Orientation Of Liquid Crystalline Polymer Research Articles

Influence of alkylene spacer length on photoinduced orientation of liquid crystalline polymer with N-benzylideneaniline side groups

ABSTRACTLiquid crystalline polymers (LCPs) comprised of N-benzylideneaniline (NBA) side groups with different alkylene spacer length (n = 2, 6, and 10) are synthesized and their photoinduced reorientation behavior is investigated. Photoinduced orientation of NBA side groups is observed for all LCP films when exposing to LP-365 nm light, but the out-of-plane motion is simultaneously generated. When the polarization of LP-365 nm light is changed, in-plane optical anisotropy is reversibly changed and the out-of-plane motion is restricted for a P1 (n = 2) film. In contrast, reversibility of the photoinduced in-plane orientation is not effective for P2 (n = 6) and P3 (n = 10) films, where out-of-plane motion of the mesogenic NBA side groups is generated when the total exposure energy increases.

PB36 側鎖にシッフ塩基を導入した側鎖型高分子液晶の合成と光配向(化学・材料,ポスター発表,2013年日本液晶学会討論会)

PB36 側鎖にシッフ塩基を導入した側鎖型高分子液晶の合成と光配向(化学・材料,ポスター発表,2013年日本液晶学会討論会)

Comparison Study on Thermally Stimulated Photoinduced Orientation of Liquid Crystalline Polymer with Cinnamate Side Groups using 313 nm and 365 nm Light

Polymethacrylates with different type of cinnamate side groups (P1, P2 and P3) were synthesized, and their photochemical and photoinduced reorientation behaviors were investigated using linearly polarized (LP) 313 nm and 365 nm light. P1 and P2 exhibited liquid crystalline (LC) characteristics, but P3 did not. Thin P1 and P2 films underwent thermally stimulated photoinduced molecular reorientation using LP 313 nm or 365 nm light and subsequent annealing, where adjusting the exposure energy and the exposing light wavelength could control the reorientation direction. Type of the cinnamate side groups, resultant photoproducts, and LC characteristics of the polymer played an important role in the thermally stimulated photoinduced molecular reorientation directions and their performances.

Generation of Anisotropic Emission by Light-Induced Orientation of Liquid Crystalline Polymers

Functionalized polymers containing mesogenic, photosensitive, and fluorescent side groups were synthesized for all-in-one films with anisotropic absorption and emission. Aligned films were prepared by a two-step bulk-alignment procedure combining a photochemical step at room temperature and a thermal aligning step at temperatures of the mesophases. The irradiation with linearly polarized light results in small values of anisotropy via angular-selective photoreactions of cinnamates, stilbenes, and anthracene moieties. The photoinduced anisotropy was significantly amplified by annealing above the glass transition temperature of the liquid crystalline polymers, resulting in a cooperative alignment of all side groups leading to dichroism values up to 0.7 (dichroic ratio up to 6.7) and ratios of anisotropic fluorescence up to 8. The irradiation conditions for the induction of anisotropy were optimized concerning wavelength and dose with respect to the absorption of photosensitive groups and the limited photostability of the dyes. Depending on the distribution of the photoproducts, alignment parallel or perpendicular to the electric field vector of the incident light was induced in dependence on the polymer composition and irradiation conditions.

Polydomain model predictions of molecular orientation in isothermal channel flows of thermotropic liquid crystalline polymers

AbstractWe report process simulations of molecular orientation of liquid crystalline polymers for isothermal channel flows in extrusion. The simulations use a “polydomain” model due to Larson and Doi (Larson and Doi, J. Rheol., 35, 539 (1991)), which is implemented by exploiting a nearly exact analogy with a fiber orientation model that is widely used for analysis of composites processing. Simulation results are compared to experimental data previously obtained using a customized X‐ray capable extrusion die that allows a wide range of channel flow geometries to be explored. Competition between inhomogeneous shear and extension in these kinematically complex flows has a profound effect on the resulting molecular orientation distributions. We find that the Larson–Doi model successfully predicts most aspects of the experimental observations, demonstrating its utility for process modeling. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Effects of Surface Conditions on Rheological Properties and Phase Orientation of Sheared LCP Melts in Nanochannels by MD Studies

