The innovation engine for new materials

A new neutron scattering tool to probe soft matter structure

Seminar Group: 


Prof. Roger Pynn


Department of Physics
Indiana University, Bloomington


Friday, September 28, 2012 - 4:00pm


ESB 1001


Prof. Phil Pincus


Neutron scattering has played an important role in establishing the structure and dynamics of a range of

soft matter systems, to a large extent because it can address relevant length and time scales and because

it is possible to “label” individual macromolecules by substituting deuterium for hydrogen. Examples

where neutrons have provided unique information can be drawn from systems as diverse as polymer

melts, emulsions, colloids and organic films and I will show a few of these examples as an

introduction. In spite of these successes, traditional neutron scattering methods for studying the

structure of materials suffer from limited spatial resolution, limited ability to access mesoscopic length

scales and difficulties in the interpretation of data obtained with strongly scattering samples. To address

these issues, we have developed a new interferometric method called spin-echo small angle neutron

scattering (SESANS).


In this talk I will introduce the method by comparing it to a relatively familiar optical analogue, the

differential interference contrast optical microscope. I will show that the method generates a real-space

picture of structure in the form of a correlation function and that it is capable of simultaneously

measuring structure over a range of lengths scales from ~ 20 nm to ~ 20 microns. Because the method

automatically accounts for multiple neutron scattering, it is suitable for measurements on strongly

scattering systems such as gels, glasses and ceramics that are often difficult to study accurately with

neutrons. I will describe data that we have obtained using SESANS to study correlations in a model

hard-sphere colloid in which interactions between particles have been tuned by adding a polymer to

generate depletion forces. Further, I will show that the new technique allows us to measure the average

density of colloidal particles confined in micron-sized grooves when the grooves are in contact with a

bulk colloidal suspension. I will show that the method should be capable of measuring colloidal

ordering in such grooves as a function of depth.