Thermal Bubble Nucleation in Nanochannels: Simulations and Strategies for Nanobubble Nucleation and Sensing
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Thermal Bubble Nucleation in Nanochannels: Simulations and Strategies for Nanobubble Nucleation and Sensing Manoj Sridhar1, Dongyan Xu2, Anthony B. Hmelo1, Deyu Li2, Leonard C. Feldman3 1
Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA. Department of Mechanical Engineering, Vanderbilt University, Nashville, TN, USA. 3 Institute of Advanced Materials, Devices and Nanotechnology, Rutgers University, New Brunswick, NJ, USA. 2
ABSTRACT Progress in the state of the art of nanofabrication now allows devices that may enable the experimental sensing of bubble nucleation in nanochannels, and the direct measurement of the bubble nucleation rate in nanoconfined water and other fluids. In this paper we report on two aspects in achieving this goal: 1) new molecular dynamics simulations of nanobubble formation in nanoconfined argon and water model systems and 2) an ultrasensitive nanofluidic device architecture potentially able to detect individual nanobubble nucleation events. INTRODUCTION The classical description of homogeneous bubble nucleation in water suggests that the critical radius is a sensitive function of temperature and pressure, but of the order of one micron at 373 K. Thus we ask a simple question: Can fluids such as water boil when confined at length scales smaller than this critical dimension? Clearly, our question is concerned with confinement effects on pre-critical density fluctuations in the bulk fluid away from confining walls. We report progress on our efforts to simulate nanobubble nucleation, to understand the nucleation rate, and recent innovations in detector technology that will enable us to directly sense individual nucleation events. Potential extensions of this device include in-situ reaction monitoring, the investigation of two-phase flow, the stability of fluids with respect to the solid-liquid transition, and the granularity of matter at the nanoscale. Such nanoscale fluidic devices are ultimately limited by fundamental noise considerations, possibly different than those of other electronic systems. One important phenomenon is the influence of spontaneous thermal bubble nucleation, which has recently been postulated as a source of detector noise in nanofludic measurements [1]. Thus the investigation of nanobubble nucleation is of intrinsic interest and has direct applicability to the ultimate performance of nanofluidic devices. MOLECULAR DYNAMICS SIMULATIONS Thermal bubble nucleation in nanoconfined spaces has attracted considerable attention in recent years [2-7]. Most of this work has focused on using canonical-ensemble (NVT) molecular dynamics (MD) simulations to study nanoscale bubble formation. Such simulations may be regarded as bubble cavitation rather than spontaneous thermal bubble nucleation. Our goal is simulate thermal bubble nucleation inside nanochannels using an isobaric-isothermal ensemble (NPT) MD approach. However we first present the results of NVT simulations of argon and
water systems to validate our approach and verify that ou
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