Liquid Crystalline Polymer Chain Research Articles

Micropatterned Cell Orientation of Cyanobacterial Liquid-Crystalline Hydrogels.

Control of cell extension direction is crucial for the regeneration of tissues, which are generally composed of oriented molecules. The scaffolds of highly oriented liquid crystalline polymer chains were fabricated by casting cyanobacterial mega-saccharides, sacran, on parallel-aligned micrometer bars of polystyrene (PS). Polarized microscopy revealed that the orientation was in transverse direction to the longitudinal axes of the PS bars. Swelling behavior of the micropatterned hydrogels was dependent on the distance between the PS bars. The mechanical properties of these scaffolds were dependent on the structural orientation; additionally, the Young's moduli in the transverse direction were higher than those in the parallel direction to the major axes of the PS bars. Further, fibroblast L929 cells were cultivated on the oriented scaffolds to be aligned along the orientation axis. L929 cells cultured on these scaffolds exhibited uniaxial elongation.

Crystal Structure and Ionic Conductivity of Soft Solid Crystals Composed of NaClO4. N,N-Dimethylformamide

There have been safety issues with liquid electrolytes used in commercial lithium/sodium batteries. This has motivated the development of solid electrolytes with desired properties to replace liquid electrolytes. Solid electrolytes made with ceramic/glass have ionic conductivities in the range of 10-3 to 10-2 S/cm [1], but are brittle, with poor adhesion to the electrodes and are difficult to process. Organic solid electrolytes, such as polyethylene oxide (PEO) [2], PEO/composite blends, PEO copolymers/blends [3-4], molecular or ionic plastic crystals, and low molecular weight glymes have lower ambient temperature conductivities (10-7-10-5 S/cm), but are flexible, with better adhesion to electrodes, and are easier to process. For PEO systems, conductivity has been shown to occur primarily through the amorphous phase, where ion migration is coupled to slow backbone segmental motions, so that decreases in crystallinity and alignment of polymer chains increase conductivity. Other approaches to improve ionic conductivities in soft-solid electrolytes are based on the observation that molecular organization rather than disordered structures foster ion mobility. In particular, this is true for materials in which there are alternative, low activation energy pathways for ion migration, such as along and between organized, aligned polymer or liquid crystalline polymer chains; along polymeric/inorganic nanoparticle interfaces possibly due to weakening of the ether O-Li+ bond and along ion channels in low molecular weight glymes and trilithium compounds. We have been investigating soft solid electrolytes that are crystalline solids in which the channel walls have low affinity for the enclosed ions. The first such material, DMF:LiCl has the highest conductivity reported to date for a soft solid organic electrolyte [7,8]. The high conductivity can be explained based on the hard and soft acids and bases (HSAB) theory [5,6]. In DMF:LiCl, the soft (charge diffuse, polarizable) C=O functionality in N,N-dimethylformamide (DMF) donors interacts poorly with the hard Li+ ions in LiCl, permitting fast ion migration. Here we report another soft solid crystal, DMF:NaClO4, which is a sodium ion conductor. Single crystal X-ray data identifies the solid as 2:1 adduct of DMF:NaClO4 (Figure 1). The structure shows the formation of 1-D covalently bonded Nan •DMFnchains in which Na ions interacting with the soft DMF matrix through weak Lewis acid/base interactions of sodium and oxygen ions. The crystal structure exhibits a linear arrangement of Na-O(DMF) rhombs arranged end to end through sodium atoms, such that a chain of closely spaced (3.232 Å) sodium ions exists parallel to the a axis of the unit cell. The melt temperature of DMF.NaClO4 is 55oC. Unlike DMF:LiCl crystals that degrade before melting, DMF:NaClO4 reversibly melts and recrystallizes. The decomposition of DMF:NaClO4 starts at 70oC. The temperature dependent conductivity of the pressed pellets (1200 psi) of air dried DMF:NaClO4 exhibits excellent room temperature conductivity 8.0x10-6 S/cm (Figure 2). This may be due to an interfacial layer of liquid-like DMF:NaClO4 between the grains, since extra drying decreases the conductivity. The liquid DMF:NaClO4 has a conductivity approximately 1 order of magnitude greater than that of the crystal. References (1) Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno, R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.; Mitsui, A. Nature Materials 2011, 10, 682. (2) P.R.Chinnam, S.L.Wunder. Journal of Materials Chemistry A 2013, 1, 1731 (3) P.R.Chinnam, Zhang, H, S.L.Wunder. Electrochimica Acta 2015 (doi:10.1016/j.electacta.2015.04.010) In press (4) P.R.Chinnam, S.L.Wunder. Chemistry of Materials 2011, 2011, 23, 5111. (5) Pearson, R. G. Journal of the American Chemical Society 1963, 85, 3533. (6) Borodin, O.; Smith, G. D. Macromolecules 2006, 39, 1620. (7) Chinnam, P.R., et al., Chemistry of Materials, 2015. 27(16): p. 5479-5482. (8) ZDILLA, M.J., S.L. Wunder, and P.R. Chinnam, Soft-solid crystalline electrolyte compositions. 2015, Google Patents. Figure 1

