HARVARD
Materials Research Science and Engineering Center
 
 
 
Calendar of MRSEC Events
2015 Events
February 28, 2015 Research Experience for Undergraduates (REU) Program, applications and transcripts due.

2014 Events
December 5, 2014 61st New England Complex Fluids Workshop at Harvard University
December 1, 2014 Science & Cooking Lecture Series
Joan Roca (@CanRocaCeller), El Celler de Can Roca
7:00pm | Science Center Hall D
El Celler de Can Roca: Roots, Innovation, and Creation
November 25, 2014 Science & Cooking Lecture Series
Nathan Myhrvold (@ModernCuisine), former CTO of Microsoft, co-founder of Intellectual Ventures, author of Modernist Cuisine
7:00pm | Science Center Hall D
Modernist Cuisine
November 17, 2014 Science & Cooking Lecture Series
Jody Adams (@JodyAdams), Rialto
7:00pm | Science Center Hall C
Fermentation: An Ancient Trend
November 14-15, 2014 Shining Light on Matter and Mind Symposium
8:15am - 10:00pm | Jefferson Physical Laboratory

A Symposium in Honor of Eric Mazur

This Symposium in honor of Eric Mazur aims to bring together a diverse collection of scientists and educators whose career paths have intersected with Eric’s and who share the passion Eric has for science, education and innovation. On the scientific side, the shared focus is the use of light to elucidate complex phenomena in materials while emphasizing the intuitive approach that has often characterized Eric's contributions to the field. On the educational front, the common thread is the use of innovative approaches to engage curious minds and to train the next generation of scientists and innovators. This event is co-sponsored by the MRSECs at several Universities across the country and is being held in the Jefferson Physical Laboratory at Harvard University on November 15, 2014.

Organizers: Ka Yee Lee (U Chicago), Eli Glezer and Iva Maxwell (Meso Scale Diagnostics), Chris Schaffer (Cornell), and Julie Schell (U Texas, Austin).
November 10, 2014 Science & Cooking Lecture Series
Daniel Humm, Eleven Madison Park
7:00pm | Science Center Hall C
Where is the Acid?
November 3, 2014 Science & Cooking Lecture Series
Christina Tosi, Milk Bar
7:00pm | Science Center Hall C
Emulsions and Foams
October 27, 2014 Science & Cooking Lecture Series
Martin Breslin (@HUDSinfo), Harvard University Dining Services
7:00pm | Science Center Hall C
The History of Culinary Thickeners
October 20, 2014 Science & Cooking Lecture Series
Ferran Adrià (@FerranAdria), elBulli Foundation
7:00pm | Science Center Hall C

Decoding the Creative Process

NOTE: TICKETED EVENT
Tickets will be made available at the Harvard Box Office (located in the Holyoke Center, 1350 Massachusetts Avenue, Cambridge, MA) beginning at noon on Tuesday, October 14. The tickets are free-but first come, first served.
October 13, 2014 Science & Cooking Lecture Series
Dominique Crenn (@DominiqueCrenn), Atelier Crenn
7:00pm | Science Center Hall C
Metamorphosis of Taste
October 8, 2014 Squishy Physics Seminar
Gabi Steinbach, NYU / Helmholtz-Zentrum Dresden-Rossendorf
5:30pm | 2nd floor Maxwell Dworkin Lounge

Magnetic Janus spheres with multipolar interaction - crystallization and phase behavior


Abstract: A basic issue in condensed matter physics is the quest for structure formation and the ability to control them. Video microscopy of colloidal ensembles established as a versatile method due to the easily accessible time and length scale. Specifically tailored particles have shown to assemble into a variety of basic structure elements such as simple lines, rings, crystallites and branching. In my talk I will present a 2D experimental study on magnetic Janus colloids with multipolar interaction. Besides translational ordering, this system allows the visualization of directional, i.e. magnetic ordering. Self-assembled finite structures show zigzag lines with antiparallel magnetic ordering which end in bifurcation points with threefold symmetry. The artificial creation of close-packed clusters on the other side show a 120? Ne?l ordering. Under 3D external fields the effective interaction potential between particles is varied, which leads to first order phase transitions. I will show under which conditions the phase transformation is fully reversible.

In the second part of the talk I present studies on magnetic ordering while the particle positions are fixed on a square or triangular lattice. We observe concentric flux-closure rings for small particle ensembles, which are broken up into a number of small vortex and anti-vortex states by external field sweeps. Similar topological excitations are observed e.g. in magnetic thin films.
October 6, 2014 Science & Cooking Lecture Series
Enric Rovira, master chocolatier
7:00pm | Science Center Hall C
Heat Transfer and Chocolate
September 29, 2014 Science & Cooking Lecture Series
Bill Yosses (@BillYosses), former White House Pastry Chef, author of The Perfect Finish
Steve Howell, project scientist, NASA Kepler & K2 missions
7:00pm | Science Center Hall C
gAstronomy
September 24, 2014 Squishy Physics Seminar
Nick Gravish, Harvard University
5:30pm | 2nd floor Maxwell Dworkin Lounge

Collective mechanics: a biological and robotic exploration of how mechanical interactions shape group behavior


