Thermophysical, dielectric, and electro-optic properties of nematic liquid crystal droplets confined to a thermoplastic polymer matrix

Abstract

The thermophysical, dielectric and electro-optic properties of polymer-dispersed liquid crystal (PDLC) films made of monodisperse polystyrene (PS) and 4-n-pentyl-4(')-cyanobiphenyl (5CB) are investigated by polarized optical microscopy, differential scanning calorimetry, ac impedance analysis, and forward transmittance measurement technique. The PS-5CB system exhibits an upper critical solution temperature (UCST) shape phase diagram with a wide isotropic+isotropic (I+I) miscibility gap between the isotropic and nematic+isotropic (N+I) regions. An absorption domain in the dielectric spectrum of PDLC films was clearly observed at low frequency, and unambiguously assigned to the confined liquid crystalline phase in both nematic and isotropic states. The correlation between the dielectric and electro-optical results for PS-5CB (30:70) samples has shown that in the vicinity of the low frequency absorption domain ( approximately 200 Hz at T=25 degrees C), a drastic decrease in the optical transmittance of the film occurs. This phenomenon can be related to an interfacial polarization process resulting from a charge accumulation at the droplet-polymer interface (Maxwell-Wagner-Sillars effect).

Study on the electro-optical properties of polyimide-based polymer-dispersed liquid crystal films

“…For PDLC films with smaller droplets, more space charge builds up at the LC droplet-polymer interface, resulting in a sizable increase of the dielectric permittivity of the matrix. [25][26][27][28][29] This should greatly reduce the field that appears across the LC droplets and increase the switching voltage. Consequently, more severe dielectric losses occurred in the film with smaller droplets.…”

Design and implementation of an all-fiber ultrafast widely tunable wavelength filter

“…The index of refraction of the matrix system increases with the addition of chromophore. Meanwhile, the higher the chromophore concentration, the higher the EO coefficient of such as chromophore doped polymer system because the EO-effect is a summation of the overall chromophore hyper polarizability [21]. The concentration of chromophore dopants was 10% wt.…”

“…Electro-Optic (EO) polymers have great potential in many optical communication and sensing systems due to their intrinsic advantages [15][16][17][18][19][20][21], including wider modulation or switching bandwidth, easy process, and lower cost. Polymeric EO materials are commonly formed by combining various types of chromophore molecules with large dipole moment into an inert polymer host matrix.…”

Investigation of liquid crystal dispersion and dielectric relaxation behavior in polymer dispersed liquid crystal composite films

“…PDLCs have found great significance because of their promising use in advanced optical device applications, such as switchable windows, large flexible displays, or paper like displays for e-books [6][7][8][9]. In industrial and institutional research, PDLC films are getting more consideration, as liquid crystal (LC) display devices using these films can be switched to an electrically visible state without the use of polarizer and alignment layer on an electrode and also due to various other advantages like low fabrication cost, ease of production and quick electrooptical response [10].…”