JPH04131133A - Preparation of silica glass capsule having minute particles enclosed therein - Google Patents

Abstract

PURPOSE:To facilitate the handling of minute particles by covering minute particles with silica glass in such a state that the aggregation thereof is prevented to encapsulate the same. CONSTITUTION:Minute particles 5 dispersed in water 2 or a silicon alkoxide 1 to form the micelle of minute liquid droplets of either one of water 2 and the silicon alkoxide 1 due to the surfactant 3 in one liquid and, further, the minute particles 5 are incorporated in the minute liquid droplets to prevent the mutual aggregation of the minute particles. In this state, the silicon alkoxide 1 and water 2 are reacted and the minute particles 5 are covered with silica glass to be encapsulated to form capsules 6. As usable silicon alkoxide 1, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane and tetrabutoxysilane are disignated. By this method, the minute particles 5 can easily be handled.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for manufacturing a silica glass capsule in which fine particles are confined, and in particular, measures are taken to prevent agglomeration of the fine particles to facilitate handling of the fine particles. Furthermore, the present invention relates to a method for producing a silica glass capsule in which fine particles are confined while maintaining their characteristics as fine particles.

[Prior Art] Fine particles are known to have properties different from those of bulk particles, and are expected to be used as functional materials. For example, when the particle size of compound semiconductor particles such as CdS becomes smaller, so-called quantum size effects such as discretization of the band structure and shift of the absorption edge toward shorter wavelengths occur (References: A, J.

Nozik et al, J, Phy, Chem.

89 (1985) 397). It is also known that such particles produce large nonlinear optical effects.

When handling such fine particles, it is important to prevent the fine particles from coagulating with each other in order to enhance the effectiveness.

The use of surfactants has traditionally been used to prevent agglomeration of fine particles, and this method has been applied in a wide range of areas in liquids (references: for example, Surfactant Handbook, Kogaku Tosho Co., Ltd.).

On the other hand, Steigerwald et al. (Reference: Steig
erwald et al., J. Am.

Chem, Soc, 110 (1988) 3046) added phenyl groups around the particles of CdSe synthesized in a solution, and due to the steric hindrance, the particles remained stable not only in solution but also during precipitation drying. It has been reported that independence is not lost (capping with phenyl group).

[Problems to be Solved by the Invention] However, the technique using a surfactant is in a solution, and it is difficult to extract the fine particles as a solid.

Furthermore, in a liquid state, it is difficult to fully exploit the functions of fine particles and apply them.

Furthermore, the dry powder obtained by the phenyl capping method has poor durability against moisture and is extremely unstable under normal conditions. Furthermore, this method is currently only applicable to selenides and sulfides.

The present invention solves the above-mentioned conventional problems, and provides a method for manufacturing silica glass capsules that confine fine particles, which facilitates handling of the fine particles, and maintains the characteristics as fine particles. The purpose is to provide

[Means for Solving the Problems] The method for producing a silica glass capsule in which fine particles are confined according to the present invention includes water and silicon alkoxide (S i (O
R) 4+ (where R is an alkyl group) In the method of manufacturing silica glass (generally called the sol-gel method), fine particles dispersed in water or silicon alkoxide are made to have surface activity using a surfactant. Form micelles of minute droplets of either water or silicon alphoxide liquid in the other liquid by using an agent, and then place fine particles into the minute droplets to prevent agglomeration of the fine particles. It is characterized by reacting soricon alkoxide with water and covering the fine particles with silica glass, which prevents the fine particles from aggregating during subsequent handling.

In the present invention, silica glass produced by a reaction between silicon alkoxide and water is used instead of a surfactant or a phenyl group as a material covering the periphery of the fine particles. Examples of silicon alkoxides that can be used in the present invention include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane.

The method of the present invention can be applied regardless of the material of the fine particles, and can also ensure sufficient durability against moisture and the like.

Moreover, since such measures are taken, handling is easy and flexibility can be increased in terms of application.

[Action Co. The present invention will be explained in detail below with reference to the drawings.

FIG. 1A schematically represents the state of micelles in the solvent of the present invention, and FIG. 1A is a schematic diagram of the state in which fine particles are confined within the micelles. In addition, Figure 1C shows the schematic solvent silicon alkoxide 1 after the reaction between the book and silicon alkoxide is completed and the fine particles are confined in the glass capsule.
is non-hydratable and does not mix with water 2, which is a reactant. A large amount of silicon alkoxide liquid is mixed with surfactant 3, which has a hydrophilic group and a hydrophobic group that form reverse micelles with water, and when water is added, the water surrounded by the surfactant turns into silicon alkoxide liquid. dispersed inside.

