Masahito Hosino

Bio: Masahito Hosino is an academic researcher from Nagoya University. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 7, co-authored 11 publications receiving 224 citations.

Nematic-Smectic Transition in an Aligned Rod System

Abstract: The nematic-smectic transition in the system of completely aligned hard cylindrical rods is investigated, by making use of the method of symmetry breaking potential. In the second virial approximation the transition is found to occur in the 3-dimensional system but not in the 1- and 2-dimensional systems, in contrast with the result obtained by Wadati and Isihara that the 2-dimensional system also exhibits such a transition. It is shown that the transition is very like the second order one. A shape effect is also studied. Furthermore, by introducing an isotropic attractive intermolecular force, the dependence of the transition on the strength of that force as well as the length and diameter of the rod molecule is investigated.

Statistical Theory of Cholesteric Ordering in Hard-Rod Fluids and Liquid Crystalline Properties of Polypeptide Solutions

Abstract: A statistical theory of lyotropic cholesteric phase in the system of long coiled rod molecules is presented. Effects of molecular exclusion and of attractive intermolecular force are both taken into consideration. On the basis of the theoretical results, experiments on the cholesteric solutions of polypeptide are investigated, where use is made of the scaled particle theory on the fluid of hard rod molecules. It is thus found that the experimental dependences of cholesteric twisting power on temperature, concentration and molecular weight of the polymer and also the experimental curvature elasticity are explained satisfactorily.

Effect of Orientational Fluctuation on Nematic-Smectic A Transition in the System of Hard Rod Molecules

Abstract: By applying the method of symmetry breaking potential to Zwanzig's three direction model for liquid crystal, the nematic-smectic as well as isotropic-nematic transitions are investigated. Particular attention is paid to the effect of orientational fluctuation on the nematic-smectic A transition. It is shown that the nematic-smectic A transition is reduced to the one of first order owing to that kind of fluctuation for the case of short molecule.

Molecular Statistical Theory of the Frank Elastic Constants of Liquid Crystals

Abstract: The Frank elastic constants K 1, K 2, K 3 are calculated in the mean field approximation by assuming that the intermolecular force is the sum of hard rod repulsion (length L and width D) and Maier-...

Temperature dependent pitch in cholesteric phase

Abstract: Orientational ordering in the cholesteric liquid crystal is investigated theoretically by assuming the intermolecular force as the sum of a repulsion of hard-core with shape of twisted rod and of dispersion forces of Maier-Saupe type and of Goossens type. A method of symmetry breaking potential is applied to obtain the free energy as a function of the order parameter and the pitch in the helical structure. Thus, the clearing temperature and the pitch are calculated as functions of the parameters involved in the intermolecular force. By comparing with the results of calculation, one can understand the temperature dependence of the pitch and also the relation between the optical activity and the pitch observed in some cholesteric liquid crystals.

A Helical Polymer with a Cooperative Response to Chiral Information

Abstract: Polyisocyanates, long studied as theoretical models for wormlike chains in dilute solution and liquid crystals, differ from their biological helical analogs in the absence of a pre-determined helical sense. These polymers have an unusual sensitivity to chiral effects that arises from a structure in which alternating right- and left-handed long helical blocks are separated by infrequent and mobile helical reversals. Statistical thermodynamic methods yield an exact description of the polymer and the cooperative nature of its chiral properties. Minute energies that favor one of the helical senses drive easily measurable conformational changes, even though such energies may be extremely difficult to calculate from structural theory. In addition, the chiral nature of the polymer can be used to test theoretical ideas concerned with cholesteric liquid crystals, one of which solves the problem of assigning the helical sense.

Entropically driven microphase transitions in mixtures of colloidal rods and spheres

Abstract: Although the idea that entropy alone is sufficient to produce an ordered state is an old one in colloid science1, the notion remains counter-intuitive and it is often assumed that attractive interactions are necessary to generate phases with long-range order. The phase behaviour for both rods and spheres has been studied experimentally1,2,3,4,5,6,7, theoretically8,9 and by computer simulations10. Here we describe the phase behaviour of mixtures of colloidal rod-like and sphere-like particles (respectively viruses and polystyrene latex or polyethylene oxide polymer) under conditions in which they act like hard' particles2,3. We find a wealth of behaviour: bulk demixing into rod-rich and rod-poor phases and microphase separation into a variety of morphologies. One microphase consists of layers of rods alternating with layers of spheres11; in another microphase of unanticipated complexity, the spheres reversibly assemble into columns, which in turn pack into a crystalline array. Our experiments, and previous theory and computer simulations11, suggest that this phase behaviour is entropically driven by steric repulsion between particles. The phenomena are likely to be quite general, applying also for example to low-molecular-mass liquid crystals12. This kind of microphase separation might also be relevant to systems of amphiphiles13 and block copolymers14, to bioseparation methods and DNA partitioning in prokaryotes15, and to protein crystallization16,17 and the manufacture of composite materials.

