JPH0799138B2 - Driving method for mechanochemical materials - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for driving a mechanochemical material which reversibly swells and contracts in response to a change in ion concentration, and more specifically, relates to a method for driving the material by electrical means. The present invention relates to a driving method of swelling and contracting by.

[Conventional technology]

It is known that the swelling and shrinkage of the crosslinked polymer material can be controlled by the chemical environment, and direct conversion of chemical energy into mechanical energy using a mechanochemical material composed of such a crosslinked polymer material. Has been tried. For example, a method of filling a cylinder with particles of a cross-linked polymer material that swells and contracts with an alkali and an acid and increasing the load has been reported by Matsushima and Mori [Matsushima and Mori; Production Research, 15 , 96 (1963)]. . In addition, pioneering research has been conducted by General Electric Company of the United States to generate an electric field around a crosslinked polymer material without supplying acid or alkali as a liquid [RP Hamlen, CEK
ent, SNShafer; Nature, 206 , 1149 (1965)]. Furthermore,
It has been attempted to form a cell that changes the pH of an aqueous solution by passing an electric current using a cation exchange membrane and an anion exchange membrane, and to expand and contract the mechanochemical material in this cell [A. Fragala et al; Electrochimica Acta, 17 , 150
7 (1972)]. In addition, Tanaka reported that a gel immersed in a solvent contracts by applying a voltage to a pair of electrodes made of the same material sandwiching the gel, and the amount of contraction is controlled by the applied voltage [ T. Tanaka et al; Scien
ce, 218, 467 (1982)]. As described above, actuators and the like using a cross-linked polymer material as a working substance have been studied for reasons such as low specific gravity, light weight, and mechanical properties similar to muscle.

On the other hand, mechanochemical materials of the type that swell and contract by interacting with specific ions have been found, and these materials have been driven by the method as described above.

That is, for example, a method is known in which a mechanochemical material that interacts with hydrogen ions is immersed in an aqueous solution, and an acidic solution or an alkaline solution is added to the aqueous solution to change the hydrogen ion concentration in the aqueous solution.

Further, for example, a mechanochemical material that interacts with copper ions is immersed in an aqueous solution, and a copper ion-containing solution is added,
A method of changing the copper ion concentration of the aqueous solution is known.

[Problems to be solved by the invention]

However, the conventional methods described above each have problems.

The method of driving without using electric means, that is, the method of directly adding ions from the outside is inferior in that the material is driven quickly and the driving device has a simple mechanism.

Therefore, judging from the above point of view, it is preferable to use an electric means for driving the mechanochemical material, but the conventional method for driving the mechanochemical material by applying a voltage to the material is also applicable. For example, there are the following problems.

The mechanism of the phenomenon of mechanical materials swelling and contracting when they are subjected to an electrical action still has uncertainties today, but if current is not applied, such swelling and contraction will not occur, and It has become clear that when such an electric current is applied, a gas or a low-conductivity deposited film is generated on the electrode.

For example, according to a conventional report, the voltage applied to the electrodes for electrically driving these crosslinked polymer materials is 1 volt or more and up to about 30V. As the liquid in which the cross-linked polymer material is dipped, a liquid mainly containing water is used. Therefore, if a voltage of 1.23 V or more, which is the theoretical decomposition voltage of water, is applied to such liquid, it is unavoidable that gas is generated from the system due to the decomposition of water. For example, if it is unavoidable to generate gas when the actuator is driven, the entire actuator cannot be sealed, and the usage environment is limited.
Further, when repeatedly used, it is necessary to periodically replenish water that is decomposed and lost, which causes a problem in the life and maintainability of the actuator. Further, an actuator that generates an acid / hydrogen mixed gas (detonation) from water when driven has a problem in safety. If a sufficiently dehydrated non-aqueous solvent system is used as the liquid, the above-mentioned problem of the explosion noise can be avoided, but the electrolysis of the solvent or solute occurs depending on the applied voltage. If the decomposition product is a gas, it causes the same problems as the electrolysis of water described above. Further, even when the decomposition products are solids or liquids, they may cover the surface of the electrode and form a film of low conductivity, which is an undesirable phenomenon.

