The fabrication and operation of micro-devices, which have important applications in microelectronics, miniaturized analytical devices, and medical technology, require a detailed understanding of liquid film dynamics on surfaces with heterogeneities in chemistry, topography, and temperature. Because the liquid-air interface is deformable with an evolving shape, the combined effects of these heterogeneities on the film can be difficult to anticipate and lead to fascinating dynamical behavior. This grant will facilitate the development of a more detailed knowledge of mechanisms that lead to non-uniformities of the liquid-air interface and the control of their potentially undesired effects, with the practical benefit of enabling the further miniaturization and development of micro-devices for numerous applications. Mathematical models will be used to gain a fundamental understanding of volatile liquid films flowing over surfaces with uneven topography and non-uniform heating. The present studies have three components. (1) The first is to quantify the effects of surface tension gradients caused by temperature variations in coating flows of resin dissolved in volatile solvent over surfaces with topographical features. These are essential components of microfabrication processes based on successive film deposition and photolithography. (2) The second component is to determine the effects of substrate topography on the suppression of recently observed rivulet instabilities in films flowing over differentially heated surfaces, which arise in many micro-scale applications with heat transfer. (3) The third component is to understand the effects of non-uniform heating, substrate wettability, and surfactants on the leveling, drying, and rupture of liquid films on textured surfaces. These dynamics are crucial to coating applications and MEMS devices involving thin films on heated walls. Educational and outreach efforts are aimed at attracting more students to postgraduate research and engineering careers. Research and education will be integrated through the development of a new course on microfluidics and interfacial hydrodynamics; the introduction of self-contained, research-based modules in core chemical engineering courses and labs to enhance student interest in graduate school and modeling research; and the expansion of research opportunities for undergraduates. The outreach activities target local high schools through UMass STEM-Ed engineering workshops for New England teachers and through the mentoring of minority and low-income high school students. Fascinating examples of intricate patterns induced by hydrodynamic instabilities at liquid-air interfaces will be used to help motivate student interest in science and engineering.
