A testing method for the elastic modulus of a rubbery polymer film adhered to the surface of a substrate

Abstract

The present invention provides a method for testing the elastic modulus of a rubbery polymer film attached to the surface of a substrate, belonging to the technical field of elastic modulus testing. In the present invention, a liquid droplet of nanoscale size is applied to the rubbery polymer film supported by the substrate. Under the competitive action of capillary action and film elasticity, the film produces a crater-like deformation; where the depth is D and the edge height is H, and both will change with the change of the crater radius R. Divide H and D by the radius to obtain the radius-scaled H / R and D / R, and both can be used as physical quantities to measure the surface deformation profile, and both will have a maximum value with the change of the radius R. By translating the abscissa 1 / R by l c to shift the maximum values of H / R and D / R to l c / R = 1, the translation factor l is obtained c . The translation factors l of samples with different thicknesses c are different. By establishing the relationship between the film translation factor l c and the thickness, the modulus-related factor is extracted therefrom to obtain the elastic modulus of the film.

Description

Technical Field

[0001] The present invention relates to the technical field of elastic modulus testing, and particularly to a method for testing the elastic modulus of a rubbery polymer film attached to the surface of a substrate. Background Art

[0002] Rubbery polymers have high elasticity with reversible deformation, can produce large deformations under very small external forces, and can return to their original state after the external force is removed. There are generally two molecular forms of rubbery polymers. One is rubber materials crosslinked chemically. These are in the rubber state for a long time, and as long as the crosslinking chemical bonds do not break, the rubber elasticity is always retained. For example, natural rubber, styrene-butadiene rubber, cis-1,4-polybutadiene rubber, chloroprene rubber, etc. are all familiar rubbery polymer materials. The other is the transient rubber state formed by physical entanglement. Conventional linear non-crosslinked polymers exhibit rubber elastic properties within a certain temperature and time range and are in the rubber state. For example, polymer materials such as polystyrene, polymethyl methacrylate, and polyvinyl chloride. The elastic deformation of rubber is due to the fact that when the internal molecules are straightened under the action of an external force, due to the thermal motion of the molecular chains, a retraction force is formed to make it return to its original natural curled state, which makes the deformation reversible. The elastic modulus is the ratio of stress to strain when a material deforms, and it characterizes the magnitude of the material's resistance to deformation. The larger the modulus, the greater the rigidity and the less likely it is to deform. Rubber-like polymers have a low elastic modulus.

[0003] In recent years, with the development of nano-devices and the progress in the bionic field, rubbery polymers have broad application prospects in the field of thin films. The elastic modulus of thin films has an important impact on the stability and reliability of equipment and devices. In these fields, rubbery polymers are often supported by substrates and have a thickness at the nanoscale. Therefore, during the preparation process or in a restricted environment, their elastic modulus may be different from that of bulk materials.

[0004] However, due to limited spatial resolution, traditional macroscopic measurement techniques cannot be used to measure the elastic modulus of thin films of materials at the nanoscale. In recent years, some methods for measuring the elastic modulus of thin films of polymer materials have been developed, such as resonance method, dynamic expansion method, nanoindentation method, micro-tensile composite method, etc. The research of these methods will be affected by factors such as substrate effect and film thickness, and there will be deviations in the measurement results. When the thickness of the thin film material is reduced to the nanoscale, it will be difficult to meet the test requirements. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for testing the elastic modulus of a rubbery polymer film attached to the surface of a substrate, and the present invention can realize the testing of the elastic modulus of a nanoscale rubbery polymer film.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for testing the elastic modulus of a rubbery polymer film attached to the surface of a substrate, comprising the following steps:

[0008] Providing a plurality of rubbery polymer films of different thicknesses attached to the surface of a substrate to be tested;

[0009] Settling a plurality of nano-sized droplets on the surfaces of the rubbery polymer films of different thicknesses to be tested;

[0010] Heating the rubbery polymer films to be tested on which the nano-sized droplets are settled, and multiple micro-deformations occur on the rubbery polymer films to be tested;

[0011] Fixing the micro-deformations of the rubbery polymer films to be tested by means of quenching;

[0012] Observing the micro-deformations of the rubbery polymer films to be tested, and recording the radius R, the edge height H and the central depth D of the micro-deformations;

