(484g) Melting Transition of Confined Lj Solid

Chandan K. Das, Jayant K. Singh^*

Department of Chemical Enggineering

Indian Institute of Technology, Kanpur, India

^*Corresponding author E-mail: jayantks@iitk.ac.in

In recent year greater attentions have given to study the melting/freezing phenomena in confinement due to its importance in different field of modern technology, like microfluidics, lubrication, adhesion and nanotechnology. Lowering of freezing temperature has been reported for oxygen in sol-gel glasses¹.  Large effects on freezing and melting temperature have been reported for Indium in porous silica glasses ². In contrast of these results, some other experiments investigated an increase in the melting temperature³. Depression or elevation of freezing temperature of LJ solid have been observed under repulsive or attractive slit confinement⁴. Both the experiments and the simulations of fluids for confined cylindrical pore  suggest that, for pore diameters smaller than 20σ the confined phase does not crystallize into a homogeneous solid phase, while for diameters smaller than 12σ the confined solid phase was amorphous throughout the pore⁵.  An abnormality in the freezing/melting point corresponding to the difference in the crystal structure has been reported⁶.

We study the melting transition of crystalline solid under confined attractive and repulsive slit pores, with the help of molecular dynamics simulation. In particular, we investigate in details, density-temperature hysteresis for various pore sizes ranging from 8 to 3 molecular diameters. In addition we examine the amplitude of atomic vibration at a certain fraction of nearest neighbor distance, also widely known as Lindemann parameter. We also compare the hysteresis loop, Lindemann criteria along with the correlation of the second and fourth moments of a 3D distribution of Drwith time t; for melting transition and generalize the criteria for locating the melting transition under confinement. We obtain shift in the melting temperature with respect to the bulk for various pore surfaces and predict the correlation of ΔTm ~H^-n. Using the correlation, crossover behavior is observed from 3D to 2D with n ranging from 2.1 to 0.6.

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²                      K. M. Unruh, T. E. Huber, and C. A. Huber, Phys. Rev. B 48 (12), 9021 (1993).

³                      J. Klein and E. Kumacheva, Science 269, 816 (1995).

⁴                      M. Miyahara and K. E. Gubbins, J. Chem. Phys. 106, 2865 (1997).

⁵                      M. Sliwinska-Bartkowiak, G. Dudziak, R. Sikorski, R. Gras, R. Radhakrishnan, and K. E. Gubbins, J. Chem. Phys. 114 (2), 950 (2001).

⁶                      T. Kaneko, T. Mima, and K. Yasuoka, Chem. Phys. Lett. 490, 165 (2010).