Polymer dispersed liquid crystal material having an extended wave-length response

An optically responsive film, comprising:

• a thin film of polymer dispersed liquid crystal material capable of scattering light and infrared radiation, said film being responsive to an applied voltage for switching between a light scattering off-state and a substantially clear, transparent on-state;
• wherein said liquid crystal material includes a polydisperse distribution of liquid crystalline microdroplet sizes having a first series of droplets with diameters equal to or less than about three micrometers, said first droplet series being at least about 10 percent of the total droplet volume fraction of the liquid crystal material;
• and
• said liquid crystal material furthermore having a second series of droplets with diameters equal to or less than bout five micrometers, said second droplet series being at least about 10 percent of the total droplet volume fraction of the liquid crystal material, said first and second droplet series being substantially uniformly dispersed throughout said liquid crystal material.

An optically responsive film, comprising:

• a thin film of polymer dispersed liquid crystal material capable of scattering light and infrared radiation, the film also being responsive to an applied voltage for switching between a light scattering off state and a substantially clear, transparent on state;
• wherein said liquid crystal material has a substantially uniform droplet size distribution characterized by a minimum droplet diameter size Dmin and a maximum droplet diameter size Dmax, such that about 10 percent of the total droplet volume fraction has a droplet diameter size smaller than Dmin and about 10 percent of the total droplet volume fraction has a droplet diameter size larger than Dmax;
• and
• wherein the totality of the droplets have a spread parameter S described by
• S=(Dmax-Dmin)/(Dmax+Dmin),
• said spread parameter S being greater than about 0.66.

A method for producing an optically responsive film containing liquid crystal microdroplets which are substantially uniformly dispersed in a polymeric film, the method comprising the steps of:

• (1) dissolving a liquid crystal material into a polymer precursor to form a substantially homogeneous mixture by vigorously mixing a ratio of from about 0.01:1 to about 5:1 of said liquid crystal material in said polymer precursor at a first temperature of about -20.degree. C. to about 200.degree. C. such that said liquid crystal material is substantially dissolved in said polymer precursor to form said mixture;
• (2) applying said mixture as a thin film onto a substrate;
• (3) partially curing said mixture at said first temperature to initiate phase separation between said liquid crystal material and said polymer precursor but not curing sufficiently to cause full phase separation, whereby liquid crystalline microdroplets having a first range of microdroplet sizes are formed;
• and
• (4) after a delay period of about 5 seconds to about 15 minutes curing is resumed at a second temperature which is about 10.degree. C. to about 100.degree. C. less than said first temperature, thereby causing the formation of a second or more ranges of liquid crystal microdroplet sizes, such that in the resulting material the liquid crystal is characterized by microdroplets with a substantially uniform size distribution of at lest two different, substantially discrete mean diameters within the polymeric film or is characterized by a spread parameter of at least about 0.66.

A method for producing an optically responsive film containing liquid crystal microdroplets which are substantially uniformly dispersed in a polymeric film, the method comprising the steps of:

• (1) dissolving a liquid crystal material into a polymer precursor to form a substantially homogeneous mixture by vigorously mixing a ratio of from about 0.01:1 to about 5:1 of said liquid crystal material in said polymer precursor at a first temperature of about -20.degree. C. to about 120.degree. C. such that said liquid crystal material is substantially dissolved in said polymer precursor to form said mixture;
• (2) applying said mixture as a thin film onto a substrate;
• (3) partially curing said mixture by irradiating with ultraviolet radiation at a power level of at least 10 mW/cm.sup.2 for a sufficient time to initiate phase separation between said liquid crystal material and said polymer precursor, but not curing sufficiently to cause full phase separation, whereby liquid crystalline microdroplets having a first range of microdroplet sizes are formed;
• and
• (4) after a delay period of about 5 seconds to about 15 minutes curing is resumed and completed by ultraviolet radiation, thereby causing the formation of a second or more ranges of liquid crystal microdroplet sizes, such that in the resulting material the liquid crystal is characterized by microdroplets with a substantially uniform size distribution of at least two different, substantially discrete mean diameters within the polymeric film.