Solid-state NMR studies of polymers, liquid crystals and surfactants at surfaces and interfaces

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The major theme of my research is NMR studies of the dynamic and structural properties of small molecules and polymers at surfaces and interfaces. Main projects include 1) organic monolayers 2) polyelectrolyte multilayers and 3) nanoparticle/ liquid crystal composites. A large range of surface and colloidal characterization techniques are used in conjunction with solids NMR such as surface infrared spectroscopy, light scattering, optical microscopy, calorimetry and electrophoresis. Previous work on organic monolayers established the surface bonding and chain dynamics of simple alkane monolayers. The next stage will focus on the binding of other molecules and macromolecules to these monolayers. Polyelectrolytes are highly charged polymers. The basic structural and dynamic properties of polyelectrolyte multilayers consisting of stong/strong and strong/weak polyanion/polycation combinations deposited on colloidal substrates have been explored by solids NMR. We will now move onto multilayers based on hydrogen bonding, deposited on nanoparticles and as hollow capsules. One goal is to understand the response of the capsules (shrinking versus swelling) to temperature, pH or salt which is relevant to their use as drug delivery agents. Our initial work on liquid crystals has focused on the "memory effect" of nanoparticle silica filled liquid crystals which have applications in display devices. These materials are initially opaque but become optically transparent in an electric field. This state persists after the field is turned off due to the formation of an ordered silica network. How such networks form is poorly understood. Wideline deuterium NMR is an excellent method for analyzing such structures. We will also study liquid crystal/ metal nanoparticle composites. The goal will be to create an ordered array so that the optical properties can be tuned by an applied field. Solids NMR will again provide a sensitive probe of the the alignment of the liquid crystal molecules at the particle surfaces.