Suppression of relaxation modes in dye dispersed SmC* phase

We report the results of dielectric and electro-optical properties of ferroelectric liquid crystal (FLC), Felix 17/100, exhibiting chiral smectic C phase and dye dispersed FLCs. The polarization measurement on pristine and dye dispersed FLC mixture shows decrease in the value of polarization, indicating the distribution of dye dipole in a direction opposite to the orientation of FLC molecule. The rotational viscosity also decreases accordingly as shown by the measurement of response time. Dielectric measurement shows existence of two relaxation modes both in pure FLC and dye dispersed FLC. The relaxation strength of Goldstone mode decreases with the dispersion of dye and the relaxation frequency of this mode shifts towards the high-frequency side. The second relaxation mode arises due to the formation of domains at the surface interface. The dispersion of dye into FLC suppresses the domains.     

Adsorption-resistant properties of copper phthalocyanine dispersed in a polymer matrix

The conduction mechanism in copper phthalocyanine (CuPc)-polymer composite thin films and their sensitivity to nitrogen dioxide are investigated. It is established that a hopping conduction mechanism in the regime of single electron hops prevails in these materials at 290–350 K, and the magnitude and rate of the adsorption-resistance sensitivity to NO₂ is higher than in pure CuPc. Fiz. Tverd. Tela (St. Petersburg) 40, 773–775 (April 1998)     

Field-induced transition from homeotropic to planar geometry in the SmC* phase of an electroclinic liquid crystal

The optical and electrical behavior was investigated of a symmetric liquid crystal (LC) cell: ITO–silane–LC–silane–ITO. The silane layer induces a perfect homeotropic alignment of the molecules of the studied electroclinic liquid crystal (ELC) material, BDH 764E. A field-induced transition from the perfect homeotropic to planar orientation in the chiral smectic C (SmC*) and smectic A (SmA) phases of the ELC was observed. Optical and dielectric studies were performed for both alignment (geometry) modes. The field-induced transition from the homeotropic to planar orientation was studied vis-à-vis the high negative dielectric anisotropy obtained in the studied material. Such an ELC with large negative dielectric anisotropy and perfect homeotropic alignment may have important implications for modern LC display technology.     

Effect of polymer viscosity on morphological and electro-optic properties of aligned polymer dispersed ferroelectric liquid crystal composite films

A room temperature ferroelectric liquid crystal mixture was dispersed in UV curable polymers of different viscosity in 30:70 wt/wt ratio. These polymer dispersed ferroelectric liquid crystal (PDFLC) composite films were prepared by polymerization induced phase separation technique. It was found that the polymer viscosity influences the droplet size and the electro-optic properties. The spontaneous polarization of PDFLC decreases with an increase in polymer viscosity. The droplet morphology and electro-optic properties of these materials have been investigated in an aligned configuration.     

Static and dynamic properties of supercooled thin polymer films

The dynamic and static properties of a supercooled (non-entangled) polymer melt are investigated via molecular-dynamics (MD) simulations. The system is confined between two completely smooth and purely repulsive walls. The wall-to-wall separation (film thickness), D, is varied from about 3 to about 14 times the bulk radius of gyration. Despite the geometric confinement, the supercooled films exhibit many qualitative features which were also observed in the bulk and could be analyzed in terms of mode-coupling theory (MCT). Examples are the two-step relaxation of the incoherent intermediate scattering function, the time-temperature superposition property of the late time α-process and the space-time factorization of the scattering function on the intermediate time scale of the MCT β-process. An analysis of the temperature dependence of the α-relaxation time suggests that the critical temperature, T _c, of MCT decreases with D. If the confinement is not too strong ( D≥10monomer diameter), the static structure factor of the film coincides with that of the bulk when compared for the same distance, T - T _c(D), to the critical temperature. This suggests that T - T _c(D) is an important temperature scale of our model both in the bulk and in the films. Received 12 September 2001     

Static and dynamic properties of a ferrite-garnet film in the neighborhood of orientational phase transitions

The static susceptibility and the spectrum of a magnetic-resonance mode of a single-crystal garnet-ferrite film with a domain structure are experimentally investigated. It is found that, in a magnetic field perpendicular to the film plane, these characteristics have features associated with the reorientation of the domain structure. The spin-wave spectrum of the film is calculated on the basis of the domain structure model proposed. It is shown that the experimentally observed features of the spectrum can be accounted for by the reorientation of magnetizations in the domains. A good agreement is obtained between experimental and theoretical values of the gap in the spin-wave spectrum at the “starting and end points of reorientation.”     

