Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C25: Polymer Solutions and Blends |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Dong Meng, Mississippi State University Room: BCEC 160A |
Monday, March 4, 2019 2:30PM - 2:42PM |
C25.00001: How tunable are the coil dimensions of polymers in ionic liquids? Aakriti Kharel, Timothy Lodge Ionic liquids are emerging as interesting solvents for polymers. The selection of an appropriate cation or anion can alter the properties of ILs, thereby establishing a platform for a wide range of solvation properties. The solvation behavior of polymers in ILs has been investigated through miscibility and phase behavior studies; however, chain dimensions of polymers in ILs remain relatively unexplored. We use small-angle neutron scattering (SANS) to measure the radius of gyration of varying chain lengths of perdeuterated poly(ethylene oxide) in imidazolium-based ILs, which vary in both cation and anion identity. The dependence of coil size on molecular weight yields Flory exponents (v) for 4 different IL-based solvent systems. For all the solvents studied, the exponents lie within 0.55 and 0.6, indicating moderately good to very good solvent behavior. However, greater expansion of d-PEO coils is observed in ILs comprising cations with longer alkyl chains and less basic anions. Interestingly, variation of the anion has a stronger effect on coil dimensions than the cation. Additional relevant parameters such as temperature and lithium salt addition on the coil dimensions of d-PEO chains in ILs are also explored. |
Monday, March 4, 2019 2:42PM - 2:54PM |
C25.00002: Phase behavior of polymer/ionic liquids mixture: a molecular dynamics study Hyuntae Jung, Arun Yethiraj The phase behavior of polymers in ionic liquids is of practical importance for use in polymer solid state batteries and temperature sensors, where the ionic liquid allows a tuning of the solution properties. There are fundamental questions regarding the LCST phase behavior: The critical point is at high polymer concentrations, and the critical temperature is insensitive to molecular weight. In this work, we study the phase behavior a mixture of poly(ethylene oxide) (PEO) and imidazolium-based ionic liquids using a new molecular simulation method we have recently developed. We explore the influence of PEO molecular weight and the C2 methylation of [BMIM] (1-butyl-3-methylimidazolium) cation, [BMMIM] (ternary 1-butyl-2,3-dimethylimidazolium) on the phase diagram. The simulations provide molecular insight into the mechanism of phase separation in these mixtures. |
Monday, March 4, 2019 2:54PM - 3:06PM |
C25.00003: Kinetics of Block Copolymer Micelle Fragmentation in Ionic Liquids Julia Early, Timothy Lodge Recently, more attention has been directed to quantifying the relaxation kinetics of block copolymer micelles. However, there are very few experimental studies quantifying the rates of fragmentation in block copolymer micelles. The micelle radius for poly(1,2-butadiene)-block-polyethylene oxide (BEO) in EO-selective ionic liquids (ILs) depends on the solution preparation method. When BEO is dissolved directly into an IL, the spherical aggregates are large and disperse in size. Upon high temperature annealing, these micelles equilibrate and decrease in size. Exploration of the equilibration kinetics for BEO in ILs is being conducted using temperature-jump light scattering, small-angle X-ray scattering, and liquid-phase transmission electron microscopy. The effects of solvent quality between the B block and the IL were explored in four different ILs. Equilibration occurs after annealing, and the relaxation times exhibit a significant dependence on concentration and solvent quality. SAXS and liquid-phase TEM demonstrate that the core radius decreases by 5 nm after annealing. These experiments demonstrate that relaxation mechanisms other than individual chain exchange dominates in these highly amphiphilic systems. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C25.00004: Effect of Solvent Selectivity on Chain Exchange Kinetics in Block Copolymer Micelles En Wang, Dan Zhao, Timothy Lodge, Frank Bates Block copolymer (BCP) micelles in selective solvents are useful for a variety of applications, such as nanolithography, drug delivery, and viscosity modification. The solvent quality is an important factor for both thermodynamics and dynamics of BCP micelles. Previous work revealed the effect of solvent selectivity on thermodynamic properties of BCP micelles formed by poly(styrene-b-ethylene-alt-propylene) (PS-PEP) diblock copolymers in mixed solvents of squalane and 1-phenyldodecane. The systematic change of solvent composition tunes the interfacial tension between the core and corona-solvent matrix, embodied in the Flory-Huggins interaction parameter χ. This should also affect the kinetics of chain exchange between micelles. This presentation will describe the consequences of varying the solvent composition on the rate of chain exchange using time-resolved small-angle neutron scattering (TR-SANS). An independent method, static light scattering (SLS), was performed to estimate χ between the core block and the solvent as a function of solvent composition and temperature. Based on TR-SANS and SLS results, the dependence of the chain exchange rate on χ can be quantified. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C25.00005: Probing Polymer Solution Conformation along Microparticle Formation Pathways with SANS William Sharratt, Marco Adamo, Joao Cabral Polymeric microparticles are ubiquitous in encapsulation and targeted release applications. Their function is predicated on their microstructure, shape and interactions, which determine stability, phase behaviour and release profiles. Polymer solution droplet extraction is an attractive route to control their formation, and understanding the thermodynamic and non-equilibrium pathways involved is crucial for their predictive design. Here, we show microfluidic droplet formation and selective solvent exchange to yield porous polymer microparticles [1] with tunable morphologies [2]. We systematically explore the process with model poly(vinyl alcohol), varying polymer functionality, size, concentration, and droplet size [3]. We map polymer solution conformation with small angle neutron scattering (SANS) and microfluidic-SANS to resolve how chain dimensions evolve with mixed solvent/non-solvents during solidification. Our study elucidates, for the first time, the spatio-temporal evolution of polymer solutions into particles, from molecular to micron scales. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C25.00006: Arrested Mobility Effects on the Spinodal Decomposition of Ternary Polymer Solutions Jan Ulric Garcia, Douglas R. Tree, Kris T Delaney, Glenn Fredrickson Many polymer membranes are made by immersion precipitation: a polymer solution film is immersed in a nonsolvent bath, inducing phase separation of the film into a polymer-rich phase that becomes the membrane matrix and a polymer-poor phase that becomes the membrane pores. Microstructure formation of these membranes is still not fully understood, given the interdepedendence of the processes involved: the mass transfer through the film-bath interface, the phase separation of the film, the coarsening of domains, and finally the glass transition that arrests the microstructure. In this work, we use phase-field models of the ternary system to solve the coupled convection-diffusion and momentum equations that describe membrane formation. We model the glass transition using mobility and viscosity contrasts between the polymer-rich and polymer-poor phases. We report how the glassy dynamics changes the microstructures formed by bulk spinodal decomposition. We also study how mass transfer between the bath and film changes with the formation of a glassy interface. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C25.00007: SANS study of the thermodynamics and demixing of highly interacting PaMSAN/dPMMA blends Yutaka Aoki, William Sharratt, Haoyu Wang, Sarah Rogers, Robert Dalgliesh, Julia Higgins, Joao Cabral Spinodal decomposition of partially miscible polymer blends has the potential to generate well-defined polymeric nanostructured materials. While the Cahn-Hilliard (CH) theory prediction for the initial spinodal lengthscale generally holds, phase sizes attained by thermally-induced demixing are, however, stubbornly much greater that Rg. Using Small Angle Neutron Scattering (SANS), we investigate a series of LCST poly(a-methyl styrene-co-acrylonitrile) and deuterated poly(methyl methacrylate) (PaMSAN/dPMMA) blends which exhibit a remarkably steep temperature dependence of G’’ (and thus c), the driving force for demixing [1,2]. We explore the role of PMMA molecular mass (MW= 40-130 kg/mol), tacticity, composition, and temperature and to map G’’ and c as a function of these parameters in the one-phase region, employing Random Phase Approximation theory. We then carry out a series of rapid jumps into the unstable and metastable regions, establishing a comprehensive map of lengthscales achieved and theoretically expected, and limits and opportunities for bicontinuous nanostructure design by this approach. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C25.00008: Single molecule studies of comb polymer dynamics in semi-dilute solutions Shivani Patel, Charles Schroeder We study the dynamics of single branched polymers in non-dilute solutions using single-molecule fluorescence microscopy (SMFM). In particular, we use a hybrid enzymatic-synthetic approach to synthesize DNA-based branched polymers (comb polymers) that contain a long backbone with multiple side branches grafted at various positions. Following synthesis, we directly study the transient stretching dynamics of single comb polymers in semi-dilute solutions in extensional flow. We compare the transient dynamics of single comb polymers in semi-dilute solutions of linear unlabeled polymers to the dynamics of comb polymers in ultra-dilute solutions. Interestingly, the transient stretching dynamics and relaxation behavior of comb polymers is markedly different in non-dilute polymer solutions, which reveals changes in molecular-scale dynamics due to chain branching and chain-chain intermolecular interactions. We further study the effects of background concentration and polymer topology on comb polymer dynamics in order to elucidate the non-equilibrium behavior of topologically complex polymers. Overall, our work shows that single polymer dynamics can be used to provide a direct link between polymer microstructure and bulk rheological properties. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C25.00009: Thermodynamics and conformation of PPPO in mixed solvents: towards nanoporous polymeric gas sensors Roisin O'Connell, Joao Cabral, Julia Higgins, Alexandra Porter
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Monday, March 4, 2019 4:18PM - 4:30PM |
C25.00010: Conformations of bottlebrush polymers in dilute solution Sarit Dutta, Mathew Wade, Dylan Walsh, Damien Guironnet, Simon Rogers, Charles Sing Bottlebrush polymers are a class of highly branched polymers consisting of a |
Monday, March 4, 2019 4:30PM - 4:42PM |
