Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A17: Dynamics of Glassy Polymers Under Nanoscale Confinement IFocus Recordings Available
|
Hide Abstracts |
Sponsoring Units: DPOLY DSOFT DCP Chair: Danielle Cangaliosi, University of the Basque Country Room: McCormick Place W-184BC |
Monday, March 14, 2022 8:00AM - 8:36AM |
A17.00001: Dynamics of Glassy Polymers Under Nanoscale Confinement Invited Speaker: Ophelia Tsui Myriads of studies have shown that glassy polymers under nanoscale confinement demonstrate changes in the dynamic properties with the size of confinement. For polymers confined in nanometer films, overwhelming evidence has shown that the thickness dependences found of the dynamic properties are caused by perturbations to the local dynamics of the polymer by the interfaces of the films. The dynamics ultimately displayed by a film is determined by the overarching effect of the two interfaces. In this talk, I will focus on how the effects of the two interfaces combine to produce changes to the whole-film dynamics as revealed by recent experiments conducted by our group on the glass transition temperature and effective viscosity of thin films of random copolymers [1,2] and polymers chemically mildly modified by ultra-violet ozone treatment [3-5]. Cases where the dynamics at one interface is modified by the opposite one will be emphasized to highlight the need to consider the interplay between the effects of the two interfaces to fully understand the dynamics of glassy polymers under nanoscale confinement. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A17.00002: Structure and Dynamics of Star-polymer/Polymer Composites Cesar A Castro, Francis Starr
|
Monday, March 14, 2022 8:48AM - 9:00AM |
A17.00003: Irreversible Adsorption in Polymer Nanocomposites Perturbs Local Tg and Dynamics Katelyn Randazzo, Rodney Priestley, Biao Zuo Irreversible adsorption can occur at a polymer-substrate interface when a polymer is annealed above its Tg—a standard step in the preparation of polymer-based systems. While irreversible adsorption has been demonstrated to significantly perturb local and bulk glassy properties in thin films, detailed investigations have yet to extend to more complex systems such as polymer nanocomposites, where the evolution and consequences of irreversible adsorption remain largely uninterrogated due to limitations imposed by indirect characterization methods. In this study, we demonstrate a novel approach combining stepwise assembly of polymer nanocomposites—that is, sequential preparation of adsorbed and unadsorbed regions—with direct characterization techniques such as transmission electron microscopy and fluorescence spectroscopy. This approach enables direct access to local features and dynamics of irreversibly adsorbed layers within nanocomposites, affording detailed measurements of layer thickness and Tg. Our approach is generalizable to diverse polymer-nanoparticle pairings and can be extended to probe a range of local properties, including governing chain dynamics. The insights provided by this work may inform the design of sophisticated new materials with desirable properties. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A17.00004: Effect of SiO2 on polymer dynamics in PEO / nanocomposites: A combined experimental and computational approach Spiros H Anastasiadis, Kiriaki Chrissopoulou, Eleni Papananou, Albert J Power, Anastassia Rissanou, Vagelis Harmandaris, Massimiliano Labardi The dynamics of polymers in PEO / SiO2 nanocomposites is investigated experimentally utilizing dielectric relaxation spectroscopy (DS) over a broad range of frequencies and for temperatures both below and above the glass transition temperature, Tg, of the neat polymer. Different compositions were chosen to cover the range from a dilute in nanoparticles (NP) system up to one where the chains are severely confined. The sub-Tg local and the segmental relaxations of the neat PEO are identified in the hybrids, as well. A very weak effect on polymer dynamics is observed in contrast to the effect on PEO conformations or crystallinity observed for these systems. In parallel, atomistic molecular dynamics (MD) simulations have been performed in equivalent systems to predict the polymer dynamic behavior and correlate it to the experimental findings. The segmental relaxation and the center of mass translational dynamics of PEO chains close to the SiO2 NP are slower compared to the bulk. Moreover, the orientational dynamics of PEO at the PEO/SiO2 interphase is found to be slower and more heterogeneous (broader distribution of relaxation times) when compared to the bulk one. Similarities and differences between the experimental and theoretical findings are discussed. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A17.00005: Conflicting role of plasticization in nanorheology of out-of-equilibrium thin polystyrene films Mithun Chowdhury, Mithun Madhusudanan, Jotypriya Sarkar We have explored dewetting hole growth dynamics in high molecular weight polystyrene (PS) thin films plasticized by dioctyl phthalate (DOP). Addition of varying amounts of plasticizer reveals an interesting interplay with elasticity and viscosity beyond existing belief. While dewetting speed in plasticized films is enhanced via a possible decrease in viscosity of PS, its early stage thermal response leads to a scenario that can only be explained through enhanced molecular recoiling stress and interfacial friction or in other way, reduction in modulus in the plasticized film. While decoupling above effects is challenging, we have tentatively explained our observations on the possible roles of plastization, antiplasticization and nonequilibrium polymer chain conformations, perturbing nanorhelogy of such plasticized films. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A17.00006: Activation free energy gradient controls interfacial mobility gradient in thin polymer films Jack F Douglas, Francis Starr, Wengang Zhang We examine the mobility gradient in the interfacial region of substrate-supported polymer films using molecular dynamics simulations and interpret these gradients within the string model of glass-formation. No large gradients in the extent of collective motion exist in these simulated films, and an analysis of the mobility gradient on a layer-by-layer basis indicates that the string model provides a quantitative description of the relaxation time gradient. Consequently, the string model indicates that the interfacial mobility gradient derives mainly from a gradient in the high-temperature activation enthalpy ΔH and entropy ΔS as a function of depth z, an effect that exists even in the high-temperature Arrhenius relaxation regime far above the glass transition temperature. To gain insight into the interfacial mobility gradient, we examined various material properties suggested previously to influence ΔH in condensed materials, including density, potential and cohesive energy density, and a local measure of stiffness that is the average mean squared particle displacement at a caging time (on the order of a ps). We find that changes in local stiffness best correlate with changes in ΔH(z) and that ΔS(z) also contributes significantly to the interfacial mobility gradient, so it must not be neglected |
Monday, March 14, 2022 9:36AM - 9:48AM |
A17.00007: Annealing Matters: Shear Wave Propagation through a Dissimilar Polymer-Polymer Interface at MHz Frequencies Measured by QCM Yannic J Gagnon, Justin C Burton, Connie B Roth Recent work by our group has demonstrated that small changes in the composition profile between dissimilar polymer domains associated with annealing can strongly alter the dynamical coupling across these domains. In contrast, other studies have reported that polymer-liquid interfaces behave similar to the interface between a polymer and a hard substrate. Collecting these ideas, we hypothesize that the mechanism underlying strong dynamic coupling across dissimilar polymer-polymer interfaces may be related to impedance matching, where similar moduli and densities and larger interfacial widths translate to more transmission of phonon modes or acoustic waves through the interface. We show using a quartz crystal microbalance (QCM) that MHz-frequency shear waves are transmitted differently through a polystyrene (PS) / poly(n-butyl methacrylate) (PnBMA) interface depending on whether the interface has been minimally annealed or annealed to equilibrium. Using a simple continuum model of shear wave reflection from an interface, we show that the data are inconsistent with the notion of only the compositional interfacial width increasing, and that there is likely a longer-ranged altered viscoelastic profile produced during the interface annealing. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A17.00008: How the polymer electrolyte PEO/LiTFSI penetrates narrow pores George Floudas, Chien-Hua Tu, Hans-Juergen Butt We investigate if and how the ionic conductivity and chain mobility of a polymer electrolyte is affected during imbibition and following imbibition in nanopores. To this end, the archetypal polymer electrolyte poly(ethylene oxide) (PEO)/LiTFSI is employed and nanoporous alumina is the confining medium. Overall the results of the evolution of conductivity in the PEO/LiTFSI polymer electrolytes suggest that the time-dependence of dc-conductivity during flow is dictated by the adsorption of polymer chains at the pore walls. They further show that at the early stages of imbibition the effective viscosity is reduced below the bulk value. It seems that at such early stages the pore walls act as lubricants for the chain segments and ions. At much later stages, polymer adsorption takes place. The time scale of adsorption is very long—much longer than chain diffusion and certainly much longer than the segmental relaxation. Adsorption involves several unfavorable configurations of the polymer chains that inevitably affect the ion dynamics by (i) increasing the effective viscosity (higher Tg) and (ii) by reducing the number of mobile ions. These results are important in the design of confined polymer electrolytes. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A17.00009: Impact of Covalently Attached Model Probes on Polymer Physical Properties - a Quantitative Assessment Mikaela Sadri Understanding polymer thin films and their properties is an important part of polymer physics however, many bulk characterization techniques cannot be easily applied to thin films. Therefore, using molecular probes is a common approach. Particularly, dyes are often employed to investigate polymer dynamics and structures, such as single-particle tracking, super-resolution optical imaging, and polymer glass transition temperature (Tg). A common assumption in these systems is that the inclusion of dilute amounts of fluorophore will not, or only minimally, alter the studied material properties. However, this assumption has not been fully validated and the development of advanced imaging techniques requires the use of higher concentration and/or larger dyes, making it necessary to systematically investigate their impact on polymer systems. This work focuses on quantitatively understanding the impact of molecular probes on chain conformation and Tg (bulk and thin film) using amino pyrene and Sudan IV covalently attached to high and low molecular weight polymer model systems, assessed over a wide range of concentrations. This research will inform the efficient use of molecular probes for understanding polymer physics. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A17.00010: Thermal and UV stability of organic glasses under extreme nanoconfinement Yueli Chen, Haonan Wang, Ahmad A Abadi, Zahra Fakhraai Extreme nanoconfinement of organic glasses can be achieved by Capillary Rise Infiltration onto self-assembled films of nanoparticles (NPs). Here we investigate thermal and UV degradations of highly confined indomethacin (IMC, Tg = 316 K) in silica NPs (3 – 30 nm average pore sizes). Upon confinement in ~ 3 nm pores, a Tg increase of ~ 30 K is observed along with a factor of ~ 7 slow-down of thermal degradation rate at elevated temperatures (Tg +137 K) under N2. These observations are consistent with previous measurements in polystyrene, where thermal stability was correlated with Tg increase. UV degradation under both low O2 and ambient conditions was explored at room temperature (Tg - 20 K). We show that the interplay between entropic and enthalpic effects under extreme nanoconfinement also leads to substantial stability towards UV degradation, however the details highly depend on the specific reaction pathways under these two conditions, both of which are kinetically limited by the transport of O2 and/or CO2. UV degradation mass loss rate is slowed down by a factor of ~ 20 (at 365 nm) under ambient conditions, while mass loss is only observed at the near surface region of the composites at low O2 condition (at 254 nm). |
Monday, March 14, 2022 10:24AM - 10:36AM |
A17.00011: Gradient of Segmental Dynamics in Stereoregular Poly(Methyl Methacrylate) Melts Confined Between Pristine or Oxidized Graphene Sheets Alireza Foroozani Behbahani, Vagelis Harmandaris Segmental dynamics in unentangled isotactic, syndiotactic, and atactic poly(methyl methacrylate) (i-, a-, and s-PMMA) melts confined between pristine graphene, reduced graphene oxide, or graphene oxide sheets is studied at different temperatures, via atomistic molecular dynamics simulations. The segmental dynamics is studied through the analysis of backbone torsional motions. Upon decreasing temperature, the ratios of the interfacial segmental relaxation times to the respective bulk relaxation times increase, revealing a stronger temperature dependence of the interfacial segmental dynamics relative to the bulk dynamics. The alteration of the segmental dynamics at different distances, d, from the surfaces is described by a temperature shift, △Tseg(d) (roughly speaking, shift of a characteristic temperature). Next to a given nanosheet, i-PMMA has a larger value of △Tseg(d) than a-PMMA and s-PMMA. This trend correlates with the better interfacial packing and longer trains of i-PMMA chains. The backbone torsional autocorrelation functions are shown in the frequency domain and are qualitatively compared to the experimental dielectric loss spectra for the segmental α-relaxation in polymer nanocomposites. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A17.00012: How Do End-Tethered Chains Alter the Local Glass Transition Temperature Next to Solid Substrates? James H Merrill, Carl Li, Connie B Roth
|
Monday, March 14, 2022 10:48AM - 11:00AM |
A17.00013: Polymer / graphite oxide nanocomposites before and after thermal reduction Kiriaki Chrissopoulou, Krystalenia Androulaki, Spiros H Anastasiadis, Massimiliano Labardi Nanocomposites of hyperbranched polymers with graphitic materials are investigated with respect to their structure, thermal properties as well as the dynamics of the polymer. Three generations of hyperbranched polyester polyols are mixed with graphite oxide, GO, and the favorable interactions between the polymers and the surfaces lead to intercalated structures. The thermal transitions of the confined chains are suppressed, whereas their dynamics show similarities and differences with the dynamics of the neat polymers. The three relaxation processes observed for the neat polymers are observed in the nanohybrids as well, however with different temperature dependencies. Thermal reduction of the graphite oxide in the presence of the polymer to produce reduced graphite oxide, rGO, reveals an increase of the reduction temperature accompanied by a decreased thermal stability of the polymer. The de-oxygenation of the graphite oxide leads to the destruction of the intercalated structure and to the dispersion of the rGO layers within the polymeric matrix because of the modification of the interactions between the polymer chains and the surfaces. A significant increase of the conductivity of the resulting nanocomposites, in comparison to both the polymers and the intercalated nanohybrids, indicates the formation of a percolated rGO network. Acknowledgements: This research has been financed by FORTH Synergy Grands-project PlaNet. |
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