12th in series – FEBRUARY 12 & 13, 2019

Sharon C. Glotzer

Professor of Chemical Engineering
University of Michigan in Ann Arbor

BIO: Sharon C. Glotzer is the Anthony C. Lembke Department Chair of Chemical Engineering at the University of Michigan in Ann Arbor. Glotzer is also the John Werner Cahn Distinguished University Professor of Engineering and the Stuart W. Churchill Collegiate Professor of Chemical Engineering, and Professor of Materials Science and Engineering, Physics, Applied Physics, and Macromolecular Science and Engineering. She is a member of the National Academy of Sciences and the American Academy of Arts and Sciences, and a fellow of the American Physical Society, the American Association for the Advancement of Science, the American Institute of Chemical Engineers, the Materials Research Society, and the Royal Society of Chemistry. Professor Glotzer’s research on computational assembly science and engineering aims toward predictive materials design of colloidal and soft matter, and is sponsored by the NSF, DOE, DOD, Simons Foundation and Toyota Research Institute. Among other notable findings, Glotzer invented the idea of “patchy particles,” a conceptual approach to nanoparticle design. She showed that entropy can assemble shapes into many structures, which has implications for materials science, thermodynamics, mathematics, and nanotechnology. Glotzer has published over 225 refereed papers and presented over 340 plenary, keynote and invited talks around the world. She has served on boards and advisory committees of the National Science Foundation, the Department of Energy, and the National Academies, and is currently a member of the Scientific Policy Committee at the Stanford Linear Accelerator (SLAC) National Accelerator Laboratory and the National Academies Board on Chemical Sciences and Technology. She is a Simons Investigator, a former National Security Science and Engineering Faculty Fellow, and the recipient of numerous other awards and honors, including the 2016 Alpha Chi Sigma Award from the American Institute of Chemical Engineers, the 2014 MRS Medal from the Materials Research Society and the 2008 Charles M.A. Stine Award from the American Institute of Chemical Engineers. 

LECTURE 1: Colloidal Crystals, Quasicrystals, Fluid-Fluid Transitions and the Entropic Bond

Entropy, information, and order are important concepts in many fields, relevant for materials to machines, for biology to economics. Entropy is typically associated with disorder; yet, the counterintuitive notion that particles with no interactions other than excluded volume might self-assemble from a fluid phase into an ordered crystal has been known since the mid-20th century. First predicted for rods, and then spheres, the thermodynamic ordering of hard shapes by nothing more than crowding is now well established. In recent years, surprising discoveries of entropically ordered colloidal crystals of extraordinary structural complexity have been predicted by computer simulation and observed in the laboratory. Colloidal quasicrystals, clathrate structures, and structures with large and complex unit cells typically associated with metal alloys, can all self-assemble from a disordered phase of identical particles due solely to entropy maximization. In this talk, we show how  entropy alone can produce order and complexity beyond that previously imagined, both in colloidal crystal structure as well as in the kinetic pathways connecting fluid and crystal phases. We show examples of purely entropic fluid-fluid transitions that precede crystallization, just as liquid-liquid phase separation precedes crystallization in tetrahedrally bonded molecular liquids and in protein solutions. We further show that, in situations where other interactions are present, the role of entropy in producing order may be underestimated. To understand these phenomena, and in loose analogy with traditional chemical bonds that produce order in atomic and molecular substances, we introduce the notion of the entropic bond.

LECTURE 2: Assembly Engineering of Colloid and Protein Crystals and Superstructures

From the Stone Age to the Silicon Age, the materials available to humankind define the world in which we live. The materials of tomorrow will be designed and engineered on demand, where and when they are needed, with precision and personalization. Computer simulation and machine learning both have critical roles to play in creating this future. Already, they allow — from a nearly infinite number of possibilities — the inverse design of nanoparticle building blocks optimized for self-assembly into colloidal crystal structures with targeted properties. In this talk, we present a new thermodynamic computational approach to the inverse design of materials, and demonstrate its use in targeting colloidal crystals with arbitrary complexity, engineered phase transitions, and targeted photonic, mechanical, and other properties. We show how machine learning can be used to autonomously identify crystal structures in hundreds of thousands of simulations, as well as to identify key alchemical attributes of particles that correlate with colloidal crystal structure. We also discuss strategies for engineering protein superstructures via supercharging.

