Self-colored crosslinked cholesteric liquid crystalline solid films of hydroxypropyl cellulose

Solutions of lyotropic cholesteric liquid crystalline hydroxypropyl cellulose (HPC) in water were self-colored due to the selective reflection of visible light, depending on the solution concentration. It was attempted to apply colored coatings of the liquid crystalline aqueous HPC solutions. HPC solid films were cast from the liquid crystalline solutions at different conditions and the color of the films was controlled. The cast films were chemically crosslinked. The crosslinked cast films were self-colored blue, yellow, or orange, but not red. Circular dichroism study of the cast films revealed that some films exhibited the peak wavelength in the red region of visible light. Scanning electron microscopy also showed that some films had the cholesteric pitch corresponding to the red region of visible light. However, colorimetry of the films indicated that no red films were prepared. This may be due to the highly varied distribution of the pitch. Some problems for applying the HPC liquid crystalline solution as colored coatings still remained open.     

Cellulosic solid films exhibiting cholesteric liquid crystalline order

Ethyl cellulose (EC) and hydroxypropyl cellulose (HPC) films were cast under different conditions and were observed optically. The creep behaviour of those films was determinedin vacuo as a function of applied stress or temperature and was analysed on the basis of the Eyring thermally activated process.EC and HPC films cast from liquid crystal-forming systems remained cholesteric liquid crystalline order (the cholesteric sense was different in each case), whereas EC film cast from non-liquid crystal system (benzene) had no liquid crystalline order and was amorphous. The Eyring activated process could be applied to the creep behaviour of our films and activated parameters could be evaluated. The activated volumeV was of the order of 1 nm³ and greatly depended on the casting conditions and testing temperature. The value ofV tended to decrease as the liquid crystalline order increased. The value ofV was smaller than the size of liquid crystalline domain.     

Cellulosic solid films exhibiting cholesteric liquid crystalline order

Static tensile, dynamic mechanical, and stress relaxation properties of ethyl cellulose (EC) films cast from liquid crystalline and non-liquid crystalline solutions at various conditions were determined.EC films exhibited a marked tensile yield behaviour at room temperature. The yield stress depended on strain rate and an activated volumeV could be evaluated from the data of the yield stress. The dependence ofV obtained from the yield behaviour on the casting conditions was almost the same as that from creep behaviour.There was a phenomenological correlation between the dynamic modulusE and the activated volumeV: the higher the value ofE, the lower the value ofV; but there was no clear correlation between the relaxation modulus andV. From the stress relaxation behaviour,V was also evaluated; however, the dependence ofV evaluated from the stress relaxation data on the casting conditions was not similar to that from the creep or yield stress data.     

Hierarchical mesoporous silica prepared from ethyl-cyanoethyl cellulose cholesteric liquid crystalline phase

Porous silica with hierarchical structures was prepared from ethyl-cyanoethyl cellulose/poly(3-(methacryloyloxy)propyl-trimethoxysilane) (E-CE)C/P(MPTOS) composites with fixed cholesteric liquid crystalline (LC) phase. The scanning and transmission electron microscopy (SEM and TEM) and N₂ sorption measurements results indicate that the silica prepared from cholesteric LC composites is of hierarchical macro-, meso- and micro-porous structures, and the average pore size of the silica can be tailored by the content of the cholesteric LC phase in the (E-CE)C/P(MPTOS) composites. The resultant silicas have high specific surface area with the highest value of 837 m²/g at the pore volume of 0.83 cm³/g. This approach provides a new choice for the preparation of porous silica materials, especially from the templates that are not compatible with aqueous system.     

PPC液晶合成、表征及PPC/PVC复合膜蛋白吸附研究

以羟丙基纤维素(HPC)为原料,通过丙酰氯酯化反应合成羟丙基纤维素丙酸酯(PPC),采用IR和NMR表征了PPC的化学结构,偏光显微镜观察证实取代度为2.06的PPC在体温37℃附近呈现胆甾型液晶态。采用溶剂成膜法制备PPC/聚氯乙烯(PVC)液晶复合膜,应用考马斯亮蓝法,测定了在体温37℃下不同液晶含量的PPC/PVC复合膜对牛血清白蛋白(BSA)的吸附。结果表明,PPC液晶/PVC复合膜的蛋白吸附随液晶含量的增加而减少,PPC液晶可以显著降低基体聚合物的蛋白吸附量,有希望用于改善聚合物的抗蛋白黏附性能。     

