"Characterizing Colloidal Depletion Interactions Using Centrifuge Force Microscopy", by Tom LeFevre

PhD Comp Presentation by Tom LeFevre, ChBE, "Characterizing Colloidal Depletion Interactions Using Centrifuge Force Microscopy"

Abstract:

Soft materials are everywhere: emulsions, polymers, pastes, and gels are found in many commercial products, and soft tissues and cells are commonplace in biology. Soft material properties are determined by structures at the “colloidal” scale: larger than individual atoms but too small to be seen by eye. To understand and control these properties, knowledge of the colloidal interactions that govern bulk properties is critical. Tools exist for measuring forces between colloids; however, few methods can perform multiple force measurements in parallel and over a broad force range. One instrument, the centrifuge force microscope (CFM) is composed of a miniaturized microscope housed inside a swinging bucket centrifuge. As the centrifuge spins, particles suspended in liquid and interacting with a cover slip experience an effective gravitational force. In this manner, well-defined forces can be applied to hundreds of colloidal-scale objects simultaneously. Here, we present a new, wireless CFM capable of performing both fluorescence and bright-field microscopy in combination with microscale force measurements. We use the CFM to explore colloidal depletion interactions. These are entropically-driven attractive interactions that are induced between colloidal particles when they are suspended in a liquid bath containing smaller colloids (e.g. surfactant micelles or nanoparticles). Depletion interactions have been well-characterized in ideal systems at equilibrium, but much remains to be studied in non-ideal and non-equilibrium systems. Knowledge gained will provide insight into the physical properties of soft and biological materials.

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