Colorimetric polymer time-temperature indicators

Abstract

A system and method for monitoring temperature includes a sealed housing comprising a main chamber with a known relative internal humidity and a polymeric nanofilm disposed in the sealed housing, where the polymeric nanofilm is configured to change color in response to a change in temperature. The systems and methods can include an absorbent in the sealed housing configured to absorb moisture released by the polymeric nanofilm.

Description

COLORIMETRIC POLYMER TIME-TEMPERATURE INDICATORSCROSS REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims the priority and benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Serial No. 63 / 633,600 filed April 12, 2024, entitled “COLORIMETRIC POLYMER TIME-TEMPERATURE INDICATORS”. U.S. Provisional Patent Application Serial Number 63 / 633,600 is herein incorporated by reference in its entirety.TECHNICAL FIELD

[0002] Embodiments are generally related to the field of temperature sensing. Embodiments are further related to temperature monitoring. Embodiments are also related to the field of polymeric film. Embodiments are further related to colorimetric polymer nanofilm. Embodiments are further directed to colorimetric polymer nanofilm-based timetemperature indicators for recording a reversible or an irreversible change of temperatures in cold chain logistics.BACKGROUND

[0003] Maintaining low-temperature cold storage conditions is an essential part of the manufacturing, quality control, storage, food transportation, and medical product (e.g., vaccine) supply chain. There are generally considered to be four types of refrigeration systems: frozen, at -18°C or below (subzero temperature); cold chilled, with temperatures ranging from 0°C to 1 °C; medium chilled, at 5°C; and exotic chilled, at 10°C-15°C.

[0004] Different products require different temperatures for effective storage or transportation. For example, the Moderna® COVID-19 vaccine needs to be stored at -15°C to -50°C to maintain the integrity of the product. Likewise, Pfizer / BioNTech® COVID-19 vaccine needs to be stored below -60°C.

[0005] Moreover, different foods require storage at different subzero temperatures. For example, the optimum temperature for one-month storage of Atlantic salmon is -24°C to - 30°C, while tilapia, and ice cream must be stored frozen at -18°C during transportation.

[0006] Temperature disruption during transportation of foods ranges from approximately - 1 .2°C to 20°C, which can cause significant damage to the appearance, taste, nutritional value, and shelf-life of the food. Most importantly, temperature-dependent perishable products degrade faster at room temperature. For example, Pfizer / BioNTech® COVID-19 vaccines have up to 2 hours of shelf-life before dilution, and up to 8 hours of shelf-life after dilution at room temperature. Moderna® COVID-19 vaccines have up to 12 hours of shelflife at room temperature. 50% of vaccines are discarded annually due to temperature disruption during storage or transportation. Hence, it is important to identify if the desired subzero temperature during storage or transportation of a product is hampered / disrupted above the shelf-life. Consequently, both monitoring and recording the history of subzero storage temperatures is critical.

[0007] Traditional electronic data loggers are commonly used for this purpose. However, these types of data loggers are expensive, energy-intensive, slow, and create the risk of data leaking. Other solutions such as radio frequency identification (RFID) with integrated circuits are another option. However, these tools are energy-dependent and can be costly.

[0008] As such, there is a need in the art for alternative approaches to monitoring temperature, particularly for cold storage and associated cold storage logistics, as disclosed herein.SUMMARY

[0009] The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[0010] It is, therefore, one aspect of the disclosed embodiments to provide a temperature sensor.

[0011] It is another aspect of the disclosed embodiments to provide methods and systems for monitoring temperature.

[0012] It is another aspect of the disclosed embodiments to provide a time temperature indicator (TTI).

[0013] It is another aspect of the disclosed embodiments to provide an irreversible time temperature indicator (TTI).

[0014] It is another aspect of the disclosed embodiments to provide a reversible temperature monitoring device.

[0015] It is another aspect of the disclosed embodiments to provide methods, systems, and apparatuses for colorimetric polymer nanofilm-based time-temperature indicators for recording changes of temperatures in the cold chain.

[0016] It will be appreciated that the methods and systems can be achieved according to the embodiments disclosed herein. For example, in an embodiment, a temperature monitoring system comprises a sealed housing comprising a main chamber with a known relative internal humidity and a polymeric nanofilm disposed in the sealed housing. In an embodiment, the temperature monitoring system further comprises an absorbent in the sealed housing. In an embodiment, the temperature monitoring system further comprises adrying module configured to house the absorbent, and a gate between the drying module and the main chamber, the gate configured to open in order to create a fluidic connection between the absorbent and moisture in the sealed housing. In an embodiment, the absorbent comprises at least one of silica gel; and / or molecular sieve. In an embodiment, the polymeric nanofilm comprises at least one of Chitosan and CMC-N3. In an embodiment, the polymeric nanofilm comprises Chitosan, and carboxymethyl cellulose. In an embodiment, the polymeric nanofilm is configured to change color as a result of an ambient temperature change. In an embodiment, the polymeric nanofilm has a characteristic color indicative of a temperature.

