Hydrophilic interactions molecular modelling

It is important to propose molecular and theoretical models to describe the forces, energy, structure and dynamics of water near mineral surfaces. Our understanding of experimental results concerning hydration forces, the hydrophobic effect, swelling, reaction kinetics and adsorption mechanisms in aqueous colloidal systems is rapidly advancing as a result of recent Monte Carlo (MC) and molecular dynamics (MO) models for water properties near model surfaces. This paper reviews the basic MC and MD simulation techniques, compares and contrasts the merits and limitations of various models for water-water interactions and surface-water interactions, and proposes an interaction potential model which would be useful in simulating water near hydrophilic surfaces. In addition, results from selected MC and MD simulations of water near hydrophobic surfaces are discussed in relation to experimental results, to theories of the double layer, and to structural forces in interfacial systems. 

A. 19.3 While the best model depends on the question being investigated, the Stern model would provide a more accurate model of the interphase because it considers molecular size and non-electrostatic molecular absorption, both of which are very important to biological systems. For example, proteins control the flow of ions through membranes based on size, so if size isn t considered, the interactions leading to flow control would be missing an essential component. Hydrophobic and hydrophilic interactions are also an important part of interphase interactions. 

In MD modeling, the molecular adsorption concept is used to interpret the Pt-C interactions during the fabrication processes. The Pt complexes are mostly attached to the hydrophilic sites on the carbon particles, viz. carbonyl or hydroxyl groups (Hao et ah, 2003). The adsorption is based on both the physical and chemical adsorptions. Many efforts have been done on the MD simulations of Pt nano-particles adsorbed on carbon with or without ionomers (Balbuena et ah, 2005 Chen and Chan, 2005 Huang and Balbuena, 2002 Lamas and Balbuena, 2003 2006). The Pt-Pt interactions are modeled with the many-body Sutton-Chen (SC) potential (Rafii-Tabar et al, 2006), whereas a Lennard-Jones (LJ) potential is used to describe the Pt-C interactions. The SC potential for Pt-Pt and Pt-C interactions provides a reasonable description of the properties for small Pt clusters. The diffusion of platinum nano-particles on graphite has also been investigated, with diffusion coefficients in the order of 10 cm s (Morrow and Striolo, 2007). 

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