Method for testing dispersibility of carbon nanotubes in mortar

Abstract

The invention discloses a method for testing dispersibility of carbon nanotubes in mortar, which comprises the following steps: dispersing carbon nanotubes subjected to surface modification treatment in water to form a dispersion liquid (prepared by a mechanical oscillation or ultrasonic dispersion process), and then mixing the dispersion liquid with cement and sand to prepare a mortar mixture; uniformly dividing the mixture into at least two groups with equal mass, respectively filling the groups into standard molds with uniform geometric structures and anti-sticking layers on the inner walls, applying continuous preset pressure to the mortar mixture in each group of molds to perform filter pressing, and collecting filter pressing liquid (multiple rounds of filter pressing can be performed and samples can be combined); and measuring the absorbance of each group of pressure filtrate within the wavelength range of 380-500nm by adopting an ultraviolet spectrophotometer, and evaluating the dispersity of the carbon nanotubes based on absorbance difference by calculating a standard deviation or a variable coefficient. The method can effectively and accurately test the dispersibility of the carbon nanotubes in the mortar, reduces the test interference, and improves the reliability of the test result.

Description

Technical Field

[0001] The present application relates to the field of material performance testing, and in particular to a method for testing the dispersion of carbon nanotubes in mortar. Background Art

[0002] In the field of building materials, mortar, as an important bonding and filling material, has long been a research focus on improving its performance. Carbon nanotubes, due to their extremely high mechanical strength—tensile strengths that can reach many times that of steel and their ability to withstand significant strain before structural failure—are considered an ideal material for enhancing the mechanical properties of mortar. With the continuous advancement of materials science, a growing number of studies are dedicated to incorporating carbon nanotubes into mortar to improve its physical and mechanical properties, providing a more superior material option for construction projects. This not only helps improve the durability and stability of buildings, but also meets the demand for high-performance materials in modern architecture.

[0003] Currently, in order to better integrate carbon nanotubes into the mortar system, carbon nanotubes are generally first dispersed in water to form a carbon nanotube dispersion, and then the dispersion is added to the mortar to form a carbon nanotube / mortar mixed material. For testing the dispersibility of carbon nanotubes, a common practice is to indirectly represent their dispersibility in the mortar by characterizing the dispersibility of carbon nanotubes in the dispersion. For example, some use nuclear magnetic resonance to test the dispersibility of carbon nanotube slurry. This method mainly focuses on the state of carbon nanotubes in the dispersion stage. Others use optical microscopy and other methods, but these are all aimed at the dispersion of carbon nanotubes in the dispersion.

[0004] However, these existing methods all have a significant drawback: they cannot characterize the actual dispersion of carbon nanotubes in the mortar after the carbon nanotube dispersion is added. Because the dispersion state of carbon nanotubes in the dispersion may differ from that in the mortar, simply testing their dispersion in the dispersion does not accurately reflect their actual dispersion in the final mortar. Summary of the Invention

[0005] In order to solve the current problem of being unable to characterize the dispersion of carbon nanotubes in mortar after the carbon nanotube dispersion is added to the mortar, the present application provides a method for testing the dispersion of carbon nanotubes in mortar.

[0006] The present application provides a method for testing the dispersion of carbon nanotubes in mortar using the following technical solution: A method for testing the dispersion of carbon nanotubes in mortar comprises the following steps: Dispersing carbon nanotubes in water to form a dispersion and then mixing it with cement and sand to form a mortar mixture; Evenly dividing the mortar mixture into multiple groups and filling them into molds respectively; The mortar mixture in each set of molds is filtered to collect the filtrate; The absorbance of each group of filtrates was measured by ultraviolet spectrophotometer, and the dispersion of carbon nanotubes was evaluated based on the absorbance difference.

