TY - JOUR
T1 - Thermal Characterization of Polymer-Dispersed Liquid Crystals by Differential Scanning Calorimetry
AU - Russell, Graham M.
AU - Paterson, Brian J.A.
AU - Imrie, Corrie T.
AU - Karl Heeks, S.
PY - 1995/1/1
Y1 - 1995/1/1
N2 - The thermal behavior of polymer-dispersed liquid crystals prepared by polymerizationinduced phase separation has been characterized using differential scanning calorimetry and polarized light microscopy. The thermally cured system studied, PolyBed 812/4-n-pentyl- 4'-cyanobiphenyl (5CB), exhibited molecular mixing up to at least 30 wt % 5CB. The liquidcrystal solubility limit, A, in the polymer matrix was calculated to be 41.8. Above 60 wt % 5CB the mixtures exhibited macroscopic as well as microscopic phase separation, and this was detected as a splitting of the nematic-isotropic peak in the DSC thermograms. The nematic-isotropic transition temperature and associated enthalpy suggested that the phaseseparated liquid crystal contained very small amounts of either prepolymer or partially cured polymer. A UV-cured system was investigated also, namely, Norland Optical Adhesive 65 (NOA65)/5CB. A very similar value of A, 42.1, was calculated for this system. For the NOA65/5CB mixtures macroscopic phase separation was not observed. The nematic droplets exhibited clearing temperatures equal to that of pure 5CB within experimental error, implying that essentially pure 5CB separates from the polymer matrix.
AB - The thermal behavior of polymer-dispersed liquid crystals prepared by polymerizationinduced phase separation has been characterized using differential scanning calorimetry and polarized light microscopy. The thermally cured system studied, PolyBed 812/4-n-pentyl- 4'-cyanobiphenyl (5CB), exhibited molecular mixing up to at least 30 wt % 5CB. The liquidcrystal solubility limit, A, in the polymer matrix was calculated to be 41.8. Above 60 wt % 5CB the mixtures exhibited macroscopic as well as microscopic phase separation, and this was detected as a splitting of the nematic-isotropic peak in the DSC thermograms. The nematic-isotropic transition temperature and associated enthalpy suggested that the phaseseparated liquid crystal contained very small amounts of either prepolymer or partially cured polymer. A UV-cured system was investigated also, namely, Norland Optical Adhesive 65 (NOA65)/5CB. A very similar value of A, 42.1, was calculated for this system. For the NOA65/5CB mixtures macroscopic phase separation was not observed. The nematic droplets exhibited clearing temperatures equal to that of pure 5CB within experimental error, implying that essentially pure 5CB separates from the polymer matrix.
UR - http://www.scopus.com/inward/record.url?scp=0000973342&partnerID=8YFLogxK
U2 - 10.1021/cm00059a029
DO - 10.1021/cm00059a029
M3 - Article
AN - SCOPUS:0000973342
VL - 7
SP - 2185
EP - 2189
JO - Chemistry of Materials
JF - Chemistry of Materials
SN - 0897-4756
IS - 11
ER -