Anisotropic charge-carrier mobilities of liquid crystalline conjugated polymers on photo-aligned PVCN dielectric insulators

We fabricated organic thin-film transistors (OTFTs) with photo-reactive poly(vinylcinnamate) (PVCN) as a dielectric layer and liquid crystalline poly(2,5-bis(3-dodecylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT) as a semiconducting layer. The PVCN layer plays an important role in the fabrication of OTFTs with solution processable PBTTT, because it provides orientation of the liquid crystalline polymer chains as well as gate insulating characteristics. The electrical properties of PBTTT-OTFTs with the UV-cured PVCN film were investigated for the films prepared with linearly polarized ultraviolet light irradiation along parallel and perpendicular to the electrode channel direction.

Alignment and properties of carbon nanotube buckypaper/liquid crystalline polymer composites

AbstractCarbon nanotubes (CNTs) have been recognized as a potential superior reinforcement for high‐performance, multifunctional composites. However, non‐uniform CNT dispersion within the polymer matrix, the lack of adequate adhesion between the constituents of the composites, and lack of nanotube alignment have hindered significant improvements in composite performance. In this study, we present the development of a layer‐by‐layer assembly method to produce high mechanical performance and electrical conductivity CNT‐reinforced liquid crystalline polymer (LCP) composites using CNT sheets or buckypaper (BP) and self‐reinforcing polyphenylene resin, Parmax. The Parmax/BP composite morphology, X‐ray diffraction, mechanical, thermal, and electrical properties have been investigated. SEM observations and X‐ray diffraction demonstrate alignment of the CNTs due to flow‐induced orientational ordering of LCP chains. The tensile strength and Young's modulus of the Parmax/BP nanocomposites with 6.23 wt % multi‐walled carbon nanotube content were 390 MPa and 33 GPa, respectively, which were substantially improved when compared to the neat LCP. Noticeable improvements in the thermal stability and glass transition temperature with increasing CNT content due to the restriction in chain mobility imposed by the CNTs was demonstrated. Moreover, the electrical conductivity of the composites increased sharply to 100.23 S/cm (from approximately 10−13 S/cm) with the addition of CNT BP. These results suggest that the developed approach would be an effective method to fabricate high‐performance, multifunctional CNT/LCP nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A study on the structural transition of a single polymer chain by parallel tempering molecular dynamics simulation

The structural transition of a single polymer chain with chain length of 100, 200 and 300 beads was investigated by parallel tempering MD simulation. Our simulation results can capture the structural change from random coil to orientationally ordered structure with decreasing temperature. The clear transition was observed on the curves of radius of gyration and global orientational order parameter P as the function of temperature, which demonstrated structural formation of a single polymer chain. The linear relationships between three components of square radius of gyration Rgx2, Rgy2, Rgz2 and global orientational order P can be obtained under the structurally transformational process. The slope of the linear relationship between x (or y-axis) component Rgx2 (or Rgy2) and P is negative, while that of Rgz2 as the function of P is positive. The absolute value of slope is proportional to the chain length. Once the single polymer chain takes the random coil or ordered configuration, the linear relationship is invalid. The conformational change was also analyzed on microscopic scale. The polymer chain can be treated as the construction of rigid stems connecting by flexible loops. The deviation from exponentially decreased behavior of stem length distribution becomes prominent, indicating a stiffening of the chain arises leading to more and more segments ending up in the trans state with decreasing temperature. The stem length Ntr is about 21 bonds indicating the polymer chain is ordered with the specific fold length. So, the simulation results, which show the prototype of a liquid-crystalline polymer chain, are helpful to understand the crystallization process of crystalline polymers.

