Dual energy dependent fluids

A dual energy dependent electroviscous fluid which becomes electroviscous upon the application of both electric potential and a second form of energy such as light or pressure. Dual energy dependent fluids support a dipole sufficient for the fluids to become significantly electroviscous only upon exposure of the aggregate to the second form of energy simultaneous with the electric potential.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the field of electroviscous fluids and more 
particularly to electroviscous fluids that exhibit an effect heretofore 
unknown and which is herein called the Reitz effect. 
2. Background Information 
Electroviscous fluids refer to fluids which exhibit the property of 
increased viscosity when the fluid is subjected to an electric field. One 
phenomenon for electrically controlling the viscosity of a fluid is 
commonly known as the Winslow effect. As used in this disclosure, the term 
Winslow effect refers to the phenomenon of electrically controlling the 
viscosity of a fluid comprising a suspension of finely divided 
electrically polarizable matter in a dielectric fluid by subjecting the 
fluid to an electric field. Within this disclosure, the finely divided 
electrically polarizable matter is referred to as aggregate. 
The Winslow effect as heretofore understood is practiced by placing the 
fluid containing the aggregate particle between spaced apart electrodes 
and applying a single energy source such as for example alternating or 
direct current between the electrodes. Even though semiconductors have 
been used as the aggregate material in the fluid, there is no suggestion 
in the prior art that it would be advantageous to use photoelectric 
properties attributable to semiconductors to formulate a fluid that would 
either cause the fluid to respond to the applied electric potential at a 
lesser value of such electric potential or to respond to the electric 
potential only after energy from a second source has been supplied. 
SUMMARY OF THE INVENTION 
Within the scope of the present invention is a new field of electroviscous 
fluids not previously shown in the prior art. These new fluids are fluids 
which exhibit significant electroviscous properties only upon exposure to 
two independent energy sources cooperating together. These fluids are 
referred to as fluids exhibiting the Reitz effect. Reitz effect fluids as 
disclosed herein differ from the Winslow effect fluids in that Reitz 
fluids behave electroviscously only in the presence of energy applied in a 
form different from the polarizing potential, such as for example, light 
or hydraulic pressure. The present invention, a dual energy dependent 
fluid comprises a dielectric fluid which is transparent to the energy 
which activates the aggregate, such as for example an optically 
translucent dielectric fluid in the case of a light activated fluid, and a 
multiplicity of energy activated aggregate particles dispersed in the 
dielectric fluid. The purpose of the second source of energy is to cause 
the particles to encourage or to actively generate an electric dipole on 
the particle independent of any dipole that may be induced on the 
particles by the polarizing potential normally associated with utilizing 
Winslow effect fluids. For this reason the fluids of the present invention 
are referred to as dual energy dependent electroviscous fluids. In one 
embodiment, exposing the aggregate particles to an energy source other 
than the polarizing potential causes dipoles to be actively generated on 
the aggregate particles. Thus, a substantial number of aggregate particles 
generate an electric potential such that an electric current could be 
extracted from the fluid were it not for the protective shield on the 
particles resisting particle to particle transmission of electric current. 
According to one embodiment of the present invention, the aggregate 
comprises a photovoltaic combination of a type well known in the art 
wherein the photovoltaic material produces electrical current upon 
exposure to light. It is believed that for the same aggregate count, a 
dual energy dependent electroviscous fluid will have a stronger particle 
to particle bond, thus increasing the viscosity of the fluid or 
solidifying the fluid at a much lower electric field potential. Suitable 
photovoltaic or photoelectrogenerative particles are prepared in a similar 
manner as for the preparation of photodiodes. Suitable particles are also 
prepared by comminuting photovoltaic cells, such as for example silicon 
solar cells, wherein small particles are obtained which retain their 
photovoltaic properties. A ready source for these is fallout from the 
manufacture of solar cells. While not desiring to be bound by theory, the 
generation of electrical voltages on the individual particles is believed 
to be the reason for a significant decrease in the applied voltage 
required to solidify a fluid made with photovoltaic particles. Apparently, 
the individual particles, when subjected to the illuminating radiation, 
add to the total of the polarizing potential causing less external 
potential to be needed. 
