STUDY ON THE PHASE TRANSITION KINETICS OF THERMOTROPIC LIQUID CRYSTALLINE AROMATIC-ALIPHATIC COPOLYESTER

The phase transition kinetics of thennotropic liquid crystalline aromatic-aliphatic regular copolyester: were studied by DSC. By means of Kissinger's method the kinetic equation and parameters including activation energy, rate order and preexponential factor for phase transition from nematic to isotropic were obtained. The activation energy from crystal to nematic was also presented.     

On the mechanism of photoinduced phase transitions in ternary liquid crystal systems near thermal equilibrium

According to their phase diagram, polyalkyl glycol ether dissolved in ternary solutions (water, alcane, and cyclohexane) lead to the formation of either liquid crystal phases or microemulsion phases. By photosensitization of the ternary system with laser dyes and choosing the adequate concentration and temperature conditions of these lyotropic systems, it is possible to photoinduce the phase transitions from the microemulsion phase to the liquid crystal phase (and vice versa). The phototransformation conditions were chosen in such a way that the system is in thermal equilibrium during the entire phase transition. The method of photo small angle x-ray scattering has been applied to investigate the mechanism of photoinduced phase transition. Spectroscopically, the mechanism of photoinduced phase transition has been characterized by optical absorption and emission techniques.     

Polymeric infrared reflective thin films with ultra-broad bandwidth

A polymeric liquid crystalline film was fabricated by photo-induced diffusion and mesogenic phase structural transition of photopolymerisable acrylate monomer mixtures that presented phase transition between cholesteric (Ch) and smectic (SmA) phases. By controlling the curing temperature to be close to SmA–Ch phase transition, a novel architecture that combined Ch and SmA-like short-range ordering (SSO) nanostructures was obtained, which reflected light with the wavelength from 0.5 to 11.5 µm. Experimental results showed that the existence of UV-absorbing dye and curing temperature were critical for the creation of asymmetrical super wide pitch gradient distribution. Moreover, the reflection wavelength and bandwidth of the cholesteric liquid crystal (CLC) films were tuneable by adjusting proportion of the compounds, and the bandwidth could be broadened up to 13 μm. It was expected to have great potential applications in fields like architectural energy conservation or infrared-stealth.     

非离子表面活性剂液晶的线性粘弹性研究

用偏光显微镜测定了十二/十四烷基聚氧乙烯醚(C12～14EO7)/水二元体系相图的液晶区,用RS-75控制应力流变仪,在固定频率(f=0.0316Hz)时,对不同样品进行应力扫描。利用线性粘弹性区内流变参数G"与G'的比值thδ对相转变敏感的特点来确定相结构的转变,并将结果与2^HNMR结果相比较,两者吻合,这表明宏观测量手段能够反映微观相结构的变化规律。对于液晶实验结果采用弹簧-粘壶模型进行解释和讨论。     

Polymerization and viscoelastic behavior of networks from a dual‐curing,liquid crystalline monomer

The network formation and viscoelastic behavior of a liquid crystalline monomer, whose structure includes both acrylate and acetylene reactive groups, have been studied. By combining both photo and thermal polymerization, the networks can be formed in two separate steps, with the initial photopolymerization dominated by acrylate crosslinking and subsequent thermal polymerization dominated by acetylene crosslinking. In addition, the monomer exhibits a liquid crystalline phase. Photopolymerization while in the liquid crystal phase locks in the molecular ordering. Dynamic mechanical analysis shows that networks formed from the liquid crystalline phase have lower crosslink densities and narrower distributions of molecular weights between crosslinks when compared to networks formed from the isotropic phase (and at higher polymerization temperatures). After thermal postcure at 250°C, the networks formed from the isotropic monomer have a 23% higher dynamic mechanical storage modulus (in the glassy state) than the networks formed from the liquid crystalline monomer. The thermally postcured networks have unusually high glass‐transition temperatures, which exceed 300°C. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1183–1190, 1999     

A morphological study of membranes obtained from the systems polylactide-dioxane-methanol,polylactide-dioxane-water and polylactide-N-methyl pyrrolidone-water

