Carbon nanotube reinforced shear thickening gel as well as preparation method and application thereof

Abstract

The invention relates to a carbon nanotube reinforced shear thickening gel which is composed of the following components in parts by mass: 50-80 parts of hydroxyl-terminated polydimethylsiloxane; 2-6 parts of boric acid; 0.1 to 1.0 part of a carbon nano tube; 10-30 parts of a solvent; the solvent is ethyl acetate and / or isopropanol. The invention further provides a corresponding preparation method and application. Through a solvent-assisted dispersion strategy, the CNT constructs a three-dimensional enhanced structure in a borate dynamic cross-linked network, and the problems of cold flow deformation, insufficient high-frequency energy storage modulus and low energy dissipation efficiency of traditional STG are solved. The invention further provides a preparation method and application in human body protection equipment, and the impact force of the helmet is reduced by 27.7% according to actual measurement.

Description

Technical Field

[0001] This invention belongs to the field of protective materials technology, specifically relating to carbon nanotube (CNT) reinforced shear-thickening gels, their preparation methods, and applications. Background Technology

[0002] Traditional shear-thickening gels (STGs) achieve rapid viscosity transitions under high-speed impact through dynamic borooxane crosslinking networks, showing potential in the field of personal protective equipment. However, existing STG materials still have significant drawbacks: First, the cold flow deformation caused by molecular chain slippage during long-term static storage leads to gradual collapse of the material under no-load conditions, making it difficult to maintain a stable geometric shape; second, the storage modulus (G') is insufficient, resulting in a slow shear-thickening response at high strain rates. For example, the G' of traditional STGs only increases to about 100 kPa at 100 Hz, which is insufficient to effectively resist high-speed impact loads; third, the energy dissipation efficiency is low, with most of the energy transferred to the human body through viscous flow during impact, causing non-penetrating damage.

[0003] To improve performance, existing technologies often employ rigid fillers (such as silica and carbon fiber) or fiber composite reinforcement strategies. For example, while the addition of carbon black (CB) can increase the modulus, filler agglomeration leads to stress concentration, resulting in brittle fracture of the material. The composite of Kevlar fiber and STG enhances energy absorption through interfacial friction, but the process is complex and significantly reduces flexibility. Furthermore, magnetic STG composites can absorb 70% of energy under low-speed impact, but their adaptability to high-speed impact is insufficient. In addition, Chinese invention patent CN104927367B discloses a multifunctional protective composite material containing a vulcanizing agent, which uses borosilicate alkyl bodies, carbon nanotubes, and a vulcanizing agent (such as peroxide), achieving performance improvement through high-temperature curing (40-180°C). However, this technology has limitations: the vulcanizing agent leads to rigidification of the cross-linked network, sacrificing dynamic reversibility, weakening strain rate sensitivity, and the process is complex and energy-intensive.

[0004] In recent years, carbon nanotubes (CNTs) have been regarded as ideal reinforcements due to their ultra-high specific surface area (>140 m² / g), excellent mechanical strength (elastic modulus of about 1 TPa) and three-dimensional network formation ability. However, their dispersion uniformity and synergistic mechanism with dynamic cross-linked networks have not been fully resolved, which limits their application in high-performance STGs.

[0005] Existing technologies (such as CN104927367B) use vulcanizing agents (peroxides) to cure borosilicate alkyl bodies. Although this can improve the modulus, it leads to the rigidification of the crosslinking network, sacrificing dynamic reversibility. Furthermore, it must rely on high-temperature curing (40-180℃) with vulcanizing agents. Vulcanizing agents convert borosilicate bonds into covalent bonds, weakening strain rate sensitivity.

[0006] Therefore, there is an urgent need to develop an STG reinforced material that combines high dispersibility, excellent mechanical properties, and cold flow resistance. Summary of the Invention

[0007] The main objective of this invention is to address the above-mentioned problems by providing a carbon nanotube-enhanced shear-thickening gel, its preparation method, and its applications.

