CN104003409B - A kind of preparation method of controlled monodisperse spherical Large stone nano silicon - Google Patents

Abstract

The present invention relates to a kind of preparation method of controlled monodisperse spherical Large stone nano silicon, with

Description

A preparation method of controllable monodisperse spherical large particle size nano-silica

Technical field:

The invention relates to a method for preparing controllable monodisperse spherical large particle size nano-silica, which utilizes A sol-gel method combined with intermittent addition of reactants can controllably synthesize spherical _SiO2 particles with excellent monodispersity, which belongs to the field of nanomaterial synthesis.

Background technique:

In recent years, nano-silica particles have been widely studied in scientific research and industrial fields. Among them, nano-silica can be used in the preparation of shear thickening fluid and in the research of soft body armor. Shear thickening fluid is generally obtained by dispersing a certain concentration of solid particles in a liquid. Shear thickening fluid generally consists of a two-phase dispersion system, one phase is composed of nanoparticles, such as silica, calcium carbonate, PMMA particles, etc., and the other phase is a carrier fluid, such as water, polyethylene glycol, etc., dispersed Phase particles are dispersed therein. Shear thickening fluid is a kind of non-Newtonian fluid, and the shear thickening behavior is the behavior of a dispersion system with a certain concentration. When it is higher than the critical shear rate, its viscosity rises sharply, and it is a liquid dispersion system from a macro perspective. transition to solid phase.

The particle size and monodispersity of nano-silica particles have a great influence on the performance of shear thickening system. Among them, the critical shear rate of the shear thickening system increases as the particle size of the nanoparticles decreases. The monodispersity of nano-silica particles decreased, which caused the critical thickening starting point of the system to move to the direction of high shear rate. This is unfavorable for the application of shear thickening liquids in soft protective materials. Therefore, the requirement for preparing nano-silica particles with excellent monodispersity and large particle size is very urgent.

For the synthesis process of nano-silica particles, there are currently three main methods. Pileni used the microemulsion method to prepare silica particles with a size up to thousands of nanometers. This method works with Compared with the synthesis method, it is more suitable for the synthesis of silica particles with a particle size of 30-60nm, and the particles have better monodispersity. However, this preparation process requires a large amount of surfactant (generally greater than the mass fraction of silica particles) to form stable micelles. Therefore, the product particles need to be further processed to remove the surfactant from the surface of the particles. In addition, it is also difficult to maintain a uniform and stable micelle composition in the soft sensitive phase.

Balthis and Mendenhall (J.H.Balthis.P.Wendenhall.Preprationofsolsfromfinelydividedsilicon, USP2614994.1952) reported a hydrolysis method using pretreated elemental silicon to prepare monodisperse small particle size nano-silica. The reaction is catalyzed by aqueous ammonia, and the reaction temperature is controlled at 20-90°C. At the same time, the obvious advantage of this method is that before the reaction, the reactants are sequentially treated with acid solution, deionized water, ethanol, and ether, and the silicon-containing oxides on the particle surface can be removed, exposing the clean silicon surface. In the patent, nano-silica particles with good regularity of 8-15nm are prepared. The particle size provided by this patent is small, which cannot meet the particle size requirements for the preparation of shear thickening liquid.

The present invention takes Based on the sol-gel method, the process conditions affecting the particle synthesis were explored, and factors such as catalyst concentration, TEOS and water reaction molar ratio were optimized. By controlling the reaction conditions, nano-silica particles with excellent dispersibility and large particle size were prepared in a small number of dropping times. The reaction system is simple and post-treatment is easy, and it is a method for controllably synthesizing large-diameter nano-silica.

Invention content:

The object of the present invention is to provide a kind of preparation method of controllable monodisperse spherical large particle size nano silicon dioxide, with Based on the sol-gel method, ethyl orthosilicate is hydrolyzed to obtain orthosilicic acid, and silicon dioxide is obtained by dehydration and condensation by intermittently adding ethyl orthosilicate. This method has simple process flow, mild conditions, and post-treatment The method is simple and convenient, the production efficiency is high, and it is suitable for industrialized production. By intermittently adding reactants, large-diameter nano-silica particles can be controlled and synthesized. The nano silicon dioxide particle product obtained by the preparation method has the characteristics of regular spherical shape, excellent monodispersity and the like.

