Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K54: Confined Polymer Glasses II: Dynamics, Surface Effects, and ArchitectureFocus
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Sponsoring Units: DPOLY GSOFT GSNP Chair: George Floudas, University of Ioannina Room: BCEC 254A |
Wednesday, March 6, 2019 8:00AM - 8:12AM |
K54.00001: β-NMR Studies of the Depth Dependence of Secondary Relaxations in Polystyrene Thin Films Iain McKenzie, Yu Chai, David Cortie, James Forrest, Derek Fujimoto, Victoria Karner, Robert F Kiefl, CDP Levy, W Andrew MacFarlane, Ryan McFadden, Gerald D Morris, Matthew Pearson, Adam Raegen, Shipei Zhu β-detected nuclear magnetic resonance (β-NMR) of implanted 8Li+ has been used to probe the depth dependence of secondary relaxation processes in thin films of atactic polystyrene (PS). β-NMR measurements of the average 8Li spin-lattice relaxation rate were used to determine the depth dependence of the fluctuation rate of the fast γ-relaxation process in PS films at 317 K, which is well below its glass transition temperature [I. McKenzie et al. Soft Matter, 14, 7324 (2018)]. A novel hole-burning (selective saturation) β-NMR technique has been used to measure the depth dependence of the fluctuation rate of the much slower β-relaxation process at the same temperature. Both the fluctuation rates of the β- and γ-relaxation processes are larger near the free surface than in the bulk and both return to the bulk value over a length scale of several nm. |
Wednesday, March 6, 2019 8:12AM - 8:24AM |
K54.00002: Reducing the Tg-Confinement Effect in Polystyrene Films by Use of Carbon Substrates and Changing the Direction of the Effect in Polystyrene-Carbon Model Nanocomposites John Torkelson, Lawrence Chen Using ellipsometry and fluorescence, we have shown that single-layer polystyrene (PS) films supported on carbon substrate exhibit suppression of the classic Tg-confinement effect due to favorable polymer-substrate interactions. Additionally, a bilayer film/fluorescence study has shown that in a bulk PS film, the 15 nm layer at the carbon interface exhibits a Tg nearly 10 K higher than bulk. The ability of PS to favorably interact at the interface with the graphitic substrate (versus silicon dioxide) was demonstrated qualitatively via a dewetting study. Because PS does not naturally wet the native oxide layer on silica, a thin 30-nm-thick, 30 kg/mol PS film readily dewets when annealed at 433 K. However, dewetting of supported thin PS films is greatly suppresses using substrates with favorable interfacial interaction with PS. Model nanocomposites were also made by sputtering a graphitic layer above PS films supported on carbon, sandwiching the film between two graphitic surfaces and providing a consolidated film with constant interlayer distance between the two hard surfaces after annealing. Single-layer PS films in this model nanocomposite geometry exhibit enhanced Tg with decreasing nanoscale thickness due to pi-pi bonding interactions of PS with the graphitic substrates. |
Wednesday, March 6, 2019 8:24AM - 8:36AM |
K54.00003: Polymer dynamics under 2D nanometer confinement George Floudas, Christos Politidis, Stelios Alexandris, Martin Steinhart The effect of confinement on polymer dynamics and the associated liquid-to-glass temperature, Tg, has been an issue of great interest in polymer physics. In this study, we investigate the effect of nanometer confinement on the dynamics of several polymers including cis-1,4-polyisoprene with molecular weights both below and above the entanglement limit. As confining medium we employ self-ordered nanoporous alumina (AAO) with diameters, d, ranging from 400 nm to 25 nm resulting in a broad 2Rg/d range. We employ Broadband Dielectric Spectroscopy (BDS) and Temperature-Modulated Differential Scanning Calorimetry (TMDSC). BDS revealed consistently faster segmental dynamics under confinement with respect to the bulk, leading to a decrease in Tg with increasing degree of confinement (2Rg/d). This is discussed in terms of the role of interfacial energy. In addition, we provide evidence for an intermediate process with an Arrhenius temperature dependence whose dielectric strength increases with increasing degree of confinement. These results are discussed in view of recent theoretical and experimental progress in understanding polymer imbibition in nanopores. |
Wednesday, March 6, 2019 8:36AM - 9:12AM |
K54.00004: Irreversible adsorption: new insights on molecular mobility, thermodynamics and interfacial interactions Invited Speaker: Simone Napolitano Irreversibly adsorbed polymer layers represent an intriguing class of novel nanomaterials with unexpected properties, strongly deviating from what observed in unbounded polymer melts. These extremely thin films are obtained via a small number of successive steps, easily reproducible: a polymer melt is placed in contact with an adsorbing substrate and nonadsorbed chains are washed away in a good solvent. Importantly, tuning the thickness of the adsorbed layer, an operational parameter equivalent to the number of chains adsorbed on a unit surface, allows modifying the interfacial free volume content and, hence, the performance of polymer coatings without affecting the interfacial chemistry. |
