Invited Speakers

(more updates coming soon)

Prof. Rafael Verduzco
Rice University
Department of Chemical and Biomolecular Engineering
"Surface Active Bottlebrush Polymer Additives for Functional Surface Coatings"

Bottlebrush polymers are a type of branched or graft polymer with polymeric side-chains attached to a linear backbone, and the unusual architecture of bottlebrushes provides a number of unique and potentially useful properties. These include a high entanglement molecular weight, enabling rapid self-assembly of bottlebrush block copolymers into large domain structures, the self-assembly of bottlebrush block copolymer micelles in a selective solvent even at very low dilutions, and the functionalization of bottlebrush side-chains for recognition, imaging, or drug delivery in aqueous environments. Here, we discuss the design and application of bottlebrush polymers as surface-active additives. Through an entropy-mediated process, bottlebrushes spontaneously accumulate at film interfaces Secondary-ion mass spectroscopy measurements show that athermal blends of bottlebrush polymers in a linear polymer matrix segregate to interfaces, driven by the increased conformational entropy of chain ends and depending on the relative lengths of polymer side-chains and linear matrix chains. Mixed side-chain bottlebrush polymers rapidly segregate to film surfaces, driven by enthalpic interactions and surface energy differences. These bottlebrush polymers segregate to film surfaces at low loading (1 wt %) and can be used to produce large changes in the surface contact angle. These studies demonstrate the role of interfaces and strategies for tailoring interfacial properties in very different types of soft materials.

Prof. Jacinta Conrad
University of Houston
Department of Chemical and Biomolecular Engineering
"Non-equiulibrium solidification of colloid-polymer mixtures: dispersity and confinement effects"

Submicron particles suspended in complex fluids containing surfactants, polymers, micelles, or other species are widely used in materials shaping and forming processes, including three-dimensional printing and nanocomposite processing, and in technical applications as paints, coatings, inks, and drilling muds. These applications require control over suspension rheology and microstructure, which are affected by interactions between the different constituents. Practically, constituents of high dispersity in size or molecular weight are inexpensive and hence widely used; fundamentally, the effects of size dispersity on suspension properties remain poorly understood, especially when the particles exhibit attractive interactions. As simple models of practical suspensions we study mixtures of submicron poly(methyl methacrylate) particles suspended in solutions of non-adsorbing polystyrene polymers, which generate a controlled entropic depletion attraction between the particles. Here, I will discuss studies in which we investigate the effect of particle dispersity and polymer dispersity on the non-equilibrium phase behavior, microstructure, and rheology of colloid-polymer mixtures, and describe the implications for the formulation of suspensions for practical applications.

Prof. Nicolay Tsarevsky
Southern Methodist University
Department of Chemistry
"Hypervalent Iodine Compounds in Polymer Synthesis"

Hypervalent iodine(III) compounds of the type ArIL2 (Ar = aryl, L = ligand such as (pseudo)halide or carboxylate) can participate in both radical and ionic reactions, which makes them very attractive reagents for the synthesis of functional, responsive, and dynamic polymers. For instance, ligand exchange reactions are known with variety of nucleophiles (Nu-), which afford the hypervalent iodine compounds ArINu2. The homolysis of the weak hypervalent I-L (or, after ligand exchange, I-Nu) bonds under thermal or photochemical conditions leads to the formation of iodoarenes ArI and radicals L• (or Nu•), which can be used to initiate polymerization or to functionalize a number of substrates, including pre-made polymers. The synthesis and properties of functional linear, star-shaped, graft, branched, and crosslinked polymers via ligand exchange reactions involving hypervalent iodine compounds, in some cases followed by decomposition of the products of the exchange, in addition to dynamic polymers containing the –I(Ar)– structural motif, will be described.

Prof. Vernita Gordon
Department of Physics
University of Texas at Austin
"Soft-matter mechanics in the initiation of bacterial biofilms"

Biofilms are communities of microbes that are embedded in a self-produced matrix of polymer and proteins.  Biofilms cause chronic, recalcitrant infections - even bacteria that are easily cleared by antibiotics and/or the immune system when they are in a free-swimming, so-called "planktonic" state become highly resistant to both antibiotics and the immune system when they are in a biofilm.  We study biofilms grown from the bacterium Pseudomonas aeruginosa, an opportunistic human pathogen that produces chronic biofilm infections in patients with cystic fibrosis, chronic obstructive pulmonary disease, and diabetes.  We find that bacteria sense that they are on a surface, and therefore change their gene expression to start making a biofilm, by sensing shear stress.  Shear stress is mediated by sticky polymers that bind the bacteria to the surface, and varying the strength of polymer-mediated adhesion changes how well the bacteria can sense that they are on a surface.  This suggests new ways to make surfaces taht resist the development of biofilms by preventing bacteria from experiencing shear stress.