Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Q50: Focus Session: Reconfiguring and Actuating Soft Matter II: Tunable Interactions |
Hide Abstracts |
Sponsoring Units: GSOFT Chair: Zorana Zeravcic, Rockefeller University Room: 218 |
Wednesday, March 4, 2015 2:30PM - 2:42PM |
Q50.00001: Magnetic field detector consisting of magnetic and semiconducting nanoparticles co-assembled in a liquid crystalline matrix Jose Amaral, Andrea Rodarte, Jacky Wan, Christopher Ferri, Makiko Quint, Ron Pandolfi, Michael Scheibner, Linda Hirst, Sayantani Ghosh An exciting area of research is using nano-constituents to create artificial materials that are multifunctional and allow for modification post-fabrication and in situ. We are investigating the ensemble behavior of iron-oxide magnetic nanoparticles (MNPs) and CdSe/ZnS quantum dots (QDs) when dispersed in an electro-optically active liquid crystalline (LC) matrix. The directed assembly of NPs in the matrix is driven by the temperature-induced transition of the LC from the isotropic to the nematic phase as the NPs are mostly expelled into the isotropic regions, finally ending up clustered around LC defect points when the transition is complete. Our results show a two-fold intensity increase of QD photoluminescence intensity with low magnetic fields (less than 100 mT). We speculate this increase is due to MNP rearrangement which produces a compaction of the clusters, resulting in the detection of increased QD emission. The individual components work together to act as a magnetic field detector and since they are direct assembled in a LC medium, they could potentially be used in a wide range of fluid-based applications. This work was funded by NSF grants DMR-1056860 and ECC-1227034. [Preview Abstract] |
Wednesday, March 4, 2015 2:42PM - 2:54PM |
Q50.00002: Computational and experimental study of magnetic colloidal assembly and martensitic transition Lin Fu, Ye Yang, Catherine Marcoux, Joshua Socolar, Patrick Charbonneau, Benjamin Yellen Colloidal self-assembly in external fields offers new ways to build up complex structures. Here, we study the self-assembly of a quasi-2D mixture of magnetic and non-magnetic spherical particles, immersed in a ferrofluid and under an external magnetic field. We calculate the external field strength-density-tilt angle phase diagram for the system by specialized Monte Carlo methods and compare the results with experiments. By tilting the external field away from the vertical, the system first undergoes magnetostriction, and then a martensitic phase transition between a checkerboard and a striped crystal. We find that the out-of-equilibrium transformation pathway depends strongly on the initial crystal orientation, external field strength and degree of confinement in the third dimension. Our findings suggest the possibility for improving the design of functional materials by selecting the specific type of transformation pathway to optimize either the shape change or the heat exchange properties. [Preview Abstract] |
Wednesday, March 4, 2015 2:54PM - 3:06PM |
Q50.00003: Magnetorheological Shear Flow Near Jamming Daniel V\aa gberg, Brian Tighe Flow in magnetorheological (MR) fluids and systems near jamming both display hallmarks of complex fluid rheology, including yield stresses and shear thinning viscosities. They are also tunable, which means that both phenomena can be used as a switching mechanism in ``smart'' fluids, i.e. fluids where properties can be tuned rapidly and reversibly by changing external parameters. We use numerical simulations to investigate the rheological properties of MR fluids close to the jamming transition as a function of the applied field and volume fraction. We are especially interested in the crossover region where both phenomena are needed to describe the observed dynamics. [Preview Abstract] |
Wednesday, March 4, 2015 3:06PM - 3:18PM |
Q50.00004: Field-induced growth of self-annealing suspended colloidal monolayers Ming Han, Erik Luijten Due to their reduced dimensionality, flexible sheet-like materials have numerous applications, e.g. offering the potential to serve as functional coatings or as a system for encapsulation, akin to biologic membranes. Here we report the ability to generate large ordered, flexible, and suspended monolayers via field-induced self-assembly. We employ anisotropic polarizable colloidal particles and stimulate their reversible aggregation by applying a static external electric field. Through molecular dynamics simulations with a self-consistent calculation of the induced dipole moments, we demonstrate that such particles form monolayers capable of eliminating defects and dislocations, and even self-healing. Potential applications, such as tube formation, are also discussed. [Preview Abstract] |
