Center for Soft Matter and Biological Physics Seminars

Fall 2018

Organizer: Vinh Nguyen

These meetings occur on Mondays from 4:00pm to 5:00pm in Robeson 304.
Refreshments are served before the semnars (unless otherwise indicated)

August 2018
August 20

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Prof. Surita Bhatia (Stony Brook University, NY)

"Stratification in Colloidal Films"

Multicomponent films based on colloidal dispersions have a wide range of applications, including antimicrobial coatings for medical instruments, conductive textiles for flexible electronics, anti-reflective coatings for optical devices, paints for humid environments that are resistant to mold growth, and drug-loaded coatings for medical implants. Often, there is a need to spatially control location of certain components in the film. For example, silver nanoparticles can be used to impart antimicrobial activity to paints, but this component is expensive and may only be needed in the top few layers of the coating, not throughout the entire film. In principle, evaporative drying of multicomponent dispersions can be used to create films with a prescribed vertical concentration profile in a one-step process. In this talk, we present our recent results from atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) on films prepared from binary colloidal dispersions containing large and small particles of varying size and initial volume fraction. Our results show evidence of different types of stratification behavior, including large-on-top (e.g., large particles migrating to the top surface of the film), small-on-top, and “sandwich”-like layering. We discuss these results in terms of recent theories for stratification during evaporative drying..

Host: Shengfeng Cheng

August 27

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar
(poster)

Dr. Kunal Mondal (North Carolina State University)

"Soft-Nano-materials, Interfaces, and Micro-Nano-fabrication to Build Tools and Functional Devices"

New competitive technologies should be developed to deal with the world’s emerging problems in healthcare, environmental, agriculture, energy and security sectors to benefit a broad spectrum of society while using minimal resources. Multifunctional interfaces of nanomaterials can be used to tackle such glitches by developing sensors and detection devices such as biosensors, explosives trace detectors, mechanical-stress sensors, wastewater management systems and energy storage devices owing to their nanoscopic surface properties. Considering this, several catalytic and photocatalytic metal/metal-oxide semiconductor nanostructures have been synthesized and used for environmental remediation, point-of-care diagnostics and energy storage applications. Several fabrication techniques including electrospinning, microfabrication, 3D printing etc. have been used to made functional nano/micro devices. Various physicochemical characterization techniques are used to study their properties in nanoscale. Furthermore, effort has been made on surface patterning and fabricating stretchable electronics by integration of conducting liquid metal in soft elastomers to explore ways to utilize these ‘softer than skin’ materials for bioelectronic applications. Finally, this concludes with an outlook and future challenges of these materials within this context.

Host: Rana Ashkar

September 2018
September 3

Monday 4:00pm
304 Robeson Hall
(poster)

Labor Day "No CSB Seminar Scheduled"

Host:

September 10

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

September 17

Monday 4:00pm
304 Robeson Hall

(poster)

Chengyuan Wen (Virginia Tech, Physics)

Host: Vinh Nguyen

September 21

Friday, 2:30pm
210 Robeson Hall
Special Seminar
(poster)

Prof. Gary Grest (Sandia National Laboratories, Albuquerque, NM)

"Going up in time and length scales in modeling polymers"

Polymer properties depend on a wide range of coupled length and time scales, with unique macroscopic viscoelastic behavior stemming from interactions at the atomistic level. The need to probe polymers across time and length scales and particularly computational modeling is inherently challenging. Here new paths to probing long time and length scales including introducing interactions into the traditional bead-spring model that has been widely used for the past thirty years and coarse graining of atomistic simulations will be compared. Using linear polyethylene as a model system, the degree of coarse graining with two to six methylene groups per coarse-grained bead derived from a fully atomistic melt simulation were probed. Using these models we were successful in probing highly entangled melts and were able reach the long-time diffusive regime which is computationally inaccessible using atomistic simulations. We simulated the relaxation modulus and shear viscosity of well-entangled polyethylene melts for scaled times of a microsecond. The long time and length scale is coupled to the macroscopic viscoelasticity where the degree of coarse graining sets the minimum length scale instrumental in defining polymer properties and dynamics. Results will be compared to those obtained from the bead-spring model to demonstrate the additional insight that can be gained from atomistically inspired coarse grained models.

