讲座题目：Surface Free Energy and the Solvation of Nanoparticles: Effect of Curvature
主讲人 : Brian B. Laird 教授
An understanding of the curvature dependence of the interfacial free energy is essential to understanding the solvation of nanoparticles in solution, as the interfacial free energy for highly curved surfaces can differ significantly from that of planar surfaces. To understand this curvature dependence, a theoretical framework, termed Morphometric Thermodynamics (MT), has been developed that reduces the shape dependence of solvation free energy to a linear combination of a small number of geometric measures with coefficients that, while they depend upon the solute-solvent and solute-solute interactions, are independent of solute shape [Phys. Rev. Lett. 93, 160601 (2004)]. The cornerstone of MT is Hadwiger's theorem from integral geometry. MT has the potential to reduce the calculation of the solvation and interfacial free energies of nanoparticles by several orders of magnitude, but currently there is little information as to the degree to which it is applicable to real systems of interest.
Using molecular-dynamics (MD) simulation, we have calculated the interfacial free energy γ between a hard-sphere fluid and hard spherical and cylindrical colloidal particles, as functions of the particle radius R and the fluid packing fraction η = ρσ^3/6, where ρ and σ are the number density and hard-sphere diameter, respectively. These results verify that MT is valid to significant precision for spherical and cylindrical surfaces up to η ≈ 0.42. In addition, earlier results for γ for this system using a geometrically based classical density-functional theory are in excellent agreement with the current simulation results for packing fractions in the range where MT is valid. However, above η ≈ 0.42, γ (R) shows significant deviations from MT indicating limitations to its use for high-density hard-sphere fluids. Using the results of this study together with MT allows one, in principle, to determine γ accurately for any sufficiently smooth surface immersed in a hard-sphere fluid. In some recent work we show with very high precision MD calculations, that that there are very small, but statistically significant deviations, from MT for this system, even at low packing fraction, in agreement with recent analytic calculations.
Brian B. Laird is a Professor of Chemistry at the University of Kansas and currently serves as Department Chair. He received Bachelor of Science degrees in Chemistry and Mathematics from the University of Texas, Austin, in 1982 and a Ph.D. in Theoretical Chemistry from the University of California, Berkeley, in 1987. Prior to his current position, he held postdoctoral and lecturer appointments at Columbia University, Forschungszentrum Jülich (NATO Fellowship) (Germany), University of Utah, University of Sydney (Australia) and the University of Wisconsin. He has been in his current position at the University of Kansas since 1994, punctuated with brief periods as a Visiting Scientist at the University of Mainz (Germany), the University of Leicester (UK), University of California, Davis and the Freiburg Institute for Advanced Study in Germany. He is the recipient of a CAREER award from the National Science Foundation. His research interests involve the application of statistical mechanics and molecular simulation to the determination of materials properties. Specific areas of research include (a) investigations into the structure, dynamics, and thermodynamics of the interfaces between condensed phase materials (crystals, liquids, amorphous materials), (b) prediction of solid-liquid, liquid-vapor coexistence properties in systems under nano-scale confinement, (c) and the development of advanced algorithms for molecular dynamics simulation. Published 111 Peer reviewed papers and received 5089 citations.