Liquid Crystalline Polymer Solutions Research Articles

Concentration Scaling on Linear Viscoelastic Properties of Cellular Suspensions and Effects of Equilibrium Phase Behavior.

Concentration scaling on linear viscoelastic properties of cellular suspensions has been studied by rheometric characterisation of Phormidium suspensions and human blood in a wide range of volume fraction under small amplitude oscillatory shear experiments. The rheometric characterisation results are analysed by the time-concentration superposition (TCS) principle and show a power law scaling of characteristic relaxation time, plateau modulus and the zero-shear viscosity over the concentration ranges studied. The results show that the concentration effect of Phormidium suspensions on their elasticity is much stronger than that of human blood due to its strong cellular interactions and a high aspect ratio. For human blood, no obvious phase transition could be observed over the range of hematocrits studied here and with respect to a high-frequency dynamic regime, only one concentration scaling exponent could be identified. For Phormidium suspensions with respect to a low-frequency dynamic regime, three concentration scaling exponents in the volume fraction Region I (0.36≤ϕ/ϕref≤0.46), Region II (0.59≤ϕ/ϕref≤2.89) and Region III (3.11≤ϕ/ϕref≤3.44) are identified. The image observation shows that the network formation of Phormidium suspensions occurs as the volume fraction is increased from Region I to Region II; the sol-gel transition takes place from Region II to Region III. In combination with analysis of other nanoscale suspensions and liquid crystalline polymer solutions reported in the literature, it is revealed that such a power law concentration scaling exponent depends on colloidal or molecular interactions mediated with solvent and is sensitive to the equilibrium phase behaviour of complex fluids. The TCS principle is an unambiguous tool to give a quantitative estimation.

Geometric pumping induced by shear flow in dilute liquid crystalline polymer solutions.

We investigate nonlinear rheology of dilute liquid crystalline polymer solutions under time dependent two-directional shear flow. We analyze the Smoluchowski equation, which describes the dynamics of the orientation of a liquid crystalline polymer, by employing technique of the full counting statistics. In the adiabatic limit, we derive the expression for time integrated currents generated by a Berry-like curvature. Using this expression, it is shown that the expectation values of the time-integrated angular velocity of a liquid crystalline polymer and the time-integrated stress tensor are generally not zero even if the time average of the shear rate is zero. The validity of the theoretical calculations is confirmed by direct numerical simulations of the Smoluchowski equation. Nonadiabatic effects are also investigated by means of simulations and it is found that the time-integrated stress tensor depends on the speed of the modulation of the shear rate if we adopt the isotropic distribution as an initial state.

Anomalous rheological behavior of long glass fiber reinforced polypropylene

Dynamic rheological properties of PP-based long glass fiber-reinforced thermoplastics (LFT) were investigated. Weight fractions of the glass fibers investigated in the present study ranged from 0.15 to 0.5, which are higher than those of previous studies. We observed very abnormal rheological behavior. Complex viscosity (η*) of the LFT increased with the glass fiber content up to 40 wt. %. However, the η* with a weight fraction of 0.5 is observed to be lower than that of LFT with a weight fraction of 0.4 in spite of higher glass fiber content. From various experiments, we found that this abnormal behavior is analogous to the rheological behavior of a lyotropic liquid crystalline polymer solution and concluded that the abnormal rheological behavior for the LFT is attributed to the formation of a liquid crystal- like structure at high concentrations of long glass fibers.

Mechanism of Helix Induction in Poly(4-carboxyphenyl isocyanide) with Chiral Amines and Memory of the Macromolecular Helicity and Its Helical Structures

