JP3025233B2 - Ionic colloid system that reversibly crystallizes due to temperature change and method for producing colloid crystal using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of colloids, and more particularly to an ionic colloid system which reversibly crystallizes due to a change in temperature and a method for producing colloidal crystals using the same.

[0002]

2. Description of the Related Art Colloid refers to a state in which colloid particles having a size of several nm to several μm are dispersed in a medium, and has many industrial uses. For example, colloids composed of inorganic fine particles such as silica are widely used as fillers for rubber and plastics, coatings for copying and photosensitive paper, microfillers for inks, abrasives for semiconductors, binders for refractories, and pigments for cosmetics. ing. In addition, colloids of organic particles such as polymer latex are used as medical test reagents, cell research samples, standard samples for electron microscopes, etc.
It is industrially important as a conductive filler and a catalyst.

[0003] In these conventional uses, the properties of colloidal fine particles are mainly used. In recent years, application development focusing on the crystal structure (colloidal crystals) formed by colloidal particles in a liquid has been studied. I have. Colloidal crystals are aggregates in which particles are regularly arranged in a three-dimensional manner. 1) Ionic colloidal particles (silica, ionic polymer latex, etc.) having a charge on the surface are mixed in a polar liquid such as water. There are cases where the particles are formed by being stabilized by strong electrostatic interaction and cases where 2) non-ionic colloid particles are formed by packing. The present invention is directed to the former ionic colloid particle system. is there.

The crystal plane spacing of colloidal crystals is much larger than that of atomic and molecular crystals, and is often used under experimental conditions (for ionic particle systems, the particle size is 0.1 to 1 μm,
In the case of the particle volume fraction of 10 ^-2 to 10 ^-1 ), it is on the order of the wavelength of visible light. For this reason, colloidal crystals are
It emits iridescent light called iridescence by agg diffraction, and has a specific absorption band (photonic band gap) for visible light. In recent years, attempts have been actively made to produce optical elements having novel characteristics using colloidal crystals based on these characteristics.

[0005] Colloidal crystals derived from ionic colloidal systems
As a method to control the generation,
Shear force was applied to the molecular latex / water dispersion system
[B. J. Ackerson and N.A. Clark, Phys. Rev. A
30, 906, (1984)] and electric field [T. Palberg, W. Moenc
h, J. Schwarz and P. Leiderer, J. Chem. Phys.Ten
2, 5082, (1995)], reversible crystallization experiments have been reported.
However, in applying these methods, the former
In this case, special equipment is required for applying the shear field.
And for the latter, impurity ions due to the electrode reaction
And there are difficulties such as hindering crystallization.
Seems to be. In addition, ionic colloidal crystals
Volume of the gel due to temperature change
Report on control of crystal plane spacing using crystallization [J. M. Weissm
an, H.B.Sunkara, A.S.Tse andS.A.Asher, Scien
ce,274, 959, (1996)].
Complicated steps are required for immobilization of
Attempts to produce crystals from disordered particle arrays have been attempted.
Not.

[0006]

SUMMARY OF THE INVENTION The main object of the present invention is to provide a technique capable of relatively easily producing colloidal crystals from various ionic colloid systems without requiring special equipment or complicated steps. To establish.

[0007]

Means for Solving the Problems The present inventor has now proposed:
The present inventors have found out that colloidal crystals can be reversibly formed by a change in temperature when a specific ionizing substance is coexisted in an ionic colloidal dispersion system, and have derived the present invention.

Thus, according to the present invention, as a means for achieving the above-mentioned object, a colloidal dispersion system in which colloidal particles having electric charges on the surface are dispersed in a liquid medium has a degree of dissociation in the liquid medium of which temperature is higher. A method for producing colloidal crystals is provided, wherein a weakly ionizing substance that changes with the change is added, and the colloidal particles are crystallized by external heating or cooling. A particularly preferred example to which the method of the present invention is applied is where the colloid particles are silica particles, the liquid medium is water, and the weakly ionizing substance is pyridine or a pyridine derivative.