Host: Shengfeng Cheng

September 24

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

September 28

Friday, 2:30pm
210 Robeson Hall
Special Seminar
(poster)

Prof. Daniel I Goldman (Georgia Tech )

"Robophysics: Physics Meets Robotics"

Robots will soon move from the factory floor and into our lives (e.g. autonomous cars, package delivery drones, and search-and-rescue devices). However, compared to living systems, locomotion by such devices is still relatively limited, in part because principles of interaction with complex environments are largely unknown. In this talk I will discuss efforts to develop a physics of moving systems -- a locomotion ``Robophysics'' -- which we define as the pursuit of the discovery of principles of self-generated motion [Aguilar et al, Rep. Prog. Physics, 2016]. We use the methods of physics to examine successful and failed locomotion in simplified laboratory devices using parameter space exploration, systematic control, and techniques from dynamical systems. Drawing from examples from my group and our collaborators, I will discuss how robophysical studies in terrestrial environments have inspired new physics questions in low dimensional dynamical systems (including creation of analog quantum mechanics and gravity systems) and soft matter physics, have been useful to develop models for biological locomotion in complex terrain, and have begun to aid engineers in the creation of devices that begin to achieve life-like locomotor abilities on and within complex environments. The rapidly decreasing cost of constructing sophisticated robot models with easy access to significant computational power bodes well for scientists and engineers to engage in a discipline which can readily integrate experiment, theory and computation.

Host: Uwe Tauber

October 2018
October 1

Monday 4:00pm
304 Robeson Hall
Condensed Matter Seminar
(poster)

Dr. Jennifer Cano (Princeton University)

"TBD"

Host: Kyungwha Park

October 8

Monday 4:00pm
304 Robeson Hall

(poster)

Prof. David M. Leitner (University of Nevada, Reno )

“Watching energy transport in proteins: Identifying dynamics networks and thermodynamic properties”

Energy transport in a protein mediates protein function and represents the early events following a reaction or photoexcitation.  New time-resolved measurements, and a variety of computational and theoretical methods allow us to map out and describe energy transport in great detail.  I will describe some of our theoretical and computational work on the nature of energy transport in proteins, with focus on what we can learn about protein dynamics and thermodynamics by watching energy flow in proteins.  By coarse graining energy transport dynamics from the all-atom to residue level, we have identified a relation between conformational dynamics at equilibrium and rates of energy transfer across non-bonded contacts.  Measurements of rates of energy transfer thus provide a window into equilibrium dynamics of proteins and entropy associated with the dynamics of the contact.

Host:Vinh Nguyen

October 15

Monday 4:00pm
304 Robeson Hall

(poster)

Jacob Carroll (Virginia Tech, Physics)

“The effects of inhibitory neuron fraction on the dynamics of an avalanching neural network”

The statistical analysis of the collective neural activity known as avalanches provides insight into the proper behavior of brains across many species. In this paper we present a neural network model based on the work of Lombardi, Herrmann, de Arcangelis et al. that captures the relevant dynamics of neural avalanches, and we show how tuning the fraction of inhibitory neurons in this model removes exponential cut-offs present in the distributions of avalanche strength and duration, and transitions the power spectral density of the network into an epileptic regime, as well as effecting the evolution of the network structure over time. We propose that the brain operates away from this regime of low inhibitory fraction to protect itself from the dominating avalanches present in these extended distributions.

Host: Uwe Tauber

October 19

Friday, 2:30pm
304 Robeson Hall
No Colloquium
(poster)

Fall Break (No Colloquium)

Host:

October 22

Monday 4:00pm
304 Robeson Hall
Condensed Matter Seminar
(poster)

Alex Grutter

"TBD"

Host: Satoru Emori

October 29

Monday 4:00pm
304 Robeson Hall

(poster)

Shadi Esmaeili (Virginia Tech, Physics)

"From disorder to self-organization: A cyclic predator-prey system and a system of frustrated coupled oscillators"

Self-organization is the emergence of spontaneous order as a result of local interactions among the elements of a system. Systems far from equilibrium that are evolving toward their self-organized state show very interesting dynamic behaviors. We study the dynamic behavior of two systems: a cyclic predator-prey system with a complex spatiotemporal pattern, as well as a system of coupled oscillators with antagonistic coupling. In the predator-prey model, the response of the system to external perturbation is used as an approach to gain insights about its dynamic behavior. On the other hand, the breaking of time translation invariance was observed during the spontaneous relaxation of a system of coupled oscillators after a parameter quench in the absence of any stochastic fluctuation.