An optically inactive poly(4-carboxyphenyl isocyanide) (poly-1-H) changed its structure into the prevailing, one-handed helical structure upon complexation with optically active amines in dimethylsulfoxide (DMSO) and water, and the complexes show a characteristic induced circular dichroism in the polymer backbone region. Moreover, the macromolecular helicity induced in water and aqueous organic solutions containing more than 50 vol % water could be "memorized" even after complete removal of the chiral amines (h-poly-1b-H), while that induced in DMSO and DMSO-water mixtures containing less than 30 vol % water could not maintain the optical activity after removal of the chiral amines (poly-1a-H). We now report fully detailed studies of the helix induction mechanism with chiral amines and the memory of the macromolecular helicity in water and a DMSO-water mixture by various spectroscopic measurements, theoretical calculations, and persistence length measurements together with X-ray diffraction (XRD) measurements. From the spectroscopic results, such as circular dichroism (CD), absorption, IR, vibrational CD, and NMR of poly-1a-H, h-poly-1b-H, and original poly-1-H, we concluded that the specific configurational isomerization around the C horizontal lineN double bonds occurs during the helicity induction process in each solvent. In order to obtain the structural information, XRD measurements were done on the uniaxially oriented films of the corresponding methyl esters (poly-1-Me, poly-1a-Me, and h-poly-1b-Me) prepared from their liquid crystalline polymer solutions. On the basis of the XRD analyses, the most plausible helical structure of poly-1a-Me was proposed to be a 9-unit/5-turn helix with two monomer units as a repeating unit, and that of h-poly-1b-Me was proposed to be a 10-unit/3-turn helix consisting of one repeating monomer unit. The density functional theory calculations of poly(phenyl isocyanide), a model polymer of h-poly-1b-Me, afforded a 7-unit/2-turn helix as the most possible helical structure, which is in good agreement with the XRD results. Furthermore, the persistence length measurements revealed that these structural changes accompany a significant change in the main-chain stiffness. The mechanism of helix induction in poly-1-H and the memory of the macromolecular helicity are discussed on the basis of these results.

Experimental Results on Fourier Transform Rheology of PBLG/m-cresol and HPC/Water Liquid Crystalline Solutions

In this work we present, for the first time, Fourier transform rheology data of liquid crystalline solutions of poly-γ-benzyl-l-glutamate, PBLG, in m-cresol and hydroxypropylcellulose, HPC, in water. The experimental results obtained show that, liquid crystalline polymer solutions possess an unusual behaviour in the non-linear regime, when compared with flexible polymers. For the latter, the ratio between the intensity of the third and the first harmonic, I3/I1 (a measurement of the nonlinear character), is an increasing function of the strain amplitude, whereas for the liquid crystalline solutions I3/I1 presents at least one relative maxima. We believe that this behaviour may be linked to the existence of different flow regimes (periodic), other than the shear aligning one. Future theoretical treatment is under progress in order to clarify this phenomenon.

Flow Induced Unstable Structure of Liquid Crystalline Polymer Solution in L-Shaped Slit Channels

An experimental study has been conducted on unstable structures induced in two-dimensional slit flows of liquid crystalline polymer solution. 50wt% aqueous solution of hydroxyl-propylcellulose (HPC) was utilized as a test fluid and its flow behavior in L-shaped slit channels with a cross section of 1mm height and 16mm width was measured optically. The inner corner of the L-shaped channel was rounded off in order to clarify the influence of the radius of curvature on the unstable behavior. A conversing curved channel was also tested. The flow patterns of the HPC solution in the channels were visualized with two crossed polarizers and we observed that typical wavy textures generated in the upstream of the corner almost disappeared after the corner flow. However, an unstable texture was developed again only from the inner corner in downstream flow. The fluctuation of the orientation angle and dichroism were also measured with a laser opto-rheometric system and it was found that the unstable behaviors of the HPC solution have periodic oscillatory characteristics at a typical frequency. In the inner side flow after the corner, the periodic motion became larger toward the downstream and then higher harmonic oscillations were superimposed. Larger rounding off of the inner corner suppressed the redevelopment of unstable behavior, and it is considered that the rapid regrowth of unstable behavior was caused by rapid deceleration at the corner flow. Moreover, the unstable structure was stabilized with an accelerated (elongated) region in the corner flow and the converging channel was helpful to obtain a stable structure in the downstream region.

Morphology development of main‐chain liquid crystalline polymer fibers during solvent evaporation

AbstractA nonequilibrium thermodynamic approach has been developed for describing the emergence of fiber morphologies from a liquid crystalline polymer solution undergoing solvent evaporation, including fibrillar structures, concentric rings, and spiral structures. We utilized Matsuyama–Kato free energy for main‐chain liquid crystalline polymer (MCLCP) solutions, which is an extension of Maier–Saupe theory for nematic ordering and incorporates a chain‐stiffening, combined with Flory‐Huggins free energy of mixing. Temporal evolution of the concentration and nematic order parameters pertaining to the above free energy density of liquid crystalline polymer solution was simulated in the context of time‐dependent Ginzburg–Landau theory coupled with the solvent evaporation rate equation under the quasi‐steady state assumption. The emerged morphological patterns are discussed in relation to the phase diagram of the MCLCP solution and the rate of solvent evaporation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 429–435, 2007

