Dynamics of cholesteric liquid crystals in the presence of a random magnetic field:stochastic dynamics of cholesteric liquid crystal

Based on dynamic renormalization group techniques, this letter analyzes the effects of external stochastic perturbations on the dynamical properties of cholesteric liquid crystals, studied in presence of a random magnetic field. Our analysis quantifies the nature of the temperature dependence of the dynamics; the results also highlight a hitherto unexplored regime in cholesteric liquid crystal dynamics. We show that stochastic fluctuations drive the system to a second-ordered Kosterlitz-Thouless phase transition point, eventually leading to a Kardar-Parisi-Zhang (KPZ) universality class. The results go beyond quasi-first order mean-field theories, and provides the first theoretical understanding of a KPZ phase in distorted nematic liquid crystal dynamics

Role of external and internal perturbations on ferromagnetic phase transitions in manganites:existence of tricritical points

A phenomenological mean-field theory is presented to describe the role of external magnetic field, pressure and chemical substitution on the nature of ferromagnetic (FM) to paramagnetic (PM) phase transition in manganites. The application of external field (or pressure) shifts the transition, leading to a field (or pressure) dependent phase boundary along which a tricritical point is shown to exist where a first-order FM-PM transition becomes second-order. We show that the effect of chemical substitution on the FM transition is analogous to that of external perturbations (magnetic field and pressure); this includes the existence of a tricritical point at which the order of transition changes. Our theoretical predictions satisfactorily explain the nature of FM-PM transition, observed in several systems. The modeling hypothesis has been critically verified from our experimental data from a wide range of colossal magnetoresistive manganite single crystals like Sm0.52Sr0.48MnO3. The theoretical model prediction of a tricritical point has been validated in this experiment which provides a major ramification of the strength of the model proposed

Effect of magnetic nanoparticles on the nematic-smectic-A phase transition

Recent experiments on mixed liquid crystals have highlighted the hugely significant role of ferromagnetic nanoparticle impurities in defining the nematic-smectic-A phase transition point. Structured around a Flory-Huggins free energy of isotropic mixing and Landau-de Gennes free energy, this article presents a phenomenological mean-field model that quantifies the role of such impurities in analyzing thermodynamic phases, in a mixture of thermotropic smectic liquid crystal and ferromagnetic nanoparticles. First we discuss the impact of ferromagnetic nanoparticles on the isotropic-ferronematic and ferronematic-ferrosmectic phase transitions and their transition temperatures. This is followed by plotting and discussing various topologies in the phase diagrams. Our model results indicate that there exists a critical concentration of nanoparticle impurities for which the second order N-SmA transition becomes first order at a tricritical point. Calculations based on this model show remarkable agreement with experiment

Effect of ferroelectric nanoparticles on the isotropic-smectic-A phase transition

Recent experimental studies have shown that ferroelectric nanoparticles play an important role on smectic liquid crystals. These include the weakly discontinuous nature of the isotropic-smectic-A transition, the decrease of the temperature metric discontinuity, the decrease of the dielectric constant and a slight increase of the transition temperature. We described all these experimental observations within phenomenological theory. The impact of ferroelectric nanoparticles on the isotropic-smectic-A transition temperature, Kerr constant and non-linear dielectric effect is discussed. The theoretical predictions were found to be in good qualitative agreement with the experimental results

Confinement-driven rotator-I to rotator-V phase transition of alkane

The behavior of the rotator-I to rotator-V $(R_I\text{-}R_V)$ phase transition of alkane in nanoconfinement situations is studied theoretically. Recent experimental studies have shown that confinement has dramatic effects on the $R_I\text{-}R_V$ phase transition. These include the weakening of the $R_I\text{-}R_V$ phase transition, decrease of the order parameters, change of the profile of the specific heat and reduction of the extent of the hysteresis region. We described these experimental observations within Landau phenomenological theory. The impact of confinement on the $R_I\text{-}R_V$ phase transition is discussed in great detail. The theoretical predictions are compared with recent experimental results

Phenomenological theory of the nematic to lamellar phase transition in lyotropic liquid crystals

A phenomenological theory is presented to describe the nematic to lamellar phase transition in lyotropic liquid crystals. The problem of the first or second order transition is explored by means of the variation of the surfactant concentration. The possibility of the tricritical point at the nematic to lamellar phase transition is discussed in a phenomenological way. The influence of the electrolyte on this transition is also discussed by varying the coupling between the electrolyte concentration variables and the order parameters. The theoretical prediction is found to be in good qualitative agreement with experimental results