Numerical study of the phase behavior of rods in solution: Warner–Flory model with polydisperse system of rods

Phase equilibria of polydisperse rods in solution are studied in terms of the Warner–Flory model. Numerical calculations are made with a Gaussian-like asymmetric distribution of rod lengths. The aim of these studies is to investigate (i) the dependence of the phase diagram on the shape of the polydispersity distribution function and (ii) the isotropic–anisotropic phase separation within the coexistence range. It is shown that, as a consequence of polydispersity, even for a narrow distribution, the phase diagram is very simple, with only one type of anisotropic phase present. However, within the biphasic range, the properties of the anisotropic phase vary significantly with temperature. At high temperatures, they are essentially governed by steric effects and at low temperatures by both steric effects and soft anisotropic interactions between the rods.     

甲基纤维素/二氯乙酸液晶溶液的相转变

本文研究了甲基纤维素/二氯乙酸液晶溶液液晶相与各向同性相之间相互转变的过程。在连续升温过程中,由于液晶相内部有序度的非均一性,升温速率对液晶相织构随温度的变化有较大的影响。在等温相转变过程中,无论是从各向同性态转变为液晶态,还是其逆过程,从液晶态转变为各向同性态,相转变曲线均具有指数方程特征。利用与 Avrami 方程相似的指数方程进行处理,在从各向同性态转变为液晶态时,指数 n 大部分约为1。但液晶相向各向同性相在低于 Tc 时的相转变中,n 均小于1。相转变速率受溶液浓度和温度的影响。在质量分数为0.259的浓度时,液晶相向各向同性相的转变在低于 Tc 时39.5℃进行得最快。     

Phase and structural transformations of liquid-crystalline polymer systems in the mechanical field

Phase LC transitions and the structure of blends based on cyanoethyl cellulose with DMA and DMF, poly-(γ-benzyl-L-glutamate) with DMF, and hydroxypropyl cellulose with ethanol, acetic acid, DMA, DMF, and water have been studied under static conditions and in a mechanical field. With decreasing molecular mass of the polymer, the boundary curves separating isotropic from anisotropic solutions are shifted to higher concentrations and lower temperatures, in agreement with the Flory theory. When solutions are deformed, the cholesteric type of liquid crystals is transformed into the nematic type; this process is accompanied by the formation of domains in solutions, and the corresponding temperature-concentration boundaries of the LC phases are changed. As the molecular mass of the polymer increases, the ability of macromolecules to orient under the shear field decreases.     

Light induced shifts of ferroelectric mesophase transitions

Several series of recently synthesized chiral azobenzene liquid crystals exhibit transitions driven by both illumination and temperature: some compounds can be 'melted' from the SmC* phase to the isotropic phase by increasing illumination only; according to the phase sequences, SmA, TGBA, N*, and blue phases are also involved in such behaviour. The observed phenomena are reversible and transition temperatures are reproducible in identical light conditions. Some specific transitions have been studied. Their temperatures can be lowered to 10 degrees below the dark transition values by increasing the illumination of samples. Under illumination, those transitions exhibit first order behaviour.     

Light induced shifts of ferroelectric mesophase transitions

Several series of recently synthesized chiral azobenzene liquid crystals exhibit transitions driven by both illumination and temperature: some compounds can be 'melted' from the SmC* phase to the isotropic phase by increasing illumination only; according to the phase sequences, SmA, TGBA, N*, and blue phases are also involved in such behaviour. The observed phenomena are reversible and transition temperatures are reproducible in identical light conditions. Some specific transitions have been studied. Their temperatures can be lowered to 10 degrees below the dark transition values by increasing the illumination of samples. Under illumination, those transitions exhibit first order behaviour.     

Synthesis and properties of organic–inorganic hybrid liquid crystal gels

Organic–inorganic hybrid liquid crystal (LC) gels have been synthesised by the thiol-ene reaction of a multifunctional cyclic siloxane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (TVMCTS) and alkane dithiols, 1,6-hexanedithiol (HDT) or 1,9-decanedithiol (DDT), in LC matrices, 4-cyano-4?-pentylbiphenyl (5CB) or 4′-n-octyl-4-cyano-biphenyl (8CB). The LC gels were prepared in an isotropic phase at 70°C or mesophases at 25°C using radical initiators. The phase transition temperatures from a mesophase to an isotropic phase of the resulting gels were lower than those of the original LCs. The gels containing 8CB (8CB gels) prepared at 25°C showed two phase transitions: smectic-to-nematic and nematic-to-isotropic transitions. By contrast, the 8CB gels synthesised in the isotropic phase showed only one phase transition from smectic phase directly to isotropic phase. Reaction conversions in the LC gels prepared at 70°C were higher than that in the gels prepared at 25°C. Scanning microscopic light scattering analysis of the LC gels cleared homogeneous small size mesh with a small amount of large defect. Polarisation micrographs of the LC gels showed framed optical textures derived from the LC molecules at room temperature. The LC gels containing more than 90 wt% of LC showed electro-optic response.     