Host: Michel Pleimling

November 2018
November 2

Friday, 2:30pm
304 Robeson Hall
Colloquium
(poster)

Prof. Michael Flatte' (University of Iowa)

"Quantum Coherent Electronic Technologies"

Electrons in most materials experience dramatic and frequent scattering from other electrons, phonons, and a variety of other excitations. Such scattering events often rapidly dissipate any memory the electron had of its quantum state, so the electrons can be described as an ensemble that is near local ther-mal equilibrium. If the electrons can retain a good memory of their quantum state, however, then they are quantum coherent and can be used for very unu-sual and exciting tasks such as quantum computing. Realizing these quantum technologies has traditionally been expected to require very special elements such as superconducting devices or very high mobility transistors, as well as very low temperatures, in order to avoid rapid loss of quantum coherence (decoherence). Over the past fifteen years we and others have identified re-markable examples of room-temperature quantum coherent behavior in con-densed matter electronic systems, usually involving spin coherence. Predicting the behavior of these spin coherent systems requires integrating theoretical techniques to cope with energy scales ranging from far smaller than the thermal energy to far larger. I will describe some examples of quantum coherent technol-ogies and identify some of the features they share.

Host: Giti Khodaparast

November 5

Monday 4:00pm
304 Robeson Hall
CM Seminar
(poster)

Brian Skinner (Massachusetts Institute of Technology)

“Percolative Phase Transition in the Dynamics of Quantum Entanglement”

When left unobserved, many-body quantum systems tend to evolve toward states of higher entanglement.  Making a measurement, on the other hand, tends to reduce the amount of entanglement in a many-body system by collapsing one of its degrees of freedom. In this talk I discuss what happens when a many-body quantum system undergoes unitary evolution that is punctuated by a finite rate of projective measurements. Using numerical simulations and theoretical scaling arguments, we show that for a 1D spin chain there is a critical measurement rate separating two dynamical phases. At low measurement rate, the entanglement grows linearly with time, producing a volume-law entangled state at long times. When the measurement rate is higher than the critical value, however, the entanglement saturates to a constant as a function of time, leading to area-law entanglement. We map the dynamical behavior of the entanglement onto a problem of classical percolation, which allows us to obtain the critical scaling behavior near the transition. I briefly discuss generalizations of our result to higher dimensions, and its implications for the difficulty of simulating quantum systems on classical computers.

Host: Uwe Tauber

November 12

Monday 4:00pm
304 Robeson Hall
Condensed Matter Seminar
(poster)

Dr. David Pappas (NIST)

"TBD"

Host: Sophia Economou

November 19

Monday 4:00pm
304 Robeson Hall

(poster)

Thanksgiving Holiday No Seminars scheduled

Host:

November 26

Monday 4:00pm
304 Robeson Hall
Condensed Matter Seminar
(poster)

Shannon Serrao (Physics, Virginia Tech)

"Fluctuation effects on a cyclic predator-prey system(May-Leonard model)"

Owing to close proximity with observed cyclic predator-prey dynamics in nature, we study the cyclic predator-prey model of May-Leonard with three species. The May-Leonard model is characterized by strong fluctuation induced effects to its non-equillibruim stationary state, notably the noise induced spatio-temporal spiral patterns on the two dimensional lattice; and the extinction of the long-lived coexistence state on account of large but rare fluctuations. We study both these stochastic effects by firstly, characterizing the size of the aforementioned spiral patterns to the lowest order using the Doi-Peliti coherent state path integral formalism and encoding the pattern quantitatively in the coefficients of the noisy complex Ginsburg-Landau equation. Secondly, on the well-mixed version of the model, we obtain the extinction times of all but one species driven by large fluctuations from a stable coexistence state and compare our results to Gillespie simulations across the transcritical bifurcation in the system.


