Positron Annihilation Studies in Some Alkyl and Alkyloxy Cyanobiphenyls

Kumar, Jitendra; Kaur, C.; Singh, K. Chandramani; Jain, P. C.

doi:10.4028/www.scientific.net/msf.105-110.1625

Cited by 2 publications

(3 citation statements)

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“…1-4. In the cooling cycle, from isotropic phase to -150 K, the behavior of the sample is similar except that the nematic phase exhibits a supercooling by -20 K. The temperatures obtained for various transitions are in agreement with the literature reported values [6,7,12,13]. It is seen from Fig.…”

Section: Resultssupporting

confidence: 90%

“…However, in case of comparatively large asymmetric molecules these cooling rates are conveniently low ( -30 K/rain) and therefore supercooling studies in such systems are practicable. As demonstrated by the earlier positron annihilation studies in these compounds [6,7], there is reasonable Ps formation even in the crystalline solid phase, indicating availability of free volume even in this state. Alkyl cyanobiphenyls fall in this category of highly anisotropic molecules which exhibit supercooling [6,7].…”

Section: Introductionsupporting

confidence: 55%

“…Simple monatomic liquids require extremely high cooling rates -10 tl K s-1 or more for them to get supercooled and, therefore, they are not practically suited for supercooling studies. Positron annihilation studies in 7CB and n-p-cyano-p-decyl biphenyl (10CB), as a function of temperature, have been carried out [6,7]. The formation of a glass-forming supercooled state is believed to be a direct consequence of the low degree of symmetry of the unstrained molecule [5].…”

Section: Introductionmentioning

confidence: 99%

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Study of molecular motions in alkyl cyanobiphenyls using positron lifetime spectroscopy

Singh

Jain

1996

Struct Chem

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Positron lifetime measurements have been carried out in two liquid-crystal-forming homologues of alkyl cyanobiphenyls, 7CB and 10CB. In each of these two compounds measurements were performed during the heating cycle of samples prepared either by quenching or by slow cooling from the respective liquid crystalline phase. In both compounds, the behavior of quenched and slow-cooled samples is found to be different. Unlike the slow-cooled sample, the material in the quenched sample seems to have transformed into a glassy solid. The o-Ps pick-off lifetime in the quenched sample exhibits a strong temperature dependence. In each case, its value exhibits six broad peaks at various characteristic temperatures which have been ascribed to various motions associated with the molecules of these compounds. The quenched samples of 7CB and 10CB exhibit glass transitions at -268 and -266 K, respectively. The present work demonstrates an interesting application of positron lifetime spectroscopy (PLS).