[0008] To achieve the above objectives, a first aspect of the present invention provides a carbon nanotube-enhanced shear-thickening gel, characterized in that it is composed of the following components: 50-80 parts by weight of hydroxyl-terminated polydimethylsiloxane (PDMS-OH); 2-6 parts by weight of boric acid; 0.1–1.0 parts by weight of carbon nanotubes; Solvent: 10-30 parts by weight; The solvent is ethyl acetate and / or isopropanol. The gel does not contain a vulcanizing agent and does not require a high-temperature curing step, making the preparation process simpler and more environmentally friendly.

[0009] Preferably, the mass fraction of the carbon nanotubes is 0.1% to 1.0%; more preferably, the mass fraction of the carbon nanotubes is 0.25%.

[0010] Preferably, the carbon nanotubes have an outer diameter of 8–15 nm, a length of 30–50 μm, and a specific surface area of ​​≥140 m² / g.

[0011] Preferably, the viscosity of the hydroxyl-terminated polydimethylsiloxane is 50–100 cSt.

[0012] A second aspect of the present invention provides a method for preparing the aforementioned carbon nanotube-enhanced shear-thickening gel, characterized by comprising the following steps: (1) Hydroxyl-terminated polydimethylsiloxane, boric acid and solvent are mixed and reacted at 120-140°C for 2-4 hours to obtain STG matrix; (2) Dissolve the STG matrix in isopropanol, add the pre-dispersed carbon nanotube suspension, sonicate for 15-30 minutes and stir magnetically for 2-4 hours, and then dry at 80-100℃ for 3-5 hours to obtain the CNT-STG composite material. Step (1) does not involve adding a vulcanizing agent, and step (2) does not involve a high-temperature curing process.

[0013] Preferably, in step (2), the mass fraction of the carbon nanotube suspension is 3.0% to 3.5%.

[0014] A third aspect of the present invention provides the application of the aforementioned carbon nanotube-reinforced shear-thickening gel in human impact protection equipment.

[0015] Preferably, the human impact protection equipment includes bulletproof armor, sports protective gear, and a helmet cushioning layer.

[0016] The present invention relates to carbon nanotube-reinforced shear-thickening gel, its preparation method and application, which, through a solvent-assisted dispersion strategy, uniformly introduces CNTs into a borate-crosslinked STG matrix to construct a three-dimensional network reinforcement structure, significantly improving the mechanical properties and impact protection capability of the material. Attached Figure Description

[0017] Figure 1 This is a comparison diagram of the frequency dependence of the storage modulus (G') and loss modulus (G'') of the CNT-STG composite material of the present invention.

[0018] Figures 2a to 2c This is a comparison curve of the compressive stress-strain behavior of CNT-STG composite material under different strain rates in Example 5 of the present invention.

[0019] Figure 3 This is a comparison curve of tensile stress-strain of CNT-STG composite material under different strain rates in Example 5 of the present invention.

[0020] Figure 4 This is a shape evolution diagram (0-60 minutes) of CNT-STG composite materials with different carbon nanotube contents under gravity in Example 5 of the present invention.

[0021] Figure 5a and Figure 5b This illustrates the application of the CNT-STG composite material in helmet protection in Embodiment 6 of the present invention. Detailed Implementation

[0022] To provide a clearer understanding of the technical content of this invention, the following embodiments are provided in detail. However, it is important to note that these descriptions are merely for further illustrating the features and advantages of this invention, and not for limiting the scope of the claims.

[0023] Unless otherwise specified, the reagents and methods involved in the examples are all commonly used in the art.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] This invention addresses the problems of cold flow deformation, insufficient storage modulus, and low energy dissipation efficiency of traditional STGs by proposing a carbon nanotube (CNT)-reinforced shear-thickening gel (CNT-STG) and its preparation method. This technology utilizes a solvent-assisted dispersion strategy to uniformly introduce CNTs into a borate-crosslinked STG matrix, constructing a three-dimensional network reinforcement structure that significantly improves the material's mechanical properties and impact resistance.

