Location: Shriver Hall Auditorium, Johns Hopkins University Homewood Campus (3400 N. Charles St, Baltimore, MD, 21218).
Arjun G. Yodh University of Pennsylvania
"From Coffee Rings to Phonons: The Particles Reveal the Insights"
Abstract: I will discuss findings from recent experiments with colloidal suspensions which reveal new phenomena associated with a surprisingly broad range of problems. The first set of experiments employ temperature- sensitive microgel particles to study phonons in colloidal glasses and their relation to the mechanical response of disordered solids. The second set explores the role of particle shape in affecting particle deposition during evaporation, i.e., the affect of particle shape on the coffee ring effect.
Charles F. Zukoski University of Illinois
"States of Particle Dispersion in Polymer Melts"
Abstract: Particles are incorporated into polymers to impart optical, electrical and mechanical properties. As the particle size shrinks novel properties emerge. In the first place, particles dispersion is very difficult to predict. In addition, glass transition temperatures are observed to increase or decrease with addition of particles. Moreover, melt viscosities can increase or decrease with addition of particles. Explanations for these phenomena are unsettled. Yet nanocomposites serve enormous markets where control of these variables is of substantial economic importance. In this talk, I will discuss experiments aimed at unraveling these mysteries. The key parameter controlling particle dispersion emerging from Polymer Reference Interaction Site Model (PRISM) theory of Schweizer is the enthalpy of interaction of a polymer segment and the particle surface εpc. When εpc is small, particles are excluded from the bulk polymer due to loss of entropy. When εpc is large, the polymer bridges between particles. Only for a region of intermediate εpc are thermodynamically stable polymer layers formed at the particle surface resulting in the particles and polymer being miscible. Details of PRISM predictions of polymer and particle microstructure are confirmed for low molecular weight polymers and correlations can be developed between εpc and composite viscoelastic properties. At these low molecular weights, the polymer is a Newtonian fluid and the particles are index matched such that residual van der Waals forces are minimized. Yet details of “continuous phase” chemistry are found to strongly influence microstructure and state of dispersion. As polymer molecular weight increases, PRISM predictions fail and polymer entanglements are induced as average particle surface-to surface separations approach ~6Rg where Rg is the polymer radius of gyration. Under these conditions composite mechanical properties are strongly influenced by the internal degrees of freedom of the “continuous phase”. From this work, a series of generalizations are drawn on the role of surface chemistry in controlling composite mechanics emphasizing that new properties seen in nanocomposites result from particle induced changes in polymer dynamics and polymer induced changes to particle dynamics.
Victor K. LaMer Award
Bo Wang University of Illinois at Urbana-Champaign
"Phospholipids, assemblies, and active transport"
Abstract: A grand challenge in colloid science is to form structures that are not frozen in place but instead reconfigures internally driven by energy throughput and adapts to its environment robustly. Predicated on fluorescence imaging at the single-particle level, this talk describes quantitative studies of how this can happen. First, the surface reconstruction of phospholipid bilayer is studied: an amazing parallel with the environmental sensitivity of hard surfaces is discovered. Second, transportation efficiency problems within living cells are studied: an amazing parallel with polymer chain trajectories is noted. From both studies, the conclusions suggest new principles and opportunities to couple energy throughput with organization and properties of “active matter”.
Liangfang Zhang University of California, San Diego, La Jolla
"Biocolloids in medicine: From cancer therapy to bacterial infection treatment"
Abstract: I will report some recent findings and ongoing research in my laboratory regarding the development of biocolloid platforms for combinatorial chemotherapy and antimicrobial drug delivery to treat bacterial infections. Specifically, I will report a top-down biomimetic approach in colloid functionalization by coating biodegradable polymeric nanoparticles with natural red blood cell (RBC) membranes including both membrane lipids and associated membrane proteins for long-circulating cargo delivery. This approach aims to camouflage the nanoparticle surface with the erythrocyte exterior for long circulation while retaining the applicability of the polymeric core. In addition, I will also present a skin-microenvironment responsive nanoparticle system to deliver antimicrobial compounds as a new, effective and safe medication for the treatment of bacterial infections including acne vulgaris and staph infections.