Tracer microrheology study of a hydrophobically modified comblike associative polymer.

The viscoelastic properties of associative polymers are important not only for their use as rheology modifiers but also to understand their complex structure in aqueous media. In this study, the dynamics of comblike hydrophobically modified alkali swellable associative (HASE) polymers are probed using diffusing wave spectroscopy (DWS) based tracer microrheology. DWS-based tracer microrheology accurately probes the dynamics of HASE polymers, and the extracted microrheological moduli versus frequency profile obtained from this technique closely matches that obtained from rotational rheometry measurements.

Microviscoelasticity of soft repulsive sphere dispersions: tracer particle microrheology of triblock copolymer micellar liquids and soft crystals.

Tracer particle microrheology using diffusing wave spectroscopy-based microrheology is demonstrated to be a useful method to study the dynamics of aqueous Pluronic™ F108 solutions, which are viewed as solutions of repulsive soft spheres. The measured zero-shear microviscosity of noncrystallizing micellar dispersions indicates micelle corona dehydration upon increasing temperature. Colloidal sphere thermal motion is shown to be exquisitely sensitive to the onset of crystallization in these micellar dispersions.

Microviscoelasticity of adhesive hard sphere dispersions: tracer particle microrheology of aqueous Pluronic L64 solutions.

DWS-based tracer particle microrheology is demonstrated to be a useful way to study the dynamics of aqueous Pluronic L64 solutions, which is viewed as a model adhesive hard sphere (AHS) system. The short-time dynamics of aqueous Pluronic L64 solutions indicate a purely hydrodynamic high frequency microviscosity as predicted by Batchelor for colloidal dispersions. The evolution of the micellar dynamics reveals a zero shear microviscosity in good agreement with steady shear viscosity measurements.

Characterization of sizing layers and buried polymer/sizing/substrate interfacial regions using a localized fluorescent probe.

A novel technique is described to investigate buried polymer/sizing/substrate interfacial regions, in situ, by localizing a fluorescent probe molecule in the sizing layer. Epoxy functional silane coupling agent multilayers were deposited on glass microscope cover slips and doped with small levels of a fluorescently labeled silane coupling agent (FLSCA). The emission of the grafted FLSCA was dependent on the silane layer thickness, showing blue-shifted emission with decreasing thickness.

Real time monitoring of lipoplex molar mass, size and density.

Time-resolved multiangle laser light scattering (TR-MALLS) is used to monitor the temporal variation of DNA/cationic liposome lipoplex molar masses and geometric sizes throughout the complexation process. The measured molar masses and geometric sizes are in turn used to estimate lipoplex density. The DNA/cationic lipid charge ratio is found to be the primary factor governing lipoplex formation kinetics and the final lipoplex molar mass, geometric size and density.

Evidence of lipoplex dissociation in liquid formulations.

Aggregation is typically cited as the root cause of lipoplex transfection efficacy loss in liquid formulations. Typically, this conclusion is based on observed increases in lipoplex hydrodynamic size. A more detailed physical characterization of the lipoplex transfection efficacy diminution has previously never been conducted.