml min -1 ; Columns: 2 X ShodexOHpak SB806 MHQ; Molar mass determination via static light scattering; or - be carried out in accordance with the following conditions: Eluent: ultrapure water + 10 ppm NaN 3 Concentration of the polymer (at least one soluble in at least one solvent) in the eluent: 5 mg·ml -1 ; Flow rate: 1.0 ml min -1 ; Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm); Calibration: PEG standards; or - be carried out in accordance with the following conditions: Eluent: 0.1 mol·l -1 NaNO 3 in water + 10 ppm sodium azide; concentration of FLOPAM FO 4650 in the eluent: 5 mg·ml -1 ; Flow rate: 1.0 ml min -1; Columns: 2 X ShodexOHpak SB806 MHQ; Calibration: Poly(dia-ilyldimethylammonium chloride) standards; or - be carried out in accordance with the following conditions: Eluent: 0.07 mol·l -1 N / a 2 HPO 4 in water + 10 ppm NaN 3 , pH 7.4; concentration of sodium alginate in the eluent: 5 mg·ml -1 ; Flow rate: 1.0 ml min -1 ; Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm); Calibration: Pullulan standards (MP 0.342 - 710 g mol -1 ).

[0026] A further preferred embodiment of the substance mixture according to the invention is characterized in that the substance mixture - at least 0.01 wt.%, preferably at least 0.1 wt.%, particularly preferably at least 1.0 wt.%, very particularly preferably at least 1.5 wt.%, in particular at least 1.8 wt.%, for example at least 2.0 wt.%, of the at least one viscosity increaser, based on the total weight of the mixture, and / or - at most 20 wt.%, preferably at most 15 wt.%, particularly preferably at most 10 wt.%, very particularly preferably at most 5.0 wt.%, in particular at most 3.0 wt.%, of the at least one viscosity increaser, based on the total weight of the mixture.

[0027] According to a further preferred embodiment of the substance mixture according to the invention, the substance mixture contains 0.01% by weight to 20% by weight, preferably 0.1% by weight to 15% by weight, particularly preferably 1.0% by weight to 10% by weight, very particularly preferably 1.5% by weight to 5.0% by weight, in particular 1.8% by weight to 3.0% by weight, for example 2.0% by weight to 3.0% by weight, of the at least one viscosity-increasing agent.

[0028] A further preferred embodiment of the substance mixture according to the invention is characterized in that the at least one viscosity-increasing agent (or the viscosity-increasing effect of the at least one viscosity-increasing agent) is characterized in that a solution comprising 2.0% by weight of the at least one viscosity-increasing agent and 98.0% by weight of the at least one solvent has a dynamic viscosity measured at 23 °C and a shear rate (or shear velocity) of 53.8 Hz that - at least 0.6 Pa s, preferably at least 0.8 Pa s, particularly preferably at least 1.0 Pa s, and / or - at most 50.0 Pa s, preferably at most 20.0 Pa s, particularly preferably at most 10.0 Pa s, and / or - in a range from 0.5 Pa s to 50.0 Pa s, preferably from 0.7 Pa s to 10.0 Pa s, particularly preferably from 0.9 Pa s to 8.0 Pa s, and / or - at least 0.5 Pa s higher, preferably at least 0.7 Pa s higher, particularly preferably at least 0.9 Pa s higher, than the dynamic viscosity, measured at 23 °C and a shear rate (or shear velocity) of 53.8 Hz, of the at least one solvent, and / or - is at least 50 times higher, preferably at least 70 times higher, particularly preferably at least 90 times higher, than the dynamic viscosity, measured at 23 °C and a shear rate (or shear velocity) of 53.8 Hz, of the at least one solvent.

[0029] Dynamic viscosity can be measured, for example, using the following additional parameters: Measurement geometry / method: SV DIN; Moment of inertia: 0.000 kg m 2 ; Damping: 30.00; Expansion coefficient: 1.100 µm / °C. Dynamic viscosity can also be measured using, for example, the "Thermo Scientific Haake Viscotester 550" device; Driver version: 44; Firmware version 1: V1 2.7-11 / 98.

[0030] According to a further preferred embodiment of the substance mixture according to the invention, the substance mixture has, in a temperature range above an initial temperature T A and below a final temperature TE a monotonic progression of their optical transparency as a function of temperature, with the temperature range (T A are E ) preferably - extends over at least 3 K, preferably over at least 5 K, and / or - is in the range from 5 °C to 300 °C, preferably from 10 °C to 95 °C, particularly preferably from 35 °C to 40 °C, very particularly preferably from 36.5 °C to 40 °C, and / or extends over this range (ie a range from 5 °C to 300 °C, preferably from 10 °C to 95 °C, particularly preferably from 35 °C to 40 °C, very particularly preferably from 36.5 °C to 40 °C).

[0031] It is further preferred that the monotonic course of the optical transparency over a temperature range from the initial temperature T A up to the final temperature T E is sufficient, where T E - T A ≥ 3 K, especially T E - T A ≥ 5 K

[0032] A further preferred embodiment of the substance mixture according to the invention is characterized in that the substance mixture is adapted so that it can be used at a temperature T above an initial temperature T A and below a final temperature T E has a monotonic course of optical transparency as a function of temperature T, so that a measurement of the optical transparency of the substance composition allows an optical determination of temperature T, where T E > T > T A , wherein preferably the monotonic course of the optical transparency over a temperature range from the initial temperature T A up to the final temperature T E is sufficient, where T E - T A ≥ 3 K, especially T E - T A ≥ 5 K

[0033] A further preferred embodiment of the substance mixture according to the invention is characterized in that adjacent upper critical mixing temperatures or adjacent lower critical mixing temperatures of the thermoresponsive polymers are within the temperature range between T A and T E have a substantially equal distance from each other.

[0034] A further preferred embodiment of the substance mixture according to the invention is characterized in that the concentration of the thermoresponsive polymers is selected such that a single one of n thermoresponsive polymers of the substance composition reduces the optical transparency of the substance composition by a maximum of 100 / n%.

[0035] According to a further preferred embodiment, the at least one thermoresponsive polymer comprises a plurality of (different) thermoresponsive polymers, for example at least two or at least three (different) thermoresponsive polymers.

[0036] A further preferred embodiment of the substance mixture according to the invention is characterized in that the at least one thermoresponsive polymer - has at least one acrylamide, methacrylamide, acrylate and / or methacrylate unit, and / or - (exclusively) has hydrogen bond acceptors, and / or - has no hydrogen bond donors, and / or - each has a lower critical mixing temperature or an upper critical mixing temperature, and / or - comprises at least two thermoresponsive polymers, which preferably have different lower critical mixing temperatures or different upper critical mixing temperatures.

