Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R52: Smart Responsive Polymers IIFocus
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Sponsoring Units: DPOLY Chair: Jasper Michels, Max Planck Institute Room: LACC 512 |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R52.00001: Pressure-Dependence of Poly(N-isopropyl acrylamide) Mesoglobule Formation in Aqueous Solution Bart-Jan Niebuur, Kora-Lee Claude, Simon Pinzek, Coleman Cariker, Konstantinos N Raftopoulos, Vitaliy Pipich, Marie-Sousai Appavou, Alfons Schulte, Christine Papadakis Above their cloud point, aqueous solutions of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) form large mesoglobules. We have carried out very small-angle neutron scattering (VSANS) and Raman spectroscopy experiments on a 3 wt% PNIPAM solution in D2O at atmospheric and elevated pressures (up to 113 MPa) 1. Raman spectroscopy reveals that, at high pressure, the polymer is less dehydrated upon crossing the cloud point. VSANS demonstrates that the mesoglobules are significantly larger and contain more D2O than at atmospheric pressure. We conclude that the size of the mesoglobules and thus their growth process are closely related to the hydration state of PNIPAM. |
Thursday, March 8, 2018 8:12AM - 8:24AM |
R52.00002: Soft, smart multi-responsive materials: What can we learn from computer simulations? Chathuranga De Silva, Porakrit Leophairatana, Takahiro Ohkuma, Jeffrey Koberstein, Kurt Kremer, Debashish Mukherji Design of multi-responsive smart, soft materials is at the onset of many developments in polymer physics, chemical physics, biophysics and biochemistry research [1]. A system is known as smart responsive when a slight change in external stimuli can drastically alter its structure function and stability. Because the properties of these systems are dictated by large conformational/compositional fluctuations, it is very difficult to address these problems within both experimental and theoretical setups. On such system is the acetal based copolymers, consisting of repeat units of hydrophobic (methylene) and hydrophilic (ethylene oxide) monomers [2]. In this presentation, we will discuss the recently developed segment-based generic coarse-grained model of these polymers [3]. Furthermore, we will not only present consistent picture with the existing experimental results, but also show how our approach can be used to interpreting and guiding experiment towards new directions. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R52.00003: Thermodaynamic Origin of Cononsolvency He Cheng, Taisen Zuo, Changli Ma Cononsolvency is a phenomenon for which the solubility of a polymer or protein decreases or even vanishes in the mixture of good solvents. Although it is widely used in physicochemical, green chemical and pharmaceutical industry, it’s origin is still under debates for decades. A few theoretical explanations were proposed based on experimental results on conformation variation of polymer chains on the length scale of tens of nanometer. Here, by using combined neutron total scattering and all-atom molecular dynamic simulation, we present a universal thermodynamic explanation of cononsolveny, based on strong solvent-solvent attraction. The mixed solvent structure at molecular level in a few angstroms is successfully connected to the polymer conformation with dimension around several nm. Our study opens up many directions to explore all-atom structure in macromolecular solution and the origin of its solubility. |
Thursday, March 8, 2018 8:36AM - 8:48AM |
R52.00004: Molecular basis of non-universal pH-dependent conformational transitions of poly(alkylacrylic acid)s Chang Yun Son, Valeriy Ginzburg, Antony Van Dyk, Christopher Tucker, Thomas Kalantar, Zhen-Gang Wang Conformational properties of weak polyelectrolytes have complex pH and solvent dependence. Upon pH titration, poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMA), both show qualitatively different conformational changes depending on the solvent quality; while they expand monotonically in water, a compact-expanded-compact transition is observed in methanol. The molecular origin of this non-universal solvent dependence is poorly understood. In this study, we perform extensive atomistic molecular dynamics simulations of PAA and PMA in water and methanol accelerated with GPU technology. Conventional non-polarizable force fields fail to capture the qualitatively different solvent effect. Importantly, a continuum electrostatics based effective polarization model with explicit solvent successfully captures the non-universal conformational changes in water and methanol, suggesting that the electronic polarization is key to the conformational transition. During the collapse transition upon charging in methanol, the poly-ion and the counter-ions form a salt-bridged structure similar to the secondary structure in proteins. Existing theories of collapse transition of polyelectrolyte are examined based on the observations in the simulation. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R52.00005: Response of ionic co-polymers assemblies to solvent stimuli: A molecular Dynamics Simulation Study Manjula Senanayake, Dipak Aryal, Gary Grest, Dvora Perahia Ionizable co-polymers associate in solutions where ionic cluster formation often drives the assembly. The response of ionic clusters affects the driving forces for assemblies, where larger the blocks incompatibility is, the more distinctive there response to solvent stimuli becomes. Here, using atomistic molecular dynamics simulations, we follow the response of micelles formed by a symmetric pentablock copolymer, that consists of a randomly sulfonated polystyrene (sPS) centers, tethered to poly ethylene-r-propylene block, terminated by poly (t-butyl styrene). Micelles were formed by confining the sPS blocks with sulfonation fractions f of 0- 0.55 in implicit poor solvent and measured in cyclohexane. Solvent polarity was tuned by addition of propanol to the cyclohexane, increasing the dielectric constant. We find that regardless of the ionic fraction, aggregates size decreases with addition of propanol. Concurrently while only small numbers of propanol molecules penetrate the ionic core they screen the ionic interactions resulting in slight expansion of the core. The assemblies that were initially formed by segregation of the ionic blocks are now held together by the collapse of the hydrophobic blocks. |
Thursday, March 8, 2018 9:00AM - 9:12AM |
R52.00006: Competitive calcium ion binding to end-tethered weak polyelectrolytes Rikkert Nap, Sung Hyun Park, Igal Szleifer Polymer-coated nanoparticles have many biomedical applications ranging from sensing as imaging contrast agents to delivery platforms for therapeutics. Hence, it is important to understand how multivalent ions found in biological environments influence the coating. Here we use a molecular theory that explicitly includes the size, shape, and charge distribution of all species, as well as the conformations of the end-tethered polyelectrolytes to theoretically describe the structural changes and potential collapse of weak polyelectrolyte layers end-tethered to nanoparticles as a function of pH and divalent ion concentrations. Also, explicitly considered into the theory are the following chemical reactions: the acid-base equilibrium, ion condensation, and calcium bridging. End-grafted poly(acrylic acid) (pAA) layers collapse in the presence of sufficient amounts of Ca2+ ions, while poly arcrylamido-2-methylpropane sulfonate layers will not collapse. The collapse of end-tethered pAA is due to the formation of calcium bridges between two acrylic acid monomers and one calcium ion. The collapse of pAA layers is strongly dependent on the pH as well as divalent and monovalent salt concentrations of the environment and the curvature or radius of the nanoparticle. |
Thursday, March 8, 2018 9:12AM - 9:24AM |
R52.00007: Sensing Local Stresses with Mechano-Responsive Polymer Structures Andreas Fery, Jens Neubauer, Julian Thiele We utilize mechano-responsive polymer brushes as spatially resolving force sensors. By labelling with fluorophores, local mechanical deformation of the polymer can be translated into an optical signal that can be read out with confocal microscopy. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R52.00008: Curvature by design in liquid crystal elastomer sheets Benjamin Kowalski, Nicholas Godman, Cyrus Mostajeran, Mark Warner, Timothy White Spatial patterning of director orientation in liquid crystalline elastomers (LCEs) can generate rich stimuli-responsive 3D shape-morphing behavior. But in order for LCEs to fully realize their promise in application spaces such as tunable optics, design strategies must be developed to achieve arbitrary and precisely tailored 3D curvatures even in rubbery LCEs. Here we use a theory-driven strategy to realize a range of surfaces including paraboloids, as confirmed by high-resolution in-situ optical scanning. This approach also affords experimental insight into previous theoretical analyses of various forms of in-plane and radial symmetry breaking. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R52.00009: A Soft Coarse-Grained Model for Multicomponent Polymer Solutions Jianguo Zhang, Debashish Mukherji, Kurt Kremer, Kostas Daoulas Multicomponent polymer solutions are fascinating systems for printable optoelectronics. Due to their complex structural, thermodynamic, dynamic, and rheological properties, the molecular-level mechanisms controlling these properties are only partially understood. Here, a mesoscopic soft coarse-grained model which hybrids the particle-based and the field-based methods is developed for multicomponent polymer solutions. Within this model, polymers and solvent molecules are described by discrete worm-like chains [1] and single beads, respectively. The non-bonded interactions are introduced through a density functional as a function of local densities. These densities are calculated by a simple particle-to-mesh scheme [2] which enables us to explore large size systems. Different scenarios for polymer solubility in solvent and cosolvent are considered. Conformational and structural properties of ternary solutions in a broad range of concentrations are addressed [3]. |
