Method for detecting residual stress caused by preparation conditions in a polymeric nanomembrane

Abstract

The application discloses a detection method of residual stress caused by preparation conditions in a polymer nanofilm, and the detection method comprises the following steps: substrate cleaning and modification; polymer nanofilm preparation; heat-induced polymer nanofilm dewetting; and residual stress calculation in the polymer nanofilm. The detection method does not need high-end detection equipment, and only needs an optical microscope, a hot stage and a computer to detect the residual stress in the polymer nanofilm, which has great significance for in-depth understanding of the molecular conformation in the polymer nanofilm and manipulation of the performance of the polymer nanofilm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of residual stress of polymer nanofilm, and particularly relates to a method for detecting residual stress caused by preparation conditions in a polymer nanofilm. BACKGROUND

[0002] In the research and production process of polymer materials, the processing and preparation of devices are very basic and important links, and the processing and preparation process has a great influence on the performance of polymer materials. Important physical properties of polymer materials such as tensile, shear, stress resistance, fatigue resistance and viscoelasticity are closely related to the processing process. These properties are derived from the movement of polymer chains at multiple levels, thereby affecting the application range and conditions of polymer materials. This is particularly true for polymer nanomaterials, because the relaxation time of the polymer is usually much longer than the preparation time, so the polymer chains in the material may be in a non-equilibrium molecular conformation caused by the preparation process, that is, there is residual stress generated in the preparation process, which may produce new properties.

[0003] Whether it is photoresist, nanocoating or thermal insulation material, polymer usually appears in the form of nanofilm. The abnormal dynamics of polymer nanofilm caused by geometric constraints and interfacial interactions have attracted great interest. So far, due to the extremely low thickness and weak mechanical properties of polymer nanofilm, it is very challenging to quantitatively correlate the preparation conditions and properties of polymer nanofilm.

[0004] The existing detection methods of residual stress mainly rely on differential scanning calorimeter, optical method and thermal shrinkage method, etc. The above methods often need relatively high-end instrument equipment or the physical quantity required for measurement is difficult to characterize, and the error is large. Therefore, there is an urgent need for a sensitive and efficient detection method of residual stress in polymer nanofilm which can be associated with preparation conditions.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The purpose of the present application is to provide a method for detecting residual stress caused by preparation conditions in a polymer nanofilm, which correlates the residual stress caused by preparation conditions with the preparation conditions, provides a guidance method for in-depth understanding of the molecular conformation in the polymer nanofilm and manipulation of the performance of the polymer nanofilm, and can clarify that the polymer nanofilms with the same film thickness obtained under different preparation conditions have different properties.

[0007] In order to achieve the above purpose of the present application, the following technical scheme is adopted:

[0008] The present application is a method for detecting residual stress caused by preparation conditions in a polymer nanofilm, comprising the following steps:

[0009] (a) substrate cleaning and modification:

[0010] The substrate is cleaned by using the cleaner for water tiger fish, then the n-heptane solution of PDMS is spin-coated on the dried substrate surface and heated, then the substrate is immersed in n-heptane, and then washed, dried to obtain a modified substrate;

[0011] (b) preparation of polymer nanofilm:

[0012] The polymer solution is spin-coated on the surface of the modified substrate to prepare a polymer nanofilm;

[0013] (c) thermal-induced dewetting of polymer nanofilm:

[0014] The polymer nanofilm is placed on a hot stage at 130℃ for dewetting, and an optical microscope is used to observe and record the dewetting phenomenon, and software ImageJ is used to statistically analyze the change of the radius of the dewetting hole appearing after different delay times with the dewetting time, and the statistical results are fitted to obtain the initial growth rate of the dewetting hole, denoted as v i (0), and the constant growth rate of the dewetting hole in the later stage, denoted as v i (∞);

[0015] (d) calculation of residual stress in polymer nanofilm:

[0016] The residual stress in the polymer nanofilm is calculated according to the formula I:

[0017]

[0018] In formula I, σ res is the residual stress in the polymer nanofilm; σ cap = |S| / h, |S| = γ pol (1-cosθ), γ pol is the surface tension between the polymer film and air, θ is the contact angle obtained by measuring the profile of the dewetting hole edge, and h is the thickness of the polymer film.

