Preparation method of directionally grafted modified hollow silica spheres and LCP composite material

Abstract

The present application relates to the technical field of hollow silica sphere preparation, and particularly relates to a preparation method of oriented grafting modified hollow silica sphere and LCP composite material, comprising the following steps: A. performing surface activation treatment on the hollow silica sphere; B. dissolving fluorine-containing silane main agent, amino silane auxiliary agent and crosslinking accelerator in an organic solvent to prepare a grafting solution and adjust the pH to 4.8-5.2; C. adding the activated hollow silica sphere into the grafting solution to perform oriented grafting reaction; and D. performing ladder program curing on the grafting product. The present application realizes the oriented anchoring of fluorine alkyl by high-density hydroxyl activation and pH control of the grafting solution, and then realizes vertical self-assembly by ladder curing, so that the surface energy of the hollow silica sphere is less than or equal to 10 mN / m, the high-density, highly-ordered and stable arrangement of the fluorine alkyl chain on the substrate surface is realized, the ideal and stable hydrophobic / oil-repellent performance is obtained, the advantages of extremely low surface energy of fluorine atoms are fully utilized, and the final anti-adhesion, self-cleaning and anti-pollution performance of the material is improved.

Description

Technical Field

[0001] This invention relates to the field of hollow silicon sphere preparation technology, and in particular to a method for preparing directional grafted modified hollow silicon spheres and LCP composite materials. Background Technology

[0002] Hollow silica spheres (HSS) exhibit great application potential in lightweight composite materials, coatings, drug carriers, thermal and sound insulation materials, and catalysis due to their low density, high specific surface area, good chemical stability, and tunable dielectric / optical properties. Especially in applications requiring surface functionalization, such as the preparation of superhydrophobic coatings, antifouling coatings, or special separation materials, low surface energy modification (e.g., fluorination) of the hollow silica sphere surface is a key approach to improving its performance.

[0003] Currently, fluorosilane modification of silicon-based materials (including hollow silicon spheres) to reduce surface energy is a common method. However, conventional fluorosilane grafting methods often face a significant technical bottleneck: achieving a high-density, highly ordered, and stable arrangement of fluoroalkyl chains on the substrate surface is difficult. This results in the modified surface energy typically being difficult to reduce to a low level (e.g., ≤15mN / m), and the obtained hydrophobic / oleophobic properties are not ideal, with poor stability. The random distribution, entanglement, or flattened state of the fluoroalkyl chains cannot fully utilize the advantage of the extremely low surface energy of fluorine atoms, affecting the material's final anti-adhesion, self-cleaning, and anti-fouling properties, thus necessitating improvement. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing directionally grafted modified hollow silicon spheres and an LCP composite material. This method achieves directional anchoring of fluoroalkyl groups through high-density hydroxyl activation and pH-controlled grafting solution, followed by step-curing to drive vertical self-assembly. This results in a hollow silicon sphere surface energy ≤10mN / m, achieving a high-density, highly ordered, and stable arrangement of fluoroalkyl chains on the substrate surface. This yields ideal and stable hydrophobic / oleophobic properties, fully leveraging the advantage of extremely low surface energy of fluorine atoms, and improving the material's final anti-adhesion, self-cleaning, and anti-fouling properties.

[0005] To achieve the above objectives, the present invention provides a method for preparing directionally grafted modified hollow silicon spheres, comprising the following steps:

[0006] A. Perform surface activation treatment on hollow silicon spheres to achieve a hydroxyl density ≥ 8OH / nm on the surface of the hollow silicon spheres. 2 ;

[0007] B. Dissolve the fluorinated silane main agent, aminosilane auxiliary agent, and crosslinking accelerator in an organic solvent to prepare the grafting solution and adjust the pH to 4.8-5.2;

[0008] C. Add the activated hollow silicon spheres to the grafting solution to carry out a directional grafting reaction;

[0009] D. The grafted product is cured in a stepwise process to make the fluoroalkyl chains form a vertical orientation and the surface energy is ≤10mN / m.

[0010] On the other hand, an LCP composite material is also provided, comprising modified hollow silicon spheres prepared by the above method and a liquid crystal polymer matrix.

[0011] The liquid crystal polymer matrix is ​​a thermotropic liquid crystal polymer synthesized by prepolymerization; the liquid crystal polymer matrix molecular chain contains carbonyl functional groups, with a carbonyl content of 5-8 mol%; the glass transition temperature is ≥280℃;

[0012] The modified hollow silicon spheres are directly connected to the liquid crystal polymer matrix via Si-O-Si covalent bonds. Fluoroalkyl chains grafted onto the hollow silicon spheres are vertically oriented with an inclination angle ≤10°. These fluoroalkyl chains form a continuous hydrophobic layer with a contact angle ≥155°. The aminosilane auxiliaries grafted onto the hollow silicon spheres form a hydrogen bond network with the carbonyl functional groups of the liquid crystal polymer matrix molecular chains, with a hydrogen bond density ≥3 bonds / nm. 2 .

[0013] The beneficial effects of this invention are as follows: high-density hydroxyl activation and pH-controlled grafting solution are used to achieve directional anchoring of fluoroalkyl groups, followed by step-curing to drive vertical self-assembly, so that the surface energy of hollow silicon spheres is ≤10mN / m. This achieves a high-density, highly ordered and stable arrangement of fluoroalkyl chains on the substrate surface, resulting in ideal and stable hydrophobic / oleophobic properties. It fully utilizes the advantage of the extremely low surface energy of fluorine atoms, thereby improving the material's final anti-adhesion, self-cleaning and anti-fouling properties. Attached Figure Description

[0014] Figure 1 This is a flowchart of a method for preparing directional grafted modified hollow silicon spheres according to the present invention. Detailed Implementation

[0015] The present invention will now be described in detail with reference to the accompanying drawings.

[0016] like Figure 1 As shown, a method for preparing a directionally grafted modified hollow silicon sphere according to the present invention includes the following steps:

[0017] A. Perform surface activation treatment on hollow silicon spheres to achieve a hydroxyl density ≥ 8OH / nm on the surface of the hollow silicon spheres. 2 Chemical treatment increases the number of silanol groups on the surface of hollow silicon spheres. The quantity provides a high density of reaction sites, ensuring high-density grafting of fluorinated silanes and laying the structural foundation for low surface energy modification.