The influence of liquid–liquid demixing, solid–liquid demixing, and vitrification on the membrane morphologies obtained from several polylactide-solvent-nonsolvent systems has been investigated. The polymers investigated were the semicrystalline poly-L-lactide (PLLA) and the amorphous poly-DL-lactide (PDLLA). The solvent-nonsolvent systems used were dioxane-water, N-methyl pyrrolidone-water and dioxane-methanol. For each of these systems it was attempted to relate the membrane morphology to the ternary phase diagram at 25°C. It was demonstrated that for the amorphous poly-DL-lactide the intersection of a glass transition and a liquid–liquid miscibility gap in the phase diagram was a prerequisite for the formation of stable membrane structures. For the semicrystalline PLLA a wide variety of morphologies could be obtained ranging from cellular to spherulitical structures. For membrane-forming combinations that show delayed demixing, trends expected on the basis of phase diagrams were in reasonable agreement with the observed membrane morphologies. Only for the rapidly precipitating system PLLA-N-methyl pyrrolidone-water were structures due to liquid–liquid demixing obtained when structures due to solid–liquid demixing were expected. Probably, rapid precipitation conditions promote solid–liquid demixing over liquid–liquid demixing, because the activation energy necessary for liquid–liquid demixing is lower than that for crystallization. © 1996 John Wiley & Sons, Inc.     

新型弯曲形双偶氮苯类液晶合成及光致异构性能研究

弯曲形偶氮苯液晶由于其偶氮键独特的光致可逆异构化性能,已成为光电子信息材料研究的热门课题,但光响应速度慢已成为制约其发展的关键因素.目前报道的弯曲型偶氮类液晶化合物的偶氮键都距离中心核较远的位置,光致异构的响应时间较长,大都在分钟以上,不利于光敏器件应用研究.本工作试图以2-甲基-1,3-间苯二胺为中心核,将偶氮键紧挨中心核两边,末端为直链烷基,设计合成了一系列新型弯曲形双偶氮苯类液晶化合物,以期缩短光响应时间.通过IR, 1H NMR, 13C NMR和ICP-MS光谱鉴定这些化合物的分子结构,经差示扫描量热仪(DSC)和偏光显微镜(POM)测定其液晶相变温度和相态织构;并通过测定2-甲基-1,3-双(4-((4-庚基苯基)酯基)-1-(E)-偶氮苯基)苯(2c)的紫外-可见光的吸收光谱研究其光致异构化性能,通过UV-Vis光谱仪和偏光显微镜(POM)测定其液晶化合物以及掺杂向列相液晶材料的光致异构现象和响应时间.实验结果表明,所有设计合成的弯曲形双偶氮苯类液晶化合物均具有近晶相相态,且相态温度范围较宽,当近晶相态化合物2c掺杂到向列相混合液晶中时,其光致异构响应时间为2~3 s,在日光下液晶态恢复时间为3~4s,在乙酸乙酯稀溶液中时10s可达到光稳态.说明这类弯曲形双偶氮液晶化合物具有较快的光致异构响应速度.     

含偶氮苯生色团的聚醚的合成与热致液晶性质

β－氯乙基缩水甘油醚（ＧＣＥ）和ＧＣＥ／羟丁基乙烯基醚（ＨＢＶＥ）分别通过阳离子聚合、光引发共聚合,获得两种聚醚,然后再分别与４－硝基－４’－羟基偶氦苯（ＮＨＡ）反应,制备了两种侧链含偶氦苯生色团的液晶聚合物（ＰＡＥＧ、ＰＡＶ）。用ＦＴＩＲ、＾１Ｈ－ＮＭＲ和ＥＡ对其化学结构及生色团含量进行了表征,以ＰＯＭ,ＤＳＣ、ＴＧＡ和ＷＡＸＤ对聚合物介晶相转变温度、织构、热稳定性及相行为进行了研究。结果表明,     

Kinetics of the adhesion of DMPC liposomes on a mercury electrode. Effect of lamellarity, phase composition, size and curvature of liposomes, and presence of the pore forming peptide mastoparan X

Liposomes suspended in aqueous electrolyte solutions can adhere at mercury electrodes. The adhesion is a complex process that starts with the docking and opening and leads to a spreading, finally resulting in the formation of islands of adsorbed lecithin molecules. The adhesion process can be followed by chronoamperometry, and a detailed analysis of the macroscopic and microscopic kinetics can be performed yielding rate constants and activation parameters. By using giant unilamellar liposomes and multilamellar liposomes, the effect of lamellarity and liposome size could be elucidated for liposomes in the liquid crystalline, gel, and superlattice phase states. Below the phase transition temperature, the time constant of opening of the liposomes (i.e., the irreversible binding of the lecithin molecules on the preliminary contact interface liposome|mercury and the therewith associated disintegration of the liposome membrane on that spot) is shown to be strongly size dependent. The activation energy, however, of that process is size independent with the exception of very small liposomes. That size dependence of time constants is a result of the size dependence of the initial contact area. The time constant and the activation energies of the spreading step exhibit a strong size dependence, which could be shown to be due to the size dependence of rate and activation energy of pore formation. Pore formation is necessary to release the solution included in the liposomes. This understanding was corroborated by addition of the pore inducing peptide Mastoparan X to the liposome suspension. The obtained results show that electrochemical studies of liposome adhesion on mercury electrodes can be used as a biomimetic tool to understand the effect of membrane properties on vesicle fusion.     