The present invention has been made in view of the above-mentioned problems, and its object is to prevent generation of gas due to a chemical reaction in an electrode,
Another object of the present invention is to provide a method for driving a mechanochemical material that does not generate deposits on the electrode that would interfere with the electrical action of the electrode, is stable in reversible driving, and can be performed quickly and easily.

[Means for solving problems]

The above object of the present invention is to provide a method for driving a mechanochemical material having a polymer that reversibly swells and contracts in response to a change in the concentration of a specific ion in a liquid that it contains. A battery is composed of electrodes,
The mechanochemical material and the electrolytic solution are allowed to coexist, and the battery is charged or discharged through the electrode to reversibly change the concentration of the specific ion in the electrolytic solution to obtain the mechanochemical material. It is achieved by a driving method of a mechanochemical material characterized by swelling and shrinking.

The mechanochemical material that can be driven by the method of the present invention is
It is a mechanochemical material having a polymer that swells and contracts reversibly in response to changes in the concentration of specific ions in the contained liquid.

Several mechanisms of swelling and shrinking of mechanochemical materials with changes in ion concentration have been described, but for example, mechanochemical materials composed of polymers having weakly acidic or weakly basic functional groups are A change in the ion concentration causes an increase or decrease in the charge density on the polymer chains, so that the magnitude of the interaction between the polymer chains changes mainly and the degree of swelling of the entire mechanochemical material changes. In addition, a mechanochemical material composed of a polymer material having a functional group capable of relatively strong interaction such as ionic bond and coordination bond with a metal ion such as a carboxyl group interacts with those ions. By doing so, the solvation state of the functional group is changed, or a new cross-linking point is formed in the polymer through these ions, so that the swelling degree also changes according to the change in the ion concentration. In addition, even in a mechanochemical material composed of a polymer material that does not have a functional group that strongly interacts with ions, a change in the ion concentration causes a difference in the osmotic pressure of the liquid inside or outside the material,
The degree of swelling changes under the influence of, for example, changing the number of solvent molecules that are solvated with a relatively polar functional group in the polymer structure.

That is, as the mechanochemical material that can be driven by the method of the present invention, it has a functional group on the main chain or side chain that can interact with a specific ion in the electrolyte solution to form a bond such as an ionic bond or a coordinate bond. Polymers can be mentioned. As such a polymer, for example, a polymer having one or more polar groups such as a carboxyl group, a sulfonic acid group, a hydroxyl group, an amino group, an imino group, and a carbonyl group in a part of its constitutional unit may be used. it can. The amount of these polar groups present is preferably in the range of 50 microequivalents or more and 50 milliequivalents or less per dry weight of the mechanochemical material. That is, when the amount of the polar group present is less than the range, even if the bond between the polar group and the above-mentioned specific ion is generated, the abundance ratio with respect to the whole polymer is small, so that the properties of the polymer can be sufficiently changed. As a mechanochemical material, it cannot be effectively deformed in the electrolytic solution. Also, if the amount of polar groups present exceeds the above range, the amount of the above-mentioned specific ions required to sufficiently change the properties of the polymer increases, so the amount of these ions can be electrically controlled by practical means. Becomes difficult to do.

On the other hand, the ionic species whose concentration is controlled to swell and shrink the mechanochemical material as described above can be any of cation species, anion species or inorganic ionic species, organic ionic species, etc., but of course, It is necessary that the above-mentioned mechanochemical material be capable of interacting with a polar group contained in its molecular structure to form a bond such as an ionic bond or a coordinate bond. Further, it is desirable that the binding equilibrium of these can be greatly extended with the control of the external ionic species concentration.

For example, when hydrogen ions are used as the ion species, the equilibrium of the bond between the polar group and the hydrogen ion depends on the value known as the acid dissociation constant of the polar group or the conjugate acid of the polar group. Can be evaluated.

