To develop viable polymer stabilized liquid crystal systems, it is crucial to understand the factors that affect polymer nanostructure evolution. This work examines the influence of the photopolymerization of aliphatic and fluorinated monoacrylate monomer within a room temperature smectic liquid crystal (LC). Additionally, the effect of LC order on polymerization kinetics, monomer and polymer organization, and the effect of the polymer on LC properties have been examined. Through this work, insight has been gained regarding the impact that the introduction of a fluorinated monoacrylate monomer has on polymerization kinetics, LC organization, and monomer/polymer segregation and organization within a polymer/LC system. Fluorinated moieties lower the surface energy of the monomer to enhance segregation between the smectic layers of the LC as compared with an analogous aliphatic monomer. Additionally, the enhanced segregation significantly increases the polymerization rate in the smectic phase and drives the continued segregation of the fluorinated polymer during and after polymerization. Fluorination also leads to the formation of an ordered polymer nanostructure if polymerized in ordered LC phases. This ordering is particularly evident when the fluorinated monomer is polymerized in the smectic phase in which the monomer is organized between the smectic layers of the LC. In addition, the ordered polymer structure found with the fluorinated monomer in the smectic phase leads to continued birefringence above the clearing point of the LC due to surface interactions between the LC and the ordered fluorinated polymer. The continued birefringence offers an exceptional opportunity to examine how factors such as polymer molecular mass and UV light intensity affect the overall polymer morphology of these polymer/LC systems. As the initiator concentration and UV light intensity are decreased, longer polymer chains form lattice-type morphologies; whereas, shorter polymer chains form smoother morphologies that more closely mirror the texture of the LC smectic phase. 相似文献
To develop viable polymer stabilized liquid crystal systems, it is crucial to understand the factors that affect polymer nanostructure evolution. This work examines the influence of the photopolymerization of aliphatic and fluorinated monoacrylate monomer within a room temperature smectic liquid crystal (LC). Additionally, the effect of LC order on polymerization kinetics, monomer and polymer organization, and the effect of the polymer on LC properties have been examined. Through this work, insight has been gained regarding the impact that the introduction of a fluorinated monoacrylate monomer has on polymerization kinetics, LC organization, and monomer/polymer segregation and organization within a polymer/LC system. Fluorinated moieties lower the surface energy of the monomer to enhance segregation between the smectic layers of the LC as compared with an analogous aliphatic monomer. Additionally, the enhanced segregation significantly increases the polymerization rate in the smectic phase and drives the continued segregation of the fluorinated polymer during and after polymerization. Fluorination also leads to the formation of an ordered polymer nanostructure if polymerized in ordered LC phases. This ordering is particularly evident when the fluorinated monomer is polymerized in the smectic phase in which the monomer is organized between the smectic layers of the LC. In addition, the ordered polymer structure found with the fluorinated monomer in the smectic phase leads to continued birefringence above the clearing point of the LC due to surface interactions between the LC and the ordered fluorinated polymer. The continued birefringence offers an exceptional opportunity to examine how factors such as polymer molecular mass and UV light intensity affect the overall polymer morphology of these polymer/LC systems. As the initiator concentration and UV light intensity are decreased, longer polymer chains form lattice-type morphologies; whereas, shorter polymer chains form smoother morphologies that more closely mirror the texture of the LC smectic phase. 相似文献
Films of a symmetric liquid‐crystalline/isotropic block copolymer consisting of a smectic LC side‐chain polymer and polystyrene were prepared by solvent casting from solution and from the isotropic melt. By annealing the solvent‐cast film in the SA phase an oriented microphase‐separated film of lamellar morphology was obtained in which both the lamellae of the block copolymer and the smectic layers of the LC block were oriented parallel to the film surface. A lamellar morphology with perpendicular orientation of lamellae and smectic layers was generated by cooling the block copolymer from the melt. 相似文献
The mean-field theory of liquid crystalline (LC) ordering is developed for a polymer brush immersed in a solvent. Additional attraction between neighbouring parallel mesogenic segments of the grafted chains is taken into account. It is shown that LC ordering in this brush is connected with the loss of solubility and occurs as a discrete first-order phase transition which is similar or even identical to the transition in polymer solution. 相似文献
