Researchers at Rensselaer Polytechnic Institute believe that the speed at which heat moves between two materials that touch one another indicates the strength of the bond between them. Moreover, they believe that flow of heat from one material to the other – in their case, between one solid and one liquid – can be altered by painting a thin atomic layer between the materials. That is, when the interface changes, the interaction between the materials changes.

“If you have a nanoparticle that is inside a liquid solution, you can’t just ‘peel away’ the liquid to measure how strongly it is bonded to the surrounding molecules,” says Pawel Keblinski, professor in RPI’s Department of Materials Science and Engineering. Keblinski, who co-led the study, further says, “Instead, we show that you can measure the strength of these bonds simply by measuring the rate of heat flow from the nanoparticle to the surrounding liquid.”

Shekhar Garde, who co-led the study with Keblinski, states, “Interfaces are an exciting new frontier for doing fundamental studies of this type. If you peek into complex biological systems – a cell, for example – they contain a high density of interfaces, between different proteins or between protein and water.” Garde, who is Elaine and Jack S. Parker Professor and head of RPI’s Department of Chemical and Biological Engineering, also says, “Our approach possibly provides another handle to quantify how proteins talk to each other or with the surrounding water.”

Kablinski and Garde used molecular dynamics simulations to measure the heat flow between solid surfaces and water. They simulated many surface chemistries and found that thermal conductance was directly proportional to how strongly the liquid adhered to the solid.

“In the case of a mercury thermometer, thermal expansion correlates directly with temperature,” Keblinski says. “What we have done, in a sense, is create a new thermometer to measure the interfacial bonding properties between liquids and solids.”

“We can use this new technique to characterize systems that are very difficult or impossible to characterize by other means,” Garde adds.

Garde continues, “This fundamental discovery, which helps to better understand how water sticks to or flows past a surface, has implications for many different heat transfer applications and processes, including boiling and condensation. Of particular interest is how this discovery can benefit new systems for cooling and displacing heat from computer chips, a critical issue currently facing the semiconductor industry.”

The authors conclude that the study provides new information of the behavior of water at various solid interfaces.

This study, titled “How wetting and adhesion affect thermal conductance of a range of hydrophobic to hydrophilic aqueous solutions,” was published April 13, 2009, by Physical Review Letters. Co-authors of the study include RPI graduate students Natalia Shenogina and Rahul Godawat.