Materials Science and Engineering Colloquium
Date: April 17, 2015 from 11:00 am to 12:00 pm EDT
Location: Columbia University
Morningside Campus
S.W. Mudd
Room 214
Contact: For further information regarding this event, please contact Svitlana Samoilina by sending email to or by calling 212-851-4266.
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Arvind Narayanaswamy
Department of Mechanical Engineering, Columbia University

"Thermal momentum and energy transfer at short length scales - van der Waals adhesion and heat conduction in nanostructures"

The adhesion between materials plays an important role in diverse fields such as phase change heat transfer and friction. van der Waals  forces play a significant role in adhesive interactions between macroscopic objects at micrometer and nanometer length scales. In the first part of this talk, I will focus on van der Waals forces in dissipative media. van der Waals forces, and the closely related Casimir forces, arise due to momentum transfer by electromagnetic waves. Lifshitz, in his seminal work, outlined a method for computing the van der Waals forces between two semi-infinite regions separated by a vacuum gap. A subsequent generalization by Dzyaloshinskii, Lifshitz, and Pitaevskii, shrouded in the language of quantum electrodynamics, forms the bedrock of our understanding of van der Waals forces. My presentation will revolve around a new solution to a long-standing problem in the field of dispersion forces - that of van der Waals or Casimir forces in dissipative media. Along the way, I will also talk about specific unsolved problems in this field that I find challenging.

In the second part, I will talk about the measurement of heat flow through an individual nanostructures using a cantilever based technique that we invented. A pair of adjacent bi-material cantilevers is proposed as a configuration for measuring thermal conductance of a nanostructure suspended between the two. In our cantilever technique, two lasers are focused, one on each cantilever.  One laser is modulated to vary the temperature at the end of one cantilever, while the second laser senses variation in heat flow through the second cantilever due to thermal conduction along the nanowire. Segments of electrospun polymeric nanowires are suspended between the two cantilevers and the heat flow through such nanowires is quantified by measuring the deflection of the sensing cantilever for a known, laser-induced deflection of the sensing cantilever. Results of measurements from polystyrene nanowires will be presented. The deflection of the sensing cantilever is influenced by two factors: (1) heat flow through the nanostructure, and (2) deflection because of mechanical coupling. I will discuss the effects of mechanical deflection and techniques to eliminate it.

Short bio: Arvind Narayanaswamy received his PhD in mechanical engineering from Massachusetts Institute of Technology in 2007, a MS in mechanical engineering from University of Delaware in 1999, and a B. Tech in mechanical engineering from Indian Institute of Technology (Madras) in 1997. As a graduate student at MIT, he worked with Prof. Gang Chen mainly on the topic of nanoscale thermal radiative transport. He joined the faculty in the Department of Mechanical Engineering at Columbia University, and is now an Associate Professor. His research interests include theoretical and experimental investigations in nanoscale thermal transport, thermodynamics of electromagnetic waves, nanoscale thermal metrology with bi-material cantilevers, interfacial fluid mechanics, and pattern formation due to particle-fluid interactions.

Host: Siu - Wai Chan