The present invention takes Based on the sol-gel method, tetraethyl orthosilicate (TEOS) is hydrolyzed to obtain orthosilicic acid, and then dehydrated and condensed to obtain silica, which is catalyzed by a weak base, and tetraethyl orthosilicate is added intermittently and step by step. Excellent dispersion, spherical large particle size nano-silica.

The preparation method of the controllable monodisperse spherical large particle size nano-silica provided by the present invention, the specific steps and conditions are as follows:

(1) Disperse ammonia water in absolute ethanol or ethanol solution, the molar ratio of ethanol to ammonia water is 8-40:1, preferably 10-20:1, stir and disperse evenly; add tetraethyl orthosilicate in the mixed solution, Control the dropping rate to 10-60ml/min, preferably 20-40ml/min, and the molar ratio of ethyl orthosilicate to H ₂ O is 1:2-20, preferably 1:3-6;

(2) At normal temperature, the stirring speed is controlled to 200-750r/min, preferably 500-750r/min, and the reaction time is 2-8h, preferably 4-6h, to obtain the silica sol;

(3) Ethyl orthosilicate is added dropwise in the silica sol obtained in step (2), the molar ratio of the amount of ethyl orthosilicate added to the ethyl orthosilicate added in step (1) is 1:10 ~4:1; preferably 1:2~4:1. Preferably, the addition of ethyl orthosilicate is divided into 2 to 4 times. After each drop is completed, the reaction is stirred for 2 to 4 hours, and then the next drop is performed.

(4) The reactant obtained in step (3) is centrifuged, the supernatant is removed, the product is redispersed in the solvent, and the product is redispersed and centrifuged repeatedly until the supernatant is neutral, and the dispersion method is preferably ultrasonic dispersion. The solvent is selected from absolute ethanol, acetone or deionized water, and finally the target product is obtained by vacuum drying and drying, and the drying temperature is preferably 60-90°C.

The reaction equation for silica preparation is:

Si(OC ₂ H ₅ ) ₄ +2H ₂ O→SiO ₂ +4C ₂ H ₅ OH

Among them, the hydrolysis of ethyl orthosilicate: Si(OC ₂ H ₅ ) ₄ +4H ₂ O→Si(OH) ₄ +4C ₂ H ₅ OH is the main reaction, which is the reaction of Si(OC ₂ H ₅ ) ₄ In nucleophilic substitution reaction, the silicon atom in TEOS is positively charged. During the reaction, the hydroxyl group of water attacks the positively charged silicon atom, and the ethoxy group leaves to obtain orthosilicic acid. Base catalysis is beneficial to the nucleophilic substitution reaction. In this reaction system, ammonia water is used as the catalyst. With the increase of the catalyst concentration, the particle size increases, but the particle size distribution becomes wider and the monodispersity decreases. Therefore, in order to take into account problems such as particle size, particle sphericity and monodispersity, it is necessary to select a suitable ammonia concentration, which is also the technical key of the present invention.

In the dispersion process of step (1), the process of adding ethyl orthosilicate not only needs to control the amount of ethyl orthosilicate added, but also needs to control the adding speed. The molar ratio of ethyl orthosilicate to water is preferably 1:3 ~1:6, the dropping rate is preferably 20~40ml/min, especially when the concentration of ammonia water is high, the dropping rate of TEOS will have a greater impact on the regularity and particle size of the balls.

During the reaction process of step (2), the stirring speed is preferably 500-750r/min. During the reaction process, the stirring speed was kept constant to avoid agglomeration of generated nanoparticles. The reaction time is preferably 4-6h. When the particle size of the nano-silica particles does not change any more, the reactants have been completely reacted, and the particles form a stable spherical shape.