Controlling the morphology of side chain liquid crystalline block copolymer thin films through variations in liquid crystalline content

In this paper, we describe methods for manipulating the morphology of side-chain liquid crystalline block copolymers through variations in the liquid crystalline content. By systematically controlling the covalent attachment of side chain liquid crystals to a block copolymer (BCP) backbone, the morphology of both the liquid crystalline (LC) mesophase and the phase-segregated BCP microstructures can be precisely manipulated. Increases in LC functionalization lead to stronger preferences for the anchoring of the LC mesophase relative to the substrate and the intermaterial dividing surface. By manipulating the strength of these interactions, the arrangement and ordering of the ultrathin film block copolymer nanostructures can be controlled, yielding a range of morphologies that includes perpendicular and parallel cylinders, as well as both perpendicular and parallel lamellae. Additionally, we demonstrate the utilization of selective etching to create a nanoporous liquid crystalline polymer thin film. The unique control over the orientation and order of the self-assembled morphologies with respect to the substrate will allow for the custom design of thin films for specific nanopatterning applications without manipulation of the surface chemistry or the application of external fields.     

Threshold behaviour for the electrical conductivity of V2O5 films reduced by heating in vacuo

Thin V₂0₅ films were converted to V02 by heating in vacuo. The transformation is associated with a delay time which obeys an Arrhenius relation with an activation energy given by the bandgap of V₂O₅.     

Tensile cracks in polycrystalline ice under transient creep: Part II — Numerical simulations

This paper discusses predictions of a numerical model presented in the companion paper (Nanthikesan and Shyam Sunder, 1995) to analyze tensile cracks in polycrystalline ice undergoing transient creep. The numerical model is based on the internal state variable constitutive theory of transient creep in ice developed by Shyam Sunder and Wu (1989a,b, 1990). The finite element model uses the boundary layer approach of Rice (1968), in conjunction with a mid-point crack-tip element and reduced integration, to simulate the asymptotic stress and deformation fields in the vicinity of the crack tip, including incompressible creep deformations.

The problem of a stationary, traction-free, tensile (mode I) crack is analyzed to predict the size, shape and time evolution of the creep-dominated fracture process zone surrounding the crack-tip. The numerical simulations quantify the effects of transient creep, material strain hardening, fabric anisotropy, loading rate, temperature, and finite fracture test-specimen boundary on the development of the creep zone. A range of stress-intensity rates from 1 to 100 kPa s⁻¹ and temperatures from −5° to −25°C is considered in the simulations.

The results from a comprehensive numerical simulation study show that: (i) transient creep increases the creep zone size by more than an order of magnitude over that for a power-law creeping material, i.e., about 40 times for the isotropic, equiaxed granular ice tested by Jacka (1984); (ii) material strain hardening significantly affects the creep zone size, i.e., the creep zone for the transversely-isotropic columnar-grained ice tested by Sinha (1978), with the crack loaded in the plane of isotropy, is about 4 times smaller than that for the granular isotropic ice; (iii) fabric anisotropy increases the size of the creep zone by a factor of at least two for cracks in the transversely-isotropic, columnar-grained ice loaded in the plane of isotropy; (iv) the Riedel and Rice (1980) equation, which was derived for an isotropic power-law creeping material subjected to a suddenly applied constant stress-intensity, overestimates the creep zone size by a factor of 4.2 for a constant stress-intensity rate loading; and (v) as the crack size increases, linear elastic fracture mechanics becomes increasingly applicable at lower loading rates and higher temperatures.     

Tensile cracks in polycrystalline ice under transient creep: Part I — Numerical modeling

The interaction between creep deformations and a stationary or growing crack is a fundamental problem in ice mechanics. Knowledge concerning the physical mechanisms governing this interaction is necessary: (1) to establish the conditions under which linear elastic fracture mechanics can be applied in problems ranging from ice-structure interaction to fracture toughness testing; and (2) to predict the ductile-to-brittle transition in the mechanical behavior of ice and, especially, the stability and growth of cracks subjected to crack-tip blunting by creep deformations. This requires a quantitative estimate of the creep zone surrounding a crack-tip, i.e., the zone within which creep strains are greater than the elastic strains.