[0026] Specifically, the matrix material is a dynamic cross-linked network formed by the polycondensation of hydroxyl-terminated polydimethylsiloxane (PDMS-OH, viscosity 50-100 cSt) and boric acid. CNTs are used as the reinforcing phase at a mass fraction of 0.1%-1.0% (preferably 0.25%). The solvent system is ethyl acetate or isopropanol to reduce the reaction viscosity and promote CNT dispersion.

[0027] The preparation process consists of two steps: First, PDMS-OH, boric acid and solvent are reacted at 120-140℃ for 2-4 hours to form an STG matrix; then, the STG matrix is ​​dissolved in isopropanol, and a pre-dispersed CNT suspension is added. The suspension is then ultrasonically treated (40kHz, 15-30 minutes) and magnetically stirred (2-4 hours) to achieve uniform dispersion. Finally, the solvent is removed by drying at 80-100℃ for 3-5 hours to obtain the CNT-STG composite material.

[0028] The core content of this invention is: Novel matrix synthesis route: This invention directly uses hydroxyl-terminated polydimethylsiloxane and boric acid polycondensation, without the need for pre-preparation of borosilicate matrix; Vulcanizing agent-free system: This invention contains no vulcanizing agent at all, avoiding the rigidity and loss of dynamism caused by covalent crosslinking; Mild curing conditions: Only 80–100°C is required to dry and remove the solvent; no high-temperature curing is needed.

[0029] This invention addresses the problems of cold flow deformation, insufficient high-frequency modulus, and low impact absorption efficiency, and performs particularly well in personal protective equipment.

[0030] Example 1 (0.25% CNT-STG) The specific preparation method of the 0.25% CNT-STG composite material in Example 1 of this invention is as follows: Matrix preparation: 65g of 70cSt PDMS-OH, 4g of boric acid and 20g of ethyl acetate were added to a 250mL three-necked flask and stirred at 130℃ for 3 hours to form a transparent and viscous STG matrix.

[0031] CNT dispersion: The STG matrix was dissolved in 100 mL of isopropanol, and 5.5 g of pre-dispersed carbon nanotube dispersion (outer diameter 10 nm, length 40 μm, specific surface area ≥140 m² / g, carbon nanotube solid content 3.15%) was added. The mixture was ultrasonically treated at 40 kHz for 20 minutes, followed by magnetic stirring for 3 hours to ensure uniform dispersion of CNTs.

[0032] Drying and molding: Pour the mixture into a polytetrafluoroethylene mold and dry it in a 90°C oven for 4 hours. After the solvent evaporates, a CNT-STG sheet with a thickness of 10 mm is obtained.

[0033] Example 2 (0.1% CNT-STG) The 0.1% CNT-STG composite material of Example 2 of this invention was prepared in the same steps as in Example 1, except that the carbon nanotube dispersion was adjusted to 2.2g and the other conditions remained unchanged.

[0034] Example 3 (0.5% CNT-STG) The 0.5% CNT-STG composite material of Example 3 of this invention was prepared in the same steps as in Example 1, except that the carbon nanotube dispersion was adjusted to 11.0 g, and the other conditions remained unchanged.

[0035] Example 4 (1.0% CNT-STG) The 1.0% CNT-STG composite material of Example 4 of this invention was prepared using the same steps as in Example 1, except that the amount of CNT was adjusted to 22.0g and the other conditions remained unchanged.

[0036] Comparative Example (Pure STG) The CNT addition step is omitted, and the rest of the preparation process is the same as in Example 1.