含茋生色团聚醚的合成与热致液晶行为

β 氯乙基缩水甘油醚 (GCE)和GCE/羟丁基乙烯基醚 (HBVE)分别通过阳离子聚合、光引发共聚合 ,获得两种聚醚 ,然后再分别与 4 硝基 4′ 羟基 (NHS)反应 ,制备了两种侧链含生色团的液晶聚合物(PSEG、PSV) .用FTIR、1H NMR和EA对其化学结构及生色团含量进行了表征 ,以POM、DSC、TGA和WAXD对聚合物介晶相转变温度、织构、热稳定性及相行为进行了研究 .结果表明 ,这类聚合物属向列型热致双向性液晶 ,液晶相转变温度较低、范围较宽 ;聚合物热稳定性较好 ,开始分解温度在 30 0℃以上 .     

Existence of time lag in crystalline to smectic A (K–SmA) phase transition of 4-decyl-4-biphenylcarbonitrile (10CB) liquid crystal

This study explores the presence of time lag in crystalline to smectic A (K–SmA) phase transition of 4-decyl-4-biphenylcarbonitrile (10CB) liquid crystal. A non-isothermal heating and cooling study were performed for 10CB liquid crystal using calorimetric technique where heating scan was performed from 250 to 350 K, and cooling scan was performed from 350 to 250 K. A clear difference in K–SmA phase transition was observed between heating and cooling scans. An attracting inclination effect in K–SmA transition was observed on cooling which is completely absent on heating. The inclination of the K–SmA transition peak increases and shows an existence of time lag during cooling, whereas other family member shows no effect i.e., 8CB. K–SmA peak shows a lower enthalpy with higher activation when compared with 8CB. The presence of time lag and increase in activation can be explained in terms of the density and nature of the material.     

Solution processing of polymer semiconductor: Insulator blends—Tailored optical properties through liquid–liquid phase separation control

It has been demonstrated that the 0‐0 absorption transition of poly(3‐hexylthiophene) (P3HT) in blends with poly(ethylene oxide) (PEO) could be rationally tuned through the control of the liquid–liquid phase separation process during solution deposition. Pronounced J‐like aggregation behavior, characteristic for systems of a low exciton band width, was found for blends where the most pronounced liquid–liquid phase separation occurred in solution, leading to domains of P3HT and PEO of high phase purity. Since liquid–liquid phase separation could be readily manipulated either by the solution temperature, solute concentration, or deposition temperature, to name a few parameters, our findings promise the design from the out‐set of semiconductor:insulator architectures of pre‐defined properties by manipulation of the interaction parameter between the solutes as well as the respective solute:solvent system using classical polymer science principles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 304–310     

Inhomogeneous phase separation kinetics in liquid binary mixtures: Sensitivity to initial local composition 2

The kinetics of phase separation subsequent to a finite temperature quench is assumed to be driven by diffusion on the altered free energy surface and is generally assumed to be slow. The situation can be different in phase separating liquid binary mixtures, especially for systems characterized by the large difference in mutual interactions between solute and solvent molecules. In such cases, the phase separation kinetics could be fast and may get completed within a short time (ns) scale. As a result, in these systems, one may observe diverse dynamical features arising out of local heterogeneity leading to the onset of phase separation through pattern formation, spinodal decomposition, nucleation, and growth. By using a coarse-grained analysis, we examine phase separation kinetics in each spatial grid and indeed observe important effects of initial heterogeneity on the subsequent evolution. Interestingly, we observe slower separation kinetics for those regions that correspond to the composition at the minimum of the high-temperature surface. The heterogeneous dynamics has been captured here through the non-linear susceptibility function, which shows a pattern similar to what is observed in the supercooled liquid. Each grid shows somewhat different dynamics in the three-stage (exponential, power-law, and logarithmic regime) phase separation dynamics. The late stage of phase separation kinetics is usually attributed to the coarsening of the phase-separated domains. However, in a liquid binary mixture, the late-stage power-law decay undergoes a further change. A new dynamical regime arises characterized by a logarithmic time dependence, which is due to the “smoothening” of the rough interface of already well-separated phases. This can also be described as opposite to the roughening transition described by Chui and Weeks [Phys. Rev. Lett. 40, 733 (1978)]. This reverse roughening transition can explain the logarithmic time dependence observed in the simulation.     