Small Angle Neutron Scattering Studies on Miscible Blends of Poly(styrene-ran-vinyl phenol) with Liquid Crystalline Polyurethane

The production of uniformly dispersed rigid-rod liquid crystalline polymer (LCP) molecules in a flexible amorphous polymer, with an experimentally accessible miscibility window, has become possible by modifying the architecture of the flexible polymer, so as to induce favorable inter-species hydrogen bonding. The conformation of LCP chains that are uniformly dispersed in a flexible coil matrix are examined by studying a system consisting of a liquid crystalline polyurethane (LCPU) and a copolymer containing 12% vinylphenol and deuterated styrene, utilizing small-angle neutron scattering. Intramolecular hydrogen bond interaction within the vinylphenol segments of the copolymer leads to the formation of a dynamically cross-linked structure, characterized by the large amount of scattering seen at low angle. Addition of the LCPU in the blend results in formation of hydrogen bonding interactions between the LCP and the copolymer; demonstrated by an initial reduction in the correlated size of the dynamic networ...

Phase and orientational ordering of low molecular weight rod molecules in a quenched liquid crystalline polymer matrix with mobile side chains.

We study the phase diagram and orientational ordering of guest liquid crystalline (LC) rods immersed in a quenched host made of a liquid crystalline polymer (LCP) matrix with mobile side chains. The LCP matrix lies below the glass transition of the polymer backbone. The side chains are mobile and can align to the guest rod molecules in a plane normal to the local LCP chain contour. A field theoretic formulation for this system is proposed and the effects of the LCP matrix on LC ordering are determined numerically. We obtain simple analytical equations for the nematic/isotropic phase diagram boundaries. Our calculation show a nematic-nematic (N/N) first order transition from a guest stabilized to a guest-host stabilized region and the possibility of a reentrant transition from a guest stabilized nematic region to a host only stabilized regime separated by an isotropic phase. A detailed study of thermodynamic variables and interactions on orientational ordering and phases is carried out and the relevance of our predictions to experiments and computer simulations is presented.

Orientational ordering of short LC rods in an anisotropic liquid crystalline polymer glass

The orientational phase diagram and ordering of guest liquid crystalline (LC) rods in a host liquid crystalline polymer (LCP) matrix quenched below the glass transition is determined by field theory. Microscopic anisotropic interactions can align the LC rods to each other and also align LCP matrix side chains and the LC rods in the plane normal to the local LCP chain contour. Our numerical analysis suggest ways to exploit host entropy, anisotropy of microscopic interactions and manipulate properties of LC rods for modern applications. We predict a nematic–nematic discontinuous orientational transition from a guest stabilized to a guest–host stabilized region and a reentrant transition from a guest stabilized nematic region to a host only stabilized regime. A detailed analysis of phase boundaries transitions and ordering is presented.

Interface between a Liquid Crystalline Polymer and a Flexible Polymer

The properties of the interfacial region between melt phases of a liquid crystalline polymer and a flexible polymer were studied using the three-dimensional bond fluctuation model. The far-field orientation has a strong effect on the magnitude of the interfacial tension and the structure of the “interphase”. The interfacial tension is an increasing function of the nematic order parameter S for a parallel far field, while it is a decreasing function for a homeotropic (orthogonal) far field, with the difference in the magnitude of the interfacial tension growing exponentially in S. The interfacial tension for both far-field orientations is insensitive to liquid crystalline polymer chain length. Chain ends penetrate the adjacent phase with a homeotropic orientation, resulting in a more diffuse interphase. There is, nevertheless, a substantial orientation parallel to the interface even with a homeotropic far field, and order parallel to the interface is induced in the flexible polymer phase with both parallel and homeotropic far fields. The computed parameters for the continuum theory of nematic/isotropic interfaces lead to an “easy axis” that is orthogonal to the interface. The interfacial tension for a parallel far field scales linearly with (ε/kBT)1/2S2, where ε is the magnitude of the repulsive interaction between unlike chain segments; similar scaling is not obtained for an orthogonal far field.