In the case of photovoltaic particles, when light of the sensitive 
frequency is incident on the aggregate particle, the bonds due to 
accumulated charge become stronger and the viscosity of the fluid 
increases in the presence of an applied electrical potential. Also, when 
light of the sensitive frequency is not impinging on the particle, the 
strength of any dipole which can be induced is too weak to cause the fluid 
to behave significantly electroviscous. Thus, in a device using a fluid 
with a photovoltaic aggregate, the high voltage potential can be applied 
without initially causing the electroviscous effect to occur. Instead, in 
a device using a dual energy dependent fluid, the electroviscous nature of 
the fluid is changed from a less viscous state to a more viscous state by 
applying energy from a second source in combination with the electric 
field normally applied to electroviscous fluids. Removing the electric 
field causes the fluid to return to the less viscous state. The fluid 
tends to remain in the more viscous state in the presence of the electric 
field even when the light source is removed. 
In order for fluids incorporating the Reitz effects to be effective, the 
core or energy dependent material of the particle are preferably shielded 
by use of an insulating material on the core to prevent significant 
particle to particle transmission of electric current. Various shielding 
and density matching techniques are used which are disclosed in a 
copending application of this inventor entitled INDUCED DIPOLE 
ELECTROVISCOUS FLUIDS, application Ser. No. 07/219,522, filed Jul. 15, 
1988, the disclosure of which is hereby incorporated by reference. Thus, 
within the fluid, a substantial portion of the aggregate particles each 
further comprise a core and an electrically non-conductive shield, the 
core being at least partially electrically photocontrollable with the 
shield partially encompassing the core, the shield adapted to prevent 
particle to particle transmission of electric current. The techniques for 
shielding a photovoltaic core are generally the same as for other 
electroviscous fluids of the aforementioned application except the shield 
material must be optically translucent to the light frequencies to which 
the photocontrollable core is sensitive. The shield comprises any material 
that is a good electric insulator, such as for example: polyurethane 
elastomers, hardened epoxy adhesive, nylon, ceramic glaze, silica, 
silicone rubber, Teflon.sup.R, glass and other good dielectric materials. 
For fluids dependent on forms of energy other than light, the shield 
material should readily transfer that form of energy to the core. The 
dielectric fluid comprises any dielectric fluid such as for example, 
dimethyl silicone oil, paraffin oil or mineral oil which is transparent to 
the form of energy used to activate the aggregate particles. 
In a dual energy dependent fluid of the present invention which is intended 
to operate as a photoelectroviscous fluid, the shield which prevents 
significant particle to particle transmission of electric current is made 
to serve a dual function enabling further tailoring of the fluid to meet 
particular needs. When the shield completely surrounds the core so as to 
form a shell, the surrounding material itself is made to transmit 
different colors or frequencies of light. Thus, a standard core material 
is made which is sensitive to a broad range of light frequencies and a 
shield or shell material is made which attenuates a portion of the light 
energy as may be impinging upon the particle from a source. Thus, using 
the same basic core material, a family of light frequency sensitive dual 
energy dependent fluids can be made, each sensitive to only a portion of 
the entire spectrum of impinging light. A use for such a fluid is in the 
field of spectrum analysis. 
An object of the present invention is to provide an energy dependent fluid 
wherein the viscosity increase of the fluid on application of a polarizing 
potential is intensified by the simultaneously applying a second form of 
energy. 
Another object of the present invention is to provide an energy dependent 
fluid wherein the aggregate responds to an energy input to generate a 
portion of the polarizing potential needed to solidify the fluid. 
Yet another object of the present invention is to provide an electroviscous 
fluid that can be tailored to respond to differing spectra of applied 
energy.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, a diagrammatical representation of an dual energy 
dependent fluid of the present invention is illustrated in an apparatus 
for demonstrating the dual energy dependent nature of the fluid. A 
reservoir for containing the fluid is illustrated schematically by glass 
beaker 12. Electrodes 13 and 14 are spaced apart in beaker 12 and are at 
least partially inserted in glass beaker 12. Electrodes 13 and 14 are made 
comprising any good electrical conductor material such as for example, 
copper, silver, aluminum, zinc, lead, steel, or bronze or any 
semiconductor material made comprising for example germanium or silicon. 
