Effect of Film Thickness on the Columnar Packing Structures of Discotic Supramolecules in Thin Films

The effects of film thickness on the columnar packing structure of discotic supramolecules in a thin supported film have been investigated by grazing‐incidence small‐angle X‐ray scattering technique using magnetically aligned cobalt octa(n‐decylthio)porphyrazine (CoS10) films on octadecyltrichlorosilane (OTS)‐functionalized substrates as model systems. Magnetically aligned CoS10 films with a range of film thicknesses (49–845 nm) form uniaxially oriented ‘edge‐on’ columnar superstructures with their columnar directors perpendicular to the applied magnetic field. However, the orientational ordering of the columnar packing in the plane perpendicular to the applied magnetic field is strongly dependent on the film thickness. While being damped by the elasticity of the side chains of CoS10, the strong interfacial interaction at the film‐substrate interface propagates up to 50–100 nm from the substrate, maintaining the orientation of columnar packing in the plane perpendicular to the applied magnetic field. When the distance from the film‐substrate interface becomes larger than about 100 nm, symmetric tilting of columnar layer orientation, which saturates at 11.5°, occurs due to longitudinal edge dislocations induced by accumulated elastic deformation.     

Magnetically Induced Orientation of Mesochannels in Mesoporous Silica Films at 30 Tesla

We demonstrate the magnetically induced orientation of mesochannels in mesoporous silica films prepared with low‐molecular‐weight surfactants under an extremely high magnetic field of 30 T. This process is principally applicable to any type of surfactant that has magnetic anisotropy because such a high magnetic field provides sufficient magnetic energy for smooth magnetic orientation. Hexadecyltrimethylammonium bromide (CTAB) and polyoxyethylene‐10‐cetyl ether (Brij 56) were used as cationic and nonionic surfactants, respectively. According to XRD and cross‐sectional TEM, mesochannels aligned perpendicular to the substrates were observed in films prepared with low‐molecular‐weight surfactants, although the effect was incomplete. The evolution of these types of films should lead to future applications such as highly sensitive chemical sensors and selective separation.     

Orientation of dye molecules in DNA-based films with chain alignment and judgment of their DNA-binding modes

Novel composite films of chain-oriented DNA, which contain the DNA-binding dyes aligned in specific orientation, were successfully prepared by drying the solution under a horizontal magnetic field. Most of the dye-DNA composite films showed linear dichroism, as revealed by polarized ultraviolet-visible (UV-vis) spectroscopy. The intercalators, ethidium bromide and acridine orange, were fixed in chain-oriented DNA films in a similar binding manner as in solutions. Also, Hoechst 33258 and 4',6-diamidino-2-phenylindole were found to be aligned along the minor groove, even in the solid films. Thus, our new method of preparing dye-DNA composite films with chain orientation is useful for aligning small molecules, and it will provide views of the novel anisotropic materials expected in various application fields. We used this method to prepare composite DNA films with newly designed original compounds. Seven of nine dyes were judged to bind obviously to DNA as intercalators by polarized UV-vis spectroscopy. The DNA-binding manners were further analyzed by fluorescence anisotropy measurements. On the basis of the curves for the rotational angle dependence of the anisotropy, we were able to estimate the angles between the transition-dipole moments of dyes and the aligned chain axis of DNA. Interestingly, two original compounds were found to be in the tilted forms with regard to the plane of base pairs. We emphasize here that the method using aligned dye-DNA films is very convenient for identifying the binding modes of the compounds for double-stranded DNA.     

Synthesis and orientation study of a magnetically aligned liquid‐crystalline chitin/poly(acrylic acid) composite

A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003     

Free-surface effects on the response of nematic liquid crystal films to a laser pulse

Abstract

The dynamic response of 5CB films with a free surface to a laser pulse is investigated. A magnetic field above the Fréedericksz transition is applied initially to induce a starting angle on the molecular orientation. A single 1·06 μm laser pulse with e ^?1 pulse width 0·2 ms is incident normally upon the films. When the laser pulse polarization is perpendicular to the magnetic field, only a thermal effect is involved. While it is parallel to the magnetic field, both molecular orientation and thermal effects are involved. The results from films with a free surface are compared with those from films sandwiched between two glass substrates. The free surface effect, beam size effect, and thermal effect are discussed by comparing with theoretical analysis.     