In step (3), in order to obtain large-diameter nano-silica particles, the "intermittent drop growth method" is used to add tetraethyl orthosilicate to the formed nano-silica particle sol, so that the resulting silica As the nucleus, the particle size increases through the further reaction of tetraethyl orthosilicate. The molar ratio of the amount of ethyl orthosilicate added to the ethyl orthosilicate added in step (1) is preferably 1:2˜4:1. During the reaction process, samples were taken at intervals for characterization, so as to obtain silica particles with the desired particle size.

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

Under the existing reaction system, the technological parameters affecting particle size and regularity in the sol-gel method were determined. By adopting the method of stepwise adding reactants, the controllable synthesis of large-diameter nano-silica particles is realized, and the particles have excellent monodispersity. The method has the advantages of simple technological process, mild conditions, convenient post-treatment method and high production efficiency, and is suitable for industrialized production. In addition, the large-diameter nano-silica particles synthesized by the method provided by the patent have potential application value in the field of shear thickening liquid.

The testing instruments used for the characterization of the present invention: German BRUKERTENSOR27 type Fourier transform infrared spectrometer, Hitachi S4800 scanning electron microscope (scanning voltage 5KV), FEI Hong Kong Co., Ltd. TecnaiG ² 20 transmission electron microscope, Japan Shimadzu XRD-6000, MCR301 rheology instrument.

Main experimental drugs used in the present invention: ammonia, analytically pure, Beijing Chemical Plant; ethyl orthosilicate, analytically pure, Beijing Yili Fine Chemicals Co., Ltd.; ethanol, analytically pure, Beijing Chemical Plant; acetone, analytically pure, Beijing chemical plant.

Description of drawings:

The particle diameter that Fig. 1. embodiment 1 makes is about _290nmSiO SEM picture

Fig. 2. SiO that embodiment ₁ makes The infrared spectrogram

The particle diameter that Fig. 3. embodiment ₂ makes is about 340nmSiO SEM picture

Fig. 4. embodiment ₂ makes SiO XRD spectrogram

The particle diameter that Fig. 5. embodiment 3 makes is about _410nmSiO SEM picture

The particle diameter that Fig. 6. embodiment 3 makes is about _410nmSiO TEM pictures

Figure 7. SEM picture of MP4540M silica produced by Nissan Chemical Co., Ltd. (1)

Figure 8. SEM picture of MP4540M silica produced by Nissan Chemical Co., Ltd. (2)

The particle diameter that Fig. 9. embodiment 4 makes is about 500nmSiO ₂ SEM pictures

The particle diameter that Fig. 10. embodiment 5 makes is about 600nmSiO ₂ SEM picture

Fig. 11. Variation curve of viscosity of shear thickening liquid with a mass fraction of 53.5% as a function of shear rate

Fig. 12. Variation curve of viscosity of shear-thickening liquid with a mass fraction of 53.5% as a function of shear stress

From Fig. 1, Fig. 3, Fig. 5, Fig. 9, and the scanning electron microscope photos of Fig. 10 silica particles, it can be seen that by controlling the process conditions of Examples 1-5, a spherical regular, monodisperse particle with a particle size of about 300-600nm has been prepared. Excellent particles. From the infrared, XRD and transmission electron microscope analysis of the product particles in Figure 2, Figure 4 and Figure 6, it can be seen that the prepared particles are amorphous solid spherical silica particles. From Fig. 5 and Fig. 6, the 410nm particles prepared in Example 3 are compared with the MP4540M particles produced by Nissan Chemical Co., Ltd., and the product particles prepared by the method provided by the present invention have regular spherical shape and excellent monodispersity.

Figures 11 and 12 show the use of silicon dioxide particles with a particle size of about 600nm in Example 5 to prepare a shear thickening liquid with a mass fraction of 53.5%. Through its rheological performance test, the critical thickening starting point of the system is relatively low. The shear thickening properties can be exhibited at a lower shear rate, indicating that the prepared product has application value.

detailed description:

The present invention will be further described below in conjunction with Comparative Examples and Examples.

