Perfluorocarbon (PFC) nanoemulsions have great potential in biomedical applications due to their unique chemical stability, biocompatibility, and possibilities for enhanced oxygen supply. The addition of amphiphilic block copolymers promotes the formation and long-term stability of emulsion-based gels. We study of the impact of adding amphiphilic triblock copolymers to water-in-perfluorocarbon nanoemulsions on their structure and viscoelasticity, utilizing small-angle neutron and X-ray scattering (SANSand SAXS) and rheology.

Multicomponent films based on colloidal dispersions have a wide range of applications, including paints and coatings with specific functionalities such as antibacterial or anti-corrosive capabilities, and inorganic-polymer films for energy applications. Often, there is a need to control location of certain components in the film, and these complex coatings are typically prepared using a multi-step process. However, recent theories have identified a means to create vertically-structured coatings in a single step during evaporative drying, a process referred to as stratification. We investigate evaporative self-assembly and stratification in multicomponent colloidal films using AFM and microbeam SAXS experiments, and have found conditions resulting in a variety of novel structures.

Hydrogels are water-based polymeric materials that find application in soft tissue engineering, wound dressings, contact lenses, and drug delivery. A current limitation of many hydrogels is poor strength. Most efforts to create more robust hydrogel-based materials are successful, but can result in fairly brittle materials. Our laboratory is investigating alginate and Pluronic® composite hydrogel formulations using rheology, mechanical compression, and drug transport. We have developed thermoresponsive composite hydrogels that are mechanically strong, yet soft to create biomedical constructs that are capable of resisting wear-and-tear while providing a suitable mechanical environment for cellular activity. An additional focus of the group has been incorporation of perfluorocarbon-based oxygen carriers into hydrogels to enhance oxygen supply and diffusivity.

New strategies are needed to control polymer gel nanostructure and microstructure while maintaining the desired rheological and transport properties. Based on previous work with the Tew group (UMass Polymer Science and Engineering), we have shown that incorporation of crystalline domains into PLA-PEO-PLA gels can lead to very stiff materials. Recently, we have been working with the Grubbs group to explore similar block copolymers synthesized with various ratios of L- to D-lactic acid in the PLA block, and find the surprising result that there is a maximum in the hydrogel storage modulus for systems with L/D ratios between 50/50 and 100/0. Thus, it appears that the PLA stereochemistry has unexpected effects on the rheology and nanoscale assembly.

Formation of stable, dense nanoparticle clusters is interesting due to both the underlying physics and use of nanoclusters in aplications such as digital printing, imaging, biosensing, and energy storage. We explore formation of nanoparticle clusters in dispersions of the model disk-shaped clay laponite. Under basic conditions, laponite forms a repulsive glass in water due to strong electrostatic interactions. Through the addition of adsorbing polymer and non-adsorbing polymer, we can modify the interparticle interactions to melt the glass into a liquid state, slow the formation of the glassy state, obtain a networked particle-polymer gel, create a fluid of stable large clusters, or form a glass of clusters. Most recently, with addition of a low molecular weight polyelectrolyte, we have shown that the ability to form clusters that are stable for several months and whose size is directly related to the polymer concentration. This may serve as an important means of tuning cluster size in products and processes based on dense nanoparticle assemblies.