Formation of a Banded Texture in Solutions of Liquid-Crystalline Polymers 11. Poly(n-Hexylisocyanate) in Toluene

The kinetics of band formation has been followed during the relaxation of anisotropic solutions of poly(n-hexylisocyanate) in toluene previously subjected to a shear rate, for a time t_s. There is a threshold at low, or t_s, below which bands do not appear (formation time t_b→ ∞). Past the threshold, t_s decreases with either or t_s, and eventually bands are seen immediately after stopping the flow (t_b = 0). However, for still larger particularly for the more viscous solutions and when the flowing solution is well oriented, t_b may increase again. The results are similar to those already reported for hydroxypropylcellulose in water and support a previous suggestion for the origin of the banded texture.     

The effect of surface treatment on the alignment and phase transition of a polypeptide liquid crystal

Poly(γ-benzyl-L-glutamate) (PBLG), was utilized as a surface coating agent in order to obtain parallel molecular orientation in thin layers of PBLG liquid-crystalline solutions confined between coated surfaces. It was found that in a thickness range much larger than the cholesteric pitch value, the texture was predominantly planar cholesteric. At film thickness comparable or smaller than the pitch, isotropic spherulites developed from a homeotropic nematic phase. Because of the coupling between the solution concentration and nematic director, as well as large differences in the elastic moduli of PBLG liquid-crystalline solutions, the long-range intermolecular interaction was unfavorable. Competition between parallel orientation induced by the surface coating of PBLG and inherent perpendicular orientation induced by PBLG molecules in the bulk would favor a short-range helix-coil transition mechanism, which results into a reentrant isotropic phase.     

Formation of band textures in hydroxypropylcellulose liquid crystals

Upon shearing, some polymeric liquid crystals develop a particular texture, called “band texture,” consisting of fine equidistant black lines as viewed between crossed polarizers. In mesomorphic hydroxypropylcellulose–water solutions, these bands are due to relaxation of the shear. The band texture appears after shearing at low shear rates and seems to exist during shearing at high shear rates (> 200 S^?1). In the latter case, the steady-state first normal-stress difference is negative. The bands relax in a few minutes and parts of the bands form elongated domains. This texture gives a H_v light-scattering pattern which can be interpreted by the theory of scattering by anisotropic rods. These domains lose their elongated shape with time.     

Development of orientation and texture during shearing of liquid-crystalline polymers

Using polarizing microscopy, we study the development of orientation and texture during slow shearing of liquid-crystalline solutions of poly(γ-benzyl-L-glutamate). Shearing of high molecular weight samples that are initially coarsely textured, or are uniformly oriented over regions of 1 mm², produces a steady state striped texture, for each of three different initial average orientations. The director field in the striped texture is on average aligned parallel to the flow direction, but with misalignment that varies periodically as we move in a direction orthogonal to flow, thus giving the sample a striped appearance under crossed polarizers, with stripes parallel to flow. After the stripes form, they become finer with increased shearing, or with increased shear rate. Along with the birefringent stripes, there are defect lines, parallel to the flow direction with a spacing similar to that of the stripes, i.e. 10 μm or less at steady state. The existence of separate time scales for the development of steady state orientation, and for the shrinkage of the texture length scale to a steady state, is consistent with a phenomenological scaling theory that had been postulated to explain the rheological behaviour of these fluids. Although the steady state striped texture is independent of initial orientation, transient textures during start-up of shearing are highly dependent on initial orientation; for some initial orientations, bands perpendicular to flow occur temporarily during shearing.     

Liquid-crystalline phases of circular superhelical plasmid DNA and their modification by the action of nuclease enzymes

CD spectra of liquid-crystalline dispersions, X-ray diffraction patterns and optical textures of liquid crystals prepared from native superhelical DNA in poly(ethyleneglycol)-containing water-salt solutions before and after treatment of DNA with micrococcal nuclease have been obtained. It was found that condensation of native superhelical DNA is accompanied by the formation of liquid crystals with a non-specific optical texture. After treatment of the DNA, liquid-crystalline dispersions, with Micrococcal nuclease the DNA is able to form two similar types of liquid crystals with abnormal optical activity which differ in the peculiarities of their textures. The data obtained demonstrate the formation of multiple types of liquid crystals from high molar mass double-stranded optically active DNA molecules.     