A novel photosensitive polyimide, poly(4,4'-stilbenylene 4,4'-oxidiphthalimide) (ODPA-Stilbene PSPI) was newly synthesized. The most surprising feature of this PSPI is that the PSPI films irradiated with linear polarized ultraviolet light (LPUVL) can favorably induce a unidirectional alignment of liquid crystals (LCs) in contact with the film surface and further switch the director of the unidirectionally aligned LCs from a perpendicular direction to a parallel direction with respect to the polarization direction of LPUVL by simply controlling the exposure dose in the irradiation process. These LPUVL-irradiated films were found to provide high anchoring energy to LCs, always giving very stable, homogeneous cells with unidirectionally aligned LCs regardless of the LC alignment directions. In the films, the PSPI polymer chains were found to undergo favorably unidirectional orientation via a specific orientation sequence of the polymer chain segments led by the directionally selective trans-cis photoisomerization of the stilbene chromophore units in the backbone induced by LPUVL exposure. Such unidirectionally oriented polymer chains of the films induce alignment of the LCs along the orientation direction of the polymer chains via favorable anisotropic molecular interactions between the oriented polymer chain segments and the LC molecules. In addition, the PSPI has an excellent film formation processibility; good quality PSPI thin films with a smooth surface are easily produced by simple spin-coating of the soluble poly(amic acid) precursor and subsequent thermal imidization process. In summary, this new PSPI is the promising LC alignment layer candidate with rubbing-free processing for the production of advanced LC display devices, including LC display televisions with large display areas. 相似文献
For efficient photoresponses of liquid‐crystal (LC) azobenzene (Az) polymer systems, planar LC orientation of the Az mesogenic group is required because the light irradiation process usually occurs with normal incidence to the film surface. However, LC molecules with a rodlike shape tend to orient perpendicularly to the film surface according to the excluded volume effect theory. This review introduces new approaches for inducing planar orientation in side‐chain LC Az polymer films via interface and surface molecular designs. The planar orientation offers efficient in‐plane photoalignment and photoswitching to hierarchical LC architectures from molecular LC mesogens and LC phases to mesoscopic microphase‐separated structures. These approaches are expected to provide new concepts and possibilities in new LC polymer devices.
Abstract We have performed a structural study of the liquid crystal (LC) octylcyanobiphenyl (8CB), deposited on gratings and flat surfaces, using high resolution X-ray scattering as a function of film thickness. 8CB is a room temperature smectic A2, with a layer spacing of 31·6 Å. Glass was used as substrate and treated with either one of the organic surfactants MAP or DMOAP. Surface tension forces cause the liquid crystal molecules to align perpendicularly with respect to the plane of the substrate at the air interface. Competing with the LC-air interface, which is a strong aligner, a grating at the LC-substrate interface produces distortions in the smectic layering with an excess of elastic energy, which favours alignment parallel to the substrate and the grooves. Our purpose was to detect the onset and evolution of parallel alignment as a function of film thickness. The studies used 9 keV (1·403 Å) X-rays focused to a spot size of 2 mm2 at the sample position. In-plane scans, which detect the smectic layers perpendicular to the plane of the substrate, were done at angles φ = 0° and 90° with respect to the gratings to ascertain the molecular orientation, at a nominal X-ray incidence angle of α = 0°. In order to observe regions of varying smectic layer orientation within the film, we performed a series of scans where the out-of-plane tilt angle χ changed from 0°, corresponding to scattering in the plane of the film, to 90°, which corresponds to scattering normal to the surface of the film. The results from these scans were fitted to a multilayer model where the orientation of the smectic layers varies as a function of film depth. The analysis confirmed our earlier observations that surface tension at the air interface plays a dominant role in the alignment of the LC molecules. 相似文献
Monte Carlo simulations are presented for a coarse-grained model of polymer brushes with polymers having a varying degree of stiffness. Both linear chains and ring polymers grafted to a flat structureless non-adsorbing substrate surface are considered. Applying good solvent conditions, it is shown that with growing polymer stiffness the brush height increases significantly. The monomer density profiles for the case of ring polymers (chain length N(R) = 64) are very similar to the case of corresponding linear chains (N(L) = 32, grafting density larger by a factor of two) in the case of flexible polymers, while slight differences appear with increasing stiffness. Evidence is obtained that the chain dynamics in brushes is slowed down dramatically with increasing stiffness. Very short stiff rings (N(R) ≤ 16) behave like disks, grafted to the substrate such that the vector, perpendicular to the disk plane, is oriented parallel to the substrate surface. It is suggested that such systems can undergo phase transitions to states with liquid crystalline order. 相似文献