Wednesday, March 4, 2015 3:18PM - 3:30PM |
Q50.00005: Directing colloidal assembly and a metal-insulator transition using quenched-disordered polymeric networks Anh Phan, Ryan Jadrich, Kenneth Schweizer Replica integral equation and effective medium theory methods are employed to elucidate how to massively reconfigure a colloidal assembly and realize equilibrium states of high electrical conductivity at low physical volume fractions [1]. This is achieved by employing variable mesh size networks of rigid rod or semiflexible polymers as a templating internal field. By exploiting bulk phase separation frustration and the tunable competing processes of colloid adsorption on the low dimensional network and fluctuation-driven colloid clustering in the pore spaces, distinct spatial organizations of greatly enhanced particle contacts can be achieved. As a result, a continuous, but very abrupt, transition from an insulating to metallic-like state can be realized via a small change of either the colloid-template or colloid-colloid attraction strength. Polymer conformational fluctuations are found to significantly modify the physical adsorption process and hence the ability of colloids to organize along the filamentary network strands. Qualitatively new physical behavior can emerge as the pore size approaches the colloid diameter, reflecting strong frustrating constraints of the template on colloidal assembly.\\[4pt] [1] R.B. Jadrich and K.S. Schweizer, Phys.Rev.Lett., 2014. [Preview Abstract] |
Wednesday, March 4, 2015 3:30PM - 3:42PM |
Q50.00006: Enhanced Mechanical Properties of Nanoparticle Networks Cross-Linked by Biomimetic Catch Bonds Badel L. Mbanga, Balaji V.S. Iyer, Victor V. Yashin, Anna C. Balazs The tunable behavior of cross-linked networks of Polymer-Grafted Nanoparticles (PGNs) makes them excellent candidates for designing novel materials with enhanced mechanical properties. The building block of a PGN network is a nanoparticle with grafted polymer chains whose free ends' reactive groups can form bonds with the end chains on the nearby particles. We use computer modeling to study the tensile behavior of 3D samples, in which some fraction of cross-links is formed through the biomimetic ``catch'' bonds. In contrast to conventional ``slip'' bonds, the catch bonds might become stronger under an applied force due to transitions between two conformational states. The mechanical properties of the PGN networks are shown to exhibit a drastic improvement upon introduction of the catch bonds into the network. We discuss how ductility, toughness, and rate of strain recovery of the network depend on the catch bond content. [Preview Abstract] |
Wednesday, March 4, 2015 3:42PM - 3:54PM |
Q50.00007: Magnetic Nano- and Micro- Particles in Living Cells: Kinetics and Fluctuations C. Pease, N. Chiang, C. Pierce, N. Muthusamy, R. Sooryakumar Functional nano and micro materials have recently been used not only as diagnostic tools for extracellular studies but also as intracellular drug delivery vehicles and as internal probes of the cell. To realize proper cellular applications, it is important not only to achieve efficient delivery of these materials to targeted cells, but also to control their movement and activity within the confines of the cell. In this presentation, superparamagnetic nano and micro particles are utilized as probes, with their responses to weak external magnetic fields enabling them to be maneuvered within a cell. In order to generate the required local magnetic fields needed for manipulation, the fields emanating from microscopic domain walls stabilized on patterned surface profiles are used in conjunction with weak external magnetic fields to create mobile traps that can localize and transport the internalized particle. Preliminary findings on creating the mobile traps suitable for applications to probe the interior of cells, and the responses, both Brownian fluctuations and directed motion, of particles ranging in size from 200 nm to 1 micron within HS-5 cells will be presented. Future applications to probe cellular behavior within the framework of emerging biomaterials will be discussed. [Preview Abstract] |