Abstract: Large collections of living, interacting, organisms fascinate us because they often display emergent, seemingly coordinated behaviors. However, these behaviors usually stem from simple rules that members of the systems follow. Recent advancements have led to a broad understanding of the behavioral rules among organisms that interact at a distance such as populations that flock, swarm, or collectively migrate. Less attention has been paid to collective systems that interact in close proximity, in situations where mechanical interactions such as collisions or fluid-structure coupling dominate. Consequently, there is much to learn about the principles of collective, mechanically interacting biological systems. This talk presents two examples of this phenomena, focusing on the collective behaviors of social insect systems, the fire ant (Solenopsis invicta) and the honeybee (Apis melifera). In both systems I will show that close-proximity mechanical interactions are integral to the collective behaviors observed. These mechanical interactions include the interlocking of limbs within in a self-assembled raft, the steric interactions that occur between ants during heavy traffic within a nest tunnel, and the fluid-mechanical interactions that occur among honeybees while ventilating a nest. This research incorporates field and laboratory experiments on these biological systems with the study of computational and robotic model systems.
September 22, 2014 Science & Cooking Lecture Series
Mark Ladner (@ChefMarkLadner), Del Posto
7:00pm | Science Center Hall C
Al Dente: When Plastic Meets Elastic
September 19, 2014 60th New England Complex Fluids Workshop at Brandeis University
September 17, 2014 Squishy Physics Seminar
Zi Chen, Dartmouth
5:30pm | 2nd floor Maxwell Dworkin Lounge

Mechanics and Geometry in Spontaneously Bent and Twisted Structures


Abstract: Mechanical forces play a key role in the shaping of versatile morphologies of thin structures in natural and synthetic systems. The morphology and deformation of thin ribbons, plates and rods and their instabilities are systematically investigated, through both theoretical modeling and table-top experiments. An elasticity theory combining differential geometry and stationarity principles is developed for the spontaneous bending and twisting of ribbons with tunable geometries in presence of mechanical anisotropy. Closed-form predictions are obtained from this theory with no adjustable parameters, and validated with simple, table-top experiments. For large deformation of ribbons and plates, a more general theory is developed to account for mechanical instability (slap-bracelet type) induced by geometric nonlinearity, due to the competition between inhomogeneous bending and mid-plane stretching energy. This comprehensive, reduced parameter model leads to unique predictions about multistability that are validated with a series of table-top experiments. Furthermore, this study has been extended to interpret a different type of snap-through instability that the Venus flytrap has been actively employing to capture insects for millions of years, and the learnt principle is used to guide the design of bio-mimetic flytrap robot.
September 15, 2014 Science & Cooking Lecture Series
Joanne Chang '91 (@jbchang), Flour Bakery, author of Flour and Flour Too
7:00pm | Science Center Hall C
The Science of Sugar
September 8, 2014 Science & Cooking Lecture Series
Dave Arnold (@CookingIssues), Booker & Dax, and host of "Cooking Issues"
Harold McGee (@Harold_McGee), writer, Curious Cook
7:00pm | Science Center Hall C
Science and Cooking: A Look at the Last Twenty Years
August 20, 2014 Squishy Physics Seminar
Douglas Brumley, MIT
5:30pm | 2nd floor Maxwell Dworkin Lounge

Flagellar Synchronization Through Direct Hydrodynamic Interactions


Abstract: Flows generated by ensembles of flagella are crucial to development, motility and sensing, but the mechanisms behind this striking coordination remain unclear. We present novel experiments in which two micropipette-held somatic cells of Volvox carteri, with distinct intrinsic beating frequencies, are studied by high-speed imaging as a function of their separation and orientation. Analysis of time series shows that the interflagellar coupling, constrained by lack of connections between cells to be hydrodynamical, exhibits a spatial dependence consistent with theory. At close spacings it produces robust synchrony for thousands of beats, while at increasing separations synchrony is degraded by stochastic processes. Manipulation of the relative flagellar orientation reveals in-phase and antiphase states, consistent with dynamical theories. Flagellar tracking with exquisite precision reveals waveform changes that result from hydrodynamic coupling. This study proves unequivocally that flagella coupled solely through a fluid can achieve robust synchrony despite differences in their intrinsic properties.
August 13, 2014 Squishy Physics Seminar
Wim L. Noorduin, Harvard
5:30pm | 2nd floor Maxwell Dworkin Lounge

Rationally designed complex hierarchical microarchitectures


Abstract: Complex nano/microstructures are of fundamental interest, and the ability to program their form has practical ramifications in fields such as optics, catalysis and electronics. We developed microstructures in a dynamic reaction-diffusion system that allows us to rationally devise schemes for precisely sculpting a great variety of elementary shapes. Detailed understanding of the underlying reaction-diffusion mechanisms allows us not only to program elementary shapes, but also steer the precipitating reactants into complex flowers, corals, vases, and patterns, with precise control over placement of stems, leaves, etc. via sequential combinatorial assembly of the developing shapes. These findings may hold profound implications for understanding and ultimately expanding upon nature's morphogenesis strategies, and outline a novel approach to use sequences of dynamic modulations of the environment to steer self-assembly processes as a route to advanced, highly complex microscale materials and devices.
August 6, 2014 Squishy Physics Seminar
Cullen R. Buie; MIT, Department of Mechanical Engineering
5:30pm | 2nd floor Maxwell Dworkin Lounge

Spreading, Splashing, and Sparkling: Drop Impingement Phenomena on Porous Media


Abstract: This study investigates drop impingement on porous media including thin films, paper, and soil. Experiments reveal previously unexplored impingement modes on porous surfaces designated as necking, spreading, and jetting. Dimensional analysis yields a new non-dimensional parameter, denoted the Washburn-Reynolds number, relating droplet kinetic energy and surface energy. The impingement modes correlate with Washburn-Reynolds number variations spanning four orders of magnitude and a corresponding energy conservation analysis for droplet spreading shows good agreement with the experimental results. The simple scaling laws presented will inform the investigation of dynamic interactions between porous surfaces and liquid drops for applications ranging from droplet microfluidics to inkjet printing.