[0007] By adopting the above technical solution, the carbon nanotubes are dispersed in water to form a dispersion liquid, which is then mixed with cement and sand to form a mortar mixture. This can provide the carbon nanotubes with an initial distribution basis in the entire mortar system, facilitating the subsequent analysis of their dispersion state in the mortar. The mortar mixture is evenly divided into multiple groups and filled into molds respectively. The multiple group division is conducive to accurately judging the uniformity of carbon nanotube dispersion by comparing the conditions of different groups, and filling into molds provides a stable environment for subsequent filter pressing operations. The mortar mixture in each group of molds is filter pressed to collect the filtrate. The method can separate the liquid containing carbon nanotubes from the mortar mixture, making it easier to infer the dispersion of carbon nanotubes in the mortar by testing the liquid. A UV spectrophotometer is used to measure the absorbance of each group of filtrate and evaluate the dispersion of the carbon nanotubes based on the absorbance difference. By using the relationship between absorbance and carbon nanotube concentration, the uniform distribution of carbon nanotubes in different groups of mortar mixtures can be intuitively analyzed based on the absorbance difference, thereby evaluating their dispersion. This solves the current problem of being unable to directly and effectively test the dispersion of carbon nanotubes in mortar. Furthermore, traditional nuclear magnetic resonance detection methods have higher sample preparation requirements and longer detection times, while UV spectrophotometry can directly test filtrate samples, making the test more convenient and faster, and more versatile and practical.

[0008] Preferably, the carbon nanotubes are surface modified before dispersion.

[0009] By adopting the above technical solution, the carbon nanotubes undergo surface modification before dispersion, which makes the carbon nanotubes more dispersed in water, thereby improving their dispersion uniformity in the mortar mixture, so that the test results can more accurately reflect the actual dispersion of the carbon nanotubes in the mortar.

[0010] Preferably, the dispersion is prepared by mechanical shaking or ultrasonic dispersion process.

[0011] By adopting the above technical solution, the dispersion liquid is treated by mechanical vibration or ultrasound, which can effectively promote the dispersion of carbon nanotubes in water, making the prepared carbon nanotube dispersion liquid more uniform, thereby improving the accuracy of the evaluation of the dispersion of carbon nanotubes in mortar in subsequent tests.

[0012] Preferably, the mold is a standard mold with a uniform geometric structure.

[0013] By employing this technical solution, the mixture is evenly divided into multiple groups and each group is filled into a standard mold with a uniform geometry. The mortar mixture in each mold is then filtered to collect the filtrate. The absorbance of each filtrate is measured using a UV spectrophotometer, and the dispersion of the carbon nanotubes is evaluated based on the absorbance differences. This uniform geometry ensures that the spatial conditions of each mortar mixture are consistent, making the filtration process more stable and controllable, reducing errors caused by mold differences, and thus more accurately evaluating the dispersion of the carbon nanotubes in the mortar based on the absorbance differences of the filtrate.

[0014] Preferably, the filter pressing process comprises applying a continuous preset pressure to the mold until liquid separation is completed.

[0015] By adopting the above technical solution, a continuous preset pressure is applied to the mold until liquid separation is completed, so that the liquid in the mortar mixture can be separated stably and reliably, facilitating the subsequent collection of accurate filtrate for absorbance measurement, and further more accurately evaluating the dispersion of carbon nanotubes.

[0016] Preferably, the ultraviolet spectrophotometer scans the press filtrate within a wavelength range of 380 nm to 500 nm.

[0017] By adopting the above technical solution, the wavelength range of the ultraviolet spectrophotometer is controlled within 380nm to 500nm, so that the ultraviolet spectrophotometer can scan the filtrate within an appropriate wavelength range, and the absorbance corresponding to the carbon nanotube concentration in the filtrate can be obtained more accurately, thereby more accurately evaluating the dispersibility of carbon nanotubes in the mortar.

[0018] Preferably, the mortar mixture is divided into no less than two groups and the quality of each group is equal.

[0019] By adopting the above technical solution, the number of groups of the prepared mortar mixture is set to no less than two and the quality of each group is equal, so that the subsequent collection of filtrate from different groups has stronger comparability. The evaluation of the dispersion of carbon nanotubes based on such absorbance differences of filtrate is more scientific and accurate, and can better solve the current problem of characterization and testing of the dispersion of carbon nanotubes in mortar after the carbon nanotube dispersion is added to the mortar.