119 二次元流路における液晶高分子の流動構造の変化に関する研究(GS1-2 壁面間流れ,界面挙動,火災,一般セッション:GS1 流体工学)

119 二次元流路における液晶高分子の流動構造の変化に関する研究(GS1-2 壁面間流れ,界面挙動,火災,一般セッション:GS1 流体工学)

Electrorheological effect in hybrid fluids with liquid crystalline additives

AbstractConventional electrorheological (ER) fluids consist of electrically polarizable particles dispersed in an inert insulating liquid. They are characterized by a development of a yield stress upon application of an external electric field. They resemble Bingham fluids with yield stress value depending on electric field. A viscosity increase in the presence of an electric field has been also found in homogeneous solutions of liquid crystalline polymers with no yield stress observed. In this study these two types of fluids and combined dispersions of the solid particles in the liquid crystalline matrix were investigated. A lyotropic liquid crystalline polymer—poly(n‐hexyl isocyanate) (PHIC)—dissolved in xylene was chosen as the active matrix. The dispersed solid phase was comprised of two kinds of polymers: pyrolyzed polyacrylonitryle (PAN) showing electron conductivity, and PAN doped with two salts (KSCN, NaSCN), resulting in ionic conductivity. The rheological measurements under an electric field were performed. The pristine xylene solution of PHIC was characterized first as well as the 15% m/m dispersions of PAN powders in silicone oil. Then the dispersions in the liquid crystalline matrix were investigated showing a strong ER effect whose magnitude was considerably enhanced in comparison to both ER active components measured separately. Copyright © 2006 John Wiley & Sons, Ltd.

2309 液晶高分子の二次元流路内での流動方向変化時の不安定挙動(S42-2 複雑流体の流動現象(2),S42 複雑流体の流動現象)

The instability of flow induced structure of liquid crystalline polymer solution has been investigated in two dimensional channel flows. The influence of round off curvature at a corner on the unstable behavior after a flow direction change has been mainly examined. The orientation angle and the dichroism were measured with a laser optical measurement system. The unstable behavior of liquid crystalline polymer solution has typical periodic oscillatory characteristics, and the periodic motion became larger toward the downstream from the corner. The increase in periodicity was significant at the inner side of the channel. The larger round off of the corner suppressed the periodic motion, so that it is considered that the shape of the corner is one of the causes of the instability.

Effect of Electric Fields on the Rheological Properties of the Isotropic Phase of phic/p-Xylene Solutions

Abstract The effect of high ac electric fields upon a liquid crystalline polymer solution, poly(n-hexyl isocyanate) in p-xylene, is examined. The results show that the solutions exhibit an increase in rheological properties proportional to the strength of the field at concentrations well below those exhibiting liquid crystalline behavior. The effects of frequency and field strength are examined as a means to explain this previously unreported phenomenon.

Wavy texture in pressure-driven startup flows of liquid crystalline polymer solutions through a slit cell: effects of polymer concentration and solution temperature

Dependences of wavy texture on polymer concentration and solution temperature were examined using aqueous solutions of hydroxypropylcellulose (HPC). The phase of aqueous solution of HPC varied from an isotropic (I) system to a liquid crystalline (LC) one through a biphasic (I+LC, LC+I) system with increasing the HPC concentration and/or decreasing the solution temperature. The wavy texture emerged not only in the LC system but also in the LC+I system. Furthermore, induction time of wavy texture was evaluated in terms of apparent shear strain. It is suggested that polydomain structures included in liquid crystalline systems and droplets of isotropic phase in biphasic systems affect the initial stage of emergence of wavy texture at low shear rates.

B209 液晶高分子溶液の平行円板間の過渡流動に関する実験的研究

We have examined the transient behavior of the liquid crystalline polymer solution in successive simple shear and squeezing flows between two parallel plates. At the first stage, the simple shear flow was applied to the liquid crystalline polymer solution, and then the squeezing flow was started. Moreover, after the squeezing motion, a simple shear flow with different gap was applied again. We had observed the structural change of the liquid crystalline polymer solution in these successive flows with polarizing microscope. Furthermore, the dichroism and orientation angle were measured with a laser optical measurement system. It was found that the structure generated in the first simple shear flow was maintained and slid for a while in the squeezing flow. Moreover, at the commencement of the last shear flow after the squeezing motion where the structure was already destroyed with the squeezing motion, a rapid and large structural change was observed.