A re-examination of the phase diagram of hard spherocylinders

Abstract: The phase transitions exhibited by systems of hard spherocylinders, with a diameter D and cylinder length L, are re‐examined with the isothermal–isobaric Monte Carlo (MC‐NPT) simulation technique. For sufficiently large aspect ratios (L/D) the system is known to form liquid crystalline phases: isotropic (I), nematic (N), smectic‐A (Sm A), and solid (K) phases are observed with increasing density. There has been some debate about the first stable liquid crystalline phase to appear as the aspect ratio is increased from the hard‐sphere limit. We show that the smectic‐A phase becomes stable before the nematic phase as the anisotropy is increased. There is a transition directly from the isotropic to the smectic‐A phase for the system with L/D=3.2. For larger aspect ratios, e.g., L/D=4, the smectic‐A phase is preceded by a nematic phase. This means that the hard spherocylinder system exhibits I–Sm A–K and I–N–Sm A triple points, the latter occurring at a larger aspect ratio. We also confirm the simulation results of Frenkel [J. Phys. Chem. 92, 3280 (1988)] for the system with L/D=5, which exhibits isotropic, nematic, smectic‐A, and solid phases. All of the phase transitions are accompanied by a discontinuous jump in the density, and are, therefore, first order. In the light of these new simulation results, we re‐examine the adequacy of the Parsons [Phys. Rev. A 19, 1225 (1979)] scaling approach to the theory of Onsager for the I–N phase transition. It is gratifying to note that this simple approach gives an excellent representation of both the isotropic and nematic branches, and gives accurate densities and pressures for the I–N phase transition. As expected for such a theory, the corresponding orientational distribution function is not accurately reproduced at the phase transition. The results of the recent Onsager/DFT theory of Esposito and Evans [Mol. Phys. 83, 835 (1994)] for the N–Sm A bifurcation point are also in agreement with the simulation data. It is hoped that our simulation results will be used for comparisons with systems with more complex interactions, e.g., dipolar hard spherocylinders and hard spherocylinders with attractive sites.

Phase transitions in liquid crystals

Abstract: Mesogenic materials exhibit a multitude of transitions involving new phases. Studies of these phases are of importance in a wide range of scientific fields and as such have stimulated considerable theoretical and experimental efforts over the decades. This review article presents a comprehensive overview until this date of the developments in this subject. An attempt is made to identify the essential key concepts and points of difficulty associated with the study of phase transitions. The article begins with a brief introduction about the symmetry, structure and types of liquid crystalline phases. This is followed by a discussion of the distribution functions and order parameters which are considered as the basic knowledge essential for the study of ordered phases. A brief discussion of the thermodynamic properties at and in the vicinity of phase transitions, which are required to understand the molecular structure phase stability relationship, is given. The most widely used experimental techniques for measuring these transition properties are critically examined. The remaining parts of the article are concerned with the current status of the theoretical developments and experimental studies in this field. The application of the various theories to the description of isotropic liquid-uniaxial nematic, uniaxial nematic-smectic A, uniaxial nematic-biaxial nematic, smectic A–smectic C phase transitions are reviewed comprehensively. The basic ideas of Landau–de Gennes theory and its applications to study these transitions are discussed. Since the formation of liquid crystals depends on the anisotropy in the intermolecular interactions, questions concerning its role in the mesophase transitions are addressed. The hard particle, Maier-Saupe and van der Waals types of theories are reviewed. The application of density functional theory in studying mesophase transitions is described. A critical assessment of the experimental investigations concerning reentrant phase transitions in liquid crystals is made and the factors which impede its proper understanding are identified. A survey is given of existing computer simulation studies of the isotropic to nematic transition, the nematic to smectic A transition, the smectic A to hexatic S B transition, the smectic A to reentrant nematic transition, and transitions to the discotic phase. The current status of the study of phase transitions involving hexatic smectic, cholesteric, polymeric and ferroelectric liquid crystals is outlined. Finally, a range of unexplored problems and some of the areas which are in greatest need of future attention are identified.