[0020] Preferably, the filtrate collection step comprises performing multiple rounds of filtration on each set of molds and combining the liquid samples.

[0021] By adopting the above technical solution, performing multiple rounds of filtration on each set of molds and combining liquid samples, carbon nanotubes can be collected more fully, making the carbon nanotube content in the filtrate more representative, and improving the accuracy and reliability of the test results.

[0022] Preferably, the absorbance measurement results are quantitatively evaluated for dispersion by calculating the standard deviation or coefficient of variation.

[0023] By employing the above technical solution, the absorbance measurement results are processed by calculating the standard deviation or coefficient of variation, enabling a quantitative evaluation of the dispersion of carbon nanotubes in the mortar. Taking the standard deviation as an example, a small standard deviation indicates that the absorbance of each group of filtrates is relatively close, implying a relatively uniform distribution of the carbon nanotubes in the mortar and good dispersion. A large standard deviation indicates large differences in absorbance, indicating an uneven distribution of the carbon nanotubes and poor dispersion. The coefficient of variation takes into account the relative dispersion of the data and can more accurately reflect the quality of carbon nanotube dispersion in different situations, making the evaluation results more scientific, intuitive, and accurate.

[0024] Preferably, an anti-sticking layer is provided on the inner wall of the mold to reduce the interference of carbon nanotube adhesion on the test results.

[0025] By adopting the above technical solution, an anti-sticking layer is provided on the inner wall of the mold, which can effectively reduce the possibility of carbon nanotubes adhering to the inner wall of the mold. Due to the existing technology, when conducting carbon nanotube dispersion tests, carbon nanotubes may adhere to the inner wall of the mold, resulting in deviations in the actual content of carbon nanotubes in the mortar mixtures in different groups of molds, thereby affecting the content of carbon nanotubes in the filtrate and the subsequent absorbance measurement. The provision of the anti-sticking layer avoids this adhesion phenomenon, so that when the mortar mixtures in each group of molds are filter-filtered, the content of carbon nanotubes in the filtrate can more accurately reflect the actual dispersion of carbon nanotubes in the mortar mixture. In this way, after using an ultraviolet spectrophotometer to measure the absorbance of each group of filtrate, the evaluation of the dispersion of carbon nanotubes based on the absorbance difference is more accurate and reliable, reducing the test error caused by the attachment of carbon nanotubes to the inner wall of the mold.

[0026] In summary, this application includes at least one of the following beneficial technical effects: 1. It solves the current problem of being unable to characterize the actual dispersion of carbon nanotubes in mortar after the carbon nanotube dispersion is added to the mortar; 2. By filtering the mortar mixture into groups and testing the absorbance of the filtrate, the dispersion effect of carbon nanotubes in the mortar can be directly and effectively reflected; 3. The dispersion of carbon nanotubes in the mortar can be more accurately evaluated based on the absorbance difference, and it can be determined whether the carbon nanotubes are evenly distributed in the mortar. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a method for testing the dispersion of carbon nanotubes in mortar according to an embodiment of the present application.

[0028] Figure 2It is a structural schematic diagram of a cylindrical filter press mold used in a method for testing the dispersion of carbon nanotubes in mortar according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] The following is combined with Figure 1-2 This application is described in further detail.

[0030] The present invention discloses a method for testing the dispersion of carbon nanotubes in mortar. Figure 1 and Figure 2 The method includes preparing a carbon nanotube dispersion, preparing a mortar mixture, grouping and filling the mold, collecting the filtrate by filtration, measuring absorbance, and evaluating the dispersion. By following these steps in sequence, the dispersion of carbon nanotubes in the mortar can be accurately determined. This is because carbon nanotubes do not participate in the mortar hydration reaction and are present in the dispersion before solidification. By filtering the dispersion and measuring its absorbance, the distribution of carbon nanotubes in the mortar can be determined based on the difference in absorbance.

