Showing papers by "Samo Kralj published in 2007"
TL;DR: It is shown that prior to the expulsion the defect core displays dramatic changes for strong enough surface anchorings, and at a critical value of E{a}, the core broadens and merges into a surface layer with a large biaxiality.
Abstract: Within the Landau-de Gennes phenomenological theory, we study the influence of an applied electric field with average strength E{a} on the position of a nematic line defect with topological charge M=+/-1/2 in a hybrid cell We explore the biaxial structure of the defect core and we describe its expulsion from the cell upon increasing E{a} We show that prior to the expulsion the defect core displays dramatic changes for strong enough surface anchorings At a critical value of E{a}, the core broadens and merges into a surface layer with a large biaxiality This transition corresponds to the reconstruction of the nematic order already observed in the bulk in response to an applied electric field A similar order reconstruction could take place even in the absence of defects, but at a higher threshold
40 citations
TL;DR: A theoretical model that takes into account the interplay of relevant mechanisms is proposed to explain the observed phenomena and the effect of chirality on the interaction of liquid crystals with aerosils is discussed.
Abstract: A detailed x-ray scattering and high-resolution ac calorimetric study has been carried out near the smectic-$A$ to chiral smectic-$C$ phase transition of liquid-crystal compounds 4-(2-methyl butyl) phenyl 4-$n$-octylbiphenyl-4-carboxylate (CE8) and $p$-($n$-decyloxy) benzylidene-$p$-amino-(2-methylbutyl) cinnamate (DOBAMBC) confined in hydrophilic and hydrophobic aerosil nanoparticle networks. The character of the transition, which is mean field near a tricritical point in bulk, is changed dramatically with an increase of aerosil-induced disorder. X-ray measurements revealed pretransitional behavior and compression of the smectic layers, phenomena that are strongly pronounced in high aerosil concentrations. A theoretical model that takes into account the interplay of relevant mechanisms is proposed to explain the observed phenomena. The effect of chirality on the interaction of liquid crystals with aerosils is discussed.
33 citations
TL;DR: It is shown experimentally that randomness and surface wetting become dominant over finite-size effects for 2R approximately<10 nm, in agreement with theoretical analysis.
Abstract: The influence of controlled-pore glass (CPG) confinement on the phase behavior of octylcyanobiphenyl liquid crystal (LC) is studied by means of x-ray scattering and high precision calorimetry. For CPG samples with pore diameter 2R>24nm, the smectic order parameter temperature dependence η(T) reveals apparent presmectic ordering far above the bulk smectic A–nematic (SmA-N) phase transition for both nontreated and silane-treated CPG matrices. The behavior of η(T) is qualitatively similar in all samples, well obeying the mean field approach (MFA) in which the surface wetting tendency plays the dominant role. In contrast, the critical fluctuations remain important in the specific heat data, which cannot be described within the MFA. We show experimentally that randomness and surface wetting become dominant over finite-size effects for 2R≲10nm, in agreement with theoretical analysis. In nontreated samples, the noncritical character of the static disorder and the interfacial LC-CPG coupling almost completely sup...
33 citations
01 Jan 2007
TL;DR: In this article, preliminary broadband dielectric spectroscopy studies in a wide range of temperatures and pressures range for a mixture of rod-like liquid crystalline 4-cyano-4-pentylalkylbiphenyl (5CB) and hydrophilic silica spheres (Aerosil 300) are shown.
Abstract: Results of preliminary broadband dielectric spectroscopy studies in a wide range of temperatures and pressures range for a mixture of rod-like liquid crystalline 4–cyano–4–pentylalkylbiphenyl (5CB) and hydrophilic silica spheres (Aerosil 300) are shown. Pretransitional anomaly, observed previously in the bulk 5CB, has been found. Temperature dynamics of the mixture was investigated with via the DC conductivity σ, coupled to the reorientational relaxation. The derivative based analysis of electric conductivity showed a clear non-Arrhenius dynamics and indicated the anomalous increase of the fragility strength coefficient on approaching the isotropic-nematic transition. Pressure investigations of the solidification from the nematic phase showed the increase of the transition temperature on pressuring but with unusual increasing of dT NS /dP coefficient.
2 citations
01 Jan 2007
TL;DR: In this paper, the annihilation of point disclinations in nematic and line edge dislocations in smectic A LC phase is studied theoretically in liquid crystals, and the whole annihilation regime is taken into account, consisting of the pre-collision, collision, and postcollision stage.
Abstract: The annihilation of defect is studied theoretically in liquid crystals (LCs). We consider the annihilation of point disclinations in nematic and line edge dislocations in smectic A LC phase, respectively. We stress qualitative similarities in these processes. The whole annihilation regime is taken into account, consisting of the pre-collision, collision, and post-collision stage.
01 Jan 2007
TL;DR: In this article, material properties of mixtures have been studied and in some cases such behaviour hinges on simple physical concepts, giving rise to universal macroscopic responses (i.e. independent of microscopic details).
Abstract: In recent years we face an increasing interest in material properties of mixtures. Of particular interest are mixtures displaying behaviour that neither of the pure constituents exhibit. In some cases such behaviour hinges on simple physical concepts, giving rise to universal macroscopic responses (i.e. independent of microscopic details).