Ph.D. Candidate, University of California, Davis
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“Thermodynamic and kinetic transition of liquids in nanoconfinement”
Nanoconfined liquid plays a pivotal role in a vast number of fields ranging from biological and materials sciences to catalysis, nanofluidics and geochemistry. In this regard, understanding the physico-chemical basis involved in the flow, structural transitions and melting/freezing behav-ior of fluids confined within nanometer-sized pores of solid materials is of paramount im-portance
for both basic research and technological applications. Using architected mesoporous silica-based matrices as the confinement hosts, this study provides detailed insights into the thermo-dynamic and kinetic transitions of nanoconfined fluids. While the melting point depression of water confined in different sizes of nanopores investigated by differential scanning calorimetry (DSC) is consistent with the prediction of Gibbs−Thomson relation, 2H nuclear magnetic reso-nance (NMR) spectroscopy provide compelling evidence that the extreme dynamical heteroge-neity of water molecules is preserved over distances as small as a few angstroms. Solidification progresses in a layer-by-layer fashion, which give rise to an apparent fragile-to-strong dynamic transition in nanoconfined water. The extreme spatial heterogeneity is also manifested in the dynamics during kinetic glass transition of ortho-terphenyl (OTP). This study demonstrates, for the first time, that despite connectivity between the pores, nanoconfined water and OTP display distinct freezing/melting points and glass transition temperatures characteristic of each pore type. Viewed as a whole, these experimental results point to the coexistence of strong spatial heterogeneities over length scales of a few nanometers in the structure and dynamics of these liquids, suggesting a close mechanistic connection between them.
Yiqing Xia, Ph.D. Candidate, University of California, Davis
Yiqing Xia is a Ph.D. candidate in the Department of Materials Science and Engineering, University of California, Davis. In 2016, he received a B.S. in materials science and engineering at Shanghai Jiao Tong University in China. His undergraduate research experience in surface-enhanced Raman spectroscopy motivated him to pursue a Ph.D. in materials science.
Currently, he is a member of the research group of Prof. Sabyasachi Sen and his current research focuses on establishing a mechanistic connection between structure and fragility of chalcogenide and phosphate liquids, using a combination of rheological measurements and NMR spectroscopy. He is also a member of the Energy Frontier Research Centers (EFRC) MUSE, where his research involves the application of DSC and NMR spectroscopy to investigate the thermodynamic and kinetic transitions of water and other glass-forming liquids nanoconfined in various mesoporous silica matrices.