Individual molecular tilt angle behavior in the smectic C region is represented upon application of a molecular statistical model to the polymorphic terepthal-bis-butylaniline (TBBA) in conjunction with the experimental layer spacings from SAXS measurements using the synchrotron X-ray beam. In the smectic A and smectic H phases of the mesogen, the order parameter fluctuations and pre-transitional effects responsible for sharp changes in the layer spacing and scattered intensities near the phase transition temperature are corroborated with varying positron annihilation lineshapes as a result of electron density fluctuations. © 2002 Published by Elsevier Science Ltd.

Archita Patnaik

Department Of Chemistry

Carrier concentration

Molecular orientation

Phase Transitions

Positron annihilation spectroscopy

Synchrotron radiation

X ray scattering

MESOGENS

Smectic liquid crystals

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Orientational ordering in polymorphic terepthal-bis-4-butylaniline (TBBA)

Solid State Communications

Conformational flexibility of the ammonium complex of macrocyclic 18-crown-6 at 100 K ≤ T ≤ 300 K is studied using a positron microprobe in conjunction with molecular dynamics simulations. The ammonium cation, encapsulated in a three-pointed hydrogen-bonding perching arrangement, undergoes unhindered facile rotation inside the crown cavity, and the ether backbone adopts itself to the dynamic cation conformation. Preferential localization of the positron in the vicinity of the encapsulated cation results in the positron sensing changes in the local electron density distribution arising from the unrestricted rotational motion of the cation as well as from the slow motion of the crown backbone and hence sensing only an average conformation of the complex. © 2005 American Chemical Society.

Journal of Physical Chemistry A

Rotational flexibility in NH4+-encapsulated 18-crown-6 studied by molecular dynamics and positron annihilation: Where does the positron localize?

Positron annihilation lineshape (S-parameter) measurements and small angle X-ray scattering (SAXS) using synchrotron X-rays on liquid crystalline terepthal-bis-butylaniline (TBBA) are reported at cryogenic temperatures. The crystalline ↔ crystalline transition at 233 K deviates from the first order nature, as evidenced by the observation of a pronounced hysteresis in the layer spacing and the S-Parameter during the heating and cooling cycles. Presence of a possible third crystalline phase at a still lower temperature of 180K is identified from X-ray diffraction patterns in corroboration with the slope change in layer spacing and electron density variations reflecting on the line-shape parameter.

Molecular Crystals and Liquid Crystals

Existence of a third crystalline phase in TBBA

Physical Review E

Effects of fluctuations in the orientational order parameter in the cyanobiphenyl(nCB)homologous series

Molecular-statistical description of the smectic-A–smectic-C phase transition

Materials Science Forum

Positron Annihilation in Polymers

Journal of the Physical Society of Japan

Positron Lifetimes in Smectic Liquid Crystals

Physical Review Letters

Evidence for a common high-temperature superconducting effect inLa1.85Sr0.15CuO4andYBa2Cu3O7

Journal	Solid State Communications
ISSN	00381098
Open Access	No