Concentrated solutions of polydisperse rodlike polymers in the isotropic and lyotropic liquid-crystalline phases. II. Model simulation of the dielectric relaxation behavior of poly(n-alkylisocyanates) in toluene and comparison with experimental results

A simulation has been made of the dielectric relaxation behavior of poly(n-hexylisocyanate) in solution covering the isotropic, biphasic, and anisotropic ranges. The simulation incorporates the Flory-Abe statistical mechanical theory for the phase behavior of rodlike macromolecules in solution and the Warchol, Vaughan, Wang, and Pecora theory for the dynamics of a rodlike molecule in a virtual cone prescribed by the neighboring molecules. It is shown that asymmetric Gaussian, Gaussian, or Poisson distributions of molecular weight do not lead to dielectric behavior of the type observed experimentally by Moscicki, Williams, and Aharoni but addition of a high-molecular-weight “tail” to such distributions and taking account of the dependence of relaxation time on molecular length gives a simulation of the dielectric increment Δε, the loss maximum ε, and frequency of maximum loss f_m, which vary with polymer concentration in a manner entirely consistent with the experimental data.     

Molecular dynamics and rheological properties of concentrated solutions of rodlike polymers in isotropic and liquid crystalline phases

A molecular theory is presented for the dynamics of rodlike polymers in concentrated solutions. The theory describes the rotational motion of rods in both the isotropic phase and the liquid crystalline phase. Combined with the molecular expression of the stress tensor, it also gives a unified rheological constitutive equation which predicts the nonlinear viscoelasticity in both phases. As an illustrative example, the steady-state viscosity η at zero-shear-rate is calculated. The predicted dependence of η on molecular weight and concentration agrees fairly well with experiments.     

Synthesis and comparative structural investigation of crystalline and liquid-crystalline phases of low molecular mass compounds and side group polymers I. Low molecular mass compounds

Low molecular mass compounds and analogous side group polymers with a thermotropic phase behaviour crystalline-smectic liquid-crystalline-isotropic have been synthesized for a comparative structural study. As characteristic features of the compounds a biphenyl group has been chosen for the mesogenic core and alkoxy parts of various lengths as terminal and spacer groups. The phase behaviour has been studied with differential calorimetric (DSC) measurements and polarization microscopic observations. The low molecular mass compounds form crystalline phases at room temperature and exhibit predominantly mosaic textures in the polarization microscope at elevated temperatures indicating high order of the packing of the molecules. The arrangements of the molecules in the crystalline and liquid-crystalline phase can best be described as layered structures according to X-ray diffraction measurements. A structural analysis of a solution grown single crystal provides valuable information on the conformation and packing of the compounds investigated in this study.     

Effect of molecular weight and its distribution on the spinodal for polydisperse polymer solutions

The Flory–Huggins interaction parameter χ(r_i) is considered as dependent on the chain length of a polymer. Therefore, a modified free energy expression of Flory–Huggins theory is obtained for the polydisperse polymer solutions. Based on this modified free energy expression and the thermodynamics of Gibbs, the expression of spinodal for polydisperse polymer solutions is obtained. For a given χ(r_i) according to de Gennes, the spinodals are calculated for polydisperse polymer solutions at different molecular weights and their distributions. It is found that all the interested variables r_n, r_w, r_z and molecular weight distribution have an effect on the spinodal for polydisperse polymer solutions, where the effect of changing r_w is much greater than that of changing r_n, r_z and molecular weight distribution.     

Thermotropic liquid-crystalline polymers. XXVII. Reentrant nematic phase of side chain liquid-crystalline polymers and their optical properties

The phase diagrams of side chain liquid-crystalline acrylic copolymers with cyanobiphenyl mesogenic groups are described. These copolymers are shown to form a reentrant nematic phase. The main regularities of the reentrant behaviour of polymer systems are studied. Certain peculiarities of the electric field induced orientation phenomena are discussed.     