Magnetically driven growth of anthracene thin films by organic molecular beam deposition

The possible use of a static magnetic field during organic molecular beam deposition of thin molecular films for inducing some preferential growth is discussed and the magnetic properties of diamagnetic molecules and molecular crystals are recalled. Considering prototypical materials, namely anthracene molecules and potassium phthalate substrates, which interact and may give rise to polycrystalline films with specific orientations, we show that in the presence of a magnetic field the films display a macroscopic preferential orientation as a result of minimization of the magnetic energy contribution. A very good agreement between the results of optical spectroscopy, atomic force microscopy, and predictions made on the basis of the anisotropic magnetic susceptibility of anthracene is found.     

Orientation of molecules by magnetic field as a new source of information on their structures

A complex procedure for quantitative allowance for small but significant effects of molecular orientation by strong static magnetic fields was elaborated. A series of high-resolution ¹H NMR spectra of 1,2,3-trichloronaphthalene recorded at magnetic field strength varied over a wide range was analyzed in the framework of a unified approach with high accuracy. The spin-spin coupling constants and the dipole-dipole coupling constants for all pairs of ¹H nuclei and the anisotropy and rhombicity parameters of the magnetic susceptibility tensor of the molecule were determined. Ab initio CSGT/RHF quantum chemical calculations of this property using a wide range of conventional diffuse and polarization basis set functions were carried out. Augmentation of the basis set with polarization functions affects the values of the calculated parameters to a lesser extent compared to augmentation with diffuse functions. The results of calculations using the 6-311G(df) and 6-311++G(df) basis sets are in good agreement with the experimental values of the magnetic susceptibility anisotropy for 1,2,3-trichloronaphthalene. The advantages of the method proposed and specific features of the effects of orientation by magnetic field as a new source of information on the structure of molecules in solution are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1309–1317, August, 2006.     

ANALYSIS AND CHARACTERIZATION OF MICROSCOPIC MORPHOLOGY AND ORIENTATION STRUCTURE OF POLYANILINE POLYMERIZED IN A CONSTANT MAGNETIC FIELD

Conductive polyaniline(PAn-_M and PAn-_O) doped with dodecylbenzene sulfonic acid(DBSA) was synthesized by using emulsion polymerization method in the presence of a constant magnetic field(0.4 T) and the absence of magnetic field, respectively.The effects of magnetic field on the microscopic morphology and orientation structure of PAn were generally analyzed and characterized by using transmission electron microscope(TEM),X-ray diffraction(XRD) and through the conductivity anisotropy of unit resistance o...     

The mechanical and magnetic alignment of liquid crystalline epoxy thermosets

The processing of a new series of liquid crystalline (LC) epoxy networks was evaluated. Above the glass transition temperature, the low crosslink density networks could be mechanically aligned. The mechanically oriented networks readily lost orientation upon heating. Highly anisotropic liquid crystalline (LC) epoxy networks were also prepared by aligning the mesophase of the prepolymer during the curing process under the influence of a magnetic field. Orientation parameters (f) of 0.13 to 0.57 were achieved by these processes as determined by x-ray diffraction analysis. The ability of the magnetically aligned networks to retain their orientation above the glass transition temperature was determined by time-resolved x-ray diffraction. The stability of the alignment of these networks was found to depend on crosslink density. The effect of the anisotropy of these networks was investigated by measuring the coefficient of thermal expansion (CTE). In the aligned networks, there was a substantial reduction in CTE parallel to the direction of the applied field compared to the randomly oriented networks. © 1992 John Wiley & Sons, Inc.     