The rheological properties and phase orientation of liquid crystalline polymer (LCP) melts flowing in a nanochannel with different surface roughness are investigated by molecular dynamics (MD) simulations. Simulation results show the surface roughness has great impact on the rheological properties and phase orientation of LCP melts in the nanochannel (cross section is 12nm). As the amplitude of serrations increases, the shear viscosity increases nonlinearly and the value of orientational order parameter decreases. When the serration amplitude is larger than 1.1nm, a phase transition (from nematic to isotropic phase) of LCP melt happens, which makes flowing in nanochannels more difficult. On the other hand, the influence of serration period on the shear viscosity and orientational order parameter are found not so obvious. Findings in this study will be helpful for injection molding plastic products with nanofeatures.

The Effect of Surface Features on Nanorheology of LCP Melts in Nanochannels by MD Simulation

The effects of wall surface features on the rheological properties and phase orientation of liquid crystalline polymer (LCP) melts flowing in a nanochannel have been first investigated by molecular dynamics (MD) simulations. The surfaces are modeled as rough atomic serrated walls whereby the roughness is characterized by the period and amplitude of serration. The molecular chains of LCPs are depicted by a newly developed molecular model named the GB-spring-bead model. Through simulating the phase formation of LCP melts, the new model was evaluated and the results have shown the new model is efficient and accurate to describe semi-flexible main-chain LCP molecules. MD simulations of the effect of wall surface features on the LCP shear flow were conducted and the results have revealed the surface features affect greatly the rheological properties and phase orientations of LCP melts in a nanochannel (the distance between the upper wall and the lower wall is 12.8nm). Findings in this study provide very useful information in the injection molding of plastic products with nanofeatures.

Molecular orientation of extruded PET/LCP blend films. Part I: Polarized infrared spectroscopy

AbstractThe polarized infrared (IR) spectroscopy technique was used to evaluate the surface uniaxial molecular orientation of films of poly(ethylene terephthalate) (PET), two thermotropic liquid crystalline polymers (LCPs), Vectra®A950 and Rodrun®LC5000, and their blends obtained by extrusion. The molecular orientation of the LCP and of the crystalline and amorphous PET phases in the draw direction was evaluated along the transverse section of the films and as a function of the blend composition. A compatibilizer agent was used to improve the interfacial adhesion between the PET and LCPs. The results showed that the surface molecular orientation of both LCPs was very high along the draw direction. However, when blended, the orientation of the LCP phase decreased drastically, it was dependent of its content and varied along the transverse section of the extruded films. The maximum orientation was observed in the blend with 5 wt % LCP content and at the position where the shear rate was maxima. The LCP Vectra®A950 showed higher orientation than the Rodrun®LC5000, as a pure material and as blended. For the PET phases, an alignment of the amorphous phase in the draw direction due to the presence of LCP and compatibilizer agent was observed. The crystalline phase of PET, however, showed no significant orientation in the draw direction. The compatibilizer agent proved efficient for both PET/LCP systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2241–2248, 2006

Study of surface conditions and shear flow of LCP melts in nanochannels through molecular dynamics simulation

