RESEARCH PAPER Thermodynamic properties of gold–water nanolayer mixtures using molecular dynamics Gianluca Puliti • Samuel Paolucci • Mihir Sen Received: 5 November 2010 / Accepted: 4 April 2011 / Published online: 21 April 2011 Ó Springer Science+Business Media B.V. 2011 Abstract The physical behavior of a fluid in contact with solid layers is still not fully understood. The present work focuses on the study and understanding of thermodynamic and structural properties of gold– water nanolayer mixtures using molecular dynamics simulations. Two different systems are considered, where approximately 1,700 water molecules are confined between gold nanolayers with separations of 7.4 and 6.2 nm, respectively. Novelties of the present work are in the use of accurate force fields for modeling the inter- and intra-molecular interactions of the components, and providing comprehensive thermodynamic properties of the mixtures. The results are validated by examination of the pure fluid and pure solid properties. Results indicate that the thermodynamics of the system does not behave as an ideal mixture. The structure of the pure fluid is also analyzed and compared against the structure of the confined fluid in the mixture. Anisotropicity is observed in the fluid structure close to the surface of the nanolayer. Higher ordering and higher flux are detected in the fluid molecules close to the fluid–solid interface. Unusual thermodynamic behavior, anisot- ropicity, liquid layering, and higher interfacial fluid flux could be just some of the factors leading to the enhanced energy transport observed in mixtures involving at least one nanoscale component, such as nanofluids. Keywords Nanofluid  Confinement  Mixture  Molecular dynamics  Gold/water  Thermodynamics  Colloids  Modeling and simulation Introduction Understanding and predicting thermodynamic prop- erties of multi-phase and multi-component mixtures using equilibrium molecular dynamics (MD) are of fundamental interest in every branch of science and engineering. While some progress has been made in these directions, much remains to be done. A self- contained MD study containing thermodynamic properties of a realistic mixture using state-of-the- art empirical potentials is still missing. Some work has been done over the past few years in solid–liquid phase transition (Egorova et al. 2006) and solid–liquid phase equilibrium (Koga 2002), mostly in the environmental and biological sciences. However, the work in these fields is usually limited to structure and phase analysis of the mixtures, subse- quently several important aspects still remain unclear today (Egorova et al. 2006). Even less understood are the phase equilibria of confined complex fluids, such G. Puliti  S. Paolucci (&)  M. Sen Department of Aerospace and Mechanical Engineering, University of Notre Dame, 366 Fitzpatrick Hall of Engineering, Notre Dame, IN 46556, USA e-mail: paolucci@nd.edu 123 J Nanopart Res (2011) 13:4277–4293 DOI 10.1007/s11051-011-0373-4