For a recap and photos of Prof. Glotzer's lecture click here. 

11th in series – May 16 & 17, 2017

Howard Stone

Professor of Mechanical and Aerospace Engineering
Princeton University

BIO: Professor Stone is the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor in Mechanical and Aerospace Engineering at Princeton University. Stone is a fluid dynamicist who uses experiments, theory and numerical simulations to study transport problems at the intersections of engineering, biology, physics and applied mathematics. He is known for developing original research directions in microfluidics including studies and applications involving bubbles and droplets, red blood cells, bacteria, chemical kinetics, etc. Stone received the Bachelor of Science degree in Chemical Engineering from the UC Davis in 1982 and the PhD in Chemical Engineering from Caltech in 1988. In 1989 Stone joined the faculty of the School of Engineering and Applied Sciences at Harvard University, where he eventually became the Vicky Joseph Professor of Engineering and Applied Mathematics. In 2000 he was named a Harvard College Professor for his contributions to undergraduate education. In July 2009 Stone moved to Princeton University. He is a Fellow of the APS and is past Chair of the Division of Fluid Dynamics. In 2008 he was the first recipient of the G.K. Batchelor Prize in Fluid Dynamics and in 2016 he received the APS Fluid Dynamics Prize. He was elected to the National Academy of Engineering in 2009, the American Academy of Arts and Sciences in 2011, and the National Academy of Sciences in 2014.

LECTURE 1: Surprising responses in common fluid flows: (i) Surface-attached bacteria, biofilms and flow and (ii) Trapping of bubbles in stagnation point flows

Fluid mechanics is often thought of as well developed so it might come as a surprise that flows in elementary configurations produce results with unexpected features. I will try to make this case by describing several distinct problems that we have studied where either bacteria interact with a simple fluid motion in unexpected ways or modest variations in an elementary laminar channel flow produce new effects. First, we investigate some influences of fluid motion on surface-attached bacteria and biofilms. In particular, we identify (a) upstream migration of surface-attached bacteria in a flow, (b) a hydrodynamic reason for the shape of the curved bacteria Caulobacter crescentus, and (c) the formation of biofilm streamers, which are filaments of biofilm extended along the central region of a channel flow; these filaments are capable of causing catastrophic disruption and clogging of industrial, environmental and medical flow systems and suggest new flow problems influenced by soft boundaries.  Second we consider flow in a T-junction, which is perhaps the most common element in many piping systems. The flows are laminar but have high Reynolds numbers, typically Re=100-1000. It seems obvious that any particles in the fluid that enter the T-junction will leave following the one of the two main flow channels. Nevertheless, we report experiments that document that bubbles and other low density objects can be trapped at the bifurcation. The trapping leads to the steady accumulation of bubbles that can form stable chain-like aggregates in the presence, for example, of surfactants, or give rise to a growth due to coalescence. Our three-dimensional numerical simulations rationalize the mechanism behind this phenomenon. 

LECTURE 2: Thinking about some new low-Reynolds-number flow problems

I present three fluid mechanics problems that we have studied recently, each of which identifies qualitatively new features inspired by classical flow problems. First, it is well known that the flow of thin liquid films has a large research literature in fluid mechanics. Also, the bending of an elastic beam has a large research literature in elasticity. Here we combine the two problems to study the spreading of a liquid over an elastic beam – the spreading fluid changes the shape of the beam and, in turn, the bending of the beam influences the fluid flow. Second, we consider the hydrodynamic resistance of a hot particle, as occurs when laser heating of a dilute suspension occurs. The viscosity varies with position about the particle which changes the familiar hydrodynamic drag. We present a solution using the Reciprocal Theorem so as to bypass many of the usual calculations and present situations that couple translation and rotation of a sphere. Finally, we show experiments and modeling to rationalize the formation of distinct layers when coffee (or an equivalent dyed solution) is poured into hot milk (a colloidal solution); a critical injection speed is shown to be responsible for the dynamics.