Wednesday, March 4, 2015 3:54PM - 4:06PM |
Q50.00008: Programming Directed Motion on the Micron Scale by Thermal Ratcheting Emily W. Gehrels, W. Benjamin Rogers, Zorana Zeravcic, Vinothan N. Manoharan We present an experimental system of DNA-functionalized colloidal particles which exhibit directed motion (``dancing'') along patterned substrates in response to temperature cycling. We take advantage of toehold exchange in the design of the DNA sequences that mediate the colloidal interactions to produce broadened, flat, or even re-entrant binding and unbinding transitions between the particles and substrate. Using this new freedom of design, we devise systems where, by thermal ratcheting, we can externally control the direction of motion and sequence of steps of the colloidal dancer. We determine the maximum work that the system can perform by measuring a maximum average velocity as a function of the thermal ratcheting rate. [Preview Abstract] |
Wednesday, March 4, 2015 4:06PM - 4:18PM |
Q50.00009: Tunable Thermal Switching via DNA-Based Nano Devices Michael Zwolak, Chih-Chun Chien, Kirill Velizhanin, Yonatan Dubi DNA has a well-defined structural transition -- the denaturation of its double-stranded form into two single strands -- that strongly affects its thermal transport properties. We show that, according to a paradigmatic model of DNA denaturation, one can engineer DNA ``heattronic'' devices that have a rapidly increasing thermal conductance over a narrow temperature range across the denaturation transition ($\sim$350 K). The origin of this rapid increase of conductance, or ``switching,'' is the softening of the lattice and suppression of nonlinear effects as the temperature crosses the transition temperature and DNA denatures. Most importantly, we demonstrate that DNA nanojunctions have a broad range of thermal tunability due to varying the sequence and length, and exploiting the underlying nonlinear behavior. We discuss the role of disorder in the base sequence, as well as the relation to genomic DNA. These results set the basis for developing thermal devices out of materials with nonlinear structural dynamics, as well as understanding the underlying mechanisms of DNA denaturation. [Preview Abstract] |
Wednesday, March 4, 2015 4:18PM - 4:30PM |
Q50.00010: Modeling the rapid de-swelling of toroidal hydrogels Svetoslav Nikolov, Ya-Wen Chang, Alexander Alexeev, Alberto Fernandez De Las Nieves The utilization of synthetic hydrogel networks as 3-D cell culture platforms has allowed researchers to more effectively study how epigenetic factors affect cell growth and physiology. As a whole, this has emphasized the biomechanical role of scaffold structures and led to a number of advances in tissue engineering. Our current research focuses on modeling temperature activated shape transformations of toroidal poly(N-isopropylacrylamide) pNIPAM gels. We use dissipative particle dynamics (DPD) to simulate the steady (slow heating rates) and unsteady (fast heating rates) de-swelling behavior of these thermo-sensitive gels. Our simulations show that for slow heating rates the aspect ratio of the tori remains constant during de-swelling. For rapid heating rates we observe buckling instabilities. Our simulations agree with the experimental observations. [Preview Abstract] |
Wednesday, March 4, 2015 4:30PM - 4:42PM |
Q50.00011: Renewable Interfaces: Surface Topography Actuation for Complex Biological Adhesion Control Luka Pocivavsek, SangHo Ye, Kathleen Cao, Ka Yee C. Lee, Sachin Velankar, William Wagner Controlling adhesion at biological interfaces is a complex problem with great biomedical importance. We use dynamic wrinkling, generated with PDMS/UVO chemistry under different macroscopic strains ($\epsilon_{ij}\sim0.3$), to create a mechanical interfacial term that frustrates particle adhesion. This device actuates surface topography between flat (zero surface confinement $\chi_{ij}$) and wrinkled surfaces ($\chi_{ij} \sim (A/\lambda)^2$, where $A$ and $\lambda$ are wrinkle amplitude and wavelength, respectively), with a maximum rate of 0.6 Hz. Un-actuated PDMS placed in contact with whole sheep blood shows near total surface coverage with adhered platelets over 90 min. Actuation showed a nearly 100-fold decrease in platelet adhesion. Interestingly, topographic actuation is four times as effective compared to flat surface actuation in controlling platelet adhesion. Our model explores the competition between surface tension terms ($U_{\gamma}=\gamma \epsilon_{ij}$) and interfacial elastic terms ($U_{\chi} = E_{ij}( t \cdot\epsilon_{ij}^2 + t^3\cdot(\chi_{ij}/\lambda^2$)) generated because of actuation and wrinkling, where $E_{ij}$ is platelet modulus and $t$ is characteristic platelet length scale. The condition for de-adhesion is $U_{\chi} > U_{\gamma}$. [Preview Abstract] |