Nature of the liquid-crystalline phase in supramolecular linear polymers

The development of the liquid crystal (LC) state in the melt of a supramolecular linear LC polymer based on a diacid and bipyridine base has been studied by IR spectroscopy and polarizing optical microscopy. Relying on experiments on the hydrogen-bonded complex formation and statistical analysis of the formation kinetics of the nematic phase, it is inferred that the system under study behaves like a binary mixture of weakly interacting components rather than a polydisperse polymer.     

Radical polymerization behavior and molecular weight development of homologous monoacrylate monomers in lyotropic liquid crystal phases

Polymerization in highly ordered lyotropic liquid‐crystalline (LLC) media enables controllable synthesis of polymers possessing interesting nanostructure and physical properties. This study investigates the radical polymerization rate and molecular weight (MW) development of monoacrylates of different aliphatic tail length in a range of LLC phases. Polymerization rate data were acquired using photodifferential scanning calorimetry, and linear polymer MW was determined with gel permeation chromatography. Polymerization occurs much more rapidly, and higher MW is attained in the ordered LLC phases relative to isotropic solutions and neat polymerization. These properties change significantly as a function of LLC phase and monomer structure. A direct relationship is observed between polymer MW formation and the polymerization rate. Definitive changes in rate and MW were observed at phase boundaries, indicating the important role of solvent order. This study demonstrates how solvent ordering effects can be used to control polymer MW and rate of polymerization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 144–154     

Effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulphates (NaCxS), where x is the number of carbon atoms in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases. The lyotropic mixtures investigated were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb₂SO₄/1-decanol/water (Na₂SO₄/1-decanol/water), separately. The uniaxial-to-biaxial nematic phase transitions were identified from the temperature dependence of the birefringences of the nematic phases by means of laser conoscopy. The micelle dimensions were obtained from small-angle X-ray scattering measurements. It was observed that the increase in the surfactant alkyl chain length causes the micellar growth in the plane perpendicular to the main amphiphile bilayer. The surfactant alkyl chain length plays a key role on the shape anisotropy of micelles, which triggers the orientational fluctuations that are responsible for the stabilisation of the different lyotropic nematic phases.     

Rheological properties of rodlike polymers in solution. 2. Linear and nonlinear transient behavior

Rheological and rheo-optical studies are reported for isotropic solutions of the mesogenic rodlike polymer poly(1,4-phenylene-2,6-benzobisthiazole) (PBT). Several PBT samples were used with average contour lengths from 95 to 135 nm. Concentrations were varied over a range just below the concentration C_c for the formation of an ordered (nematic) state. The predictions of a single-integral constitutive equation of the BKZ type utilizing experimental estimates of the distribution of discrete relaxation times is compared with experimental data on the steady-state viscosity η_κ, the recoverable compliance function R_κ, and the steady-state flow birefringence as functions of the shear rate κ, with satisfactory results. The relaxation of the shear stress and the flow birefringence on cessation of steady-state flow at shear rate κ are also compared with the single-integral constitutive equation, and it is found that in the nonlinear response range the data can be superposed over a wide range in κ. The overall behavior is qualitatively similar to that for flexible chains, which can also be fitted by the single-integral constitutive equations over similar ranges of η₀R₀κ, with η₀ and R₀ the limiting values of η_k and R_κ for small κ. Of course, the dependence of η₀ and R₀ on concentration and molecular weight differs markedly for rodlike and flexible-chain polymers.     

Studies on dilute solutions of rodlike macroions. II. Electrostatic effects

A group of rodlike polymers soluble only in strong protic acids was studied using light scattering and viscosity techniques. These include poly(1,4-phenylene benzobisoxazole), poly(1,4-phenylene benzobisthiazole) and poly(1,4-phenylene terephthalamide). The solution properties were dependent on the ionic strength of the acid used as solvent. In a low ionic strength acid such as chlorosulfonic acid, the polymer solutions exhibited decreased unpolarized scattering, an extremely small translational diffusion coefficient, and high viscosity. All of these effects could be eliminated by the addition of a salt such as lithium chlorosulfonate, which increased the ionic strength of the solvent. The effects were attributed to a pseudo ordering of the polymer solvent system caused by electrostatic repulsions between protonated polymer chains effective over large distances (ca. 100 Å) in the low ionic strength solvent. This type of ordering is distinct from actual anisotropic phase formation, which occurs at higher concentrations in these systems. Analysis of data at infinite dilution gave a persistence length of at least 45 nm for poly(1,4-phenylene terephthalamide), larger than previous experimental results, but in accord with recent rotational isomeric state calculations and similar to experimental data for poly(p-benzamide).     