[0019] Preferably, the method for detecting the residual stress caused by the preparation conditions of the polymer nanofilm further comprises step (e) preparation condition normalization processing and residual stress correlation:

[0020] The preparation conditions of the polymer nanofilm are normalized, and then correlated with the residual stress obtained by dewetting.

[0021] Preferably, the normalization processing comprises:

[0022] The high polymer solution spin coating process includes a transition phase, and the time for entering the transition phase is calculated according to formula II;

[0023]

[0024] In formula II, t tr is the time for entering the transition phase; E is the film thickness reduction value per second; v = η s / p, η s and p are the dynamic viscosity and density of the high polymer solution respectively; and ω is the rotation speed;

[0025] η s The concentration dependence of η

[0026]

[0027] In formula III, β is determined according to formula IV; η0 is the dynamic viscosity of the solvent; and c is the concentration of the high polymer solution;

[0028]

[0029] In formula IV, c* is the overlap concentration; c** ≈ 5c* represents the concentration of the high polymer entanglement in the solution; and c* is determined by formula V and VI;

[0030]

[0031]

[0032] In formula V and VI, a is the statistical chain segment length; M w = N·m0, N is the number of monomers constituting a single high polymer, and m0 is the monomer mass;

[0033] According to formula III, formula IV, formula V and formula VI, the concentration dependence of η s is determined by formula VII;

[0034] η S ≈ η0·(1 + (c / c * ) β ) …… formula VII;

[0035] According to formula VII and formula II, the t tr calculation formula is shown in formula VIII;

[0036]

[0037] The t tr is related to the degree of the chain conformation deviating from equilibrium, and the t trA dimensionless parameter is defined in relation to the characteristic time embodying the balance kinetics of the polymer chain as shown in formula IX.

[0038]

[0039] In formula IX, p is a dimensionless parameter; τ ref = 1 s.

[0040] Preferably, the dimensionless parameter is correlated with the residual stress in the polymer nanofilm to obtain a quantitative relationship between the two.

[0041] Preferably, the substrate is a single-throw thermal silicon oxide wafer.

[0042] Preferably, the polymer thin film has a thickness of 10-100 nm.

[0043] Preferably, the polymer nanofilm is made of any one of polystyrene, polymethyl methacrylate, poly-D,L-lactic acid, polyethylene glycol, polyurethane, polyamide and polyvinyl acetate.

[0044] Compared with the prior art, the present application has at least the following beneficial effects:

[0045] The present application realizes quantitative measurement of the residual stress in the polymer nanofilm prepared by spin coating by preparing a PDMS irreversible adsorption layer on the surface of a single-throw thermal silicon oxide substrate, spin coating a polymer nanofilm on the single-throw thermal silicon oxide substrate modified by PDMS, inducing dewetting of the nanofilm by heat, and recording the dewetting phenomenon by an optical microscope. The present application realizes quantitative correlation between the preparation conditions of the nanofilm and the residual stress caused by the preparation conditions by normalizing the preparation conditions of the nanofilm. The detection method of the present application does not need high-end detection equipment, but only needs an optical microscope, a hot stage and a computer to detect the residual stress in the polymer nanofilm, which is of great significance for in-depth understanding of the molecular conformation in the polymer nanofilm and manipulation of the performance of the polymer nanofilm. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0047] Figure 1 The optical microscope photos of representative dewetting are shown in the figure, the preparation conditions of a are 20 mg / ml, 5000 rpm, and the preparation conditions of b are 20 mg / ml, 12000 rpm.

[0048] Figure 2 Representative plot of the radius of dewetted holes appearing after different delay times as a function of dewetting time, where a is prepared under the condition of 20 mg / ml, 5000 rpm, and b is prepared under the condition of 20 mg / ml, 12000 rpm;

[0049] Figure 3 Representative plot of the initial growth rate of dewetted holes as a function of delay time under different preparation conditions; the preparation conditions are 20 mg / ml, 5000 rpm and 12000 rpm;

[0050] Figure 4 Plot of the correlation between the residual stress in the polystyrene nanofilm and the normalized parameter p of the preparation condition. DETAILED DESCRIPTION

[0051] The technical solutions of the present application will be described in detail below with reference to the examples. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0052] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present application should be understood as the usual meanings understood by the skilled person in the field of the present application.

