Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H9: Multimodal Characterization of Soft Materials in Complex Environments III |
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Sponsoring Units: DPOLY Chair: Wei Chen, ANL Room: 268 |
Tuesday, March 14, 2017 2:30PM - 2:42PM |
H9.00001: EMPTY SLOT |
Tuesday, March 14, 2017 2:42PM - 2:54PM |
H9.00002: EMPTY SLOT |
Tuesday, March 14, 2017 2:54PM - 3:06PM |
H9.00003: EMPTY SLOT |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H9.00004: Gelation of Polymer-grafted SiO$_{\mathrm{2}}$ Nanoparticle Colloid Studied with 20 us X-ray Photon Correlation Spectroscopy (XPCS) Qingteng Zhang, Eric Dufresne, Suresh Narayanan, Alec Sandy, Divya Bahadur, Subramanian Ramakrishnan, Piotr Maj, Pawel Grybos The nanoscale and microsecond resolved structure and dynamics associated with the gelation of octadecyl-grafted silica nanoparticles dispersed in decalin with a volume fraction of 0.2 was studied via XPCS in the small-angle x-ray-scattering geometry. The length-scale resolved dynamics of the colloidal particles was measured from 20 us to 2 s in delay time using a prototype 50 kHz frame rate x-ray area detector providing spatial sensitivity that spans from the self-diffusion to collective diffusion regimes. Above the gel point, the correlation functions are well described by a stretched exponential function. The diffusion coefficient decreases with decreasing temperature. At and just below the gel point, the correlation functions show a two-stage decay as a function of delay time corresponding to, first, fast dynamics from free particle diffusion and, second, slow dynamics from gel network. Our results reveal the nanoscale behavior of colloidal nanoparticles during gelation at unprecedented time and spatial scales and provide information that can be used to test various models and deepen our understanding of the gelation process. [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H9.00005: Confined relaxations of grafted polymer in solutions of linear polymer Ryan Poling-Skutvik, Ramanan Krishnamoorti, Jacinta Conrad Using neutron spin echo spectroscopy (NSE), we investigate the relaxations of polymer grafted to silica nanoparticles dispersed in semidilute solutions of linear polymer. The grafted polymer has a radius of gyration comparable to radius of the silica nanoparticle with a moderate grafting density so that the grafted polymer is more extended than a Gaussian chain. On length scales ranging from 1 to 20 nm and time scales less than 100 ns, the dynamics of the grafted polymer deviate from the standard Zimm model derived for linear polymers. Instead, the polymer chains are confined and unable to fully relax over the experimental time. The confinement length agrees with the distance between chains decreases as the linear polymer concentration is increased. Additionally, the confinement length is independent of linear polymer molecular weight, suggesting that linear polymer cannot penetrate the grafted layer. Instead, the grafted chains collapse onto themselves, similar to the structural changes observed in systems of star and linear polymers at high concentrations of linear polymer. We verify this physical picture using small-angle x-ray scattering and atomic force microscopy to observe aggregation of grafted particles at high concentrations of linear polymer. [Preview Abstract] |
Tuesday, March 14, 2017 3:30PM - 3:42PM |
H9.00006: Diffusion of Small Sticky Nanoparticles in a Polymer Melt: A Dynamic Light Scattering Study Bobby Carroll, Vera Bocharova, Shiwang Cheng, Umi Yamamoto, Alex Kisliuk, Ken Schweizer, Alexei Sokolov The study of dynamics in complex fluids such as polymers has gained a broad interest in advanced materials and biomedical applications. Of particular interest is the motion of nanoparticles in these systems, which influences the mechanical and structural properties of composite materials, properties of colloidal systems, and biochemical processes in biological systems. Theoretical work predicts a violation of Stokes-Einstein (SE) relationship for diffusion of small nanoparticles in strongly-entangled polymer melt systems, with diffusion of nanoparticles much faster than expected D$_{SE}$. It is attributed to differences between local and macroscopic viscosity. In this study, the diffusion of nanoparticles in polymer melts below and above entanglement molecular weight is measured using dynamic light scattering. The measured results are compared with simulations that provide quantitative predictions for SE violations. Our results are two-fold: (1) diffusion at lower molecular weights is slower than expected D$_{SE}$ due to chain absorption; and (2) diffusion becomes much (20 times) faster than D$_{SE}$, at higher entanglements due to a reduced local viscosity. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H9.00007: Investigating Block-Copolymer Micelle Dynamics for Tunable Cargo Delivery Xiuli Li, Bryce Kidd, Tyler Cooksey, Megan Robertson, Louis Madsen Block-copolymer micelles (BCPMs) can carry molecular cargo in a nanoscopic package that is tunable using polymer structure in combination with cargo properties, as well as with external stimuli such as temperature or pH. For example, BCPMs can be used in targeted anticancer drug delivery due to their biocompatibility, in vivo degradability and prolonged circulation time. We are using NMR spectroscopy and diffusometry as well as SANS to investigate BCPMs. Here we study a diblock poly(ethylene oxide)-b-(caprolactone) (PEO-PCL) that forms spherical micelles at 1{\%} (w/v) in the mixed solvent D$_{\mathrm{2}}$O/THF-d8. We quantify the populations and diffusion coefficients of coexisting micelles and free unimers over a range of temperatures and solvent compositions. We use temperature as a stimulus to enhance unimer exchange and hence trigger cargo release, in some cases at a few degrees above body temperature. We present evidence for dominance of the insertion-expulsion mechanism of unimer exchange in these systems, and we map phase diagrams versus temperature and solvent composition. This study sheds light on how intermolecular interactions fundamentally affect cargo release, unimer exchange, and overall micelle tunability. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H9.00008: A novel generic method for size-selective purification of nanoparticles based on the critical Casimir effect Hongyu Guo, Gheorghe Stan, Yun Liu The properties and applications of nanoparticles (NPs) strongly depend on their size and size distribution. However, NPs, unlike atoms, are never monodisperse, making it is highly desirable to reduce the polydispersity for well-defined properties and functions. Notwithstanding the continual improvement of synthesis methods, purification and size-selective separation of NPs remain significant challenges. Here we conclusively demonstrate the effectiveness of a novel size-selective particle purification method based on the physical phenomenon of critical Casimir forces induced selectively reversible aggregations of colloidal particles immersed in a binary solvent through temperature and composition control. Moreover, due to the universality of the involved critical phenomena, our method is generic for many colloidal particles and can be instrumental in tailoring their nanoscale properties and applications. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H9.00009: Branching, Chain Scission, and Solution Stability of Worm-Like Micelles. Greg Beaucage, Karsten Vogtt, Hanqui Jiang As salt is added to a simple micelle solution such as SDS or SLES, the zero shear rate specific viscosity rises rapidly followed by a maximum and decay. The rapid rise in viscosity is associated with formation of elliptical and extended chain worm-like micelles, WLMs. Entanglement of these long chain micelles leads to the viscoelastic behavior we associate with shampoo and body wash. The plateau and drop in viscosity at high salt concentrations is caused by a special type of topological branching where the branch points have no energy penalty to motion along the chain according to Cates theory. These have some similarity to catenane crosslinks. Predictive dynamic theories for WLMs rely on structural details; the diameter, persistence length, contour length, branch length, segment length between branch points, and mesh size. Further, since the contour length and other large scale features are in kinetic equilibrium, with frequent chain breakage and formation, the thermodynamics of these long chain structures are of interest both in terms of chain scission as well as in terms of the stability of the colloidal solution as a whole. Recent structural studies of WLMs using static neutron scattering based on new scattering models will be presented demonstrating that these input parameters for dynamic models of complex topological systems are quantitatively and directly available. In this context it is important to consider a comparison between dynamic features, for instance entanglement, and their static analogs, chain overlap. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H9.00010: Thermodynamic control of star polymer architecture. Durgesh K. Rai, Gregory Beaucage, Kedar Ratkanthwar, Peter A. Beaucage, Ramnath Ramachandran, Nikos Hadjichristidis Star polymers differ from linear chains due to steric interactions between the arms. These steric interactions have not been previously quantified. This presentation will report on the extent that star arms are straightened under variable temperature and solvent as well as star functionality. The second virial coefficient is directly measured for the stars. The topological consequences of variable solvation are quantified using dilute solution neutron scattering and a hybrid unified scattering function coupled with the RPA equation. The results contradict the predictions of the Daoud-Cotton model and reflect a new uniform fractal model for star polymers at low functionality below about 8 arms. A transition to Daoud-Cotton behavior might be anticipated for high functionality stars and dendrimers. [Preview Abstract] |
Tuesday, March 14, 2017 4:30PM - 4:42PM |