[0018] B. Dissolve the fluorinated silane main agent, aminosilane auxiliary agent, and crosslinking accelerator in an organic solvent to prepare a grafting solution and adjust the pH to 4.8-5.2; by controlling the pH, an acidic environment (pH 4.8–5.2, preferably 4.8, 5.0, and 5.2) promotes silane hydrolysis. and condensation with silanol Aminosilane auxiliaries The directional adsorption of fluorinated silanes is guided by catalytic condensation reactions or hydrogen bonding via aminosilane auxiliaries. Crosslinking promoters enhance the covalent crosslinking network between silane molecules and with the substrate, achieving efficient and uniform grafting of fluorinated groups. The aminosilane auxiliaries facilitate preliminary "directional" adsorption, laying the foundation for the vertical orientation step D.

[0019] C. The activated hollow silicon spheres are added to the grafting solution for directional grafting; the activated hollow silicon spheres undergo silane condensation reaction in the optimized grafting solution. By chemically bonding fluorinated alkyl chains to the surface of silicon spheres, low surface energy properties are imparted.

[0020] D. The grafted product is cured using a step-by-step process to achieve a vertically oriented alignment of the fluoroalkyl chains, with a surface energy ≤10 mN / m. The gradually increasing temperature curing process drives the molecular motion, rearrangement, and self-assembly of the fluoroalkyl chains, resulting in low surface energy end groups. The fluoroalkyl chains are arranged in an outward, orderly manner, maximizing the reduction of surface energy; the surface energy is ≤10mN / m, achieving a superhydrophobic / oleophobic level.

[0021] Specific steps for the work:

[0022] Step A: Surface activation,

[0023] Hollow silicon spheres undergo strong oxidizing treatment to thoroughly remove surface organic matter, thereby breaking down siloxane bonds. Fracture, generating high-density silanol groups ≥8OH / nm 2 It forms uniform and highly active anchoring sites, providing reaction sites for subsequent high-density grafting.

[0024] Step B: Directional preparation of grafting solution.

[0025] Fluorinated silanes, aminosilanes, and crosslinking agents are dissolved in alcohol solvents;

[0026] The pH is adjusted to 4.8–5.2 by adding a weak acid to promote the hydrolysis of silanes and their condensation with silanol groups. This example uses a pH of 5.0. (In other examples, pH values ​​of 4.8, 4.9, 5.1, and 5.2 may also be used.)

[0027] Fluorosilanes hydrolyze: Si-OCH3 + H2O → Si-OH + CH3OH;

[0028] Protonation of aminosilane, -NH2+H + →-NH3 + (Electrostatic repulsion inhibits self-aggregation);

[0029] -NH3 of aminosilane + Pre-adsorbed onto the negatively charged surface of silicon spheres (around pH 5.0) via electrostatic interaction. Weak ionization to SiO - This guides the fluorinated silanes to initially move closer together, constructing a reaction system containing a directional inducing factor to ensure orderly grafting.

[0030] Step C: Directed grafting reaction (interfacial covalent bonding).

[0031] When activated silicon spheres are added to a grafting solution, the surface Si-OH groups attack the electrophilic silicon atoms (Si-OH groups) of the fluorinated silane. + ), condensation occurs: ;

[0032] The -NH2-catalyzed condensation reaction of aminosilanes lowers the energy barrier, while the steric hindrance of their long chains promotes the extension of fluorine-containing chains (Rf).

[0033] The crosslinking agent reacts simultaneously with the silicon spheres / silane to form a three-dimensional network that enhances the bonding force; achieving high-density, ordered pre-arrangement chemical bonding of fluoroalkyl chains (Rf).

[0034] Step D: Stepped curing (vertical orientation self-assembly)

[0035] Step 1 (low temperature, such as 60°C): The solvent evaporates slowly, eliminating internal stress, and the unreacted silane completes the final condensation.

[0036] Step 2 (intermediate temperature, such as 100℃): The fluoroalkyl chain (Rf) gains kinetic energy, and the low surface energy -CF3 end group migrates to the air interface;

[0037] Step 3 (high temperature, such as 150℃): The chain segments move fully, and the -CF3 groups are tightly packed by van der Waals forces to form a vertically oriented crystalline arrangement (similar to liquid crystal self-assembly). Thermodynamics drives the vertical orientation of the fluoroalkyl chains, achieving a surface energy of ≤10mN / m, which is close to the 18.5mN / m of polytetrafluoroethylene (PTFE) and far lower than the >15mN / m of conventional grafting.

[0038] The surface activation treatment described in this embodiment includes:

[0039] Hollow silicon spheres are immersed in a 2.5-3.5 wt% hydrofluoric acid solution and ultrasonically cleaned for 25-35 minutes. The weakly bonded silicon oxide on the surface of the spheres is selectively etched using the 2.5-3.5 wt% hydrofluoric acid solution, removing impurities and exposing a fresh silicon layer. Ultrasonic cavitation enhances the uniformity of cleaning, resulting in a highly clean surface that lays the foundation for subsequent activation; it also prevents impurities from hindering hydroxyl group formation.

[0040] After being washed with deionized water until neutral, O2 plasma activation was carried out under nitrogen protection. The O2 plasma activation parameters were: O2 flow rate 18-22 sccm, power increased from 200W for 1-3 min to 250W for 2-4 min.

[0041] By using low-power initiation, surface silicon atoms are gently excited to form the initial... To avoid thermal damage. High-power penetration, high-energy plasma bombardment fracture. Bonds, generating high density O2 flow ensures a sufficient supply of reactive oxygen species. Hydroxyl group density ≥ 8OH / nm 2 Stepped power avoids the collapse of hollow spheres in nanostructures.

[0042] Micro-etching process:

[0043] The silicon spheres were ultrasonically treated with a 0.05-0.1 vol% tetramethylammonium hydroxide solution for 5-8 min to perform anisotropic etching, preferentially dissolving along crystal plane defects. Ultrasonic-assisted etching rate uniformity was controlled to form a honeycomb-like surface microcavity structure, significantly increasing the specific surface area and anchoring points. The specific parameters of the honeycomb-like surface microcavity structure were: pore size 50-80 nm, aspect ratio 0.8-1.2, and pore density (8±1)×10⁻⁶. 10 pcs / cm 2 .

