Method for testing Young modulus of single fiber and application thereof

Abstract

The invention discloses a method for testing the Young modulus of a single fiber and application thereof, and belongs to the technical field of material characterization, the method for testing the Young modulus of the single fiber comprises the following steps: etching a silicon wafer with grooves and letter positioning marks; transferring a fiber to be detected to the silicon wafer; positioning the silicon wafer bearing the fiber to be detected; scanning to obtain a fiber morphology graph; performing a force curve test at the center point of the sample; analyzing the obtained force curve, and calculating the Young modulus of the sample; according to the method, the process is simple, the silicon wafer with the grooves and the letters for positioning is adopted, the sample to be tested can be accurately positioned in a large number of samples, the mechanical property of the nanofiber is tested through the method, and errors possibly occurring in experimental testing can be effectively eliminated.

Description

Technical Field

[0001] The present invention belongs to the technical field of material characterization, and in particular relates to a method for testing the Young's modulus of a single fiber and an application thereof. Background Art

[0002] The preparation of functional materials requires various characterizations to investigate their actual performance. In materials science, understanding the mechanical properties of materials is crucial to the research and development of new materials. These mechanical properties, including elastic modulus, stiffness, hardness, plastic deformation, and fracture toughness, determine the reliability and application range of the material. Therefore, a deep understanding of the mechanical properties of materials is fundamental for scientists and engineers to optimize material design and develop stronger, more durable, and more reliable materials. With the development of nanotechnology, testing the mechanical properties of materials at the microscale has become increasingly important. Nanotechnology is a technology specifically designed to manufacture and manipulate nanoscale materials. At the nanoscale, the mechanical properties of materials may differ from those at the macroscale. Therefore, testing their mechanical properties at the microscale is essential when developing new materials and applying nanomaterials.

[0003] Testing equipment such as nanoindentation testers can test materials at the microscopic scale, obtaining information related to their mechanical properties. Nanoindentation testing calculates the material's mechanical properties by applying a load to the surface and measuring the relationship between the surface topography and load. Other methods include nanotensile testing, nanocompression testing, and nanoscratch testing. These test results can be used to optimize material design and provide fundamental data for the development of new materials.

[0004] Current testing methods are unable to precisely locate the sample under test within a large sample pool, and direct measurement of Young's modulus using atomic force microscopy (AFM) can result in inaccurate results. Therefore, testing the mechanical properties of materials at the microscale is a key research area in materials science and engineering. By gaining a deeper understanding of the mechanical properties of materials, we can develop stronger, more durable, and more reliable materials, contributing to improvements in human well-being and technological advancement. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention proposes a method for testing the Young's modulus of a single fiber and its application.

[0006] A method for testing the Young's modulus of a single fiber comprises the following steps:

[0007] Etching silicon wafers with grooves and letter positioning marks;

[0008] Transferring the fiber to be tested onto the silicon wafer;

[0009] Positioning the silicon wafer carrying the fiber to be tested;

[0010] Scan to obtain fiber morphology;

[0011] Perform force curve test at the center point of the sample;

[0012] The force curve obtained above was analyzed to calculate the Young's modulus of the sample.

[0013] Preferably, the groove width of the silicon wafer is 10 microns.

[0014] Preferably, the transfer method of the fiber to be tested includes one or more of probe transfer, direct deposition and electron beam deposition.

[0015] Preferably, said scanning comprises a tapping mode.

[0016] Preferably, the groove depth of the silicon wafer is 50 microns.

[0017] Preferably, letter marks are engraved on the groove in both the horizontal and vertical directions.

[0018] Application of the above method in testing the mechanical properties of nanofibers.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The process is simple, using silicon wafers with grooves and letter positioning, which can accurately locate the sample to be tested among a large number of samples.