In addition, high-speed imaging has revealed evidence of aerosol generation during drop impingement on dry porous media including soils. After impact, tiny gas bubbles form inside the droplet, fed by air escaping the porous media. The tiny bubbles break resulting in microscale jets that quickly break up into droplets. Within a specific range of impact velocity, we observe furious ejection of tiny droplets, producing aerosol clouds above the surface. Aerosol generation can be predicted with knowledge of the surface properties and impact conditions. This work illustrates that aerosols can easily be generated on porous surfaces, with intriguing environmental and engineering implications.
July 30, 2014 Squishy Physics Seminar
Nicolas Vogel, Harvard
5:30pm | 2nd floor Maxwell Dworkin Lounge

Photonic Balls


Abstract: Materials in nature are characterized by structural order over multiple length scales evolved for maximum performance and multi-functionality and are often produced by self-assembly processes. A striking example of this design principle is structural coloration, where interference, diffraction and absorption effects result in vivid colors. Mimicking this emergence of complex effects from simple building blocks is a key challenge for man-made materials.

Here we show that a simple confined self-assembly process leads to a complex hierarchical geometry which displays a surprising variety of optical effects. Colloidal crystallization in an emulsion droplet creates micron-sized superstructures, termed photonic balls. The curvature imposed by the emulsion droplet leads to frustrated crystallization, resulting in spherical colloidal crystals with ordered, crystalline layers and a disordered core. This geometry produces multiple optical effects. The ordered layers give rise to Bragg diffraction that is strongly influenced by the curvature, leading to limited angular dependence of color and cut-off in transmitted light. The disordered core contributes non-resonant scattering that induces a macroscopically whitish appearance, which we can mitigate by incorporating absorbing gold nanoparticles that suppress scattering and macroscopically purify the color. With increasing size of the constituent colloidal particles, grating diffraction effects dominate, which result from order along the crystal's curved surface and induce a vivid polychromatic appearance.

The control of the multiple optical effects induced by the hierarchical morphology in photonic balls paves the way to employ them as building blocks for complex optical assemblies ? potentially as more efficient mimics of structural color as it occurs in nature.
July 23, 2014 Squishy Physics Seminar
Tim Still, University of Pennsylvania
5:30pm | 2nd floor Maxwell Dworkin Lounge

Colloidal Hydrogel Particles, Glass Transition, Jamming, and Friction


Abstract: Since the first synthesis of colloidal poly(N-isopropylacrylamide) (PNIPAM) particles by Pelton in 1986, stimuli-responsive colloidal hydrogels have become extremely versatile model systems to study a plethora of physical phenomena, including phase transitions, glass physics, and photonic materials.

In this talk, I will first discuss some properties of temperature-responsive PNIPAM particles and how these properties depend on the synthesis scheme. The second part of the talk focuses on studies that employ such PNIPAM particles to investigate the liquid-solid transition as a function of packing fraction via rheology and microscopy. The relations between the glass transition and jamming physics will be elucidated. In a similar manner, microscopy allows us to measure phonons in soft colloidal crystals and glasses, and an analysis based on jamming theory enables us to estimate inter-particle friction between PNIPAM particles.
July 20-22, 2014 7th Annual Future Faculty Workshop
MIT (Co-sponsored by the NSF MRSECs at MIT (CMSE) and Harvard University)
July 16, 2014 Squishy Physics Seminar
Jian Qin, University of Chicago
5:30pm | 2nd floor Maxwell Dworkin Lounge

Counting polymer knots to find the entanglement length


Abstract: Linear polymers are flexible chain molecules containing many chemical repeat units. The motion of individual polymers in a dense polymer liquid (molten plastic) is severely constrained by surrounding chains, and by the fact that chains cannot cut through one another. Effectively, polymers may be considered as being confined inside a tube-like region. The tube diameter, or the entanglement length, is the key parameter needed by the standard molecular theory for polymer rheology. But a molecular understanding of the origin of the tube diameter is still lacking. We approach this problem by closing polymers into rings, in order to obtain a system with well-defined, permanent topology, and using tools from the mathematical theory of knots to identify and count topological entanglements. For simulated polymer melts, this approach enables us to get a tube diameter value that is based on topological considerations alone, and that agrees with values obtained by more heuristic methods. We use this approach to study the effects of chain flexibility and addition of diluents upon the tube diameter.
July 9, 2014 Squishy Physics Seminar
Michael Murrell, University of Wisconsin
5:30pm | 2nd floor Maxwell Dworkin Lounge

Force Generation within Biological Materials


Abstract: Mechanical forces generated by cells modulate global shape changes required for essential life processes, such as polarization, division and spreading. The shape of the cell is governed primarily by a network of entangled polymers attached to the inside of the cell membrane ("cytoskeleton"). This polymer network is pushed out of equilibrium by motor proteins which convert chemical energy in the form of ATP into mechanical work, gripping and contracting the network. Thus, the interaction between the cytoskeleton, motor proteins, and the cell membrane are known to mediate the myriad changes in cell shape through mechanical force production, although little is understood regarding the mechanism as cells are complex with many components and regulatory processes. To reduce this complexity, I engineer simplified versions of the cellular machinery from the "bottom-up", building it piece by piece with reconstituted proteins and synthetic membranes. With this approach, I can recapitulate various aspects of the mechanical behavior of cells devoid of cellular regulation. I will present two such examples. First, I will present how a "biomimetic" non-muscle cell can actively generate forces within a disordered cytoskeleton via motor protein activity. Second, I will present an alternative method for generating equivalent forces independent of the cytoskeleton and the consumption of ATP, which relies on the ability of membranes to harvest adhesion energy and alter the hydrostatic pressure of the cell, thereby exerting forces on its surroundings.
July 2, 2014 Squishy Physics Seminar
Renko de Vries, Wageningen UR
5:30pm | 2nd floor Maxwell Dworkin Lounge