H9.00011: Quantification of Aggregate Topology in Fumed Silica Andrew Mulderig, Gregory Beaucage, Karsten Vogtt, Hanqiu Jiang Ceramic aggregates are fractal structures consisting of aggregated primary particles and the nanostructure is widely characterized in terms of primary particle size, aggregate size and mass fractal dimension. However, these quantities alone fail to quantitatively describe branching in these materials. Many important properties of fumed silica are derived from its highly ramified aggregate topology. Ultra-small angle X-ray scattering (USAXS) is a powerful technique to characterize fractal structures over a range of length scales. Application of the Unified scattering function across the hierarchical levels allows the topological parameters to be quantified. The parameters determined from USAXS were then compared with TEM micrographs. Aggregates of smaller primary particles showed significantly higher degrees of aggregation and displayed higher branch fractions compared to aggregates of larger primary particles. Topological parameters from scattering were compared with results from simple models and were in good agreement. Quantification of aggregate topology lays the framework for predictive modelling of silica's topological contribution to its valuable reinforcement and rheological properties in commercial applications. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H9.00012: Revealing nanoparticle assembly under high pressure. Hongyou Fan Precise control of structural parameters through nanoscale engineering to improve optical and electronic properties of functional nanoparticles continuously remains an outstanding challenge. Previous work on nanoparticle assembly has been conducted largely at ambient pressure. Here I will present a new Stress-Induced Fabrication method in which we applied high pressure or stress to nanoparticle arrays to induce structural phase transition and to consolidate new nanomaterials with precisely controlled structures and tunable properties. By manipulating nanoparticle coupling through external pressure, a reversible change in their assemblies and properties can be achieved and demonstrated. In addition, over a certain threshold, the external pressure will force these nanoparticles into contact, thereby allowing the formation and consolidation of one- to three-dimensional nanostructures. Through stress induced nanoparticle assembly, materials engineering and synthesis become remarkably flexible without relying on traditional crystallization process where atoms/ions are locked in a specific crystal structure. Therefore, morphology or architecture can be readily tuned to produce desirable properties for practical applications. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H9.00013: Directed Self-Assembly of Lamellar Block Copolymers for High Energy Density Capacitors Alamgir Karim, Saumil Samant, Christopher Grabowski, Michael Durstock, Sushil Satija Energy storage is a fundamental issue driving the development of new materials and their associated fabrication. We report the development of high energy density solid-state capacitors fabricated using multicomponent block copolymer dielectric films (BCDF) with soft-shear driven highly oriented self-assembled lamellar diblock copolymers (BCP). Results of a model polystyrene-b-polymethyl methacrylate system processed by a unique Cold Zone Annealing-soft shear method show approximately 50{\%} enhancement in the dielectric breakdown performance of self-assembled multilayer lamellar BCP films compared to unordered as-cast films, indicating that the breakdown is highly sensitive to the nanostructure of the BCP. We also report the effect of molecular weight (MW) and layer thickness on dielectric properties of self-assembled BCPs by studying ternary blends of BCP/homopolymers with compositions such that the homopolymers selectively segregate into respective BCP domains. The blend compositions help to decouple the effects of MW and layer thickness demonstrating that the polymer chain ends act as defect sites by contributing to the free volume in the system that are responsible for the breakdown of BCDF. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H9.00014: Adenine-Functionalized Block Copolymers via RAFT polymerization Eunseol Kim, Avnish Kumar Mishra, K. L. Vincent Joseph, Jin Kon Kim Nucleobase functionalized polymers have been used in various fields because they have complementary multiple hydrogen bonding between nucleobases. However, the polymerization of these polymers is hard due to poor solubility in a solvent. In this study, adenine functionalized block copolymers, poly(9-(4-vinylbenzyl)adenine)-b-polystytene (PVBA-b-PS), were synthesized successfully using RAFT polymerization in polar solvents and characterized by GPC and NMR. Phase behavior of PVBA-b-PS with various volume fractions of PS block (f$_{PS}$) was investigated via small-angle X-ray scattering and transmission electron microscopy. With increasing f$_{PS}$ from 0.1 to 0.9, body-centered-cubic spheres (BCC), hexagonally packed cylinders (HEX), and lamellae (LAM) were observed. Interestingly, PVBA-b-PS with f$_{PS}$ of 0.77 showed asymmetric lamellar microdomains. [Preview Abstract] |
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