Brownian motion in polymer and surfactant solutions

The objective of this work is to investigate the dynamical behavior of aqueous polymer solutions, and aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), commercially available as Pluronic(TM), triblock copolymer surfactant solutions at elevated temperatures and pressures. Diffusing wave spectroscopy is utilized to monitor the thermal motion of dispersed colloidal particles in the solutions. The measured mean squared displacement (MSD) of the colloidal particles is used to infer the microrheological properties of the solutions, since the MSD is directly proportional to the microscopic creep compliance. This technique allows for the motion of the colloidal particles to be resolved at times as short as ~10-6 s, allowing access to the microrheological properties at frequencies as large as 1MHz.; For the case of aqueous poly(ethylene oxide) (PEO) solutions, the MSD of the colloidal particles is shown to change with temperature and pressure variations, owing to modification of water hydrogen bonding properties. These colloidal sphere MSD variations reflect changes in the solvent quality of water for PEO.; The MSD of tracer particles is also used to study aqueous Pluronic(TM) F108 solutions, which exhibit rich phase behavior with concentration, temperature, and pressure. These solutions are shown to behave essentially as soft, repulsive spheres. Also, the effect of Pluronic-R(TM) 25R4 on the phase behavior and microrheological properties of F108 solutions is studied. The observed microrheological behavior of these systems is discussed within the context of theoretical descriptions of high-frequency colloidal dynamics.