[0013] For a certain rubbery polymer film, plotting 1 / R on the abscissa and H / R on the ordinate, and multiplying 1 / R by a translation factor l c , such that the abscissa l c / R corresponding to the maximum value of the ordinate H / R is 1; or, plotting 1 / R on the abscissa and D / R on the ordinate, and multiplying 1 / R by a translation factor l c , such that the abscissa l c / R corresponding to the maximum value of the ordinate D / R is 1;

[0014] Obtaining the l corresponding to the rubbery polymer films of different thicknesses h according to this method c , l c The relationship with h satisfies Equation 1:

[0015]

[0016] In Equation 1, l c is the translation factor, with the unit of nm;

[0017] γ is the surface tension of the rubbery polymer film to be tested, with the unit of N / m;

[0018] E is the elastic modulus, with the unit of kPa;

[0019] h is the thickness of the rubbery polymer film to be tested, with the unit of nm;

[0020] Deforming Equation 1 to obtain Equation 2:

[0021]

[0022] Plot the equation 2 to obtain the intercept of the linear equation of lgh and lgl c and obtain the elastic modulus E of the rubbery polymer film attached to the substrate surface according to the intercept and the known surface tension γ.

[0023] Preferably, the thickness of the rubbery polymer is 10 nm to 10 μm.

[0024] Preferably, the nano-sized droplets are obtained by atomizing with an atomizer.

[0025] Preferably, the radius of the nano-sized liquid is 0.1 to 10 μm.

[0026] Preferably, the rubbery polymer film to be measured after heating reaches the rubber elastic plateau.

[0027] Preferably, the heating temperature is Tg + 15 °C.

[0028] Preferably, the instrument for observing the microscopic deformation of the rubbery polymer film to be measured is an atomic force microscope.

[0029] Preferably, the rubbery polymer is polystyrene, natural rubber, styrene-butadiene rubber, cis-1,4-polybutadiene rubber, chloroprene rubber, poly(α-methylstyrene), poly(4-tert-butylstyrene), polymethylsiloxane or propylene-butylene rubber.

[0030] The present invention provides a method for testing the elastic modulus of a rubbery polymer film attached to a substrate surface. In the present invention, nano-sized droplets act on the rubbery polymer film supported by the substrate. Under the competitive action of capillary action and film elasticity, the film produces a crater-like deformation; where the depth is D and the edge height is H, and both will change with the change of the crater radius R. Divide H and D by the radius to obtain the radius-scaled H / R and D / R, and both can be used as physical quantities to measure the surface deformation profile, and both will have a maximum value with the change of the radius R. By translating the abscissa 1 / R by l c to move the maximum values of H / R and D / R to l c / R = 1, and obtain the translation factor l c . The translation factors l c of samples with different thicknesses are different. By establishing the relationship between the film translation factor l c and the thickness, extract the modulus-related factors from it to obtain the elastic modulus of the film. The results of the examples show that the elastic modulus E of the polystyrene nano-film with a weight average molecular weight of 49 kDa measured by the method of the present invention is 186.4 kPa, which is close to the expected value. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of a micro-droplet settling on the surface of a film sample to be measured;

[0032] Figure 2 Morphology diagram of the surface deformation of a thin film sample with a thickness of 600 nm;

[0033] Figure 3 Cross-sectional diagram of the surface deformation of a thin film caused by a 1.9 μm radius droplet extracted from a thin film sample with a thickness of 600 nm;

[0034] Figure 4 Relationship between H, D and 1 / R of a thin film sample with a thickness of 600 nm;

[0035] Figure 5 Relationship between H / R and l c / R of a thin film sample with a thickness of 600 nm;

[0036] Figure 6 Relationship between D / R and l c / R of a thin film sample with a thickness of 600 nm;

[0037] Figure 7 Relationship between l c and thickness h in Example 1;

[0038] Figure 8 Modulus of the rheological measurement platform of polystyrene (Mn = 49 kDa);

[0039] Figure 9 Relationship between l c and thickness h in Example 2;

[0040] Figure 10 Relationship between l c and thickness h in Example 3. Specific implementation manner

[0041] The present invention provides a method for testing the elastic modulus of a rubbery polymer thin film attached to the surface of a substrate, comprising the following steps:

[0042] Provide a plurality of rubbery polymer thin films to be tested attached to the surface of a substrate with different thicknesses;