[0017] In an embodiment, a temperature monitoring method comprises disposing a temperature monitoring system comprising a polymeric nanofilm in a main chamber of a housing, in an environment and identifying a change in color of the polymeric nanofilm, the change in color being indicative of a temperature change. In an embodiment, the temperature monitoring method further comprises exposing an internal volume of the housing to an absorber with a gate formed between the main chamber and a drying module. In an embodiment, the absorber absorbs moisture released by the polymeric nanofilm when the temperature changes. In an embodiment, the polymeric nanofilm has a characteristic color indicative of a temperature.

[0018] In an embodiment, a method of manufacturing a temperature monitoring system comprises disposing a polymeric nanofilm in a main chamber of a housing, identifying a relative humidity of an interior volume of the main chamber of the housing, and sealing the housing. In an embodiment, the method of manufacturing a temperature monitoring system further comprises attaching a drying module to the housing, the drying module configured to house an absorber and forming a gate sealing the drying module from the main chamber when the gate is closed. In an embodiment, the method of manufacturing a temperature monitoring system further comprises establishing a fluidic connection between the absorber and the main chamber when the gate is open. In an embodiment, the method of manufacturing a temperature monitoring system further comprises selecting a mass of the absorber to store a desired volume of moisture released by the polymeric film as a result of a temperature change. In an embodiment, the method of manufacturing a temperature monitoring system further comprise manufacturing the polymeric nanofilm. In anembodiment, manufacturing the polymeric nanofilm further comprises plasma treating a silicon wafer so that a surface of the silicon wafer is negatively charged, immersing the silicon wafer in a positively charged chitosan solution, and exposing the silicon wafer to UV-light. In an embodiment, manufacturing the polymeric nanofilm further comprises washing the silicon wafer after the plasma treatment. In an embodiment, the polymeric nanofilm comprises Chitosan, carboxymethyl cellulose, and 4-azidoaniline hydrochloride.BRIEF DESCRIPTION OF THE FIGURES

[0019] The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.

[0020] FIG. 1 A depicts a temperature monitoring system, in accordance with the disclosed embodiments;

[0021] FIG. 1 B depicts a temperature monitoring system with the absorber disposed in the main chamber, in accordance with the disclosed embodiments;

[0022] FIG. 2A depicts a chemical formula of aspects of the polymeric nanofilm, in accordance with the disclosed embodiments;

[0023] FIG. 2B depicts aspects of the polymeric nanofilm, in accordance with the disclosed embodiments;

[0024] FIG. 3 depicts a block diagram of a method of monitoring temperature change with a temperature monitoring system, in accordance with the disclosed embodiments;

[0025] FIG. 4 depicts a flow chart of steps associated with a method of manufacturing a temperature monitoring system, in accordance with the disclosed embodiments;

[0026] FIG. 5 depicts a flow chart of steps associated with a method of manufacturing a polymeric nanofilm, in accordance with the disclosed embodiments;

[0027] FIG. 6 depicts an exemplary image of a temperature monitoring system before and after a temperature change, in accordance with the disclosed embodiments;

[0028] FIG. 7 depicts a chart of response time for absorption and desorption associated with a temperature monitoring system, in accordance with the disclosed embodiments;

[0029] FIG. 8 depicts a chart of film thinknoet: rwr multiple temperature change cycles, inaccordance with the disclosed embodiments;

[0030] FIG. 9 depicts charts of response time as a function of relative humidity and surface area of polymeric films in a temperature monitoring system, in accordance with the disclosed embodiments;

[0031] FIG. 10 depicts an image illustrating changes in color as a result of temperature for polymeric films in a temperature monitoring system, in accordance with the disclosed embodiments;

[0032] FIG. 11 depicts a chart illustrating changes in total color difference (AE) as a result of temperature change for polymeric films in a temperature monitoring system, in accordance with the disclosed embodiments;

[0033] FIG. 12 depicts an image illustrating thickness of polymeric films based on temperature in a temperature monitoring system, in accordance with the disclosed embodiments;

[0034] FIG. 13 depicts a chart of temperature change histories for polymeric films in a temperature monitoring system, in accordance with the disclosed embodiments;

[0035] FIG. 14A depicts exemplary images of polymeric films subject to temperature changes in a temperature monitoring system, in accordance with the disclosed embodiments; and

[0036] FIG. 14B depicts a chart of color transition histories for polymeric films subject to temperature changes in a temperature monitoring system, in accordance with the disclosed embodiments.DETAILED DESCRIPTION

[0037] Embodiments and aspects of the disclosed technology are presented herein. The particular embodiments and configurations discussed in the following non-limiting examples can be varied, and are provided to illustrate one or more embodiments, and are not intended to limit the scope thereof.

[0038] Reference to the accompanying drawings, in which illustrative embodiments are shown are provided herein. The embodiments disclosed can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. Like numbers refer to like elements throughout.

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0040] Throughout the specification and claims, terms may have nuanced meanings suggested or implied in context beyond an explicitly stated meaning. Likewise, the phrase “in one embodiment” as used herein does not necessarily refer to the same embodiment and the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment. It is intended, for example, that claimed subject matter include combinations of example embodiments in whole or in part.