Example 1

(1) Disperse a certain amount of ammonia water in the ethanol solution, the molar ratio of ethanol to ammonia water is 16:1, disperse evenly with electric stirring, add tetraethyl orthosilicate in the mixed solution, control the dropping rate to 25ml/min, TEOS and The H ₂ O molar ratio is 1:5.

(2) At room temperature, control the stirring speed to 650r/min, react for 5h, and obtain the silica sol.

(3) Add TEOS step by step to the silica sol obtained in step (2), control 650r/min constant speed stirring, add TEOS dropwise to the constant pressure funnel, control the dropping rate to 25ml/min, and add The molar ratio of TEOS is 1:2, and it is added at one time. After the dropwise addition is completed, it is controlled to stir at a constant speed of 650r/min and react for 4h.

(4) The reactant obtained in step (3) is centrifuged, the supernatant is removed, and the centrifuge is redispersed in acetone. Repeat the dissolution and separation operations until the supernatant is neutral.

(5) Place the product in a vacuum drying oven, and dry it at 80°C for 20 hours.

After adding TEOS in step (1) and step (3), samples were taken respectively, and tested by SEM and laser particle size analysis. The particle size obtained in step (1) was about 170nm, and the particle size obtained after the reaction in step (3) was 290nm. In addition, it can be seen from the infrared test results that the method successfully prepares nano-silica particles, and the post-treatment method is feasible, and the product has high purity.

From the analysis of the infrared spectrum of the product, the strong and broad absorption band at 1103cm ^-1 is the Si-O-Si antisymmetric stretching vibration peak, the peaks at 800cm ^-1 and 470cm ^-1 are the Si-O bond symmetric stretching vibration peaks, and 3442cm ^- The broad peak at ¹ is the structural water-OH antisymmetric stretching vibration peak, the peak near 1633 cm ^-1 is the HOH bending vibration peak of water, and the peak at 950 cm ^-1 belongs to the bending vibration absorption peak of Si-OH.

There are no other peaks of other groups in the spectrogram, indicating that the preparation and post-treatment process is feasible.

Example 2

(1) Disperse a certain amount of ammonia water in the ethanol solution, the molar ratio of ethanol to ammonia water is 13:1, disperse evenly with electric stirring, add tetraethyl orthosilicate in the mixed solution, control the dropping rate to 20ml/min, TEOS and The H ₂ O molar ratio is 1:4.

(2) At room temperature, control the stirring speed to 600r/min, react for 5h, and obtain the silica sol.

(3) Add TEOS step by step to the silica sol obtained in step (2), control the stirring speed at 600r/min, add TEOS dropwise through the constant pressure funnel, control the rate of addition to be 20ml/min, and add TEOS with step (1). The molar ratio of TEOS was 1:1, and it was added in two times. After each dropwise addition, the stirring speed was controlled to 600r/min and stirred at a constant speed, and the reaction was carried out for 3h.

(4) The reactant obtained in step (3) is centrifuged, the supernatant is removed, and the centrifuge is redispersed in absolute ethanol. Repeat the dissolution and separation operations until the supernatant is neutral.

(5) Put the product in a vacuum drying oven, and dry it at 70°C for 22 hours.

After adding TEOS in step (1) and step (3), samples were taken respectively, and tested by SEM and laser particle size analysis. The particle size obtained in step (1) was about 210nm. In step (3), TEOS was added twice, and finally Silica particles with a particle diameter of 340 nm were obtained. It shows that by adding TEOS step by step, the particle size of silica can be gradually increased, and the reaction conditions are mild, and the reaction process is controllable.

In addition, from the XRD pattern of the particles, a broad diffraction peak appears at 2θ of about 23°, and the nanoparticles prepared by the reaction are amorphous materials.

Example 3

(1) Disperse a certain amount of ammonia water in the ethanol solution, the molar ratio of ethanol to ammonia water is 11:1, electric stirring is used to disperse evenly, and ethyl orthosilicate is added to the mixed solution, and the dropping rate is controlled to be 40ml/min, TEOS and The H ₂ O molar ratio is 1:6.