[0053] The present application provides a method for detecting the residual stress in a polymer nanofilm caused by the preparation condition, comprising the following steps:

[0054] (a) substrate cleaning and modification:

[0055] The substrate is cleaned with a water tiger liquid, and then the n-heptane solution of PDMS is spin-coated on the surface of the dried substrate and heated, then the substrate is immersed in n-heptane, and then washed, dried to obtain a modified substrate;

[0056] Specifically includes the following processes:

[0057] A piranha cleaning solution was prepared using a 7:3 volume ratio of 98% concentrated sulfuric acid and 30% hydrogen peroxide aqueous solution. Single-sided polished hot-dip oxidized silicon wafers were immersed in the solution for 30 minutes. Then, each wafer was carefully removed using tweezers, thoroughly rinsed with plenty of deionized water, dried completely, and stored in a sealed container. A 3% (w / w) solution of polydimethylsiloxane (PDMS) in n-heptane was prepared using n-heptane as a solvent. A spin coater was used with the spin coating settings set to 3000 rpm. After 30 seconds, a heptane solution of PDMS is spin-coated onto the cleaned single-sided polished thermally oxidized silicon wafer to obtain a single-sided polished thermally oxidized silicon wafer with a PDMS coating. The single-sided polished thermally oxidized silicon wafer with the PDMS coating is placed on a hot plate and heated at 180°C for 6 hours. Then, the single-sided polished thermally oxidized silicon wafer with the PDMS coating is immersed in heptane overnight to remove unadsorbed PDMS molecules. The single-sided polished thermally oxidized silicon wafers with irreversible PDMS adsorption layer after immersion are picked out one by one, rinsed with heptane, and thoroughly dried for later use.

[0058] (b) Preparation of polymer nanofilms:

[0059] Polymer nanofilms with a thickness of 10–100 nm were prepared by spin coating polymer solution onto PDMS-modified single-layer hot-sprayed silica using a spin coater with spin coating conditions set to 500–12000 rpm.

[0060] (c) Thermally induced dewetting of polymer nanofilms:

[0061] The polymer nanofilm was placed on a hot stage at 130°C for dewetting, and the dewetting phenomenon was observed and recorded using an optical microscope. The recorded data at different delay times (t) were then analyzed using ImageJ software. delay The radius (R) of the dewetting hole that appears after dewetting time (t) varies with the dewetting time. dew The changes in ) were statistically analyzed, and the initial growth rate of the dewetting pores was obtained by fitting a curve and extrapolating the statistical results, denoted as v. i (0), and the constant growth rate in the later stage of dewetting pores, denoted as v i (∞);

[0062] (d) Calculation of residual stress in polymer nanofilms:

[0063] v i (0) and v i The ratio of (∞) is related to the ratio of the total driving force for dewetting to the capillary force. The driving force for dewetting is divided into capillary force and residual stress generated during the preparation process. Residual stress is a measure of the non-equilibrium conformation in polymer nanofilms. The residual stress in polymer nanofilms is calculated according to the formula shown in Equation I:

[0064]

[0065] In formula I, σ res is the residual stress in the polymer nanofilm; σ cap = |S| / h, |S| = γ pol (1-cosθ), γ pol is the surface tension between the polymer thin film and air, θ is the contact angle obtained by measuring the profile of the dewetting hole edge, and h is the thickness of the polymer thin film.

[0066] In some embodiments, the method for detecting the residual stress in the polymer nanofilm caused by the preparation conditions further comprises step (e) preparation condition normalization processing and residual stress correlation:

[0067] The preparation conditions of the polymer nanofilm are normalized, and then correlated with the residual stress obtained by dewetting.