[0041] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. Itwill be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0042] It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

[0043] It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

[0044] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

[0045] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0046] The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAG, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0047] All of the compositions and / or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and / or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

[0048] Embodiments disclosed herein are generally related to colorimetric polymer nanofilm-based time temperature indicators (TTI) for recording a change in temperature, in cold chain logistics or other fields. In certain embodiments, the time temperature indicator can be an irreversible temperature monitoring (iRTM) device that comprises a polymeric nanofilm fabricated with chitosan and azide-modified carboxymethyl cellulose that displays full-spectrum colors when environmental temperature or relative humidity changes, and a drying module containing a precise amount of moisture absorber in a sealed compartment. The disclosed TTI and iRTMs provide quick color response in temperature ranges from room temperature (nominally 23°C) to -30°C in fewer than 50 seconds.

[0049] The embodiments can be also configured to have a selected threshold time (ttn). The threshold time can be precisely tuned by adjusting moisture absorber types, the weight of the absorber, the interior relative humidity (RH) in the sealed compartment, and the storage temperature. Threshold times can be achieved for temperature disruptions from -30°C to23°C for a time range of 5 minutes to 7 hours, which aligns with the ideal shelf-life for various vaccines and other bioreagents at room temperature. The threshold time can be expanded to over 30 hours by tuning the parameters.

[0050] The disclosed polymer nanofilm-based TTIs and iRTMs can be used as a low-cost, and sustainable solution for temperature monitors in cold chain logistics, and can be used for other temperature monitoring applications in cold storage facilities for wine and preserved food, smart vehicles, and anticounterfeiting devices. The disclosed embodiments are energy independent so they will not fail if power is disrupted, and are robust to physical jarring in a manner many prior art solutions are not.

[0051] FIG. 1A illustrates aspects of a temperature monitoring system 100 in accordance with the disclosed embodiments. In this embodiment, the system 100 is an irreversible time temperature indicator, but in other embodiments, it should be appreciated that it is possible to configure a system as a reversible temperature indicator, as further detailed herein.

[0052] The irreversible temperature monitoring system 100 comprises a polymeric nanofilm 105 that displays a spectrum of temperature dependent colors when environmental temperature (or associated relative humidity “RH”) changes. The polymeric nanofilm 105 is housed in a housing 110. The housing 1 10 is generally sealed from external air, to prevent the introduction of ambient moisture. The housing 1 10 is configured of a material that is transparent or otherwise sufficiently translucent that the interior volume is visible.

[0053] The housing 110 of the irreversible temperature monitoring system 100 further comprises a drying module 1 15, containing a precise amount of moisture absorber 120. As illustrated in FIG. 1 A, the drying module 115 can be attached to (e.g., on top of, or on other parts of) the main chamber 125 of the housing 110 with the polymeric nanofilm 105 inside.

[0054] The housing 110 and / or drying module 1 15 is further configured with a gate 130, that allows the moisture absorber 120 to be released into the main chamber 125 on demand. It should be appreciated that the gate 130 can comprise any number of configurations that initially separate the moisture absorber 120 from the polymeric nanofilm 105, that can then be moved, punctured or otherwise, modified to allow the moisture absorber 120 to be in fluidiccontact with the moisture released by the polymeric nanofilm 105 in the housing 110.

[0055] FIG. 1 B shows the gate 130 removed so that the moisture absorber 120 is dispensed into the main chamber 125 of the housing 1 10.

[0056] When the moisture absorber 120 is not present inside the main chamber 125, moisture is exchanged freely between the polymer nanofilm 105 and the air surrounding it, which allows for a reversible color display as temperature changes. For example, when the temperature increases, the polymeric nanofilm 105 in the main chamber 125 de-swells as it releases moisture into the surrounding air. The de-swelling causes the polymeric nanofilm 105 to change color in a well-behaved way, such that the color of the polymeric nanofilm 105 is indicative of the temperature.

[0057] If the temperature decreases, the polymeric nanofilm 105 in the main chamber 125 swells as it absorbs moisture from the surrounding air. The swelling similarly causes the polymeric nanofilm 105 to change color.

[0058] The moisture absorber 120, allows the system 100 to act as an irreversible timetemperature indicator. When the moisture absorber 120 is introduced into fluidic connection with the polymeric nanofilm 105, for example as illustrated in FIG.1 B where the moisture absorber 120 is presented in the main chamber 125, the moisture absorber 120 will permanently absorb the moisture released during the de-swelling of the polymeric nanofilm 105 in the air when the temperature rises. Thus, the moisture will be totally unavailable (or potentially partially available) for the polymeric nanofilm 105 depending on the type and amount of moisture absorber 120 and drying time, if / when the temperature decreases. As a result, the polymeric nanofilm 105 cannot change back to its original color.