Novel photo‐crosslinkable liquid crystalline polymers containing vanillylidene cycloalkanones and azobenzene units

Two series of novel liquid crystalline photo‐crosslinkable bis(vanillylidene‐azobenzene) cycloalkanone containing polymers, namely poly(vanillylidene alkyloxy‐4,4′‐azobenzenedicarboxylic ester)s, have been synthesised from bis[m‐hydroxyalkyloxy(vanillylidene)cycloalkanone] (m = 6, 8, 10) with azobenzene dicarbonylchloride by solution polycondensation method at ambient temperature. Polymers with varying spacer lengths have been synthesised and characterised by spectroscopic techniques. These variations have been correlated with the thermal properties and transition temperatures. Thermal transitions were analysed by differential scanning calorimetry (DSC) and the mesophases were identified by hot stage optical polarised microscopy (HOPM). All of the polymers were found to exhibit liquid crystalline properties. Transition temperatures were observed to decrease with increasing spacer length. The thermogravimetric analysis reveals that all of the polymers were stable up to 280°C undergo two‐stage decomposition. Using the UV–visible photolysis studies we investigated the simultaneous behaviour of reactivity rates of crosslinking in the vanillylidene unit and isomerisation caused by the azobenzene unit in the photo‐crosslinkable main chain liquid crystalline polymers. The photolysis of liquid crystalline bis(vanillylidene)cycloalkanone‐based polymers reveals that there are two kinds of photoreactions in these systems: the EZ photoisomerisation of azobenzene unit and 2p+2p addition by vanillylidene units. The EZ photoisomerisation in the liquid crystal phase disrupts the parallel stacking of the mesogens, resulting in the transition from the liquid crystal phase to isotropic phase. The photoreaction involving 2p+2p addition of the bis(vanillylidene)cycloalkanone units in the polymers results in the conjoining of the chains. The cyclopentanone polymers exhibited a faster rate of photolysis than the cyclohexanone polymers.     

电场增强催化作用探讨

The effect of equi weight electrostatic field on transesterification of MeCOOBu with EtOH in the presence of base catalyst in liquid phase was investigated. The conversion of forward reaction and backward reaction was slightly enhanced in the equi weight field ( E =1×10 5 V/m). SCC DV X α calculations showed that the HOMO energy level of CH 2O was decreased by about 9 6 eV in H + field, while increased by about 23 7 eV in O 2- field. It is concluded that the activation energy of the reaction in equi weight electrostatic field is almost the same as in free field, owing to the same potential energy change of the reactants, transition states and products. In the unequi weight electrostatic field, the negative charge center seems to be the active site for reactants or products, while the positive one seems to be the active site for transition states, resulting in great decrease in the activation energy.     

Investigation of dielectric relaxations associated with the glass transition of vinylidene fluoride and trifluoroethylene copolymers by thermally stimulated current

Thermostimulated current (TSC) spectroscopy was applied to the characterization of dielectric relaxations associated with the glass transition of a series of P(VDF/TrFE) copolymers. The maximum temperature of the β-mode increases slightly as the TrFE unit content is increased, in the same manner as the glass transition temperature. By using the technique of fractional polarizations to the resolution of this relaxation mode, we have isolated, for all the polymers investigated, a series of elementary relaxation times that obey a compensation law. This behavior is characteristic of the free amorphous phase of polymers. The mean activation energy of this mode increases as the TrFE unit content is increased, due to a stiffening of molecular chains. Annealing of the copolymers above their ferroelectric-to-paraelectric transition induces a strong crystallinity increase of the materials. As a matter of fact, the amorphous phase is squeezed in to dimensions lower than the characteristic length scale associated with the glass transition. © 1995 John Wiley & Sons, Inc.     