The rheological properties and phase orientation of liquid crystalline polymer (LCP) melts flowing in a nanochannel with different surface roughness are investigated by molecular dynamics (MD) simulations. The molecular chains of LCPs are depicted by a newly developed molecular model named GB-spring-bead model, which has proved to be efficient and accurate in studying the phase transition behaviors of semi-flexible main chain LCPs [Yung KL, He L, Xu Y, Shen YW. Polymer 2005;46:11881 [1]]. The surfaces are modeled as rough atomic serrated walls whereby the roughness is characterized by the period and amplitude of serrations. Simulation results have shown that the surface roughness affects greatly the rheological properties and phase orientations of LCP melts in a nanochannel (the distance between the upper wall and the lower wall is 12.8 nm). As the amplitude of serration increases, the shear viscosity of LCP increases nonlinearly while its orientational order parameter decreases. When the serration amplitude reaches a certain magnitude, a phase transition (from nematic to isotropic phase) happens, which increases the viscosity of the nano LCP flow drastically. On the other hand, the influence of serration period on the shear viscosity and orientational order parameter is not so obvious relatively. Findings in this study provide very useful information in the injection molding of plastic products with nanofeatures.

Analysis of Flows of Polymeric Solutions and Liquid Crystals

Flows of polymeric fluids and liquid crystalline polymers (LCPs) were studied in complex flow geometries. In the present paper, however, there is a focus on the flow analysis of the flow of LCPs. Numerical simulations of flows of LCPs were carried out using the modified Doi equation with the quadratic closure approximation. Molecular orientation of LCPs is strongly affected by the velocity field including both the shear and elongational flows in the complex geometry while the velocity distribution is modified by the molecular orientation. Numerical simulations for a flow between parallel plates containing a cylinder and a spinning flow are presented as examples. A novel rubbing-free alignment layer for LCs was proposed as an application of flow-induced molecular orientation of LCPs. The development of wavy texture in startup flows of LCPs through a slit cell was discussed.

Nonhomogenous patterns with core defects in elongational flows of liquid crystal polymers

The interaction between flow and orientation of liquid crystalline polymers (LCPs) creates remarkable heterogeneous patterns in which defects, or singular solutions, serve to mediate a confluence of ordered nematic phases. The origin of defects remains a mystery. It is therefore valuable to have models for LCP flows that provide some evidence of defects, and of the corresponding physical competition between flow and LCP properties. In this direction, the flow-orientation moment-averaged Doi model is studied with an imposed elongational flow. Nonhomogeneous, biaxial nematic patterns are discovered in both axial and planar elongation. These exact solutions consist of spatially varying directors in the plane orthogonal to the flow axis, coupled with homogeneous biaxial order parameter equilibria fixed by the LCP concentration (N) and elongation rate (ν). For each (N,ν), the following patterns coexist all with identical order parameter values: the homogeneous patterns of [Macromol. Theory Simul. 4, 857872 (1995)]; radially symmetric director patterns; and finally, director patterns periodic in the cylindrical azimuthal angle. The nonhomogeneous structures are distinguished by the presence of core defects along the axis of flow symmetry, characterized by a logarithmic pressure singularity at the core.

Pressure-driven channel flows of a model liquid-crystalline polymer

Shear flows disrupt molecular orientation in liquid-crystalline polymers (LCPs) through director tumbling, and this causes difficulty in controlling the polymer structure and properties in injection molding and extrusion. In this paper we simulate LCP channel flows using the Doi theory. A Bingham closure is used to preserve director tumbling and wagging. The objective is to examine how contractions and expansions in a channel affect LCP orientation and to explore the possibility of using the channel geometry as a means of manipulating LCP order. A finite-element method is used to solve the coupled equations for fluid flow and polymer configuration. Results show that a contraction aligns the director with the streamline and improves molecular order, while an expansion drives the director away from the flow direction and reduces molecular order. If the expansion is strong enough, an instability develops downstream as disturbances in the flow and polymer configuration reinforce each other through the polymer stress. This instability generates a wave that spans roughly the central half of the channel and propagates downstream at the centerline velocity. For abrupt contractions or expansions, disclinations of ±1/2 strength arise in the corner vortex. The numerical results agree qualitatively with experiments when comparisons can be made. In particular, the wavy pattern following a sudden expansion is remarkably similar to previous experimental observations. The simulations suggest that using contractions and expansions may be a feasible strategy for controlling LCP order and morphology in processing.