Electrodes 13 and 14 are connected through electrically conductive wires 
15 and 16 through switch 17 to high voltage power supply 18. Dual energy 
dependent fluid 20 is in contact with electrodes 13 and 14. 
Dual energy dependent fluid 20 is comprised of electrically non-conductive 
aggregate particles 21 substantially dispersed throughout a dielectric 
fluid 22. The term non-conductive when used in relation to the 
characteristics of the aggregate means that the separate aggregate 
particles are individually adapted to avoid or minimize the transmission 
of electrical current from one aggregate particle to another aggregate 
particle. 
Electrically non-conductive aggregate particles 21 comprise a core 23, said 
core 23 being photocontrollable, and a shield 24, said shield 24 further 
comprising substantially non-conductive material. 
Core 23 comprises any suitable material which is photocontrollable. The 
term photocontrollable as used herein includes both photoconductive 
materials and photovoltaic materials. Photoconductive materials are those 
elements, alloys, compositions which exhibit the property of increased 
electrical conductivity in the presence of light. The construction of such 
materials is well known in the art of electronics. Examples of suitable 
photoconductive material include polycrystaline indium antimonide, cadmium 
sulfide, cadmium sulfoselenide, lead sulfide, gallium arsenide, silicone 
and germanium. When photoconductive material is used as core 23, the fluid 
is said to be a passive dipole dual energy dependent fluid. 
Alternately, core 23 comprises a photovoltaic material or combination. 
Photovoltaic materials are those compositions and combinations which 
generate an electrical potential in the presence of light. When a 
photovoltaic material is used as core 23, the fluid is said to be an 
active dipole dual energy dependent fluid. Photovoltaic materials are well 
known in the field of electronics. Photovoltaic materials are essentially 
bipolar junction diodes made from materials such as for example germanium 
or silicone and optimized to produce electric current upon exposure to 
light. One economical source of suitable core material is to grind up 
photovoltaic or solar cells such as the functional discards from voltaic 
cell production. The parts of the comminuted cells which will function as 
photoelectroviscous aggregate are then screened out electrically as 
discussed below. 
Shield 24 comprises any material that is a good electric insulator, such as 
for example: polyurethane elastomers, hardened epoxy adhesive, nylon, 
ceramic glaze, silica, silicone rubber, glass and other good dielectric 
materials. Preferably, shield 24 encapsulates core 23 and must be 
translucent to the frequencies of interest. However, complete 
encapsulation is not necessary to the performance of either passive or 
active dipole photoelectroviscous fluids of the present invention. All 
that is necessary is for shield 24 to substantially prevent the particle 
to particle transmission of electric current. 
Dielectric fluid 22 comprises any dielectric fluid such as for example, 
dimethyl silicone oil, paraffin oil or mineral oil. The particular 
dielectric fluid to be used in a particular application will usually 
require routine selection based on the anticipated end use of the dual 
energy dependent fluid. In photoelectroviscous fluids, the dielectric 
fluid must be translucent to the frequencies to which the core is 
sensitive. 
Referring now to FIG. 1 and 2, the functioning of a passive dipole dual 
energy dependent fluid is illustrated. With switch 17 in the open position 
as shown, electrodes 13 and 14 have no energizing potential applied, thus 
there is no electric field across dual energy dependent fluid 20. As 
indicated in FIG. 1, aggregate particles 21 are randomly oriented 
throughout dielectric fluid 22. When switch 17 is closed as in FIG. 2, 
electrodes 13 and 14 an electric field is permeated through dual energy 
dependent fluid 20 attempting to induce charges on the surface of core 23. 
Since in the absence of a second form of energy, core 23 is not 
sufficiently conductive, charges 26 and 27 have difficulty forming and the 
particles do not line up as shown in FIG. 2. When a second form of energy, 
such as for example, light source 30 is illuminated, core 23 becomes 
sufficiently conductive to allow charges 26 and 27 to form on the core, 
thus causing the particles to line up as shown in FIG. 2. 