[0059] It should be appreciated that the system can comprise a reversible temperature monitoring system simply by keeping the drying module 115 sealed off from the main chamber 125. Alternatively, a reversible temperature monitoring system can comprise the polymeric nanofilm 105 disposed in a sealed housing.

[0060] FIG. 2A illustrates a chemical formula for constituent particles, in an embodimentof the polymeric nanofilm 105, in accordance with the disclosed embodiments. The polymeric nanofilm 105 generally comprises biocompatible and environment-friendly polymers, including chitosan (CHI) 205, and azide-modified carboxymethyl cellulose (CMC-N3) 210. In an exemplary embodiment, the polymeric nanofilm 105 can comprise Chitosan (Mw=50000- 190000), carboxymethyl cellulose (Mw=250000, degree of substitution^.?), and 4- azidoaniline hydrochloride.

[0061] In certain embodiments, the moisture absorber 120 can comprise silica gel (SG) and / or molecular sieve (MS). In one embodiment, the silica gel can have a pore size of 60 A, 230-400 mesh size, 60-63 pm. In an embodiment, a molecular sieve comprises 4A, 0.4-0.8 mm beads.

[0062] FIG. 2B illustrates an exemplary embodiment of the polymeric nanofilm 105, with an exploded view 250 showing moisture capture via the film. As illustrated, the nanofilm 105 generally comprises chitosan 205 and CMC-N3 210 configured as a polymeric nanofilm 105. Moisture 220 is captured in the polymeric nanofilm 105. The amount of moisture capture in the polymeric nanofilm 105 is temperature dependent. As such, moisture 220 may also be present in the surrounding ambient environment, depending on the temperature.

[0063] The color of the polymeric nanofilm 105 is a function of the amount of moisture 220 captured by the polymeric nanofilm 105, and the amount of moisture 220 is a function of temperature. As such, the color of the polymeric nanofilm 105 is indicative of the ambient temperature.

[0064] FIG. 3 illustrates a method 300 associated with temperature monitoring using a time temperature indicator system, such as system 100, as detailed herein. At the first step 305, a temperature indicator system 100 can be activated by dispensing the absorbing material 120 into fluidic connection with the polymeric nanofilm 105 in a housing 1 10 sealed off to external moisture.

[0065] In this exemplary diagram, the starting temperature is a “low” temperature 306. This is meant to suggest that the temperature could be frozen, cold chilled, medium chilled, or exotic chilled. The starting temperature in this example is selected as “low” because in manyapplications it is desirable to monitor, for example, a frozen product environment during transportation, to ensure the frozen product did not unfreeze during transport. However, the starting temperature need not be cold, and the method can more generally apply to any starting temperature.

[0066] At its initial low temperature 306, the polymeric nanofilm 105 is moisture dense. This is illustrated in the exploded view of the film 105, where moisture 220 is shown in the film 105. As such, there is little ambient moisture in the sealed chamber 125, and therefore very little moisture in the absorber material 120. At this initial condition, the polymeric nanofilm 105 has a characteristic color, in this case a pink, indicative of the cold temperature surrounding the system 100.

[0067] At step 315, the surrounding temperature has increased to a “high” temperature 316 as illustrated by arrow 310. This could perhaps be the result of a power outage causing a freezer to stop cooling for a period of time, resulting in the temperature increasing. In this context, a “high” temperature can refer to any temperature above a desired threshold, such as for example, room temperature, although it should be appreciated any temperature exceeding the acceptable cold temperature threshold could be considered a “high” temperature 316.

[0068] The polymeric nanofilm will release moisture 220 into the housing, when the temperature rises. The ambient moisture 220 is then absorbed by, and encapsulated in, the moisture absorber 120. The lower moisture content in the polymeric nanofilm 105 causes the polymeric nanofilm 105 to shrink (for example to a smaller size or thickness). As the polymeric nanofilm 105 changes size the visible color of the polymeric nanofilm 105 changes, in this case to a light green color. The change in color can thus be indicative of an increase in the ambient temperature above a threshold temperature. The threshold temperature can be suited to the application as further detailed herein.

[0069] At step 315, as the moisture 220 is released from the polymeric nanofilm 105, the moisture absorber 120 absorbs the moisture 220. The moisture absorber 120, unlike the polymeric nanofilm 105, can be selected to not release the absorbed moisture 220 with changes in ambient conditions such tomnAratiiro in certain embodiments, the moistureabsorber 220 can comprise silica gel (SG) and / or molecular sieve (MS), although any moisture absorber that exhibits one way absorption of moisture could be used.

[0070] Arrow 320 indicates that the temperature may return to a lower temperature, which could be any temperature below the threshold temperature. For example, at arrow 320, power could be restored to the freezer, causing the freezer to cool the internal volume back to the low temperature 306. Note, this presents a particularly dangerous situation for a product that might be compromised by a temporary increase in temperature, since an unsuspecting person might open the freezer, feel that it is cold, and assume it has remained cold.