This situation is schematically shown in FIG. 1a. If the fine particles 5 are dispersed in water in advance, the inside of the micelle will be in a state as schematically shown in Figure 1.

For example, TMS (tetramethoxysilane) and water form silica, which is the main component of glass, based on the following reaction formula.

S i (OCH3) 4+ 4 H20=S i (
OH), +4CH,OH 8i (OH)4: Sio2+2 H20 The reaction progresses by adding an acid or alkali catalyst to the water or heating it, and the water in the micelles reacts with the silicon alkoxide solvent to form silica. form glass. The fine particles that were in the water are trapped in the glass as they are, and the glass thus produced can function as a capsule 6 as shown in FIG. 1C. The thus formed silica glass capsules containing fine particles are precipitated, filtered, washed, and dried to obtain silica powder containing fine particles.

In addition, contrary to the above method, fine particles can be similarly encapsulated by using water as a solvent to confine silicon alkoxide in which fine particles are dispersed in micelles and carrying out the above reaction.

[Example] The present invention will be explained in more detail by giving examples below.

Place TMS 70 cc in a beaker and mix therein with 3 cc of AOT (a type of sulfosuccinic acid ester surfactant, trade name). Apart from this, 0
．． 1 c of Cd(CIO2)2 aqueous solution of 067 mol/I
C1o, 095 mol/1 Na2S aqueous solution is prepared in lcc. By mixing these two aqueous solutions, the
It is possible to form a colloid of CdS ultrafine particles having a particle size of about 0 nm. When two aqueous solutions are mixed with the TMS liquid, the aqueous solutions are trapped in the AOT micelles,
Emulsified and dispersed in TMS. Furthermore, in aqueous solution, CdS
is generated and simultaneously trapped in the aqueous solution in the micelles. Since the Cd(CIO4), Na, and S aqueous solution is alkaline, it also acts as a catalyst for the reaction between TMS and water.
It changes into fine glass particles and precipitates in about 1 minute. AOT by repeating displacement precipitation several times with organic solvents such as alcohol.
was removed and dried to obtain glass particles.

The obtained glass particles had a pale yellow color. Commercially available reagent powder with large CdS particles (about several micrometers) is brown in color. This difference is thought to be due to the fact that the CdS particles are confined in the glass with a size of approximately ionm, so that the light absorption edge due to the quantum size effect is shifted to the shorter wavelength side. This indicates that the particles were well confined within the glass and no aggregation of the fine particles occurred. Further, when the spectral characteristics of the fine particles were measured, the absorption edge was found to be approximately 490 nm, which was shifted to a shorter wavelength than the bulk absorption edge of 520 nm. When this powder was observed with a transmission electron microscope, C
The dS fine particles were confined within the glass, and the particle size of the CdS fine particles at that time was about 10 nm.

The glass capsule containing CdS obtained in this way is
No change in its properties was observed even when it was placed in organic solvents such as methanol and acetone, as well as in water.

[Effects of the Invention] According to the present invention, handling of fine particles, which was difficult in the past, has become easier by covering the fine particles with silica glass to prevent agglomeration and encapsulating the fine particles. Furthermore, it has become possible to extract fine particles in a form that can sufficiently withstand environmental conditions such as moisture, making it easier to fully utilize the functions of fine particles and increasing the degree of freedom in terms of application.

[Brief explanation of the drawing]

FIG. 1A schematically represents the state of micelles in the solvent of the present invention, and FIG. 1A is a schematic diagram of the state in which fine particles are confined within the micelles. In addition, Figure 1C shows the state in which the reaction between water and silicon alkoxide has finished and the fine particles are confined in the glass capsule.Scheme 1...solvent (silicon alkoxide), 2...water, 3...surface activity agent, 5.
...Fine particles, 6...Glass capsule in which fine particles are trapped. Near i+i^÷. Figure C Description of water surfactant reaction vessel

Claims (1)

[Claims] In a method (generally called sol-gel method) for producing silica glass by the reaction of water and silicon alkoxide (Si(OR)_4, where R is an alkyl group), fine particles dispersed in water or silicon alkoxide are mixed at the interface. Using an activator, micelles of microdroplets of either water or silicon alkoxide liquid are formed in the other liquid, and microparticles are placed in the microdroplets to form particles that interact with each other. A method for producing a silica glass capsule containing fine particles, which is characterized by preventing agglomeration, reacting silicon alkoxide with water in that state, covering the fine particles with silica glass, and preventing the fine particles from agglomerating with each other during subsequent handling. .