[0068] In an embodiment, the normalization processing comprises:

[0069] Before the start of spin coating, a large amount of solution is dropped on a flat substrate. During the spin casting process, the centrifugal acceleration will cause the solution to diffuse and cause most of the solution to be discharged from the substrate. This process is called spin-off. During this process, the amount of solution evaporation is usually negligible. Then, the spin coating process enters a transition stage, in which the spin-off of the solution gradually weakens, and the solvent evaporation gradually increases. In this transition stage, the polymer chains are frozen in a non-equilibrium conformation. The characteristic time of entering this transition stage is denoted as t tr The time of entering the transition stage is calculated according to formula II:

[0070]

[0071] In formula II, t tr is the time of entering the transition stage; E is the thickness reduction value per second; ν = η s / ρ, η s and ρ are the dynamic viscosity and density of the polymer solution, respectively; ω is the rotation speed;

[0072] η s The concentration dependence of η

[0073]

[0074] In formula III, β is determined according to formula IV; η0 is the dynamic viscosity of the solvent; c is the concentration of the polymer solution;

[0075]

[0076] In formula IV, c* is the overlap concentration; c**≈5c* represents the concentration of the polymer in solution entanglement; c* is determined by formula V and VI;

[0077]

[0078]

[0079] In formula V and VI, a is the statistical segment length; M w =N·m0, N is the number of monomers constituting a single polymer, m0 is the monomer mass;

[0080] According to formula III, formula IV, formula V and formula VI, η s The concentration dependence of η

[0081] η S ≈η0·(1+(c / c * ) β )…Formula VII;

[0082] According to formula VII and formula II, t tr is calculated as shown in formula VIII;

[0083]

[0084] t tr is related to the degree of deviation of the chain conformation from equilibrium, and t tr is related to the characteristic time reflecting the equilibrium dynamics of the polymer chain, and a dimensionless parameter is defined as shown in formula IX;

[0085]

[0086] In formula IX, p is a dimensionless parameter; τ ref =1s.

[0087] In an embodiment, the dimensionless parameter is related to the residual stress in the polymer nanofilm, and a quantitative relationship between the two is obtained.

[0088] The material of the polymer nanofilm is not specifically limited in the present application, and in an embodiment, the material of the polymer nanofilm is selected from any one of polystyrene, polymethyl methacrylate, poly-D,L-lactic acid, polyethylene glycol, polyurethane, polyamide and polyvinyl acetate.

[0089] The technical solutions of the present application are further described in detail through specific examples.

[0090] Example 1

[0091] Preparation of modified substrate

[0092] The single polished thermal oxidized silicon wafer was placed in the solution, soaked for 30 min, and then taken out one by one using tweezers, washed with a large amount of deionized water, dried, and sealed for storage.

[0093] A 3% by mass polydimethylsiloxane (PDMS) n-heptane solution was prepared using n-heptane as the solvent, and a spin coating device was used to set the spin coating conditions to a rotation speed of 3000 rpm and a spin coating time of 30 s. The PDMS n-heptane solution was spin coated on the cleaned single polished thermal oxidized silicon wafer to obtain a single polished thermal oxidized silicon wafer with a PDMS coating. The single polished thermal oxidized silicon wafer with the PDMS coating was placed on a hot stage, and the temperature was set to 180°C and heated for 6 h. Then, the single polished thermal oxidized silicon wafer with the PDMS coating was soaked in n-heptane overnight to remove the unabsorbed PDMS molecules. The single polished thermal oxidized silicon wafer with the irreversible PDMS adsorption layer after soaking was taken out one by one, washed with n-heptane, and dried for use.

[0094] Example 2

[0095] Preparation of a PS nanofilm with a thickness of 88 nm

[0096] A PS toluene solution with a concentration of 15 mg / ml was prepared using toluene as the solvent, and a spin coating device was used to set the spin coating conditions to a rotation speed of 3000 rpm and a spin coating time of 30 s. The PS toluene solution was spin coated on the PDMS-modified single polished thermal oxidized silicon wafer to prepare a PS nanofilm with a thickness of 88 nm.

[0097] Example 3

[0098] Preparation of a PS nanofilm with a thickness of 64 nm

[0099] A PS toluene solution with a concentration of 15 mg / ml was prepared using toluene as the solvent, and a spin coating device was used to set the spin coating conditions to a rotation speed of 5000 rpm and a spin coating time of 30 s. The PS toluene solution was spin coated on the PDMS-modified single polished thermal oxidized silicon wafer to prepare a PS nanofilm with a thickness of 64 nm.

[0100] Example 4

[0101] Preparation of a PS nanofilm with a thickness of 54 nm

[0102] A toluene solution of PS with a concentration of 15 mg / ml was prepared, and a spin coating apparatus was set to a rotation speed of 8000 rpm and a spin coating time of 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare a PS nanofilm with a thickness of 54 nm.