[0037] A further preferred embodiment of the substance mixture according to the invention is characterized in that the at least one thermoresponsive polymer - selected from the group consisting of • alkyl-substituted poly[(meth)acrylamide]s, particularly preferably poly(dialkylacrylamide)s, e.g. poly(diethylacrylamide); poly[oligo(ethylene glycol methacrylate)]s, particularly preferably poly[2-(2-methoxyethoxy)ethyl methacrylate)] and copolymers thereof and poly(2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) and copolymers thereof; poly[oligo(ethylene glycol acrylate)]s; poly(N-vinylamide)s, particularly preferably poly(N-vinyllactam)s; polymethylvinyl ethers; poly(oxazoline)s; and mixtures thereof, • (at the terminal end of the repeating unit) polyvinyl ethers carrying cationic groups, as well as mixtures thereof, • Poly(butadiene), Poly(styrene), Poly(dimethylacrylamide), Poly(isopropylacrylamide), Poly(tert-butylacrylamide), Poly(methyl methacrylate), Poly(n-butyl methacrylate), Poly(benzyl methacrylate), Poly(3-fluorobenzyl methacrylate), Poly(3-methylbenzyl methacrylate), Poly(3-methoxybenzyl methacrylate), Poly(2-phenylethyl methacrylate), Poly(4-phenylbutyl methacrylate), poly(4-(phenylazo)phenyl methacrylate), poly(N-(4-vinylbenzyl)carbazole), poly(glycidyl(2-ethoxyethyl) ether), poly(glycidyl methyl ether), poly(glycidyl ethyl ether), poly(ethylene glycol), poly(propylene glycol), and mixtures thereof, • Poly(vinylbenzyldialkylamine)s, preferably poly(dialkyl-(4-vinylbenzyl)amine), and mixtures thereof • Poly(2-chloroethyl vinyl ether-alt-maleic anhydride), • Poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide), • and mixtures thereof, and / or - is contained in the substance mixture in a concentration in the range from 0.01 g / l to 100 g / l, preferably from 0.1 g / l to 10 g / l, particularly preferably from 1.0 g / l to 5.0 g / l.

[0038] The polyvinyl ethers carrying cationic groups at the terminal end of the repeating unit are preferably polyvinyl ethers according to one of the following two structural formulas: where A is selected from Cl, Br, PF 6 , BF 4 , N(CF 3 SO 2 ) 2 (NTf 2 ), where R is selected from CH 3 (Me), nC 4 H 9 (Bu), nC 5 H 11 (Pe), and nC 8 H 17 (Oc), and where x is an integer in the range 3 to 50000.

[0039] A further preferred embodiment of the substance mixture according to the invention is characterized in that the at least one polymer soluble in the at least one solvent is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethylcelluloses, hydroxyethylcelluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl radicals of C 1 to C 3 ; Poly(styrene); Poly(methyl methacrylate); Poly(2-hydroxyethyl methacrylate); Poly(acrylamide-co-choline acrylate); Hydroxypropylcellulose; and mixtures thereof.

[0040] A further preferred embodiment of the substance mixture according to the invention is characterized in that - the ionic liquids each comprise or consist of (or are constituted by) at least one cation and at least one anion, where • the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphosphonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or • the at least one anion is selected from the group consisting of bis(trifluoromethanesulfone)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof, and / or - the substance mixture additionally contains at least one surfactant (or detergent), preferably if the at least one solvent is or contains at least one ionic liquid, wherein the at least one surfactant is preferably sodium dodecyl sulfate.

[0041] If the substance mixture additionally contains at least one surfactant (or detergent), preferably sodium dodecyl sulfate, it is preferred that the at least one solvent is water, at least one ionic liquid, or a mixture of water and at least one ionic liquid. The at least one surfactant serves, on the one hand, to prevent phase separation between the thermoresponsive polymer and the ionic liquid. In aqueous systems, the at least one surfactant leads to a shift in the phase transition temperature toward higher temperatures, so that the phase transition temperature and thus the measurement range can be adjusted if necessary.

[0042] In the event that the at least one solvent is or contains at least one ionic liquid, the substance mixture additionally contains at least one surfactant (or detergent), wherein the at least one surfactant is preferably sodium dodecyl sulfate.

[0043] A further preferred embodiment of the substance mixture according to the invention is characterized in that the at least one solvent - Water is, wherein the at least one thermoresponsive polymer is selected from the group consisting of alkyl-substituted poly[(meth)acrylamides], more preferably poly(dialkylacrylamides), e.g. poly(diethylacrylamide); poly[oligo(ethylene glycol methacrylate)]s, more preferably poly[2-(2-methoxyethoxy)ethyl methacrylate)] and copolymers thereof as well as poly(2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) and copolymers thereof; poly[oligo(ethylene glycol acrylate)]s; poly(N-vinylamides), more preferably poly(N-vinyl lactams); polymethyl vinyl ethers; poly(oxazolines); and mixtures thereof, and wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethylcelluloses, hydroxyethylcelluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(acrylamide-co-choline acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl radicals of C 1 to C 3 ; and mixtures thereof, or - at least one ionic liquid, wherein the at least one thermoresponsive polymer is selected from the group consisting of poly(butadiene), poly(styrene), poly(dimethylacrylamide), poly(isopropylacrylamide), poly(tert-butylacrylamide), poly(methyl methacrylate), poly(n-butyl methacrylate), poly(benzyl methacrylate), poly(3-fluorobenzyl methacrylate), poly(3-methylbenzyl methacrylate), poly(3-methoxybenzyl methacrylate), poly(2-phenylethyl methacrylate), poly(4-phenylbutyl methacrylate), poly(4-(phenylazo)phenyl methacrylate), poly(N-(4-vinylbenzyl)carbazole), poly(glycidyl(2-ethoxyethyl)ether), poly(glycidyl methyl ether), poly(glycidyl ethyl ether), poly(ethylene glycol), poly(propylene glycol), and mixtures thereof, wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such asCarboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethylcelluloses, hydroxyethylcelluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(acrylamide-co-choline acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl radicals of C. 1 to C 3 and mixtures thereof, and wherein preferably • the at least one ionic liquid comprises or consists of at least one cation and at least one anion (or is constituted thereof), wherein the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphosphonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or the at least one anion is selected from the group consisting of bis(trifluoromethanesulfon)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof, and / or • the mixture additionally contains at least one surfactant, preferably sodium dodecyl sulfate, or - chloroform or a mixture of chloroform and methanol, wherein the at least one thermoresponsive polymer is selected from the group consisting of polyvinyl ethers carrying cationic groups (at the terminal end of the repeating unit), and mixtures thereof, and wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of poly(styrene), poly(methyl methacrylate), poly(2-hydroxyethyl methacrylate), and mixtures thereof, or - methanol or a mixture of methanol and water, wherein the at least one thermoresponsive polymer is selected from the group consisting of poly(vinylbenzyldialkylamines), preferably poly(dialkyl-(4-vinylbenzyl)amine), and mixtures thereof, and wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of hydroxypropylcellulose, poly(2-hydroxyethyl methacrylate), and mixtures thereof, or - butyl acetate, preferably n-butyl acetate, wherein the at least one thermoresponsive polymer is poly(2-chloroethyl vinyl ether-alt-maleic anhydride), and wherein the at least one polymer soluble in the at least one solvent is poly(methyl methacrylate), or - ethanol, propanol, preferably n-propanol, or butanol, preferably n-butanol, or a mixture thereof, wherein the at least one thermoresponsive polymer is poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide), and wherein the at least one polymer soluble in the at least one solvent is poly(2-hydroxyethyl methacrylate).

