JPH0686864B2 - Sealed mechanochemical element - Google Patents

Description

TECHNICAL FIELD The present invention can reversibly expand and contract by changing the acidity in a solution, and can be used for robots, artificial legs, artificial hands, artificial hearts, chemical engines, switches, sensors, and The present invention relates to a mechanochemical element that can be used in a wide range of industrial fields as a power source for presses and jacks.

Conventional technology The mechanochemical reaction that can directly convert chemical energy into mechanical energy is characterized by its small size, light weight, high efficiency, flexibility, low pollution, and other medical devices such as artificial muscles and artificial legs of robots and artificial hearts. It was thought to be very promising, and research and development became active. At present, insoluble gels made of organic polymer materials have the highest responsiveness, and expansion and contraction with respect to inputs such as acidity, salt concentration, electricity, light, and heat have been investigated. For example, a gel in which polymethacrylic acid and polyvinyl alcohol are partially polymerized and insolubilized has properties such as a stretching rate of 20 to 35%, a response speed of several minutes, and a tensile strength of about 1000 times its own weight due to changes in acidity. Has been obtained. In addition, collagen, which is a biological substance, has similar characteristics with changes in salt concentration. A chemical engine (USP.3,32) that utilizes expansion and contraction of collagen fibers
1,907) has been prototyped.

Problems to be Solved by the Invention By the way, as a means for obtaining a change in acidity, there is a method by electrolysis of water. According to the reaction formula shown below, the anode becomes acidic while generating oxygen gas, and the cathode becomes alkaline while generating hydrogen gas, and oxygen and hydrogen gas are generated from any of the electrodes in proportion to the amount of electricity supplied. . Therefore, it is impossible to seal the mechanochemical element, which is a problem from a practical point of view. In addition, the release of gas causes a decrease in water and the need to replenish water.

Anode _{2H 2 O → O 2 + 4H} + + 4e ...... (1) E 0 = 1.228-0.0591pH cathode _{4H 2 O + 4e → 2H 2} + 4OH - ...... (2) E 0 = 0-0.0591pH to solve the problem Means As an electrochemical reaction, the acidity of the solution is reversibly changed by using a metal redox reaction as described below. That is, the reactions of the equations (3) and (4) are used instead of the equations (1) and (2).

Hg + H ₂ O = HgO + 2H ^+＋ 2e …… (3) HgO ＋ H ₂ O ＋ 2e ＝ Hg ＋ 2OH ⁻ …… (4) In this way, H ⁺ and OH ⁻ without generating oxygen or hydrogen gas.
Can be created to change the acidity.

In this case, it is not preferable because it is necessary to use an ion exchange membrane when acidic and alkaline reactants such as metal oxides and metals are dissolved. As a matter of course, since these reactions need to occur before the oxygen and hydrogen generation reactions, the standard redox potentials are 0 and 1.228V VS.NHE.
It is a necessary condition to be in between.

As an electrochemical reaction system that satisfies these conditions, the above Hg / H
In addition to gO, there are Hg / Hg (OH) ₂ , Pd / Pd (OH) ₂ , Pt / PtO. The reaction formulas at the anode of these systems and the standard redox potential and the potential change due to acidity are shown.

_{Hg + 2H 2 O = Hg (} OH) 2 + 2H + + 2e E 0 = 1.034-0.0591pH Pd + H 2 O = PdO + 2H + + 2e E 0 = 0.897-0.0591pH Pt + H 2 O = PtO + 2H + + 2e E 0 = 0.980-0.0591pH The above The equilibrium potential of Eq. (3) for Hg / HgO is as follows.

E ₀ = 0.926-0.0591 pH action Since these electrochemical reactions can be used to reversibly change the acidity without the generation of gas, it is possible to make a sealed device. Therefore, an artificial muscle and a mechanochemical element that can be easily maintained and handled can be provided.