[0044] The high aspect ratio of the microcavities allows for near-vertical pore walls, providing a vertically oriented template for subsequent fluoroalkyl chains. The ultra-high pore density results in a denser spatial distribution of surface hydroxyl groups, and the microcavity walls guide the vertical alignment of the fluoroalkyl chains, achieving directional grafting reinforcement. The micro-nano composite structure enhances hydrophobicity and further reduces surface energy.

[0045] Example 1: Conservative process (parameters taken at lower limits)

[0046]

[0047] Microscopic effects:

[0048] Hydroxyl group density: 8.2 OH / nm 2 (XPSO1s / Si2p=1.82).

[0049] Microcavity structure: Depth: 50±5nm, Aperture: 20±3nm, Density: 120±10 cavities / μm 2 ,

[0050] Grafting effect: Grafting density 2.85 chains / nm 2 (XPSF / Si=0.36), surface energy 8.1mN / m.

[0051] Example 2: Enhancement process (parameters taken at upper limits)

[0052]

[0053] Microscopic effects:

[0054] Hydroxyl group density: 12.5 OH / nm 2 (XPSO1s / Si2p=2.78)

[0055] Microcavity structure: Depth: 80±3nm, Aperture: 35±2nm, Density: 80±5 cavities / μm 2 ,

[0056] Grafting effect: Grafting density 3.45 chains / nm 2 (XPSF / Si=0.43), surface energy 7.2mN / m.

[0057] Example 3: Process Optimization (Parameters at Median Values)

[0058]

[0059] Microscopic effects:

[0060] Hydroxyl group density: 10.3 OH / nm 2 (XPSO1s / Si2p=2.30).

[0061] Microcavity structure: Depth: 65±4nm, Aperture: 28±2nm, Density: 95±8 cavities / μm 2 ,

[0062] Grafting effect: Grafting density 3.12 chains / nm 2 (XPSF / Si=0.39), surface energy 7.5mN / m.

[0063] Key Effects Comparison

[0064]

[0065] Recommended equipment

[0066]

[0067] Example 2 achieves the highest grafting density (3.45 chains / nm) 2 It has the lowest surface energy (7.2 mN / m), but the lowest microcavity density;

[0068] Example 1 shows the highest microcavity density (120 cavities / μm). 2 It is suitable for scenarios requiring a high specific surface area;

[0069] Example 3 achieves the best balance in all indicators and is recommended as the preferred solution for mass production.

[0070] Preferably, the surface hydroxyl density is determined using a fluorescent labeling method after activation.

[0071] The sample was immersed in a 0.1 mmol / L FITC ethanol solution and reacted in the dark for 2 hours. Specifically, the isothiocyanate group (-N=C=S) of FITC (fluorescein isothiocyanate) covalently bonds with the hydroxyl group (Si-OH) on the surface of the silicon sphere: Si-OH + FITC → Si-OC(S)-NH- (fluorescent label). The dark-protected condition prevents the photodegradation of FITC. This achieves specific and quantitative labeling of hydroxyl groups and eliminates interference from non-hydroxyl groups.

[0072] A fluorescence spectrophotometer measures the intensity of emitted light at 510 nm; specifically, FITC emits 510 nm yellow-green fluorescence under specific excitation light, and the measured value of the 510 nm yellow-green fluorescence intensity is directly proportional to the number of bonded FITC (i.e., the number of hydroxyl groups). It provides a digital, highly sensitive quantitative signal of hydroxyl groups, converting the fluorescence signal into a digital representation.

[0073] Hydroxyl density formula: (OH / nm) 2 );

[0074] The surface hydroxyl density was determined by fluorescent labeling and directly converted to surface hydroxyl density (OH / nm). 2 ( ), satisfying the requirement that the density of hydroxyl groups is ≥8OH / nm 2 Quantitative requirements.

[0075] in The relative fluorescence intensity is... Specific surface area of ​​hollow silicon spheres (nm) 2 / g). This solves the problem of accurately measuring the hydroxyl density of high specific surface area micro / nano structures.

[0076] The grafting solution preparation method of this embodiment is as follows: the mass ratio of the fluorinated silane main agent, the aminosilane auxiliary agent and the crosslinking promoter is (8.5-9.5):1:(0.1-1) dissolved in anhydrous toluene or supercritical CO2 to prepare a grafting solution with a concentration of 4-6wt%.

[0077] Control the degree of hydrolysis to 65-75%;

[0078] Tracking via online FTIR:

[0079] 1110cm -1 The peak area decreased to the initial value of (40±2)%.

[0080] 950cm -1 The peak area increased to the initial value of (220±5)%%;

[0081] Acetic acid was added within 15±1 min after the addition of silane to adjust the pH to 4.8-5.2;

[0082] The fluorinated silane main agent is tridecafluorooctyltriethoxysilane, the aminosilane auxiliary agent is γ-aminopropyltriethoxysilane, and the crosslinking promoter is 3-glycidyl etheroxypropyltrimethoxysilane.

[0083] Specifically, a high proportion of fluorinated silane main agent (tridecylfluorooctyltriethoxysilane) ensures the surface fluorinated alkyl chain (-C8F) 13 Density; fixed ratio of aminosilane auxiliaries (γ-aminopropyltriethoxysilane) for catalytic condensation and directional guidance; trace amounts of crosslinking promoters (3-glycidyl etheroxypropyltrimethoxysilane) to enhance the epoxy ring-opening crosslinking network. Precise control of the functional group ratio avoids self-polymerization due to excessive aminosilane or gelation caused by excessive crosslinking agents.

[0084] Premature hydrolysis of silanes is inhibited by using anhydrous toluene as a low-polarity solvent; penetration into the silicon sphere microcavities is promoted by supercritical CO2 with zero surface tension; and low concentrations prevent silane self-aggregation into particles. This ensures the stability of the grafting solution and sufficient wetting of the microcavity structure.

[0085] By controlling the degree of hydrolysis to 65-75% and using online FTIR tracking, 1110 cm⁻¹ -1 When the peak area decreases to 40±2%, the hydrolysis of ethoxysilane groups (Si-OC2H5) decreases;

[0086] 950cm -1 When the peak area increases to 220±5%, the generation of silanol groups (Si-OH groups) increases; the hydrolysis degree is quantified by changing the bimodal ratio, the degree of hydrolysis is monitored in real time, the optimal reaction activity is ensured, and insufficient hydrolysis reduces the grafting rate, while excessive hydrolysis leads to self-polymerization.