[0031] In the carbon nanotube dispersion preparation step, the carbon nanotubes can be single-walled carbon nanotubes, multi-walled carbon nanotubes, or pre-treated single-walled or multi-walled carbon nanotubes, such as those that have undergone surface modification. Surface modification can alter the chemical properties of the carbon nanotube surface, making it easier to disperse in water. For example, oxidation of the carbon nanotubes can increase the number of hydrophilic groups on their surface. There are various methods for dispersing carbon nanotubes in water to form a dispersion. Chemical modification dispersion involves attaching hydrophilic groups to the carbon nanotube surface through a chemical reaction. For example, by adding 0.1%-1% sodium dodecylbenzenesulfonate (SDBS) or polyvinylpyrrolidone (PVP) as a dispersant to inhibit carbon nanotube aggregation. Mechanical agitation or ultrasonic dispersion methods are also available. Mechanical agitation can be performed using a stirrer or other equipment to initially disperse the carbon nanotubes in water. A specific agitator can be a high-speed shear emulsifier, operating at 5,000-10,000 rpm for 10-30 minutes to achieve initial dispersion of the carbon nanotubes. Ultrasonic dispersion utilizes the cavitation effect of ultrasound to further break up agglomerated carbon nanotubes. Ultrasonic dispersion is preferably performed at a frequency of 20-40 kHz, a power density of 100-300 W / L, and a treatment time of 30-60 minutes. An ice bath (<40°C) can be used to control the temperature during the process to prevent overheating and dispersant decomposition. A combination of methods can also be used, such as mechanical vibration followed by ultrasonic dispersion, or the addition of chemical dispersants during the ultrasonic dispersion process.

[0032] During the mortar mixture preparation step, cement, sand, and the previously prepared carbon nanotube dispersion are added to a mixing pot according to the specified proportions and mixed according to standard methods. This standard method can be the mortar mixing specifications commonly used in the construction industry to ensure thorough and uniform mixing of all ingredients. Specifically, the cement-to-sand mass ratio can be set at 1:2 to 1:3, and the carbon nanotube dispersion is added at a rate of 0.01%-0.5% of the cementitious material mass to ensure the nanomaterial's reinforcing effect while avoiding excessive cost increases. The water-cement ratio is controlled between 0.4 and 0.6, adjusted based on the desired workability of the mortar. The mixing process is divided into a dry mixing phase (mixing the cement and sand for 90 seconds) and a wet mixing phase (adding the dispersion and continuing mixing for 120 seconds). The mixing speed is set to alternate between low (140 ± 5 rpm) and high (285 ± 10 rpm) to ensure homogenization.

[0033] In the step of grouping and filling the mold, the stirred mortar mixture is evenly divided into multiple groups, with no less than two groups and equal quality in each group, so as to ensure the accuracy of subsequent tests. Here, the mortar mixture is evenly divided into 4 groups. The filled mold is a standard mold with a uniform geometric structure, such as a cylindrical mold of the same shape and size. In addition, an anti-sticking layer is provided on the inner wall of the mold. The anti-sticking layer can be made of non-stick materials such as Teflon. The purpose is to reduce the adhesion of carbon nanotubes to the inner wall of the mold and interfere with the test results. Specifically, the inner wall of the mold is sprayed with a polytetrafluoroethylene (Teflon) coating with a thickness of 20-50μm, and its surface roughness Ra≤0.2μm to minimize the adhesion of carbon nanotubes.

[0034] In the step of collecting the filtrate by filtration, the mortar mixture in each group of molds is filtered, and the filtration process includes applying a continuous preset pressure to the mold until the liquid separation is completed. A special filter press device can be used to apply pressure to the mold through a hydraulic system. In order to collect the filtrate more comprehensively, the filtrate collection step includes performing multiple rounds of filtration on each group of molds and combining the liquid samples. Multiple rounds of filtration can filter out as much water as possible from the mortar and reduce errors. Specifically, the filtration pressure range is set to 0.5-2 MPa, and the pressure holding time is 10-30 minutes. Multiple rounds of filtration can be designed as 3 cycles. After each filtration, the pressure is released and the material is allowed to stand for 2 minutes to relax the internal stress of the material, thereby improving the liquid separation efficiency. The cumulative filtrate collection rate can reach more than 85%.