[0043] Deposit a plurality of nano-sized droplets on the surfaces of the rubbery polymer thin films to be tested with different thicknesses;

[0044] Heat the rubbery polymer thin films to be tested on which the nano-sized droplets are deposited, and multiple micro deformations occur in the rubbery polymer thin films to be tested;

[0045] Fix the micro deformations of the rubbery polymer thin films to be tested by means of quenching;

[0046] Observe the micro deformations of the rubbery polymer thin films to be tested, and record the radius R, the edge height H and the center depth D of the micro deformations;

[0047] For a certain rubbery polymer film, plot with 1 / R as the abscissa and H / R as the ordinate, and multiply 1 / R by a translation factor l c such that the abscissa corresponding to the maximum value of the ordinate H / R is l c / R = 1; or, plot with 1 / R as the abscissa and D / R as the ordinate, and multiply 1 / R by a translation factor l c such that the abscissa corresponding to the maximum value of the ordinate D / R is l c / R = 1;

[0048] Obtain l corresponding to rubbery polymer films with different thicknesses h according to this method c l c The relationship between l and h satisfies Equation 1:

[0049]

[0050] In Equation 1, l c is the translation factor, with the unit of nm;

[0051] γ is the surface tension of the rubbery polymer film to be measured, with the unit of N / m;

[0052] E is the elastic modulus, in kPa;

[0053] h is the thickness of the rubbery polymer film to be measured, in nm;

[0054] Deform Equation 1 to obtain Equation 2:

[0055]

[0056] Plot Equation 2 to obtain the intercept of the linear equation of lgh and lgl c , and obtain the elastic modulus E of the rubbery polymer film attached to the substrate surface according to the intercept and the known surface tension γ.

[0057] The present invention provides rubbery polymer films with multiple different thicknesses attached to the substrate surface. In the present invention, the rubbery polymer is preferably polystyrene, natural rubber, styrene-butadiene rubber, cis-1,4-polybutadiene, chloroprene rubber, poly(α-methylstyrene), poly(4-tert-butylstyrene), polymethylsiloxane or propylene-butylene rubber. In the present invention, the rubbery polymer film attached to the substrate surface is preferably a rubbery polymer coating. In the present invention, the thickness of the rubbery polymer is preferably 10 nm to 10 μm, more preferably 100 nm to 1 μm.

[0058] The present invention has no special requirements for the preparation method of the rubbery polymer films with different thicknesses attached to the substrate surface, and any method well-known to those skilled in the art can be used, such as spin coating method.

[0059] In the present invention, a plurality of nano-sized droplets are respectively sedimented on the surfaces of rubbery polymer thin films to be tested with different thicknesses. In the present invention, the nano-sized droplets are preferably obtained by atomizing with an atomizer. In the present invention, the components of the nano-sized droplets are not miscible with the rubbery polymer. Preferably, the components of the nano-sized droplets are preferably ionic liquids, and more preferably [Emim]BF4.

[0060] In the present invention, the radius of the nano-sized liquid is preferably 0.1 - 10 μm.

[0061] In the present invention, the rubbery polymer thin film to be tested on which the nano-sized droplets are sedimented is heated to cause multiple micro-deformations in the rubbery polymer thin film to be tested. In the present invention, the heating temperature and time are determined according to the type of the rubbery polymer, and after heating, the rubbery polymer thin film to be tested reaches the rubber elasticity plateau. As a specific embodiment of the present invention, the heating temperature is Tg + 15°C.

[0062] In the present invention, after heating, the present invention preferably quenches and cleans the heated rubbery polymer thin film to be tested to fix the micro-deformations of the rubbery polymer thin film to be tested. In the present invention, the quenching temperature is preferably 5°C. In the present invention, the cleaning liquid used for cleaning is preferably deionized water.

[0063] In the present invention, the micro-deformations of the rubbery polymer thin film to be tested are observed, and the radius R, the edge height H, and the center depth D of the micro-deformations are recorded. In the present invention, the instrument for observing the micro-deformations of the rubbery polymer thin film to be tested is an atomic force microscope.