[0087] Adjusting the pH to 4.8-5.2 within 15±1 min after adding silane results in a degree of hydrolysis of 30-40% (predicted by FTIR). The weakly acidic environment accelerates the subsequent hydrolysis-condensation equilibrium, preventing premature pH adjustment from inhibiting hydrolysis or premature pH adjustment from inducing self-polymerization. This locks in the optimal reaction window and improves grafting efficiency and reproducibility.

[0088] Example 4: Conservative process (parameters taken from lower limit)

[0089]

[0090] Example 5: Enhancement process (parameters taken at upper limits)

[0091]

[0092] Example 6: Process Optimization (Median Parameter Values)

[0093]

[0094] Key parameters and effect comparison

[0095]

[0096] Recommended equipment

[0097]

[0098] Example 5 demonstrates the highest performance (surface energy 7.1 mN / m), but requires a large amount of crosslinking agent (increasing cost by 15%).

[0099] Example 4 has the lowest cost, but its performance is close to the critical value (surface energy 8.0 mN / m).

[0100] Example 6 achieves the best balance between performance and cost and is recommended as the preferred solution for mass production.

[0101] The grafting solution in this embodiment contains 3-7 wt% of phosphorus-containing silane as a phosphorus-nitrogen synergistic flame retardant, and the molar ratio of the DOPO group of the phosphorus-containing silane to the amino group of the amino silane auxiliary is 1:1-1:1.5.

[0102] Stepwise annealing is performed after the addition of phosphorus-containing silanes:

[0103] Step 1: Hold at 50℃ for 20 minutes to allow the DOPO groups to melt and spread;

[0104] The second step is to raise the temperature to 80°C at a rate of 2°C / min to complete the PN condensation.

[0105] The phosphorus atom enrichment depth on the surface is ≥3nm, which makes the flame retardant oxygen index of the modified hollow silicon spheres ≥30%.

[0106] Specifically, the DOPO group (C) of phosphorosylsilanes 12 H9O2P provides the phosphorus source; the aminosilane auxiliary provides the nitrogen source (-NH2), forming a PN synergistic flame-retardant structure with DOPO. The flame-retardant elements are directly chemically bonded to the surface of the silicon spheres, avoiding migration failure.

[0107] When the molar ratio of the DOPO group of the phosphorus-containing silane to the amino group of the aminosilane auxiliary is 1:1, PN reacts completely to form a thermally stable phosphorus-nitrogen ring (such as a PN bond). When the molar ratio of the DOPO group of the phosphorus-containing silane to the amino group of the aminosilane auxiliary is at the upper limit of 1:5, the excess amino group promotes the cross-linking network, coating the DOPO group and improving thermal stability. Precise control of the degree of PN reaction balances flame retardant efficiency and thermal stability.

[0108] Through a step-by-step annealing process

[0109] Step 1 (50℃, 20min): The DOPO group has a melting point of about 50℃. After melting, it spreads evenly on the surface of the silane layer.

[0110] The second step (2℃ / min → 80℃) involves slowly increasing the temperature to allow the P=O bond of the DOPO group to condense with the amino group (-P=O + H2N- → -P(O)-NH-). This avoids local aggregation of DOPO groups and ensures uniform formation of the PN bond throughout the entire domain.

[0111] Phosphorus atom enrichment depth ≥3nm, DOPO groups melt spread and slowly condense, phosphorus atoms migrate and enrich to the surface; the ≥3nm enrichment layer forms a continuous flame retardant barrier. Surface flame retardant oxygen index ≥30% (UL94V-0 level).

[0112] By using a chemically bonded PN flame-retardant structure and a stepwise annealing process, the safety issues of the flammability of hollow silicon spheres are solved without affecting the directional grafting function. The enrichment depth of phosphorus atoms on the surface (≥3nm) and the oxygen index (≥30%) are quantifiable technical barriers.

[0113] Example 7: Minimum flame retardant load (3wt%)

[0114]

[0115] Example 8: Optimization of flame retardant loading (5wt%)

[0116]

[0117] Example 9: Maximum flame retardant load (7wt%)

[0118]

[0119] Key parameters and effect comparison

[0120]

[0121] Recommended equipment

[0122]

[0123] Example 8 (5wt% + 1:1.2) showed the best overall performance: OI = 34.2% + UL94V-0;

[0124] Example 9 showed the fastest flame retardant response (self-extinguishing time 2s), but its OI was slightly lower (32.8%) and its cost was higher.

[0125] Example 7 is suitable for scenarios with lower flame retardancy requirements, reducing costs by 25%.

[0126] Recommended Example 8 is a mass production solution, in which the P / N molar ratio and annealing process work together to achieve the best flame retardant performance.

[0127] In this embodiment, when supercritical CO2 is used as the solvent...

[0128] The reaction pressure is 7.3-7.5 MPa, the temperature is 31-33℃, and the pressure fluctuation is ≤0.1 MPa; the system density is maintained at 0.7-0.9 g / cm³. 3 The gas-liquid interface disappearance time is ≤30s as monitored through a high-pressure viewing window; CO2 water activity (aw) is ≤0.01; and online FTIR real-time tracking is performed at 1110 cm⁻¹. -1 The peak disappears, and the pH is dynamically adjusted with an accuracy of ±0.05.

[0129] Specifically, the critical point of CO2 is 7.38 MPa / 31.1℃, which falls within the supercritical state, exhibiting both gas diffusivity and liquid solubility; its density is 0.8 g / cm³. 3 Corresponding to the range with the strongest solvation capability (dielectric constant ≈ 1.5), it penetrates into the 50-80nm microcavity of hollow silicon spheres with zero surface tension, achieving full-domain wetting and solving the problem that traditional solvents cannot achieve full-domain wetting.

[0130] Pressure fluctuation ≤ 0.1 MPa and density maintenance, density ρ is strongly correlated with pressure P (ρ ∝ P), fluctuation ≤ 0.1 MPa, density fluctuation ≤ 0.02 g / cm³ 3 A constant density ensures stable solvation capability. It prevents grafting fluid overflow / cavity collapse due to sudden pressure changes in the nanocavities.

[0131] The gas-liquid interface disappears within ≤30s, meaning the interface disappears when supercritical CO2 and the grafted liquid reach thermodynamic equilibrium; ≤30s indicates rapid homogenization of the system. This proves that the solvent and solute are mixed at the molecular level, eliminating the diffusion-controlling step.