Supramolecular Design of a Minimal Coat-Protein for an Artificial Virus


Abstract: Virus particles are highly effective vehicles to deliver genetic material into susceptible host cells. A necessary condition highlighted by theoretical models for the successful formation of infective virus particles is precisely tuned co-operativity of the self-assembly process. There have been many attempts to construct self-assembling virus-like particles but to date the key property of cooperativity has not been explicitly incorporated in any design of artificial viruses. Here we show the rational design of a minimal viral coat protein based on three simple polypeptide domains which do feature precise control over the co-operativity of its co-assembly with single DNA molecules into rod-shaped virus-like-particles (VLPs). We use polypeptide domains that previously we have used for a range of hydrogel-forming polypeptides, and which are inspired by natural structural proteins such as silks and collagens. The triblock polypeptides are produced by secreted expression in the yeast Pichia Pastoris. We confirm the validity of our design principles by showing that the kinetics of self-assembly of our VLPs follows our previous model for Tobacco Mosaic Virus (TMV) assembly. Mature VLPs protect DNA against enzymatic degradation and transfect cells with considerable efficiency, making them promising scaffolds for delivery vehicles. Being biosynthetic and protein-based, our design also paves the way for developing viruses that are completely artificial and yet can replicate in a cellular host.
June 27, 2014 59th New England Complex Fluids Workshop at Cabot Business & Technology Center, Billerica, MA
June 18, 2014 Squishy Physics Seminar
Anupam Sengupta, MIT
5:30pm | 2nd floor Maxwell Dworkin Lounge

Topological Microfluidics: Exploring anisotropic fluids in microfluidic environment


Abstract: Liquid crystals (LCs) are complex anisotropic fluids, well-known for display applications. Their properties are in contrast to the isotropic fluids which we typically employ for state-of-the-art microfluidic science and technology. The tunable anisotropy allows us to explore LCs as an inherently functional material for microfluidics that harnesses the coupling between the flow, the molecular orientation, and the spontaneous ordering or topology of the system. A feature which is particularly promising for future applications is that topological defects in liquid crystals can serve as soft rails for colloidal particles, aqueous droplets or other microfluidic cargo. At a more fundamental level, hydrodynamic stagnations leading to topological singularities, provide a rich platform to study the dynamics between singularities of distinct genesis. We shall discuss suggestive experiments to understand these interactions, and conclude the talk with a perspective view on the emerging area of Topological Microfluidics.
June 11, 2014 Squishy Physics Seminar
Daphne Klotsa, Michigan
5:30pm | 2nd floor Maxwell Dworkin Lounge

Packing polyhedra: from ancient math to advanced materials


Abstract: The densest way to pack objects in space, also known as the packing problem, has intrigued scientists and philosophers for millenia. Today, packing comes up in various systems over many length scales from batteries and catalysts to the self-assembly of nanoparticles, colloids and biomolecules. Despite the fact that so many systems' properties depend on the packing of differently-shaped components, we still have no general understanding of how packing varies as a function of particle shape. Here we carry out an exhaustive study of how packing depends on shape by investigating the packings of over 55,000 polyhedra. By combining simulations and analytic calculations, we study families of polyhedra interpolating between Platonic and Archimedean solids such as the tetrahedron, the cube, and the octahedron, via continuous vertex and edge truncations. We find maximum packing-density surfaces that reveal unexpected richness and complexity. We expect our density surface plots to guide experiments that utilize shape and packing in a similar way that phase diagrams are used to do chemistry. Our findings demonstrate the importance of thinking about a shape no longer as a static property but rather as but one point in a higher dimensional "shape space" where the neighborhood around the given shape, as achieved by small deformations, needs to be taken into account as it may reveal why we can assemble certain crystals, transition between them, or get stuck in kinetic traps.
June 4, 2014 Squishy Physics Seminar
Hideyuki Arata, Nagoya University
5:30pm | 2nd floor Maxwell Dworkin Lounge

Studying plant reproduction on artificial microscale platform


Abstract: I would like to talk about our recent study on plant-on-a-chip microsystem for quantitative analysis of pollen tube guidance, which is a key mechanism in plant reproduction and seed development. A new pollen tube growth assay using microchannel-system was proposed to perform guidance assay and to analyze pollen tube growth. Various types of microsystems have been developed to perform real-time observation of pollen tube guidance by the signaling molecule released from female tissues. This study enabled by microsystem might lead us to the systematic understanding of complex in vivo mechanisms about "how a female tissue call a pollen tube" and elucidate important knowledge for understanding cell-cell communication, one of the most important topics in the next generation of biology.

Affiliations and titles:
Group Leader, Nano-Engineering Group, JST-ERATO Higashiyama Live-Holonics Project/Designated Associate Professor, Graduate School of Science, Nagoya University, Japan/Visiting Scholar, School of Engineering and Applied Sciences, Harvard University
May 28, 2014 Squishy Physics Seminar
Alfredo Alexander-Katz, MIT
5:30pm | 2nd floor Maxwell Dworkin Lounge

