Electronheological Fluids

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 represents a lateral section of a yield point meter used to determine the variation of developed static yield stress with applied electrical field strength for electrorheological fluids of the invention; and

FIGS. 2 to 16 represent graphically the results obtained for exemplified such fluids.

In FIG. 1, the yield point meter 1 comprises a conductive receptacle 2 for the electrorheological fluid 3 under test which receptacle also acts as a first electrode. Above the receptacle are positioned two horizontal parallel ground glass rods 4, polished with silicone grease, on which a second electrode 5 is slidably mounted. The gap between the two electrodes is 0.5 mm. A micrometer screw 6 is mounted to transmit effort to a third order lever 7 a portion of which is arranged as a beam 8 which is deflectable between the second electrode and pivot 9. This beam carries a strain gauge bridge 10 and its flexure is capable of being monitored by related recording instrumentation (not shown).

In use, the electrorheological fluid 3 to be determined is placed in receptacle 2 and the second electrode 5 is stationed on rods 4 over, and in contact with, the electrorheological fluid with a gap as aforesaid. The micrometer screw 6 is then rotated urging beam 8 to force the second electrode along the rods and thus through the fluid. The frictional resistance causes the beam 8 to deflect prior to slip. This maximum deflection is recorded graphically, the peak .chi..sub.o being proportional to the frictional resistance of the apparatus. The two electrodes 2, 5 are next connected in series to a variable 2 kV unidirectional power supply and ammeter (not shown). The experiment is repeated for a series of applied electric field strengths, the recorded peaks .chi. being proportional to the frictional resistance and any static yield stress developed in the fluid. A plot of (.chi.-.chi..sub.o) against the electric field strength is thus a measure of the dependence of developed static yield stress on applied electric field strength.

Absolute numerical values may be obtained by calibrating the yield point meter. This is effected by leaving the micrometer screw unaltered and instead applying effort to the second electrode 5 by adding a succession of differing loads, for example weights W. The area of the second electrode is 4.times.10.sup.-4 m.sup.2 and thus the yield stresses, represented by .chi., can be quantified from the quotient of applied load/area.

The following Examples illustrate the invention.

A series of electrorheological fluids in accordance with the invention was prepared by incorporating different amounts of copper phthalocyanine (ex Eastman Kodak, dried at 72 hours at 50.degree. C.); or metal-free phthalocyanine (ex ICI plc) in a 3:1 paraffin oil: paraffin grease (ex BDH Chemicals Ltd.), dried by passage through an alumina column (ex Woelm Pharma) at 70.degree. C., the viscosity of which was approximately 50 cS at ambient temperature. They were then tested in the yield point meter hereinbefore described; the test results are depicted graphically in FIGS. 2 to 6 inclusive.

In these Figures:

FIG. 2 depicts, for a 15% v/v copper phthalocyanine suspension, the variation of developed static yield strength (kPa) as ordinate with the applied electric field strength (MVm.sup.-1) as abscissa;

FIG. 3 depicts, for a 22% v/v copper phthalocyanine suspension, the variation of developed static yield strength (kPa) as ordinate with the applied electric field strength (MVm.sup.-1) as abscissa;

FIG. 4 depicts, for a 25% v/v (.DELTA.); 15 v/v (); and 8% v/v (), respectively, copper phthalocyanine suspension, the variation of developed static yield strength (kPa) as ordinate with the square of the applied electric field strength (MVm.sup.-1).sup.2 as abscissa;

FIG. 5 depicts, for the liquid of FIG. 2, the current density passed (Am.sup.-2) as ordinate with the applied electric field strength (MVm.sup.-1) as abscissa;

FIG. 6 depicts, for a 7% v/v metal-free phthalocyanine suspension, the variation of developed static yield strength (kPa) as ordinate with the applied electric field strength (MVm.sup.-1) as abscissa.

This Example illustrates the preparation of a series of poly(acene-quinone)s; and their formulation and testing as electrorheological fluids in accordance with the invention.