[0021] 2. Using the method of the present invention to test the mechanical properties of nanofibers can effectively eliminate errors that may occur in experimental tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] Figure 1 The topography images obtained in tapping mode are shown, showing the precise positioning of the sample to be tested;

[0024] Figure 2 Schematic diagram of the linear part of the force-deflection curve of the nanofiber;

[0025] Figure 3 A model diagram of the three-point bending test method for a single nanofiber;

[0026] Figure 4 Schematic diagram of the AFM probe tip deflection under downward pressure;

[0027] Figure 5 This is the theoretical model diagram of the three-point bending test;

[0028] Figure 6 is the equivalent vibration model diagram, indicating the existence of probe deformation error;

[0029] Figure 7 is the FD curve obtained by repeating the three-point bending test at the midpoint of the suspended PVDF nanofiber;

[0030] Figure 8 FD curves obtained by repeating the three-point bending test at the midpoint of the suspended PVDF-HFP nanofiber;

[0031] Figure 9 is the Young's modulus of PVDF and PVDF-HFP nanofibers with different diameters. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] An embodiment of the present invention provides a method for measuring the Young's modulus of a single fiber at a microscale, comprising the following steps:

[0034] Step 1) Etch a silicon wafer with grooves and lettering to serve as a substrate for subsequent testing samples. The grooves on the wafer are 10 microns wide and 50 microns deep. Each groove is engraved with letters in both the horizontal and vertical directions.

[0035] Step 2) Transfer the fiber to be tested onto a silicon wafer. Sample transfer can be done by using a microprobe to pick up the nanofiber and place it on the silicon wafer groove. Alternatively, the sample can be directly deposited onto the groove. If the sample itself cannot be fixed to the groove, electron beam deposition can be used for fixation.

[0036] Step 3) Place the silicon wafer holding the fiber to be tested into an atomic force microscope and locate the specific sample quickly and accurately by locating the letters.

[0037] Step 4) Scan the image using an atomic force microscope to obtain a fiber morphology image (such as Figure 1 (as shown), which provides a reference for subsequent force curve drawing at the fiber center point. Use the tapping mode to scan the image and select a softer probe.

[0038] Step 5) Use an atomic force microscope to make a force curve at the center point of the sample. The force curve can be measured multiple times on a very small area at the center point of the fiber to reduce experimental errors.

[0039] Step 6) Analyze and calculate the Young's modulus of the sample based on the force curve obtained in step 5). Analyzing the force curve to calculate the Young's modulus requires considering the indentation produced by the sample itself after being subjected to force and excluding the bending of the probe itself.

[0040] The error caused by the deformation of the sample can be analyzed and processed as follows:

[0041] The pressure curves at the midpoint and end points of the fiber are as follows Figure 2 As shown, two lines with different slopes can be obtained. The red line represents the position of the AFM tip in the suspended nanofiber (i.e. Figure 3 The FZ curve is obtained by contacting the AFM tip with the nanofiber on the rigid substrate (point B in the figure). The black line represents the position of the AFM tip and the nanofiber on the rigid substrate (point B in the figure). Figure 3 The curve obtained by contacting point A in the figure.

[0042] Here's the net offset:

[0043]

[0044] Further converted to:

[0045]

[0046] The calculation formula of Young's modulus can be expressed as:

[0047]

[0048] Where: θ is the position of the AFM probe at the point where the nanofiber contacts the rigid substrate ( Figure 3 The inclination angle of the FZ curve obtained by the AFM probe at the midpoint of the suspended section of the nanofiber ( Figure 3 The inclination angle of the FZ curve obtained at point B in the figure relative to the horizontal axis; L is the span of the three-point bending fulcrum; and D is the diameter of the test specimen. Therefore, by correcting the Young's modulus of the nanofiber, the influence of indentation can be eliminated.

[0049] The error caused by deformation of the probe can be analyzed and processed as follows:

[0050] Since the force-displacement curve measured by AFM is actually the deflection of the cantilever along the Z direction and the displacement curve of the piezoelectric ceramic along the Z direction, it is necessary to take the modulus of the needle tip into consideration, solve the actual force and displacement of the fiber as a beam in the three-point bending model, and finally enter it into the formula to obtain Young's modulus.

[0051] Depend on Figure 4-6 It can be seen that the total drop caused by the piezoelectric crystal is divided into the bending amount of the fiber and the deflection amount of the AFM probe.