[0064] For a certain rubbery polymer thin film, with 1 / R as the abscissa and H / R as the ordinate to plot a graph, multiply 1 / R by a translation factor l c , such that the abscissa l c / R corresponding to the maximum value of the ordinate H / R = 1; or, with 1 / R as the abscissa and D / R as the ordinate to plot a graph, multiply 1 / R by a translation factor l c , such that the abscissa l c / R corresponding to the maximum value of the ordinate D / R = 1;

[0065] According to this method, the l c , l c corresponding to rubbery polymer thin films with different thicknesses h is obtained, and the relationship between l

[0066]

[0067] and h satisfies Equation 1: c In Equation 1, l

[0068] γ is the surface tension of the rubbery polymer film to be measured, with the unit of N / m;

[0069] E is the elastic modulus, with the unit of kPa;

[0070] h is the thickness of the rubbery polymer film to be measured, with the unit of nm.

[0071] In the present invention, the surface tension of the rubbery polymer film to be measured is a known quantity. The present invention has no special requirements for the surface tension of the rubbery polymer film to be measured, and it can be measured by using the solid surface tension test method well-known to those skilled in the art. As a specific embodiment of the present invention, γ of the polystyrene is 0.034 N / m.

[0072] Equation 1 is transformed to obtain Equation 2:

[0073]

[0074] A graph is plotted for Equation 2 to obtain the intercept of the linear equation of lg h and lg l c , and the elastic modulus E of the rubbery polymer film attached to the substrate surface is obtained according to the intercept and the known surface tension γ.

[0075] The following combines examples to elaborate in detail on the test method for the elastic modulus of the rubbery polymer film attached to the substrate surface provided by the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0076] Example 1

[0077] (1) Polystyrene (PS) with a weight average molecular weight of 49 kDa is selected as the sample to be measured, and films with thicknesses of 233 nm, 600 nm, 878 nm, 1290 nm, and 2000 nm are prepared by spin coating, and vacuum treatment is carried out at 120 °C for 24 h to remove the solvent.

[0078] (2) The sample to be measured in step (1) is placed in a closed container, and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EIm]BF4) is dispersed into nano-sized micro-droplets by an atomizer and filled into the closed container, and left standing to allow the micro-droplets to fully settle on the surface of the sample film to be measured. The schematic diagram is as Figure 1 shown.

[0079] (3) The sample with micro-droplets settled on the surface in step (2) is taken out and placed on a precision temperature-controlled hot stage, and the temperature of the polymer film is controlled to be 115 °C (T g + 15 °C), and at this time the polymer is in a viscoelastic state.

[0080] After the placement time of 1800 s, when the PS sample was in the elastic plateau region, the sample was quickly transferred to a 5 °C steel plate for quenching, and the surface-settled micro-droplets were washed away with secondary deionized water.

[0081] (5) The surface deformation caused by micro-droplets with a contact radius ranging from 200 to 8000 nm was measured using a Multimode-8 atomic force microscope (AFM).

[0082] The topographic map of the surface deformation of the 600-nm-thick film sample is as Figure 2 shown.

[0083] The cross-sectional view of the surface deformation of the 600-nm-thick film sample caused by 1.9-μm-radius droplets extracted from the sample is as Figure 3 shown. Figure 3 In it, the highest point of the edge deformation height is defined as H, the lowest point of the central depth is defined as D, and the lateral distance between the two is the contact radius R.

[0084] The relationship between H, D and 1 / R of the 600-nm-thick film sample is as Figure 4 shown.

[0085] (6) Divide H and D on the ordinate by the radius R, and a maximum value will exist for the ordinates H / R and D / R. Then, translate the abscissa by l c , so that the maximum values of the ordinates H / R and D / R are at l c / R = 1. Among them, the relationship between H / R and l c / R is as Figure 5 shown, and the relationship between D / R and l c / R is as Figure 6 shown.

[0086] (7) Extract l c , l c for film samples with different thicknesses. The relationship between l

[0087]

[0088] Figure 7 c and the thickness h is shown in Equation 2, which includes the elastic modulus E: Figure 7 As shown, the intercept is 0.56524. On the premise of knowing γ = 0.034 N / m, E can be extracted through the intercept, and the elastic modulus E = 186.43 kPa can be calculated.

[0089] The rheological measurement plateau modulus of polystyrene (Mn = 49 kDa) is as Figure 8 shown, and the modulus value of its rubber plateau is approximately 2×10 5Pa, it can be seen that the elastic modulus E tested in the present invention is close to G, which conforms to the expected value.

