Two thermosetting matrices based, respectively, on an unsaturated polyester resin and a bifunctional epoxy resin were employed to realise Polymer Dispersed Liquid Crystal (PDLC) systems. Electro-optical properties of the two different PDLC films have been investigated. The observation of an electro-optical switching effect from an opaque to a transparent state occurring at a threshold value of the applied field in a PDLC is here presented. Optical responses of the composite films under the conditions of an externally applied ac electric field (40-200 Vp-p), were determined using an Argon laser (wavelength 514 nm). The experimental results showed promising switching times with a rise time of 0.8 ms and a decay time of 80 ?s for the unsaturated polyester based system and a very high contrast ratio up to 410 for the epoxy-based PDLC. These results demonstrate the validity of employing these new PDLCs in electro-optical devices. The thermo-optical properties of the PDLC epoxy based film are also investigated and presented. We analysed the switching effect, from the scattering state to the transmission one, and viceversa, and report the experimental evidence of thermally induced optical bistability at the nematic-isotropic phase transition. We show also, how the hysteresis cycle depends on both the modulation frequency of the incident light and the sample temperature. We performed an experimental analysis using two different laser beams propagating inside our material in order to study the output light modulation (probe beam) optically induced by a pump beam. Our experimental results show such light modulation and demonstrate that the used epoxy based PDLC is promising for applications as a thermo-optical switch, temperature sensor, or to design devices with thermally modulated light.
Optical switching in Polymer Dispersed Liquid Crystals with different polymeric matrices
Petti L;Mormile P;
2002
Abstract
Two thermosetting matrices based, respectively, on an unsaturated polyester resin and a bifunctional epoxy resin were employed to realise Polymer Dispersed Liquid Crystal (PDLC) systems. Electro-optical properties of the two different PDLC films have been investigated. The observation of an electro-optical switching effect from an opaque to a transparent state occurring at a threshold value of the applied field in a PDLC is here presented. Optical responses of the composite films under the conditions of an externally applied ac electric field (40-200 Vp-p), were determined using an Argon laser (wavelength 514 nm). The experimental results showed promising switching times with a rise time of 0.8 ms and a decay time of 80 ?s for the unsaturated polyester based system and a very high contrast ratio up to 410 for the epoxy-based PDLC. These results demonstrate the validity of employing these new PDLCs in electro-optical devices. The thermo-optical properties of the PDLC epoxy based film are also investigated and presented. We analysed the switching effect, from the scattering state to the transmission one, and viceversa, and report the experimental evidence of thermally induced optical bistability at the nematic-isotropic phase transition. We show also, how the hysteresis cycle depends on both the modulation frequency of the incident light and the sample temperature. We performed an experimental analysis using two different laser beams propagating inside our material in order to study the output light modulation (probe beam) optically induced by a pump beam. Our experimental results show such light modulation and demonstrate that the used epoxy based PDLC is promising for applications as a thermo-optical switch, temperature sensor, or to design devices with thermally modulated light.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