(2) At room temperature, control the stirring speed to 700r/min, react for 6h, and obtain silica sol.

(3) Add TEOS step by step in the silica sol obtained in step (2), control the stirring speed at 700r/min, add TEOS dropwise to the constant pressure funnel, control the rate of addition to be 40ml/min, and add in the step (1) The molar ratio of TEOS is 2:1, and it is added three times. After each dropwise addition, the stirring speed is controlled to 700r/min to stir at a constant speed, and the reaction is carried out for 2h.

(4) The reactant obtained in step (3) is centrifuged, the supernatant is removed, and the centrifuge is redispersed in absolute ethanol. Repeat the dissolution and separation operations until the supernatant is neutral.

(5) Place the product in a vacuum drying oven, and dry it at 90°C for 16 hours.

After step (1) and step (3) have reacted, sampling is characterized by SEM and laser particle size analysis test. The particle size obtained in step (1) is about 260nm, and the particle size after step (3) is completely reacted is 410nm ( As shown in Fig. 8), Fig. 9 and Fig. 10 are scanning electron microscope pictures of MP4540M (large particle size particle is 450nm) produced by Nissan Chemical Company, Japan. By comparison, the product particles obtained in Example 4 are spherical and regular, and have excellent monodispersity.

Example 4

(1) Disperse a certain amount of ammonia water in the ethanol solution, the molar ratio of ethanol to ammonia water is 10:1, electric stirring is used to disperse evenly, and ethyl orthosilicate is added to the mixed solution, and the dropping rate is controlled to be 30ml/min, TEOS and The H ₂ O molar ratio is 1:1.

(2) At room temperature, control the stirring speed to 750r/min, react for 6h, and obtain silica sol.

(3) Add TEOS step by step to the silica sol obtained in step (2), control the stirring speed to 750r/min, add TEOS dropwise through the constant pressure funnel, and the molar ratio to the TEOS added in step (1) is 1:3 , Add in three times, after the dropwise addition is completed, control the stirring speed to 750r/min and stir at a constant speed, and react for 2h.

(4) The reactant obtained in step (3) is centrifuged, the supernatant is removed, and the centrifuge is redispersed in deionized water. Repeat the dissolution and separation operations until the supernatant is neutral.

(5) Place the product in a vacuum drying oven, and dry it at 90°C for 16 hours.

After the reaction in step (3) is completed, samples are taken and characterized by SEM and laser particle size analysis. The particle size obtained is about 500nm. From the scanning electron microscope pictures of the product particles, it can be observed that the product particles are spherical and regular, and have excellent monodispersity.

Example 5

(1) Disperse a certain amount of ammonia water in the ethanol solution, the molar ratio of ethanol to ammonia water is 10:1, electric stirring is used to disperse evenly, and ethyl orthosilicate is added to the mixed solution, and the dropping rate is controlled to be 30ml/min, TEOS and The H ₂ O molar ratio is 1:1.

(2) At room temperature, control the stirring speed to 750r/min, react for 6h, and obtain silica sol.

(3) Add TEOS step by step to the silica sol obtained in step (2), control the stirring speed at 750r/min, add TEOS dropwise through the constant pressure funnel, control the rate of addition to be 30ml/min, and add TEOS with step (1). The molar ratio of TEOS was 1:4, and it was added in 4 times. After each dropwise addition, the stirring speed was controlled to 750r/min at a constant speed, and the reaction was carried out for 2h.

(4) The reactant obtained in step (3) is centrifuged, the supernatant is removed, and the centrifuge is redispersed in deionized water. Repeat the dissolution and separation operations until the supernatant is neutral.

(5) Place the product in a vacuum drying oven, and dry it at 90°C for 16 hours.

After the reaction in step (3), samples were taken and characterized by SEM and laser particle size analysis tests. The particle size obtained was about 600nm. From the scanning electron microscope pictures of the product particles, it can be observed that the product particles are spherical and regular, and have excellent monodispersity.

