Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V10: Polymers Adsorbed onto Solids - Interplay Among Structures, Dynamics, and Properties IIFocus
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Sponsoring Units: DPOLY Chair: Tad Koga, Stony Brook University Room: 269 |
Thursday, March 16, 2017 2:30PM - 3:06PM |
V10.00001: How irreversible adsorption affects segmental dynamics and glass transition temperature Invited Speaker: Simone Napolitano Growing experimental evidence shows that the behavior of thin polymer layers strongly depends on the degree of adsorption, the number density of monomers pinned onto the supporting substrate. Several groups have independently observed that properties as wettability, viscosity and thermal expansion are affected by prolonged annealing in the liquid state, even at timescales exceeding the equilibration time of a bulk melt. In this talk, after introducing the physics behind the mechanisms of irreversible adsorption, I shall review some of these observations, focusing on those related to the thermal glass transition and to the segmental dynamics. Based on the information collected on several polymers, I will discuss on different models that could explain the origin of the striking correlation between the value of the glass transition temperature of 1D confined polymers and the degree of adsorption. After presenting new results on the interplay between segmental dynamics and formation of adsorbed layers, I will demonstrate that, differently than what currently speculated, the transformations materials undergo during adsorption do not mimic physical aging. A new molecular mechanism is proposed. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V10.00002: Dynamics of Poly(methyl methacrylate) and Polystyrene Thin Films on Hydrophobic and Hydrophilic Surfaces Mesfin Tsige While an extensive literature dealing with the structure and dynamics of polymers at surfaces and interfaces exist, there has been a paucity of information regarding the length scale of the influence of the surface on polymer mobility and its dependence on polymer-surface interaction. To address this issue, we have investigated using molecular dynamics simulations the dynamics of PMMA and PS films of similar system sizes on two different surfaces as a function of film thickness, polymer molecular weight, and temperature. The dynamics of the polymer chains in the film on two different surfaces will be discussed in the context of a three-layer model. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V10.00003: Thin Film Stability of Polystyrene with a Functional End Group Keiji Tanaka, Shinichiro Shimomura, Manabu Inutsuka, Koichiro Tajima, Masaaki Nabika, Satoru Moritomi, Hisao Matsuno The thin film stability of omega-$N$-(3-(dimethylamino)propyl)propylamide-terminated polystyrene (PS-N) and its mixture with conventional polystyrene (PS-H) spin-coated on silicon wafers with a native oxide layer was studied. While a 20 nm-thick film of PS-H with a number-average molecular weight of approximately 50k was broken at 423 K, a comparable PS-N film and blend films with a PS-N fraction higher than 40 wt{\%} were stable. Although the local conformation of chains at the substrate interface was not the same for PS with/without the functionalized terminal group, the glass transition temperature at the interface was identical for PS-H and PS-N. The residual adsorbed layer on the substrate after washing the films with toluene was thicker for PS-N than for PS-H. This implies that the end functionalization impacts chain movement on a large scale rather than via segmental dynamics. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V10.00004: Modifying Effects of Plasticizer, Chain Connectivity, and Chain Adsorption on the Physical Aging and Interfacial Gradient in Dynamics in Thin Polystyrene Films Michael Thees, Connie Roth How the glass transition and physical aging in thin films change with confinement is nontrival, with studies in the literature showing that these effects can be modified by various factors including chain adsorption to substrate interfaces and addition of diluents. Some studies indicate that addition of plasticizer appears to eliminate confinement effects such as Tg gradients and possibly impacts chain adsorption to substrates. In contrast, how plasticizer affects physical aging in glassy polymers has been largely unexplored experimentally, despite various theoretical and simulation efforts. Previously we have shown that for neat polystyrene (PS) films, with molecular weights MW < 3000 kg/mol, physical aging rates in thin films decrease with decreasing film thickness consistent with expectations from local Tg gradients. However, we have recently found that for very high molecular weights, MW > 7000 kg/mol, the physical aging rate in thin films was more bulk like, suggesting a diminished gradient in dynamics related to chain connectivity and possibly chain adsorption to the substrate interface. Here, we explore how the addition of dioctyl phthalate (DOP) plasticizer to PS can alter the physical aging rate of thin films and possibly modify the adsorbed layer. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V10.00005: Polymer-Substrate Interactions in Irreversible Adsorption Mary J. Burroughs, Rodney D. Priestley Annealing a supported polymer film in the melt state, a common practice to relieve residual stresses and clear thermal history, results in the growth of an irreversibly adsorbed layer. This layer of polymer chains physically adsorbed to the substrate has been shown to influence thin film properties such as diffusion and glass transition temperature. Its growth is attributed to many simultaneous interactions between individual monomer units and the substrate, stabilizing chains against desorption. This suggests that specific polymer-substrate interactions influence its development. A better understanding of how these interactions influence the growth and properties of the adsorbed layer is needed, particularly given how strongly the properties of confined polymeric systems are impacted by their interfaces. We strive to give insight into how these different interaction strengths influence the growth and behavior of the adsorbed layer. Both homopolymers and random copolymers are used to examine the influence of chemical composition and resulting polymer-substrate interactions on the growth and structure of these adsorbed layers. Understanding the implications of annealing and their variation with polymer-substrate interactions is essential in determining proper selection and processing of polymer thin films for applications. [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V10.00006: Modifying Surface Fluctuations of Polymer Melt Films with Substrate Modification Yang Zhou, Qiming He, Fan Zhang, Feipeng Yang, Suresh Narayanan, Guangcui Yuan, Ali Dhinojwala, Mark Foster Deposition of a plasma polymerized film on a silicon substrate changes surface fluctuations of a sufficiently thin, glass-forming film on the substrate. X-ray photon correlation spectroscopy measurements show that the surface fluctuations on a 43 nm thick melt film of 131 k linear polystyrene (PS) on a silicon wafer can be described using a hydrodynamic continuum theory (HCT) that assumes the film is characterized by the bulk viscosity. When a plasma polymerized layer is placed on the silicon wafer, the same is seen for a 43 nm film. However, when film thickness is reduced to 32 nm, the fluctuations are slower than predicted by the HCT. The confinement effect for PS on silicon is larger than that for PS on the plasma polymerized film. We attribute this to the variation in the thickness of a bound layer at the substrate with the surface chemistry of the substrate. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the DOE's Office of Science under Contract DE-AC02-06-CH11357. DoD funding provided through the TCC ({\#}FA7000-14-2-20016). [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V10.00007: Two-dimensional phase separated structures of block copolymers on solids Mani Sen, Naisheng Jiang, Maya Endoh, Tadanori Koga, Alexander Ribbe The fundamental, yet unsolved question in block copolymer (BCP) thin films is the self-organization process of BCPs at the solid-polymer melt interface. We here focus on the self-organization processes of cylinder-forming polystyrene-block-poly (4-vinylpyridine) diblock copolymer and lamellar-forming poly (styrene-block-butadiene-block-styrene) triblock copolymer on Si substrates as model systems. In order to reveal the buried interfacial structures, the following experimental protocols were utilized: the BCP monolayer films were annealed under vacuum at T\textgreater $T_{\mathrm{g}}$ of the blocks (to equilibrate the melts); vitrification of the annealed BCP films via rapid quench to room temperature; subsequent intensive solvent leaching (to remove unadsorbed chains) with chloroform, a non-selective good solvent for the blocks. The strongly bound BCP layers were then characterized by using atomic force microscopy, scanning electron microscopy, grazing incidence small angle X-ray scattering, and X-ray reflectivity. The results showed that both blocks lie flat on the substrate, forming the two-dimensional, randomly phase-separated structure irrespective of their microdomain structures and interfacial energetics. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V10.00008: Monte Carlo Simulation of Polymer Adsorption on Rough Substrates Vikram Kuppa, Abishek Venkatakrishnan Polymer films adsorbed on atomistically smooth substrates have been studied for decades, but little is known about adsorption on surfaces displaying both physical and chemical inhomogeneities. Such interfaces are more realistic, and exhibit rich behavior arising from intricate relaxation processes. Focusing on physical irregularities, we investigate the molecular mechanisms governing chain adsorption. Monte Carlo simulations are employed to study the freely rotating chains adjacent to self-affine substrates, exploring the influence of surface fractal dimension and amplitude. The adsorbed polymers are characterized by density and orientation profiles, adsorbed fraction and chain topologies. Our results reveal chain attachment and film structure can be controlled solely by manipulating entropic factors such as surface physical heterogeneities and adsorbate molecular weight distributions. The correlation between adsorbed chain fraction and surface topology is revealed, and shows a counter-intuitive and non-monotonic dependence on roughness. [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V10.00009: Structure of Irreversibly Adsorbed Star Polymers Bulent Akgun, Meryem Seyma Aykan, Seda Canavar, Sushil K. Satija, David Uhrig, Kunlun Hong Formation of irreversibly adsorbed polymer chains on solid substrates have a huge impact on the wetting, glass transition, aging and polymer chain mobility in thin films. In recent years there has been many reports on the formation, kinetics and dynamics of these layers formed by linear homopolymers. Recent studies showed that by varying the number of polymer arms and arm molecular weight one can tune the glass transition temperature of thin polymer films. Using polymer architecture as a tool, the behavior of thin films can be tuned between the behavior of linear chains and soft colloids. We have studied the effect of polymer chain architecture on the structure of dead layer using X-ray reflectivity (XR) and atomic force microscopy. Layer thicknesses and densities of flattened and loosely adsorbed chains has been measured for linear, 4-arm, and 8-arm star polymers with identical total molecular weight as a function of substrate surface energy, annealing temperature and annealing time. Star polymers have been synthesized using anionic polymerization. XR measurements showed that 8-arm star PS molecules form the densest and the thickest dead layers among these three molecules. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V10.00010: Structure and Dynamics of Thin Polyacrylate Gel Films Supported on a Polymeric Substrate Sriramvignesh Mani, Rafikul Islam, Rajesh Khare Recently, we have used molecular dynamics (MD) simulations to demonstrate the viability of polyacrylate gel membranes for pervaporation based separation processes. In practice, these polymeric membranes are usually in the form of thin films that are supported on another polymeric substrate such as polysulfone or cellulose acetate. The structure and dynamics of the polymer constituting the membrane play an important role in governing the separation efficiency of these membranes. Since chain structure and dynamics in supported polymer thin films deviate significantly from their bulk values, it is necessary to understand the effect of the soft polymeric support on the properties of the polymer constituting the membranes. In this work, the structural and dynamic properties of polyacrylate gels that are supported on polysulfone are studied using molecular simulations. Specifically, three different networks formed by poly butyl acrylate (PBA), 50-50 random copolymer of butyl acrylate and 2-hydroxy ethyl acrylate (P(BA50-HEA50)), and poly 2-hydroxyethyl acrylate (PHEA) are considered. The properties of the supported thin film gel systems are characterized by determining the gel structure, glass transition temperature, and chain dynamics. The effect of the polysulfone support on the system behavior is determined by comparing the properties of the supported thin films systems with those of the bulk gel systems. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V10.00011: Functionality of Chloroform Treatment to Improve Adhesion of Deposited Au Thin Films on PMMA Luis Royo Romero The deposition of Au thin films onto polymer surfaces is a crucial step in the fabrication of a variety of microfabricated devices including displays, microelectronics, biomedical and microfluidic devices. Au is characterized by having high electrical and thermal conductivity making it a good choice for micro-electrodes. However, due to its relative chemical inertness, it is difficult to fabricate on polymeric substrates due to the low adhesion to polymer's surface. Previous experiments have studied various methods to improve the adhesion of vapor-deposited Au thin films onto poly (methylmethacrylate) (PMMA). In this study, we deposit 14 nm of Au onto 1.50 mm thick PMMA via magnetron sputter deposition and exposed the samples to a chloroform vapor in a chamber at 70\textdegree C using a hot plate. The force required to remove the Au thin film is quantified as a function of the polishing force and the transmittance acquired using UV-VIS spectroscopy. Conducive of data confirming the effectiveness of chloroform post-treatment, we conducted a study on selective pattering by isolating regions using PDMS masks and attaining quantitative data by pixel counting using a Matlab script. Both methods demonstrate a similar inverse relation, the reduction of Au on the PMMA as incremental of applied force, displaying the potency of chloroform exposure. [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V10.00012: Studying polymer films deposited on solid surfaces using generic microscopic and mesoscopic soft models Jianguo Zhang, Debashish Mukherji, Kurt Kremer, Kostas Daoulas Polymer films deposited on solid substrates are fundamentally interesting and have tremendous industrial applications. We develop a particle-based soft model where polymers are represented as worm-like chains, while non-bonded interactions are defined via a simple density functional[1]. The form of the functional and the values of involved parameters are specified taking into account certain thermodynamic properties known from experiments, e.g. phase-equilibria data. Films of poly(methyl methacrylate) adsorbed on silica are chosen as a test system. The soft model is validated by direct comparison with smaller scale simulations based on a generic microscopic model representing the same system. To compare the two models, we study chain-shape, structure of the adsorbed layer, as well as the statistics of loops, tails, and trains. The two models are found to be consistent with each other. Some deviations observed in polymer conformations and structure of adsorbed layer can be rationalized by the simplified description of polymer/surface interactions and local liquid packing in the soft model. [1] J. Zhang, D. Mukherji, and K. Daoulas, Eur. Phys. J. Special Topics 225, 1423 (2016) [Preview Abstract] |
Thursday, March 16, 2017 5:18PM - 5:30PM |
V10.00013: Kinetics of Chain Collapse Induced by Adding Non-Solvent zhengnan yang, Ali Dhinojwala Previous studies have shown that decreasing the temperature of dilute polymer solution below theta condition results in a coil-to-globule transition. This kinetics of this transition involves a formation of a sausage-shaped structure which collapses to a globule (two-stage transition). Here, we have studied this coil-to-globule transition by adding a non-solvent (water) into a solution containing high molecular weight poly(methyl methacrylate) (PMMA) in THF. By measuring radius of gyration and hydrodynamic radius, we found a three-stage transition finally forming a multi-chain globular aggregate. We will discuss the kinetics of this transition as a function of concentration of non-solvent and molecular weight. [Preview Abstract] |
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