Haluk Ozbek

Verified

Haluk verified their affiliation via an institutional email.

Learn more

Verified

Haluk verified their affiliation via an institutional email.

Learn more

• PhD
• Faculty Member at Istanbul Technical University

Within the entire mesomorphic range, high-precision dielectric anisotropy data with the high-temperature resolution is presented for a highly polar smectic-A liquid crystal 8CB (octylcyanobiphenyl) as well as 8CB nanocomposites doped with both pristine multi-walled carbon nanotubes (p-MWCNTs) and carboxyl group (-COOH) functionalized MWCNTs (f-MWCN...

The high-resolution optical birefringence study was carried out to experimentally study the impact of surface functionalized CdSe nanoparticles on the phase transitions of a smectic A liquid crystal 8CB (octylcyanobiphenyl). The birefringence data have then been used to probe the temperature variation of the nematic order parameter across both the...

High-resolution optical birefringence measurements are reported on the weakly first order nematic-isotropic (N–I) and the continuous nematic-smectic A (N–Sm A) phase transitions in smectic liquid crystal 8CB (octylcyanobiphenyl) doped with both pristine multi-walled carbon nanotubes (p-MWCNTs) and carboxyl group (-COOH) functionalized MWCNTs (f-MWC...

We investigate in this work the effect of carboxyl group (-COOH) functionalized multi-walled carbon nanotubes (f-MWCNTs) on physical properties of a highly polar smectic liquid crystal octyl cyanobiphenyl (8CB). We report new experimental data of the temperature variation of optical birefringence, dielectric anisotropy, electrical conductivity anis...

We present new high-resolution experimental data for the temperature behavior of optical birefringence for a series of mixture of the liquid crystals octyloxycyanobiphenyl (8OCB) and nonyloxycyanobiphenyl (9OCB) by using a rotating analyzer technique. The birefringence data have been used to probe the temperature dependence of the nematic order par...

We report optical birefringence data for a series of mixtures of the liquid crystals octylcyanobiphenyl (8CB) and decylcyanobiphenyl (10CB). Nematic order parameter S data in the nematic and smectic A phases have been derived from phase angle changes obtained in temperature scans with a rotating analyzer method. These S values have been used to arr...

We proposed a simple procedure to determine high-accuracy extraordinary (n_e) and ordinary refractive indices (n_o) of LCs both in the N and Sm A phases based on the birefringence measurements.

Monte Carlo (MC) simulations and the Mueller matrix formalism were applied to investigate electro optical properties of a LC cell with planar boundary conditions for various thicknesses. Field dependent global order parameter and the optical transmissions were analyzed in common. Three characteristic regions of the periodicity of optical transmissi...

Although the nematic-smectic A (N-SmA) transition in liquid crystals (LCs) has been extensively studied up to now, it has still been quite controversial [1]. Without any long-range positional order, the N phase is characterized by long-range orientational order. In the SmA phase, in addition to long-range orientational order, one-dimensional layeri...

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 or...

Determination of Order Parameters of Polar and Non-Polar Liquid Crystals

We present high sensitivity and high temperature resolution experimental data on the temperature dependence of the optical birefringence in the nematic and smectic A phases of nonpolar monolayer smectogen 4-butyloxyphenyl-4'-decyloxybenzoate liquid crystal by using a rotating-analyzer technique. We have used the birefringence data to probe the temp...

We present the results of electro-optical characteristics of the liquid crystal octyl-cyanobiphenyl (8CB) doped with well-dispersed multiwall carbon nanotubes (MWCNT) under an AC driving voltage. 8CB-MWCNT composites were prepared by following the procedures in literature [1-4]. Polarized optical microscopy (POM) has been performed to check the hom...

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 o...

The effect of thin films on the orientational and optical properties of nonpolar monolayer smectogen 4-butoxyphenyl-4′-decyloxybenzoate $(\overline{10}.{\rm O}.\overline{4})$ liquid crystal has been studied by polarizing microscopy and high-resolution photon transmission method. The uniform planar textures of $\overline{10}.{\rm O}.\overline{4}$ on...

We have performed a dielectric spectroscopy study of four homologous cyanobiphenyl polyacrylates with long side chains. The α- and δ-relaxation times were found to be sensitive to the sequential transformations between mesophases. The τδ in the isotropic phase exhibits the characteristics that obeys VFT relation and depend strongly on spacer length...