Electric charges 26 and 27 on the surface of core 23 are of opposite 
polarity with respect to the charges on electrodes 13 and 14 respectively. 
Electric charges 26 and 27 of each aggregate particle 21 cause aggregate 
particles 21 to align themselves along the electric lines of flux of the 
permeating electric field. On a fine particle dimensional scale, alignment 
of aggregate particles 21 gives the dual energy dependent fluid a 
structure which is periodic and is similar to the structure of crystalline 
solids. Thus, the effective viscosity of the fluid is greater under the 
conditions illustrated in FIG. 2 than the effective viscosity of such 
fluid under the conditions illustrated in FIG. 1. When electrodes 13 and 
14 are electrically discharged so that they have no net charge on them, 
the phenomenon is reversed and dual energy dependent fluid 20 returns to 
the conditions illustrated in FIG. 1. Even though aggregate particles 21 
may be touching, current will not be transmitted through the particles 
from electrode 13 to electrode 14 because shields 24 resist current 
transmission between cores 23. 
A more pronounced Reitz effect is noted when cores 23 are made from an 
active material, such as for example, photovoltaic material. In the latter 
case, the dipole induced by the application of an electric field is 
supplemented by a dipole generated on the core in response to the 
application of light although it is believed that the dipole actively 
created on core 23 is stronger than a dipole merely induced in core 23 by 
the electric field alone. 
Referring now to FIG. 1 and 2, the functioning of an active dipole dual 
energy dependent fluid is illustrated in a similar manner. With switch 17 
in the open position as shown, electrodes 13 and 14 have no energizing 
potential applied, thus there is no electric field across dual energy 
dependent fluid 20. As indicated in FIG. 1, aggregate particles 21 are 
randomly oriented throughout dielectric fluid 22. When switch 17 is closed 
as in FIG. 2, electrodes 13 and 14 an electric field is permeated through 
dual energy dependent fluid 20 attempting to induce charges on the surface 
of core 23. Since in the absence of energy enabling the cores to produce 
an electric charge, cores 23 are not electrogenerative and charges 26 and 
27 are not formed in abundance on cores 23 and particles 21 do not line up 
as shown in FIG. 2. When a second form of energy, such as for example, 
light source 30 is applied, cores 23 become electrogenerative 
(photovoltaic in the case of photovoltaic particles in the presence of 
light) forming an abundance of charges 26 and 27 on the core 23, thus 
causing the particles to line up as shown in FIG. 2. 
Electric charges 26 and 27 on the surface of cores 23 are of opposite 
polarity with respect to the charges on electrodes 13 and 14 respectively. 
Electric charges 26 and 27 of each aggregate particle 21 cause aggregate 
particles 21 to align themselves along the electric lines of flux of the 
permeating electric field. On a fine particle dimensional scale, alignment 
of aggregate particles 21 gives the dual energy dependent fluid a 
structure which is periodic and is similar to the structure of crystalline 
solids. Thus, the effective viscosity of the fluid is greater under the 
conditions illustrated in FIG. 2 that the effective viscosity of such 
fluid under the conditions illustrated in FIG. 1. When electrodes 13 and 
14 are electrically discharged so that they have no net charge on them, 
the phenomenon is reversed and dual energy dependent fluid 20 returns to 
the conditions illustrated in FIG. 1. Even though aggregate particles 21 
may be touching, significant current will not be transmitted through the 
particles from electrode 13 to electrode 14 because shields 24 prevent 
current transmission between cores 23. 