[0071] At step 325, the temperature reversion to a lower temperature does not change the color of the polymeric nanofilm 105. This is a result of the moisture 220 having been entrained in the absorber material 120. As a result, the cooler temperature does not result in the moisture being re-absorbed in the polymeric nanofilm 105, leaving the polymeric nanofilm 105 at the same size (e.g. thickness) and same color. As such, if a person opens the freezer and finds it cold, they will nevertheless be aware that the internal temperature in the freezer rose above the threshold temperature for a certain amount of time as indicated by the change in color of the polymeric nanofilm 105.

[0072] FIG. 4 illustrates a fabrication method 400 for manufacturing a time-temperature monitoring device as disclosed herein. The method begins at step 405. At step 410 a polymeric nanofilm can be fabricated. Next at step 415, the film is disposed into a housing. The relative humidity inside the housing can be carefully controlled as the temperature monitoring is dependent on the color of the polymeric film which is dependent on absorbing or emitting moisture.

[0073] If the system is meant to be an irreversible time temperature indicator, the housing can further be fitted with a drying module and a gate, and can be configured to hold a precise amount of moisture absorber.

[0074] Once the polymeric film is in the housing, and the optional moisture absorber is disposed in the drying module, the housing can be sealed at step 420. The system is nowready for use, and the method ends at 425.

[0075] FIG. 5 illustrates a method of fabricating a polymeric nanofilm as shown at step 410 of the method 400. The process can comprise the use of “layer-by-layer” (LbL) technology. First, at step 505 a solution of chitosan and CMC-N3 (optionally 2 mg / ml) can be prepared using DI water. The pH of the solutions can be adjusted to nominally pH 4 by using 0.1 M HCI / NaOH at step 510. It should be appreciated that the amounts provided herein are exemplary and different amounts and levels can be used according to design considerations.

[0076] The layer-by-layer process can be conducted by using an ND-R rotary LbL dip coater. First, at step 515 a silicon wafer can be plasma-treated so that the surface is negatively charged. At step 520 the wafer can be immersed into a positively charged chitosan solution. To complete one layer of the LbL film, the silicon wafer is washed at step 525 and then dipped into a negatively charged CMC-N3 solution at step 530. The process is repeated creating several bilayers of the nanofilm as illustrated by arrow 535.

[0077] After the dipping cycles are finished, the film is crosslinked with UV-light at step 540. In an exemplary embodiment this can comprise treatment with, for example, a 13.92 mW / cm2power for 10 minutes with an optional photomask on top of it. The photomask is used to create a pattern by allowing UV light through a designed area if desired. At step 545, under UV light, the azido groups (-N3) break into nitrogen and highly reactive nitrene (-N). The nitrene group forms covalent bonds with the neighboring molecules. Placing the patterned mask over the film leaves the exposed area of the film crosslinked, whereas the unexposed areas remain un-crosslinked. Thus, designed crosslinked structures can be created on the film.

[0078] As noted, the embodiments disclosed herein can comprise a reversible temperature monitoring system, or an irreversible temperature monitoring system. Applications for these embodiments may differ but fundamentally, they are both controlled by the moisture content of the polymeric nanofilm.

[0079] As noted, the reversible temperature monitoring system can be fabricated at a controlled temperature (e.g., room temperature) and at a controlled relative humidity (e.g.,nominally 60%, representing the dewpoint inside the device at a given temperature). For example, the nanofilm provides a consistent green color at 23°C and 60% in relative humidity (RH), and a pink color at -30°C and a saturated condition (100% RH) as illustrated in image 600 of FIG. 6.

[0080] FIG. 7 illustrates a chart 700 showing response time during absorption and desorption cycle. The thickness of the nanofilm will increase in response to a temperature change from, for example, room temperature to -30°C as illustrated by chart 800 in FIG. 8.

[0081] Moreover, the film has cyclic thickness changes from nominally 325 ± 5 nm to 500 ± 5 nm thickness, as illustrated by chart 800 in FIG. 8 showing 22 cycles due to simultaneous absorption of moisture at -30°C and desorption of condensed moisture at 23°C. These exemplary values are meant to illustrate operational parameters of the disclosed embodiments.

[0082] The response time to change the color from 23°C to -30°C (absorption cycle) and -30°C to 23°C (desorption cycle) is relatively fast; response to a temperature change by changing color can be for example, 2 minutes for the absorption cycle and around 40 seconds for the desorption cycle as shown in chart 700 of FIG. 7. Here, the desorption cycle represents the temperature disruption / fluctuation from subzero (-30°C) to room temperature (23°C). The response can be further tailored by controlling the relative humidity in the system at fabrication and surface area of the nanofilm, as illustrated in chart 900 of FIG. 9 providing response time as a function of relative humidity, and chart 950 illustrating response time as a function of surface area. Fast color-changing behavior is possible within a time scale of roughly 50 seconds.

[0083] Furthermore, the color of the film shifts from green, yellowish green, pinkish yellow, and pink and so forth as illustrated in chart 1000 of FIG 10. It is noteworthy that the film can show inherent patterns if desired at all subzero temperatures, indicating the ability of the film to display encoded complex information (e.g., a warning that the temperature reached an unsafe level for a given application).