[0103] Example 5

[0104] In this example, a PS nanofilm with a thickness of 47 nm was prepared as follows:

[0105] A toluene solution of PS with a concentration of 15 mg / ml was prepared, and a spin coating apparatus was set to a rotation speed of 8000 rpm and a spin coating time of 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare a PS nanofilm with a thickness of 54 nm.

[0106] Example 6

[0107] In this example, a PS nanofilm with a thickness of 71 nm was prepared as follows:

[0108] A toluene solution of PS with a concentration of 17.5 mg / ml was prepared, and a spin coating apparatus was set to a rotation speed of 5000 rpm and a spin coating time of 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare a PS nanofilm with a thickness of 71 nm.

[0109] Example 7

[0110] In this example, a PS nanofilm with a thickness of 64 nm was prepared as follows:

[0111] A toluene solution of PS with a concentration of 17.5 mg / ml was prepared, and a spin coating apparatus was set to a rotation speed of 6500 rpm and a spin coating time of 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare a PS nanofilm with a thickness of 64 nm.

[0112] Example 8

[0113] In this example, a PS nanofilm with a thickness of 58 nm was prepared as follows:

[0114] A toluene solution of PS with a concentration of 17.5 mg / ml was prepared, and a spin coating apparatus was set to a rotation speed of 8000 rpm and a spin coating time of 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare a PS nanofilm with a thickness of 58 nm.

[0115] Example 9

[0116] This example is the preparation of PS nanofilm with a thickness of 53 nm:

[0117] A toluene solution of PS with a concentration of 17.5 mg / ml was prepared, and a spin coating apparatus was used to set the spin coating conditions as follows: rotation speed 12000 rpm, spin coating time 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare PS nanofilm with a thickness of 53 nm.

[0118] Example 10

[0119] This example is the preparation of PS nanofilm with a thickness of 87 nm:

[0120] A toluene solution of PS with a concentration of 20 mg / ml was prepared, and a spin coating apparatus was used to set the spin coating conditions as follows: rotation speed 5000 rpm, spin coating time 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare PS nanofilm with a thickness of 87 nm.

[0121] Example 11

[0122] This example is the preparation of PS nanofilm with a thickness of 74 nm:

[0123] A toluene solution of PS with a concentration of 20 mg / ml was prepared, and a spin coating apparatus was used to set the spin coating conditions as follows: rotation speed 6500 rpm, spin coating time 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare PS nanofilm with a thickness of 74 nm.

[0124] Example 12

[0125] This example is the preparation of PS nanofilm with a thickness of 69 nm:

[0126] A toluene solution of PS with a concentration of 20 mg / ml was prepared, and a spin coating apparatus was used to set the spin coating conditions as follows: rotation speed 8000 rpm, spin coating time 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare PS nanofilm with a thickness of 69 nm.

[0127] Example 13

[0128] This example is the preparation of PS nanofilm with a thickness of 61 nm:

[0129] A toluene solution of PS with a concentration of 20 mg / ml was prepared, and a spin coating apparatus was used to set the spin coating conditions as follows: rotation speed 12000 rpm, spin coating time 30 s. The toluene solution of PS was spin coated on the PDMS-modified single-throw thermal silicon oxide to prepare PS nanofilm with a thickness of 61 nm.

[0130] Example 14

[0131] This embodiment demonstrates thermally induced dewetting of polymer nanofilms.

[0132] The hot stage was set to a dewetting temperature of 130℃. The prepared PS nanofilm sample was placed on the hot stage for dewetting, and the dewetting phenomenon was observed and recorded using an optical microscope. Figure 1 The recorded dewetting behavior was statistically analyzed using the ImageJ software, with different delay times (t) delay The radius (R) of the dewetting hole that appears after dewetting time (t) varies with the dewetting time. dew Changes in ) Figure 2 ).