The solvent of the electrolytic solution that can be used in carrying out the driving method of the present invention is not particularly limited as long as it is a polar solvent capable of solvating the ionic species as described above, but for example, water. , Or a mixed solvent mainly containing water is preferably used. When water or a mixed solvent containing water as a main component is used, the hydrogen ion concentration that can usually be achieved is in the range of 1 mol / l or 10 ^-4 mol / ^{l, and} 10 ^-1 mol if easy control is taken into consideration. / ^Or less, 10 ^-3 mol / or more. Therefore, it is desirable that the acid dissociation equilibrium of the polar group of the polymer that constitutes the mechanochemical material or the conjugate acid of the polar group of the polymer that constitutes the mechanochemical material greatly changes due to changes in the hydrogen ion concentration in this range. The constant should be 10 ^-2 mol / or less, 10 ^-12 mol / or more, and particularly preferably 10 ^-3 mol / or less, 10 ^-3 mol / or less.
The range of ^-11 mol / or more is desirable. When using water as a solvent of the electrolytic solution, or a mixed solvent mainly containing water,
Considering the hydroxide ion, which is a conjugate base for the solvent instead of the hydrogen ion, for the same reason, as the acid dissociation constant of the polar group or the conjugate acid of the polar group of the polymer that constitutes the mechanochemical material. It will be clear that suitable ranges are similar to those mentioned above.

Also, when the solvent of the electrolytic solution used in the present invention contains no or almost no water, there is an optimum range of acid dissociation constant depending on each solvent.

As with hydrogen ions, using other ionic species,
If the ion used can form an ionic bond or a coordinate bond with the polar group of the polymer constituting the mechanochemical material, the mechanochemical material can be driven according to the present invention. And the complex dissociation constant between the ion species and the ionic species must be appropriate values. The reason is that when the concentration of ionic species is controlled by the electrochemical method of the present invention, the concentration range to be used is usually 10 ^-1 mol / or less, 10 ^-7 mol / or more, which is usually practical. In the concentration range above this level, a large amount of electricity is required to obtain a significant concentration change, and therefore sufficient deformation of the mechanochemical material cannot be obtained unless the current density or the energization time is increased. In addition, there is a drawback in that it is difficult to avoid the influence of other coexisting ion species if it is intended to control a small amount of ions of 10 ^-7 mol / or less. (The above-mentioned hydrogen ions can be controlled at a level of 10 ^-7 mol / or less,
This is because it is possible to equivalently control the hydrogen ion concentration by controlling the concentration of a conjugated base such as a hydroxide ion at a relatively high concentration). It is desirable that the complex dissociation constant with the ion of 10 is within a certain range, and the range is 10 ^-1 mol / or less,
^-11 mol / mol or more is preferable.

The complex formation reaction generally proceeds through a plurality of stages, and the complex dissociation constant referred to here means a sequential complex dissociation constant for each of those stages.

The electrode that can be used in the present invention is capable of electrochemically reversibly changing the concentration of the above ions in the electrolytic solution, and is limited as long as it has this property. Not a thing. However, since it is desirable that a gas such as hydrogen or oxygen is not generated by the reaction on the electrode, in the electrolyte used,
It is desirable to use a combination of ions and electrodes that can control the ion concentration at a potential that does not exceed the generation potential of hydrogen, oxygen, and the like. Furthermore, at least a pair of electrodes is used to pass an electric current through the system, but it is necessary that all the electrodes are not made of the same material. The reason is that when a current is supplied from a single power source with one electrode as the anode and the other as the cathode, the ions are supplied to the electrolytic solution from one electrode, but the same type of ions are applied to the other electrode in principle. This is because the same amount is consumed, and as a result, the purpose of changing the ion concentration is not achieved. Therefore, the electrode pair to be used in the driving method of the mechanochemical material of the present invention is such that the ion species released into the electrolyte solution or supplied from the electrolyte solution by the electrode reaction that controls the electrode potential of one electrode is the same as the other ion species. It must satisfy the condition that it does not participate in the electrode reaction, which is consumed in the same amount on the electrode. This can be achieved more specifically by satisfying the following conditions.
(1) As the electrode, one in which the anion in the electrolytic solution participates in the electrode reaction and one in which the cation participates in the electrode reaction are used, and an electric current is passed between them. (2) The material is selected such that the potential at which the anion is oxidized on the opposite electrode is more positive than the potential of the electrode reaction involving the cation on that electrode. (3) Similarly, the material is selected so that the potential at which the cation is reduced on the opposite electrode is more negative than the potential of the electrode reaction involving the anion on that electrode.