Nonionic urea surfactants: influence of hydrocarbon chain length and positional isomerism on the thermotropic and lyotropic phase behavior

The thermotropic and lyotropic phase behavior of 1- and 5-decyl urea, and 1-, 2-, 4-, and 6-dodecyl urea have been studied. This allowed the effect of positional isomerism to be examined. Intermolecular hydrogen bonding by the urea moiety is the dominant factor in determining the solid-state thermal behavior and crystal solubility boundary of these linear nonionic surfactants. The positional isomers where the urea moiety was not situated at the terminus of the hydrocarbon chain exhibited higher melting points than the 1-alkyl ureas. This has been rationalized by postulating interdigitated chains in the solid state. In the urea surfactant-water systems, three phases are observed, viz. crystalline solid, a dilute aqueous solution of the alkyl urea, and an isotropic liquid. The last two phases coexist in the low-surfactant, high-temperature region of the binary phase diagram. An overview of structure-property correlations for linear nonionic urea surfactants is presented in light of the new physicochemical data obtained for the decyl urea and dodecyl urea positional isomers.     

Flow behavior of colloidal rodlike viruses in the nematic phase

The behavior of a colloidal suspension of rodlike fd viruses in the nematic phase, subjected to steady state and transient shear flows, is studied. The monodisperse nature of these rods combined with relatively small textural contribution to the overall stress make this a suitable model system to investigate the effects of flow on the nonequilibrium phase diagram. Transient rheological experiments are used to determine the critical shear rates at which director tumbling, wagging, and flow-aligning occurs. The present model system enables us to study the effect of rod concentration on these transitions. The results are in quantitatively agreement with the Doi-Edwards-Hess model. Moreover, we observe that there is a strong connection between the dynamic transitions and structure formation, which is not incorporated in theory.     

High-pressure phases in polymers. III. The nature of the high-pressure phase in cis-polyisoprene

The morphology and growth of the disordered hexagonal phase which crystallizes in films of cis-polyisoprene at pressures in excess of 3 kbar is discussed. A two-stage growth process is proposed consisting of nucleation and crystallization followed by a pressure-enhanced thickening process. The phase is metastable and is replaced by normal spherulitic growth at long times. It transforms into lamellar sheafs with higher than usual lamellar thicknesses when pressure is lowered at constant temperature.     

Specific features of the field-induced effects in comb-like liquid-crystalline polymers

The main problems concerning the liquid crystalline polymers and their behaviour in outer fields are discussed. The influence of the mesophase structure type of the side-chain LC polymers on the orientation processes in mechanical, electrical and magnetical fields is shown. The field effects in polymers permit to evaluate the specific peculiarities of the polymeric state of liquid crystals. During the last 10 years the field of Liquid-Crystalline (LC) polymers has been developed and is going to expand so intensively that one could not predict this at the time when first lyotropic and thermotropic LC-systems were discovered. Not only thousand of new LC polymers were synthesized and our Symposium gives a good example of very interesting papers devoted to this area, but it became clear that LC-state of polymers should be considered as normal, thermodynamically stable, widespread state of macromolecular substances - the idea which you hardly could find in textbooks a decade ago. First applications of thermotropic LC-polymers start to be described (memory devices, optical filters, ferroelectric polymers) while lyotropic systems continue its victorial march in the field of high tenacity fibers and films. It is absolutely impossible to give in one lecture an overall review of what is going on in this area because this would need at least 5–6 lectures of two hours each. That is why on preparing this talk we decided to concentrate ourself onto only one side of this rich picture - the field induced effects in comb-like LC thermotropic polymers.     