Static and time-dependent properties of polymer gels around the volume phase transition

Recent progress in the study of the volume phase transition of polymer gels is reviewed. The phenomenological theories of swelling equilibrium and phase transition of gels are summarized, and some basic experimental results on poly-N-isopropylacrylamide (NIPA) gels are compared with the prediction from these theories. Special attention is paid to the elastic properties of the gel network near the volume phase transition. The effect of external stresses on the swelling and the phase transition is analyzed. Some anomalous and unique characteristics revealed in NIPA gels such as shape- and size-dependent swelling and phase transition properties, curious phase coexistence, and domain structure are presented. Experimental results on some time-dependent phenomena such as phase separation, spinodal decomposition, and pattern formation are also presented and discussed. Some problems inherent to gels from biological bodies are briefly discussed.     

The effect of matrix composition on the electro-optical properties of polymer dispersed liquid crystal

A new type of polymer dispersed liquid crystal (PDLC) composite film has been made by polymerizing the mixture of di-methacrylates, methacrylates containing various groups and E-7. It was found that the long chain alkyl and mesogenic groups in methacrylate monomers greatly affected the saturation and threshold voltages and response time. The sharpness could be improved by addition of methacrylate monomers containing long chain alkyl and 4-butoxylbisphenyl based mesogenic group in appropriate ratios.     

In situ reduction of graphene oxide dispersed in a polymer matrix

Silicon wafers coated with a film of Ag pattern are used for investigating roles of Ag in the fabrication of silicon nanowire arrays (SiNWs) by the electroless chemical etching technique. The diameter of SiNWs grown in the mixed AgNO₃/HF solution ranges from 20 to 250?nm. A growth mechanism for such obtained SiNWs is proposed and further experimentally verified. As a comparison as well as to better understand this chemical process, another popular topic on growing SiNWs in the H₂O₂/HF solution is also studied. Originating from different chemical reaction mechanisms, Ag film could protect the underneath Si in the AgNO₃/HF solution and it could, on the contrary, accelerate etching of the underneath Si in the H₂O₂/HF solution.     

Static and dynamic properties of grafted ring polymer: Molecular dynamics simulation

The static and dynamic properties of a system of end-grafted flexible ring polymer chains grafted to a flat substrate and exposed to a good solvent are studied by using a molecular dynamics method. The monomers are described by a coarse-grained bead-spring model. Varying the grafting density ρ and the degree of polymerization or chain length N, we obtain the density profiles of monomers, study the structural properties of the chain (radius of gyration, bond orientational parameters, etc.), and also present the dynamic characteristics such as chain energy and bond force. Compared with a linear polymer brush, the ring polymer brush exhibits different static and dynamic properties for moderate or short chain length, while it behaves like linear polymer brush in the regime of long chain length.     

Static and dynamic properties of polymer brush with topological ring structures: Molecular dynamic simulation

By defining a topological constraint value(rn),the static and dynamic properties of a polymer brush composed of moderate or short chains with different topological ring structures are studied using molecular dynamics simulation,and a comparison with those of linear polymer brush is also made.For the center-of-mass height of the ring polymer brush scaled by chain length h~N~v,there is no significant difference of exponent from that of a linear brush in the small topological constraint regime.However,as the topological constraint becomes stronger,one obtains a smaller exponent.It is found that there exists a master scaling power law of the total stretching energy scaled by chain length N for moderate chain length regime,F_(ene)~Np~v,for ring polymer brushes,but with a larger exponent v than 5/6,indicating an influence of topological constraint to the dynamic properties of the system.A topological invariant of free energy scaled by(c)~(5/4) is found.     

Electro-optic and dielectric studies of silica nanoparticle doped ferroelectric liquid crystal in SmC* phase

We present the results based on the electro-optic and dielectric properties of silica nanoparticle (SNP) doped ferroelectric liquid crystal (FLC) in SmC* phase. Switching time, spontaneous polarization and rotational viscosity decreases with increase in the silica concentration. An improvement in switching time after doping the silica nanoparticle is due to enhancement in anchoring energy exist between silica nanoparticle and ferroelectric liquid crystal. We noticed that the dielectric permittivity and dielectric strength decreases with increasing the concentration of silica nanoparticle in SmC* phase. Relaxation frequency increases with increasing the silica concentration and temperature in SmC* and decreases as we approaches towards transition temperature.     

Optical and resonant X-ray diffraction studies confirm a SmC*FI2-SmC* liquid crystal phase sequence reversal

Employing both null transmission ellipsometry and resonant x-ray diffraction, we confirmed the SmC*FI2-SmC* phase sequence reversal in one liquid crystal compound and specially prepared binary mixtures. This phase sequence reversal was predicted by two recent theoretical advances. Moreover, the temperature range for the SmC*FI2 phase increases significantly in the mixture suggesting that such a phase sequence may exist in other compounds.     