Since it is necessary that the concentration of the ion be sufficiently changed by passing an electric current, the anion and the cation are not formed as a salt between them or between the ion previously dissolved in the electrolytic solution. , Must be one that can be dissolved at a sufficient concentration in the solvent used for the electrolyte.

If a pair of electrodes selected with the above points in mind is dipped in a suitable electrolyte containing the ions corresponding to the electrodes, a battery is formed and a potential difference develops between the electrodes (of course in special cases. The potential difference can be zero). By charging or discharging such a battery in reverse, an electrochemical reaction proceeds on each electrode, and the concentration of specific ions in the electrolytic solution changes. Therefore, if a mechanochemical material having a property of swelling and contracting in accordance with a change in the concentration of the ions is present in the electrolytic solution, it can be expanded and contracted.

As the electrode used in the present invention for electrochemically controlling various ion concentrations as described above, conventionally known electrodes may be used. That is, as an electrode for releasing or recovering a specific cation into the electrolytic solution, for example, a metal electrode corresponding to the cation can be used. When a protic solvent is used as the solvent of the electrolytic solution, it is necessary that the ionization tendency of the metal used as the electrode in the solvent is smaller than that of hydrogen. If the metal electrode acts as an anode, the cations of the metal are released into the electrolyte, and if it acts as the cathode, the cations of the metal in the electrolyte are deposited on the metal electrode. Further, when an electrode composed of a mixture of two sparingly soluble salts of two metals having an anion in common and a first metal is used, the ion concentration of the second metal in the electrolytic solution can be increased by applying an electric current. It is known that it can be increased or decreased, and this electrode can be used even when the ionic tendency of the second metal is larger than that of hydrogen.

Further, as an electrode for controlling the concentration of a specific anion in the electrolytic solution, a metal that forms a salt that is sparingly soluble in the solvent used together with the anion is selected, and the surface of the metal is loaded with the sparingly soluble salt. What you have to use. In this type of electrode, if it functions as a cathode, the salt decomposes, and an anion is released into the electrolytic solution. Conversely, if it functions as an anode, the anion in the electrolytic solution becomes a salt and deposits on the electrode.

When there are ions that generate new ions by the oxidation or reduction reaction in the electrolytic solution, the electrode itself is made of a material that is electrochemically inactive, and electrons are transferred to and from the ions. The concentration can be controlled only by

Further, an organic material can be used as the electrode. That is, polyaniline, which is known as a conductive polymer material,
Polymers such as polypyrrole, polythiophene, polyphenylene, polyazulene, and polyacetylene are known to reversibly release and absorb anions or cations along with the oxidation-reduction reaction of polymer chains. Alternatively, other electrode materials can be used as a substrate, and the surface can be coated with these conductive polymer materials to form electrodes, and the concentration of anions or cations can be controlled by energizing in an electrolytic solution. be able to.

In addition, a so-called surface-modified electrode in which a substance capable of performing a redox reaction such as quinones and phenothiazines is carried on an electrochemically inactive electrode surface is also capable of releasing hydrogen ions, for example, by passing an electric current. -It can be used because the import is reversible.

In this way, it is possible to drive the mechanochemical material by controlling the ion concentration in the electrolytic solution by passing an electric current through the pair of electrodes, and if an electrochemically reversible system is selected,
Reversible drive of mechanochemical materials is possible. It is clear that this method can be applied to new actuators and the like. In addition, it is also one of the preferred embodiments of the present invention to use a large number of electrodes for the purpose of rapidly and evenly changing the ion concentration in the electrolytic solution.

