Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components
Patent
1983-02-03
1985-03-05
Lieberman, Paul
Compositions
Heat-exchange, low-freezing or pour point, or high boiling...
Organic components
252 781, 252581, 524363, 524371, 524393, 556465, 556489, 568 27, 568 28, 568 34, 568 35, 568 56, 568 58, 568639, 570182, 570184, H01B 324, C09K 300
Patent
active
045029733
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electroviscous (EV) fluids.
Electroviscous fluids are suspensions of finely divided hydrophilic solids in hydrophobic liquids. When an electric field is applied to such a suspension, it changes from an approximately Newtonian material to a Bingham plastic. The change is very rapid and reversible. The currents passed are extremely low. Such fluids may hence be used as an interface between electronics and power hydraulics.
The hydrophilic solids used in EV fluids have been much studied, for example see UK Pat. No. 1,501,635. The liquid components of such fluids have been much less studied. Some desirable properties of a base liquid may be summarised as follows:
1. High boiling point and low freezing point, giving the EV fluid a wide temperature range (ideally ca-40.degree. C. to 200.degree. C.) and low vapour pressure at normal working temperatures.
2. Low viscosity, to give the fluid a low no-field viscosity.
3. High electrical resistance and high dielectric strength, to ensure that the fluid draws little power in operation and may be used over a wide range of applied field strengths.
4. High density (generally greater than 1.2 and typically 1.3-1.6 g/ml) since it is preferable for the EV solid and liquid components to have the same density, to prevent settling on standing.
5. Chemical stability.
It should also be of relatively low cost and toxicity and preferably bio-degradeable.
There appear, moreover, to be other more subtle physico-chemical factors involved in determining whether a liquid is suitable. Synergistic effects occur, and it is found that although two liquids may separately give good EV fluids they may not do so when mixed and certain liquids may be effective only with certain solids. These chemical features are not yet understood.
In practice it is difficult to combine the above requirements in a single liquid, and some of these properties tend to be mutually exclusive. The most difficult objective to achieve is chemical stability without environmental persistence and a consequential pollution hazard: there is at present legislation restricting the use of persistent materials and this legislation is likely to increase. Although EV devices can be constructed so as to be totally enclosed, it would seem to be a retrograde step to introduce another commercial use for suspect materials.
Of the three types of materials used at present as EV liquids, hydrocarbons, certain fluorinated polymeric materials and polychlorinated biphenyls, none is entirely suitable. Hydrocarbons suffer from the disadvantages of low density and the difficulty of combining high boiling points with low viscosities. The fluorinated materials which have been considered, such as the trifluoro-chloro-ethylene polymer `Fluorolube` suffer from the disadvantages of environmental persistence, high cost, and a tendency to be immiscible with other liquids which might otherwise be used as inert diluents to achieve density matching with EV solids. Polychlorinated biphenyls have high viscosities and additionally have been recognised as dangerous pollutants.
It is one object of the present invention to provide an EV fluid that employs a liquid component that meets more fully the desirable characteristics listed above.
Other objects and advantages will become apparent from the description set out below.
According to the present invention there is provided an electroviscous fluid comprising a hydrophilic solid and hydrophobic liquid component wherein the hydrophobic liquid component comprises at least one diaryl derivative of general formula I ##STR2## wherein R is CY.sub.2, O, S, SO.sub.2, Si F.sub.2 or O-Si(Y.sub.2)-O, X.sup.1 and X.sup.2 are either the same or different and are F, Cl or Br, each of m and n is 0, 1, 2 or 3, each of p and q is 0, 1 or 2 and Y is H, F or a methyl or ethyl group, provided that, for the said diaryl derivatives in the liquid component, the average value of (m+n) is from 1 to 3 inclusive and the average value of (p+q) is from 0 to 1 inclusive.
The term "average value" as used above ref
REFERENCES:
patent: 2165813 (1939-07-01), Prutton
patent: 3402204 (1968-09-01), Plummer et al.
patent: 3472782 (1969-10-01), Nowotny
patent: 4033892 (1977-07-01), Stangroom
patent: 4118363 (1978-10-01), Smith
patent: 4260506 (1981-04-01), Munch et al.
Lieberman Paul
National Research Development Corporation
Wax Robert A.
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