[0044] The polyvinyl ethers carrying cationic groups at the terminal end of the repeating unit are preferably polyvinyl ethers according to one of the following two structural formulas: where A is selected from Cl, Br, PF 6 , BF 4 , N(CF 3 SO 2 ) 2(NTf 2 ), where R is selected from CH 3 (Me), nC 4 H 9 (Bu), nC 5 H 11 (Pe), and nC 8 H 17 (Oc), and where x is an integer in the range 3 to 50000.

[0045] Furthermore, the present invention relates to a fiber optic measuring system for temperature measurement comprising (at least) one temperature-sensitive element, at least one light-conducting optical fiber, a light source, and at least one optical detector, wherein the (at least one) temperature-sensitive element comprises a substance mixture according to the invention.

[0046] A preferred embodiment of the fiber optic measuring system according to the invention is characterized in that - the (at least one) temperature-sensitive element comprises a container in which the substance mixture is arranged, wherein the container preferably comprises a metallic material, and / or - the (at least one) temperature-sensitive element is connected to at least one light-conducting optical fiber, wherein preferably the (at least one) temperature-sensitive element is connected to the at least one detector via at least one light-conducting optical fiber and / or is connected to the light source via at least one light-conducting optical fiber, and / or - the at least one optical detector is configured such that it can detect a change in the light output of a light emanating from the light source and passing through the (at least one) temperature-sensitive element.

[0047] A further preferred embodiment of the fiber optic measuring system according to the invention is characterized in that the fiber optic measuring system additionally comprises at least one fiber optic coupling element, wherein the at least one fiber optic coupling element preferably - is selected from the group consisting of fiber optic couplers, fiber optic multiplexers, fiber optic switches, and combinations thereof, and / or - is connected to the light source by at least one optical fiber, and / or - is connected to the thermosensitive element by at least one optical fiber, and / or - is connected to at least one detector by at least one optical fiber.

[0048] A further preferred embodiment of the fiber optic measuring system according to the invention is characterized in that the at least one fiber optic coupling element comprises at least one first fiber optic coupling element and at least one second fiber optic coupling element, wherein - the at least one first fiber-optic coupling element is connected to the thermosensitive element and to the at least one detector via at least one optical fiber, and / or - the at least one second fiber-optic coupling element is connected to the thermosensitive element and to the at least one detector via at least one optical fiber, and / or - the at least one first fiber optic coupling element is connected to the at least one second fiber optic coupling element via at least one optical fiber.

[0049] According to a further preferred embodiment of the fiber optic measuring system according to the invention, the light source is an LED, an OLED, a laser, an incandescent lamp, a fluorescent lamp or a gas discharge lamp.

[0050] The present invention also relates to a method for temperature measurement using a fiber optic measuring system according to the invention, in which a) light from the light source is coupled into the thermosensitive element and into the at least one detector by means of the at least one optical fiber, wherein light passing from the light source to the at least one detector at least partially passes through the thermosensitive element on its way to the at least one detector; b) the intensity of the light that has passed through the thermosensitive element is determined using the detector; c) using the measured intensity (of the light) a value for the temperature of the thermosensitive element is determined.

[0051] A preferred variant of the method according to the invention is characterized in that - after step c) the determined temperature value is transmitted to a control and monitoring unit, and / or - additional light emanating from the light source is guided to the detector without passing through the thermosensitive element and serves as a reference signal.

[0052] Possible applications of the substance mixture according to the invention and / or the fiber optic measuring system according to the invention and / or the method according to the invention are, for example, temperature measurement in bioreactors in the food, pharmaceutical, and cosmetics industries. Furthermore, the substance mixture according to the invention and / or the fiber optic measuring system according to the invention and / or the method according to the invention offer the possibility of monitoring the temperature of processes in high-frequency, microwave, and magnetic fields. For example, the substance mixture according to the invention and / or the fiber optic measuring system according to the invention and / or the method according to the invention can be used for temperature monitoring during the charging of battery cells in high-voltage environments, which is indispensable for electromobility. Specialized applications also include, for example:Temperature monitoring in transformers or patient monitoring in MRI scanners with strong electromagnetic fields.

[0053] The present invention will be explained in more detail with reference to the following figures and examples, without limiting it to the specific embodiments and parameters shown here. Synthesis and characterization of the thermoresponsive polymers used. Synthesis example 1: Synthesis of poly(diethylacrylamide) by radical polymerization and characterization of the reaction product.

[0054] In a 100 ml single-necked round-bottom flask, 5.0 g of diethylacrylamide (39.3 mmol) were placed and dissolved in 60 ml of ethanol. The initiator (azobisisobutyronitrile, 71 mg, 0.43 mmol) was weighed and transferred to the flask. The flask was sealed with a septum. To remove oxygen, nitrogen was passed through the solution via a cannula while stirring for 1 h. The flask containing the clear, colorless solution was then heated in an oil bath at 68 °C for 24 h. After this time, a sample was taken to determine the conversion by 1H-NMR spectroscopy. Within the accuracy of the method, no residual monomer could be detected. Therefore, the reaction was terminated after this time by cooling and opening the reaction vessel. For purification, the ethanol was evaporated, the colorless solid was dissolved in water, and the solution was dialyzed against water for 60 h (details of the dialysis tubing: Spectra / Por 7 dialysis membrane, pre-treated regenerated cellulose tubing, nominal cutoff: 1 kDa). The characterization of the dialyzed product is carried out using 1 H-NMR spectroscopy and gel permeation chromatography (GPC).

