Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session W44: Focus Session: Dynamics of Polymers-Phenomena due to Confinement - Diffusion, Particles, & Pores |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Karin Jacobs, Saarland University, Germany Room: A309 |
Thursday, March 24, 2011 11:15AM - 11:27AM |
W44.00001: Single-molecule measurements of adsorbed polymer Changqian Yu, Juan Guan, Sung Chul Bae, Steve Granick Single-molecule tracking is used to study the surface mobility of PEG (polyethylene glycol) chains adsorbed to the solid-liquid interface from dilute aqueous solution. The end-labeled chains are visualized by objective-based total internal reflection fluorescence microscopy (TIRFM) and their trajectories are analyzed after cleaning the images with denoising algorithms. Surface mobility, which in this system depends on pH, is decomposed into one family of chains which remains adsorbed over the observation time window, and another family that appears to translate from point to point by hopping. This we quantify with nm-level resolution. [Preview Abstract] |
Thursday, March 24, 2011 11:27AM - 11:39AM |
W44.00002: Segmental motion in polystyrene thin film: a single molecule fluorescence study Zhongli Zheng, Jiang Zhao Single molecule fluorescence de-focus microscopy is used to study the segmental motion by observing the rotational motion of single fluorophores chemically attached to polystyrene chain ends. The collective nature of the rotational motion was noticed: a sudden change of the fraction of rotating fluorophores was discovered at a temperature 60 degree below the glass transition temperature of polystyrene. The dependence of the critical temperature on film thickness and surface chemistry was investigated and the results show that the effect of confinement, surface interaction and free surface. [Preview Abstract] |
Thursday, March 24, 2011 11:39AM - 11:51AM |
W44.00003: Order of Magnitude Decrease in Dye Diffusion in Nanoconfined Polymer Films: Fluorescence Nonradiative Energy Transfer Technique Hui Deng, Manish Mundra, John Torkelson A fluorescence nonradiative energy transfer/multilayer film technique was used to determine the diffusion coefficient of the dyes decacyclene and Disperse Red 1 in supported polystyrene (PS) films as a function of film thickness. Previous studies on the glass transition temperature (Tg) of PS show a decrease in Tg as films are nanoconfined. This Tg-reduction is due to the enhanced role of the polymer/air interface which results in a region of increased polymer mobility as thickness is reduced. However, dye diffusion coefficients decrease upon film nanoconfinement, with the onset of diffusion coefficient reduction appearing at film thicknesses much thicker than the onset of Tg-confinement effects. These results can be explained by the fact that Tg reflects the longer time side of the polymer relaxation time distribution while dye diffusion reflects the shorter time side of the relaxation distribution. We hypothesize that confinement suppresses the shorter time side of the relaxation distribution which results in the observed decrease in diffusion coefficients. [Preview Abstract] |
Thursday, March 24, 2011 11:51AM - 12:03PM |
W44.00004: Non-classical diffusion of PDMS confined in a surface forces apparatus Subhalakshmi Kumar, Changqian Yu, Sung Chul Bae, Steve Granick We present FRAP measurements inside a surface forces apparatus. Polydimethylsiloxane (PDMS), well above its glass transition, was confined into molecularly-thin films between atomically smooth mica sheets. Translational diffusion was measured using fluorescence recovery after photobleaching (FRAP) as the polymer film thickness was changed from tens of Rg to 3 Rg . The FRAP recovery curves of confined films are distinctly non-classical. Huge heterogeneity is suggested by stretched exponential behavior in which the power of time varies smoothly from $\beta $=1 (thick films) to $\beta $=0.3 (confined films) with a sharp transition between these limits. [Preview Abstract] |
Thursday, March 24, 2011 12:03PM - 12:15PM |
W44.00005: Probing In-Plane Diffusion of Nano-Confined Polymers in Ultrathin Films Joshua Katzenstein, Justin Chandler, Haley Hocker, Christopher Ellison In-plane (parallel to the substrate) polymer diffusion at and near interfaces has significant implications for polymeric surfactants used in tertiary oil recovery, exfoliation of clay sheets in polymer nano-composites, and several other high technology applications. Here, we report a study on the in-plane diffusion of whole polymer chains confined between interfaces using fluorescence recovery after photobleaching. Adapted from quantitative biology, FRAP provides a platform to independently study the effect of temperature, molecular weight, and film thickness on in-plane diffusion of polymers confined between interfaces. Fluorescently labeled polymers were synthesized, spin coated onto quartz substrates and the self-diffusion coefficient was measured by irreversibly photobleaching fluorophores in a pre-defined pattern and monitoring recovery of fluorescence over time. Preliminary results indicate that for thick films the diffusion coefficient is consistent with bulk values. [Preview Abstract] |
Thursday, March 24, 2011 12:15PM - 12:27PM |