甲壳型液晶高分子的一种非寻常热致液晶行为

根据液晶相的稳定性 ,热致性液晶有双向性和单向性之分 .前者在升温和降温过程中都能形成液晶 ,而后者只能在降温过程中形成液晶 .原因是单向性液晶的液晶相不稳定 ,清亮点Ｔｉ 低于熔点Ｔｍ .升温时 ,样品熔融后直接进入各向同性的熔体 ;降温时 ,由于结晶过程的过冷 ,冷结晶温度Ｔｃ 低于Ｔｉ,样品先从各向同性态进入液晶态 ,然后才结晶 .一般情况下 ,如果液晶化合物自身是非晶的 ,所形成的有序结构不会由于冷却而遭到破坏 .最近 ,我们在研究分子量和液晶基元末端长度对甲壳型液晶高分子液晶性影响的时候发现 ,聚 [2 ,5 双 ( 4′ 正己氧基…     

Effect of temperature on the phase equilibrium of aqueous two-phase systems containing polyvinylpyrrolidone and disodium hydrogen phosphate or trisodium phosphate

Phase diagrams and liquid–liquid equilibrium (LLE) data of the aqueous polyvinylpyrrolidone–disodium hydrogen phosphate and aqueous polyvinylpyrrolidone–trisodium phosphate systems have been determined experimentally at 298.15, 308.15, 318.15 and 328.15 K. The effect of temperature and the type of salt on the binodal and tie-lines has been studied. It was found that, for the studied systems in the polyvinylpyrrolidone (PVP)-rich region, an increase in temperature caused the expansion of one-phase area; while, for the salt-rich region, expansion of the two-phase area was observed with increase in the temperature. It was also observed that the slope of all equilibrium tie-lines increased with increasing temperature. Furthermore, it was found that, as temperature is increased, these aqueous two-phase systems exhibit a phase inversion. Specifically, the PVP-rich phase – which at low temperatures is the less dense top phase – becomes the lower phase at elevated temperatures. Finally, an extended Flory–Huggins theory proposed in our previous paper has been used for correlation of LLE data.     

Rheological properties of anisotropic poly(para-benzamide) solutions

A study has been made of the viscous properties of poly(para-benzamide) (PBA) solutions in dimethyl acetamide, which undergo a transition from an isotopic to an anisotropic (liquid-crystal) state at a definite concentration C^*. The polymer solutions behave in many respects (as regards the concentration and temperature dependence of viscosity, etc.) like solutions of low molecular weight compounds forming a liquid crystal phase, although the transitions are less pronounced in the polymer solutions owing to their polydispersity. It is shown that the viscometric method, being extremely sensitive to C^*, is convenient for determining phase diagrams of anisotropic polymer solutions. The values of C^* as related to the molecular weight of PBA have been determined, and a general criterion for transition from isotropic to anisotropic solutions established; the latter has the form (CM?)^* ≈ 1.3 × 10⁵ at 20°C. This criterion is in line with the condition for the formation of the liquid-crystal structure in a dispersion of rodlike particles as proposed by Flory. Generalized concentration dependences of viscosity have been plotted by reducing concentration to C^* and viscosity, to the maximum viscosity at the phase transition point. In investigating the flow properties of PBA solutions we revealed the existence of a yield point in the range of low shear stresses, and an intersection of the flow curves of solutions of different concentration at high shear stresses, which excludes a generalized representation of the flow curves in reduced ordinary-type coordinates.     

Determination of fluid--solid transitions in model protein solutions using the histogram reweighting method and expanded ensemble simulations

Protein crystallization conditions are usually identified by empirical screening methods because of the complexity of the process, such as the existence of nonequilibrium phases and the different crystal forms that may result from changes in solution conditions. Here the crystallization of a model protein is studied using computer simulation. The model consists of spheres that have both an isotropic interaction of short range and anisotropic interactions between patch-antipatch pairs. The free energy of a protein crystal is calculated using expanded ensemble simulations of the Einstein crystal, and NpT-Monte Carlo simulations with histogram reweighting are used to determine the fluid-solid coexistence. The histogram reweighting method is also used to trace out the complete coexistence curve, including multiple crystal phases, with varying reduced temperature, which corresponds to changing solution conditions. At a patch-antipatch interaction strength five times that of the isotropic interaction, the protein molecules form a stable simple cubic structure near room temperature, whereas an orientationally disordered face-centered-cubic structure is favored at higher temperatures. The anisotropic attractions also lead to a weak first-order transition between orientationally disordered and ordered face-centered-cubic structures at low temperature, although this transition is metastable. A complete phase diagram, including a fluid phase, three solid phases, and two triple points, is found for the six-patch protein model. A 12-patch protein model, consistent with the face-centered-cubic structure, leads to greater thermodynamic stability of the ordered phase. Metastable liquid-liquid phase equilibria for isotropic models with varying attraction tails are also predicted from Gibbs ensemble simulations.     