Relationships between ringed spherulitic morphology and miscibility in blends of poly(ɛ-caprolactone) with poly(benzyl methacrylate) versus poly(phenyl methacrylate)

 Ringed spherulites are an interesting phenomenon that is observed only in very few miscible systems. For the first time, the relationship between the state of chain intermixing and the ring-band pattern was demonstrated. Two previously demonstrated miscible blend systems, poly(ɛ-caprolactone) (PCL) with poly(benzyl methacrylate) (PBzMA) and PCL with poly(phenyl methacrylate) (PPhMA), were studied in order to understand the mechanism of ring-band formation in the spherulites and the relationships between the ring-band pattern and the state of miscibility. In both miscible PCL/PBzMA and PCL/PPhMA systems, extinction rings were observed within the PCL spherulites. In the PCL/PBzMA blend, the extinction rings are not as distinct (owing to distortion) as those in the PCL/PPhMA blend system. Analysis was performed and discussions were made to reveal relationships between miscibility, interaction strength, and the pattern of the ring bands in the PCL spherulites in polymeric mixtures. Received: 5 January 2000/Accepted: 14 March 2000     

Preparation and liquid-crystalline properties of toluene-4-sulphonyl urethane of hydroxypropylcellulose

A novel liquid-crystalline polymer, the toluene-4-sulphonyl urethane of hydroxypropylcellulose (TSUHPC), was prepared through chemical modification of hydroxypropylcellulose (HPC) of M_w = 60000 g mol^-1. The resulting polymer was characterized by infrared spectroscopy, differential scanning calorimetry (DSC) and polarizing microscopy. It was found that thermotropic liquid crystal phases are formed between about 60°C and 110°C. Concentrated solutions of TSUHPC in acetone and N,N-dimethylacetamide exhibit cholesteric behaviour, at room temperature. When approaching the lyotropic mesophase to solid transition, either by cooling or by solvent evaporation, very interesting arborescent structures of a seemingly fractal nature may be observed, depending on the kinetics of the transition. A banded texture can be observed when the polymer is sheared near the transition to the isotropic phase.     

Invite Article: The Liquid-Crystalline Phases of Double-Stranded Nucleic Acids in Vitro and in Vivo

This article describes the state of and progress in experimental studies of liquid crystals of naturally occurring nucleic acids and synthetic polynucleotides. The areas considered in this review include: (i) the liquid-crystalline phase of nucleic acids in aqueous salt solutions, (ii) the liquid-crystalline phase of nucleic acids in aqueous polymer solutions, (iii) the liquid-crystalline phase of nucleic acids in living systems. Some unsolved problems which are of interest from both a physicochemical and a biological point of view are discussed.     

Periodic extinction bands composed of all flat‐on lamellae in poly(dodecamethylene terephthalate) thin films crystallized at high temperatures

Using in‐house synthesized poly(dodecamethylene terephthalate) (P12T) as a model, periodic extinction‐banded spherulites melt‐crystallized at high T_cs (100–115 °C) are expounded in terms of growth mechanism. The extinction‐banded spherulites wildly differing from the usual blue/orange double ring‐banded spherulites are composed of all flat‐on discrete single‐crystalline lamellae packed like roof shingles (or fish scales) along the circularly curved bands and the lamellae in the extinction bands are flat with a lozenge shape with no continuous twisting at all. For P12T films of more than 10 µm crystallized at T_c = 105–115 °C, no periodic bands were seen, and all spherulites were ringless, where periodic growth precipitation of crystals to extinction does not occur until impingement. Extinction bands in the P12T spherulites with the inter‐ring spacing steadily decrease with decreasing film thickness, because for thinner films (submicrons to 2 µm), draining or depletion of available molten species takes place more frequently, leading to bands of smaller inter‐ring spacing. The petal‐like extinction bands are discussed and analyzed in detail using 3D AFM imaging. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 601–611     

The 2012 Luckhurst–Samulski Prize

Abstract

This article describes the state of and progress in experimental studies of liquid crystals of naturally occurring nucleic acids and synthetic polynucleotides. The areas considered in this review include: (i) the liquid-crystalline phase of nucleic acids in aqueous salt solutions, (ii) the liquid-crystalline phase of nucleic acids in aqueous polymer solutions, (iii) the liquid-crystalline phase of nucleic acids in living systems. Some unsolved problems which are of interest from both a physicochemical and a biological point of view are discussed.     