[0133] For Rt dew The curve was fitted to obtain R(t) dew Find the function expression of ), and then find R(t). dew ) on dewetting time t dew The first derivative R'(t) dew The growth rate v of easily de-wetting pores can be obtained. g (t dew )=R'(t dew Let t dew If the value approaches zero, then the initial growth rate v of any dewetting pore can be obtained. i ;

[0134] The initial growth rate vi of dewetting the pores is decoupled from the delay time t. delay Drawing ( Figure 3 It can be observed that as the delay time t increases, delay The extension of the initial growth rate v of the dewetting pores i Gradually decrease until it remains constant, denoted as v i (∞); delay time t delay Approaching 0, t can be obtained by fitting. delay The initial growth rate v of dewetting pores when = 0 i , denoted as v i (0).

[0135] Example 14

[0136] This example demonstrates the calculation of residual stress within a polymer nanofilm:

[0137] v i (0) and v iThe ratio of (oo) is related to the ratio of the total driving force of dewetting and capillary force, the driving force of dewetting is divided into capillary force and residual stress generated in the preparation process, the residual stress is a measure of the non-equilibrium conformation in the polymer nanofilm, and the residual stress in the polymer nanofilm is calculated according to formula I:

[0138]

[0139] In formula I, σ res is the residual stress in the polymer nanofilm; σ cap is the capillary force, σ cap = |S| / h, |S| = γ pol (1-cosθ), γ pol is the surface tension between PS and air, θ is the contact angle obtained by measuring the profile of the dewetting hole edge, and h is the thickness of the polymer film; The experiment shows that γ pol = 17.59 mN / m, θ = 0.36 rad; The residual stress σ res in the polystyrene nanofilm can be obtained by the above formula I equation.

[0140] Example 15

[0141] This embodiment is the normalization of preparation conditions and the correlation of residual stress:

[0142] Before the start of spin coating, a large amount of solution is dropped on a flat substrate, and during the spin casting process, the centrifugal acceleration will cause the solution to diffuse and cause most of the solution to be discharged from the substrate, which is called spin-off, and during this process, the amount of solution evaporation is usually negligible; Then, the spin coating process enters a transition stage, in which the spin-off of the solution gradually weakens, and the solvent evaporation gradually increases, and in this transition stage, the polymer chain is frozen in a non-equilibrium conformation, and the characteristic time of entering this transition stage is t tr , the time of entering the transition stage is calculated according to formula II;

[0143]

[0144] In formula II, t tr is the time of entering the transition stage; E is the thickness reduction value per second of the film; ν = η s / ρ, η s and ρ are the dynamic viscosity and density of the polymer solution respectively; ω is the rotation speed; for the solvent toluene used in the present application, E ≈ 3 μm / s, η0≈0.5866 mPa·s; the concentration dependence of ηs is defined according to the specific viscosity thereof shown in formula III;

[0145]

[0146] In formula III, β is determined according to formula IV; η0 is the dynamic viscosity of the solvent; and c is the concentration of the polymer solution.

[0147]

[0148] In formula IV, c* is the overlap concentration; c** ≈ 5c* represents the concentration of the polymer entanglement in the solution; and c* is determined by formula V and VI.

[0149]

[0150]

[0151] In formula V and VI, a is the statistical segment length; M w = N·m0, N is the number of monomers constituting a single polymer, and m0 is the monomer mass; and in examples 2-13 of the present application, the concentration c satisfies c* < c < c**.

[0152] According to formula III, formula IV, formula V and formula VI, the concentration dependence of ηs is determined by formula VII.

[0153] η s ≈ η0·(1 + (c / c * )1.3) …… formula VII.

[0154] According to formula VII and formula II, t tr is shown in formula VIII.

[0155]

[0156] t tr is related to the degree of deviation of the chain conformation from equilibrium, and t tr is related to the characteristic time reflecting the equilibrium dynamics of the polymer chain, and a dimensionless parameter is defined as shown in formula IX.

[0157]

[0158] In formula IX, p is a dimensionless parameter; τ ref is a function of the molecular weight and chemical properties of the polymer, and since the present example is only used for atactic polystyrene, τ ref should be constant; for simplicity, τ ref = 1s.

[0159] Through the above equation, the preparation conditions of the spin-coated polystyrene nanofilm can be normalized and integrated into a single dimensionless parameter p.

