Phase Transformation Studies in Decyl Cyanobiphenyl Investigated by Positron Annihilation Spectroscopy

  • Mrityunjay Sharma

Abstract

Positrons are being used as a nuclear probe to investigate the matter for almost last six decades. They are obtained from the radioactive decay of neutron deficient nuclide. On entering into the medium they loss almost all their energy in collisions with the atoms and molecules of the surrounding medium. The thermalised positrons then eventually annihilate with electrons belonging to the medium. Thus the state of the electrons of the medium, in fact, determines the characteristics of positron annihilation process.

Positron annihilation technique (PAT) has already been used in the study of water, ice, wood etc. The changes occurring in chemical compounds due to certain regions have also been studied using PAT. The PAT is also found sensitive towards the structural changes taking place in biological systems. Positron annihilation parameters exhibit their sensitivity toward the structure of DNA. Positron annihilation technique (PAT), in its application, cuts across many interdisciplinary areas like physics, astrophysics, material science, chemistry, biochemistry, biophysics, biotechnology, physical metallurgy etc. It also presents an interesting application in medical diagnostics in the form of positron emission tomography (PET). The possibility of using antimatter (like positron) fuel in spacecrafts is the topic of discussion these days among scientific communities.

In the present study the PAT is used to investigate the phase transformation occurring in liquid crystalline material decyl cyanobiphenyl (10CB). The positron lifetime measurements were recorded as a function of temperature. The positron annihilation parameters are found to exhibit strong dependence on temperature. It is found that the ortho-positronium (o-Ps) pick-off lifetime shows changes which strongly support the existence of some memory of more ordered solid phase on passing to the liquid crystal phase. The changes were also observed in o-Ps formation probability I3, indicating a systematic transformation of the solid phase from a close-pack structure to an open-pack structure. On extending our studies to low temperature range, a change in molecular packing in the solid phase of 10CB has been observed.

 

Published
2019-12-15
Section
Articles