[0132] Water activity aw ≤ 0.01, aw = P / P0 (P: partial pressure of water vapor in CO2, P0: saturated vapor pressure of pure water); aw ≤ 0.01, water content < 10 ppm (silane hydrolysis rate drops to 1‰ of atmospheric pressure). Precisely suppress premature silane hydrolysis to ensure the target hydrolysis degree of 65-75% in step B.

[0133] Online FTIR tracking and dynamic pH adjustment (±0.05), 1110 cm -1 The disappearance of the peak indicates complete hydrolysis of Si-OC2H5 and the peak of grafting activity. Immediately after hydrolysis is complete, adjust the pH to 4.8-5.2 (accuracy ±0.05) to lock in the optimal grafting time window and avoid transitional side reactions.

[0134] The supercritical system overcomes two major challenges—uniform grafting in nanocavities and uncontrolled hydrolysis-condensation equilibrium—through precise five-dimensional control (critical state, density, interface, moisture, and pH), providing an ideal reaction environment for directional grafting.

[0135] Example 10: Low-pressure, low-density process (parameters taken from lower limit)

[0136]

[0137] Example 11: High-pressure, high-density process (parameters taken at the upper limit)

[0138]

[0139] Example 12: Process Optimization (Median Parameter Values)

[0140]

[0141] Key parameters and effect comparison

[0142]

[0143] Recommended equipment

[0144]

[0145] Commonality Verification of Examples

[0146]

[0147] Example 11 (High Pressure, High Density) demonstrates optimal performance: surface energy 7.1 mN / m + grafting rate ≥96%.

[0148] Example 12 maintains stability under fluctuating conditions: all indicators are still met when pressure fluctuates by ±0.05 MPa.

[0149] All embodiments achieve three core breakthroughs:

[0150] Ultra-fast blending (interface disappears in ≤30s);

[0151] Extreme dryness (a w ≤0.01);

[0152] Precise hydrolysis control (FTIR tracking ±0.05 pH);

[0153] Example 11 is recommended as the optimal performance solution, and Example 12 is the preferred solution for industrial mass production.

[0154] In this embodiment, the acetic acid is added in three parts:

[0155] When an initial addition of 60% is made, the conductivity rises to its peak value (80±5μS / cm), triggering the reaction. Acetic acid ionizes, causing the conductivity to surge. The peak value corresponds to the period of maximum hydrolysis rate of silane, precisely activating hydrolysis and avoiding pH over-adjustment that inhibits the reaction.

[0156] Adding 30% acid after 30 minutes triggers the process when the conductivity drops to its peak value of (60±2)%. The decrease in conductivity indicates the end of the hydrolysis-dominant period (decrease in Si-OC2H5) and the beginning of the condensation-dominant period, generating water-based dilution ions as a byproduct. Secondary acid replenishment maintains pH stability in the condensation phase to ensure grafting efficiency.

[0157] Add 10% after 60 min. When the rate of change in conductivity is ≤0.5 μS / (cm·min), the reaction is triggered. The rate of change in conductivity approaches zero, and the hydrolysis-condensation dynamic equilibrium is reached (the reaction is complete). The final amount of acetic acid neutralizes the residual alkali and locks in the final pH (4.8-5.2).

[0158] By using a phased triggering method based on conductivity kinetics curves, the problem of uneven grafting caused by pH oscillations is solved, breaking through the traditional ±0.1 pH control limit.

[0159] The directional grafting reaction in this embodiment is:

[0160] Activated hollow silicon spheres were added to the grafting solution and stirred at a constant temperature of 58-62℃ and 190-210 rpm for 3.5-4.5 hours. The temperature (58-62℃) was slightly higher than the glass transition temperature of the fluorinated silane to promote chain segment movement. The constant temperature stirring at 190-210 rpm created laminar vortices (Reynolds number Re≈50), preventing the nanospheres from colliding and breaking. The stirring time of 3.5-4.5 hours matched the half-life of the grafting reaction within the specified time window. The grafting rate was ≥95%, which is superior to the grafting rate <85% achieved by traditional methods.

[0161] Specifically, the mixture was stirred at 58°C and 190 rpm for 3.5 hours; or at 60°C and 200 rpm for 4 hours; or at 62°C and 210 rpm for 4.5 hours.

[0162] Argon gas is introduced for protection during the reaction, and 0.1-0.3 wt% of 2,6-di-tert-butyl-p-cresol and 0.05-0.1 wt% of disodium ethylenediaminetetraacetate are added. The oxidation chain reaction is terminated by 2,6-di-tert-butyl-p-cresol, ensuring that the fluoroalkyl chain retains an integrity rate >99.5%. Disodium ethylenediaminetetraacetate inhibits metal-catalyzed hydrolysis, preventing silane self-condensation and ensuring precise control of the degree of hydrolysis in the grafting reaction (65-75%), thus avoiding uncontrolled gelation.

[0163] Specifically, 0.1 wt% of 2,6-di-tert-butyl-p-cresol and 0.05 wt% of disodium ethylenediaminetetraacetate; or 0.2 wt% of 2,6-di-tert-butyl-p-cresol and 0.07 wt% of disodium ethylenediaminetetraacetate; or 0.3 wt% of 2,6-di-tert-butyl-p-cresol and 0.1 wt% of disodium ethylenediaminetetraacetate.

[0164] 0.5-1 wt% block copolymer; induces the formation of mushroom-shaped nanoprotrusion structures on the surface of hollow silicon spheres. Specifically, 0.5 wt% block copolymer, 0.8 wt% block copolymer, or 1 wt% block copolymer.

[0165] Among them, the block copolymer is a triblock structure polyoxyethylene-polyoxypropylene-polyoxyethylene copolymer (PEO-PPO-PEO). The hydrophobic PPO of the block copolymer anchors the silicon spheres, while the hydrophilic PEO extends outward, inducing the formation of mushroom-shaped protrusions in the nanophase separation template.

[0166] The mushroom-shaped nanoprotrusions have a protrusion height of 15-20 nm, matching the length of the fluoroalkyl chain; the apex diameter is 8-12 nm, enabling control over the PEO canopy; the spacing distribution variation coefficient is ≤10%, ensuring the ordered self-assembly of the template. The mushroom-shaped protrusions utilize the cushion effect (Cassie state) to reduce the surface energy from ≤10 mN / m to <8 mN / m (close to the theoretical limit of 6.7 mN / m);

[0167] By transforming solid-liquid contact into point contact through nano-protrusions, the contact area is reduced by more than 60%, achieving biomimetic reinforcement of the "lotus effect." This enables hollow silicon spheres to maintain superhydrophobic self-cleaning and zero adhesion failure even in ultra-high pressure / high pollution environments, solving a long-standing pain point in industrial coatings.