Relationship between lens properties and director orientation in a liquid crystal lens

Lenses with a homogeneously aligned liquid crystal having a Fresnel structure have been prepared by using a nematic with a positive dielectric anisotropy. Their focal length can be varied continuously from the value f_e for an extraordinary ray to f _o for an ordinary ray by applying an electric field across the lens cell. The effective refractive index of the lens where the director is aligned perpendicular to the grooves of the Fresnel structure becomes smaller than when the director is aligned parallel to the grooves. Then the liquid crystal lens has a characteristic aberration which could not be observed in a conventional glass lens; that is, the focal length of the lens becomes different according to the incidence of rays on the different parts of the lens. The properties of the liquid crystal lens can be improved by making the director orientation axially symmetric, in the form of a concentric circle, but the polarization component rotated 90° from the incident extraordinary ray appears when the voltage is applied across the lens cell. This phenomenon is discussed in relation to the optical properties and the director orientation in a liquid crystal prism cell.     

Phase and orientational behaviors in liquid crystalline main-chain/side-group block copolymers

The phase and orientational behaviors of a series of liquid crystalline (LC) AB-type diblock copolymers comprising thermotropic main-chain (MC) polyester and side-group (SG) polymethacrylate blocks were investigated by X-ray diffraction. The MC and SG blocks were phase separated and gave rise to their individual mesophases that coexisted at equilibrium. The samples were oriented by using either a magnetic field or a mechanical field. In magnetically aligned samples both the MC and SG microphases were oriented with their smectic planes orthogonal to the magnetic field direction, independent of the copolymer composition. Mechanically aligned, fiber samples showed different orientations of the MC and SG smectic planes for different sample compositions. In this case the disposition of the smectic planes of the MC and SG blocks was driven by the relative length of the two blocks. Some features of the X-ray patterns of the copolymers were compared to those of the MC and SG homopolymers. In addition, the MC smectic domains crystallized on annealing without affecting the orientation that had been achieved by applying a magnetic field. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 21–29, 1998     

Layer-by-layer electrostatic assembly with a control over orientation of molecules: anisotropy of electrical conductivity and dielectric properties

While forming layer-by-layer (LbL) electrostatic assembly of a magnetic organic molecule, namely, nickel phthalocyanine (NiPc), we apply a magnetic field. The field orients the magnetic moment of the molecules on a monolayer along the direction of magnetic field. Such an orientation of the molecules is then electrostatically immobilized with a monolayer of a polycation. By repeating the dipping cycle, we form LbL films with planar NiPc molecules facing a particular direction. With NiPc's moment perpendicular to the molecular plane, two types of LbL films were formed: (a) NiPc's molecular plane parallel to the substrate (moment is perpendicular) and (b) molecules perpendicular to the substrate and facing one particular direction, the direction of magnetic field. Such films, with the molecules lying either (a) parallel or (b) perpendicular to the substrate, provide unique systems to study anisotropy of optical, dielectric, and electrical characteristics in these planar organic molecules. The latter film responds to the polarization of incident beam in electronic absorption spectroscopy. Here we show methods to obtain an orientation of molecules in LbL films and study anisotropy of dielectric constant and conductivity of the molecules in ultrathin films.     

Unprecedented observation of days-long remnant orientation of phospholipid bicelles: a small-angle X-ray scattering and theoretical study