[0084] The points indicating the colnr nf tho filmdistinguishable in response to eachtemperature and relative humidity. The average L, a, and b values of the film color at for example 25%, 50%, and 85% internal relative humidity were calculated and are illustrated in Table 1 .TABLE 1

[0085] The total color difference (AE) can be calculated using average L, a, and b values, which is an important quantitative parameter for measuring color changes. The values are plotted at different temperatures and relative humidities in chart 1100 of FIG. 11 .

[0086] As shown by chart 1200 of FIG. 12, the thickness of the film varies with the temperatures and relative humidity of the device. Notably, each thickness is responsible for a particular color on the film. The amount of condensed moisture on the film increases with a decrease in temperatures, and an increase in relative humidity before freezing. The film can be used to monitor subzero temperatures (down to -30°C) in the most common refrigeration systems with distinctive colors and fast response to temperature disruptions.

[0087] In other embodiments, the system can comprise an irreversible time-temperature monitoring system. The irreversible color changing behavior is incorporated in the system by introducing the moisture absorber inside the system which permanently traps moisturereleased by the film, effectively preventing the color from returning when temperatures change, thereby preserving the temperature history to which the system is exposed.

[0088] Both silica gel (SG) and molecular sieve (MS) absorbers have excellent absorbing capacities, and can be used as in the disclosed embodiments. The absorption capacity of SG and MS at 50% interior / internal RH varies with respect to time. For example, SG has a maximum absorption of 0.078 g / g at 10 hours, whereas MS has a maximum of 0.18 g / g at 10 hours.

[0089] This time-dependent absorption capacity can be utilized to introduce irreversible color changing behavior for recording temperature history. For example, based on the amount of moisture condensed on the film and the rate of moisture absorption, a given amount of absorber can absorb all the condensed moisture on the film and it is possible to limit color change to a period of time that the temperature has exceeded a threshold. This is how the color change for a threshold time (tth) is established.

[0090] For example, an irreversible time-temperature system as disclosed herein, with 50% relative humidity containing 0.018 ± 0.001 g SG in the absorber compartment can be held at -15°C in a freezer. Then, three temperature courses with no disruption within 10 hours of monitoring time frame can be performed as illustrated by chart 1300 of FIG. 13. Course 1 is represented as 10 hours at -15°C; Course 2 is represented as 1 hour at 23°C plus 9 hours at -15°C; and Course 3 is represented as 4 hours at 23°C plus 6 hours at -15°C.

[0091] Under these exemplary circumstances, the film displays a pink color after 2 minutes in the freezer at -15°C. At this condition, the moisture inside the system is frozen, and SG is added inside the device by opening the gate while preserving the air tightness within the housing. Next, the film shows a pinkish or pinkish yellow color for up to 10 hours without any disruption in temperature (-15°C) at this state because most of the moisture inside the device is frozen, leading to insufficient absorption of moisture by SG. On the other hand, after placing the system at 23°C, the film shows a green color after 1 minute due to desorption of moisture.

[0092] In the exemplary circumstances of Course 2, the system shows a yellowish or pinkish color (thickness 450 ± 30 nmt at aft^r keeping it for 1 hour at 23°C. In thisexemplary case, due to insufficient drying time below the tth (i.e., 3 hours), the SG does not absorb all the moisture. Hence, the residual unabsorbed moisture inside the device is condensed again on the film to change the color as temperature changes back to -15°C. However, the final color can be slightly different due to the reduced condensation of moisture on the film.

[0093] In the exemplary circumstances of Course 3 where drying time is above the tth (4 hours at 23°C), the film maintains a green color at -15°C, even after 6 hours of additional storage at -15°C. This is due to the absence of moisture condensed on the film, as all available moisture was absorbed by SG in 3 hours.

[0094] The film thickness maintains agreement with the color change with respect to time in these 3 Courses. Specifically, in Course 1 , the film thickness does not decrease significantly after introducing the SG inside the system for up to 10 hours in the freezer without any disruptions. In Course 2, the thickness changes from 451 nm to 340 nm after putting the film at 23°C for 1 hour, the thickness then changes to 426 nm after placing the device back in -15°C and does not change significantly until 10 hours. In Course 3, the thickness changes to 340 nm at 23°C for 4 hours and stays the same at -15°C temperature for 6 hours.

[0095] It is an aspect of the disclosed embodiments to tune the threshold time tth, as the system provides distinguishable color differences between different temperature conditions. The time-dependent irreversible color changing behavior can be achieved with the disclosed systems by leveraging the time-dependent absorbing capacity of the absorber. The threshold time tth for the irreversible color-changing behavior can be controlled by controlling parameters associated with the system including absorber types, the weight of the absorber, the relative humidity, and storage temperature.