W44.00006: Screening Effect of Supercritical Carbon Dioxide on Polymer/Substrate Interactions Peter Gin, Naisheng Jiang, Maya Endoh, Bulent Akgun, Sushil Satija, Tad Koga The kinetics and thermodynamic properties of polymer melts near interfaces and in confined geometries can vary significantly from their bulk counterparts. This behavior can be attributed to the presence of an immobile layer at the polymer/substrate interface, which has been reported to hinder the mobility of polymer chains in thin films even at a large length scale. Here, we investigate the use of supercritical carbon dioxide (scCO$_{2})$ as a medium to screen the polymer/substrate interactions and enhance chain mobility in polymer thin films. In-situ neutron reflectivity was utilized to measure the interdiffusion of deuterated polystyrene (d-PS) into various matrices of hydrogenated PS (h-PS) with thicknesses ranging from 0.5 Rg to 5 Rg. We found that at the unique T (36\r{ }C) and P (8.2 MPa) conditions, where the anomalous adsorption of CO$_{2}$ molecules in polymer thin films occurs, the diffusion constants remained unchanged regardless of bottom layer thickness, while no diffusion occurred below 1Rg at high temperature (170\r{ }C). [Preview Abstract] |
Thursday, March 24, 2011 12:27PM - 12:39PM |
W44.00007: The Glass Transition at Silica/PMMA Nanocomposite Interfaces Rahmi Ozisik, Katelyn Parker, Ryan T. Schneider, Richard W. Siegel, Juan Carlos Cabanelas, Berna Serrano, Claire Antonelli, Juan Baselga Local glass transition temperatures (Tg) have been measured in the interfaces of solution blended silica/poly(methyl methacrylate) (PMMA) nanocomposites using florescence spectroscopy and compared with Tg measured by differential scanning calorimetry (DSC). It was found that the two types of measurements yielded significantly different information. Combinations of silanes and poly(propylene glycol)- based molecular spacers bound to fluorophores were covalently linked to the surface of the nanoparticles, allowing for variation of the fluorophore response with respect to the distance from the nanofiller surface. Increases in the bulk Tg from the neat PMMA value were found upon the addition of nanofillers, but were independent of the nanofiller concentration when the filler concentration was above 2\% by weight. Furthermore, as the size of the grafted molecular spacer was increased, Tg values were found to decrease and approach Tg of the neat PMMA. Owing to variable conformations of the spacers, an effective distribution of fluorophore-silica distances exists, which influences the fluorophores' response to the transition. [Preview Abstract] |
Thursday, March 24, 2011 12:39PM - 12:51PM |
W44.00008: Structural Relaxation of 3-Dimensionally Confined Polymer Glasses: Isobaric versus Isochoric Glass Formation Yunlong Guo, Chuan Zhang, Rodney Priestley We have measured the glassy-state structural relaxation of aqueous suspended polystyrene (PS) nanoparticles and the corresponding silica-capped PS nanoparticles via modulated differential scanning calorimetry. Suspended and capped-PS nanoparticles undergo glass formation and subsequent physical aging under isobaric and isochoric conditions, respectively. To account for glass transition temperature (Tg) changes with confinement, physical aging measurements were performed at a constant value of Tg minus Ta, where Ta is the aging temperature. With deceasing diameter, aqueous suspended PS nanoparticles exhibited enhanced physical aging rates in comparison to bulk PS. At all values of Tg minus Ta investigated, capped-PS nanoparticles aged at reduced rates compared to the corresponding aqueous suspended PS nanoparticles. Due to differences in paths to glass formation, suspended and capped-PS nanoparticles aged to different apparent equilibrium states. We captured the physical aging behavior of all nanoparticles via the Tool, Narayanaswamy, and Moynihan (TNM) model of structural relaxation. [Preview Abstract] |
Thursday, March 24, 2011 12:51PM - 1:03PM |
W44.00009: Molecular Dynamics Study of Single Conjugated Polymers Confined to Nanoparticles Sabina Maskey, Flint Pierce, Dvora Perahia, Gary Grest Optically active polymers confined into nanoparticles are highly fluorescent and have potential applications in intracellular fluorescence imaging, bio-sensors and other optoelectronic devices. Internal conformation and dynamics of the polymers determines their optical properties. Using molecular dynamics (MD) simulations, we have explored the structure and dynamics of nanoparticles formed by conjugated polymers in a collapsed conformation, which is not the most stable conformation of the polymer. Nanoparticles were formed in a collapsed conformation and followed as the function of time in both poor and good solvents. We found that these nanoparticles are stable and remain collapsed in a poor solvent but rapidly expands and unraveled in a good solvent. The lengths of the side chains affect the internal packing of the side chains which in turn affect the size of the nanoparticles. S(q,t) was measured to characterize the internal dynamics of the collapsed nanoparticles. [Preview Abstract] |
Thursday, March 24, 2011 1:03PM - 1:15PM |
