Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S16: Self-Assembled PolymersRecordings Available
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Sponsoring Units: DPOLY Chair: Kenny Mineart, Bucknell University Room: McCormick Place W-184A |
Thursday, March 17, 2022 8:00AM - 8:12AM |
S16.00001: Blending of Ionizable Polymers: Molecular Dynamics Simulation Study Rosita Sivaraj, Gary S Grest, Dvora Perahia Ionomer containing polymers blends exhibit the potential to incorporate the unique transport ability of ionomers with the viscoelasticity of non-ionic macromolecules, opening the way to a broad range of innovative technologies currently hampered by the challenge that under the conditions where transport is optimized, mechanical stability is often reduced. Similar to blending highly incompatible polymers, mixing of ionizable polymers in non-ionic ones presents significant challenges. Here using molecular dynamics simulations, we probe blending of associating polymers using a bead-spring model as the strength of the associative groups is varied from 1 to 10KT. In parallel, we probe the structure evolution and dynamics of blends of polystyrene and sulfonated polystyrene of different sulfonation fractions. Cluster characteristics including size, shape and internal packing are extracted and correlated with the static structure factor S(q). S(q) is fit with the random phase approximation model (RPA) and the degree of segregation is extracted. Surprisingly, atomistic simulations of PS and PSS blends reveal a higher compatibility than expected. The correlation between associating bead interactions strength and the degree of phase segregation will be discussed. |
Thursday, March 17, 2022 8:12AM - 8:24AM |
S16.00002: Phase Behavior of Colloids with Attractive Polymer-Mediated Interactions Mariah J Gallegos, Diego Soetrisno, Nayoung Park, Jacinta C Conrad Attractive bridging interactions driven by polymers that adsorb to the particle surface are prevalent in separation processes. How the phase behavior, structure, and dynamics of the suspension depend on the strength of bridging interactions remains incompletely understood. We investigate the phase behavior of a colloid-polymer mixture with attractive bridging interactions in which the strength of the polymer adsorption can be tuned through the pH of the solution. Bridging interactions were induced between trifluoromethyl methacrylate-co-tert-butyl methacrylate (TtMA) by introducing poly(acrylic acid) (PAA) to the system. The formation of hydrogen bonds between PAA and stabilizers on the surface of the particles decreases as pH is increased. We find that the particles form flocs and networks at low pH but largely remain dispersed at high pH. By quantifying the dynamics and structure, we show that suspensions of TtMA particles and PAA undergo fluid to gel transition by decreasing pH or increasing polymer concentration at both low (φ = 0.15) and high (φ = 0.40) particle volume fractions. |
Thursday, March 17, 2022 8:24AM - 8:36AM |
S16.00003: Self-assembled hybrid multilamellar vesicles of phospholipids and block copolymers for efficacious delivery of insoluble drugs to cells Nurila Kambar, Cecilia Leal A surprisingly high number of drugs (>70%) emerge as insoluble compounds. Paclitaxel is aneffective chemotherapeutic drug against many forms of cancer. However, low solubility and crystallization inaqueous environments have compromised its efficacious clinical use. A promising strategy is to encapsulatepaclitaxel in drug carriers such as polymer or lipid membranes. Previous work on multilayered lipid–polymerhybrid films have shown to accommodate large paclitaxel loads and suppress crystallization. A hybrid materialcomposed of phospholipids and amphiphilic block copolymers display synergistic structural, phase-separation,and dynamical properties not seen in pure components. Using a combination of confocal laser scanningmicroscopy and X-ray scattering it is possible to, for the first time, directly monitor the formation of lipid-rich andblock copolymer-rich phase-separated domains and prove the existence of nano and microscopic domainformation in lipid-polymer hybrid multilamellar vesicles. To date, the physical and molecular factor governingthe phase separation in these hybrid polymer/lipid membranes are only partially understood. Accordingly, thiswork offers new perspectives in reaching and understanding controlled formation of novel hybrid vesicles forsmall-drug delivery systems. |
Thursday, March 17, 2022 8:36AM - 8:48AM |
S16.00004: Stimuli-driven jamming in dense suspensions: training and memory Hojin Kim, Hongyi Zhang, Shrayesh Patel, Heinrich M Jaeger, Stuart J Rowan Shear-induced jamming and its impact-induced solidification of dense suspensions is an important behavior that can allow access to stress mitigating functional materials. We have designed responsive particles whose crosslink density can be reversibly tuned in the presence of external stimuli. Upon exposure of these particles to either ultraviolet light or an electric field, a significant impact on the jamming transition is observed. We found that the exposure of such external stimulus to a dense suspension of these particles triggered jamming and solidification and that the material relaxes back to a fluid upon removal of the stimulus. It is also shown that the suspension can be “trained” by oscillatory shear in which structural memory is introduced, and thus the yield strain may be tailored. The structural memory from the training persists even after the external stimulus is removed. The trained suspension can unjam and lose its memory when the applied strain exceeds the training strain under no external stimuli. Introduction of shear memory enhances the functionality of impact-resisting suspensions that one can load with erasable structural memory by switching on and off the external stimulus. |