[0096] An exemplary set of parameters is provided for purposes of illustration. It should be understood these parameters are not meant to limit the scope of possible parameters. As an example, four samples containing 0.002 g (Control 1 ), 0.011 g (iRTM 1 ), 0.018 (iRTM 2), and 0.08 g (Control 2) of SG at 50% of interior relative humidity were used to monitor and record -15°C storage condition for 10 houm with riocirmpri hours of drying time. The moistureabsorbers were disposed in the housing with the film during the monitoring period. Control 1 displayed reversible color changing behavior for the whole 10 hours of the monitoring period due to the low amount of absorber which failed to absorb all the moisture within the specific drying time, i.e., a maximum of 10 hours. Control 2 showed irreversible color changing behavior, even with 5 minutes of drying at room temperature (23°C), due to the presence of the excessive amount of absorber inside the device that quickly absorbed all the interior moisture.

[0097] Exemplary iRTM 1 has a temperature threshold (tth) of 7 hours with 0.011 g SG. With the increase of the weight of the SG to 0.018 g in iRTM 2, the tth is decreased to 3 hours. Due to the increase in weight of SG, the absorption rate of moisture increases, which resulted in a decrease of the tth. For the -30°C storage condition, a tth of 5 hours is obtained with the iRTM device containing 0.016 g SG, with Control 1 containing 0.002 g SG and Control 2 containing 0.09 g SG, respectively. Thus, compared to iRTM working at -15°C, iRTM working at -30°C requires more SG to absorb the excess moisture within the specific drying time because more moisture is condensed at -30°C at the same initial relative humidity.

[0098] The color of the film samples at this condition after 0, 2, 4, 6, 8, and 10 hours is shown in image 1400 of FIG. 14A. Likewise, the tth of 5 hours and 4 hours achieved using the iRTM devices with SG at 40% relative humidity and -30°C is illustrated in chart 1450 of FIG. 14B.

[0099] The exemplary weight of absorbers in the control devices and iRTM devices for different conditions is provided in Table 2.TABEL 2

[0100] Due to the higher absorption rate of MS, a very low amount of absorber (~4-5 mg) is needed to achieve 4 hours of tth and can be tuned to achieve other tth. Furthermore, the calculated weights of SG absorbers required for monitoring a given temperature disruption target sample storage temperatures (i.e., 3h and 7h at -15°C, and 5h at -30°C) have been compared with the experimental weight at the same conditions. The theoretical and experimental weights are in good agreement.

[0101] As such, the disclosed systems can achieve any custom tth by tuning the above parameters (i.e., absorber types, the weight of the absorber, interior / internal RH (inRH), and storage temperature) to monitor and record any desired subzero storage temperatures. Moreover, the polymer nanofilms disclosed herein show different colors based on the thickness of the film at different surrounding temperatures. Given the robustness of the films, the same nanofilm sample can be recycled and reused to fabricate multiple systems where relative humidity and the weight of absorbers can be varied and controlled, providing low maintenance and high sustainability of the disclosed systems.

[0102] With this in mind, in certain embodiments, the system can comprise multiple systems, such as system 100, connected or provided independently, with varying levels of absorber material, film layers, and relative humidity, such that the threshold time for each of the systems 100 can be set independently. In this way, the combined systems can be used to identify whether the temperature in an enclosure has exceeded various temperatures for various amounts of time.

[0103] For example, it may be the case that slight variances in temperature are not sufficient to spoil a product. A frozen food product may be safe to consume if the frozen temperature rises from -30°C to -25°C, even for extended periods of time (say 8 hours). However, if the temperature increases from -30°C to -5°C for even one hour the product mayspoil. Likewise, if the temperature rises above freezing for any amount of time, the product may spoil. In such a scenario, three systems 100 can be disposed in the freezer, one tailored to identify an ambient temperature above -25°C for more than 8 hours, another tailored to identify an ambient temperature exceeding -5°C for one hour, and a final system tailored to identify an ambient temperature exceeding the freezing point for 5 minutes. In this way, it is simple to identify if any of these temperature thresholds have been exceeded for the time required for spoliation.

[0104] Based on the foregoing, it can be appreciated that a number of embodiments, preferred and alternative, are disclosed herein. In an embodiment, a temperature monitoring system comprises a sealed housing comprising a main chamber with a known relative internal humidity and a polymeric nanofilm disposed in the sealed housing. In an embodiment, the temperature monitoring system further comprises an absorbent in the sealed housing. In an embodiment, the temperature monitoring system further comprises a drying module configured to house the absorbent, and a gate between the drying module and the main chamber, the gate configured to open in order to create a fluidic connection between the absorbent and moisture in the sealed housing. In an embodiment, the absorbent comprises at least one of silica gel and / or molecular sieve. In an embodiment, the polymeric nanofilm comprises at least one of: Chitosan and CMC-N3. In an embodiment, the polymeric nanofilm comprises: Chitosan and carboxymethyl cellulose. In an embodiment, the polymeric nanofilm is configured to change color as a result of an ambient temperature change. In an embodiment, the polymeric nanofilm has a characteristic color indicative of a temperature.