Nanometric bilayer-based self-assembled micelles commonly named as bicelles, formed with a mixture of long and short chains phosphatidylcholine lipids (PC), are known to orient spontaneously in a magnetic field. This field-induced orientational order strongly depends on the molecular structure of the phospholipids. Using small-angle X-ray scattering (SAXS), we performed detailed structural studies of bicelles and investigated the orientation/relaxation kinetics in three different systems: saturated-chain lipid bicelles made of DMPC (dimyristoyl PC)/DCPC (1,2-dicaproyl PC) with and without the added paramagnetic lanthanide ions Eu(3+), as well as bicelles of TBBPC (1-tetradecanoyl-2-(4-(4-biphenyl)butanoyl)-sn-glycero-3-PC)/DCPC. The structural study confirmed the previous NMR studies, which showed that DMPC bicelles orient with the membrane normal perpendicular (defined here as "nematic" orientation) to the magnetic field, whereas they orient parallel (defined here as "smectic" orientation) to the magnetic field in the presence of Eu(3+). The TBBPC bicelles also show smectic orientation. Surprisingly, the orientational order induced in the magnetic field remains even after the magnetic field is removed, which allowed us to investigate the orientation and relaxation kinetics of different bicelle structures. We demonstrate that this kinetics is very different for all three types of bicelles at the same lipid concentration; DMPC bicelles (~40 nm diameter) with and without Eu(3+) orient faster than TBBPC bicelles (~80 nm diameter). However, for the relaxation, DMPC bicelles (nematic) lose their macroscopic orientation only after one hour, whereas both DMPC bicelles with Eu(3+) and TBBPC bicelles (smectic) remarkably stay oriented for up to several days! These results indicate that the orientation mechanism of these nanometric disks in the magnetic field is governed by their size, with smaller bicelles orienting faster than the larger bicelles. Their relaxation mechanism outside the magnetic field, however, is governed by the degree of ordering. Indeed, the angular distribution of oriented bicelles is much narrower for the bicelles with smectic orientation, and, consequently, they keep aligned for much longer time (days) than those with nematic ordering (hours) outside the magnetic field. The understanding of the orientation/relaxation kinetics, as well as the morphologies of these "molecular goniometers" at molecular and supramolecular levels, allows controlling such an unprecedented long-range and long-lived smectic ordering of nanodisks and opens a wide field of applications for structural biology or material sciences.     

Field Effects in Nematic Liquid Crystals in Terms of Catastrophe Theory

Abstract

The field effects in nematic liquid crystal layers are reanalysed using catastrophe theory. The layer with pretilted director orientation and obliquely applied magnetic field, the hybrid aligned nematic cell and twisted nematic structures are considered. The stable solutions are identified and transitions between them are specified. The results are in essential agreement with previous work. Some details concerning the behaviour near the threshold are revealed.     

Calorimetric study of the isotropic to nematic phase transition in an aligned liquid crystal nano‐colloidal gel

A high‐resolution calorimetric study of the specific heat (C_p ) has been carried out for the isotropic to nematic phase transition in an aligned liquid crystal (octylcyanobiphenyl ‐ 8CB) and aerosil nano‐colloid gel. A stable alignment was achieved by repeated thermal cycling of the samples in the presence of a strong uniform magnetic field, which introduces anisotropy to the quenched random disorder of the silica gel. In general, the specific heat features of the I?N transition in aligned (anisotropic) gel samples are consistent with those seen in random (isotropic) gel samples, namely the observance of two C_p peaks and non‐monotonic transition temperature shifts with increasing silica concentration. However, larger transition temperature shifts with silica density, modification of the phase conversion process in the two‐phase coexistence region, and a larger effective transition enthalpy are observed for the aligned samples. The lower‐temperature aligned C_p peak is larger and broader while exhibiting less dispersion than the equivalent peak for the random gel. This may be a consequence of the alignment altering the evolution from random‐dilution‐dominated to random‐field‐dominated effects. The exact origin of the larger transition temperature shifts is uncertain but the larger enthalpy suggests that the nematic state is different in the aligned system than in random gels. The general non‐monotonic behaviour of the transition temperature is interpreted using dimensional analysis as a combination of an effective elastic stiffening of the liquid crystal combined with a liquid crystal and aerosil surface interaction energy.     