10th in series – november 4 & 5, 2014

Zhenan Bao

Professor of Chemical Engineering
Stanford University

BIO: Zhenan Bao is a Professor of Chemical Engineering at Stanford University, and by courtesy a Professor of Chemistry, Material Science and Engineering. Prior to joining Stanford in 2004, she was a Distinguished Member of Technical Staff in Bell Labs, Lucent Technologies from 1995-2004. She has over 300 refereed publications and over 40 US patents. Bao served as a Board Member for the National Academy Board on Chemical Sciences and Technology and Board of Directors for the Materials Research Society (MRS). She is an Associate Editor for Chemical Sciences. She serves on the international advisory board for Nature Asia Materials, Advanced Materials, Advanced Functional Materials, Advanced Energy Materials, ACS Nano, Chemistry of Materials, Nanoscale, Chemical Communication, Organic Electronics, Materials Horizon and Materials Today. She is a Fellow of ACS, AAAS, MRS, SPIE, ACS PMSE and ACS POLY. She is a recipient of the ACS Polymer Division Carl S. Marvel Creative Polymer Chemistry Award 2013, ACS Author Cope Scholar Award 2011, Royal Society of Chemistry Beilby Medal and Prize 2009, IUPAC Creativity in Applied Polymer Science Prize 2008, American Chemical Society Team Innovation Award 2001, R&D 100 Award 2001. She was selected by MIT Technology Review magazine in 2003 as one of the top 100 young innovators. She is among the world’s top 100 materials scientists by Thomson Reuters.

LECTURE 1: Integrated Materials Design of Organic Semiconductors

Organic semiconductor materials are interesting alternatives to inorganic semiconductors in applications where low cost, flexible or transparent substrates, and large area format is required. Currently they have been incorporated into organic thin-film transistors, integrated display driver circuits, photovoltaics artificial electronic skin, and radio frequency identification tags. One of our fundamental interests is to understand how we can ultimately perform rational design of organic semiconductors. In this talk, I will present our efforts on understanding of molecular design rules for achieving efficient charge carrier transport in organic semiconductor thin films. I will also present realizing strained organic semiconductors (meta-stable molecular packing structure) by tuning processing conditions, which resulted in unprecedented charge carrier mobility in organic semiconductors.

LECTURE 2: Skin-Inspired Electronics from Organic and Carbon Nanomaterials

Skin is the body’s largest organ, and is responsible for the transduction of a vast amount of information. This conformable material simultaneously collects signals from external stimuli that translate into information such as pressure, pain, and temperature. The development of an electronic material, inspired by the complexity of this organ is a tremendous, unrealized engineering challenge. However, the advent of carbon-based electronics may offer a potential solution to this longstanding problem. In this talk, I will describe the design of materials to enable flexible devices to transduce mechanical, temperature and chemical stimuli into electrical signals. Applications of these devices for health monitoring, disease diagnosis and implanted devices will be presented.

9th in series – May 29 & May 31, 2012

Michael D. Graham 

Professor of Chemical and Biological Engineering
University of Wisconsin-Madison

BIO: Michael D. Graham is the Harvey D. Spangler Professor of Chemical and Biological Engineering at the University of Wisconsin-Madison, and also holds appointments in the departments of Mechanical Engineering and Engineering Physics. He received his B.S. in Chemical Engineering from the University of Dayton in 1986 and his PhD. from Cornell University in 1992. After postdoctoral appointments at the University of Houston and Princeton University, he joined the Chemical Engineering faculty at the University of Wisconsin-Madison in 1994. He chaired the department from 2006 to 2009. Among Mike's awards are a Best Student Paper Award from the Environmental Division of AIChE in 1986, a CAREER Award from NSF in 1995 and the François Frenkiel Award for Fluid Mechanics from the American Physical Society Division of Fluid Dynamics in 2004. He was elected a Fellow of the American Physical Society in 2011 and received a Kellett Mid-Career Award from UW-Madison in 2012. He is a member of the editorial board of the Journal of Non-Newtonian Fluid Mechanics and is an Associate Editor of the Journal of Fluid Mechanics.