Magnetic properties of MnO nanocrystals dispersed in a silica matrix

Magnetic nanocrystalline MnO particles have been synthesized in a silica glass matrix by the sol-gel method at calcination temperatures up to 1000 °C. EPR spectra of 0.1 mol% MnO doped silica gel and glasses studied in the temperature range 10-290 K show with the exception of those samples calcined at 900 and 1000 °C 6-line characteristic Mn(II) hyperfine (HF) lines. Additionally five spin-forbidden doublets have been observed at 100 K and below. Small spreads in spin Hamiltonian parameters (D and E) imply that the ligand field environments of Mn(II) ions embedded in the silica glass are nearly uniform. Monotonous decrease in HF linewidth in going from 120 °C gel to 800 °C calcined glass has been interpreted as the continuous decrease in population of isolated Mn²⁺ ions in silica glass matrix resulting in the decrease of magnetic dipolar interactions leading to the observed decrease in HF linewidth. XRD and TEM of sample calcined at 1000 °C shows the presence of nanocrystals of MnO having orthorhombic crystalline phase and sizes about 10 nm. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of MnO nanocrystals in the 5-300 K temperature interval have demonstrated that the MnO nanocrystals display superparamagnetic-ferromagnetic transition at low temperatures. X-band EPR linewidth data plotted versus inverse of temperature (1/T) for samples calcined at 900 and 1000 °C (EPR recorded in the vicinity of 0.35 T applied field) depict similar transitions.     

表面摩擦处理对全息聚合物分散液晶光栅电光特性的影响

为了提高全息聚合物分散液晶光栅的衍射效率并降低其驱动电压,改善光栅的电光特性,研究了表面平行摩擦取向对全息聚合物分散液晶光栅电光特性的影响.理论分析认为,改善相分离结构和降低液晶微滴之间的有序度差异是优化光栅电光特性的根本所在.由于进行表面取向处理后的液晶和单体之间达到扩散匹配,使得相分离的程度大幅提高,在衍射能力增强的同时驱动电压也实现了大幅下降,而且,表面取向作用也使光栅内的液晶分子均匀排列,降低了液晶微滴之间的有序度差异,从而减少了光栅的散射损失.实验结果表明:进行取向处理后的光栅其衍射效率由传统光 关键词： 全息聚合物分散液晶 衍射效率 驱动电压     

Effect of graphene oxide dispersion in antiferroelectric liquid crystal mixture in the verge of SmC* to SmCA* phase transition

The continuous growing demand for nanoscience applications and the improvement in the performance of liquid crystal based devices has been extensively required by the technological world. Recent progress in the field of liquid crystals has found its practical implementation in various display and non display devices which experiences obstacle due to impurity effects that reduces its performance. The dispersion of nanoparticles in liquid crystal medium helps in the reduction of impurity ions and thus improving the performance of liquid crystal based devices. The present work is based on the collective dielectric relaxation processes that have been observed in antiferroelectric liquid crystal (AFLC) mixture W1000 dispersed with 0.1% wt/wt and 0.3% wt/wt concentrations of graphene oxide. Graphene oxide itself favors vertical alignment and the coupling of AFLC W1000 mixture with graphene oxide affects its molecular ordering. This has been confirmed from the polarizing optical micrographs. The dielectric relaxation modes have been observed with and without the application of bias voltage in SmC* to SmC_A* phase transition during cooling cycle. The appearance and disappearance of P_L, P_H and X modes have been observed and are explained on the basis of molecular interactions. Graphene oxide dispersed system favors homeotropic alignment (dark state) and the application of bias field will convert it into homogenous alignment (bright state). Graphene oxide dispersion find prospective applications in good contrast display devices, supercapacitors, electronic gadgets, rechargeable batteries. Electro optical results unveil the faster response time, decreased rotational viscosity and spontaneous polarization with no change in tilt angle for the dispersed system. These observations can be exploited in photonic switches with sub millisecond response time which are required for fabricating faster liquid crystal devices.     

Static and dynamic quenching of luminescent species in polymer media

A method developed for quantitative determination of static and dynamic contributions to luminescence quenching is applied to Ru(II) complexes in polymer matrices (silica gel and polystyrene), quenched by oxygen. This method is based on both intensity and lifetime quenching experiments. The curvature of intensity Stern-Volmer plots is related to the results.     

Static and dynamic properties of pseudoscalar mesons

We report the results of form factors, charge radii and decay constants of both light and heavy flavoured pseudoscalar mesons in a QCD inspired quark model. We use the quantum mechanical perturbation theory and discuss its limitations in the present problem. Several predictions are also made for bottom and top flavours.