The order in thin films of a combined liquid crystalline polymer is studied by X-ray reflection. Films of thicknesses of less than 200 nm on float glass are investigated as a function of temperature. The polymer with mesogenic groups in the main and side-chains exhibits smectic and cholesteric mesophases. Measurements in the smectic phases show a Bragg peak and smectic layers are oriented parallel to the substrate. The sample is thus macroscopically ordered by the influence of substrate and free surface. The film surface is very smooth after spincoating; surface roughness is typically 0.8 nm. First annealing of samples leads to a significant roughening of the free surface; roughness increases to 2.1 nm. Order as a function of film thickness depends on the interaction of the polymer with the substrate and free surface. These interactions give rise to a typical correlation length of perturbations in smectic ordering. 相似文献
In the present work, we are studying the local conformation of chains in a thin film of polystyrene adsorbed on a solid substrate by using atomistically detailed simulations. The simulations are carried out by using the readily available and massively parallel molecular dynamics code known as LAMMPS. In particular, a special emphasis is given to the density and orientation of side chains (which consist of phenyl groups and methylene units) at solid/polymer and polymer/vacuum interfaces. Three types of substrates were used in our study: α-quartz, graphite, and amorphous silica. Our investigation was restricted to atactic polystyrene. Our results show that the density and structural properties of side chains depend on the type of surface. An excess of phenyl rings is observed near the α-quartz substrate while the film adsorbed on graphite is depleted in C(6)H(5). Moreover, the orientation of the rings and methylene units on the substrate/film interface show a strong dependence on the type of the substrate, while the rings at the film/vacuum interface show a marked tendency to point outward, away from the film. The results we obtained are in a large part in good agreement with previous experimental and simulation results. 相似文献
Dynamic infrared dichroism techniques have been used to study a complex side chain liquid crystalline segmented polyurethane. The obtained dynamic spectra were analyzed using two dimensional infrared techniques (2D-IR) that allow the easier interperation of the dynamic response of this system. Side chain mesogens are monitored by the cyano tag at the end of the molecule while the hard segments can be viewed in the carbonyl spectral region. A study of the different parts of the macromolecule leads to an understanding of the elastic and the viscous orientation behavior of the polymer. We find that the elastic component of the strain aligns smectic layers parallel and hard domains perpendicular to the direction of strain. The viscous strain component, on the other hand, induces a perpendicular smectic layer and parallel hard domain orientation behavior. These observations are consistent with a model proposed in earlier work that the hard segments and the smectic layers change orientation as the applied strain is increased from low to high strains. In addition, we show further evidence for the coupling of the mechanical deformation behavior of the smectic layers and the hard domains and identified two primary relaxation times in this system. 相似文献
We report on the structure, uniaxial orientation, and photoluminescent properties of CdS nanorods that form stable nanocomposites with smectic C hydrogen-bonded polymers from the family of poly(4-(n-acryloyloxyalkoxy)benzoic acids. TEM analysis of microtomed films of nanocomposites reveals that CdS nanorods form small domains that are homogeneously distributed in the LC polymer matrix. They undergo long-range orientation with the formation of one-dimensional aggregates of rods when the composite films are uniaxially deformed. The Stokes photoluminescence was observed from CdS NRs/LC polymer composites with emission peak located almost at the same wavelength as that of NRs solution in heptane. An anti-Stokes photoluminescence (ASPL) in polymer nanocomposites was found under the excitation below the nanoparticles ground state. The mechanism of ASPL was interpreted in terms of thermally populated states that are involved in the excitation process. These nanocomposites represent an unusual material in which the optical properties of anisotropic semiconductor nanostructures can be controlled by mechanical deformation of liquid-crystalline matrix. 相似文献
Liquid crystal (LC) alignment techniques based on various kinds of ultrathin organized molecular films are reviewed. The mechanisms of LC alignment on the organized films are discussed. For the homeotropic alignment of LCs the main anchoring mechanism is due to the dipole–dipole interaction between polar groups of an aligning agent and LC molecules while the homogeneous alignment is mainly attributed to the orientation of polymer chains or polymer aggregates. An experimental system for an anchoring transition induced by a conformation change of aligning molecules is introduced. Finally the AFM experimental observations on the rubbed polymer films and its mechanisms are summarized. 相似文献
Monolayers of amphiphilic di-block copolymer, PEO40-b-PMA(Az)19 on water surface and solid surfaces, such as silicon wafer and quartz glass, were analyzed by surface pressure — molecular
area (π-A) isotherm, UV-Vis spectroscopy, atomic force microscopy (AFM) and total X-ray reflectivity (TXR). The monolayer
prepared at 22 mN m-1 consisted of H aggregated azobezene (Az) moieties, which orientated perpendicular to the solid surface.
The monolayer structure, including H aggregated Az and orientation of Az, was stable after annealing at 98°C, at which temperature
the hydrophilic PEO domain was the liquid phase and the hydrophobic PMA(Az) was in the smectic A phase. 相似文献