LECTURE 1: Hydrodynamic coordination of bactierial motions: from bundles to biomixing

Fluid mechanics plays an important role in many aspects of locomotion in microorganisms. For example, many bacteria propel themselves though their fluid environment by means of multiple rotating flagella that self-assemble to form bundles. At a larger scale, the fluid motion generated by an individual microbe as it swims affects the motions of its neighbors. Experimental observations indicate the presence of long-range order and enhanced transport in suspensions of bacteria – these phenomena may be important in many aspects of bacterial dynamics including chemotaxis and development of biofilms. This talk describes progress toward understanding these two aspects of bacterial locomotion. 

We first describe theory and simulations of hydrodynamically interacting microorganisms, using very simple models of the individual organisms. In the dilute limit, simple arguments reveal the dependence of swimmer and tracer velocities and diffusivities on concentration. As concentration increases, we show that cases exist in which the swimming motion generates large-scale flows and dramatically enhanced transport in the fluid. A physical argument supported by a mean field theory sheds light on the origin of these effects. 

The second part of the talk focuses on the dynamics of the flagellar bundling process, using a mathematical model that incorporates the fluid motion generated by each flagellum as well as the finite flexibility of the flagella. The initial stage of bundling is driven purely by hydrodynamics, while the final state of the bundle is determined by a nontrivial and delicate balance between hydrodynamics and elasticity. As the flexibility of the flagella increases a regime is found where, depending on initial conditions, one finds bundles that are either tight, with the flagella in mechanical contact, or loose, with the flagella intertwined but not touching. That is, multiple coexisting states of bundling are found. The parameter regime at which this multiplicity occurs is comparable to the parameters for a number of bacteria.

LECTURE 2: Drag reduction and the dynamics of turbulence in simple and complex fluids

At low speed, flow in a pipe or over an aircraft is smooth and steady. At higher speeds, it becomes turbulent – the smooth motion gives way to fluctuating eddies that sap the fluid's energy and make it more difficult to pump the fluid through the tube or to propel the aircraft through the air. For flowing liquids, adding a small amount of very large polymer molecules or micelle-forming surfactants can dramatically affect the turbulent eddies, reducing their deleterious effects on energy efficiency. This phenomenon is widely used, for example in the Alaska pipeline, but it is not well-understood, and no comparable technology exists to reduce turbulent energy consumption in flows of gases, in which polymers or surfactants cannot be dissolved. The most striking feature of this phenomenon is the existence of a so-called maximum drag reduction (MDR) asymptote: for a given geometry and driving force, there is a maximum level of drag reduction that can be achieved through addition of polymers. Changing the concentration, molecular weight or even the chemical structure of the additives has no effect on this asymptotic value. This universality is the major puzzle of drag reduction. 

We describe direct numerical simulations of turbulent channel flow of Newtonian fluids and viscoelastic polymer solutions. Even in the absence of polymers, we show that there are intervals of “hibernating” turbulence that display very low drag as well as many other features of the MDR asymptote observed in polymer solutions. As viscoelasticity increases, the frequency of these intervals also increases, while the intervals themselves are unchanged, leading to flows that increasingly resemble MDR. A simple theory captures key features of the intermittent dynamics observed in the simulations. Additionally, simulations of “edge states”, dynamical trajectories that lie on the boundary between turbulent and laminar flow, display characteristics that are similar to those of hibernating turbulence and thus to the MDR asymptote, again even in the absence of polymer additives. Based on these observations, we propose a tentative unified description of rheological drag reduction. The existence of “MDR-like” intervals even in the absence of additives sheds light on the observed universality of MDR and may ultimately lead to new flow control approaches for improving energy efficiency in a wide range of processes.