[0055] GPC (eluent DMF, calibration with poly(methyl methacrylate) standards): M w = 11000 g mol -1 , M n = 5300 g mol -1 1 H-NMR (500 MHz, D 2 O): 3.6 - 2.9 ppm (broad): 4 H, H B 2.8 - 2.1 ppm (broad): 1 H, H C 1.9 - 0.7 ppm (broad): 8 H, H D + H A Synthesis Example 2: Synthesis of poly(N-vinylcaprolactam) by radical polymerization and characterization of the reaction product

[0056] In a 100 ml single-necked round-bottom flask, 5.0 g of N-vinylcaprolactam (35.9 mmol) were placed and dissolved in 60 ml of ethanol. The initiator (azobisisobutyronitrile, 35 mg, 0.21 mmol) was weighed and transferred to the flask. The flask was then sealed with a septum. To remove oxygen, nitrogen was passed through the solution via a cannula while stirring for 1 h. The flask containing the clear, colorless solution was then heated in an oil bath at 65 °C for 24 h. After this time, a sample was taken to determine the conversion by 1H-NMR spectroscopy. The residual monomer content was approximately 4 mol%. Therefore, the reaction was terminated after this time by cooling and opening the reaction vessel. For purification, the ethanol was evaporated, the colorless solid was dissolved in water, and the solution was dialyzed against water for 60 h (details of dialysis tubing: Spectra / Por 7 dialysis membrane, pre-treated regenerated cellulose tubing, nominal cutoff: 1 kDa). The dialyzed product was characterized using 1 H-NMR spectroscopy and gel permeation chromatography (GPC).

[0057] GPC (eluent DMF, calibration with poly(vinylpyrrolidone) standards): M w = 31000 g mol -1 , M n = 11000 g mol -1 1 H-NMR (500 MHz, D 2 O): 4.6 - 4.0 ppm (broad): 1 H, H B 3.5 - 2.8 ppm (broad): 2 H, H C 2.7 - 2.1 ppm (broad): 2 H, H G 2.1 - 0.6 ppm (broad): 8 H, H A , H D , H E , H F Synthesis Example 3: Synthesis of poly(oligoethylene glycol methyl ether methacrylate-block-2-(2-methoxyethoxy)ethyl methacrylate) by controlled radical polymerization (reversible addition fragmentation chain transfer, RAFT) and characterization of the reaction product. 1st step: Synthesis of poly(oligoethylene glycol methyl ether methacrylate)

[0058] In a 50 ml single-necked round-bottomed flask, 55.8 mg of 4-cyano-4-(thiobenzoylthio)pentanoic acid (0.2 mmol), 3.3 mg of azobisisobutyronitrile (0.02 mmol), and 3575 mg of oligoethylene glycol methyl ether methacrylate (7.15 mmol) were weighed and dissolved in 10 ml of ethanol. The flask was then sealed with a septum. To remove oxygen, nitrogen was passed through the solution via a cannula while stirring for 30 min. The flask containing the clear, red solution was then heated in an oil bath at 70 °C for 8 h. After this time, a sample was taken to determine the conversion by 1 H-NMR spectroscopy. Since approximately 47% of residual monomer was still present, another 1.65 mg of initiator was added, the oxygen was removed again, and the reaction continued at 70 °C for 8 h. The conversion was again determined by 1H-NMR spectroscopy. Since the residual monomer content had dropped to approximately 9%, the reaction was stopped. To isolate the reaction product, the ethanol was evaporated, the remaining red-colored viscous mass was dissolved in water, and the solution was dialyzed against water for 60 h (dialysis tubing: Spectra / Por 7 dialysis membrane, pre-treated regenerated cellulose tubing, nominal cutoff: 1 kDa). The characterization of the dialyzed product was performed with 1 H-NMR spectroscopy and gel permeation chromatography (GPC).

[0059] GPC (eluent DMF, calibration with poly(methyl methacrylate) standards): M w = 17000 g mol -1 , M n = 14000 g mol -1 1 H-NMR (500 MHz, D 2 O): 8.0 ppm (broad): H G 7.8 ppm (broad): H H 7.6 ppm (broad): H F 4.4 - 4.0 ppm (broad): 2 H, H A 4.0 - 3.2 ppm (broad): 37H, H B 2.8 - 0.6 ppm (broad, overlaid): 5 H, H C , H D , also H I , H J , H K 2nd step: Synthesis of the block copolymer

[0060] In a 50 ml single-necked round-bottom flask, 1000 mg of poly(oligoethylene glycol methyl ether methacrylate) (0.067 mmol of end groups), 1.1 mg of azobisisobutyronitrile (0.0067 mmol), and 1267 mg of 2-(2-methoxyethoxy)ethyl methacrylate (6.73 mmol) were weighed and dissolved in 10 ml of ethanol. The flask was then sealed with a septum. To remove oxygen, nitrogen was passed through the solution via a cannula while stirring for 30 min. The flask containing the clear, red solution was then heated in an oil bath at 70 °C for 50 h. After this time, a sample was taken to determine the conversion by 1H-NMR spectroscopy. Since considerable amounts of residual monomer were still present, a further 1.1 mg of initiator was added, the oxygen was again removed, and the reaction continued at 70 °C for 70 h. Since the conversion was still not very high, these steps were repeated one more time. Then the reaction was terminated at approximately 75% conversion. To isolate the reaction product, the ethanol was evaporated off, the remaining red-colored viscous mass was dissolved in water, and the solution was dialyzed against water for 60 h (dialysis tubing: Spectra / Por 7 dialysis membrane, pre-treated regenerated cellulose tubing, nominal cutoff: 1 kDa). The dialyzed product was characterized using 1 H-NMR spectroscopy and gel permeation chromatography (GPC).

[0061] GPC (eluent DMF, calibration with poly(methyl methacrylate) standards): M w = 28000 g mol -1 , M n = 18000 g mol -1 1 H-NMR (500 MHz, D 2 O): 4.4 - 4.0 ppm (broad): H A 4.0 - 3.2 ppm (broad): H B 2.8 - 0.6 ppm (broad, overlaid): H C , H D Signals of the end groups H F , H G , H H and H I , H J , H K are no longer recognizable Data of the polymers used as viscosity increasers

[0062] Since the molar masses stated by the manufacturers of the polymers used as viscosity increasers were determined in very different and partly unknown ways, the molar masses of the polymers used were additionally determined by gel permeation chromatography (GPC).