[0035] During the absorbance measurement and dispersion evaluation step, the absorbance of each press filtrate was measured using an ultraviolet spectrophotometer. The UV spectrophotometer scanned the 380nm-500nm wavelength range, as carbon nanotubes have significant light absorption characteristics within this wavelength range. The absorbance measurement results were used to quantitatively evaluate dispersion by calculating the standard deviation or coefficient of variation. According to the Lambert-Beer law (A=εbc), when the cell thickness b and the molar absorptivity ε of the substance are constant, the absorbance of the solution is proportional to the concentration of the substance in the solution. Therefore, the absorbance of the solution can be used to semi-quantitatively characterize the concentration of carbon nanotubes in the dispersion. If the absorbance differences between the press filtrates are small (≤10%), it indicates that the carbon nanotube content in each group is similar, indicating that the carbon nanotubes are evenly distributed in each part of the mortar and the dispersion is good. Conversely, if the absorbance differences are large (>10%), it indicates that the carbon nanotubes are unevenly distributed in each part of the mortar and the dispersion is poor.

[0036] It should be noted that the experiment was carried out under constant temperature (23 ± 2 °C) and constant humidity (50 ± 5% RH) conditions throughout the experiment to avoid the influence of temperature and humidity fluctuations on the mortar hydration rate and filter press efficiency.

[0037] The working principle of this example is as follows: Through a series of steps, carbon nanotubes are first dispersed in water, then mixed with cement and sand to form a mortar mixture. The filtrate is then filtered and collected in groups, and finally, the absorbance is measured to evaluate dispersion. This method overcomes the limitation of existing technologies that only test the dispersibility of carbon nanotubes in a dispersion liquid. It can directly and accurately reflect the actual dispersion of carbon nanotubes in the mortar. Through group testing and quantitative evaluation, the accuracy and reliability of the test results are improved, providing strong support for evaluating the application effect of carbon nanotubes in mortar.

[0038] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method for testing the dispersion of carbon nanotubes in mortar, characterized by: The following steps are involved: Dispersing carbon nanotubes in water to form a dispersion and then mixing it with cement and sand to form a mortar mixture; Evenly dividing the mortar mixture into multiple groups and filling them into molds respectively; The mortar mixture in each set of molds is filtered to collect the filtrate; The absorbance of each group of filtrates was measured by ultraviolet spectrophotometer, and the dispersion of carbon nanotubes was evaluated based on the absorbance difference.

2. The method for testing the dispersion of carbon nanotubes in mortar according to claim 1, wherein: The carbon nanotubes are surface modified before being dispersed.

3. The method for testing the dispersion of carbon nanotubes in mortar according to claim 1, wherein: The dispersion is prepared by mechanical shaking or ultrasonic dispersion process.

4. The method for testing the dispersion of carbon nanotubes in mortar according to claim 1, wherein: The mold is a standard mold with a uniform geometric structure.

5. The method for testing the dispersion of carbon nanotubes in mortar according to claim 1, wherein: The filtration process involves applying a continuous preset pressure to the mold until liquid separation is complete.

6. The method for testing the dispersion of carbon nanotubes in mortar according to claim 1, wherein: The ultraviolet spectrophotometer scans the press filtrate within a wavelength range of 380 nm to 500 nm.

7. The method for testing the dispersion of carbon nanotubes in mortar according to claim 1, wherein: The mortar mixture is divided into no less than two groups and the quality of each group is equal.

8. The method for testing the dispersion of carbon nanotubes in mortar according to claim 1, wherein: The filtrate collection step includes performing multiple rounds of filtration on each set of molds and combining liquid samples.

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