Effect of molecular weight distribution on the liquid-liquid phase separation behavior of polydispersed polyethylene solutions at high temperatures

The phase behaviors of the hexane + polydispersed polyethylene (PE) systems were measured to clarify the effect of the molecular weight distribution (MWD) of PE on liquid-liquid (LL) phase boundaries. The weight fraction for the PE portion of a maximum LL phase separation pressure in the LL phase boundary decreased as the polydispersity of PE increased. Moreover, depression of the phase separation pressure from the maximum phase separation pressure on the higher PE weight fraction side was more drastic as the polydispersity of the PE increased. The LL phase boundaries were correlated using the Sanchez-Lacombe equation of state (S-L EOS). For the correlations, the polydispersed PEs were regarded as mixtures of 16 types of monodispersed PEs with different molecular weights, and the characteristic parameters of the S-L EOS, P*, ρ* and T*, were assigned the same values for all monodispersed PEs even though the molecular weights differed. However, the interaction parameters of the hexane-PE pairs depended on the molecular weight of the PE and the temperature. The correlated results capably reproduced the effect of the MWD of the PE on the LL phase boundaries for the hexane + polydispersed PE systems.     

A dissipative particle dynamics description of liquid-crystalline phases. I. Methodology and applications

Simulations of nematic and smectic mesophases based on a dissipative particle dynamics approach are discussed. Mesogenic units are built in the form of standard semirigid bead-spring chains. It is shown that nematic phases can be formed for chains containing at least eight beads, provided that the conservative soft-repulsive potential between nonconnected beads is sufficiently strong. Smectic phases are observed only by modifying the repulsive interaction between the main-chain and terminal beads. The simulations indicate that the smectic-nematic and smectic-isotropic phase transitions take place through the buckling of the smectic layering in the system.     

Laterally attached liquid-crystalline polymers as stationary phases. Effect of temperature in RP HPLC and comparison with a commercial C18 stationary phase

Summary Specific side-on-fixed liquid-crystalline polymers (SOLCP) have been synthesized for use in silica-modified stationary phases in high-performance liquid chromatography (HPLC). The mesogenic side group of the SOLCP is composed of three benzoate-type phenyl rings with terminal alkoxy chains and is laterally linked to a polysiloxane backbone via an alkyl ester spacer arm. The dependence of the logarithm of the retention factor on the reciprocal temperature showed that the liquid-crystalline anisotropic order was conserved in the small pores (200 ? diameter) of the silica gel. The first-order nematic-isotropic transition is lost and probably becomes second-order. Adsorption enthalpies for the liquid-crystalline stationary phases have been measurement for three polycyclic aromatic hydrocarbon isomers (ortho-terphenyl, triphenylene, and chrysene) and compared with those for a commercial C₁₈ phase. The adsorption enthalpies never exceeded 30 kJ mol⁻¹, i.e. ten times the thermal agitation energy,RT. They were always less on the SOLCP stationary phase than on the C₁₈ column, emphasizing the more rigid structure of the liquid crystalline phase and its mechanism based upon adsorption. Better separation of steroids, pesticides and amino acids were obtained with the LCP-coated silica than the commercial bonded C₁₈ column. Four small peptides were successfully separated by using pure water as mobile phase.     

Molecular weights and molecular weight distribution of polymers by equilibrium ultracentrifugation. Part I. Average molecular weights

From the sedimentation-diffusion equilibria of some polymer solutions the average molecular weights M?_n, M?_w, M?_z, and M?_z+1 have been determined in different ways. In particular, the applicability of Fujita's method, which utilizes concentration gradient values at the midpoint of the solution column at a number of rotor speeds, was examined. It appears that if the gradients at some other places in the column are also used, a smaller range of rotor speeds suffices. This method is generally applicable for determining the average molecular weights specified above.