Dielectric spectroscopy of liquid crystalline cyanobiphenyl polyacrylates (CBPA6) with six methylene groups in the side chain has been investigated in the frequency range of 30 Hz–13 MHz and in the temperature interval from 100 to 470 K. From the temperature dependence of ε'(T), the anomalies corresponding to sequential phase transitions of liquid...

In this adiabatic scanning calorimetry (ASC) study we investigated the liquid crystal 4-butyloxyphenyl-4′-decyloxybenzoate ( ) with the emphasis on the nematic-to-smectic A (N-SmA) and the nematic-to-isotropic (N-I) phase transitions. Because of the high resolution ASC technique we were able to accurately determine the latent heat of the first orde...

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...

In situ photon transmission method was applied to study thermal phase transitions of ι-carrageenan in CaCl2 solution. Coil-to-helix (c–h) and helix-to-dimer (h–d) transitions were detected upon cooling. An extra dimer-to-dimer (d–d) transition was observed as well during cooling at low-temperature region. Upon heating only dimer-to-helix (d–h) and...

Random copolymers of poly(ethylene oxide) macromonomer with p-vinylbenzyl end-functional group (PEOVB) and liquid crystalline monomer, namely 6-(4-cyanobi- phenyl-40-oxy)hexyl acrylate (COA), were prepared by conventional free radical polymerization. A living anionic polymerization technique was employed for the synthesis of PEO macromonomers beari...

Thermal phase transitions of κ-carrageenan in pure water and in KCl solution were studied using photon transmission technique. Photon transmission intensity, Itr, was monitored against temperature to determine the critical coil-to-helix (Tch) and helix-to-coil (Thc) temperatures and exponents, β. Tch, and Thc values were found to be higher for the...

The photon transmission method was applied to study the scaling of thermal hysteresis at the nematic-smectic-A transition in a binary mixture of 4-ethoxy-4(')-(6-vinyloxyhexyloxyl) azobenzene monomer, smectogen, and 4-hexoxy-3(')-methly-4(')-(6-acryloyloxyhexyloxy) azobenzene. The thermal hysteresis loops were obtained under linearly varying temper...

The ultraviolet/visible photon transmission technique was applied to study the phase diagram of a mixture of 4-ethoxy-4′-(6-vinyloxyhexyloxyl) azobenzene (VE), a smectogen, and 4-hexoxy-3′-methyl-4′-(6-acryloyloxyhexyloxy) azobenzene (AH), which by itself exhibits no liquid crystalline behavior. It has been found that the N-Sm-A phase line terminat...

Photon transmission measurements were applied to study the phase transitions of an acrylate monomer, 3-(4-cyanobiphenyl-4 -oxy)propyl acrylate (LC3), its homopolymer (PLC3) and its graft copolymer (GLC3) with polytetrahydrofuran grafts. In PLC3 drastic decrease in the transmitted light intensity was attributed to a first-order isotropic–nematic pha...

Ultraviolet/visible photon transmission technique was applied to study the phase diagram of the BOPDOB-BOPOOB liquid crystal system. It was observed that the nematic-smectic A transition becomes first order, as the weight percentage of BOPDOB in the binary mixture is increased. The smectic A-C-A reentrance disappears when the BOPDOB percentage appr...

Ultraviolet/visible photon transmission measurements[1] were applied to study liquid crystal phase transitions in the eutectical BOPDOB-BOPOOB mixture. A sequence exhibiting a new reentrance, namely isotropic-nematic-smectic A-C-A as temperature is lowered, is identified. For the smectic A-C transition, the critical exponent beta is seen to crossov...

A photon transmission technique was used to monitor the multiple phase transitions in a 4-butoxyphenyl4(')-declyoxybenzoate (BOPDOB) liquid crystal. Drastic decreases in the transmitted photon intensity (I) were attributed to the sequential phase transitions in BOPDOB upon cooling. In this paper, it is assumed that the order parameter rho is propor...

We present a static solution to the classical field equations of a purely spinorial model with SO(2n) internal symmetry in 2n dimensions. The model contains composite vector fields which have solutions of the Wu-Yang monopole type.