EXAMPLE 1 
A finely ground bulk material comprising gallium arsenide, a well known 
photoconductive material, is encapsulated in a plastic material 
commercially known as Ultra Glow and obtained from ETI, Fields Landing, CA 
and allowed to harden into a slab. The resulting composite material is 
then ground and grindings or aggregate mixed with Part B of a two part 
adhesive identified as Duro Depend II, manufactured by Locktite Corp., 
Cleveland Ohio. An appropriate quantity of glass microspheres about 50 
microns in diameter is mixed with Part A of the adhesive. These glass 
microspheres are hollow spheres of glass in which air is entrapped. These 
hollow spheres are available commercially from the 3M Company and have a 
density of less than 0.2 g/cc. The Part A mix and the Part B mix are then 
mixed together to form a paste. The paste is then mixed with 50 cp 
dimethyl silicone oil having a density of 0.98 g/cc. The paste and the 
silicone oil are thoroughly mixed in a blender. A clear glass container 
containing the fluid is placed in a darkened area and an attempt is made 
to collect a portion of the fluid in a probe using a high voltage probe 
with spaced apart electrodes having a planar surface of about 1.9 
centimeters (cm) by 2.5 cm oppositely opposed at a spacing which was 
adjustable from about 0.32 cm to about 0.48 cm. A similar probe is 
described in greater detail in application Ser. No. 07/219,522. A bright 
light is then used to illuminate the fluid in the clear glass container. 
Upon application of the light, it is noted that the fluid solidifies and 
remains within the electrodes of the probe as the probe is withdrawn from 
the fluid. It is further noted that the fluid remains solidified between 
the electrodes even though the light source is extinguished, thus 
demonstrating that the fluid is photoelectroviscous. 
EXAMPLE 2 
A small quantity of 2.5 cm.times.5.0 cm silicon solar cells was purchased 
from a retail electronics supply source. The cells were sold by Radio 
Shack under the Archer.sup.R brand name as Catalog No. 276-124. Radio 
Shack is a Division of Tandy Corp., Ft. Worth, Tex. Using a bench grinder 
the solar cells were ground into small particles. The resulting ground 
solar cell material particles or core material was mixed with Part B of a 
two part adhesive identified as Duro Depend II, manufactured by Locktite 
Corp., Cleveland Ohio. An appropriate quantity of glass microspheres of 
the type more specifically described in Example 1 was mixed with Part A of 
the Duro Depend II two part adhesive. The Part A mix and the Part B mix 
were then mixed together to form a paste. The paste was then mixed with 50 
cp dimethyl silicone oil having a density of 0.98 g/cc. The paste and the 
silicone oil were thoroughly mixed in a blender. It was observed that some 
of the aggregate particles had positive buoyancy, some had negative 
buoyancy, and others had neutral buoyancy. The clear glass container 
containing the fluid was placed in a darkened area and an attempt was made 
to collect a portion of the fluid in a high voltage probe having a spacing 
ranging from 0.32 cm to 0.48 and opposed surface areas of about 1.8 
cm.sup.2. With the electrode spacing at about 0.32 cm, it was noted that 
the fluid did not solidify even at a potential of up to about 3000 volts 
(about 1000 volts/mm). A bright light from a desk lamp was then used to 
illuminate the fluid which was in the clear glass container. Upon 
application of the light, it was noted that the fluid solidified and 
remained within the electrodes of the probe as the probe was withdrawn 
from the fluid, thus demonstrating that the fluid is dual energy dependent 
or in this case photoelectroviscous. It was further noted that the fluid 
remained solidified between the electrodes even though the light source 
was extinguished. Solidification occurred at an electrode potential of 
about 2000 volts (about 625 volts/mm). 
Other embodiments of the invention will be apparent to the skilled in the 
art from a consideration of this specification or practice of the 
invention disclosed herein. It is expected that fluids dependent on other 
dual forms of energy are also realizable, such as for example 
piezoelectric particles in combination with hydraulic pressure, 
thermoelectric particles in combination with thermal energy and Hall 
effect devices in combination with magnetic energy. A suitable composition 
for core of piezoelectric particles is comminuted piezoelectric crystal 
material PZT-5 taken from transducers available from the Vernitron Corp. 
Piezoelectric Div. located in Bedford, Ohio. A suitable shield material 
for piezoelectric particles is RTV 108 silicone rubber manufactured By 
General Electric Co., Waterford, N.Y. It is intended that the 
specification and examples be considered as exemplary only, with the true 
scope and spirit of the invention being indicated by the following claims.