MSE Seminar - Proessor Darrin Pochan, Univ. of Delaware
Professor Darrin Pochan
Professor and Chair, Materials Science and Engineering
University of Delaware
Monday, November 16, 2015
4:00 p.m. MARC (GTMI/Callaway Bldg.) Auditorium
Reception at 3:30 p.m. in the MARC Atrium
Self-assembly of molecules into materials is an attractive materials construction strategy primarily due to its simplicity in application. By considering properly designed peptidic or synthetic polymer molecules in the bottom-up materials solution assembly process, one can take advantage of inherently biomolecular attributes; intramolecular folding events, secondary structure, and electrostatic interactions; in addition to more traditional self-assembling molecular attributes such as amphiphilicty, to define hierarchical material structure and consequent properties. Two classes of molecules will be discussed: peptides and synthetic block copolymers.
Local nanostructure control is realized through proper peptide molecule design as well as desired solution assembly pathway. One-dimensional fibril growth with designed beta-hairpin peptides will be discussed. Changes in the assembling peptide molecules are manifested in the supramolecular fibril structure. If properly designed, hydrogel networks can be formed from the peptide assembly. Examples of nanostructure control as well as control of overall hydrogel network structure, and resultant shear-thinning and rehealing viscoelastic and cell-level biological properties, will be presented. In addition, peptide fibrils can be used to template the growth of inorganic materials as well as the assembly of inorganic nanoparticles. More recently, theoretical efforts afford the construction of arbitrary peptide nanostructures not observed in natural proteins. Initial examples of the theory-defined sequences and nanostructures will be presented.
Finally, kinetic pathways and temporal stabilities of synthetic block copolymers in solution have been used to construct exotic nanoparticles. Due to low molecular chain exchange dynamics between block copolymeric aggregates and solvent, global thermodynamic equilibrium is extremely difficult, if not impossible, to achieve in block copolymer assembly. However, by taking advantage of this slow kinetic behavior of polymeric nanostructures in solution, one can purposely produce multicompartment nanoparticles and mulitgeometry nanoparticles by forcing different block copolymers to reside in the same nanoscale structure through kinetic processing. While kinetically trapped in common nanostructures, local phase separation can occur producing compartments. This compartmentalization can be used within common micelle geometries to make complex spheres and cylinders or can be used to make new nanostructures such as multigeometry aggregates (e.g. hybrid cylinder-sphere aggregates, disk-cylinder nanoparticles). Other particle nanostructures such as toroids, disks, and helical cylinders have been constructed.
Cryo transmission electron microscopy (cryoTEM), transmission electron microscopy (TEM), small angle neutron or x-ray scattering (SANS, SAXS), atomic force microscopy, oscillatory rheology, spectroscopy, in vitro cell culturing and preliminary in vivo animal experiments have all been used to characterize the nano-through-microstructure and material properties of the above self-assembled systems.
Darrin Pochan is currently Professor and Chair of the Materials Science and Engineering Department as well as a member of the Delaware Biotechnology Institute and the Department of Chemistry and Biochemistry at the University of Delaware. Since joining the department in 1999 after a Ph.D. in Polymer Science and Engineering at the University of Massachusetts-Amherst and a National Research Council Post-doctoral fellowship at the National Institute of Standards and Technology in Gaithersburg, MD he has developed a research program around the construction of new materials and nanostructures via solution assembly mechanisms. Areas of focus are biomaterials and materials for nanotechnology and energy applications through organic/inorganic hybrids. Recent honors for Darrin include an NSF Career Award, the DuPont Young Faculty Award, the Dillon medal from the American Physical Society, fellowship in the American Physical Society and the American Chemical Society. Currently, Darrin also serves as Associate Editor for of Soft Matter, a new interdisciplinary journal from the Royal Society of Chemistry in the United Kingdom.