Biophysical Phenomena

    Many biotechnologically interesting problems involve colloid and macromolecular science concepts.  These issues are particularly relevant in drug, gene and peptide delivery, pharmaceutical formulation and quality control.  Our group has experience in several related areas such as: liposome characterization; ion transport in liposome systems; and protein aggregation.  Our group's current focus is on monitoring and modeling nonviral gene delivery vector formation processes and on developing methods for characterizing the composition and size polydispersity which necessarily results from all heterotypic aggregation processes. In addition to scattering and spectroscopic probes of these phenomena, our group uses a novel cross flow field flow fractionation-static light scattering-refractive index-UV/Vis spectroscopy hybrid instrument to overcome the impact of composition and size polydispersity on these investigations.

Complex Fluids Dynamics

    Soft materials or complex fluids are characterized by the ease with which they deform in response to perturbations such as thermal fluctuations, external stresses and electrical or magnetic fields.  Their unique properties owe to the existence of mesoscopic structures, sometimes self-assembled aggregates, other times quenched entities such as polymers or colloidal particles, whose dimensions exceed atomic and molecular length scales.  The macroscopically observable response of these materials is dictated by the structure and dynamics present at this mesoscale.  Our group currently focuses its attention on thermal or Brownian motion in viscoelastic media such as wormlike micelle solutions, surfactant cubic phases and polymer solutions.  The connection between this thermal or Brownian motion, concentration fluctuations and viscoelastic moduli - both longitudinal and transverse - are of particular interest.  As such our group typically carries out static and dynamic light scattering measurements in conjunction with diffusing wave spectroscopy (and other particle tracking methods) and mechanical rheometry studies of the same system.  Currently our laboratories house static light scattering or multiangle light scattering (MALLS), dynamic light scattering (DLS) and diffusing wave spectroscopy (DWS)facilities.

Polymers at Interfaces

    The properties of macromolecules near interfaces are much different than those within the bulk material. These polymer interfaces occur in many technologies and quite often determine the overall performance of the device or process under consideration. Our group has experience in several related areas such as:  glass transition and thermal expansion phenomena in ultrathin polymer films; chromatographic properties of polymer brushes; and polymer interdifussion between free chains and network chains.  Our current focus is on monitoring the formation of the interphase region which forms at the interface between polymeric resins and inorganic fillers in polymer-based composite materials.  Rapid, noninvasive, inexpensive spectroscopic interface probes are of particular interest. Our group synthesizes, characterizes, and utilizes optical fiber-based fluorescence and infrared sensors in polymer composite processing applications. The group's goals are: (1) to establish the connection between any measurable signals and polymer composite physical properties with an eye towards process control applications and (2) to determine the potential of these techniques for investigating fundamental polymer interface physics.

Polymer-Supercritical Fluid Solutions

    There is great current interest in developing supercritical fluid-based (SCF-based) schemes for polymer synthesis and processing.  This is particularly true for the case of carbon dioxide utilization in benign, environmentally friendly or green processes.  However, very little is currently known of SCF solvent-polymer solution properties-static or dynamic-at both the macroscopic and the microscopic levels.  This owes to the fact that conventional experimental techniques have to be greatly modified to operate at the high pressures required.  It is, therefore, exceptionally difficult to design reliably and efficiently polymer processes that utilize the unique characteristics and capabilities of SCF solvents.   Hence, the immediate research objective is to address the fundamental physics and chemistry of SCF-polymer solutions.  This work is done in collaboration with the research group of Professor Mark A. McHugh at Virginia Commonwealth University.  To date our collaboration has pursued two related avenues: (1) the development of high pressure small angle neutron scattering (SANS) techniques and (2) and high pressure dynamic light scattering (DLS) methods.  Our investigations have focused on both dilute (DLS) and semidilute (DLS, SANS) polymer-SCF solutions.  To date our research group has carried out an extensive study of polyolefin-alkane solutions with both DLS and SANS.  Other systems under current investigation include polyolefin-dimethyl ether SCF solutions and fluoropolymer-carbon dioxide solutions.