[0168] By using triple protection of the reaction field (thermodynamic, kinetic, and chemical stability) and a self-assembled biomimetic structural template of block copolymers to form quantifiable mushroom-shaped nanoprotrusions, the bottleneck of the inability to simultaneously achieve graft layer uniformity and superhydrophobicity is overcome.

[0169] Example 13: Conservative process (parameters taken at lower limits)

[0170]

[0171] Example 14: Enhancement process (parameters taken at upper limits)

[0172]

[0173] Example 15: Process Optimization (Median Parameter Values)

[0174]

[0175] Key parameters and effect comparison

[0176]

[0177] Recommended equipment

[0178]

[0179] Example Effect Verification

[0180]

[0181] Mechanical stability test: retention rate of protrusion structure after ultrasonic treatment (100W, 10min): Example 13: 78%, contact angle decreased to 152°; Example 14: 98%, contact angle remained at 170°; Example 15: 95%, contact angle remained at 166°.

[0182] Summary of technical value:

[0183] Example 14 achieves optimal performance: 172° contact angle, close to the superhydrophobic limit; 7.1 mN / m surface energy, close to the theoretical limit of 6.7 mN / m for fluorocarbon; 3.5:1 cap-to-handle ratio mushroom structure, improving mechanical stability by 150%.

[0184] The grafting density of the directional grafting reaction in this embodiment is ≥2.8 chains / nm. 2 To achieve surface activation treatment of hollow silicon spheres, the hydroxyl group density on the surface of the hollow silicon spheres is ≥8OH / nm. 2 This provides sufficient anchor points for the grafting reaction.

[0185] Verification was made by measuring F1s / Si2p ≥ 0.35 using XPS; where F1s (binding energy 688eV) is the characteristic signal of fluorine atoms, and its area is proportional to the surface fluorine content.

[0186] Si2p (binding energy 103 eV): a characteristic signal of silicon substrate, the area of ​​which reflects the bulk mass of silicon spheres.

[0187] Atomic ratio conversion formula: (S) F S Si (Instrument sensitivity factor)

[0188] Threshold setting basis ≥0.35 corresponds to a fluoroalkyl chain density ≥2.8 chains / nm 2 A quantitative relationship is established through standard calibration, and non-destructive elemental analysis directly verifies that the grafting density meets the standard, eliminating the error (>20%) of traditional indirect detection methods (such as staining titration).

[0189] Grafting density Calculate using the following formula:

[0190]

[0191] in,

[0192] AF represents the area of ​​the characteristic peak of fluorine atoms.

[0193] SF is the sensitivity factor for fluorine.

[0194] NA is Avogadro's constant (6.022 × 10⁻⁶). 23 mol -1 ),

[0195] Specific surface area of ​​hollow silicon spheres (unit: nm) 2 / g);

[0196] Using XPS elemental ratio (F / Si) and physical density (chain / nm) 2 The direct conversion of ) solves the industry problem of the inability to accurately quantify the surface grafting density of micro and nano structures, and provides core data support for the effect of ultra-low surface energy.

[0197] The step-curing process in this embodiment is as follows: in a nitrogen environment, pre-crosslinking at 80℃ for 1 hour, main condensation at 120℃ for 2 hours, and interface strengthening at 150℃ for 0.5 hours are performed sequentially. During the interface strengthening stage, an axial static magnetic field of 0.8-1.2T is applied, with the magnetic field direction having an angle of ≤5° with the normal of the hollow silicon sphere, to form a vertically oriented structure of fluoroalkyl chains.

[0198] Specifically, pre-crosslinking at 80℃ for 1 hour triggers silane condensation (Si-OH + HO-Si → Si-O-Si), forming a primary crosslinked network. Primary condensation at 120℃ for 2 hours unwinds the fluoroalkyl segments, enhancing molecular thermal motion and leading to initial segment orientation. Interface strengthening at 150℃ for 0.5 hours allows the fluorocarbon (CF) bond dipole moment to respond to the magnetic field at high temperature, achieving vertical orientation.

[0199] The fluorocarbon bond (CF) has a strong dipole moment (4.7D) and is driven to orient itself in a magnetic field by a torque τ = μ × B; τ is the torque vector, a physical quantity that drives the rotation of the dipole; where μ is the molecular dipole moment vector, pointing from the negative charge to the positive charge; and B is the vector of the applied static magnetic field, pointing along the normal to the hollow silicon sphere.

[0200] An included angle of ≤5° ensures that the magnetic field force is parallel to the normal of the hollow silicon sphere, avoiding orientation deviation. The vertical orientation degree of the fluoroalkyl chain is >95%, which is superior to the 70-80% vertical orientation degree of traditional thermosetting.

[0201] Step curing endpoint passed FTIR 1040cm -1 The peak intensity is determined by reaching 95% of the peak intensity at the end of the pre-crosslinking process at 80℃, accurately locking the endpoint and avoiding over-curing.

[0202] Through four precise controls, (1) spatial orientation: laser-servo magnetic field calibration (θ≤0.5°) ensures effective torque τ=μ×B; (2) environmental purification: nitrogen purging (O2<10ppm) eliminates oxidation or hydrolysis side reactions; (3) process quantification: FTIR endpoint determination ( =95%), breaking through the limitations of experience-based curing; (4) Energy efficiency optimization: the magnetic field only needs to be turned on at 150℃, reducing energy consumption by 40%. Finally, through the magnetic field-oriented step-curing process, the vertical orientation rate of fluoroalkyl chains is >95%, the surface energy is ≤8mN / m, and the grafting density is ≥2.8 chains / nm. 2 (XPS verification showed F / Si≥0.35), and the process stability RSD<3%, achieving a dual breakthrough in superhydrophobicity and industrial-grade repeatability.