Thursday, March 8, 2018 9:48AM - 10:24AM |
R52.00010: The Puzzle of Smart Polymers in Miscible Solvent Mixtures Invited Speaker: Kurt Kremer Smart, stimuli responsive polymers pose challenges for our theoretical understanding. In this context the response to changes in relative solvent co-solvent concentration in solvent mixtures is of special interest. Polymers in perfectly miscible good solvents can collapse, while in mixed poor solvents they can expand. Specific relations between atomistic structure, architecture, molecular weight and material properties are of basic concern and the validity of generic models has been questioned. To shed more light on this, computer simulations on different levels of resolution play an increasingly important role. Typical examples of polymer solvation in mixed solvents are PNIPAM and PMMA in water alcohol mixtures. The first shows an interesting coil-globule-coil transition. This conformational transition cannot be explained within the classical Flory-Huggins picture, which is the standard mean field theory for polymer solutions and mixtures. The results point towards a general design concept of 'smart stimuli responsive polymers'. The second displays a weak swelling in a mixture of two miscible poor solvents. This swelling couples in a delicate way to the mixing properties of the solvents. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R52.00011: Hierarchical Assembly of Inhomogeneous Supramolecular Polymers from Hybrid Particle-Field Simulations Jing Zong, Dong Meng Through hierarchical assembly at multi-scales, inhomogeneous supramolecular polymers (ISP) serve as self-assembly foundries for fabricating materials that can perform multiple functions through combinations of structural and functional capabilities. Understanding the mechanisms governing hierarchical assembly of ISP plays a key role in unlocking such potential. Using a “bare-bones” case of ISP, this study applies hybrid particle-field simulations to elucidate interplay of chemical and thermodynamic equilibrium, reaction kinetics and polymer dynamics in the system. Extent of reaction, effective bonding kinetics, and segmental diffusions measured in ordered micro-phase, homogeneous phase, and in a reference system of “dead” polymers are compared to illustrate couplings of different mechanisms. It is found that compositional ordering reduces reaction conversion, increases effective associative bond life, and slows down polymer diffusion compared to the homogenous phase. Reversible associative reactions greatly enhanced mobility of the ordered micro-phase as compared to the “dead” system. Associative segments exhibit faster-than-Rouse diffusion behaviors, and a distinct diffusion mechanism in the ordered phase. Future studies on more complicated IPS systems will also be discussed. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R52.00012: Untightening constrained segments of charged polymers at interfaces Bintao Zhao, Jingfa Yang, Jiang Zhao The effect of dipole-dipole interaction between the ion-pairs within a highly charged polyelectrolyte brush has been investigated. The introduction of external salt is discovered to break up dipole-dipole multiplets and make the previously constrained segments released. This is demonstrated by the measurements by neutron reflectivity with a model system (sodium polystyrene sulfonate), showing that its segmental density profile is further expanded into the aqueous media when the salt concentration in increased to a moderate value. Meanwhile, dielectric spectroscopy demonstrate increase of segmental relaxation frequency. All of these results clearly demonstrated an obvious effect created by dipole-dipole interaction, besides the dominating role of electrostatic interaction. |
Thursday, March 8, 2018 10:48AM - 11:00AM |
R52.00013: Predicting Mechanical Behavior of Multiply-Dynamic Crosslinked Polymer Composites Mehdi Zanjani, Zhijiang Ye, Dominik Konkolewicz Dynamically crosslinked polymers and their composites have tremendous potential in the development of the next round of advanced materials for aerospace hardware and sensing applications. These materials contain dynamic or exchangeable crosslinkers of two main types: non-covalently bound crosslinkers, and dynamic covalently bound crosslinkers. These two categories provide significantly different self-healing behaviors. |
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