Microscopic Walkers: Exploiting Friction at the Microscopic Scale


Abstract: Friction is at the core of almost every locomotion strategy used in the natural world, from nanomotors to complete organisms. In this presentation, I will talk about our work on exploiting friction between colloids and surfaces to create microscopic walkers, or more shortly, microwalkers. These active systems are chains of superparamagnetic beads that are magnetically self-assembled, and they can break since there are no permanent bonds holding the colloids together. Upon rotation of the magnetic field, these chains start to rotate. In the vicinity of an interface, rotational and translational degrees of freedom become coupled through friction, and the microwalkers start to walk on these surfaces. During this talk, I will show how such chains display several regimes of motion depending on the strength of the magnetic field and the rotational frequency. When many of these chains walk together on a surface, large fluid flows develop and the magnitude of such flows is intimately related to the microscopic details of the chains, as will be shown. Finally, I will finalize with the case of inhomogeneous friction environments, where it is possible to create Tribotaxis. This phenomenon is the process by which microwalkers can find regions of high mobility while performing a random walk. In this particular case, we have created such friction gradients by spatially modulating the density of complementary receptors, so these microwalkers are also performing chemotaxis.
May 21, 2014 Squishy Physics Seminar
Paul Blainey, Broad Institute of MIT and Harvard, Assistant Professor of Biological Engineering, MIT
5:30pm | 2nd floor Maxwell Dworkin Lounge

Molecular Sleds: Discovery and Application


Abstract: Many proteins are known to be capable of thermally-driven motion along DNA, a protein activity thought to play a role in these proteins" ability to locate targets within DNA. We recently described the first case where this activity is utilized to mediate reactions among adenoviral proteins on DNA rather than search for DNA loci. The 11 amino acid viral peptide pVIc that stimulates these reactions itself has a capability for thermally activated sliding along DNA, recasting presumed requirements for DNA-templated biomolecule transport. The existence of such "molecular sleds" has broad implications for natural biochemical processes and applications in biotechnology.
May 14, 2014 Squishy Physics Seminar
Rui Ni, Yale University
5:30pm | 2nd floor Maxwell Dworkin Lounge

The response of insect swarms to sound


Abstract: Midges are small flying insects that closely resemble mosquitoes. Male midges can form large swarm to attract the females and mate. This emergent behavior is a classical example of dynamical self-organization, which is usually characterized with simple models without considering the biological interaction between individuals. In this talk, I will present two experiments to understand biological behaviors of midges. In the first experiment, we use time-frequency analysis of midges' trajectories to demonstrate that the high-frequency motion of the midges may be associated to their biological goal to determine the identities of neighbors. In addition, since the familiar buzz of flying midges is an important social signal, we also use externally played male and female midge's sound to test the response of the swarm. Although individual midge does not follow the sound exactly, there is a very clear population level response. Our results suggest that properly accounting for biological behavior is necessary for accurately modeling collective animal motion.
May 7, 2014 Squishy Physics Seminar
Kobi Barkan, Tel Aviv University
5:30pm | 2nd floor Maxwell Dworkin Lounge

Targeted Self-Assembly of Soft-Matter Quasicrystals


Abstract: A large number of soft-matter systems, whose building blocks range in size from several nanometers to almost a micron, have been shown in recent years to form ordered phases with dodecagonal (12-fold) symmetry (for a recent review see [1]). Contrary to metallurgic quasicrystals, whose source of stability remains a question of great debate to this day, we show that the stability of certain soft-matter quasicrystals "interacting via pair potentials with repulsive cores, which are either bounded or only slowly diverging" can directly be explained. Their stability is attributed to the existence of two natural length scales in their isotropic pair potentials, along with an effective three-body interaction arising from entropy. We establish the validity of this mechanism at the level of a mean-field theory [2], and then use molecular dynamics simulations in two dimensions to confirm it beyond mean field, and to show that it leads to the formation of cluster crystals [3]. We demonstrate that our understanding of the stability mechanism allows us to generate a variety of desired structures, including decagonal and dodecagonal quasicrystals, suggesting a practical approach for their controlled self-assembly in laboratory realizations using synthesized soft-matter particles. We also apply similar principles to the design of pair potentials for controlling the self-assembly of multi-component systems and verify that our design principles indeed work using numerical simulations.

  1. T. Dotera, Isr. J. Chem. 51, 2011, 1197-1205.
  2. K. Barkan, H. Diamant, and R. Lifshitz, Phys. Rev. B 83, 2011, 172201.
  3. K. Barkan, M. Engel, and R. Lifshitz, arXiv:1401.4475, 2014.
April 30, 2014 Squishy Physics Seminar
Alain Karma, Northeastern
5:30pm | 2nd floor Maxwell Dworkin Lounge

Stochasticity in excitable dynamics of rogue heart cells


Abstract: The bulk of heart tissue consists of excitable cells that fire an action potential in a perfectly predictable and orderly fashion when they receive a sufficient current stimulus from their neighboring cells. However, under pathological conditions, some heart cells can also fire an action potential in a seemingly random way without currents from their neighbors, acting transiently or for long periods of time as local pacemakers. This rogue behavior is believed to underlie several life-threatening inherited and acquired heart rhythm disorders (triggered arrhythmias) but remains poorly understood. This talk will discuss progress to understand the origin of stochasticity underlying this rogue behavior from both biological and nonlinear dynamics viewpoints.
April 23, 2014 Squishy Physics Seminar
Ken Kamrin, MIT
5:30pm | 2nd floor Maxwell Dworkin Lounge

Modeling the strange flow behaviors of granular media


Abstract: Despite the ubiquity of granular matter in the world around us, the challenge of predicting the motion of a collection of flowing grains has proven to be a difficult one, from both computational and theoretical perspectives. In this talk, we begin by presenting a number of the "unusual" behaviors exhibited by dry granular media, which have posed hurdles from the perspective of developing a continuum model. These behaviors include: steady-flow fields that do not obey any local flow rheology, flow onset and stoppage phenomena that do not abide by a standard yield stress, and the motion-induced "quicksand" effect whereby far-away motion changes the flow resistance everywhere. We then proceed to develop a non-local constitutive relation for granular matter, and demonstrate how the model is capable of reconciling these various phenomena in a general manner. This is achieved by comparing its predictions to hundreds of existing experimental data sets, which elucidate the aforementioned behaviors.
April 16, 2014 Squishy Physics Seminar
Wonho Jhe, Seoul National University
5:30pm | 2nd floor Maxwell Dworkin Lounge