[0203] Example 16: Low electric field strength (0.8T)

[0204]

[0205] Example 17: High Field Strength (1.2T)

[0206]

[0207] Example 18: Midfield Strength (1.0T)

[0208]

[0209] Key parameters and effect comparison

[0210]

[0211] Recommended equipment

[0212]

[0213] Breakthrough Performance Comparison

[0214]

[0215] Through the synergistic effect of an axial static magnetic field of 0.8-1.2T and interface strengthening at 150℃, near-ideal vertical orientation of fluoroalkyl chains (tilt angle ≤5°) was achieved for the first time, setting a new benchmark for superhydrophobic performance. Example 17 (1.2T) represents peak performance and is suitable for high-value applications such as aerospace anti-icing; Example 18 (1.0T) balances cost and performance and is suitable for mass production of consumer electronics.

[0216] Preferably, verification after curing shows that grazing incidence XRD (incident angle 0.5°) exhibits a β-phase (001) crystal plane diffraction peak at 2θ=16.5°, indicating an orientation degree of [missing information]. ≥0.92 fluoroalkyl chains form β-phase hexagonal columnar crystals; lattice constant c=1.68nm, domain size ≥100nm 2 X-ray diffraction (XRD) is a technique that determines the crystal structure of a material by analyzing the diffraction pattern of X-rays.

[0217] Specifically, the extremely low incident angle (0.5°) allows the X-ray penetration depth to be approximately 5 nm, probing only the surface fluoroalkyl chain structure and avoiding interference from the bulk silicon sphere signal. This enables precise characterization of the crystal structure within 10 nm of the surface, eliminating interference from bulk data.

[0218] fluoroalkyl chain (-C8F) 17 (001) Crystal plane: normal plane of chain axis direction (c-axis); 2θ=16.5°: corresponding interplanar spacing CuKα radiation (λ = 0.154 nm) directly proves the vertical orientation structure of the fluoroalkyl chain.

[0219] Calculated from the ratio of the intensity of peak (001) to that of the isotropic reference peak: Where I(001) is the diffraction peak intensity of the (001) crystal plane in the oriented sample (perpendicular alignment direction), Iiso is the diffraction peak intensity of the (001) crystal plane in the isotropic (non-oriented) sample (random orientation reference), quantifies the degree of vertical alignment (≥0.92 corresponds to >95% chain vertical), and supports the surface energy ≤8mN / m.

[0220] via the tridecylfluorooctyl chain (-C8F) 17 The straightened length is approximately 1.65 nm; c = 1.68 nm contains bonded silicon atoms (approximately 0.03 nm), allowing the chain to fully extend. This ensures that the -CF3 end groups are 100% outward-facing (the structural basis for minimizing surface energy).

[0221] Calculated using Scherrer's formula: (β is the half width at half maximum of (001) peak, K≈0.9), large single crystal domains (>10×10nm), uniform surface energy distribution (fluctuation <0.3mN / m).

[0222] in,

[0223] D is the average grain size (in nm) perpendicular to the direction of the crystal plane (hkl).

[0224] K is the shape factor (user-specified K≈0.9, usually taken as 0.89-0.94, and 0.943 for cubic grains).

[0225] λ is the X-ray wavelength;

[0226] β is the half-width at half-maximum of the (001) peak (unit: radians, the angle value needs to be converted to radians: βrad=βdeg×π / 180).

[0227] θ is the Bragg diffraction angle (unit: radians, same conversion as above);

[0228] This verification method addresses the industry pain point of "the inability to directly characterize superhydrophobic structures" in the background technology by combining surface-sensitive XRD with crystallographic quantitative indicators. The high degree of agreement between the lattice constant c=1.68nm and the theoretical length of the fluoroalkyl chain (1.65nm) particularly demonstrates the precision of molecular-level design.

[0229] On the other hand, an LCP composite material is also provided, comprising modified hollow silicon spheres prepared by the above method and a liquid crystal polymer matrix.

[0230] The liquid crystal polymer matrix is ​​a thermotropic liquid crystal polymer synthesized by prepolymerization; the liquid crystal polymer matrix molecular chain contains carbonyl functional groups, with a carbonyl content of 5-8 mol%; the glass transition temperature is ≥280℃;

[0231] The modified hollow silicon spheres are directly connected to the liquid crystal polymer matrix via Si-O-Si covalent bonds. Fluoroalkyl chains grafted onto the hollow silicon spheres are vertically oriented with an inclination angle ≤10°. These fluoroalkyl chains form a continuous hydrophobic layer with a contact angle ≥155°. The aminosilane auxiliaries grafted onto the hollow silicon spheres form a hydrogen bond network with the carbonyl functional groups of the liquid crystal polymer matrix molecular chains, with a hydrogen bond density ≥3 bonds / nm. 2 .

[0232] The composite material addresses the industry pain points of weak interfaces between nanofillers and LCPs and failure in humid and hot environments in traditional technologies through continuous hydrophobic layers and hydrogen bond networks.

[0233] Example 19: Low carbonyl content (5 mol%)

[0234]

[0235] Example 20: High carbonyl content (8 mol%)

[0236]

[0237] Example 21: Optimization of carbonyl content (6.5 mol%)

[0238]

[0239] Key parameters and effect comparison

[0240]

[0241] Real-world performance breakthrough

[0242]

[0243] Key points of implementation process

[0244]

[0245] Example 20 (8 mol% carbonyl) achieves a comprehensive performance breakthrough:

[0246] 169° contact angle (superhydrophobic limit); 5.3 bonds / nm 2 Hydrogen bond density (molecular-level toughening); 38% oxygen index (self-extinguishing material);

[0247] Example 21 (6.5 mol% carbonyl) achieves the best balance between processability and performance: higher melt index (10 vs 8 g / 10 min); flexural strength 210 MPa + oxygen index 35%;

[0248] The carbonyl content of 5-8 mol% is precisely matched with aminosilane to construct a high-density hydrogen bond network; the vertical fluoroalkyl chain (tilt angle ≤5°) and Si-O-Si covalent bond simultaneously achieve superhydrophobicity and high mechanical strength. Example 20 is recommended for extreme aerospace environments, and Example 21 is recommended for mass production of electronic packaging.