Example First, a 3 wt% aqueous solution of polymethacrylic acid (molecular weight of about 8000) and 3 wt% of polyvinyl alcohol (molecular weight of about 1800)
Mix with the aqueous solution in a weight ratio of 1: 3, and mix this mixture with 10 cm ³
Put in a petri dish with a diameter of 12 cm, and dried at about 45 ° C.
It was peeled from the container and cut into a width of 5 mm and a length of 70 mm. Thickness is about
It was 30 μm. Then, the mixture was kept at about 115 ° C. for about 2 hours to polymerize it to make it insoluble. Eighty such films were produced, bundled, and then immersed in water to swell. This is about 10
It was filled in a rubber tube having a diameter of 10 cm and a diameter of 10 mm. Then,
Mercury oxide electrodes containing 0.4 g each of mercury oxide (HgO) and mercury were inserted at both ends. Then, both ends of the tube were sealed in a state where the bundle of films and the electrodes were connected to each other so that the liquid did not leak to the outside of the rubber tube.

The mercury oxide electrode was manufactured by using a platinum wire (0.2φ) as the electrode core material, adding about 3% of fluororesin dispersion as the binder, and drying and molding at a pressing pressure of 500 kg / cm ³ . The size was 3 mm × 10 mm and the thickness was about 2 mm, and the theoretical filling capacity was 200 mAh in both the oxidation and reduction directions.

FIG. 1 shows a schematic cross-sectional view of an element for observing that the central portion moves left and right by energization by bending it from the central portion to form a bimetal shape. Further, FIG. 2 is a schematic cross-sectional view of the element for fixing both ends of the element and observing that the metal fitting fixed to the central portion moves by energization. In the figure, 1 and 3 are Hg / HgO electrodes, 2 and 4 are these electrode terminals, 5 is the elastic film, 6 is a rubber outer case, 7 is a central metal fitting fixed to the outer case, and 8 is 0.05. Electrolyte solution of M sodium chloride solution.

A direct current voltage of about 3 V was applied between both electrodes, and the change in the rotation angle of the tip of the bimetal-shaped element shown in FIG. 1 and the movement speed of the central metal part of the element shown in FIG. 2 were measured. Curves A and B are shown in the figure respectively. From curve A, left 30 ° to right
It turns out that 60 ° up to 30 ° rotates in about 5 minutes. On the other hand, from curve B, the central part is 10mm to the left and right, that is, 20mm in total.
Showed the move. This can be repeated, during which the current changed regularly between 2 and 20 mA.

The above example was the case where Hg / HgO electrodes were used for both electrodes, but it is possible to seal using any of the electrode reactions shown above, and similar effects occur with other mechanochemical materials. It was Furthermore, the response time could be further shortened by making the electrode larger than that of this example, or by leaving only the central portion and using the electrode.

As a result of the invention, since the mechanochemical element can be hermetically sealed as described above, it becomes possible to handle the element easily compared with the conventional open type, and it has been possible to advance to the practical application of this element.

[Brief description of drawings]

1 and 2 are schematic longitudinal sectional views showing examples of the mechanochemical element of the present invention, and FIG. 3 is a view showing the performance of these elements. 1,3 …… Hg / HgO electrodes, 2,4 …… Terminals, 5 …… Stretch film, 6 …… Rubber outer case, 7 …… Center part metal fittings, 8 ……
Electrolyte.

Claims (3)

[Claims] 1. An electrode is disposed inside both ends of a stretchable outer case, and the outer case is filled with an insoluble polymer that expands and contracts reversibly according to a change in the acidity of the solution and an electrolytic solution. In a mechanochemical element that responds to expansion and contraction due to changes in acidity due to input, Hg / HgO, Hg /
A sealed mechanochemical element characterized by using at least one of the electrode reactions of Hg (OH) ₂ , Pd / Pd (OH) ₂ and Pt / PtO. 2. A central part of a mechanochemical element is bent,
The sealed mechanochemical element according to claim 1, wherein both ends provided with both electrodes are brought close to each other to have a bimetal shape and are bent by an electric input. 3. The sealed mechanochemical element according to claim 1, wherein both ends of the mechanochemical element are fixed, and the lateral movement of the central portion is used as a force source.