(624b) Direct Measurement of Conservative and Dissipative Colloidal Forces in the Presence of Adsorbing and Nonadsorbing Polymer

Colloidal and macromolecular dispersions are important in many industrial applications and in biological and environmental systems. The macromolecular induced interactions have been shown to be important mediators in biological processes and drug delivery applications. A good understanding of these interactions is key to practical and scientific approaches in soft matter and biophysics. In this talk we report the implementation of a novel dynamic analysis to measure colloidal conservative and dissipative forces from ensemble colloidal particle probe excursions normal to an underlying substrate. The analysis is based on Bayesian Inference analysis of particle trajectories to find a set of potential energy and particle diffusivity profiles. This analysis enables the direct estimation of both Thermodynamic and Hydrodynamic interactions between single particles and a wall with non-intrusive probes. We test this analysis by measuring particle-wall interactions for particles stabilized by adsorbed polymer brushes in the presence of non-adsorbing polymer in solution that induce a depletion attraction between particles and the underlying wall. Our results show agreement with standard Boltzmann probability analysis of long trajectories for potential energy profiles and theory. The resulting particle diffusivity profiles are shown to follow known hydrodynamic contributions that include the surface separation dependence and the effect of both adsorbed polymer brush and non-adsorbing polymer in solution. This is the first time that these theories have been validated by means of a non intrusive experimental methodology. Further work on this topic includes the measurement of biomacromolecule forces (both conservative and dissipative) to allow a deeper understanding of the fundamental mechanisms of life.