Host: Uwe C. Tauber

December 2018
December 3

Monday 4:00pm
304 Robeson Hall
(poster)

Prof. Sarah Perry (University of Massachusetts, Amherst)

"Molecular Engineering of Polyelectrolyte Complex Materials"

Electrostatic interactions and polyelectrolyte complexation can be used in the self-assembly of a wide range of responsive, bioinspired soft materials ranging from dehydrated thin films and bulk solids to dense, polymer-rich liquid complex coacervates, as well as more complex hierarchical structures such as micelles and hydrogels. This responsiveness can include swelling and dissolution or solidification, which can be harnessed to facilitate encapsulation and the subsequent fabrication of functional materials. In particular, we draw inspiration from biomolecular condensates, or membraneless organelles, which utilize liquid-liquid phase separation to create transient compartments in cells. These condensates are commonly formed due to weak, multivalent interactions involving intrinsically disordered proteins. Furthermore, these materials have been shown to enable the selective uptake of specific enzymes. We utilize polypeptides as model sequence-controlled polymers to study how the patterning or presentation of charges and other chemical functionalities can modulate the potential for liquid-liquid phase separation via complex coacervation. We further examine how the distribution of charge on globular proteins can be used to facilitate selective uptake into coacervate phases, and how such materials can be used to stabilize proteins against denaturation. This molecular-level understanding of polyelectrolyte complexation is further enhanced by detailed rheological and thermodynamic examinations of the molecular nature of the various material transitions present in these systems. Our experimental efforts are supported by the parallel development of computational approaches for modeling and predicting the phase behavior of patterned polymeric materials. Our goal is to establish molecular-level design rules to facilitate the tailored creation of materials based on polyelectrolyte complexation that can both illuminate self-assembly phenomena found in nature, and find utility across a wide range of real-world applications.

Host: Vinh Nguyen

Center for Soft Matter and Biological Physics Seminars

Spring 2019

Organizer: Vinh Nguyen

These meetings occur on Mondays from 4:00pm to 5:00pm in Robeson 304.
Refreshments are served before the semnars (unless otherwise indicated)

January 2019
January 21

Monday 4:00pm
304 Robeson Hall
(poster)

"Martin Luther King Holiday (No Classes-University Offices Closed)

Host:

January 28

Monday 4:00pm
304 Robeson Hall
(poster)

Faculty Search (No Seminar)

Host:

February 2019
February 4

Monday 4:00pm
304 Robeson Hall
(poster)

Bart Brown (Virginia Tech)

"TBD"

Host: Michel Pleimling

February 11

Monday 4:00pm
304 Robeson Hall
Condensed Matter Seminar
(poster)

Sam Carter (Naval Research Lab)

"TBD"

Host: Sophia Economou

February 18

Monday 4:00pm
304 Robeson Hall

(poster)

Cihan Nadir Kaplan (Harvard University)

"TBD"

Host: Rana Ashkar

February 25

Monday 4:00pm
304 Robeson Hall

(poster)

Trung Dac Nguyen (Northwestern University)

"TBD"

Host: Daniel Capelluto

March 2019
March 4

Monday 4:00pm
304 Robeson Hall

(poster)

APS Meeting (No Seminar)

Host:

March 11

Monday, 4:00pm
304 Robeson Hall

(poster)

Spring Break (No Seminars)

Host:

March 18

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

March 25

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

April 2019
April 1

Monday 4:00pm
304 Robeson Hall
Condensed Matter Seminar
(poster)

Prof. Herbert Fotso (University at Albany)

"TBD"

Host: Ed Barnes

April 8

Monday 4:00pm
304 Robeson Hall
Joint CM Seminar

(poster)

Prof. Chih Kuan Tung (North Carolina A&T State University)

"TBD"

Host: Shengfeng Cheng

April 15

Monday 4:00pm
304 Robeson Hall

(poster)

Dr. Ulrich Dobramsyl (University of Cambridge)

"TBD"

Host: Uwe Tauber

April 22

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

April 29

Monday 4:00pm
304 Robeson Hall

(poster)

Host:

May 2019
May 6

Monday 4:00pm
304 Robeson Hall
(poster)

Host:

May 13

Wednesday,
210 Robeson Hall
(poster)

Final Exam Week
(No Seminars)