RESEARCH PAPER Diffusion of fluid confined to nanotube with rectangular cross section Reena Devi • Jyoti Sood • Sunita Srivastava • K. Tankeshwar Received: 8 December 2009 / Accepted: 11 February 2010 / Published online: 17 March 2010 Ó Springer-Verlag 2010 Abstract A dynamical model is proposed to study self- diffusion coefficient by confining the fluid in rectangular nanotube. The theoretical model is based on the consider- ation that the confinement affects the movement at atomic level. The model predicts that the diffusion parallel to walls of channel is different from that of diffusion perpendicular to the walls. Near the walls the dynamics of fluid has been found to slow down to an extent that below a certain value of ratio of width to the diameter of particle, the molecules behave as if these belong to solid. The results are con- trasted with the result obtained from the model based on similar considerations for a fluid confined only in one direction. It is found that tendency of freezing near the wall increases due to confinement from second direction. Empirical relation which governs the behavior of diffusion coefficient as function of distance from the confining walls has also been proposed. The effect of confinement is more pronounced for denser fluids than for dilute fluid. Keywords Nanotube  Diffusion  Confinement 1 Introduction During last decade the flow of fluid in a nanometer size object with at least one dimension below 100 nm has gathered attention of many researchers. This is due to the occurrence of phenomena which have many applications in science and technology (Schoch 2008; Bocquet and Barrat 1996). Owing to the development of nanoscience, a number of interesting diffusion-related behaviours in varieties of systems with strong geometric confinement have been recently observed. In addition to simple fluid, these systems include complex systems like biological (Gambale et al. 1996) and artificial (Siwy et al. 2005; Reguera et al. 2006) channels, carbon nanotubes (Hinds et al. 2004), templated porous materials (Kresge et al. 1992; Davis 2002), molecularly imprinted materials (Katz and Davis 2000), nanoporous catalysts (Hahn et al. 1996; Gupta et al. 1996), and membrane fuel cells (Steele and Heinzel 2001). For example, the study of diffusion of benzene confined to nanochannels studied by Neutron Scattering spectrometer (Mamontov et al. 2005) has revealed that the benzene liquid, when confined, freezes much below its freezing temperature. The measurement of dynamics of single DNA molecule confined in nano- channels has also shown that below a critical width of channels the Brownian dynamics of the molecule gets altered (Reisner et al. 2005). The study of dynamic model of biomolecular diffusion through two-dimensional nano- channels has shown that diffusion through the membrane can be controlled by varying the porosity (Cosentino et al. 2005). The study of self diffusion in slit and cylindrical pores carried by molecular dynamic calculations (Kim et al. 2008) has revealed that the diffusion coefficient in the axial direction is reduced relative to bulk fluids for pore size less than about ten molecular diameters (Cui R. Devi  S. Srivastava Department of Physics, Panjab University, Chandigarh 160014, India J. Sood University Institute of Engineering & Technology, Panjab University, Chandigarh 160014, India K. Tankeshwar (&) Computer Center, DCSA, Panjab University, Chandigarh 160014, India e-mail: tankesh@pu.ac.in; tankesh12@yahoo.com 123 Microfluid Nanofluid (2010) 9:737–742 DOI 10.1007/s10404-010-0587-2