Wednesday, March 6, 2019 9:12AM - 9:24AM |
K54.00005: Confinement Effects on Dye Translational Diffusivity in Polystyrene Thin Films Depend on Polymer Molecular Weight: Connection to Fragility-Confinement Effects Tong Wei, Tian Lan, John Torkelson The impact of confinement on the translational diffusivity, Ddye, of small-molecule dye 9,10-bis(phenylethynyl)anthracene is studied in supported, thin films by fluorescence. Relative to bulk films and near Tg, Ddye is reduced by 80 - 90% in 100-nm-thick, high molecular weight (MW) PS (400 kg/mol) films. In contrast to Tg, which reflects the slow portion of the cooperative segmental relaxation distribution, Ddye reflects the fast relaxation regions, which can be many orders of magnitude faster than slow regions. Ddye results are associated with fragility, which reflects the relaxation distribution breadth, and its confinement effects: with sufficient confinement, the relaxation distribution narrows (and high MW PS fragility decreases) with the fast relaxation tail becoming slower, leading to a decrease in Ddye. In yet thinner films, the slow relaxation regions become faster, decreasing Tg. Because low MW PS (6 kg/mol) exhibits a lower bulk fragility than high MW PS, confinement has a much-reduced effect on low MW PS fragility, and both fragility and Ddye in 100-nm-thick low MW PS films are unchanged from bulk. |
Wednesday, March 6, 2019 9:24AM - 9:36AM |
K54.00006: Comparing Refractive Index and Density Changes with Decreasing Film Thickness in Thin Supported Films Across Different Polymers Yixuan Han, Connie Roth Density or specific volume changes in thin films have been investigated in relation to glass transition and other property changes with decreasing film thickness. Often such density changes are inferred from values of the refractive index through the Lorentz-Lorenz equation. Our group’s previous work on supported polystyrene (PS) films concluded that recently reported large changes in apparent film density are likely erroneous because assumptions in the derivation of the Lorentz-Lorenz relation become invalid for thin films less than ~20 nm. Unexpected non-monotonic changes in refractive index with decreasing thickness were observed for PS films as measured by spectroscopic ellipsometry. Here we compare these PS results to similar measurements of refractive index on poly(2-vinylpyridine) (P2VP) and poly(methyl methacrylate) (PMMA) supported films, polymers typically associated with attractive substrate interactions. Surprisingly, we find P2VP shows identical thickness-dependent refractive index changes to PS, with a more muted behavior for PMMA. We explore whether such trends arise from alignment of monomers near the substrate interface by measuring substrates with different surface chemistries. |
Wednesday, March 6, 2019 9:36AM - 9:48AM |
K54.00007: Prediction of the Structural Relaxation Time from Vibrational Dynamics in Thin Films Andrea Giuntoli, Matteo Becchi, Dino Leporini The structural relaxation time of glass forming liquids correlates with the cage vibrational dynamics at the picosecond, making it possible to predict one from the other despite a separation of more than ten orders of magnitude in the time scales. |
Wednesday, March 6, 2019 9:48AM - 10:00AM |
K54.00008: How does star polymer architecture affect dynamical heterogeneity? Jinpeng Fan, Hamed Emamy, Alexandros Chremos, Jack Douglas, Francis Starr The formation of an amorphous solid by polymers is one of the most important features for polymer applications. While glass formation of linear chain polymers has been widely explored, comparatively little is known about glass formation of star polymers. We study the dynamical heterogeneity and cooperative nature of star polymer melts via molecular dynamics simulations. In particular, we quantify how the number of arms and the length of those arms affect the collective string-like motion of monomers. We find that, while the star geometry can significantly affect the size and time scale of collective motions, the relationship between the size scale of the collective motions and the overall relaxation time follows the same Adam-Gibbs like relationship previously found to describe simple linear polymers. |
Wednesday, March 6, 2019 10:00AM - 10:12AM |
