Evolution of electrooptical properties of epoxy-amine thermoset/liquid crystal blends during polymerization after the gel point of the polymer matrix

• Published in: Journal of applied polymer science 2004-05, Vol.92 (4), p.2621-2628
• Main Authors: Sannier, Lucas, Masood Siddiqi, Humaira, Maschke, Ulrich, Dumon, Michel
• Format: Article
• Language: English
• Subjects: Applied sciences; crosslinking; Exact sciences and technology; gelation; morphology; Physicochemistry of polymers; polymer dispersed liquid crystals (PDLCs); Polymer industry, paints, wood; Technology of polymers; thermosets
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.20268

Polymer dispersed liquid crystals (PDLC) were obtained by polymerization‐induced phase separation of the nematic E7 liquid crystal in a reactive diepoxide–diamine thermosetting matrix prepared by polycondensation (in two thermal steps). The evolution of some important electrooptical characteristics (transmittance in the off‐state, threshold voltage, maximum transmittance of the on‐state, transmittance at maximum applied voltage) were studied at three different reaction conversions of the polymer matrix beyond the gel point. The electrooptical curves greatly depended on the reaction conversion, especially beyond the gel point of the polymer matrix. It was found that the transmission in both the off‐state and the on‐state decreased with the extent of cure. In addition, threshold and saturation voltages increased with the reaction conversion. The electrooptical curve showed unusual behavior at approximately 60% of reaction conversion (i.e., near the gel conversion). At higher conversions, the expected normal mode was recovered. We discussed these electrooptical characteristics in the light of the very significant evolution of some properties of the crosslinked polymer matrix (glass‐transition temperatures, concentration of crosslink points, molar mass, and weight fraction of the residual uncrosslinked oligomers), whereas the droplet morphology did not exhibit dramatic changes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2621–2628, 2004