Molecular structure and the occurrence of smectic A and smectic c phases

Jeu, Wim H. de

doi:10.1051/jphys:0197700380100126500

Cited by 58 publications

(22 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…[25] McMillan's model of the SmC phase was developed based primarily on the fact that, at the time, the majority of molecular architectures known to support the formation of the SmC phase all possessed polar functionalities, that is, esters, ethers, Schiff's bases, etc., which were positioned towards the ends of the rigid aromatic core system. [24,26,27] Thus, it was assumed that these 'terminal outboard dipolar units' were responsible for driving the formation of a tilted molecular arrangement. In McMillan's model of the SmC phase formation, the molecular rotations are assumed to freeze at the SmA-SmC transition, and the tilt is driven by the intermolecular dipolar torque formed by the interactions of the 'terminal outboard dipolar units'.…”

Section: Molecular Tilt and Space Fillingmentioning

confidence: 99%

What makes a liquid crystal? The effect of free volume on soft matter

et al. 2015

View full text Add to dashboard Cite

In this article, we probe the formation of liquid crystal and soft crystal phases as a consequence of minimising the free volume of the system either through design engineering of molecular shape or through deformation of molecular architecture. Following this concept, a number of realisations were made, for example, smectic A phases with variable layer spacing, smectic C phases without layer shrinkage, lattices of free space and fibres in N TB phases.Prologue: At the start of my thesis research in 1974, the knowledge of the structures of smectic liquid crystals was somewhat limited. Even though his thought predated the discovery of ferreoelectric behaviour in liquid crystals, George Gray had the idea that smectic C (SmC) liquid crystals might underpin potential new display applications. As I launched into synthesising new SmC variants, I started to think about why molecules should tilt over in their layers, and then onwards to question why do certain materials exhibit different forms of smectic B (SmB) phases, which was before their classification as hexatic and crystal B phases, etc. In those days I became very much interested in how the molecules pack together in condensed phases. With protractors, compasses and graph paper, the Cartesian coordinates of the atoms of a variety of molecular structures in their all trans forms were located, and their mass axes were determined for their structures by computer methods using ticker-tape which used to shoot out of the machine in volumes to yield just one result -the minimum moment of inertia. Flipping the structures about their inertia axes by 180°yielded the surface contours and the rotational volumes of the molecules. Packing them together in ways to minimise the free volume gave snapshot pictures of the local structures of various mesophases.[1] Over the passing years, I discarded this methodology for the following reasons: (1) the molecules in liquid crystal phases are rotationally disordered and are in dynamic fluctuation as demonstrated by neutron scattering studies [2,3]; (2) X-ray data showed that the molecules pack close enough together that they interpenetrate each other's independent rotational volumes, meaning they share each other's space [4,5]; (3) there were no ways to simulate the interpenetration of space, and what was free space and what was not; (4) there were only a few families of materials that could provide full data sets on structure versus phase formation; to this day there are still relatively few full homologous series of materials being reported; and lastly (5) there was no discussion of how to determine the energy cost of not fully packing space with molecules in order to minimise the remaining free volume. However, with the advent of research exploring liquid crystal materials of unconventional structure and new modelling methods such as density functional theory (DFT) simulations becoming available, our work again began to explore the steric packing arrangements of the molecules in condensed phases. [6][7][8][9][10] Then recently, one o...

show abstract

Section: Molecular Tilt and Space Fillingmentioning

confidence: 99%

What makes a liquid crystal? The effect of free volume on soft matter

et al. 2015

View full text Add to dashboard Cite

show abstract

“…1) Not only the popular nematic phase but also smectic-A, -B, -C phases, all possessing layered structure, have captured researcher's interests since the various phase transitions accompanied by symmetry breaking can be easily observed under a conventional polarizing microscope. 2) Since the late twenties, both the experimental [3][4][5] and theoretical 1,6,7) works have been actively done on the phase transition especially from smectic-A to smectic-C phases, which induces the abrupt or continuous molecular tilt from zero to a certain angle from the layer normal. The phenomenological models based on the continuum theory could explain and reproduce the experimental results satisfactorily, 1,6,7) while several molecular models [8][9][10] were also proposed to explain why the rod-like molecules should spontaneously tilt in smectic-C phase.…”

Section: Introductionmentioning

confidence: 99%

Tilted and Non-tilted Liquid Crystalline Langmuir Monolayers: Analogy to Bulk Smectic Phases

Watanabe

Tabe

2007

J. Phys. Soc. Jpn.

View full text Add to dashboard Cite

Hydrophobic compounds of smectic liquid crystals are spontaneously spread on a liquid surface to form softly-condensed monomolecular films. The constituent molecules are coherently tilted from the surface normal when they form smectic-C phase in the bulk state, while the molecules are aligned perpendicular to the surface when they form smectic-A or -B phase in the bulk. The result proves that the tilting property in the smectic liquid crystals should be determined only by the intralayer molecular interaction. The molecular dynamics simulations can reproduce the experimental result satisfactorily and also suggest that the molecular dipole moment should play an essential role to cause the coherent molecular tilt in smectic liquid crystals.

show abstract

“…All these molecules, except 22COOH, have bulk LC phase(s) [5,6]. The SPC (simple point charge) water model [7] was used for the water model in the subphase.…”

Section: Simulation Model and Methodsmentioning

confidence: 99%

Molecular Dynamics Simulations of Liquid Crystal Molecules at an Air-Water Interface

Yoneya

Aoki

Tabe

et al. 2004

Molecular Crystals and Liquid Crystals

View full text Add to dashboard Cite

Molecular dynamics simulations were done for terminally alkyl and alkoxy substituted azobenzene liquid crystal (LC) molecules at an air-water interface using realistic (LC and water) molecular models. The simulation result were compared with those of a corresponding amphiphilic modification, i.e. terminal x-carboxyalkoxy substituted azobenzene. Comparison with a LC with a different mesogen core, phenylpyrimidine, was also made. The interaction energetics were found to be more or less similar both in the alkyl and alkoxy terminated azobenzene and its amphiphilic modification, i.e. cohesive energy dominated over adhesive energy. In contrast, a large difference was found between alkyl and alkoxy terminated azobenzene and phenylpyrimidine LCs; cohesive and adhesive energy contributions were competitive in the latter molecule.

show abstract

Molecular structure and the occurrence of smectic A and smectic c phases

Cited by 58 publications

References 18 publications

What makes a liquid crystal? The effect of free volume on soft matter

What makes a liquid crystal? The effect of free volume on soft matter

Tilted and Non-tilted Liquid Crystalline Langmuir Monolayers: Analogy to Bulk Smectic Phases

Molecular Dynamics Simulations of Liquid Crystal Molecules at an Air-Water Interface

Contact Info

Product

Resources

About