K54.00009: How does polymer architecture affect the fragility of ultra-thin films? Amber Storey, Wengang Zhang, Jack Douglas, Francis Starr It is widely understood that the glass transition temperature and fragility of thin polymer films can drastically differ from that of the bulk polymer. In this talk, our focus is to show how polymer architecture affects glass formation in thin films, with an emphasis on changes of fragility. We use molecular dynamics simulations to contrast the behavior of coarse-grained supported polymer films of PEO (which has no sidegroup) and PMMA (which does have a sidegroup). The differences between these polymers are most noticeable in the vicinity of the supporting substrate and free interface, where packing consideration are more affected by the polymer architecture. |
Wednesday, March 6, 2019 10:12AM - 10:24AM |
K54.00010: Structure and Dynamics of Bio-Based Polymers in the Bulk and under Confinement Kyriakh Chrissopoulou, Krystalenia Androulaki, Spiros Anastasiadis, Massimiliano Labardi The structure and the dynamics of two bio-based polyester polyols are investigated in the bulk and close to surfaces when the polymers are intercalated within the galleries of a hydrophilic sodium montmorillonite, Na+-MMT. The morphology of the neat polymers as well as the structure of the nanohybrids are investigated with X-ray diffraction and their thermal properties are studied by differential scanning calorimetry. One of the investigated polyesters is amorphous whereas the second one is a semi-crystalline polymer with an intriguing thermal behavior. Hybrids have been synthesized in a broad range of compositions and intercalated structures are always obtained. Dielectric relaxation spectroscopy was utilized to study the polymer dynamics. It revealed multiple relaxation processes for the neat polymers both below and above their glass transition temperatures whereas, in the nanocomposites, similarities and differences are observed depending on the specific mode of dynamic process. The results are compared with the ones of hyperbranched polymers of similar chemistry but non-linear architecture. This research has been co-financed by the Greek General Secretariat for Research and Technology (Action: Roadmap of Research Infrastructures, project INNOVATION EL, MIS: 5002772). |
Wednesday, March 6, 2019 10:24AM - 10:36AM |
K54.00011: The Role of Architecture on the Structure of Irreversibly Adsorbed Polymer Layers Makbule Gizem Kirevliyasi, Sumeyye Ozer, Ayse Caglayan, David Uhrig, Bulent Akgun
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Wednesday, March 6, 2019 10:36AM - 10:48AM |
K54.00012: Direct observation of chain morphology of deoxyribonucleic acid adsorbed on a solid interface Yuma Morimitsu, Hisao Matsuno, Keiji Tanaka Understanding of polymer behavior at a solid interface is of pivotal importance to design and construct highly-functionalized polymer materials and devices. However, it is far away from a sufficient progress for a moment due to experimental difficulties to look at molecular events of a single chain. We here try to observe directly the chain morphology of lambda phage deoxyribonucleic acid (DNA), which is a model system, adsorbed on a solid surface using atomic force microscopy (AFM). This DNA took a random coil conformation in a solution state and the radius of gyration (Rg) determined by small-angle X-ray scattering was 284 nm. AFM samples were prepared by incubating a DNA buffer solution on a substrate, mica disk, for a given time. AFM height image revealed that DNA chains adsorbed on the mica surface took Gauss conformation with an Rg of approximately 400 nm. A possible explanation for this chain expansion at the interface is that the chain was first immobilized on to the mica surface owing to the strong interaction. In presentation, we will discuss quantitatively the adsorption processes of DNA chains at the mica surface. |
Wednesday, March 6, 2019 10:48AM - 11:00AM |
K54.00013: Phase transition of physically confined 2-decanol: effect of bulk Jason L Turner, Caleb Novins, Alexander Clain, Samuel Amanuel We have studies the melting and freezing behaviors of physically confined 2-decanol inside porous silica using a differentials scanning calorimeter. The melting temperature of the confined 2-decanol decreased as the size of the pores confining it decreased in agreement with the Gibbs-Thomson equation. The freezing temperature of the confined 2-decanol, however, was dependent whether there was bulk 2-decanol outside the pores or not. 2-decanol confined in larger pores crystallized using the bulk outside the pores as a nucleating site and went under phase transition at a higher temperature in comparison to 2-decanol confined without bulk. The freezing temperature of 2-decanol confined in smaller pores, however, was not influenced by the presence or lack of the bulk outside the pores. The distinction between the large and small comes from the comparison of melting point of the confined 2-decanol to the freezing point of the bulk 2-decanol. When the melting point of the confined 2-decanol is smaller than the freezing point of the bulk 2-decanol, then the bulk does not act as a nucleation site for the confined 2-decanol. |
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