8th in series – May 19 & 20, 2010

Kristi Anseth

Professor of Chemical and Biological Engineering
University of Colorado at Boulder

BIO: Kristi S. Anseth earned her B.S. degree from Purdue University in 1992 and her Ph.D. degree from the University of Colorado in 1994. She then conducted post-doctoral research at MIT as an NIH fellow and subsequently joined the Department of Chemical and Biological Engineering at the University of Colorado at Boulder as an Assistant Professor in 1996. Dr. Anseth is presently a Howard Hughes Medical Institute Investigator and Distinguished Professor of Chemical and Biological Engineering. Her research interests lie at the interface between biology and engineering where she designs new biomaterials for applications in drug delivery and regenerative medicine. Dr. Anseth’s research group has published over 190 publications in peer-reviewed journals and presented over 170 invited lectures in the fields of biomaterials and tissue engineering. She was the first engineer to be named a Howard Hughes Medical Institute Investigator and received the Alan T. Waterman Award, the highest award of the National Science Foundation for demonstrated exceptional individual achievement in scientific or engineering research. Most recently, she was elected a member of the National Academy of Engineering and the Institute of Medicine. Dr. Anseth is also a dedicated teacher, who has received four University Awards related to her teaching, as well as the American Society for Engineering Education’s Curtis W. McGraw Award. Dr. Anseth is a Fellow of the American Association for the Advancement of Science and the American Institute for Medical and Biological Engineering. She serves on the editorial boards or as associate editor of Biomacromolecules, Journal of Biomedical Materials Research — Part A, Acta Biomaterialia, and Biotechnology & Bioengineering.

LECTURE 1: Body Building:  Designer Gels to Promote Tissue Regeneration

Hydrogels are a unique class of polymeric materials that imbibe large amounts of water and possess a tissue-like elasticity, and when locally modified with appropriate signaling molecules, these synthetic niches can facilitate the regeneration of tissues. While the gel environment is often >90% water, the microscopic architecture and local chemistry play important roles in dictating cell function, including migration and proliferation, the secretion and distribution of extracellular matrix molecules, and ultimately the formation of tissue structures. This talk will illustrate several examples where the regeneration of tissues is highly coupled to the biophysical and biochemical properties of the gels, and demonstrate how appropriate tuning of the gel properties can create microenvironments that simply permit cells to function to those that actively promote specific cell functions. Integral to this understanding is the ability to manipulate the underlying gel chemistry and properties through the synthesis of macromolecular precursors and control of the gelation process. In this regard, photoinitiated polymerization is increasingly used to form hydrogel biomaterials and deliver cells and biomacromolecules under physiological conditions. As an example, our recent work exploiting thiol-ene photopolymerizations to form proteolytically-degradable PEG hydrogels will be presented. Specifically, the incorporation of peptides and the role of peptide functionality on wound healing and bone regeneration will be highlighted. The overall goal of the talk will be to illustrate some of the current advances and challenges in designing gels for tissue engineering applications and place this in the broader context of potential biological applications.