[0063] Different types of molar masses are given below. Where M w for the mass-average molar mass, M n for the number average molecular weight and M vfor a viscosity-based molar mass. Hydroxyethylcelluloses (HEC) Polymer samples used: Details HECs according to manufacturer HEC 776 kg·mol -1 HEC 155 kg·mol -1 2-Hydroxyethylcellulose 2-Hydroxyethylcellulose Sigma-Aldrich Sigma-Aldrich Lot# MKBD2868V Pcode: 1003429775 Pcode:1000852844 Source: MKCQ6758 average M v = 1300000 Da (Herstellerangabe) average M v = 90000 Da (manufacturer's information) GPC characterization: GPC characterization: M w = 776000 g·mol -1 M w = 155000 g·mol -1 M n = 499000 g·mol -1 M n = 69000 g·mol -1 Eluent: 0,1 mol·l -1 NaNO 3 in Eluent: 0.1 mol·l -1 NaNO 3 in Water + sodium azide Water + sodium azide Concentration of HEC in the eluent: 5 mg·ml -1 Flow rate: 1.0 ml min -1 Columns: Concentration of HEC in the eluent: 5 mg·ml -1 Flow rate: 1.0 ml min -1 Columns: 2 X ShodexOHpak SB806 MHQ Molar mass determination via static light scattering 2 X ShodexOHpak SB806 MHQ Molar mass determination via static light scattering PEG 100

[0064] Polyethylene glycol Sigma-Aldrich Lot# 01426CU-010 average M w = 100000 g mol -1 (Manufacturer information) GPC characterization: M w = 135000 g mol -1 M n = 11000 g mol -1 Eluent: ultrapure water + 10 ppm NaN 3 Concentration of PEG 100 in the eluent: 5 mg·ml -1 Flow rate: 1.0 ml min -1 Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm) Calibration: PSS PEG standards PEG 5000

[0065] Polyethylene glycol Sigma-Aldrich Lot# 97117-078 average M v= 5000000 g mol -1 (Manufacturer information) GPC characterization: M w = 675000 g mol -1 M n = 109000 g mol -1 Eluent: ultrapure water + 10 ppm NaN 3 Concentration of PEG 5000 in the eluent: 5 mg·ml -1 Flow rate: 1.0 ml min -1 Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm) Calibration: PSS PEG standards FLOPAM FO 4650

[0066] FLOPAM FO 4650 SNSF SA Lot# GE3948 average molar mass = 4500 - 7100 kg mol -1 (Manufacturer's information) 45 mol% amide (x), 55 mol% cationic groups (y) Poly(acrylamide-co-cholineacrylate) GPC characterization: M w = 890000 g mol -1 M n = 150000 g mol -1 Eluent: 0.1 mol·l -1 NaNO 3in water + 10 ppm sodium azide Concentration of FLOPAM FO 4650 in the eluent: 5 mg·ml -1 Flow rate: 1.0 ml min -1 Columns: 2 X ShodexOHpak SB806 MHQ Calibration: Poly(diallyldimethylammonium chloride) standards Sodium alginate

[0067] Alginic acid sodium salt Roth Batch 263193296 Viscosity (1% solution, 20 °C) 350-550 mPas (manufacturer's information) GPC characterization: M w = 551000 g mol -1 M n = 246000 g mol -1 Eluent: 0.07 mol·l -1 N / a 2 HPO 4 in water + 10 ppm NaN 3 , pH 7.4 Concentration of sodium alginate in the eluent: 5 mg·ml -1 Flow rate: 1.0 ml min -1 Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm) Calibration: PSS pullulan standards (MP 0.342 - 710 g mol -1 ) Experiments with thermoresponsive mixturesComparative Example 1: Aqueous solution of poly(diethylacrylamide) (prepared according to Synthesis Example 1) without additive

[0068] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to Synthesis Example 1) is shaken for 2 h at a concentration of 3 g l -1 in H 2 O solved.

[0069] The turbidity measurement was carried out at a constant temperature of 41.4 °C over a period of 70 h. The result of the turbidity measurement is shown in Fig. 1. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l -1) without a temperature-independent, water-soluble polymer additive. The transmission increases over the course of the experiment from an initial value of just over 50% to a final value of almost 90%. Since the turbidity value does not remain constant over time, this solution is unsuitable for fiber optic temperature measurement over extended periods. Comparative Example 2: Aqueous solution of poly(diethylacrylamide) (prepared according to Synthesis Example 1) additived with 2 wt.% HEC 155 kg mol -1

[0070] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to Synthesis Example 1) is shaken for 2 h at a concentration of 3 g l -1 in H 2 O. Then as much HEC as 155 kg mol -1 added so that its concentration reaches 2.0 wt%.

[0071] The turbidity measurement was carried out at a constant temperature of 38.0 °C over a period of 70 h. The result of the turbidity measurement is shown in Fig. 2. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l-1) with 2.0 wt% HEC 155 kg·mol -1 (M w = 155 kg mol -1 ) as a temperature-independent, water-soluble polymer additive. Despite the addition of the additive, the transmittance increased over the course of the experiment from an initial value of approximately 40% to a final value of approximately 80%. At the concentration used, the additive did not have the desired stabilizing effect on the turbidity value. Example 1: Aqueous solution of poly(diethylacrylamide) (prepared according to Synthesis Example 1) additived with 2 wt.% HEC 776 kg·mol -1

[0072] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to Synthesis Example 1) is shaken for 2 h at a concentration of 3 g l -1 in H 2 O. Then, while stirring, add as much HEC as 776 kg mol -1 added so that its concentration reaches 2.0 wt%.

[0073] The turbidity measurement was carried out at a constant temperature of 39.5 °C over a period of 70 h. The result of the turbidity measurement is shown in Fig. 3. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l -1 ) with 2.0% by weight HEC 776 kg mol -1 (M w = 776 kg mol -1) as a temperature-independent, water-soluble polymer additive. The straight, continuous line is a linear fit through all measurement points. In the case of the high-molecular-weight HEC, the additive exhibits the desired effect. Within the limits of measurement accuracy, the turbidity values ​​remain constant over a period of 70 hours. This solution with a composition according to the invention is suitable for fiber-optic temperature measurement over extended periods. Example 2: Influence of viscosity: Aqueous solutions of poly(diethylacrylamide) (prepared according to synthesis example 1) additived with different weight fractions of HEC 776 kg mol -1

[0074] Preparation of the additive polymer solutions for viscosity measurements: The polymer masses calculated for a given concentration were weighed and the required masses of H 2O was added. The mixtures were then shaken on an automatic shaker until clear solutions were obtained.

[0075] Dynamic viscosities of these solutions were determined. In the graph in Fig. 4 are the determined dynamic viscosities of the aqueous solutions of HEC 776 kg mol-1 (M w = 776 kg mol -1 ) as a function of polymer concentration. As can be seen, the dynamic viscosity increases with increasing polymer concentration.

[0076] Preparation of solutions for turbidity measurements: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to Synthesis Example 1) is stirred for 2 h at a concentration of 3 g l -1 in H 2 O. Then, while stirring, add as much HEC as 776 kg mol -1 (M w = 776 kg mol -1 ) is added until its concentration reaches the desired weight fraction.

