NONEQUILIBRIUM MOLECULAR-DYNAMICS (NEMD) SIMULATIONS AND THE RHEOLOGICAL PROPERTIES OF LIQUID NORMAL-HEXADECANE

Non-equilibrium molecular dynamics (NEMD) simulations of liquid n-hexadecane have been performed and its rheological properties have been studied in detail. The Ryckaert and Bellemans model of hydrocarbons has been adopted and extended by using appropriate bond-stretching and angle-bending harmonic potentials. The so-called SLLOD equations of motion which impose and maintain a homogeneous shear rate have been employed in conjunction with an iterative algorithm for determining the Gaussian thermostatting multiplier which maintains the kinetic energy explicitly constant. A number of phenomena have been observed (shear thinning, shear dilatancy, normal stress effects and molecular alignment) and studied in detail using standard rheological viscometric functions and appropriate geometrical analysis parameters. NEMD results have been compared with theoretical and empirical expectations from polymer rheology and indicate that a large-n (eg. n = 16) liquid alkane has some striking similarities to polymer melts with appropriately scaled molecular weights.