Water at the nanoscale: physics and applications


Abstract: Liquid exhibits unique peculiarities at the nanoscale compared with bulk liquid, similarly to the case of solid. I will discuss abnormal dynamic as well as mechanical properties of both nanofilm and nanobridge of water.
April 9, 2014 Squishy Physics Seminar
Jeffrey Guasto, Tufts University
5:30pm | 2nd floor Maxwell Dworkin Lounge

Shear-induced unmixing in bacterial suspensions


Abstract: Motile bacteria play integral roles in biophysical processes ranging from biogeochemical cycling in the oceans to the spread of infections in the human body. Their ability to seek out nutrients and chemical signals for survival is conferred through swimming using long, thin, actuated flagella. However, these processes can be disrupted by the ubiquitously dynamic fluid environments in which they live. In this seminar, we will discuss microfluidic experiments using video microscopy to uncover transport mechanisms that lead to bacterial unmixing in flowing fluids. In particular, hydrodynamic shear produces striking spatial heterogeneity in suspensions of motile bacteria, characterized by up to 70% cell depletion from low-shear regions due to cell 'trapping' in high-shear regions. A Langevin model reveals that trapping arises from the competition between the alignment of elongated bacteria with the flow and the stochasticity in their swimming orientation. Finally, we show that shear-induced trapping directly impacts bacterial survival strategies, suppressing chemotaxis by hampering directional motility and more than doubling surface attachment by increasing the transport of bacteria towards surfaces.
April 3, 2014 Squishy Physics Seminar
Esther Amstad, Harvard SEAS
5:30pm | 2nd floor Maxwell Dworkin Lounge

The microfluidic nebulator: Production of amorphous nanoparticles


Abstract: The usefulness of many hydrophobic substances is limited by their poor solubility in water; this restricts their applicability for example in the pharmaceutical, biomedical, and food industry. The dissolution kinetics can be increased if they are formulated as nanoparticles as it scales with the surface-to-volume ratio. The dissolution kinetics can be increased even more if these substances are formulated as amorphous nanoparticles as the amorphous phase has a higher solubility than the crystal; amorphous substances thus dissolve faster and in higher quantities. However, many materials have a high propensity to crystallize as this is the energetically most favorable state; it is thus difficult to make these materials amorphous. I will present a microfluidic spray drier, we call it a microfluidic nebulator that produces unprecedentedly small nanoparticles that are amorphous. Nanoparticles are produced in small drops that are formed inside the nebulator through the use of supersonic air. The nanoparticle size is determined by the number of solute molecules contained in the drop. The nanoparticle structure is determined by the probability for a crystalline nucleus to form as the drop evaporates; this probability is typically very high in supersaturated solutions as crystalline solids readily form under these conditions. However, the formation of a crystalline nucleus itself entails some time delay. We demonstrate that the nebulator can kinetically suppress the formation of crystalline nuclei; thereby, it produces amorphous nanoparticles from many different materials, even from materials that have a very high propensity to crystallize.
March 26, 2014 Squishy Physics Seminar
Igor Sokolov, Tufts
5:30pm | 2nd floor Maxwell Dworkin Lounge

Squishing Molecules, Polymers, Cells, etc., with AFM


Abstract: Atomic Force Microscopy (AFM) is probably one of the major tools responsible for the emergence of what is now called Nanoscience and Nanotechnology. We observe a tremendous proliferation of AFM applications in the fields of soft condensed matter, materials science, chemistry, bioengineering, and nanotechnology. AFM has a particular advantage in dealing with biological objects, soft condensed matter in general, where the ability to image objects in their natural environment is paramount.

In this talk I will briefly overview the basic principles of the AFM work, and show examples of applications of this technique in soft condensed matter physics, from single molecules and polymers to cells (and if time permits, the study of small creatures, like beetles). Specifically, I will describe what information can be obtained when the AFM probes squiring soft objects, in the study of molecular self-assembly, immunorecognition, mechanics of cells, etc.

Biography: Igor Sokolov received his B.S. in Physics from St. Petersburg State University (Russian Harvard), Russia in 1984, and earned his Ph.D. from D.I. Mendeleev Institute for Metrology (similar to NIST), Russia in 1991. He is a professor and the Bernard M. Gordon Senior Faculty Fellow in the Departments of Mechanical, Biomedical Engineering, Physics of Tufts University. He has 135 refereed publications, more than 20 patents issued and pending, 100+ invited and 100+ contributed presentations. He serves as an editorial board member in a number of journals. Igor?s current research focuses on nanomechanics of soft materials, nanophotonics (fluorescence and sensing), nanocomposite materials, early detection of cancer, etc.
March 19, 2014 Squishy Physics Seminar
Susmita Bose, Washington State University
5:30pm | 2nd floor Maxwell Dworkin Lounge

