Water nanodroplet thermodynamics : quasi-solid phase boundary dispersivity

• Main Authors: Zhang, Xi, Sun, Peng, Huang, Yongli, Ma, Zengsheng, Liu, Xinjuan, Zhou, Ji, Zheng, Weitao, Sun, Chang Qing
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2015
• Subjects: DRNTU::Science::Chemistry::Physical chemistry::Thermodynamics
• Online Access: https://hdl.handle.net/10356/96193; http://hdl.handle.net/10220/38481
• Institution: Nanyang Technological University

It has long been puzzling that water nanodroplet undergoes simultaneously “supercooling” at freezing and “superheating” at melting. Recent progress [Sun et al., J Phys Chem Lett 2013, 4: 2565; ibid, 4: 3238] enables us to resolve this anomaly from the perspective of hydrogen bond (O:H-O) specific-heat disparity. A superposition of the specific-heat x(T) curves for the H-O bond (x = H) and the O:H nonbond (x = L) defines two intersecting temperatures that form boundaries of the quasi-solid phase between ice and liquid water. Molecular undercoordination (with fewer than four nearest neighbours in the bulk) stretches the H(T) curve by raising the Debye temperature DH through H-O bond shortening and phonon stiffening. The H(T) stretching is coupled with the L(T) depressing because of the Coulomb repulsion between electron pairs on oxygen ions. The extent of dispersion varies with the size of a droplet that prefers a core-shell structure configuration – the bulk interior and the skin. Understandings may open an effective way of dealing with the thermodynamic behaviour of water droplets and bubbles from the perspective of O:H-O bond cooperativity.