Transport properties of highly aligned polymer light-emitting diodes

We investigate hole transport in polymer light-emitting-diodes in which the emissive layer is made of liquid-crystalline polymer chains aligned perpendicular to the direction of transport. Calculations of the current as a function of time via a random-walk model show excellent qualitative agreement with experiments conducted on electroluminescent polyfluorene demonstrating non-dispersive hole transport. The current exhibits a constant plateau as the charge carriers move with a time-independent drift velocity, followed by a long tail when they reach the collecting electrode. Variation of the parameters within the model allows the investigation of the transition from non-dispersive to dispersive transport in highly aligned polymers. It turns out that large inter-chain hopping is required for non-dispersive hole transport and that structural disorder obstructs the propagation of holes through the polymer film.

Continuous and Discrete Dynamics of Heterogeneous Mesogenic Polymer Chain

Abstract Two types of dynamic models–continuous and lattice–are considered describing a heterogeneous liquid-crystalline polymer chain built from mesogenes and spacers. The chain heterogeneity leads to enriching a set of possible motions of the chain. Each branch of the chain relaxation spectrum consisting of the isotropic phase of one acoustic and some optical branches is shown to be split into a longitudinal and transverse components. The magnitude of the splitting is found to depend on the scale of motions and the mechanism of the chain mobility. The dependence of the relaxation times on the degree of order is shown to be different for the chains with rigid and flexible spacers.

Effect of drawing on structure and properties of a liquid crystalline polymer and polycarbonate in‐situ composite

AbstractFibers (strands) with various draw ratios were spun from the liquid crystalline state of a pure aromatic liquid crystalline copoly(ester amide) and the melts of its blend with polycarbonate. Scanning electron microscopy (SEM), wide angle X‐ray scattering (WAXS), and differential scanning calorimetry (DSC) were employed to investigate the structure and properties of the resulting fibers. Mechanical properties of the fibers were also evaluated. It was found that both the crystallite size and heat of fusion of the liquid crystalline polymer (LCP) increase steadily with draw ratio. However, the crystal‐nematic transition temperature of the LCP is virtually unaffected by drawing. Moreover, heat of fusion of LCP is much smaller than that of isotropic condensation polymers despite the presence of very sharp diffraction peaks in WAXS measurements. These results are ascribed to the (semi)rigid rod nature of the LCP chains and the persistence of an ordered structure in the LCP melt, i.e., entropy effect. It was further observed that tensile modulus and tensile strength along fiber axis rise with draw ratio for the composite fibers. The elastic modulus of the composite fibers were found to be as high as 19 GPa and tensile strength reached 146 MPa with draw ratios below 40 and an LCP content of 30 wt%. Compared with the thermoplastic matrix, the elastic modulus and tensile strength of the in‐situ composite have increased by 7.3 times and 1.4 times, respectively, with the addition of only 30 wt% LCP. This improvement in mechanical properties is attributed to fibrillation of the LCP phase in the blend and the increasing orientation of the LCP chains along the fiber axis during drawing.

Blends containing liquid crystalline polymers: Preparation and properties of melt‐drawn fibers, unidirectional prepregs, and composite laminates

AbstractThis paper discusses the effect of melt drawing on the mechanical properties and morphology of liquid crystalline polymer (LCP) and thermoplastic polymer blends. Extruded fibers and films of LCP/polymer blends were melt drawn to develop uniaxial orientation of the dispersed LCP phase. The longitudinal modulus increased with increasing draw. The increase in modulus was due to higher aspect ratio of the LCP fibrils and improved molecular orientation of the LCP chains within the fibrils. Laminated composites were prepared using the extruded sheets as prepregs. The mechanical properties and the coefficient of thermal expansion (CTE) of the prepreg and the laminates agreed well with predictions from conventional composite lamination theories.