[0160] The residual stress σ resCorrelating the obtained dimensionless parameter p normalized with the preparation conditions, it can be found that the residual stress σres increases approximately linearly with the dimensionless parameter p. Figure 4

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the description of the present application.​

Claims

1. A method for detecting a residual stress caused by a preparation condition in a polymer nanomembrane, characterized by, It comprises the following steps: (a) substrate cleaning and modification: The substrate is cleaned by using the cleaner for water tiger, then the n-heptane solution of PDMS is spin-coated on the dried substrate surface and heated, then the substrate is soaked in n-heptane, and then washed and dried to obtain a modified substrate; (b) preparation of polymer nanofilm: The polymer solution is spin-coated on the surface of the modified substrate to prepare a polymer nanofilm; (c) thermal-induced dewetting of the polymer nanofilm: The polymer nanofilm is placed on a hot stage at 130℃ for dewetting, and the dewetting phenomenon is observed and recorded by using an optical microscope, then the radius of the dewetting hole appearing after different delay times is counted by using the software ImageJ, and the initial growth rate of the dewetting hole vi(0) and the constant growth rate of the dewetting hole in the later period vi(∞) are obtained by curve fitting and extrapolation of the statistical results; (d) calculation of residual stress in the polymer nanofilm: The residual stress in the polymer nanofilm is calculated according to the formula I: In formula I, σ res is the residual stress in the polymer nanofilm; σ cap = |S| / h, |S| = γ pol (1 - cos θ), γ pol is the surface tension between the polymer thin film and air, θ is the contact angle obtained by measuring the profile of the dewetting hole edge, and h is the thickness of the polymer thin film.

2. The method according to claim 1, wherein the residual stress in the polymer nanomembrane is caused by the fabrication conditions. It also comprises step (e) preparation condition normalization processing and residual stress correlation: The preparation conditions of the polymer nanofilm are normalized, and then correlated with the residual stress obtained by dewetting.

3. The method according to claim 2, wherein the residual stress in the polymer nanomembrane is detected by measuring the change in the thickness of the polymer nanomembrane. The normalization processing comprises: The spin-coating process of the polymer solution comprises a transition stage, and the time of entering the transition stage is calculated according to the formula II; In formula II, t tr is the time to enter the transition phase; E is the film thickness reduction value per second; v = η s / p, η s and p are the dynamic viscosity and density of the polymer solution, respectively; ω is the rotational speed; The concentration dependence of ηs is defined according to the specific viscosity thereof as shown in the formula III; In the formula III, β is determined according to the formula IV; η0 is the dynamic viscosity of the solvent; and c is the concentration of the polymer solution; In the formula IV, c* is the overlap concentration; c**≈5c* represents the concentration of the polymer entanglement in the solution; c* is determined by the formula V and VI; In formulae V and VI, a is the statistical segment length; M w = N-m0, N is the number of monomers constituting a single polymer, m0is the monomer mass; According to the formula III, formula IV, formula V and formula VI, the concentration dependence of ηs is determined by the formula VII; η s ≈ η0· (1 + (c / c * ) β ) …… Equation VII; t is represented by formula VII in conjunction with formula II, as shown in formula VIII tr Calculation formula; t tr is linked to the degree of deviation from equilibrium of the chain conformation and t tr is linked to the characteristic time embodying the kinetics of equilibrium of the macromolecular chain, defining the dimensionless parameter as shown in formula IX; In formula IX, p is a dimensionless parameter; τ ref = 1 s.

4. The method according to claim 3, wherein the residual stress in the polymer nanomembrane is detected by measuring the change in the thickness of the polymer nanomembrane. The dimensionless parameter is correlated with the residual stress in the polymer nanofilm to obtain the quantitative relationship between the two.

5. The method according to claim 1, wherein the residual stress in the polymer nanomembrane is caused by the fabrication conditions. The substrate is a single-throw thermal oxide silicon wafer.

6. The method according to claim 1, wherein the residual stress in the polymer nanomembrane is caused by the fabrication conditions. The thickness of the polymer thin film is 10-100 nm.

7. The method according to claim 1, wherein the residual stress in the polymer nanomembrane is caused by the fabrication conditions. The material of the polymer nanofilm is selected from any one of polystyrene, polymethyl methacrylate, poly-D,L-lactic acid, polyethylene glycol, polyurethane, polyamide and polyvinyl acetate.

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