Further, the present invention is directed to a colloid system which can be applied not only to the production of the above-mentioned colloidal crystals but also to various functional materials. That is,
The present invention also provides a colloid system comprising colloid particles having a charge on the surface, a liquid medium in which the colloid particles are dispersed, and a weakly ionized substance in which the degree of dissociation changes with a change in temperature in the liquid medium. .

[0010]

According to the method for producing colloidal crystals of the present invention, a weakly ionized substance (weakly electrolyte) whose degree of dissociation (degree of ionization) changes with a change in temperature is simply added to the ionic colloidal dispersion system. Thus, the ionic colloidal dispersion can be crystallized thermoreversibly by external heating or cooling. As described above, in an ionic colloid system, crystallization occurs with an increase in electrostatic interaction between particles, where the magnitude of the electrostatic interaction is determined by the effective surface charge density (σ _e) of the particles. ), Increased volume fraction of particles (φ), or decreased added salt concentration (C _s ) has been found by the present inventors [eg J. Yam
anaka, T. Koga, N. Ise and T. Hashimoto, Phys. R
ev. E 53, R 4314, (1996)]. According to the present invention, a weakly ionized substance whose dissociation degree changes with temperature change is added,
It is understood that the coexistence changes the σ _e (effective surface charge density) of the colloid particles depending on the temperature, and therefore, the crystallization of the ionic colloid system can be controlled by the temperature change.

Until now, the control of the σ _e value should be positively changed by changing the surface charge density of the colloid particles.
It has been performed by adding a strong ionizing substance (strong electrolyte) exclusively to the colloidal dispersion system. For example, we have also shown in previous experiments that sodium hydroxide N
An attempt was made to change the degree of dissociation of the weakly acidic silanol groups (Si-OH) on the surface of the silica particles by adding aOH [Phys. Rev. E 53, R 4314, (1996) mentioned above]. NaO
H is a strong base and its dissociation (NaOH → Na ⁺ + OH
^- ) Can be considered almost perfect regardless of the temperature.

The present inventor has noticed that the degree of dissociation of a weakly ionized substance depends on the temperature, which is different from the conventional idea, and utilized this for crystallization of an ionic colloid. For example, the degree of dissociation of pyridine (Py; dissociated with Py + H ₂ O → PyH ⁺ + OH ^{− in an} aqueous solution), which is a weak base, increases with increasing temperature (pK _b in a salt-free aqueous solution of pyridine determined by electric conductivity measurement _). The values were 9.28 and 8.53 at 10 and 50 ° C. and decreased linearly with temperature). Therefore, when Py (pyridine) is allowed to coexist in a colloidal dispersion system such as a silica colloidal dispersion system, it is considered that the σ _e value of the colloidal particles increases as the temperature rises. Moreover, the above-mentioned dissociation at various temperatures reaches an equilibrium state in a much shorter time than the time required for the temperature change of the system under normal use conditions. That is, the σ _e value is uniquely determined by the sample temperature and does not depend on the temperature history or the like up to that point, so that crystallization occurs thermoreversibly.

[0013] In the weakly ionized substance present invention may be used various weak base such as dissociation degree changes (increases or decreases), the weak acid or salt as the weak ionization material due to temperature changes. Hereinafter, the weak base, the weak acid, and the salt that can be used in the present invention are exemplified, but the weakly ionized substance used in the present invention is not limited to these.

Preferred weak bases include, for example, pyridine and pyridine derivatives (monomethylpyridine, dimethylpyridine, trimethylpyridine, etc.), which increase in the degree of dissociation with increasing temperature. These pyridines or pyridine derivatives have a pK _b value suitable for crystallization of silica particles, and are particularly preferred for use in the present invention because the change in pK _b value with temperature is sufficiently large. In addition, as a weak base,
Uracil, quinoline, toluidine, aniline (and derivatives thereof) and the like can also be used, and these also increase in the degree of dissociation with increasing temperature.