[0037] Example 5 Performance Tests and Results Rheological properties (standard test method): tested using a rotational rheometer (Anton Paar MCR 302). Results are as follows. Figure 1As shown, the 0.25% CNT-STG in Example 1 has a G' of 124.5 kPa at 0.1 Hz (22.1 kPa for pure STG) and a G' of 284.2 kPa at 100 Hz, with the loss modulus (G'') increasing to 148.6 kPa. The carbon nanotube content has a significant concentration-dependent dual regulatory effect on the dynamic viscoelastic behavior of STG: at low frequency (0.1 Hz), 0.1% carbon nanotubes in Example 2 simultaneously increased the storage modulus (G') and loss modulus (G'') but maintained viscosity dominance (G''>G'), while a content of 0.25% induced a significant phase transition (G' increased to 124.5 kPa, G'' increased to 81.3 kPa and G'>G''), indicating the formation of an elastically dominant structure of the three-dimensional carbon nanotube network; however, when the content exceeds 0.25%, the interfacial defects caused by aggregation cause both G' and G'' to decrease significantly (G'=87.0 kPa at 0.5% and G'=19.9 kPa at 1.0%), disrupting the gelation kinetics. All samples exhibited shear thickening characteristics in the high-frequency (>10Hz) region. Among them, the STG composite with 0.25% content reached the peak G' (284.2 kPa at 100Hz, an increase of 87.5% compared to the 0% sample). The increase of G' from low frequency to high frequency (128%) was significantly higher than that of G'' (83%), indicating that elastic energy storage was dominant and the energy dissipation pathway was optimized. The results show that carbon nanotubes at low concentrations ≤0.25% enhance elastic behavior by forming an efficient interfacial network through uniform dispersion, while agglomeration at >0.25% causes local stress concentration and structural defects, leading to performance degradation. This confirms that the optimization of macroscopic mechanical properties requires balancing the dispersion quality of carbon nanotubes and the interfacial coupling efficiency.

[0038] Mechanical properties: Compression test (standard test method): according to ISO 7743 standard, such as... Figure 2b As shown, the compressive modulus of 0.25% CNT-STG at a strain rate of 100 mm / min is 259 kPa (93 kPa for pure STG), and the stress-strain curve exhibits linear elastic behavior.

[0039] Tensile test (standard test method): such as Figure 3 As shown, at a loading rate of 100 mm / min, the maximum tensile stress of 0.25% CNT-STG is 82.7 kPa, and no fracture occurs, while that of pure STG is only 3.8 kPa.

[0040] like Figures 2a to 3As shown, the carbon nanotube-reinforced STG composite material of this invention exhibits significant performance improvements under both compressive and tensile loads, showing a clear strain rate dependence. Regarding compressive performance, at low loading rates (10 mm / min), the material exhibits a nonlinear stress-strain curve, stemming from molecular chain relaxation. However, when the loading rate increases to 100 mm / min and 250 mm / min, the material transitions to linear elastic behavior, accompanied by a significant shear thickening effect, resulting in a substantial increase in instantaneous stiffness. The carbon nanotube content shows a non-monotonic relationship with the compressive modulus, reaching a peak at 0.25% (259 kPa at 100 mm / min), a 178% improvement compared to pure STG (0% CNTs, 93 kPa). This indicates that carbon nanotubes significantly improve load transfer efficiency and optimize energy dissipation pathways through high specific surface area and strong interfacial bonding. However, when the carbon nanotube content exceeds 0.25%, stress concentration and reduced dispersion quality due to agglomeration lead to a sharp decrease in modulus (only 105 kPa at 1.0%), highlighting the importance of proper dispersion. In terms of tensile properties, the 0.25% carbon nanotube sample exhibited excellent mechanical properties at different loading rates. At 10 mm / min and 100 mm / min, the maximum tensile stresses reached 6.4 kPa and 82.7 kPa, respectively, significantly higher than pure STG (only 3.8 kPa at 100 mm / min), representing an increase of 1045% (100 mm / min). Even under high-speed loading (250 mm / min), although the material eventually failed, its stress still reached 137.4 kPa, demonstrating higher strain rate sensitivity. At low-speed loading, the shear thickening mechanism dominated energy dissipation, and the synergistic effect of the gel network and carbon nanotubes delayed crack propagation and maintained high ductility (smooth fracture surface); however, under high-speed loading, the material underwent brittle fracture (ridged fracture surface) due to insufficient internal relaxation.