[0105] In an embodiment, a temperature monitoring method comprises disposing a temperature monitoring system comprising a polymeric nanofilm in a main chamber of a housing, in an environment and identifying a change in color of the polymeric nanofilm, the change in color of the polymeric nanofilm being indicative of a temperature change. In an embodiment, the temperature monitoring method further comprises exposing an internal volume of the housing to an absorber with a gate formed between the main chamber and a drying module. In an embodiment, the absorber absorbs moisture released by the polymeric nanofilm when the temperature changes. In an embodiment, the polymeric nanofilm has acharacteristic color indicative of a temperature.

[0106] In an embodiment, a method of manufacturing a temperature monitoring system comprises disposing a polymeric nanofilm in a main chamber of a housing, identifying a relative humidity of an interior volume of the main chamber of the housing, and sealing the housing. In an embodiment, the method of manufacturing a temperature monitoring system further comprises attaching a drying module to the housing, the drying module configured to house an absorber and forming a gate sealing the drying module from the main chamber when the gate is closed. In an embodiment, the method of manufacturing a temperature monitoring system further comprises establishing a fluidic connection between the absorber and the main chamber when the gate is open. In an embodiment, the method of manufacturing a temperature monitoring system further comprises selecting a mass of the absorber to store a desired volume of moisture released by the polymeric film as a result of a temperature change. In an embodiment, the method of manufacturing a temperature monitoring system further comprises manufacturing the polymeric nanofilm. In an embodiment, the method of manufacturing a temperature monitoring system further comprises plasma treating a silicon wafer so that a surface of the silicon wafer is negatively charged, immersing the silicon wafer in a positively charged chitosan solution, and exposing the silicon wafer to UV-light. In an embodiment, manufacturing the polymeric nanofilm further comprises washing the silicon wafer after the plasma treatment. In an embodiment, the polymeric nanofilm comprises Chitosan and carboxymethyl cellulose.

[0107] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, it should be appreciated that various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

Claims

CLAIMSWhat is claimed is:1 . A temperature monitoring system comprising: a sealed housing comprising a main chamber with a known relative internal humidity; and a polymeric nanofilm disposed in the sealed housing.

2. The temperature monitoring system of claim 1 further comprising: an absorbent in the sealed housing.

3. The temperature monitoring system of claim 2 further comprising: a drying module configured to house the absorbent; and a gate between the drying module and the main chamber, the gate configured to open in order to create a fluidic connection between the absorbent and moisture in the sealed housing.

4. The temperature monitoring system of claim 2 wherein the absorbent comprises at least one of: silica gel; and / or molecular sieve.

5. The temperature monitoring system of claim 1 wherein the polymeric nanofilm comprises at least one of:Chitosan; andCMC-N3.

6. The temperature monitoring system of claim 1 wherein the polymeric nanofilm comprises:Chitosan; and carboxymethyl cellulose.

7. The temperature monitoring system of claim 1 wherein the polymeric nanofilm is configured to change color as a result of an ambient temperature change.

8. The temperature monitoring system of claim 1 wherein the polymeric nanofilm has a characteristic color indicative of a temperature.

9. A temperature monitoring method comprising: disposing a temperature monitoring system comprising a polymeric nanofilm in a main chamber of a housing, in an environment; and identifying a change in color of the polymeric nanofilm, the change in color of the polymeric nanofilm being indicative of a temperature change.

10. The temperature monitoring method of claim 9 further comprising: exposing an internal volume of the housing to an absorber with a gate formed between the main chamber and a drying module.1 1 . The temperature monitoring method of claim 10 wherein the absorber absorbs moisture released by the polymeric nanofilm when the temperature changes.

12. The temperature monitoring method of claim 9 wherein the polymeric nanofilm has a characteristic color indicative of a temperature.

13. A method of manufacturing a temperature monitoring system comprising: disposing a polymeric nanofilm in a main chamber of a housing; identifying a relative humidity of an interior volume of the main chamber of the housing; and sealing the housing.

14. The method of manufacturing a temperature monitoring system further comprising: attaching a drying module to the housing, the drying module configured to house an absorber; andforming a gate sealing the drying module from the main chamber when the gate is closed.

15. The method of manufacturing a temperature monitoring system of claim 14 further comprising: establishing a fluidic connection between the absorber and the main chamber when the gate is open.

16. The method of manufacturing a temperature monitoring system of claim 14 further comprising: selecting a mass of the absorber to store a desired volume of moisture released by the polymeric film as a result of a temperature change.

17. The method of manufacturing a temperature monitoring system of claim 13 further comprising: manufacturing the polymeric nanofilm.

18. The method of manufacturing a temperature monitoring system of claim 17 wherein manufacturing the polymeric nanofilm further comprises: plasma treating a silicon wafer so that a surface of the silicon wafer is negatively charged; immersing the silicon wafer in a positively charged chitosan solution; and exposing the silicon wafer to UV-light.

19. The method of manufacturing a temperature monitoring system of claim 18 wherein manufacturing the polymeric nanofilm further comprises: washing the silicon wafer after the plasma treatment.

20. The method of manufacturing a temperature monitoring system of claim 13 wherein the polymeric nanofilm comprises:Chitosan; andcarboxymethyl cellulose.

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