[0090] Example 2

[0091] According to the same method as in Example 1, PS with a weight-average molecular weight of 49 kDa was selected as the sample to be tested, and films with thicknesses of 400 nm, 752 nm, 985 nm, and 1314 nm were prepared. Micro-droplets were deposited on their surfaces, and the maximum values of H / R and the central depth D / R at different thicknesses were respectively monitored at l c / R = 1 for the translation factor l c , combined with Equation 2, a linear fit was performed (the slope k was 0.75). It can be seen that the intercept was 0.56635. On the premise that γ = 0.034 N / m was known, E was extracted through the intercept, and the elastic modulus E = 184.54 kPa could be calculated, where l c The relationship with the thickness h is shown in Figure 9 .

[0092] Example 3

[0093] According to the same method as in Example 1, PS with a weight-average molecular weight of 28 kDa was selected as the sample to be tested, and films with thicknesses of 144 nm, 215 nm, 333 nm, and 437 nm were prepared. Micro-droplets were deposited on their surfaces, and the maximum values of H / R and the central depth D / R at different thicknesses were respectively monitored at l c / R = 1 for the translation factor l c , combined with Equation 2, a linear fit was performed (the slope k was 0.75). It can be seen that the intercept was 0.56841. On the premise that γ = 0.034 N / m was known, E was extracted through the intercept, and the elastic modulus E = 181.07 kPa could be calculated, where l c The relationship with the thickness h is shown in Figure 10 .

[0094] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for testing the elastic modulus of a rubbery polymer film attached to the surface of a substrate, comprising the following steps: Provide a plurality of rubbery polymer films to be tested with different thicknesses attached to the surface of a substrate; Deposit a plurality of nano-sized droplets on the surfaces of the rubbery polymer films to be tested with different thicknesses respectively; Heat the rubbery polymer films to be tested on which the nano-sized droplets are deposited, and multiple micro-deformations occur on the rubbery polymer films to be tested; Fix the micro-deformations of the rubbery polymer films to be tested by means of quenching; Observe the micro-deformations of the rubbery polymer films to be tested, and record the radius R, the edge height H and the center depth D of the micro-deformations; For a certain rubbery polymer film, plot with 1 / R on the abscissa and H / R on the ordinate, and multiply 1 / R by a translation factor l c such that the abscissa l c / R corresponding to the maximum value of the ordinate H / R is 1; alternatively, plot with 1 / R on the abscissa and D / R on the ordinate, and multiply 1 / R by a translation factor l c such that the abscissa l c / R corresponding to the maximum value of the ordinate D / R is 1; Obtain the corresponding l for rubbery polymer films with different thicknesses h according to this method c , l c The relationship between l and h satisfies Equation 1: In Equation 1, l c is the translation factor with the unit of nm; γ is the surface tension of the rubbery polymer film to be tested, with the unit of N / m; E is the elastic modulus, with the unit of kPa; h is the thickness of the rubbery polymer film to be tested, with the unit of nm; Deform Equation 1 to obtain Equation 2: Plot the equation 2 to obtain the intercept of the linear equation of lgh and lgl c and obtain the elastic modulus E of the rubbery polymer film attached to the substrate surface according to the intercept and the known surface tension γ.

2. The test method according to claim 1, characterized in that, The thickness of the rubbery polymer is 10 nm to 10 μm.

3. The test method according to claim 1, wherein The nano-sized droplets are obtained by atomizing with an atomizer.

4. The test method according to claim 1 or 3, characterized in that The radius of the nano-sized droplets is 0.1 to 10 μm.

5. The test method according to claim 1, wherein After heating, the rubbery polymer film to be tested reaches the rubber elastic plateau.

6. The test method according to claim 5, wherein The heating temperature is Tg + 15°C.

7. According to the testing method described in claim 1, characterized in that the instrument for observing the micro-deformations of the rubbery polymer film to be tested is an atomic force microscope.

8. The test method according to claim 1, wherein The rubbery polymer is polystyrene, natural rubber, styrene-butadiene rubber, cis-1,4-polybutadiene rubber, neoprene, poly(α-methylstyrene), poly(4-tert-butylstyrene), polymethylsiloxane or propylene-butylene rubber.

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