Band texture formation of sheared polymeric liquid crystalline state

The phenomenon of band texture formation of sheared main chain liquid crystalline polymers is reviewed. The bands seen in a polarizing microscope are optical effects. The macromolecular chains are aggregated into zig-zag bent fibrils perpendicular to the bands. The band texture is formed during shear relaxation. The induction period depends on the shear rate applied, the shearing time, solution concentration (lyotropic), solution layer thickness, temperature and the nature of the polymer. There exists a critical shear deformation to bring a multi-domain nematic or cholesteric phase into a monodomain continuous phase, from which the band texture is formed. These two phases show quite different rheological behavior. In certain cases randomly oriented regions of bands can also be formed during quenching of a thermotropic nematic polymer melt or during standing of a lyotropic nematic polymer solution, where the nematic domains in the melt or in the solution have grown to a sufficient size.     

Preparation and liquid-crystalline properties of toluene-4-sulphonyl urethane of hydroxypropylcellulose

Abstract

A novel liquid-crystalline polymer, the toluene-4-sulphonyl urethane of hydroxypropylcellulose (TSUHPC), was prepared through chemical modification of hydroxypropylcellulose (HPC) of M_w = 60000 g mol^?1. The resulting polymer was characterized by infrared spectroscopy, differential scanning calorimetry (DSC) and polarizing microscopy. It was found that thermotropic liquid crystal phases are formed between about 60°C and 110°C. Concentrated solutions of TSUHPC in acetone and N,N-dimethylacetamide exhibit cholesteric behaviour, at room temperature. When approaching the lyotropic mesophase to solid transition, either by cooling or by solvent evaporation, very interesting arborescent structures of a seemingly fractal nature may be observed, depending on the kinetics of the transition. A banded texture can be observed when the polymer is sheared near the transition to the isotropic phase.     

Endor investigations of biradicals in liquid crystals

It is shown that ENDOR spectroscopy of biradicals with small zero-field splitting (¦D¦ < 1 mT) can be successfully performed in liquid-crystalline solutions. An intense signal at the free-proton Larmor frequency establishes the triplet-state character. The signs of hyperfine coupling constants can be deduced from the intensity pattern.     

Horse heart cytochrome c entrapped into the hydrated liquid-crystalline phases of phytantriol: X-ray diffraction and Raman spectroscopic characterization

Small angle X-ray diffraction (SAXD), resonance Raman (RR) spectroscopy with 413 nm excitation, and non-resonance Raman technique with 785 nm excitation were used to probe the influence of entrapped cytochrome c (Cyt c) on the structure of hydrated phytantriol (Phyt) liquid-crystalline phases as well as conformational changes of heme group and secondary structure of the protein. SAXD measurements indicated that incorporation of Cyt c affects both nanostructure dimensions and type of liquid-crystalline phases of hydrated Phyt. The unit cell dimensions decrease with increasing Cyt c concentration for all phases. In addition, protein perturbs the nanostructure of Q(230) and Q(224) liquid-crystalline phases of hydrated Phyt to such an extent that they transform into the Q(229) phase with the Im3m space group. RR data revealed that entrapment of oxidized Cyt c into the Q(230) phase at 1 wt.% content results in near complete reduction of central iron ion of the heme group, while its low-spin state and six-ligand coordination configuration are preserved. Based on the analysis of heme out-of-plane folding vibration near 568 cm(-1) (γ(21)) and ν(48) mode at 633 cm(-1), it was demonstrated that the protein matrix tension on the heme group is relaxed upon incorporation of protein into Q(230) phase. Non-resonant Raman bands of difference spectra showed the preservation of α-helix secondary structure of Cyt c in the liquid-crystalline phase at relatively high (5 wt.%) content. The Cyt c induced spectroscopic changes of Phyt bands were found to be similar as decrease in temperature.     

Shear-induced band texture of side group liquid crystalline polymers

The shear-induced band texture of conventional end-on fixed side group liquid crystalline polymers (LCPs) has been investigated by using polarizing optical microscopy (POM), small angle light scattering (SALS) and infra-red dichroism techniques. The band spacing is about 1 μm, which increases very slightly on increasing the temperature of shearing and is independent of shearing rate within the range studied. The band texture is not seen to exhibit an interchange of dark and bright bands on rotation of the sample with respect to the polarizer/analyser, but a typical periodical structure is reflected by the SALS patterns of the band texture. The relaxation behaviour of the bands indicates that the band texture formed here is the result of the orderly aligning of domains exhibiting the focal-conic texture, and this is totally different from the case of main chain LCPs where the band texture is substantially an optical effect of the periodic zigzag or sinusoidal structure of parallel aligned microfibrils. Infra-red dichroism and rotating parallel-plate shearing measurements show that the axes of the backbone of the polymer tend to orient in the shearing direction and the end-on fixed mesogenic side groups tend to align perpendicular to the shearing direction.     