Optical Gratings Fabricated by Deposition of Liquid Crystalline Polymer Films with Linearly Polarized UV Laser

Polyimide layer on a glass substrate was exposed with a linearly-polarized UV laser through a photo-mask having line-and-space patterns of 2.2 μm. UV laser chemical vapor deposition of liquid crystalline polymer was carried out on the treated substrate. The deposited films showed optical diffraction due to periodic change of molecular orientation of liquid crystalline polymer. The efficiency of optical diffraction was changed with polarization of incident light.

Determination of the Chain Orientation in Liquid Crystalline Polymers by Means of Microfocus X-ray Scattering Measurements

A microfocus camera with a focus of 7 μm fwhm and a flux of 10 11 photons/s at the ESRF in Grenoble was used to investigate the microstructure of liquid crystalline polymer samples of 4-oxybenzoate-co-6-oxy-2-naphthoate (73 :27) (Vectra A950 from Hoechst-Celanese). These samples show isotropic scattering when examined by means of a conventional X-ray camera with a large focus (2 mm). In melt-pressed thin films, we observed local variations of the direction of molecular orientation, which is due to the presence of disclinations. Except at the center of the disclinations, the order parameter is nearly constant within the scanned area. In samples cut out of the center part of an injection-molded bar, we detected a four-point scattering pattern due to a zigzag chain conformation.

Synthesis and characterization of a semiflexible liquid crystalline polyester with a broad nematic region

Abstract In this paper, we report on the synthesis and detailed characterization of a new semiflexible nematic liquid crystalline polyester which could serve as a ‘model’ polyester for a variety of physical and physico-chemical investigations. The polymer is a nematic liquid over a wide temperature range–from the glass transition temperature at ∼95°C to the isotropic transition at ∼240°C. We expect this polyester to be particularly useful for studying the effect of flow on the orientation of liquid crystalline polymers, as well as the production and removal of disclinations.

Simulation of director orientation of liquid crystalline polymers in 2-D flows

The flow-induced orientation of liquid crystalline polymers (LCPs) would substantially affect the mechanical and optical properties of the finished product. In order to investigate the director orientation of nematic polymers in complex geometrical configurations, an efficient and accurate algorithm for the fluid particle tracking technique as well as an iterative scheme are introduced in this article. The simplified Leslie -Ericksen equations were employed and calculated on the basis of the high viscosity approximation. Director orientations predicted by other numerical schemes were found to be polluted by the artificial cross-wind diffusion of improper numerical upwinding methods, especially in the recirculation regions. This was circumvented in the proposed algorithm by integrating the director transport equation along streamlines with a fourth-order Runge-Kutta method. Therefore, the director orientation in a steady recirculation zone could be visualized and the numerical computation was also confirmed to be more stable. To demonstrate the power of the numerical method as well as the effects of the director orientation parameter and anisotropic viscosities on the director orientation, two examples, i.e., expansion flow and contraction flow, were studied. The rheological parameter λ was found to have a strong influence on the director orientation, while β 1 and- β 2 were found to affect the pressure drop across the flow field.

Shear‐Induced orientation in liquid crystalline polymers

AbstractThe orientation development characteristics in shear flow of wholly aromatic thermotropic liquid crystalline polymers were studied. Based on the analysis of shear flow in a capillary followed by elongational flow, an experimental setup has been proposed to determine the shear‐induced orientation. Experimental results have indicated that shear‐induced orientation depends on total shear strain. However, orientation enhancement due to shear flow is much less effective compared with orientation buildup in the case of elongational flow. Thermotropic liquid crystalline polymers that exhibited higher orientability in elongational flow exhibited also higher orientability in shear flow. Finally, to obtain high, shear orientation in processing of thermotropics, special care should be exercised in the design of dies and molds and in optimizing processing conditions, so that high shear rates and/or long shearing times should prevail.