LIQUID CRYSTALLINE BEHAVIOR OF AROMATIC COPOLYAMIDE IN CONCENTRATED SULPHURIC ACID

The liquid crystalline behavior of anisotropic solutions in 100% sulphuric acid ofaromatic copolyamide obtained by low-temperature solution copolycondensation of tere-phthalic acid chloride (TPC), p-phenylene diamine (PPD) and 4, 4'-diamino-diphenylether(DAPE) has been studied by optical microscopy and X-ray diffeaction. The effects ofinherent viscosity, concentration of copolyamide in sulphuric acid, the content of the thirdmonomer (DAPE) and sequence distribution of copolyamide on the critical concentration,isotropic temperature, phase diagram and texture of liquid crystal were investigated. Theschlieren texture was observed and the results of X-ray diffraction indicate that the con-centrated solutions of copolyamide exhibit nematic liquid crystalline behavior.     

羟乙基纤维素醋酸酯热致液晶性和相转变

本文研究了羟乙基纤维素醋酸酯的热致液晶和相转变过程。发现升温时,在130～185℃范围内羟乙基纤维素醋酸是各向异性的熔体,在温度高于185℃以后是各向同性的熔体。降温时,各向异性相在165℃时开始形成,进一步冷却到室温,形成液晶玻璃态。在降温过程中,相转变和液晶相织构的形成都很快,而且一旦液晶相的织构形成以后就不再随时间和温度降低而变化。羟乙基纤维素醋酸酯的热致液晶性还受其分子量影响,分子量越高,相转变温度越高。但是,在适当的分子量下,羟乙基纤维素醋酸酯才有最大的动力学相转变能力。     

Phase equilibria and phase separation dynamics in a polymer composite containing a main-chain liquid crystalline polymer

Various topological phase diagrams of blends of main-chain liquid crystalline polymer (MCLCP) and flexible polymer have been established theoretically in the framework of Matsuyama–Kato theory by combining Flory–Huggins (FH) free energy for isotropic mixing, Maier–Saupe (MS) free energy for nematic ordering in the constituent MCLCP, and free energy pertaining to polymer chain-rigidity. As a scouting study, various phase diagrams of binary flexible polymer blends have been solved self-consistently that reveal a combined lower critical solution temperature (LCST) and upper critical solution temperature (UCST), including an hourglass phase diagram. The calculated phase diagrams exhibit liquidus and solidus lines along with a nematic–isotropic (NI) transition of the constituent MCLCP. Depending on the strengths of the FH interaction parameters and the anisotropic (nematic–nematic) interaction parameters, the self-consistent solution reveals an hourglass type phase diagram overlapping with the NI transition of the constituent MCLCP. Subsequently, thermodynamic parameters estimated from the phase diagrams hitherto established have been employed in the numerical computation to elucidate phase separation dynamics and morphology evolution accompanying thermal-quench induced phase separation of the MCLCP/polymer mixture. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3621-3630, 2006     

Phase diagrams and morphology of polymer-dispersed liquid crystals: An analysis

Thermal and morphological studies of polymer-dispersed liquid crystals (PDLCs) for various compositions of liquid crystalline material 4-undecyloxybenzoic acid (UDBA) in two polymer matrices, polyvinylidenefluoride-co-hexafluoropropylene P(VdF–HFP) or polyethylene oxide (PEO), have been carried out using differential scanning calorimetry (DSC) and polarising optical microscopy (POM). Phase diagrams for different series of PDLCs have been analysed using the Flory–Huggins theory of isotropic mixing and the Maier–Saupe–McMillan theory, to include the anisotropic contributions. Mesogenic transitions of UDBA are observed to be greatly influenced when dispersed in these polymers. The morphologies and miscibility studies of these PDLCs suggest that UDBA is highly miscible in PEO, only partially miscible in poly(methyl methacrylate) (PMMA), but almost immiscible in P(VdF–HFP).     

Phase equilibria in Pr0.7Cd0.3MnO3 and Pr0.7Bi0.3MnO3

A solid state synthesis and phase transitions of solid solutions Pr_0.7Cd_0.3MnO₃ (PCM) and Pr_0.7Bi_0.3MnO₃ (PBM) have been studied within 20–1150°C temperature range. At room temperature, PCM and PBM phases are rhombic within Pnma space group. At high temperatures, Mn-O bonds in PCM are highly anisotropic, the anisotropy becoming insignificant at low temperatures.     

