INTERNAL ELECTRIC-FIELD AND 2ND-HARMONIC GENERATION IN THE BLENDS OF VINYLIDENE FLUORIDE-TRIFLUOROETHYLENE COPOLYMER AND POLY(METHYL METHACRYLATE) WITH A PENDANT NONLINEAR-OPTICAL DYE

This paper presents the internal electric field created by the preferentially oriented beta-crystallite dipoles in the blends of 75 mol % vinylidene fluoride-25 mol % trifluoroethylene copolymer (P(VDF-TrFE)) and poly(methyl methacrylate) (PMMA), and the second harmonic generation (SHG) from the oriented beta-crystallite dipoles and that from the nonlinear optical (NLO) dyes noncentrosymmetrically aligned by the internal electric field. We have also prepared the copolymer of methyl methacrylate (MMA) with a vinyl monomer having a NLO pendant amino-nitro-azobenzene (P(MMA-co-MMA-DR1)) as a SHG active polymer. The blends of both P(VDF-TrFE)/PMMA and P(VDF-TrFE)/P(MMA-co-MMA-DR1) with low DR1 content (experimentally up to 4 mol %) show optical clarity that is desirable for SHG materials. Internal electric fields (E(i)) of 1.7-3.2 MV/cm, which is significantly larger than the applied field of 0.8 MV/cm, were measured at the P(VDF-TrFE) content above 70 mol %. SHG coefficient d33 values are 3.3 x 10(-9), 2.3 x 10(-9), and 0.9 X 10(-9) esu for P(VDF-TrFE), (90/10) P(VDF-TrFE)/PMMA, and (90/10) P(VDF-TrFE)/P(MMA-co-MMA-DR1), respectively. Temperature profiles of E(i) for the blends are shared by those of pyroelectricity and those of d33. Their activities are not significantly depressed at the glass transition temperature T(g) but are drastically lost at the temperature around the Curie transition temperature, which is higher than T(g). We will discuss the nature of the thermal stability of the internal electric field, pyroelectricity, and SHG activity, relating to the order-disorder transition of beta-crystallite dipoles at the Curie transition temperature.