W44.00010: The Glass Transition Temperature of Polymer Nanoparticles under Soft and Hard Confinement Chuan Zhang, Yunlong Guo, Rodney Priestley When confined to the nanoscale, the glass transition temperature (Tg) of polymers can deviate substantially from the bulk, i.e., the Tg-confinement effect. Due to ease of processing, most studies have focused on the size-dependent Tg of thin films, while few have extended investigations to other geometries. As polymers confined in higher geometrical dimensions become the enabling material in technologies ranging from drug delivery to plastic electronics, a greater understanding of size effects on Tg is warranted. Here, we investigate the effect of soft and hard three-dimensional confinement on the Tg of polymer nanoparticles. Via modulated differential scanning calorimetry, we show that Tg decreases with size for bare polymer nanoparticles, i.e., the case of soft confinement while Tg is invariant with size for silica-capped polymer nanoparticles, i.e., the case of hard confinement. These results suggest that the free surface is a key factor in Tg reductions of three-dimensionally confined polymer. [Preview Abstract] |
Thursday, March 24, 2011 1:15PM - 1:27PM |
W44.00011: Statics and dynamics of confined DNA in a nanopit array Alexander Klotz, Walter Reisner Polymers have been proposed as tools for self-assembly in nanotechnology. There is interest in controlling the movement and conformation of the polymers by modifying the free energy landscape of their environment. It is necessary to understand the free energy and equilibrium behavior of a polymer in a nanoscale environment in order to control its dynamics. In these experiments, DNA molecules are placed in slits on the order of 100 nanometers. The slits are embedded with a lattice of square pits that act as entropic traps for which it is energetically favorable for the DNA to occupy. Based on the geometric properties of the lattice, the molecule in equilibrium will occupy a discrete number of pits. The dynamics of the system can be understood in terms the number of occupied pits. A partition function based on these states can be used to make testable predictions. Measurement of the static conformations of DNA in these pits, as well as the diffusion of the molecule throughout the lattice, as a function of geometric parameters can be used to test models of polymer free energy. Measurements show that the mean occupancy state scales as expected with various pit parameters. Early diffusion results indicate that the diffusion of DNA can be fine tuned by modifying the topography. [Preview Abstract] |
Thursday, March 24, 2011 1:27PM - 1:39PM |
W44.00012: Modeling of Free Radical Polymerization of Methyl Methacrylate (MMA) in Nanoporous Confinement Fatema Begum, Sindee Simon Nanoconfinement of methyl methacrylate free radical polymerization is known to impact the molecular weight and molecular weight distribution of the polymer produced, and the results in the literature generally indicate an increase in molecular weight and a concommitant decrease in polydispersity index. In the present work, the mathematical model described by Verros et al. (2005) for free radical bulk polymerization of methyl methacrylate is extended to account for polymerization in nanopores. The model of Verros et al. (2005) incorporates diffusion effects and is capable of describing the conversion and the number- and weight-average molecular weights of the resulting poly(methyl methacrylate) as a function of polymerization time and process conditions. The model is extended by incorporating the effect of nanoconfinement on diffusivity using the scaling reported in the literature. The results indicate that nanoconfinement will lead to higher molecular weights, lower polydispersity, and the gel effect occurs earlier. The results are compared to experimental work and implications discussed. [Preview Abstract] |
Thursday, March 24, 2011 1:39PM - 1:51PM |
W44.00013: Effect of Nanopore Confinement on the Polymerization Rate of Linear Polymers Po-Han Lin, Rajesh Khare Confinement to a nanopore has a significant impact on the thermal properties as well as the rate of chemical reactions such as polymerization as compared to these processes in the bulk. In this work, we have studied the effect of nanopore confinement on the rate of free radical polymerization by using molecular simulations. In order to capture the physics of this process, we have implemented a coarse-grained model to carry out reactive molecular dynamics simulations. Our simulation method considers the three stages of polymerization process: initiation, propagation and termination. Our simulation results will be used to compare the polymerization rate in the confinement with that in the bulk. The results will be explained by focusing on the dynamics of the reacting species in the confinement. [Preview Abstract] |
Thursday, March 24, 2011 1:51PM - 2:03PM |
W44.00014: Theoretical Study of Tethered Polymers inside a Cylindrical Tube Tongchuan Suo, Mark Whitmore We present a numerical self-consistent mean-field theoretical (SCMFT) study of polymer chains tethered to the inside walls of cylindrical tubes. We consider cases ranging from relatively thin to relatively thick tubes, from low to high tethering densities, and in various solvents. Our focus is on the polymer concentration profiles and the chain end distributions, in particular the concentrations and chain overlap at the tube centers. We show that these quantities depend primarily on only two parameters, and that this dependence becomes exact in the limit of low polymer concentration. We find that there can be significant polymer interpenetration at the tube centers even in cases where the tube radius is greater than the polymer $R_{\rm g}$, and this can be tuned by changing the solvent quality and/or tethering density. [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. |
© 2025 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