The prediction of the creep zone in previous ice mechanics studies is based on the theory developed by Riedel and Rice (1980) for tensile cracks in creeping solids. This theory is valid for a stationary crack embedded in an isotropic material obeying an elastic, power-law creep model of deformation and for a suddenly applied uniform far-field tension load that is held constant with time. The deformation of ice at strain-rates ahead of a crack (i.e., 10⁻⁶ to 10⁻² s⁻¹) is dominated, however, by transient (not steady power-law) creep and the loading, in general, is not instantaneous and constant.

A numerical model is developed in this paper to investigate the role of transient creep and related physical mechanisms in predicting the size, shape and time evolution of the creep zone surrounding the tip of a static crack in polycrystalline ice. The model is based on the fully consistent tangent formulation derived in closed form (Shyam Sunder et al., 1993) and used in the solution of the physically-based constitutive theory developed by Shyam Sunder and Wu (1989a, b) for the multiaxial behavior of ice undergoing transient creep. The boundary value problem involving incompressible deformations ahead of a stationary, traction-free mode I crack in a semi-infinite medium is modeled and solved by a finite element analysis using the boundary layer approach of Rice (1968). This model is verified by comparing its predictions with (i) the known theoretical solutions for the elastic and HRR asymptotic stress and strain fields in an elastic-plastic material of the Ramberg-Osgood type, and (ii) the creep zone size for an isotropic material obeying the elastic power-law creep model of deformation.     

Molecular relaxations in the composites of liquid crystalline cellulose derivatives with poly(acrylic acid)

The molecular relaxation phenomena of the specific polymer composites obtained by photopolymerisation of the oriented lyotropic liquid-crystalline systems composed of cellulose derivatives dissolved in photopolymerisable acrylic acid are studied. We have investigated the composites based on two cellulose derivatives, which differ by the length of their side-chains and consequently by their physical properties. In this work, the molecular relaxations of such anisotropic composites were studied by dielectric relaxation spectroscopy and by thermooptical analysis. In the dielectric relaxation spectroscopy two representations were analysed: temperature dependences of dielectric loss ɛ"(T) and of electric modulus M "(T). The electric modulus representation is especially convenient to monitor the relaxations in a high temperature range where the ionic conductivity dominates the dielectric response. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

Micro orientation and anisotropy of conductivity in liquid crystalline polymer films filled with carbon nanotubes

In this communication we report the preferential orientation of single wall carbon nanotubes (SWNT) in a nematic liquid crystalline (LC) polymer matrix. The alignment of the nanotubes was characterized through anisotropy of electrical conductivity of the composite measured in directions parallel and perpendicular to the nematic director. The anisotropy of the nanocomposite films strongly depends on the nanotube concentration in the range from 1 to 10% and vanished at higher loads. The electrical conductivity of nanocomposites is related to their structural features revealed by atomic force microscopy and Raman spectroscopy experiments and is explained by a strong coupling between the nanotubes and the polymer matrix.     

Transition from a disordered to a crystalline state in II–VI and III–V films

The initial stages of HgCdTe growth on Al₂O₃, GaAs, CdTe, and KCl substrates have been studied by electron diffraction. HgCdTe films were produced by pulsed laser deposition and isothermal vapor phase epitaxy. InGaAs films were grown by isothermal chloride epitaxy on GaAs substrates. In the initial stages of the growth process, we observed a transition from an amorphous to a textured polycrystalline phase and then to a mosaic single-crystal structure. We have calculated the critical size of crystalline grains below which amorphization occurs in II-VI and III-V compounds. The critical grain size agrees with the grain size of the disordered (amorphous) phase that forms in the initial stage of epitaxy. We have determined some characteristics of the heterostructures: critical film thickness below which pseudomorphic growth is possible without misfit dislocation generation, elastic stress in the epitaxial system, surface density of dangling bonds at dislocations, and the critical island radius above which no interfacial misfit dislocations are generated.     