[0077] Turbidity measurements were carried out with these solutions over a period of 70 hours. The results of the turbidity measurements are shown in Fig. 5. This shows the time course of the transmission through solutions of the thermoresponsive polymer (c = 3.0 g·l -1 ) with different concentrations of HEC 776 kg·mol -1 as a temperature-independent, water-soluble polymer additive. The straight lines are fits through all points of each measurement. The drift of the transmission values ​​over time, illustrated by the linear fit to the respective measurement curve, correlates with the dynamic viscosity of the solution, as shown in Fig. 5. The measurement curves show that even lower concentrations than 2 wt% of HEC 776 kg·mol -1and thus correspondingly lower viscosities already lead to an improvement in the stability of the solution compared to a solution without viscosity enhancers. From a dynamic viscosity of about 1 Pa s, which in the case of the HEC used is 776 kg mol -1 corresponds to an additive concentration of about 2 wt.%, the transmission values ​​then remain constant over the entire test period within the limits of the measurement accuracy. Comparative Example 3: Aqueous solution of poly(diethylacrylamide) (prepared according to Synthesis Example 1) additived with 2 wt.% PEG 100

[0078] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to Synthesis Example 1) is shaken for 2 h at a concentration of 3 g l -1 in H 2 O. Then add as much PEG 100 (M w = 135 kg mol -1 ) was added until its concentration reached 2.0 wt%.

[0079] The turbidity measurement was carried out at a constant temperature of 34.6 °C over a period of 70 h. The result of the turbidity measurement is shown in Fig. 6. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g l-1) with 2.0 wt.% PEG 100 as a temperature-independent, water-soluble polymer additive. Despite the addition of the additive, the transmission increases over the course of the experiment from an initial value of approximately 48% to a final value of approximately 69%. At the concentration used, the additive does not have the desired stabilizing effect on the turbidity value. Example 3: Aqueous solution of poly(diethylacrylamide) (prepared according to Synthesis Example 1) additived with 2 wt.% PEG 5000

[0080] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to Synthesis Example 1) is shaken for 2 h at a concentration of 3 g l -1in H 2 O. Then, sufficient PEG 5000 is added to achieve a concentration of 2.0 wt.%. Turbidity was measured at a constant temperature of 34.5 °C over a period of 70 h. The result of the turbidity measurement is shown in Fig. 7. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l -1 ) with 2.0 wt.% PEG 5000 (M w = 675 kg mol -1) as a temperature-independent, water-soluble polymer additive. The straight, continuous line is a linear fit through all measurement points. In the case of the high-molecular-weight PEG, the additive exhibits the desired effect. An increase in turbidity values ​​is observed over a period of 70 hours, but this is so slight that it remains within the range of the instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber optic temperature measurement over longer periods. Example 4: Aqueous solution of poly(diethylacrylamide) (prepared according to Synthesis Example 1) additived with 2 wt.% FLOPAM FO 4650

[0081] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to Synthesis Example 1) is shaken for 2 h at a concentration of 3 g l -1 in H 2 O. Then add as much FLOPAM FO 4650 (M w = 4500 - 7100 kg mol-1 ) was added until its concentration reached 2.0 wt%.

[0082] The turbidity measurement was carried out at a constant temperature of 31.5 °C over a period of 76 h. The result of the turbidity measurement is shown in Fig. 8. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l -1 ) with 2.0 wt.% FLOPAM FO 4650 as a temperature-independent, water-soluble polymer additive. The straight, continuous line is a linear fit through all measurement points. FLOPAM FO 4650 demonstrates the desired effect as an additive. A decrease in the turbidity values ​​is observed over a period of 76 hours, but this is so slight that it remains within the range of the instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber optic temperature measurement over longer periods. Example 5: Aqueous solution of poly(diethylacrylamide) (prepared according to Synthesis Example 1) additived with 2 wt.% sodium alginate

[0083] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to Synthesis Example 1) is shaken for 2 h at a concentration of 3 g l -1 in H 2 O. Then add as much sodium alginate (M w = 551000 g mol -1 ) was added until its concentration reached 2.0 wt.%.

[0084] The turbidity measurement was carried out at a constant temperature of 32.1 °C over a period of 70 h. The result of the turbidity measurement is shown in Fig. 9. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l -1) with 2.0 wt.% sodium alginate as a temperature-independent, water-soluble polymer additive. The straight, continuous line is a linear fit through all measurement points. Sodium alginate demonstrates the desired effect as an additive. An increase in turbidity values ​​is observed over a period of 70 hours, but this is so slight that it remains within the range of the instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber optic temperature measurement over longer periods. Embodiment Example 6: Aqueous solution of poly(oligoethylene glycol methyl ether methacrylate-block-2-(2-methoxyethoxy)-ethyl methacrylate) (prepared according to Synthesis Example 3) additived with 2 wt.% HEC 776 kg mol -1

[0085] Preparation of the solution: The thermoresponsive polymer poly(oligoethylene glycol methyl ether methacrylate-block-2-(2-methoxyethoxy)-ethyl methacrylate) (prepared according to Synthesis Example 3) is shaken for 2 h at a concentration of 3 g l -1 in H 2 O. Then HEC is dissolved in 776 kg mol -1 (M w = 776 kg mol -1 ) was added until its concentration reached 2.0 wt%.

[0086] The turbidity measurement was carried out at a constant temperature of 29.8 °C over a period of 70 h. The result of the turbidity measurement is shown in Fig. 10. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l -1 ) with 2.0% by weight HEC 776 kg mol -1as a temperature-independent, water-soluble polymer additive. The straight line is a linear fit through all measurement points. For the thermoresponsive polymer poly(oligoethylene glycol methyl ether methacrylate-block-2-(2-methoxyethoxy)-ethyl methacrylate), the addition of the temperature-independent additive HEC also yields 776 kg mol -1 achieve long-term stabilization of turbidity values. Although a decrease in turbidity values ​​is observed over a period of 70 hours, this decrease is so slight that it remains within the limits of the instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber optic temperature measurement over longer periods. Example 7: Aqueous solution of poly(N-vinylcaprolactam) (prepared according to Synthesis Example 2) additived with 2 wt.% HEC 776 kg mol -1

[0087] Preparation of the solution: The thermoresponsive polymer poly(N-vinylcaprolactam) (prepared according to Synthesis Example 2) is stirred for 2 h at a concentration of 3 g l -1 in H 2 O. Then HEC is dissolved in 776 kg mol -1 (M w = 776 kg mol -1 ) was added until its concentration reached 2.0 wt.%.