[0041] Impact test: Using a drop hammer impact device (impact energy 10J), the peak impact force of 0.25% CNT-STG is 3331N, which is 80.1% lower than that of the unbuffered case (16750N), and the energy absorption time is extended to 0.990ms (0.550ms for pure STG).

[0042] Cold flow suppression: After the spherical sample has been left to stand for 5 minutes, if... Figure 4 As shown, the deformation rate of 0.25% CNT-STG is <5%, while the collapse rate of pure STG is >50%.

[0043] Example 6 like Figure 5a As shown, 0.25% CNT-STG was integrated as a buffer layer into the inner top area of ​​the riot helmet (10mm thick), and a drop hammer impact test was conducted according to the GA 294-2023 standard.

[0044] like Figure 5b As shown, the peak impact force decreased from 4663N to 3373N, a reduction of 27.7%, and the impact duration increased from 0.01038 seconds to 0.01310 seconds, verifying its effectiveness in actual protection scenarios.

[0045] As can be seen from the above embodiments, in the material of the present invention, the CNT network and the borooxane dynamic cross-linking network work synergistically to achieve graded energy dissipation through interface sliding, dislocation movement, and elastic energy storage. Performance tests show that the addition of 0.25% CNT increases the storage modulus (G') to 124.5 kPa at 0.1 Hz (463% higher than pure STG), and further increases it to 284.2 kPa at 100 Hz (128% higher); the compressive modulus increases from 93 kPa to 259 kPa at a strain rate of 100 mm / min, and the tensile stress reaches 82.7 kPa (21.8 times that of pure STG). In the impact test, the peak force is reduced by 80.1% (3331 N vs 16750 N), the energy absorption time is extended by 206.5%, and the cold flow deformation rate is less than 5%, which is significantly better than traditional STG.

[0046] In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the invention. Therefore, this specification should be considered illustrative rather than restrictive.

Claims

1. A carbon nanotube-reinforced shear thickening gel, characterized in that, consists of: hydroxyl-terminated polydimethylsiloxane 50-80 parts by mass; boric acid 2-6 parts by mass; carbon nanotubes 0.1-1.0 parts by mass; solvent 10-30 parts by mass; the solvent is ethyl acetate and / or isopropyl alcohol.

2. The carbon nanotube reinforced shear thickening gel of claim 1, wherein, the mass fraction of the carbon nanotubes is 0.1%-1.0%.

3. The carbon nanotube reinforced shear thickening gel of claim 1, wherein, the mass fraction of the carbon nanotubes is 0.25%.

4. The carbon nanotube reinforced shear thickening gel of claim 1, wherein, the carbon nanotubes have an outer diameter of 8-15 nm, a length of 30-50 μm, and a specific surface area of ≥140 m² / g.

5. The carbon nanotube reinforced shear thickening gel of claim 1, wherein, the viscosity of the hydroxyl-terminated polydimethylsiloxane is 50-100 cSt.

6. A method of preparing a carbon nanotube reinforced shear thickening gel according to any one of claims 1 to 5, characterized in that, comprising the following steps: (1) mixing hydroxyl-terminated polydimethylsiloxane, boric acid and solvent, and reacting at 120-140°C for 2-4 hours to obtain an STG matrix; (2) dissolving the STG matrix in isopropyl alcohol, adding a pre-dispersed carbon nanotube suspension, and after ultrasonic treatment for 15-30 minutes and magnetic stirring for 2-4 hours, drying at 80-100°C for 3-5 hours to obtain a CNT-STG composite material; wherein step (1) does not add a vulcanizing agent, and step (2) does not contain a high-temperature curing process.

7. The production method according to claim 6, wherein in step (2), the mass fraction of the carbon nanotube suspension is 3.0%-3.5%.

8. Use of the carbon nanotube-reinforced shear-thickening gel according to any one of claims 1-5 in human impact protection equipment.

9. Use according to claim 8, characterized in that, the human impact protection equipment includes bulletproof armor, sports protective gear and helmet cushioning layers.

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