Anticlinic smectic C phase in new and novel five-ring hockey stick-shaped compounds

The synthesis of a new homologous series of novel five-ring compounds composed of hockey stick-shaped molecules derived from 4-hydroxybiphenyl-3-carboxylic acid which exhibit an interesting sequence of phase transitions is presented. Uniaxial nematic and smectic A phases, anticlinic smectic C phase and an unidentified smectic phase at a lower temperature than the latter have been observed. This is perhaps the first example of hockey stick-shaped compounds exhibiting anticlinic smectic C phase directly from the isotropic phase. Polarised light optical microscopy, differential scanning calorimetry, X-ray diffraction measurements and electro-optical switching studies were carried out to identify the mesophases.     

Phase transitions in solutions of hydroxypropoyl cellulose and cyanoethyl cellulose

LC phase transitions in mixtures of cyanoethyl cellulose and hydroxypropyl cellulose with different solvents have been studied by the cloud point and polarization microscopy methods and polarization photoelectric measurements. It has been found that, as the solvent polarity is decreased and the molecular mass of a polymer is increased, boundary curves delimiting the regions of isotropic and anisotropic solutions shift to the region of lower concentrations.     

N.M.R. and X-ray diffraction of the 7,7'-disodiumcromoglycate-water lyomesophases

Aqueous solutions of 7,7'-disodiumcromoglycate (7,7'-DSCG) form a variety of mesophases, whose natures depend on concentration and temperature. We have used optical microscopy, N.M.R. (of ²H, ¹⁷O and ²³Na) and X-ray techniques to construct a phase diagram for this system and to characterize the various mesophases. In the concentration range 3 to 25 wt % 7,7'-DSCG four different mesophases are found. On cooling the isotropic solution an opaque gel phase is first obtained, followed on further cooling by a birefringent glassy liquid. At concentrations below 14wt% it is nematic, while at higher concentrations it appears to be a different, more ordered, phase. At lower temperatures a hexagonal phase is formed which finally solidifies on cooling to - 15°C. The N.M.R. and X-ray characteristics of these mesophases are discussed.     

Nanostructured nonionic thymidine nucleolipid self-assembly materials

Three nucleoside lipids have been synthesized: 3'-oleoylthymidine, 3',5'-dioleoylthymidine, and 3'-phytanoylthymidine. Differential scanning calorimetry and X-ray diffraction have been employed to characterize the physical properties of these neat lipids. Polarizing optical microscopy, small-angle X-ray scattering, and cryo-transmission electron microscopy techniques have been used to investigate the phase behavior in aqueous systems. Both oleoyl-based nucleoside lipids adopted a lamellar crystalline phase in the neat form at room temperature, and the phytanoyl derivative exhibited a fluid isotropic phase. Under excess water conditions, the presence of one branched (phytanoyl) or one unsaturated (oleoyl) chain promoted the formation of a liquid-crystalline lamellar phase at physiological temperatures. In contrast, the 3',5'-dioleoylthymidine derivative is nonswelling and does not exhibit lyotropic liquid-crystalline phase behavior. The nucleolipids' propensity for DNA-type binding and recognition has been evaluated by using a monolayer system to measure surface pressure-area isotherms in a Langmuir trough and indicates that the nucleoside base is available for nonspecific hydrogen bonding in the monolayer liquid expanded state for the single-chain nucleolipids but not for the dual-chain amphiphile.     

Physical & thermal properties of model polysiloxane rubbers: impact of crosslink density and tin concentration

The influence of the tin octanoate catalyst on the physical and thermal properties of RTV 5370 polysiloxane rubbers has been studied. To assess the likely influence of crosslinking on a number of physical and thermal properties in polysiloxanes, “model siloxane networks” (representing networks of well defined composition/structure) have been formulated by the hydrosilylation of polysiloxane diols of known average molecular weight with tetraethoxysilane curing agent. It was found that linear swell and the crystallisation melting transitions of these systems were both significantly affected by changes in crosslink density. A selection of RTV5370 foamed rubbers with different tin concentrations were prepared in a similar manner to assess the influence of the tin catalyst. For these materials it was found that the area of the crystalline melting transition decreased with increasing tin concentration, an effect indicative of increased crosslinking. Samples with double the standard amount of tin (10% wt catalyst) show a shift in the crystallisation transition to higher temperature with no further effect beyond this concentration. Furthermore, the storage modulus (E') of the rubbers at room temperature appears to be independent of the tin catalyst concentration. Through correlation with the data from the model siloxanes, these results suggests that increasing the catalyst concentration appears to induce additional crosslinking interactions that are stable at low temperatures but not stable at room temperature.