〔The invention's effect〕

As described above, according to the present invention, the mechanochemical material can be driven by a simple electric operation (charging and discharging of the battery), so that the material can be driven quickly and easily. Furthermore, by using an electrode made of a material that can easily change the ion concentration in the electrolytic solution, it is possible to drive a mechanochemical material effectively with a small operating current, and a gas (hydrogen, etc.) generated by an electrochemical reaction or The ion concentration in the solution can be reversibly controlled without the generation of low-conductivity deposits on the electrodes.

In addition, since there is no generation of gas, the drive mechanism can be completely sealed, and when it is used for an actuator, for example, it is possible to prevent volatilization of mechanochemical materials and volatile substances in the electrolyte solution, and It is not necessary to replenish these volatile substances, and the usage environment can be expanded.

In addition, since a low-conductivity deposit is not generated on the electrode, a sufficient current can be supplied from the electrode to the electrolytic solution at a suitable time, and the mechanochemical material can be rapidly driven.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 FIG. 1 is a sectional view showing an example of an apparatus used in the method for driving a mechanochemical substance according to the present invention.

Reference numeral 1 is an electrode, 2 is an electrode made of a material different from 1, 3 is a mechanochemical material, and 4 is an electrolytic solution.

A copper plate was used for the electrode 1. As the electrode 2, a platinum plate having a polyaniline layer formed on the surface thereof by electrolytic polymerization at 25 ° C. and 6 mA for 20 minutes using sulfate ion as a counter anion was used.
As the electrolytic solution 4, 0.02 mol / aqueous solution of sodium sulfate was added with sulfuric acid, and the aqueous solution whose pH value was adjusted to about 5.8 was degassed and used.

Acrylamide 0.6 mol /, N-methylol acrylamide 0.12 mol /, sodium acrylate 0.12 mol /
(30 ml) of the monomer aqueous solution was prepared, 12 μm of tetramethylethylenediamine and 5 mg of ammonium persulfate were added as an initiator, and radical polymerization was performed at 3 ° C. for 90 minutes to obtain a polymer solution. After filtering and defoaming this solution, it is extruded into a saturated aqueous sodium sulfate solution from a nozzle with a diameter of 0.4 mm to coagulate,
Filiform. The filamentous polymer was vacuum dried at 150 ° C. for 3 hours, and then thoroughly washed with a solution having the same composition as the electrolytic solution 4 to collect 50 filamentous polymers, a length of 12 mm and a diameter of about 0.
7 mm cylindrical mechanochemical material 3 was used.

The above materials are arranged as shown in FIG. 1 and placed in an insulative container 5, and a connector 7 is adhered to the free end of the mechanochemical material 3, and then two containers are attached to the silicone flexible film 6. Closed.

When a predetermined amount of electricity of 0.72C is applied to the device thus prepared with the electrode 1 as the anode and the electrode 2 as the cathode, the concentration of copper ions in the electrolytic solution increases and the mechanochemical material 3 becomes about 70% of the initial length. It was observed that the connector 7 was pulled up and the connector 7 was pulled up. Next, when the same amount of electricity as before was applied in the opposite direction, the copper ion concentration decreased and the length of the mechanochemical material 3 recovered to about 98% of the initial length. In this way, the energization and the energization in the opposite direction were repeated 5 times, and it was confirmed that reversible expansion and contraction of the mechanochemical material occurred and during this period, generation of bubbles was not visually observed in the container.

Example 2 An electrode 1 was prepared by applying a silver chloride paste on a silver plate and drying it at 120 ° C. for 90 minutes. In addition, an electrode 2 was prepared by applying a paste of an equal mixture of lead oxalate and calcium oxalate onto a lead plate and firing it at 120 ° C. for 60 minutes.

Degassed potassium chloride 0.033 mol / water solution as electrolyte 4
As the mechanochemical material 3, the same material as that used in Example 1 was used after being sufficiently washed with 0.033 mol / potassium chloride aqueous solution. The above is the same as the first embodiment.
When the device of the form shown in the figure is used and a predetermined amount of electricity of 1.2 C is passed between the electrodes 1 and 2, the Ca ²⁺ ion concentration in the electrolytic solution increases and the mechanochemical material 3 contracts in Example 1. It was observed almost the same as. Also in the device of this example, the mechanochemical material reversibly expanded and contracted depending on the direction of the electric current, and at this time, generation of bubbles was not recognized in the device.