The weak acids used in the present invention include:
Acids whose degree of dissociation decreases with increasing temperature in an aqueous solution, for example, formic acid, acetic acid, propionic acid, butyric acid, chloroacetic acid, phosphoric acid, oxalic acid, malonic acid and the like can be mentioned. On the other hand, an acid such as boric acid or carbonic acid whose dissociation degree increases with increasing temperature can also be used. Further, the salts obtained by neutralization of the weak base and the weak acid as described above also have a temperature dependence in the degree of dissociation, and can be used as the weakly ionized substance in the present invention. Whether the degree of dissociation increases or decreases depending on the temperature depends on the magnitude relationship between the acid and the base.

Colloidal Dispersion System A particularly preferred example of a colloidal dispersion system to which the method for producing a colloidal crystal of the present invention is applied is a system in which fine silica particles are dispersed in water. When these silica fine particles are dispersed in water, the OH of the weakly acidic silanol group (Si-OH) covering the surface thereof is partially dissociated, and has a negative charge (O ⁻ ). Brass ions (H ⁺ ) called counter ions are distributed. Here, when an ionizing substance such as pyridine as described above is added to this system, the dissociation degree of the silanol group changes, and the charge density (charge amount per unit surface area) of the particles changes. Such a property that the charge density can be relatively easily controlled is an advantage of silica particles, and a colloid crystal can be prepared by using the same.

However, the method for producing a colloidal crystal of the present invention is not limited to the silica-water system, and the colloidal particles having a charge derived from a weak acid or a weak base on the surface are dispersed in a liquid medium, and the above-described weakly ionized material is dispersed. Is added, the ionized substance dissociates (ionizes) in the liquid medium, and the present invention can be applied to other ionic colloidal dispersion systems in which the charge on the surface of the colloidal particles can be changed.

That is, as long as the colloidal particles have a weak acid on the surface, they can be used in the same manner as silica. For example, fine particles of titanium oxide or carboxy-modified latex (latex having a carboxyl group on the surface) or the like can be used. Can be. Further, if the surface has a weak base, by adding a weak acid, a function similar to that of the silica + pyridine system can be exhibited. As the corresponding colloidal particles, aluminum oxide and amino groups are used. Latex and the like.

The present invention is also applicable to colloidal systems composed of globular proteins having both weak acids and weak bases and clay minerals. Furthermore, by a surface modification method such as introducing a weak base to the silica particle surface using a silane coupling agent having an amino group, a system containing various colloidal particles in which various weak acids and weak bases are introduced to the particle surface. The present invention can also be applied.

As for the liquid medium, if the dissociation group (charge-providing group) on the surface of the colloidal particles and the high dielectric constant capable of dissociating the weakly ionized substance (weak acid, weak base, salt) added can be exhibited, Liquids other than water can also be used. For example, formamides (eg, dimethylformamide) and alcohols (eg, ethylene glycols) can be used. These can be used as they are depending on the combination of the colloidal particles and the weak ionizing substance to be added, but are generally preferably used as a mixture with water.

Crystallization Method In order to form colloidal crystals according to the method of the present invention, a weakly ionized substance (weak base, weak acid, salt) is added to a colloidal dispersion system comprising colloidal particles and a liquid medium as described above. The system may be externally heated or cooled. In other words, when a weakly ionized substance whose degree of dissociation increases with increasing temperature is used, a colloidal crystal is generated by heating, while when a weakly ionized substance whose dissociation degree decreases with increasing temperature is used. Cooling produces colloidal crystals.

The colloidal dispersion system to which the weakly ionized substance is added is as follows:
Commercially available colloidal particles may be dispersed in an appropriate liquid medium such as water, or those synthesized by a sol-gel method or the like may be used. Generally, colloidal crystals are formed by the presence of a trace amount of salt (ionic impurity). Production is inhibited,
In preparing a colloidal dispersion system, sufficient desalting is required. For example, in the case of using water, first, dialysis is performed on purified water until the electric conductivity of the used water becomes substantially the same as the value before use, and then a sufficiently washed ion exchange resin (cationic resin) is used. And a mixed bed of an anion exchange resin) coexisting in the sample for at least one week to perform desalination purification.