Calcium phosphate ceramics in bone tissue engineering and drug delivery


Abstract: There are an estimated one million bone grafting procedures performed annually in the U.S. and a few million worldwide to repair fractures, craniomaxillofacial defects, bone defects, tumors, as well as hip and knee replacements. Increase in the number of procedures is strongly tied to the increase in musculoskeletal disorder, aging population segment and sports related injuries. World dental implant and bone graft market could top $6 billion by 2014, and hip and knee implants market to reach $21 Billion by 2016. Calcium phosphate (CaP) ceramic being compositionally similar to the inorganic part of bone, show significant promise towards drug delivery and bone graft applications. We have used CaP scaffolds, fabricated using 3-D printing technology, for bone tissue engineering. Dopant chemistry in CaP plays a vital role in controlling their resorption or degradation kinetics as scaffolds, mechanical strength, and biological properties of resorbable CaPs. 3D interconnected channels in CaP scaffolds provide pathways for micronutrients, improved cell-material interactions, and increased surface area allows improved mechanical interlocking between scaffolds and surrounding bone. In vivo studies show improved osteogenesis and angiogenesis with these 3D printed scaffolds. These systems with controlled strength degradation and drug release, show promise for use in orthopedic and bone tissue engineering applications. Our study on doped CaP coated metal implants shows enhanced in vitro cell material interactions and improved osseointegration in vivo. We have used induction plasma spray system to coat metal implants to improve coating interfacial strength and antibacterial properties while showing effect of dopants on osteoblast and osteoclast cell performance. The presentation will include recent scientific and technological advances towards developing next generation ceramics, composites and scaffolds for bone implants and drug delivery.

Biography: Susmita Bose is a Professor in the School of Mechanical and Materials Engineering, an affiliate professor in the Department of Chemistry at Washington State University (WSU). Dr. Bose received the prestigious Presidential Early Career Award for Scientist and Engineers (PECASE, the highest honor given to a young scientist by the US President at the White House) award in 2004 from the National Science Foundation. Dr. Bose was named as a ?Kavli fellow? by the National Academy of the Sciences. In 2009, she received the prestigious Schwartzwalder-Professional Achievement in Ceramic Engineering (PACE) Award from the American Ceramic Society, which is an international award given to one scientist annually below the age of 41. Dr. Bose is an editorial board member for five different international journals including Acta Biomaterialia and Journal of the American Ceramic Society (Associate Editor). Dr. Bose has published over 200 technical papers with ~ 4400 citations, ?h? index 37. Dr. Bose is a fellow of the American Institute for Medical and Biological Engineering (AIMBE) and the American Ceramic Society (ACerS).
March 12, 2014 Squishy Physics Seminar
Qi Wen, WPI
5:30pm | 2nd floor Maxwell Dworkin Lounge

Decoupling effects of substrate nanotopography and stiffness on tissue cells


Abstract: Tissue cells can sense and respond to both physical and biochemical signals. It has been demonstrated that mechanical stiffness and topographical features of the extra cellular matrix (ECM) can affect cellular function including migration, proliferation and gene expression. In a real tissue, the ECM mechanical properties are often coupled with its the micro- and nano structure and hence the nanotopography. I will discuss the synergistic effects of topography and mechanical stiffness on cytoskeletal stiffness and morphology of NIH 3T3 fibroblasts cultured on polydimethysloxane (PDMS) surfaces with different stiffness and surface roughness. By characterizing cell-ECM adhesions on the single molecular level, we try to elucidate how stiffness and nanotopography regulate cellular function. We hope this study on cell-ECM interactions will provide insights to guide the design of materials for tissue engineering and hopefully the mechanism of tumor formation and metastasis.
March 5, 2014 Squishy Physics Seminar
Andrejs Cebers, University of Latvia
5:30pm | 2nd floor Maxwell Dworkin Lounge

Magnetotactic bacteria as self-propelling magnets


Abstract: Magnetotactic bacteria are microorganisms which use chains of magnetic nanoparticles (magnetosomes) to navigate in the magnetic field of the Earth. Their behavior in magnetic fields of different configurations will be described. As the simplest case the transition from a synchronous to a non-synchronous regime of a non-motile bacterium in a rotating field will be considered. Thermal fluctuations near the threshold of the non-synchronous regime cause the phase lag slips. Trajectories of motile magnetic bacteria under the action of a rotating magnetic field will be described. They are circles in the synchronous regime and complex curves in the non-synchronous. Experimental results of their study will be demonstrated. The random switching of rotary motors of a bacterium leads to peculiar diffusion process of curvature centers of its trajectory. The results of analytical and numerical calculations of the diffusion coefficient of this random process will be given and compared with experimental results. An interesting phenomenon noticed during the experiments in a rotating magnetic field is splitting of the chains of magnetosomes during division of bacterium now studied in detail by several groups. Magnetotactic bacteria are anaeorobic. This is illustrated by a band formation in a constant magnetic field along the axis of capillary where the oxygen gradient is created. The model of this phenomenon will be described. Finally some phenomena with flexible filaments of ferromagnetic particles which mimic the chains of magnetosomes are demonstrated behavior of flexible ferromagnetic filament at magnetic field inversion, its self-propulsion driven by an AC magnetic field and other.
February 28, 2014 58th New England Complex Fluids Workshop at MIT
February 26, 2014 SEED
Pierce Hall 100F
February 19, 2014 IRG II
McKay 402
February 19, 2014 Squishy Physics Seminar
Justin Burton, Emory University

Iceberg capsize hydrodynamics and the source of glacial earthquakes


Abstract: Accelerated warming in the past few decades has led to an increase in dramatic, singular mass loss events from the Greenland and Antarctic ice sheets, such as the catastrophic collapse of ice shelves on the western antarctic peninsula, and the calving and subsequent capsize of cubic-kilometer scale icebergs in Greenland's outlet glaciers. The latter has been identified as the source of long-period seismic events classified as glacial earthquakes, which occur most frequently in Greenland's summer months. The ability to partially monitor polar mass loss through the Global Seismographic Network is quite attractive, yet this goal necessitates an accurate model of a source mechanism for glacial earthquakes. In addition, the detailed relationship between iceberg mass, geometry, and the measured seismic signal is complicated by inherent difficulties in collecting field data from remote, ice-choked fjords. To address this, we use a laboratory scale model to measure aspects of the post-fracture calving process not observable in nature. Our results show that the combination of mechanical contact forces and hydrodynamic pressure forces generated by the capsize of an iceberg adjacent to a glacier's terminus produces a dipolar strain which is reminiscent of a single couple seismic source.
February 13, 2014 IRG III
Pierce Hall 100F
February 12, 2014 IRG I
Pierce 309
February 5, 2014 Squishy Physics Seminar
Alfredo Alexander-Katz, MIT
5:30pm | 2nd floor Maxwell Dworkin Lounge

