Study On Effects Of The Mesogenic Structures On The Electro-optical Properties Of Polymer Dispersed Liquid Crystal Films

Polymer dispersed liquid crystals(PDLC)films are composite materials that consist of randomly dispersed liquid crystal(LC)droplets embedded in a polymer matrix.LC molecules as one of the important components of PDLC system play a vital role in achieving good electro-optical properties of the PDLC films.In this article,PDLC films were fabricated by UV-initiated free-radical and thermally-initiated polymerization induced phase separation method,respectively.The main research contents are listed as follows:(1)LC mixtures(LCs)were prepared by doping the fluorinated LC molecules into the host LCs E8.It was found that the Vth,Vsat and the contrast ratio of the PDLC films decreased,owing to the LCs properties,the ??increased,and the ?n decreased with increasing the relative weight ratio of the fluorinated LC molecules.Besides,the sizes of the LC domain decreased at first and then increased slightly with the rise of mass fraction of the fluorinated LC molecules.An optimal mass fraction of the fluorinated LC to E8 was supposed to be 8.0 wt%for obtaining PDLC films with low-driving voltage and other good electro-optical properties.The study of the influences of the terminal chain length of the fluorinated LC molecules also showed that adding the fluorinated LC molecules with a shorter terminal chain length to E8 lowers Vth and Vsat of the PDLC films,while adding the fluorinated LC molecules with a longer terminal chain length to E8 leads to a fast response time of PDLC films.(2)LCs were prepared by doping the fluorinated alkene-terminated LC molecules and the analogous fully saturated compounds into the host LCs E8.It was found that LCs with the fluorinated alkene-terminated LC molecules possessed higher ?n value,lower ? and ?? values compared with the LCs containing the analogous fully saturated compounds.Both fluorinated alkene-terminated LC molecules and the analogous fully saturated compounds doped with E8 reduced the Vth and Vsat of PDLC films.Besides,PDLC films with the fluorinated alkene-terminated LC molecules possessed higher contrast ratio and faster response time than that of the PDLC films prepared by adding the same mass fraction of the analogous fully saturated compounds.Moreover,the LC domain sizes were slightly different between them,because the viscosity of the LCs/polymer monomers was subtle difference.Effects of different contents of the fluorinated alkene-terminated LC molecule adding to E8 on the microstructures and electro-optical properties of PDLC films,which were prepared by UV-initiated free-radical polymerization induced phase separation method,have also been studied.Results indicated that the LC domain size decreased at first and then enhanced with increasing the content of the fluorinated alkene-terminated LC molecule.The Vth,Vsat and the contrast ratio of PDLC films decreased mainly owing to the change of the LCs parameters.An optimal mass fraction of the fluorinated alkene-terminated LC molecule was 8.0 wt%for obtaining PDLC films with low-driving voltage and other good electro-optical properties.(3)LCs were prepared by doping the tolane compounds into the host LCs E8.It was found that LCs with the compounds containing three rigid cores exhibit higher ?n,??,and TNI values compared with the LCs E8.Besides,LCs doped with the tolane-based LC molecules have larger An,??,and TNI values compared with the LCs doped with the biphenyl-based LC molecules.Moreover,LCs doped with the tolane based compounds exhibit higher solubility and An values compared with the LCs doped with the ester based molecules.On the whole,all of the tolane compounds doped PDLC films exhibited a lower Vth and Vsat than that doped with the host LCs E8.PDLC films with the cyclohexyl tolane molecules had lower driving voltage,higher CR than the phenyl-tolane-doped PDLC films.Besides,the ton of PDLC films,which were prepared by thermally-initiated polymerization induced phase separation,decreased and the toff increased.