Haluk Özbek

Bio: Haluk Özbek is an academic researcher from Istanbul Technical University. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 8, co-authored 25 publications receiving 220 citations. Previous affiliations of Haluk Özbek include Katholieke Universiteit Leuven & Feza Gürsey Institute.

Critical behavior of a nonpolar smectogen from high-resolution birefringence measurements.

Abstract: We report high-sensitivity and high-temperature resolution experimental data for the temperature dependence of the optical birefringence of a nonpolar monolayer smectogen 4-butyloxyphenyl-4'-decyloxybenzoate (10[over ¯].O.4[over ¯]) liquid crystal by using a rotating-analyzer technique. The birefringence data cover nematic and smectic-A phases of the 10[over ¯].O.4[over ¯] compound. The birefringence data are used to probe the temperature behavior of the nematic order parameter S(T) in the vicinity of both the nematic-isotropic (N-I) and the nematic-smectic-A (N-SmA) transitions. For the N-I transition, from the data sufficiently far away from the smectic-A phase, the average value of the critical exponent β describing the limiting behavior of S(T) is found to be 0.2507±0.0010, which is in accordance with the so-called tricritical hypothesis, which predicts β=0.25 and excludes higher theoretical values. The critical behavior of S(T) at the N-I transition is discussed in detail by comparing our results with the latest reports in the literature and we conclude that by comparing with the previously reported results, the isotropic internal field assumption by the Vuks-Chandrasekhar-Madhusudana model is adequate to extract the critical behavior of S(T) from the optical birefringence data. We observe that there is no discontinuous behavior in the optical birefringence, signaling the second-order nature of the N-SmA transition. The effect of the coupling between the nematic and smectic-A order parameters on the optical birefringence near the N-SmA transition is also discussed. In a temperature range of about 4K above and below the N-SmA transition, the pretransitional evidence for the N-SmA coupling have been detected. From the analysis of the optical birefringence data above and below the N-SmA transition by means of various fitting expressions we test the validity of the scaling relation λ=1-α between the critical exponent λ describing the limiting behavior of the nematic order parameter and the specific heat capacity exponent α. We then show that the temperature derivative of the nematic order parameter S(T) near T(NA) exhibits the same power-law divergence as the specific heat capacity with an effective critical exponent of 0.2303±0.0035.

Critical behaviour at the isotropic–nematic and nematic–smectic A phase transitions of 4‐butyloxyphenyl 4′‐decyloxybenzoate liquid crystal from refractive index data

Abstract: We present new high‐resolution experimental data on the temperature dependence of the refractive index in the isotropic (I), nematic (N) and smectic A (SmA) phases of the 4‐butyloxyphenyl 4′‐decyloxybenzoate ( ) liquid crystal. From an analysis of the data, using both the Vuks and Neugebauer models for the internal electric field, information on the orientational order parameter S(T) was derived. From a fitting procedure consistent with mean‐field theory and the first‐order character of the N–I transition, we obtain a value of 0.246±0.06 for the exponent β describing the critical behaviour of S(T) at the N–I transition, which is in good agreement with the tricritical value β = 0.25. In a temperature range of about 4 K above and below the N–SmA transition temperature, pre‐transitional evidence for the coupling between the nematic and smectic order parameters was observed. We show, for the first time, that the temperature derivative of the S(T) curve below and above the N–SmA transition has the same power l...

High-resolution birefringence investigation of octylcyanobiphenyl (8CB): an upper bound on the discontinuity at the smectic-A to nematic phase transition.

Abstract: We report optical birefringence data by two different methods with high temperature resolution for octylcyanobiphenyl (8CB) near the smectic-A to nematic (Sm-A-N) phase transition temperature T(AN). Within the resolution of our experiments, we find that the Sm-A-N phase transition is continuous. For a possible discontinuity in the orientational order parameter S(T) at T(AN), we arrive at an upper limit of 0.0002, which is substantially smaller than other estimates in literature, but consistent with the value of 0.00008 derived from the upper limit of the latent heat from high-resolution adiabatic scanning calorimetry (ASC), which is itself consistent with the Halperin-Lubensky-Ma theory. The temperature derivative of the order parameter exhibits a power law divergence with a critical exponent that is consistent with the value α = 0.31 ± 0.03 for the specific heat capacity obtained by ASC.

Recent Advances in Edible Polymer Based Hydrogels as a Sustainable Alternative to Conventional Polymers.

Abstract: The over increasing demand of eco-friendly materials to counter various problems, such as environmental issues, economics, sustainability, biodegradability, and biocompatibility, open up new fields of research highly focusing on nature-based products. Edible polymer based materials mainly consisting of polysaccharides, proteins, and lipids could be a prospective contender to handle such problems. Hydrogels based on edible polymer offer many valuable properties compared to their synthetic counterparts. Edible polymers can contribute to the reduction of environmental contamination, advance recyclability, provide sustainability, and thereby increase its applicability along with providing environmentally benign products. This review is highly emphasizing on toward the development of hydrogels from edible polymer, their classification, properties, chemical modification, and their potential applications. The application of edible polymer hydrogels covers many areas including the food industry, agricultural appl...

Physical Properties of Liquid Crystalline Materials

Abstract: W H de Jeu 1980 New York: Gordon and Breach ix + 133 pp price $32 It is to be regretted that the practice is growing, even among those knowledgeable in the field, of writing about liquid crystals as though a single type existed and the two processes for their formation produced similar molecular distributions. The distinction between thermotropic and lyotropic liquid crystals is not made in the title of this book.

Effects of graphene on electro-optic response and ion-transport in a nematic liquid crystal

Abstract: A small quantity of graphene, containing both monolayer and multilayer flakes, was doped in a nematic liquid crystal (LC), and the nematic electro-optic switching was found to be significantly faster in the LC + graphene hybrid than that of the pure LC. Additional studies revealed that the presence of graphene reduced the free ion concentration in the nematic media by ion-trapping process. The reduction of mobile ions in the LC was found to have subsequent impacts on the LC's conductivity and rotational viscosity, allowing the nematic director to respond quicker on switching the electric field on and off.