Wednesday, March 4, 2015 4:42PM - 4:54PM |
Q50.00012: Underwater Reversible Adhesion Between Oppositely Charged Weak Polyelectrolytes Latifah Alfhaid, Mark Geoghegan, Nicholas Williams, William Seddon Force-distance data has shown that the adhesion between two oppositely charged polyelectrolytes: poly(methacrylic acid) (PMAA, a polyacid) and poly[2-(diethylamino)ethyl methacrylate] (PDEAEMA, a polybase), was controllable by varying the pH level of their surrounding. Accordingly, adhesive force at the interface between these two polymers was higher inside basic surroundings at pH 6 and 7, and then it started to decrease at pH level below 3 and above 8. Stimulating adhesion between PMAA gel and PDEAEMA brushes by adding salt to their surrounded water has only a limited effect on the adhesive force between them, contradicting previous results. Increasing the molar concentration of sodium chloride (NaCl) in the surrounded water of these two polymers from 0.1 to 1M did not decrease the adhesion forces between a PMAA gel and a grafted PDEAEMA layer (brush). The JKR equation was used to evaluate the adhesion forces between the polymer gel and the brushes and it was observed that the adhesion increased with the elastic modulus of the gel decreased. [Preview Abstract] |
Wednesday, March 4, 2015 4:54PM - 5:06PM |
Q50.00013: Observing polymersome dynamics in controlled microscale flows Subhalakshmi Kumar, Anish Shenoy, Charles Schroeder Achieving an understanding of single particle rheology for large yet deformable particles with controlled membrane viscoelasticity is major challenge in soft materials. In this work, we directly visualize the dynamics of single polymersomes ($\sim$ 10 $\mu $m in size) in an extensional flow using optical microscopy. We generate polymer vesicular structures composed of polybutadiene-block-polyethylene oxide (PB-b-PEO) copolymers. Single polymersomes are confined near the stagnation point of a planar extensional flow using an automated microfluidic trap, thereby enabling the direct observation of polymersome dynamics under fluid flows with controlled strains and strain rates. In a series of experiments, we investigate the effect of varying elasticity in vesicular membranes on polymersome deformation, along with the impact of decreasing membrane fluidity upon increasing diblock copolymer molecular weight. Overall, we believe that this approach will enable precise characterization of the role of membrane properties on single particle rheology for deformable polymersomes. [Preview Abstract] |
Wednesday, March 4, 2015 5:06PM - 5:18PM |
Q50.00014: pH-induced structural changes in aqueous CTAB/NaSal solutions Chinedu Umeasiegbu, Ramanan Krishnamoorti, Vemuri Balakotaiah Cationic surfactants in the presence of hydrotropic salts exhibit pH-sensitive changes to rheological properties and can thus be utilized in ensuring effective stimulation of heterogeneous carbonate reservoirs. In this study, we investigate the pH-induced changes in microstructure and viscoelasticity of aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal), and their dependence on temperature, NaSal-to-CTAB ratio (CS/CD) and CTAB concentration (CD). It was observed that the solutions can be switched between gel-like (viscoelastic) and fluid-like (non-viscoelastic) behavior over a narrow pH range, and that the transition pH and associated change in viscoelasticity were strongly dependent on CS/CD. Dynamic light scattering and small-angle neutron scattering results revealed a hitherto unseen re-entrant transition in which micelles transition from cylindrical to spherical micelles but revert to flexible cylindrical micelles on reduction in pH. Our observations suggest that in addition to the well described electrostatic and hydrophobic interactions in cationic surfactant - hydrotrope mixtures, the pH-induced microstructural changes are governed by complementary cation-$\pi $ interactions and hydrogen bonding. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700