Instabilities, thermal fluctuations, defects and dislocations in the crystal-RI-RII rotator phase transitions of n-alkanes.

Abstract

The theoretical study of instabilities, thermal fluctuations, and topological defects in the crystal-rotator-I-rotator-II (X-R_I-R_II) phase transitions of n-alkanes has been conducted. First, we examine the nature of the R_I-R_II phase transition in nanoconfined alkanes. We propose that under confined conditions, the presence of quenched random orientational disorder makes the R_I phase unstable. This disorder-mediated transition falls within the Imry-Ma universality class. Next, we discuss the role of thermal fluctuations in certain rotator phases, as well as the influence of dislocations on the X-R_I phase transition. Our findings indicate that the herringbone order in the X-phase and the hexatic order in the R_II-phase exhibit quasi-long-range characteristics. Furthermore, we find that in two dimensions, the unbinding of dislocations does not result in a disordered liquid state.