Ionic liquid crystal precursors for inorganic particles: phase diagram and thermal properties of a CuCl nanoplatelet precursor

We have recently reported (Angew. Chem. Int. Ed. 2004, 43 (40), 5380) the formation of CuCl nanoplatelets from an ionic liquid crystal precursor (ILCP) consisting of a 50/50 (wt/wt) mixture of bis(dodecylpyridinium) tetrachlorocuprate 1 and 6-O-palmitoyl ascorbic acid 2. Here we present the full ILCP phase diagram and the thermal behavior from a mixing ratio of 1/0 (i.e., pure 1) to 0/1 (i.e., pure 2). The ILCP exhibits a crystalline-smectic-isotropic phase transition at all mixing ratios, and the liquid crystal region is up to 90 degrees C wide. DSC shows a broad exothermic peak between ca. 70 and 170 degrees C, which is associated with the thermally induced CuCl formation. The reaction enthalpies reach -150 kJ/mol at around 50/50 (wt/wt) mixtures of the two components, and the activation energy for CuCl formation is ca. 190 kJ/mol. Thermogravimetric analysis shows that the samples degrade above ca. 200 degrees C.     

Mechanism and Tafel lines of electro-oxidation of water to oxygen on RuO2(110)

How to efficiently oxidize H(2)O to O(2) (H(2)O → 1/2O(2) + 2H(+) + 2e(-)) is a great challenge for electrochemical/photo water splitting owing to the high overpotential and catalyst corrosion. Here extensive periodic first-principles calculations integrated with modified-Poisson-Boltzmann electrostatics are utilized to reveal the physical origin of the high overpotential of the electrocatalytic oxygen evolution reaction (OER) on RuO(2)(110). By determining the surface phase diagram, exploring the possible reaction channels, and computing the Tafel lines, we are able to elucidate some long-standing puzzles on the OER kinetics from the atomic level. We show that OER occurs directly on an O-terminated surface phase above 1.58 V vs NHE, but indirectly on a OH/O mixed phase below 1.58 V by converting first the OH/O mixed phase to the O-terminated phase locally. The rate-determining step of OER involves an unusual water oxidation reaction following a Eley-Rideal-like mechanism, where a water molecule from solution breaks its OH bond over surface Os with concurrent new O-OH bond formation. The free energy barrier is 0.74 eV at 1.58 V, and it decreases linearly with the increase of potential above 1.58 V (a slope of 0.56). In contrast, the traditionally regarded surface oxygen coupling reaction with a Langmuir-Hinshelwood mechanism is energetically less favored and its barrier is weakly affected by the potential. Fundamentally, we show that the empirical linear barrier~potential relation is caused by the linear structural response of the solvated transition state to the change of potential. Finally, the general strategy for finding better OER anode is also presented.     

弹性散射法研究间规聚苯乙烯的冷结晶行为

用弹性光散射方法研究了间规聚苯乙烯(s-PS)的非等温冷结晶行为和等温结晶动力学.结果表明,弹性散射信号对s-PS的冷结晶过程中的构象变化非常敏感.弹性散射法所得的大分子链玻璃化转变温度Tg以及冷结晶温度Tc与DSC的测量结果一致.此外,通过散射强度随温度的变化可以更为清晰地分辨出冷结晶过程中各个阶段,包括晶体成核期,晶核生长期以及二次结晶期.通过等温弹性散射测试,同时结合Arrhenius方程,计算得到s-PS冷结晶表观活化能Ea为309 kJ/mol.     

A new model to study the phase transition from microstructures to nanostructures in ionic/ionic surfactants mixture

The phase behavior and aggregate structures of mixtures of the oppositely charged surfactants cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) are explored at high dilution by pulsed field gradient stimulated echo (PFG-STE) NMR. The aggregation numbers and hydrodynamic radii of vesicles and mixed micelles were determined by a combination of viscosity and self-diffusion coefficient measurements. The average size of the mixed micelles was larger than that of micelles containing uniformly charged head groups. Analysis of the variations of the self-diffusion coefficient and viscosity with changing concentration of CTAB or SDS in the cationic-rich and anionic-rich regions revealed a phase transition from vesicles to mixed micelles. Differences in the lengths of the CTAB and SDS hydrophobic chains stabilize vesicles relative to other microstructures (e.g., liquid crystalline and precipitate phase), and vesicles form spontaneously over a wide range of compositions in both cationic-rich and anionic-rich solutions. The results obtained from conductometry measurements confirmed this transition. Finally, according to the capacitor model, a new model was developed for estimating the surface potentials and electrostatic free energy (g(elec)). Then we investigated the variations of electrostatic and transfer free energy in phase transition between mixed micelle and vesicle.