Equimolar quantities of 1,2,4,5-benzenetetracarboxylic dianhydride (ex Aldrich Clemicals Co. Ltd.) and an aromatic acene (either naphthalene ex Hopkin and Williams Ltd. or pyrene ex Aldrich Chemicals Co. Ltd.) were mixed by trituration in a mortar. Two moles of zinc chloride (ex BDH Chemicals Ltd.) per mole of the dianhydride were then added, as catalyst, to the mixture; this mixture was next placed in a Pyrex tube ("PYREX" is a registered Trade Mark) and heated to 300.degree. C. in a constant temperature bath for 24 hours. (It had been found, in experiments of Pohl et al. (ubi supra), that the presence or otherwise of air in the reaction vessel had but little effect on the conductivity of the resulting polymer; accordingly, in this series of preparations the Pyrex tube was simply stoppered.)

At the end of that time, the resulting polymer was filtered off and ground to a fine powder. The powder was then leached with dilute (2N) hydrochloric acid for 24 hours to assist in removing zinc chloride. The leached powder was subsequently extracted with distilled, deionised water for 24 hours; ethanol (ex May and Baker Ltd.) for 24 hours; and benzene (ex May and Baker Ltd.) for 72 hours, all in a Soxhlet apparatus.

The poly(acene-quinone)s were then dried at 50.degree. C. for 72 hours in a vacuum oven. After drying, the polymers (which were black in colour) were finely ground in a micronising mill and stored in a dessicator.

The density of the poly(pyrene-quinone) was found to be 1.51 g cm.sup.-3 ; that of the poly(naphthalene-quinone) was 1.50 g cm.sup.-3. Different volume fractions, detailed below, of each polymer were dispersed in the 3:1 paraffin oil:paraffin grease mixture decribed above, the viscosity of which permitted a stable dispersion of the polymer to be formulated. Different volume fractions, again detailed below, of each polymer were dispersed in a polychlorinated hydrocarbon (CERECLOR 50 LV ex ICI plc) to formulate a stable dispersion of the polymer. A further volume fraction of each such polymer dispersed in a silicone oil (DC550 ex Hopkin & Williams) to formulate a stable dispersion of the polymer.

The dispersions were electrorheological fluids of the invention: they were then tested in the yield point meter hereinbefore described; the test results are depicted graphically in FIGS. 7 to 16 inclusive.

In these Figures:

FIG. 7 depicts, for a 17% v/v poly(pyrene-quinone) suspension in paraffin, the variation of developed static yield strength (kPa) as ordinate with the applied electric field strength (MVm.sup.-1) as abscissa;

FIGS. 8, 9 and 10 depict, for 21, 33 and 40% v/v, respectively, poly(pyrene-quinone) suspensions in paraffin, the variation of developed static yield strength (kPa) as ordinate with the applied electric field strength (MVm.sup.-1) as abscissa;

FIG. 11 depicts, for a 30% v/v poly(pyrene-quinone) suspension in silicone oil, the variation of developed static yield strength (kPa) as ordinate with the applied field strength (MVm.sup.-1) as abscissa;

FIG. 12 depicts, for a 40% v/v poly(pyrene-quinone) suspension in polychlorinated hydrocarbon, the variation of developed static yield strength (kPa) as ordinate with the applied field strength (MVm.sup.-1) as abscissa;

FIGS. 13 and 14 depict, for 30 and 38% v/v, respectively, poly(naphthalene-quinone) suspensions in paraffin, the variation of developed static yield strength (kPa) as ordinate with the applied field strength (MVm.sup.-1) as abscissa;

FIG. 15 depicts, for a 40% v/v poly(naphthalene-quinone) suspension in polychlorinated hydrocarbon, the variation of developed static yield strength (kPa) as ordinate with the applied field strength (MVm.sup.-1) as abscissa; and

FIG. 16 depicts, for the liquid of FIG. 15, the current density passed (Am.sup.-2) as ordinate with the applied field strength (MVm.sup.-1) as abscissa.

In each case, even in the absence of water, a yield stress was developed; that developed from poly(acene-quninone)s dispersed in chlorinated hydrocarbon being particularly noteworthy.