The silicon dioxide particles with a particle diameter of about 600nm obtained in Example 5 were used for the preparation of the shear thickening solution, and 4.6g of product particles were dispersed in 4g of PEG400 (polyethylene glycol), and 40ml of absolute ethanol was added to increase the system dispersion. Disperse with magnetic stirring at room temperature for 6 hours to obtain a uniform dispersion system. The system was distilled in a water bath at 80°C to remove ethanol, a small molecular substance, and a shear-thickened liquid with a mass fraction of 53.5% was obtained. After the system was cooled to room temperature, vacuum was applied to remove air bubbles in the system.

The prepared shear thickening liquid is subjected to a rheological test using a MCR301 rheometer, and the test procedure is:

1. 0.1-1000pa for stress scanning for 180s

2. Creep at a shear rate of 1s-1 for 60s

3. At zero shear, zero stress recovery for 60s

4. Stress scanning from 0.1-1000pa

Figure 11 and Figure 12 show the variation curves of the viscosity of the shear thickening fluid with the shear rate and shear stress. From Figure 11, it can be seen that the shear thickening system exhibits shear thinning characteristics at low shear rates, 0.2 s ^-1 is the critical thickening point. When the shear rate increases further, the viscosity of the system has a large change, showing the performance of shear thickening. Compared with the domestic literature, the threshold of critical thickening is lower, that is, at low shear rate, it can show the performance of shear thickening. (Xu Yulei, Gong Xinglong, Jiang Wanquan, et al. Preparation and Characterization of Shear Thickening Liquid[J]. Functional Materials, 2007,38(10):3904-3906.)

Claims (8)

1. A preparation method of controllable monodisperse spherical large particle size nano-silica, based on the sol-gel method, obtains orthosilicic acid by hydrolysis of ethyl orthosilicate, dehydration condensation obtains silica, adopts weak Alkali catalysis, the method of adding tetraethyl orthosilicate intermittently and step by step, to prepare monodisperse spherical large particle size nano-silica, the specific steps and conditions are as follows: (1) Disperse ammonia water in absolute ethanol or ethanol solution, the molar ratio of ethanol to ammonia water is 8-40:1, stir and disperse evenly; add tetraethyl orthosilicate into the mixed solution, control the dropping rate to 10-60ml /min, the molar ratio of tetraethyl orthosilicate to H ₂ O is 1:2～20; (2) Under normal temperature, stir and react for 2 to 8 hours to obtain silica sol; (3) Add ethyl orthosilicate dropwise to the silica sol obtained in step (2), and add ethyl orthosilicate in 2 to 4 times. After each drop is completed, stir and react for 2 to 4 hours. Carry out the next dropwise addition, the molar ratio of the amount of ethyl orthosilicate added in the step (1) to the ethyl orthosilicate is 1:10～4:1; (4) The reactant obtained in step (3) is separated, the supernatant is removed, and the product is washed, dried, and oven-dried to obtain the target product. 2. The preparation method according to claim 1, characterized in that: in step (1), the molar ratio of ethanol to ammonia water is 10-20:1, and the molar ratio of tetraethylorthosilicate to _H2O is 1:3-6 , Control the dropping rate to 20-40ml/min. 3. The preparation method according to claim 1, characterized in that: the molar ratio of the amount of ethyl orthosilicate added in step (3) to the ethyl orthosilicate added in step (1) is 1:2 to 4:1 . 4. according to the preparation method of claim 1, it is characterized in that: in the reaction of step (2), the stirring speed is controlled to be 200～750r/min. 5. The preparation method according to claim 1, characterized in that: the reaction time of step (2) is 4 to 6 hours. 6. according to the preparation method of claim 1, it is characterized in that: the product after removing the supernatant in the step (4) is dispersed in the solvent again, through repeated redispersion, centrifugation, until the supernatant is neutral, solvent selection The target product is obtained from absolute ethanol, acetone or deionized water, and finally vacuum-dried and oven-dried. 7. The preparation method according to claim 6, characterized in that: in step (4), the dispersion method is ultrasonic dispersion. 8. The preparation method according to claim 6, characterized in that: in step (4), the drying temperature is 60-90°C.