[0088] The turbidity measurement was carried out at a constant temperature of 36.1 °C over a period of 70 h. The result of the turbidity measurement is shown in Fig. 11. This shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l -1 ) with 2.0% by weight HEC 776 kg mol -1as a temperature-independent, water-soluble polymer additive. The straight line is a linear fit through all measurement points. For the thermoresponsive polymer poly(N-vinylcaprolactam), the addition of the temperature-independent additive HEC also yields 776 kg mol -1 a long-term stabilization of the turbidity values. Although an increase in the turbidity values ​​is observed over a period of 70 hours, this is so slight that it remains within the limits of the instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber optic temperature measurement over longer periods. Example 8: Poly(propylene glycol) (PPG) in 1-butyl-3-methylimidazolium bis-trifluoromethanesulfonylimide, additived with 2 wt.% poly(ethylene glycol) (PEG 5000)

[0089] PPG is dissolved in the ionic liquid 1-butyl-3-methylimidazolium bis-trifluoromethanesulfonylimide to form a mixture with a PPG content of 10 wt.%. As soon as this solution is heated to the transition temperature range, macroscopic phase separation occurs between the polymer and the ionic liquid, which persists even upon cooling without mechanical action. Only shaking or stirring at lower temperatures restores a clear solution. In this composition, the mixture is unsuitable for fiber optic temperature measurements in several respects: it phase separates in the transition temperature range instead of exhibiting temperature-dependent turbidity, and the phase separation is not reversible without mechanical action.

[0090] When 0.4 wt% sodium dodecyl sulfate and 2.0 wt% PEG 5000 (M w = 675 kg mol -1), the turbidity values ​​of this mixture are stabilized in the temperature range of the phase transition. The result of the turbidity measurement is shown in Fig. 12. This shows the time course of the transmission through the solution of PPG in 1-butyl-3-methylimidazolium bis-trifluoromethanesulfonylimide with 0.4 wt.% sodium dodecyl sulfate and 2.0 wt.% PEG 5000 as a temperature-independent soluble polymer additive. The transmission follows the temperature course in all cycles; however, stabilization is not complete, as the transmission values ​​in later cycles at high temperature no longer reach the minimum transmission of the first cycles. Even though stabilization is not complete, a very significant improvement in stability compared to the unadditized sample is achieved. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2015 100 097 A1

[0002]