[0249] The above description is only a preferred embodiment of the present invention. For those skilled in the art, there will be changes in the specific implementation and application scope based on the ideas of the present invention. The content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing directionally grafted modified hollow silica spheres, characterized in that, Includes the following steps: A. Surface activation treatment is performed on the hollow silica spheres, so that the surface hydroxyl density of the hollow silica spheres is ≥8OH / nm 2 ; B. Dissolve the fluorinated silane main agent, aminosilane auxiliary agent, and crosslinking accelerator in an organic solvent to prepare the grafting solution and adjust the pH to 4.8-5.2; C. Add the activated hollow silicon spheres to the grafting solution to carry out a directional grafting reaction; D. The grafted product is cured in a stepwise process to make the fluoroalkyl chains form a vertical orientation and the surface energy is ≤10mN / m; The surface activation treatment includes: Hollow silicon spheres were immersed in a 2.5-3.5 wt% hydrofluoric acid solution and ultrasonically cleaned for 25-35 minutes. After being washed with deionized water until neutral, they were activated by O2 plasma under nitrogen protection. The O2 plasma activation parameters are: O2 flow rate 18-22 sccm, power increased from 200W for 1-3 min to 250W for 2-4 min; Micro-etching process: The surface was ultrasonically treated with a 0.05-0.1 vol% tetramethylammonium hydroxide solution for 5-8 minutes to form a honeycomb-like microcavity structure. The grafting solution is prepared by dissolving the fluorinated silane main agent, aminosilane auxiliary agent and crosslinking promoter in an anhydrous toluene or supercritical CO2 at a mass ratio of (8.5-9.5):1:(0.1-1) to prepare a grafting solution with a concentration of 4-6 wt%. Control the degree of hydrolysis to 65-75%; Through online FTIR tracking 1110 cm -1 Peak area dropped to (40 ± 2)% of initial value, 950 cm -1 Peak area increased to (220 ± 5) % of initial value. Acetic acid was added within 15±1 min after the addition of silane to adjust the pH to 4.8-5.2; The fluorinated silane main agent is tridecafluorooctyltriethoxysilane, the aminosilane auxiliary agent is γ-aminopropyltriethoxysilane, and the crosslinking promoter is 3-glycidyl etheroxypropyltrimethoxysilane.

2. The method for preparing directionally grafted hollow silica spheres according to claim 1, characterized in that, The grafting solution contains 3-7 wt% of phosphorus-containing silane as a phosphorus-nitrogen synergistic flame retardant, and the molar ratio of the DOPO group of the phosphorus-containing silane to the amino group of the amino silane auxiliary is 1:1-1:1.

5. Stepwise annealing is performed after the addition of phosphorus-containing silanes: Step 1: Hold at 50℃ for 20 minutes to allow the DOPO groups to melt and spread; The second step is to raise the temperature to 80°C at a rate of 2°C / min to complete the PN condensation. The phosphorus atom enrichment depth on the surface is ≥3nm, which makes the flame retardant oxygen index of the modified hollow silicon spheres ≥30%.

3. The method of preparing directionally grafted hollow silica spheres according to claim 1, wherein, When using supercritical CO2 as a solvent, Reaction pressure 7.3-7.5 MPa, temperature 31-33 °C, pressure fluctuation ≤0.1 MPa; maintain system density 0.7-0.9 g / cm 3 ; through high-pressure visual window monitoring gas-liquid interface disappearance time ≤30 s; CO2water activity aw≤0.01; online FTIR real-time tracking 1110 cm -1 -1 peak disappearance, dynamic adjustment of pH accuracy ±0.

05.

4. The method of preparing directionally grafted hollow silica spheres according to claim 1, wherein, The acetic acid was added in three portions: Initially, 60% is added, and the circuit is triggered when the conductivity reaches its peak value (80±5μS / cm). Add 30% after 30 minutes, and trigger when the conductivity drops to (60±2)% of the peak value; The circuit is triggered when 10% is added after 60 minutes and the rate of change in conductivity is ≤0.5μS / (cm·min).

5. The method of preparing directionally grafted hollow silica spheres according to claim 1, wherein, The directional grafting reaction is: The activated hollow silica spheres were added to the grafting solution and stirred at a constant temperature of 58-62℃ and 190-210 rpm for 3.5-4.5 h. During the reaction, argon gas was introduced for protection and the following were added: 0.1-0.3 wt% 2,6-di-tert-butyl-p-cresol; 0.05-0.1 wt% disodium ethylenediaminetetraacetate; and 0.5-1 wt% block copolymer. Mushroom-shaped nanoprotrusion structures were induced to form on the surface of the hollow silica spheres.

6. The method of preparing directionally grafted hollow silica spheres according to claim 1, wherein, The grafting density of the grafting reaction is ≥ 2.8 chains / nm 2 verified by XPS measurement of F1s / Si2p ≥ 0.35; Grafting density was calculated according to the following equation: in, AF represents the area of ​​the characteristic peak of fluorine atoms. SF is the sensitivity factor for fluorine. NA is the Avogadro's number (6.022 x 10 23 mol -1 ), Specific surface area of ​​hollow silicon spheres (unit: nm) 2 / g).

7. The method of preparing directionally grafted hollow silica spheres according to claim 1, wherein, The step-by-step curing process involves sequentially performing pre-crosslinking at 80℃ for 1 hour, main condensation at 120℃ for 2 hours, and interface strengthening at 150℃ for 0.5 hours in a nitrogen environment. During the interface strengthening stage, an axial static magnetic field of 0.8-1.2T is applied, with the magnetic field direction having an angle ≤5° with the normal of the hollow silicon sphere, to form a vertically oriented structure of fluoroalkyl chains. Stepwise cure end point by FTIR 1040 cm -1 Peak intensity reaches 80°C pre-crosslinking end point when peak intensity reaches 95% of peak.

8. An LCP composite material comprising modified hollow silicon spheres prepared by any one of claims 1-7 and a liquid crystal polymer matrix, characterized in that: The liquid crystal polymer matrix is ​​a thermotropic liquid crystal polymer synthesized by prepolymerization; the liquid crystal polymer matrix molecular chain contains carbonyl functional groups, with a carbonyl content of 5-8 mol%; the glass transition temperature is ≥280℃; The modified hollow silicon spheres are directly connected to the liquid crystal polymer matrix via Si-O-Si covalent bonds. Fluoroalkyl chains grafted onto the hollow silicon spheres are vertically oriented with an inclination angle ≤10°. These fluoroalkyl chains form a continuous hydrophobic layer with a contact angle ≥155°. The aminosilane auxiliaries grafted onto the hollow silicon spheres form a hydrogen bond network with the carbonyl functional groups of the liquid crystal polymer matrix molecular chains, with a hydrogen bond density ≥3 bonds / nm. 2 .

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