In addition, attention must be paid to the size and distribution of the colloid particles. For example, in the case of silica particles, silica particles having a particle size of several thousand mm or more are not suitable because of remarkable sedimentation. A sample having a wide particle size distribution is unlikely to produce crystals, and it is desirable to use particles having a distribution of about 10% or less.

Next, a colloidal crystal can be formed by adding and coexisting a weakly ionized substance and causing a temperature change in the substance. In this case, as described above, the electrostatic interaction between the colloid particles that governs crystallization in the ionic colloid system depends on the effective surface charge density (σ) of the particles.
_In addition to _e ), it is also affected by the volume fraction (φ) of the particles and the added salt concentration (C _s ). Therefore, the amount of the temperature and the weakly ionized substance that crystallization occurs depends φ and C _s of the original colloidal dispersion system. For example, pyridine (P
When adding y), when compared at a constant temperature and φ conditions, generally, crystallization occurs at a higher Py concentration as C _s value is higher condition.

In general, a colloidal dispersion system having φ (volume fraction of colloidal particles) of about 0.01 to 0.05 and C _s (addition salt concentration) of about 2 to 10 μM is prepared, and a weakly ionized substance is added thereto. Added. To this end, the specific gravity of the colloid particles is determined by a picometer method or the like, and the φ value of the purified colloidal dispersion system is determined by the absolute drying method using this value. This is diluted with a liquid medium such as purified water to prepare a dispersion having a predetermined φ value. φ value is
The calculation is performed so that the colloidal crystal has a crystal plane spacing according to the desired characteristics. Further, if necessary, to control the C _s value by adding a low molecular salt solution such as NaCl.

In the above sample preparation, it is necessary to avoid contamination by ionic impurities as much as possible. In this regard, the use of glass containers and equipment is avoided because basic impurities elute from the glass into the water and increase the σ _e value of the particles. Since carbon dioxide in the air is dissolved in water to generate carbonic acid, it is desirable to perform the preparation under an atmosphere such as nitrogen. Further, containers and equipment should be thoroughly washed with purified water (electrical conductivity 0.6 μS / cm or less) before use.

The colloid system prepared as described above may be heated or cooled, the presence or absence of crystals may be confirmed, and the crystallization temperature may be evaluated. For confirmation of crystal formation, X-ray scattering, optical microscopy, spectrophotometry (reflection or transmission spectrum measurement) and the like can be applied in addition to observing iridescence.

Effects of the Method for Producing Colloidal Crystals of the Present Invention In the method of the present invention, crystallization of colloidal particles can be caused thermoreversibly by simple means of simply heating or cooling the system from the outside. This crystallization can be controlled by changing the concentration of a weakly ionized substance such as pyridine, but in this case, the concentration of the weakly ionized substance needs to be strict as in the case where a strong base such as NaOH is added. Absent. That is, since the concentration of the dissociated species is very small compared to the concentration of the weakly ionized substance added, the change in the surface charge density (σ _e ) of the colloidal particles with respect to the concentration of the weakly ionized substance is more gradual than when a strong base is added. It is also an advantage that a certain concentration range is allowed.

Further, in the present invention, since the system can be maintained in a closed system, a high-performance colloidal crystal can be obtained by preventing contamination by ionic impurities. Thus,
INDUSTRIAL APPLICABILITY The present invention is expected to be widely applied to the manufacture of optical elements and the like whose light response characteristics can be controlled.

Other Uses of Weakly Ionized Substance-Containing Colloidal System As described above, the method for producing a colloidal crystal of the present invention comprises a colloidal particle having a charge on its surface, a liquid medium in which the colloidal particle is dispersed, and the liquid medium. It is based on using a colloidal system containing a weakly ionized substance whose degree of dissociation changes with temperature change, and applying a temperature change to the outside to generate colloidal crystals. Such a weakly ionized substance-containing colloidal system reversibly crystallizes due to a change in temperature and changes its physical properties. By utilizing this property, it is possible to apply the present invention to applications other than the production of colloidal crystals.