Claims

[1] A mixture of substances for a fiber-optic measuring system for temperature measurement, comprising at least one thermoresponsive polymer, at least one viscosity increaser and at least one solvent selected from the group consisting of water, methanol, ethanol, propanol, butanol, butyl acetate, chloroform, ionic liquids and mixtures thereof, wherein the at least one viscosity increaser is at least one polymer soluble in the at least one solvent and having a mass-average molar mass M w of at least 200 kg / mol. [2] Mixture of substances according to the preceding claim, characterized by that the mass-average molar mass M w of the at least one polymer soluble in at least one solvent - at least 300 kg / mol, preferably at least 400 kg / mol, particularly preferably at least 500 kg / mol, very particularly preferably at least 600 kg / mol, in particular at least 700 kg / mol, for example at least 800 kg / mol, and / or - at most 20,000 kg / mol, preferably at most 6,000 kg / mol, particularly preferably at most 3,000 kg / mol, very particularly preferably at most 2,000 kg / mol, in particular at most 1,500 kg / mol, for example at most 1,000 kg / mol. [3] Mixture of substances according to one of the preceding claims, characterized by that the mixture of materials - at least 0.01 wt.%, preferably at least 0.1 wt.%, particularly preferably at least 1.0 wt.%, very particularly preferably at least 1.5 wt.%, in particular at least 1.8 wt.%, for example at least 2.0 wt.%, of the at least one viscosity increaser, based on the total weight of the mixture, and / or - at most 20 wt.%, preferably at most 15 wt.%, particularly preferably at most 10 wt.%, very particularly preferably at most 5.0 wt.%, in particular at most 3.0 wt.%, of the at least one viscosity increaser, based on the total weight of the mixture. [4] Mixture of substances according to one of the preceding claims, characterized by that the at least one viscosity increaser is characterized in that a solution comprising 2.0 wt.% of the at least one viscosity increaser and 98.0 wt.% of the at least one solvent has a dynamic viscosity, measured at 23 °C and a shear rate of 53.8 Hz, which - at least 0.6 Pa s, preferably at least 0.8 Pa s, particularly preferably at least 1.0 Pa s, and / or - at least 0.5 Pa s higher, preferably at least 0.7 Pa s higher, particularly preferably at least 0.9 Pa s higher, than the dynamic viscosity, measured at 23 °C and a shear rate of 53.8 Hz, of the at least one solvent, and / or - is at least 50 times higher, preferably at least 70 times higher, particularly preferably at least 90 times higher, than the dynamic viscosity, measured at 23 °C and a shear rate of 53.8 Hz, of the at least one solvent. [5] Mixture of substances according to one of the preceding claims, characterized by that the mixture of substances in a temperature range above an initial temperature T A and below a final temperature T E has a monotonous progression of its optical transparency as a function of temperature, wherein the temperature range preferably - extends over at least 3 K, preferably over at least 5 K, and / or - is in the range from 5 °C to 300 °C, preferably from 10 °C to 95 °C, particularly preferably from 35 °C to 40 °C, very particularly preferably from 36.5 °C to 40 °C, and / or extends over this range. [6] Mixture of substances according to one of the preceding claims, characterized by that the at least one thermoresponsive polymer - selected from the group consisting of • alkyl-substituted poly[(meth)acrylamide]s, particularly preferably poly(dialkylacrylamide)s, e.g. poly(diethylacrylamide); poly[oligo(ethylene glycol methacrylate)]s, particularly preferably poly[2-(2-methoxyethoxy)ethyl methacrylate)] and copolymers thereof and poly(2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) and copolymers thereof; poly[oligo(ethylene glycol acrylate)]s; poly(N-vinylamide)s, particularly preferably poly(N-vinyllactam)s; polymethylvinyl ethers; poly(oxazoline)s; and mixtures thereof, • polyvinyl ethers carrying cationic groups at the terminal end of the repeating unit, as well as mixtures thereof, • Poly(butadiene), Poly(styrene), Poly(dimethylacrylamide), Poly(isopropylacrylamide), Poly(tert-butylacrylamide), Poly(methyl methacrylate), Poly(n-butyl methacrylate), Poly(benzyl methacrylate), Poly(3-fluorobenzyl methacrylate), Poly(3-methylbenzyl methacrylate), Poly(3-methoxybenzyl methacrylate), Poly(2-phenylethyl methacrylate), Poly(4-phenylbutyl methacrylate), poly(4-(phenylazo)phenyl methacrylate), poly(N-(4-vinylbenzyl)carbazole), poly(glycidyl(2-ethoxyethyl) ether), poly(glycidyl methyl ether), poly(glycidyl ethyl ether), poly(ethylene glycol), poly(propylene glycol), and mixtures thereof, • Poly(vinylbenzyldialkylamine)s, preferably poly(dialkyl-(4-vinylbenzyl)amine), and mixtures thereof • Poly(2-chloroethyl vinyl ether-alt-maleic anhydride), • Poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide), • and mixtures thereof, and / or - is contained in the substance mixture in a concentration in the range from 0.01 g / l to 100 g / l, preferably from 0.1 g / l to 10 g / l, particularly preferably from 1.0 g / l to 5.0 g / l. [7] Mixture of substances according to one of the preceding claims, characterized by that the at least one polymer soluble in the at least one solvent is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethylcelluloses, hydroxyethylcelluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl radicals of C 1 to C 3; Poly(styrene); Poly(methyl methacrylate); Poly(2-hydroxyethyl methacrylate); Poly(acrylamide-co-choline acrylate); Hydroxypropyl cellulose; and mixtures thereof. [8] Mixture of substances according to one of the preceding claims, characterized by , that - the ionic liquids each comprise or consist of at least one cation and at least one anion, where • the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphosphonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or • the at least one anion is selected from the group consisting of bis(trifluoromethanesulfone)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof, and / or - the substance mixture additionally contains at least one surfactant, preferably sodium dodecyl sulfate, preferably if the at least one solvent is or contains at least one ionic liquid. [9] Mixture of substances according to one of the preceding claims, characterized by that at least one solvent - Water is, wherein the at least one thermoresponsive polymer is selected from the group consisting of alkyl-substituted poly[(meth)acrylamide]s, particularly preferably poly(dialkylacrylamide)s, e.g. poly(diethylacrylamide); poly[oligo(ethylene glycol methacrylate)]s, particularly preferably poly[2-(2-methoxyethoxy)ethyl methacrylate)] and copolymers thereof and poly(2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) and copolymers thereof; poly[oligo(ethylene glycol acrylate)]s; poly(N-vinylamide)s, particularly preferably poly(N-vinyllactam)s; polymethyl vinyl ethers; poly(oxazoline)s; and mixtures thereof, and wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as e.g.Carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethylcelluloses, hydroxyethylcelluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(acrylamide-co-choline acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl radicals of C. 1 to C 3 ; and mixtures thereof, or - is at least one ionic liquid, wherein the at least one thermoresponsive polymer is selected from the group consisting of poly(butadiene), poly(styrene), poly(dimethylacrylamide), poly(isopropylacrylamide), poly(tert-butylacrylamide), poly(methyl methacrylate), poly(n-butyl methacrylate), poly(benzyl methacrylate), poly(3-fluorobenzyl methacrylate), poly(3-methylbenzyl methacrylate), poly(3-methoxybenzyl methacrylate), poly(2-phenylethyl methacrylate), poly(4-phenylbutyl methacrylate), poly(4-(phenylazo)phenyl methacrylate), poly(N-(4-vinylbenzyl)carbazole), poly(glycidyl(2-ethoxyethyl)ether), poly(glycidyl methyl ether), poly(glycidyl ethyl ether), poly(ethylene glycol), poly(propylene glycol), and mixtures thereof, wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethylcelluloses, hydroxyethylcelluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(acrylamide-co-choline acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl radicals of C 1 to C 3 ; and mixtures thereof, and wherein preferably • the at least one ionic liquid comprises or consists of at least one cation and at least one anion, wherein the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-alkylimidazolium; 1-butylpyridinium; triethylpentylphosphonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or the at least one anion is selected from the group consisting of bis(trifluoromethanesulfon)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof, and / or • the mixture additionally contains at least one surfactant, preferably sodium dodecyl sulfate, or - chloroform or a mixture of chloroform and methanol, wherein the at least one thermoresponsive polymer is selected from the group consisting of polyvinyl ethers carrying cationic groups at the terminal end of the repeating unit, and mixtures thereof, and wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of poly(styrene), poly(methyl methacrylate), poly(2-hydroxyethyl methacrylate), and mixtures thereof, or - methanol or a mixture of methanol and water, wherein the at least one thermoresponsive polymer is selected from the group consisting of poly(vinylbenzyldialkylamines), preferably poly(dialkyl-(4-vinylbenzyl)amine), and mixtures thereof, and wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of hydroxypropylcellulose, poly(2-hydroxyethyl methacrylate), and mixtures thereof, or - butyl acetate, preferably n-butyl acetate, wherein the at least one thermoresponsive polymer is poly(2-chloroethyl vinyl ether-alt-maleic anhydride), and wherein the at least one polymer soluble in the at least one solvent is poly(methyl methacrylate), or - ethanol, propanol, preferably n-propanol, or butanol, preferably n-butanol, or a mixture thereof, wherein the at least one thermoresponsive polymer is poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide), and wherein the at least one polymer soluble in the at least one solvent is poly(2-hydroxyethyl methacrylate). [10] Fiber optic measuring system for temperature measurement comprising at least one temperature-sensitive element, at least one light-conducting optical fiber, a light source, and at least one optical detector, wherein the at least one temperature-sensitive element comprises a substance mixture according to one of the preceding claims. [11] Fiber optic measuring system according to claim 10, characterized by , that - the temperature-sensitive element comprises a container in which the substance mixture is arranged, wherein the container preferably comprises a metallic material, and / or - the temperature-sensitive element is connected to at least one light-conducting optical fiber, wherein preferably the temperature-sensitive element is connected to the at least one detector via at least one light-conducting optical fiber and / or is connected to the light source via at least one light-conducting optical fiber, and / or - the at least one optical detector is configured such that it can detect a change in the light output of a light emanating from the light source and passing through the temperature-sensitive element. [12] Fiber optic measuring system according to claim 10 or 11, characterized by that the fiber optic measuring system additionally comprises at least one fiber optic coupling element, wherein the at least one fiber optic coupling element is preferably - is selected from the group consisting of fiber optic couplers, fiber optic multiplexers, fiber optic switches, and combinations thereof, and / or - is connected to the light source by at least one optical fiber, and / or - is connected to the thermosensitive element by at least one optical fiber, and / or - is connected to at least one detector by at least one optical fiber. [13] Fiber optic measuring system according to claim 12, characterized by that the at least one fiber optic coupling element comprises at least one first fiber optic coupling element and at least one second fiber optic coupling element, wherein - the at least one first fiber-optic coupling element is connected to the thermosensitive element and to the at least one detector via at least one optical fiber, and / or - the at least one second fiber-optic coupling element is connected to the thermosensitive element and to the at least one detector via at least one optical fiber, and / or - the at least one first fiber optic coupling element is connected to the at least one second fiber optic coupling element via at least one optical fiber. [14] A method for temperature measurement using a fiber optic measuring system according to any one of claims 10 to 13, in which a) light from the light source is coupled into the thermosensitive element and into the at least one detector by means of the at least one optical fiber, wherein light passing from the light source to the at least one detector at least partially passes through the thermosensitive element on its way to the at least one detector; b) the intensity of the light that has passed through the thermosensitive element is determined using the detector; c) using the determined intensity, a value for the temperature of the thermosensitive element is determined. [15] Method according to claim 14, characterized by , that - after step c) the determined temperature value is transmitted to a control and monitoring unit, and / or - additional light emanating from the light source is guided to the detector without passing through the thermosensitive element and serves as a reference signal.

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