Example 3 Two platinum films were irradiated with ultrasonic waves in a suspension of alumina powder to roughen the surface. One sheet was subjected to electrolytic polymerization of pyrrole in the presence of chloride ions for 30 minutes at 25 ° C. and 4 mA to form a chloride-doped polypyrrole film on the surface. The other one is electrolytic polymerization of pyrrole in the presence of potassium polystyrene sulfonate having an average molecular weight of about 70,000 for 40 minutes at 25 ° C. and 5 mA to form a mixed film of polystyrene sulfonate and polypyrrole on the surface. In the same solution, an amount of electricity corresponding to 8% of the amount of electricity required for electrolytic polymerization was passed in the opposite direction to partially reduce the mixed film. The two electrodes thus created were designated as electrode 1 and electrode 2, respectively.

Also, an aqueous solution of 3 × 10 ⁻³ mol of potassium chloride was used as the electrolytic solution 4.

30 ml of a monomer aqueous solution containing 0.6 mol of N-isopropylacrylamide / 0.12 mol of N-methylolacrylamide / 0.08 mol of sodium acrylate was prepared, and polymerization, coagulation, heating and vacuum drying were carried out in the same manner as in Example 1, and finally. Was washed with 3 × 10 ⁻³ mol / potassium chloride aqueous solution to obtain mechanochemical material 3.

Using the above-mentioned materials, otherwise the same as in Example 1,
The apparatus has the configuration shown in FIG. When a current is passed between the electrodes 1 and 2 in an air thermostat at 32.7 ° C, the concentration of potassium chloride in the electrolytic solution changes and the mechanochemical material 3 is considered to be most contracted. The same drive results as in Example 1 were obtained, except that the length of was about 78% of the initial length. In addition, generation of bubbles was not recognized in the apparatus.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an apparatus used in the method for driving a mechanochemical material according to the present invention. 1, 2 ... Electrode 3 ... Mechanochemical material 4 ... Electrolyte 5 ... Container 6 ... Flexible film 7 ... Connection tool

Claims (5)

[Claims] 1. A method for driving a mechanochemical material having a polymer that reversibly swells and contracts in response to a change in the concentration of a specific ion in a contained liquid, wherein an electrolytic solution containing the specific ion and a plurality of electrodes are used. A battery is constituted, the mechanochemical material and the electrolytic solution coexist, and the concentration of the specific ion in the electrolytic solution is reversibly changed by charging or discharging the battery through the electrode, A method of driving a mechanochemical material, which comprises swelling and shrinking the mechanochemical material. 2. At least one of the plurality of electrodes contains a conductive polymer, and by charging and discharging the battery, the specific ions are reversibly doped and dedoped into the conductive polymer, The method for driving a mechanochemical material according to claim 1, wherein the ion concentration of the specific ion in the electrolytic solution is reversibly changed. 3. The specific ion is a metal ion, at least one of the plurality of electrodes contains a metal forming the metal ion, and the metal is oxidized and reduced by charging and discharging the battery, The method for driving a mechanochemical material according to claim 1, wherein the concentration of the metal ion in the electrolytic solution is reversibly changed. 4. The battery according to claim 1, wherein the specific ion is an anion, and at least one of the plurality of electrodes includes a metal and a salt composed of the metal and the anion, the salt being sparingly soluble in the electrolytic solution. The method for driving a mechanochemical material according to claim 1, wherein the concentration of the anion in the electrolytic solution is reversibly changed by charging and discharging. 5. The first specific ion is a metal ion, and at least one of the plurality of electrodes has a mixture of a sparingly soluble salt of a first metal and a second metal having a common anion in the electrolytic solution. A second metal is a metal that constitutes the metal ions, and the concentration of the metal ions in the electrolytic solution is reversibly changed by charging and discharging the battery. 2. A method for driving a mechanochemical material according to item 1 of the above.