Nanofluidics and the Navier boundary condition

Nanofluidics is the study of fluid flow in or around nano scale systems. At this scale, conventional ideas of fluid mechanics do not apply, and the long-standing traditional approaches to fluid mechanics problems need to be adjusted to correctly reflect the importance of the interaction between a fluid and a solid boundary. This is because as devices are miniaturised, the surface-to-volume ratio increases and surface-related phenomena become increasingly important. Nanofluidics is not new, but has existed without a name of its own for many years, and has been studied within a diverse range of disciplines. The term 'nanofluidics' came about recently with the rise of microfluidics and the current advancement in nanoscience and nanotechnology, which prompted the establishment of the international journal Microfluidics and Nanofluidics in March 2004. Existing experimental results of fluid flow in nano devices are contradictory, demonstrating the difficulty of experiments at this scale and the lack of a guiding rational theory. Despite the fact that complicated nanosystems, such as nano-electro-mechanical systems, are already being built and studied, and with the invention and wide availability of many new advanced experimental apparatus such as the atomic force microscope and the scanning tunnel microscope, the fundamental fluid mechanics is still not thoroughly understood, which has made the study and application of nanofluidics quite significant. In this paper these issues are fully discussed and some recent work of the authors involving the continuum description of nanofluidics with altered boundary conditions at fluid-solid interfaces which reflects the importance of surface related phenomena is reviewed.