[0052] Z Piezo =Z Nanofiber +Z Probe

[0053] Here Z Piezo is the total displacement produced by the piezoelectric crystal (nm), Z Nanofiber is the displacement of the nanofiber (nm), Z Probe is the displacement of the probe (nm).

[0054] According to Newton's third law, the force applied at the midpoint of the fiber is

[0055] F=K Probe ×Z Probe

[0056] Here K Probe The probe box is marked as 0.3 to 4.8 (N / m). The specific value can be obtained by performing Thermal on the probe in the AFM software.

[0057]

[0058] Therefore, the modified three-point bending formula for calculating Young's modulus is

[0059]

[0060] Therefore, by correcting and calculating the Young's modulus of the nanofiber, the influence of the deformation of the probe itself can be eliminated.

[0061] By combining the two, the error of the experiment itself can be eliminated to obtain the accurate Young's modulus of the nanofiber.

[0062] The following experiments verify that the method of the present application can accurately measure the Young's modulus of a single fiber at a microscale.

[0063] Example 1

[0064] A method for measuring the Young's modulus of a single fiber at a microscale comprises the following steps:

[0065] Step 1) Prepare PVDF solution.

[0066] Step 2) The prepared solution is loaded into an electrospinning device for electrospinning, and a specially made silicon wafer with grooves and positioning letters is used to receive the sample.

[0067] Step 3) Place the silicon wafer holding the sample to be tested into the AFM and find the fiber to be tested.

[0068] Step 4) A morphology map of the fiber to be tested was drawn using AFM in tapping mode, with the probe AC240TS being used.

[0069] Step 5) Use AFM in contact mode to make a force curve at the center point of the sample. Multiple force curves can be made on a very small area at the center point of the fiber in the previously obtained topography to reduce experimental errors.

[0070] Step 6) Taking into account the indentation produced by the sample after being subjected to force and excluding the bending of the probe itself, the obtained force curve is analyzed and calculated to obtain the Young's modulus of the sample.

[0071] Example 2

[0072] The steps of Example 1 were repeated using PVDF-HFP solution.

[0073] In the tests of Examples 1 and 2, the force curves were made by selecting other positions near the midpoint and the tested fibers with the same preparation parameters, repeating the experiment and recording all the FD curves. The extension and contraction speed of the AFM cantilever was set to 1 μm / s, and the trigger force for each measurement was fixed to 30 nN. That is, when the force applied by the probe reaches this value, the probe begins to retract. After the above steps, the FD curves of different tested fibers can be obtained. Figure 7 and Figure 8 As shown in the figure, by performing a three-point bending test on the midpoint of a single nanofiber, overlapping FD curves were obtained, proving that this method has high stability, thus ensuring the test accuracy. The Young's modulus obtained after analysis is as follows: Figure 9 As shown in the figure, this method can accurately obtain the Young's modulus of fibers with different diameters, providing a feasible method for characterizing the mechanical properties of materials at the microscale.

[0074] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0075] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for testing the Young's modulus of a single fiber, characterized in that: The following steps are involved: Etching silicon wafers with grooves and letter positioning marks; Transferring the fiber to be tested onto the silicon wafer; Positioning the silicon wafer carrying the fiber to be tested; Scan to obtain the fiber morphology; Perform force curve test at the center point of the sample; The force curve obtained above was analyzed to calculate the Young's modulus of the sample.

2. The method for testing the Young's modulus of a single fiber according to claim 1, characterized in that: The groove width of the silicon wafer is 10 microns.

3. The method for testing the Young's modulus of a single fiber according to claim 1, characterized in that: The transfer method of the fiber to be tested includes one or more of probe transfer, direct deposition and electron beam deposition.

4. The method for testing the Young's modulus of a single fiber according to claim 1, characterized in that: The scanning includes a tapping mode.

5. The method for testing the Young's modulus of a single fiber according to claim 1, characterized in that: The groove depth of the silicon wafer is 50 microns.

6. The method for testing the Young's modulus of a single fiber according to claim 1, characterized in that: Letter marks are engraved in the horizontal and vertical directions of the groove.

7. Use of the method according to any one of claims 1 to 6 in testing the mechanical properties of nanofibers.

Images