132 二次元流路内の角を曲がる流れにおける液晶高分子溶液の流動構造に関する研究(S34-3 複雑流体の流れとその応用(3),S34 複雑流体の流れとその応用)

In this study, we have investigated the flow induced structure of liquid crystalline polymer solution in a flow through a two dimensional channel with a corner. The orientation angle and the dichroism were measured with a laser optical measurement system. The orientation angle had smoothly changed from the upstream of the corner to the downstream. A periodic oscillation in orientation angle was observed in the upstream flow, but it became smaller after the flow direction change. The dichroism also became a bit higher in the downstream region. In spite of no significant change in orientation angle and dichroism, a typical texture was obtained at the downstream region in polarized observation.

A Kinetic Theory for Solutions of Nonhomogeneous Nematic Liquid Crystalline Polymers With Density Variations

The kinetic theory developed in [1] for solutions of nonhomogeneous nematic liquid crystalline polymers (LCPs) of spheroidal molecular configurations is extended to account for the translational diffusion and the related spatial density variation. The new theory augments the effect of the density variation to the intermolecular potential, Smoluchowski equation and the elastic stress. It accounts for the molecular aspect ratio as well as the finite range molecular interaction so that it is applicable to liquid crystals ranging from rodlike liquid crystals at large aspect ratios to discotic ones at small aspect ratios. It also exhibits enhanced shape effects in the viscous stress and warrants a positive entropy production, thereby, the second law of thermodynamics. Moment averaged, approximate, mesoscopic theories for complex flow simulations are obtained via closure approximations. In the limit of weak distortional elasticity, weak translational diffusion, and weak flows, the theory yields the torque balance equation of the well-known Ericksen-Leslie theory.

Scaling behavior of kinetic orientational distributions for dilute nematic polymers in weak shear

Analytical descriptions of shear-aligned nematic monodomains have a long history across continuum, mesoscopic and mean-field kinetic models. Their value lies in the prediction of explicit scaling properties of the orientational distribution and of normal and shear stresses, with respect to molecular and flow parameters. At the coarsest scale of continuum Leslie–Ericksen theory [Arch. Rational Mech. Anal. 4 (1960) 231; Arch. Rational Mech. Anal. 28 (1968) 265], an explicit macroscopic alignment angle formula always exists in terms of bulk Miesowicz viscosities; the theory applies only to nematic (highly concentrated) liquids with low molecular weight and in the weak flow limit [Phys. Soc. Jpn. 52 (1983) 3486; Phys. Soc. Jpn. 53 (1984) 1031; J. Chem. Phys. 116 (2002) 9120; A hydrodynamic theory for solutions of non-homogeneous nematic liquid crystalline polymers with density variations, in: Proceedings of ASME International Mechanical Engineering Congress, IMECE2002-32189, N.O., LA, 17-22 November 2002]. At mesoscales, orientation tensor models [J. Chem. Phys. 103 (1995) 3108; The Physics of Liquid Crystals, Oxford University Press, Oxford, 1993; Thermodynamics of Flowing Systems with Internal Microstructure, Oxford Science Publications, Oxford, 1994; J. Chem. Phys. 103 (1995) 807; The Structure and Rheology of Complex Fluids, Oxford University Press, Oxford, 1998] apply at all concentrations and shear rates; explicit “Leslie angle” formulas exist only in the weak shear limit [Macromolecules 23 (1990) 4446; J. Rheol. 37 (1993) 413; J. Rheol. 37 (1993) 289; J. Rheol. 41 (1997) 943; Phys. A 267 (1999) 294; J. Non-Newtonian Fluid Mech. 90 (2000) 283; Rheol. Acta 42 (2003) 20; J. Rheol. 47 (2003) 105], inheriting hysteresis in alignment properties from the quiescent isotropic–nematic transition. Since the fundamental results of Onsager [Ann. N.Y. Acad. Sci. 51 (1949) 627] for quiescent nematic equilibria, exact probability distribution functions (PDFs) of kinetic theory have proven elusive for flow-driven nematic states. In their stead, flow-aligned and unsteady PDF formulas, elegant though implicit, have been derived by Kuzuu–Doi [Phys. Soc. Jpn. 52 (1983) 3486; Phys. Soc. Jpn. 53 (1984) 1031] and Semenov [Sov. Phys. JETP 66 (1983) 321] by weak flow asymptotic analysis, and by Marrucci and Maffettone [Macromolecules 22 (1989) 4076] by restriction to two dimensions. A simpler problem concerns the dilute concentration regime where the quiescent equilibrium is isotropic, non-degenerate, and stable, which is the focus of this paper. Using weak-flow asymptotics, we explicitly construct, and establish stability of, stationary, shear-perturbed PDFs for dilute concentrations; our formulas prove unsteady tumbling of perturbed isotropic states cannot occur. Exact scaling properties are predicted, including explicit Leslie alignment angle and degree-of-alignment (birefringence) formulas, as well as normal and shear stresses, in terms of molecular parameters and normalized shear rate for dilute nematic polymers. Our formulas apply except in a neighborhood of the isotropic instability transition, which See et al. [J. Chem. Phys. 92 (1990) 792] analyzed by a singular perturbation analysis. We then show how to bridge our method with that of See et al. [J. Chem. Phys. 92 (1990) 792], thereby completing the existence, construction, and stability of shear-perturbed isotropic equilibria for all concentrations. We verify the formulas both by numerical simulations and by comparison with mesoscopic model predictions [Rheol. Acta 42 (2003) 20; J. Rheol. 47 (2003) 105; J. Chem. Phys. 92 (1990) 792].