For example, it is possible to develop a novel heat-sensitive material (heat-sensitive paint, temperature sensor, etc.) utilizing the fact that the physical property changes due to a temperature change. Also, if a system in which the colloid system is crystallized by increasing the temperature is used, the viscosity of the system is expected to increase with temperature. On the other hand, in ordinary simple liquids, the viscosity generally decreases monotonically as the temperature increases. Utilization of such a unique viscosity-temperature characteristic is expected to be applied to, for example, improvement of the temperature characteristic of a liquid (oil for clutch, etc.) used in a conventional stress transmission system.

The contents of the colloidal particles, the liquid medium and the weakly ionized material in the weakly ionized material-containing colloidal system when applied to these applications are essentially the same as those described in connection with the method for producing a colloidal crystal. It is. However, in these applications, the colloidal system containing a weakly ionized substance is a colloidal solution (sol) as in the case of producing colloidal crystals.
In addition, it may take a gel state as needed.
Therefore, the colloid system in this case refers to both the sol state and the gel state.

[0033]

EXAMPLES In order to further clarify the features of the present invention, an example is shown in which pyridine (Py) was added to a silica-water colloid system to obtain a crystallization phase diagram. However, the present invention is not limited by this example. It is not something to be done. Nippon Shokubai Co., Ltd. silica colloid particles KE-P10W (diameter 0.12 ± 0.01 μm, specific gravity 2.24)
Was sufficiently purified by a dialysis method and an ion exchange method and used for the experiment. The _e value without Py determined by electrical conductivity measurement was about 0.1 μC / cm ² . The C _s value was determined as the sum of the concentration of the added salt (NaCl) and the concentration of ionic impurities (2 μM) in the water used.

Under the conditions of φ = 0.03 and C _s = 7 μM, the crystallization phase diagram was determined by observing iridesense at various Py concentrations. The results are shown in FIG. White and black circles indicate conditions under which iridescence was observed and those under which iridescence was not observed, and correspond to a crystalline phase and a disordered phase, respectively. In the case of this example, by coexisting Py of the order of 10 ⁻⁴ M, it was possible to obtain a silica colloid dispersion system that crystallized by heating in a temperature range of about 0 to 50 ° C. The crystallization was thermoreversible, and upon cooling the sample crystallized by heating, the system became disordered.

[Brief description of the drawings]

FIG. 1 is a phase diagram showing conditions under which pyridine is added to a silica-water colloidal dispersion system to form colloidal crystals according to the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takeharu Hashimoto 19, Yoshida-Nakaoji-cho, Sakyo-ku, Kyoto-shi, Kyoto (56) References JP-A-62-7430 (JP, A) JP-A-9-913 (JP, A) JP-T3-504462 (JP, A) Chem. Phys. Vol. 94, No. 7, PP. 5222-5225 Baifukan Co., Ltd. Colloid Chemistry First Edition May 30, 1967 Page 257 Creative Science and Technology Promotion Project 1997 Creative Science and Technology Research Report (Tokyo) Part 4 Abstracts Collection of Colloid Polym Sci, Vol. 266, no. 2, pp. 173-179 (1988) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 13/00 B01D 9/02 611 C01B 33/14

Claims (3)

(57) [Claims] 1. A colloidal particle having a charge on its surface is dispersed in a liquid medium, and the volume fraction of the colloidal particle is from 0.01 to 0.01.
Adding a weakly ionizing substance whose dissociation degree in the liquid medium changes with a temperature change to a colloidal dispersion system of 0.05 and crystallizing the colloidal particles by external heating or cooling. A method for producing a colloidal crystal. 2. The method according to claim 2, wherein the colloidal particles are silica particles, the liquid medium is water, and the weakly ionizing substance is pyridine or a pyridine derivative. 3. The method according to claim 1, wherein the surface has a charge and a volume fraction of 0.01 to
A colloidal particle of 0.05, a liquid medium in which the colloidal particle is dispersed, and a weakly ionized substance in which the degree of dissociation changes with the temperature change.
A colloid system characterized by reversible crystallization .