Nano-particle based variable transmission devices
A variable transmission medium comprises a fluid and a plurality of nanoparticles dispersed in the fluid, wherein addition of acid to the fluid causes the nanoparticles to flocculate and form aggregates of particles that scatter light. The nanoparticles may comprise at least one metal oxide, such as titanium dioxide, zinc oxide or zirconium dioxide. The fluid may have a dielectric constant less than about 10. The medium may be used in, for example, privacy glass for a conference room.
1. A method of varying the opacity of a variable transmission assembly comprising:
providing a variable transmission assembly including a first light-transmissive electrode, a second light-transmissive electrode, and a variable transmission medium disposed between the first and second light-transmissive electrodes, wherein the variable transmission medium comprises zirconium dioxide nanoparticles, titanium dioxide nanoparticles, or zinc oxide nanoparticles dispersed in a fluid having a dielectric constant less than 10, wherein the zirconium dioxide nanoparticles, titanium dioxide nanoparticles, or zinc oxide nanoparticles have adsorbed thereon a stabilizing material that comprises a carboxylic acid or carboxylate group attached to a chain of at least 10 carbon atoms;
providing a first electric current between the first and second light-transmissive electrodes and through the variable transmission medium, wherein the first electric current has a square or sinusoidal AC form and includes one or more rests, wherein a zero potential is applied during the rest, and wherein the first electric current produces a proton gradient in the variable transmission medium, causing the nanoparticles to flocculate and form aggregates that scatter light; and
providing a second electric current, wherein the second electric current is an AC current having frequency of 60 Hz and higher, causing thermally-induced de-flocculation of the nanoparticles that increases the light-transmissivity of the variable transmission assembly.
2. The method of claim 1 , wherein the variable transmission medium is contained within a plurality of microcapsules, microcells, or discrete droplets, the discrete droplets being surrounded by a continuous phase comprising a polymeric material.
3. The method of claim 1 , wherein the stabilizing material comprises stearic acid.
4. The method of claim 1 , wherein the fluid comprises an aliphatic hydrocarbon or a terpene.
5. The method of claim 4 , wherein the terpene is limonene.
6. The method of claim 1 , wherein the first or second light-transmissive electrode comprises indium tin oxide (ITO) or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT).
7. The method of claim 1 , wherein the zirconium dioxide nanoparticles, titanium dioxide nanoparticles, or zinc oxide nanoparticles are between 10 and 100 nm in diameter.
8. The method of claim 1 , wherein the fluid of the variable transmission medium is a petroleum distillate having molecular weight of less than about 1000 g/mole.
9. The method of claim 1 , wherein the fluid of the variable transmission medium further comprises a polymer which is soluble in the fluid, wherein the polymer has molecular weight of from about 10,000 to about 1,000,000 g/mole.
10. The method of claim 1 , wherein the variable transmission medium further comprises a soluble polymer having a molecular weight greater than about 1,000,000 g/mole.
11. The method of claim 1 , wherein the first and second light-transmissive electrodes are not coated by a polymer.