A wavelet-Galerkin method for simulating the Doi model with orientation-dependent rotational diffusivity

A numerical method based on wavelet approximations is developed to solve the diffusion equations that arise from kinetic theory models of polymer dynamics and for coupling with continuum calculations for simulating complex flows of polymer solutions. The dynamics of a liquid crystalline polymer solution in a simple, homogeneous shear flow is computed by using the Doi model with orientational-dependent rotational diffusivity as a function of Deborah number, De, and different initial conditions. Stochastic methods were previously used for computing this flow, and aperiodic behavior was found at high De. Calculations with the wavelet-Galerkin method demonstrate a stable limit cycle in the same parameter regime. The existence of the time-periodic solution is traced to a supercritical Hopf bifurcation at De=De Hopf; the value of De Hopf scales with ( U− U c) α , where U is the strength of the intermolecular potential. The exponent in this correlation, α, depends on the form of the mean-field intermolecular potential and can be used to characterize the anisotropic environment experienced by the polymer molecules.

715 スリット流路内流れにおける高分子液晶の波状テクスチャー : 溶液の温度と濃度の影響

Mechanism of the occurrence of the wavy texture in slit flows of liquid crystalline polymer (LCP) solutions is studied in pressure-driven start-up flows using 50wt%, 55wt% and 60wt% aqueous solutions of hydroxypropylcellulose (HPC). The average shear strain at the onset of the wavy texture is examined in the flows through slit cells with various entrance geometries. The concentration of aqueous solution of HPC increases the average shear strain at the occurrence of the wavy texture. The temperature of aqueous solution of HPC affects the shear rates at the occurrence of the wavy texture.

A hydrodynamic theory for solutions of nonhomogeneous nematic liquid crystalline polymers of different configurations

A hydrodynamic theory is developed for solutions of nonhomogeneous nematic liquid crystalline polymers (LCPs) of a variety of molecular configurations in proximity of spheroids, extending the Doi kinetic theory for rodlike molecules. The new theory accounts for the molecular aspect ratio as well as the finite range molecular interaction so that it is applicable to liquid crystals ranging from the rodlike liquid crystal at large aspect ratios to the discotic one at small aspect ratios. It also exhibits enhanced shape effects in the viscous stress and warrants a positive entropy production, thereby, the second law of thermodynamics. When restricted to uniaxial symmetry in the weak flow limit, the theory recovers the director equation of the Leslie–Eriksen (LE) theory, but the stress tensor contains excessive gradient terms in addition to the LE stress tensor. The theory predicts that the elastic moduli K1, K2, and K3 obey the ordering K3<K1<K2 for stable, discotic (oblate spheroidal) LCPs in the weak flow limit. The ordering is reversed for rodlike (prolate spheroidal) LCPs. It yields a positive Leslie viscosity α2 (α3) in the flow-aligning (tumbling) regime for oblate (prolate) spheroidal LCPs. Moment averaged, approximate, mesoscopic theories for complex flow simulations are obtained via closure approximations.

1323 液晶高分子水溶液のスリット流路内流れにおける波状テクスチャの発生と構造

1323 液晶高分子水溶液のスリット流路内流れにおける波状テクスチャの発生と構造