A Chat with Sunil Sinha, Distinguished Professor of Physics at the University of California–San Diego

March 2012, Interview by Deborah Counce

Sunil Sinha

Sunil Sinha, University of California–San Diego Distinguished Professor of Physics.

The second lecture in the CNMS (Center for Nanophase Materials Sciences) and SNS (Spallation Neutron Source) Research Forum featured Sunil Sinha, Distinguished Professor of Physics at the University of California–San Diego. The lecture was titled "Grazing Incidence Scattering Studies of Thin Films of Soft Matter and Nanoparticles."

The joint seminar series is sponsored by the two Oak Ridge National Laboratory user facilities to highlight research at the interface of neutron scattering and nanoscience.

In the following exchange, Dr. Sinha discussed the lecture, his research, and a new cyber course in neutron scattering for which he is an instructor. He is a prominent condensed matter physics experimental researcher and a leader in the neutron scattering and x ray scattering communities. A fellow of the American Physical Society and the American Association for the Advancement of Science, he has been recognized with the Department of Energy’s Ernest O. Lawrence Award, the MRS Medal, and the Arthur H. Compton Prize of the Advanced Photon Source.

What are your principal research interests?

They range from using neutron and x ray scattering to characterize the magnetic behavior of magnetic nanostructures, and the dynamic behavior of quantum crystals such as solid helium, to characterizing the structural properties and phase behavior of phospholipid bilayers, the stuff that is the major component of cell membranes.

What findings will you be talking about in your CNMS-SNS lecture?

I’ll be talking about how thin films of complex fluids, such as polymer melts, differ from the corresponding bulk material. This is important because many polymer applications are in the form of either polymer films or composites of polymers and nano-objects such as nanoparticles. The shapes and mobility of the polymer chains in these films, which can dramatically affect their properties, may be quite different. In addition, the mobility of the nanoparticles in these entangled chains depends on various length scales—particle size, length between entanglements on the polymer chains, size of the polymer chains. So we can’t always trust theoretical predictions for viscous liquids.

A related problem that poses questions is the glass transition in polymer films. This is complicated, because it proceeds via a variety of length and time scales. I’ll show how scattering experiments can address some of these issues. Although the research I’ll be talking about was done with synchrotron x-rays, very similar information has been obtained with neutron scattering.

How does neutron scattering contribute to your research?

Neutron scattering is an amazing characterization tool. It provides detailed information about the structural, dynamic, and magnetic behavior of materials in a nondestructive way without producing significant radiation damage. It also deeply penetrates bulk matter. It cannot provide direct images of the material at the molecular scale, but it can provide global statistical information about structure or dynamics in one shot. It can also probe what goes on at buried interfaces.

Have you conducted experiments at SNS? How do you expect it to advance the state of science?

I’ve carried out experiments at the Magnetic Reflectometer at SNS and plan to conduct experiments on some of the inelastic spectrometers. I believe the high neutron flux of the SNS and the novel capabilities of some of the instruments will enable rapid scientific advance over broad areas of science, and we can expect a few major discoveries over the next decade.

What are the most exciting recent developments in your specialty?

Some of the most exciting are the development of high-flux spallation neutron sources such as SNS, J-PARC in Japan, and the upcoming European Spallation Source, and of the x-ray free electron laser sources. The latter have ultra-fast, very intense and coherent pulses of x-rays. They have the capability to make “movies” of systems at the nanoscopic level using coherent x rays, and probe nonequilibrium femtosecond (quadrillionth of a second) phenomena with pump-probe techniques using optical and infrared lasers.

What will be the focus of the quantum condensed matter cyber course offered by ORNL Neutron Sciences that you’ll be helping teach this fall?

It will examine how scattering techniques can be applied to fundamental problems in areas such as quantum magnetism and highly correlated electron systems. This is the first remotely available neutron course to introduce researchers to neutron scattering research and methods. As such, it may reach a wider audience than the national schools on neutron and x-ray scattering can accommodate. The audience will be similar: graduate students and postdoctoral researchers interested in learning how scattering techniques will help their research. It will help to increase the number of knowledgeable users of SNS and other national facilities.