LECTURE 2: Goodbye Flat Biology?  Hello Hydrogels

Methods for culturing mammalian cells in a biologically relevant context are increasingly needed to study cell and tissue physiology, expand and differentiate progenitor cells, and to grow replacement tissues for regenerative medicine. Two-dimensional culture has been the paradigm for in vitro cell culture; however, evidence and intuition suggest that cells behave differently when they are isolated from the complex architecture of their native tissues and constrained to petri dishes or material surfaces with unnaturally high stiffness, polarity, and surface to volume ratio. As a result, biologists are often faced with the need for a more physiologically relevant 3D culture environment, and many researchers are realizing the advantages of hydrogels as a means of creating custom 3D microenvironments with highly controlled chemical, biological and physical cues. Further, the native ECM is far from static, so ECM mimics must also be dynamic to direct complex cellular behavior. In general, there is an un-met need for materials that allow user-defined control over the spatio-temporal presentation of important signals, such as integrin-binding ligands, growth factor release, and biomechanical signals. Developing such hydrogel mimics of the ECM for 3D cell culture is an archetypal engineering problem, requiring control of numerous properties on multiple time and length scales important for cellular functions. New materials systems have the potential to significantly improve our understanding of how cells receive information from their microenvironment and the role that these dynamic processes may play in controlling the stem cell niche to cancer metastasis. This talk will illustrate our recent efforts to advance hydrogel chemistries for 3D cell culture and dynamically control biochemical and biophysical properties through orthogonal, photochemical reaction mechanisms.

7th in Series – May 13 & 14, 2008

Norman J. Wagner

Professor of Chemical Engineering
University of Delaware

LECTURE 1: The Rheology of Colloidal & Nanoparticle Dispersions: “STF Armor”-Nanoparticle Composites for Flexible Ballistic Materials​

Colloidal and nanoparticle dispersions can exhibit shear thickening, which is an active area of research with consequences in the materials and chemical industries, as well as an opportunity to engineer novel energy adsorbing materials. A fundamental understanding of shear thickening has been achieved through a combination of model system synthesis, rheological, rheo-optical and rheo-small angle neutron scattering (SANS) measurements, as well as simulation and theory. Novel ballistic, stab and impact resistant flexible composite materials are synthesized from colloidal & nanoparticle shear thickening fluids (STFs). Through ballistic, stab & laboratory testing, the mechanism of energy adsorption at ballistic rates is demonstrated to result from reversible shear thickening. As a basis for the rational design of flexible ballistic & stab resistant materials, we report a rheological and microstructural investigation of the high shear rheology of colloidal and nanoparticles dispersions. Control of particle size, size distribution, shape, surface and bulk properties is shown to be critical to performance. Statistical mechanical modeling provides a framework for the rational design of materials to meet specific threats. Potential applications of these dispersions as novel energy absorbing materials are discussed, including commercial body armor.

LECTURE 2: A Tale of Two Surfactants: Structure and Rheology of Shear-Banding Wormlike Micellar Solutions​

Cationic surfactants that self-assembly into viscoelastic, worm-like micelles (WLM) can exhibit an interesting flow anomaly known as shear-banding, which is characterized by extreme shear thinning and the formation of stratified flow. This transition has been postulated to be due to a flow-aligned state, which is often associated with a nearby (in composition space) equilibrium phase. Here, we exploit some unique opportunities afforded by the development of new flow-SANS instrument, coupled with rheology and particle tracking velocimetry, to elucidate the mechanism of this rheological anomaly. Measurements of the micellar segmental alignment, flow kinematics, and microstructure are presented for two model WLM solutions. A special SANS flow cell enables the first direct measurements of the microstructure and micellar alignment in each individual band. These gap resolved 1-2 plane experiments demonstrate that the degree and orientation of segmental alignment of the micelles by the shear flow correlate with the measured shear viscosity, providing the first local measurements of the microstructure and rheology through the shear banded state. Distinct differences in behavior are observed for two different classes of surfactants that correlate with the underlying equilibrium phase behavior and surfactant topology. In one, shear banding is associated with increased segmental alignment of the WLMS, while in the other, shear banding results from strong density fluctuations associated with surfactant network formation. The results demonstrate that different flow-induced microstructures can result in shear banding and that the behavior correlates with the underlying phase behavior of each surfactant. We demonstrate how the combination of rheology, flow kinematics, and SANS measurements of flow-induced microstructure locally in the flow field can be used to critically evaluate constitutive equations for WLMs. Finally, a method to direct the structuring of WLM fluids by the addition of nanoparticles is illustrated, opening new avenues for formulating viscoelastic fluids of industrial interest.