Deformation band studies of oriented polyethylene and polyethylene terephthalate

Deformation bands formed at the yield point in tensile tests on oriented high-density polyethylene have been studied by optical microscopy and wide-angle x-ray (WAXS) diffraction. The observations of the rotation of the optical extinction direction are shown to obey a simple scheme proposed previously by us: the principal directions of the refractive index ellipsoid within the deformation bands are everywhere parallel to the principal axes of the plastic strain ellipsoid, zero strain referring to the isotropic state. This result is similar to that obtained previously for polyethylene terephthalate (PET) and polypropylene despite the much higher crystallinity obtained with polyethylene. Independent measurements of the molecular reorientation in the deformation bands made using wide-angle x-ray scattering broadly confirm the optical measurements. The results taken together suggest that the material within the band, whether crystalline or not, becomes realigned about the new direction of maximum elongation as if controlled by the deformation of an effective molecular network.     

Electron microscopic study of dehydration transformations. II. The formation of “superstructures” on the dehydration of goethite and diaspore

It is shown that the satellites observed in the diffraction pattern of the dehydrated single crystal of the mineral goethite, which were previously attributed to a “superstructure,” are better interpreted in terms of small angle scattering by a “texture” of the dehydration product hematite. This texture consists of rows of cavities parallel to the H(003) = G(100) planes with an average distance of 30–50 Å, depending on the stage of the transformation, in a highly twinned hematite matrix. In corundum resulting from the dehydration of diaspore a more isotropic texture is formed and the diffraction pattern exhibits “halos” instead of rows of satellite spots.     

Analysis of NAD 2D-NMR spectra of saturated fatty acids in polypeptide aligning media by experimental and modeling approaches

The overall and detailed elucidation (including the stereochemical aspects) of enzymatic mechanisms requires the access to all reliable information related to the natural isotopic fractionation of both precursors and products. Natural abundance deuterium (NAD) 2D-NMR experiments in polypeptide liquid-crystalline solutions are a new, suitable tool for analyzing site-specific deuterium isotopic distribution profiles. Here this method is utilized for analyzing saturated C14 to C18 fatty acid methyl esters (FAMEs), which are challenging because of the crowding of signals in a narrow spectral region. Experiments in achiral and chiral oriented solutions were performed. The spectral analysis is supplemented by the theoretical prediction of quadrupolar splittings as a function of the geometry and flexibility of FAMEs, based on a novel computational methodology. This allows us to confirm the spectral assignments, while providing insights into the mechanism of solute ordering in liquid-crystalline polypeptide solutions. This is found to be dominated by steric repulsions between FAMEs and polypeptides.     

A novel type of microscopic size chip based on double-stranded nucleic acids

The double-stranded molecules of nucleic acids (NA) of B- and A-families fixed in the structure of cholesteric liquid-crystalline dispersions, formed as a result of phase exclusion of these molecules from polymer-containing solution, have been used as 'building blocks' for the molecular design. Using the formation of polymeric chelate bridges between NA molecules, three-dimensional structures consisting of alternating NA, anthracycline and copper ions, were created. The formation of the polymeric chelate bridges allows one to stabilize the initial spatial mode of ordering of neighboring NA molecules in a form of so-called 'molecular constructions', immobilize these constructions onto supporting film and evaluate their sizes and shape. The creation of NA molecular constructions is accompanied by an 'extra-increase' in the amplitude of the bands in the CD spectra, despite the initial sense of cholesteric twisting characteristic of liquid-crystalline dispersions. Destroying of polymeric chelate bridges between NA molecules by action of biologically relevant compounds results in disintegration of NA liquid-crystalline molecular constructions. Three-dimensional NA molecular construction can be used as a microscopic size multifunctional chemical unit (chip) for biological or chemical needs.     

Investigations of comblike polysiloxanes. I. The influence of spacer length on dielectric relaxation studies of aligned samples

Dielectric relaxation studies on aligned liquid-crystalline comblike polysiloxanes are presented. The polymers differ only in the length of the flexible spacer separating the mesogenic side groups from the polysiloxane backbone. The characteristic features of the observed relaxation process as a function of frequency and temperature, in both the liquid-crystalline and isotropic phases, are described, and the effect of the spacer length is discussed. Within the liquid-crystalline phase a narrow single loss process is observed, due to the relaxation of the mesogenic side groups around the polymer backbone, whereas in the isotropic phase a much broader loss curve is seen. The transition from an aligned polymer mesophase to the randomly aligned isotropic phase is also studied in detial, and comparison with earlier work on comblike polyacrylate and methacrylate liquid crystals is presented.