C25.00011: Diffusion Driven Nonsolvent Induced Phase Separation Douglas R. Tree, Lucas Francisco Dos Santos, Caden B Wilson, Timothy R Scott, Jan Ulric Garcia, Glenn Fredrickson Nonsolvent induced phase separation (NIPS) occurs when a polymer solution is brought into contact with a miscible nonsolvent, leading to the precipitation of a polymer-rich phase. Because of its simplicity, NIPS processes are widely used to generate a variety of microstructures in polymer materials such as membranes and micro/nanoparticles. Despite its prevalence, predicting and controlling the microstructure generated by NIPS remains a difficult challenge, owing to the complex interactions between the diffusive transport, hydrodynamics and phase-separation kinetics in the process. In our approach, we use simulations of a "multi-fluid" phase-field model of a ternary polymer solution that incorporates all of these kinetic processes. In the case of NIPS driven by purely diffusive solvent/nonsolvent exchange, we find two regimes capable of generating microstructure via spinodal decomposition: one at times much shorter than the diffusion time of the nonsolvent and one at much longer times. We then use our model to predict (i) which compositions of polymer solution will lead to microstructure formation at both short and long times and (ii) what microstructures emerge as composition is varied. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C25.00012: Effects of Side-Chain Deuteration of Poly(N-isopropylacrylamide) on the Thermal Transition Behaviors in Water Dongsook Chang, Kunlun Hong Polymers with lower critical solution temperature (LCST) in water are promising building blocks in designing temperature-responsive materials. The thermal transition of polymer and proteins in water is known to depend on deuteration (either of solvent or of polymer/protein), but a full understanding of this phenomenon remains elusive. In this study, we focus on the fact that although partially deuterated poly(N-isopropylacrylamide) (PNIPAm) has been widely used in many studies due to its facile synthesis, its thermal transition behavior has not been independently characterized. We investigate the effect of side-chain deuteration of PNIPAm on its electronic structure, hydrogen bonding, and hydration in water. The thermal transition of PNIPAm with its isopropyl side chain deuterated (d7-PNIPAm) is broader and approximately 2 °C higher than that of h-PNIPAm in dilute solution when measured by microcalorimetry. While the underlying mechanisms are complex, our results currently point to weaker hydrogen bonding of d7-PNIPAm due to a small destabilization of the negative dipole in the amide nitrogen, which results in a weaker cooperativity in hydration. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C25.00013: Increasing block copolymer dispersity leads to more uniform micelles Sriteja Mantha, Shuanhu Qi, Matthias Barz, Friederike Schmid Synthetic polymers posses some inherent dispersity in their length due to the mechanism of the underlying polymerization reaction. Since nearly every property of the polymers depend strongly on the length of the chain, it is expected that the polymer chain dispersity effects different structural, dynamic and their self-assembly properties in the solution as well as in the melt conditions. In this work we investigate the effect of amphiphilic diblock copolymer chain length dispersity on the size distribution of the spherical micelles formed by them in the solution. Using self-consistent field theory calculations, we show that the monodisperse diblock copolymers form micelles of different sizes in the solution, whereas polydisperse diblock copolymers form micelles which are uniform in size. We attribute this to the fact that the packing of the solvophobic monomers in the micellar core can be optimized if the constituent polymers have different length. |
Monday, March 4, 2019 5:06PM - 5:18PM |
C25.00014: Particle Packings in Bidisperse Diblock Copolymer Blends Aaron Lindsay, Ronald Lewis, Bongjoon Lee, Micah J. Howard, Timothy Lodge, Frank Bates Recent investigation into the phase behavior of compositionally asymmetric diblock copolymers has resulted in the discovery of a host of previously unanticipated particle packings, including a dodecagonal quasicrystal and several Frank-Kasper (FK) phases. Conformational asymmetry has been shown to favor these fascinating morphologies. However, the number of sufficiently conformationally asymmetric systems available for study is limited. An alternative approach, simply blending two diblocks, has been predicted by self-consistent field theory to allow access to these FK phases, potentially enabling study of these morphologies in a wider range of systems. In this work, we investigated the phase behavior of bidisperse blends of polystyrene-b-poly(1,4-butadiene); the nominally single component diblock copolymer melts show no evidence of FK phase formation. The core block length and relative volume fraction of each polymer was varied, keeping constant the length of the corona block. Small angle X-ray scattering and transmission electron microscopy revealed a rich phase behavior, providing a new means of accessing various particle-packings in diblock copolymer melts. |
Monday, March 4, 2019 5:18PM - 5:30PM |
C25.00015: Investigating the Properties and Phase Behavior of Ionic Liquid and Polymer Blends Caitlin Donovan, Oscar Morales, Malgorzata Chwatko, Aaron A Burkey, Alysha Helenic, Seungmin Oh, Joan Brennecke, Nathaniel A Lynd Atmospheric carbon dioxide (CO2) traps heat and increases global temperatures. Both ionic liquids (ILs) and polymers have been investigated for use in CO2 capture technologies. However, composite polymer/IL materials could enhance capture and maintain favorable physical properties for industrial usage. Previously, we identified 1-hexyl-3-methylimidazolium bis(trifuloromethylsulfonyl)imide ([hmim][Tf2N]) as an IL with excellent physical CO2 solubility. We are interested in polyether and ionic liquid composite materials specifically because of the favorable interactions polyethers have with CO2. It is a necessary first step to investigate the phase behavior and properties of these blends. |
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