The fracture of poly(hydroxybutyrate) Part III Fracture morphology in thin films and bulk systems

This paper is the final part of a three paper series describing the fracture and ageing behaviour of poly(hydroxybutyrate). In the first two parts conventional fracture mechanics methods were used to monitor changes both during the detrimental room temperature ageing process that occurs and after a subsequent annealing process that had been reported to reverse the ageing process. This paper reports on our studies of the morphology of fracture surfaces and how fracture proceeds in different ways in the original, ductile, fresh, material, the more brittle, aged material and the ductile, annealed material. We have used optical and electron microscopic techniques to examine fracture surfaces of samples which had already been well characterised by mechanical testing. The effect of ageing and high temperature annealing on the resultant fracture morphology is detailed for both thin films and bulk samples. We have found that PHB undergoes crazing before failure regardless of annealing history. We have studied the craze morphology using optical microscopy and scanning electron microscopy. Both aged and un-aged samples are found to deform in approximately the same manner, the primary difference on ageing being the volume of material that is plastically deformed. After high temperature annealing a different craze morphology has been observed. In thin films this is characterised by the formation of a dense zone of micro-crazes over a relatively large area. In bulk samples there is a distinct change in the resultant fracture surface. In both thin films and bulk systems there is an increased occurrence of fracture initiation in the spherulite cores after high temperature annealing which helps to extend the craze zone.     

Simulation of growth dynamics in atomic layer deposition. Part III. Polycrystalline films from tetragonal crystallites

Materials with one- and two-dimensional crystal structures often form crystals with the shape of needles and platelets, respectively. This should be expected to have great influence on the properties of thin films grown from such materials, and the effect on texture and topography is shown in this paper by a series of simulations. The topic of this paper is the effect of different aspect ratios of crystals with tetragonal symmetry on the resulting thin films. However the major results should also apply to crystals of other types of symmetry having aspect ratios deviating from one. The growth dynamics in atomic layer deposition of polycrystalline thin films have been simulated for randomly oriented and randomly positioned crystallites. Crystalline seed objects adapting shapes of tetragonal boxes with aspect ratios from 0.1 (platelets) to 10 (needles) has been used as examples for growth of films from tetragonal crystals. The dependence of roughness, surface crystal density, and texture on the film thickness is shown. Topography and cross sections of simulated films with different aspect ratios are discussed. Non-linear growth regimes are consistently found in the initial stage of the film formation. A conversion from type-2 to type-1 substrate inhibited growth is observed as the aspect ratio deviates significantly from one.     

Phase structures, transition behavior and surface alignment in polymers containing rigid-rod backbones with flexible side chains Part VI Novel band structures in a combined main-chain/side-chain liquid crystalline polyester: From liquid crystal to crystalline states

Physical origins of banded structures appearing on different length scales have been investigated using polarized light and atomic force microscopies (PLM and AFM), polarized Fourier Transform infrared spectroscopy (FT-IR) and wide angle X-ray diffraction (WAXD) in a combined main-chain/side-chain liquid crystalline (LC) polyester, PEFBP(n). This series of PEFBP(n) polymers was synthesized from the polycondensation of 2,2-bis(trifluoromethyl)-4,4-biphenyldicarbonyl chloride with 2,2-bis{-[4-(4-cyanophenyl)-phenyoxy]-n-alkoxycarbonyl]}-4,4-biphenyl diol. In this paper, we focus on one polymer [PEFBP(n = 11)] of this series to illustrate the band structural formation on different length scales during the evolution from liquid crystal to crystalline states. Alternating bands of the films mechanically-sheared at 190 °C are formed with a spacing of 3 ± 0.5 m in PLM, and recognized to be primary bands. PLM and AFM results show that these bands are seen due to the change of optical birefringence constructed mainly by alternating film thickness (and thus, retardation). Based on polarized FT-IR results, both the backbones and side chains of the polymers are orientated parallel to the shear direction. Secondary fibrillar bands develop within the primary bands after the sample is subsequently crystallized at 105 °C. These bands show a zigzag arrangement and possess a lateral size of 250 ± 50 nm determined by AFM. High resolution AFM observations illustrate that these bands consist of aggregated edge-on crystal lamellae having a thickness of approximately 20 nm. The lamellar crystals are assembled together and lie across the film thickness direction. The mechanism for the formation of these secondary zigzag bands originates from the expansion of the lattice dimension along the chain direction on a molecular scale during the nematic to crystalline phase transition and crystallization in the partially confined LC primary bands, which form macroscopic zigzag buckling.