Eric Furst of the University of Delaware Laser Tweezer Microrheology and Micromechanics of Colloidal Gels lecture as part of ChBE's Fall 2006 Seminar Series.

Refreshments will be served from 3:30-4:00PM
The seminar will be held 4:00-5:00PM

Abstract
At the heart of the current push in nanotechnology lies the promise that manipulating matter at the nanoscale will deliver unique functionality and utility for applications ranging from advanced photonic materials to new medical therapies. Our research focuses on the roles nanoscale structures and interactions play in determining the properties of soft materials and complex fluids, such as polymers, biopolymers and colloidal suspensions. These constitute a range of economically important materials, from consumer care products to specialty performance coatings, ceramics and biomimetic polymer scaffolds; therefore, understanding their underlying physical characteristics enables molecular and nanometer scale manipulation with the aim of engineering useful and novel properties. We study these materials using emerging experimental methods, including laser tweezer manipulation, microrheology and confocal microscopy.

To illustrate our approach, I will present unique experiments that provide a critical missing link between the macroscopic mechanical properties of colloidal gels and the particle nanoscale interfacial phenomena from which these properties ultimately originate. Gels form when colloidal particles aggregate to form an open, space-filling network. The elasticity, yield behavior and stability of materials made from colloidal gels depend on the mechanical strength of the gel microstructure; that is, the tendency of the network to deform and rupture under applied stresses. Using the micromanipulation and piconewton force sensing capabilities of laser tweezers, we have led the investigation of the properties of colloidal gels by developing methods to directly assemble model aggregates and measure their bending rigidity and failure mechanics.
From this knowledge, we develop models that accurately describe the dependence of the gel elastic properties on solution conditions, and even find regimes where the boundary friction between particles determines the yield stress of gels. These studies provide the insight necessary to control gel rheology by tailoring the chemical and nanometer scale properties of the colloidal particle surfaces.