Blood Clotting-Inspired Polymer Physics


Abstract: Nature has devised creative and efficient ways of solving complex problems, and one of these problems is that of blood clotting in flowing conditions. In fact, nature has used a novel combination of polymer physics and chemistry that enhances the self-healing propensity of a vessel when strong flows are present while avoiding coagulation when the flow is diminished, a rather counter-intuitive phenomenon. Underlying this process is a globular biopolymer, the so-called von Willebrand Factor, whose function is strongly regulated by flow. In this talk I will present our work on this macromolecule starting from the single molecule approach and building up to the multi component system that more closely resembles blood. I will emphasize how new concepts have emerged from trying to understand such a complex system, in particular I will show how these polymers can display giant non-monotonic response to shear, as well as a very large propensity to form polymer-colloid composites in flow while being a stable dispersed suspension in quiescent conditions. In fact, the aggregation behavior is universal and can be explained with simple scaling arguments. These novel concepts and results are in principle not unique to blood clotting and can have important ramifications in other areas.
January 29, 2014 Squishy Physics Seminar
Maria Kilfoil, UMass Amherst
5:30pm | 2nd floor Maxwell Dworkin Lounge

Seeing how biology feels: Nonthermal fluctuations in the cell nucleus


Abstract: In this talk I will present direct measurements of fluctuations in the nucleus of yeast cells. While prior work has shown these fluctuations to be active and non-thermal in character, their origin and time dependence are not understood. We show that nuclear fluctuations can be quantitatively understood by uncorrelated, active force fluctuations driving a nuclear medium that is dominated by an uncondensed DNA solution, for which we perform rheological measurements on an in vitro model system under similar conditions to what is expected in the nucleus. We conclude that the eukaryotic nucleus of living cells is a nonequilibrium soft material whose fluctuations are actively driven, and are far from thermal in their time dependence. I will also introduce a new in vitro system we developed to study active processes in the nuclear microenvironment.
January 22, 2014 Squishy Physics Seminar
Randall Erb, Harvard
5:30pm | 2nd floor Maxwell Dworkin Lounge

Manufacturing Ordered Composites with Colloidal Assembly


Abstract: Recently, we have found an ultra-high magnetic response in stiff anisotropic particles by adsorbing nominal amounts of magnetite nanoparticles onto the surface of the particle [1]. This modification allows for the remote control of particle orientation and spatial positioning under magnetic fields only an order of magnitude larger than the Earth?s magnetic field. This level of control, among numerous exciting possibilities, can lead to the positioning of particle reinforcement in manmade materials that mimics the structures found in natural systems such as seashells or mammalian bone.

We have developed an energy model for these particle suspensions that explain this ultra-high response and suggest the key parameters essential in these systems. To help validate these parameters, we consider an idealized system and analyze the dynamic response of isolated platelets under magnetic fields. We find that using theoretical Perrin friction factors, originally developed to describe rotational drag for anisotropic molecules, we can precisely predict the interplay between magnetic, viscous and gravitational torques on these particles. We extend our model to describe the alignment of the platelets second major axis under rotating magnetic fields. We have found a relationship between the viscosity of the suspension and the critical frequency required to change from "rolling" to "fully-aligned" modes.

We use these techniques to create a family of advanced materials exhibiting 3-d reinforcements, spatial gradients, and various deliberate alignments. These composites exhibit the 3-D reinforced biological structures predicted to have enhanced material properties, such as higher stiffness and "wear-free" characteristics. This manipulation technique further enables fabrication of a diverse family of reinforced hydrogels. These systems have structures and anisotropic swelling that mimics natural systems [2]. These include hydrogels with the following: 1) in-plane reinforcement leading to swelling with high anisotropy (*plant stems*); 2) simple bilayer reinforcement leading to curled swelling (*pinecones*); 3) orientationally unique bilayers that swell into helical configurations (*orchid tree seed pods*). This work offers a way forward in recreating these defined reinforcement architectures within manufactured polymers.

[1] R. M. Erb, R. L. Libanori, N. Rothfuchs, A. R. Studart, *Science*, *335*, 199-204, 2012.

[2] R. M. Erb, J. Sanders, R. Grish, A. R. Studart, *Nature Communications*, *4*, 1712, 2013.
January 15, 2014 Squishy Physics Seminar
Andrej Kosmrlj, Harvard
5:30pm | 2nd floor Maxwell Dworkin Lounge

Elasticity, Geometry, and Buckling


Abstract: In this talk I present how geometrical shape affects the mechanical properties of thin solid membranes and how buckling instabilities change the geometry of periodic microstructures in materials. Using methods rooted in statistical physics, we find that random shape fluctuations and thermal excitations of thin solid membranes significantly modify their mechanical properties. Such membranes are much harder to bend, but easier to stretch, compress and shear. Finally, I show how methods from solid state physics can help us deduce the geometry of buckled periodic microstructures. Buckling instabilities can change the microstructure symmetries, including a spontaneous chiral symmetry breaking, which drastically modifies the material properties.

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