Refreshments served at 2:45 PM
Functional Soft Matter: From Programmed Colloidal Assembly to Hydrogel Electronics
Abstract: We will present strategies for the fabrication of novel electrically functional structures from particles or gels operating in water environment. In the first part of the talk we will discuss how electric fields can be used to assemble metallic or dielectric particles and live cells into electrical connectors, networks and sensor prototypes. The structures formed include microwires from metallic nanoparticles, crystals with conductive lanes, and biocomposites from live cells. We will demonstrate how Janus and patchy metallodielectric spheres can be assembled in unusual colloidal crystals and gels and how the type of structures formed can be precisely controlled by the induced frequency-dependent dipolar and quadrupolar interactions. A new class of permanently bound linear structures was recently field-assembled from binary mixtures of microspheres of opposite charge with strongly attractive interactions. The assembly rules for these structures are based on the size ratio and number ratio of the two types of particles. In the second part of the talk we will discuss how water-based gels doped with polyelectrolytes can be used as the core of novel diodes, memristors, actuators and photovoltaic cells operating on the conductance of the counterionic layers around the gel molecular backbone. A new class of “soft” diodes with rectifying junction formed by interfacing water-based gels doped with polyelectrolytes of opposite charge was developed. We also demonstrated a radically new concept of bio-inspired hydrogel solar cells. The matrix of these photovoltaic cells is made of ionic agarose gels doped with photosensitive organic molecules. Such gel-based “artificial leaves” can be flexible, inexpensive and environmentally friendly.
Biography: Dr. Orlin Velev received M.Sc. and Ph.D. degrees from the University of Sofia, Bulgaria, while also spending one year as a researcher in Nagayama Protein Array Project in Japan. After graduating in 1996, Velev accepted a postdoctoral position with the Department of Chemical Engineering, University of Delaware. He initiated an innovative program in colloidal assembly and nanomaterials and was promoted to research faculty in 1998. In 2001 he formed his new research group in the Department of Chemical and Biomolecular Engineering, North Carolina State University, where he was promoted to an Associate Professor with tenure in 2006, to full professor in 2008 and to Invista chaired professor in 2009. He has contributed more than 130 publications, which have been cited more than 8300 times, and has presented more than 160 invited presentations at major conferences and at universities and companies. Recent awards include NSF Career, Camille Dreyfus Teacher-Scholar, Sigma Xi, Ralph E. Powe, NC State Alcoa Distinguished Engineering Research, NC State Innovator of the Year and election to an ACS Fellow. Velev is a member of the Editorial Advisory Boards of Langmuir and Chemistry of Materials, as well as of Biomicrofluidics and Particle.
Velev has established a record of innovative research in the area of nanostructures with electrical and photonic functionality, biosensors and microfluidic devices. He has been the first to synthesize “inverse opals”, one of the most widely studied types of photonic materials today. He has also pioneered principles for microscopic biosensors with direct electrical detection, discovered techniques for electric field assembly of nanoparticle microwires and biosensors and investigated novel types of self-assembling supraparticles, Janus particles, rod-like particles and nanofibers. Recently Velev’s group also reported new studies where external fields power self-propelling devices, acting as prototypes of autonomous microrobots, micropumps and micromixers. Velev has been an advocate of incorporating the latest advancements in the areas of nanoscience and nanotechnology in the engineering curriculum.
Faculty Host: Rama Bansil
Student Host: Joseph Hardcastle