C‐oriented and {010} Facets Exposed BiVO4 Nanowall Films: Template‐Free Fabrication and their Enhanced Photoelectrochemical Properties

Vertically aligned BiVO₄ nanowall films on indium tin oxide (ITO) glass have been fabricated through a template‐free hydrothermal method for the first time. Based on the structural understanding of both BiVO₄ and ITO, the lattice matches ({020}_BiVO4 and {040}_ITO, {200}_BiVO4 and {004}_ITO, respectively) and the similarity of metal atomic arrangement parallel to {001} planes turn out to be crucial for the fabrication of the nanowalls. Consequently, the growth of a BiVO₄ film begins from heteroepitaxy and undergoes an Ostwald ripening process to form an extended network, resulting in a c‐orientation and exposing {010} facets. Through this process, it is much easier to obtain a range of nanowall films with different packing densities, as the surface state of ITO glass is alterable by adjusting the concentration of acid. The films can be directly used as an electrode, which exhibits an excellent response to visible light, especially light with low intensity, allowing for the electrical interconnection, highly active surface, appropriate orientation, and a good contact with the substrate. There are great benefits in improving the technique for detecting the weak light source signals.     

Visualizing cell extracellular matrix (ECM) deposited by cells cultured on aligned bacteriophage M13 thin films

Topographical features ranging from micro- to nanometers can affect cell orientation and migratory pathways, which are important factors in tissue engineering and tumor migration. In our previous study, a convective assembly of bacteriophage M13 resulted in thin films which could be used to control the alignment of cells. However, several questions regarding its underlying reasons to dictate cell alignment remained unanswered. Here, we further study the nanometer topographical features generated by the bacteriophage M13 crystalline film, which results in the alignment of the cells and extracellular matrix (ECM) proteins. Sequential imaging analyses at micro- and nanoscale levels of aligned cells and fibrillar matrix proteins were documented using scanning electron microscopy and immunofluorescence microscopy. As a result, we observed baby hamster kidney cells with higher degree of alignment on the ordered M13 substrates than NIH-3T3 fibroblasts, a difference which could be attributed to the intrinsic nature of the cells' production of ECM proteins. The results from this study provide a crucial insight into the topographical features of a biological thin film, which can be utilized to control the orientation of cells and surrounding ECM proteins.     

Field Effects in Nematic Liquid Crystals in Terms of Catastrophe Theory

The field effects in nematic liquid crystal layers are reanalysed using catastrophe theory. The layer with pretilted director orientation and obliquely applied magnetic field, the hybrid aligned nematic cell and twisted nematic structures are considered. The stable solutions are identified and transitions between them are specified. The results are in essential agreement with previous work. Some details concerning the behaviour near the threshold are revealed.     

Nanostructural properties of zinc oxide thin films grown on non‐planar substrates

The crystallographic structure of zinc oxide thin films grown on optical fibres using single source chemical vapour deposition (SSCVD) was analysed using near edge X‐ray absorption fine structure (NEXAFS). Zinc diethyl carbamate was used as a precursor for the growth of highly conformal films in a one‐step deposition process without substrate rotation and at substrate temperatures of 400–575 °C. It was found that the growth temperatures greatly affected the crystallographic structure of the film with no preferred crystallographic orientation and negligible crystallinity at low temperatures and very high crystallinity with pure c‐axis orientation at high temperatures. Cross‐sectional analysis of the films by scanning electron microscopy (SEM) showed the presence of a film at all points around the fibre. These films generally consisted of densely packed columns that bore a strong resemblance to c‐axis‐oriented films grown on planar substrates. Copyright © 2005 John Wiley & Sons, Ltd.     

IR dichroism study of orientational ordering of liquid-crystalline acrylates

Orientational ordering of four liquid-crystalline acrylates induced by the surface of KBr plates over a wide temperature range was studied by the IR dichroism technique. IR spectra of homogeneously aligned samples were used to calculate the angles between the direction of the transition moment for a series of vibrations of the mesogenic fragment and its long axis. A method for calculation of the homeotropic orientation parameter of molecules was proposed. The orientation parameters of homogeneously and homeotropically aligned samples in the nematic, smectic (A), and chiral smectic (I andH) phases were calculated. Thein situ photopolymerization of acrylates in the smectic phases occurs with retention of the orientational ordering in the polymer films formed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 319–323, February, 1999.