Thursday, March 17, 2022 8:48AM - 9:00AM |
S16.00005: Charge regulation effects in nanoparticle self-assembly and polyelectrolyte complexation Erik Luijten, Tine Curk Nanoparticles, polyelectrolytes and biomolecules in solution acquire charge through the dissociation or association of surface groups. Thus, a proper description of their electrostatic interactions requires the use of charge-regulating boundary conditions rather than the commonly employed constant-charge approximation. Although this phenomenon has been theoretically studied since the seminal work by Kirkwood in the 1950s, the assumption that all objects carry a constant charge is still widely employed. We present a hybrid Monte Carlo/molecular dynamics scheme that dynamically adjusts the charges of individual ionizable groups of objects while evolving the trajectories of these objects. Charge regulation effects are shown to result in global charge redistribution and thereby qualitatively alter important structural properties, such as the nature of self-assembled aggregates and the polyelectrolyte coil–globule transition. These insights are used to design efficient hydrogel-based nano-actuators. |
Thursday, March 17, 2022 9:00AM - 9:12AM |
S16.00006: Ion-specific nanoscale forces in charged soft matter Catherine McCarthy, Emanuela del Gado, Abhay Goyal, Francis Dragulet In charged soft matter, surface forces are often ion-specific and cohesive in ways that cannot be captured by existing theories such as DLVO. We use semi-atomistic Monte Carlo and Molecular Dynamics simulations of counterions and explicit water confined between charged surfaces in order to unravel the origin of ion specificity and nanoscale cohesion relevant to systems ranging from biological membranes to clays or hydrated cement. We find that both effects are the consequence of the formation of hydrated-ion structures that are induced by the confinement and dramatically reduce water dielectric screening. Our results for different counterions allow us to disentangle the distinct effects and interplay of ion size and valency in the water-ion structuring, which then naturally lead to ion-specific nanoscale forces. |
Thursday, March 17, 2022 9:12AM - 9:24AM |
S16.00007: Electrostatic and Van der Waal Control of Charged Chiral Assemblies Joseph Mccourt, Changrui Gao, Sumit Kewalramani, Erik W Roth, Steven J Weigand, Monica Olvera De La Cruz, Michael J Bedzyk Charged, chiral molecules assemble into a variety of chiral mesoshapes. However, the interplay between electrostatics and van der waals interactions in chiral shape selection is not well understood. To tackle this, we analyzed self-assembly in a homologous series of amphiphiles (CnK) consisting of an ionizable amino acid (lysine (K)) coupled to alkyl tails with n = 12, 14 or 16 carbons. Solution small/wide angle X-ray scattering (SAXS/WAXS) reveal that at low pH, where the headgroups are ionized (+1), the assembly is dictated by tail length resulting in disordered aggregates (n = 12), spherical micelles (n = 14) and high aspect ratio (L/W > 10:1) planar bilayers (n = 16). However, regardless of the tail length, assemblies transform to helical bilayers and then to bilayer stacks as the average headgroup charge is reduced by increasing pH. The helix radius (60-100 nm) increases both with decreasing molecular charge (fixed tail length) and decreasing tail length (fixed pH). Overall, our study represents a step towards a rational electrostatics-based approach for meso-shape selection and for controlling nm-scale structure in a continuous manner for chiral assemblies. |
Thursday, March 17, 2022 9:24AM - 9:36AM |
S16.00008: Self-assembly of charged nanocrystals into strongly electronically coupled all-inorganic supercrystalline solids Josh Portner, Igor Coropceanu, Eric Janke, Dmitri V Talapin Colloidal nanocrystals of different metals, semiconductors, and other functional materials can self-assemble into long-range ordered crystalline phases. However, insulating organic surface ligands prevent the development of collective electronic states in ordered nanocrystal assemblies. Here we report reversible self-assembly of colloidal, charged nanocrystals with conductive inorganic ligands into superlattices exhibiting optical and electronic properties consistent with strong electronic coupling between the constituent nanocrystals. We show that the phase behavior of charge-stabilized nanocrystals can be rationalized and navigated using phase diagrams computed for particles interacting through short range attractive potentials similar to previous reports for globular proteins and PMMA spheres. By finely tuning conditions, the assembly can proceed either via one-step nucleation or non-classical two-step nucleation pathways. The ability to grow ordered all-inorganic assemblies of strongly coupled nanoscale building blocks, combined with the already available synthesis toolset for engineering nanocrystal size, shape, and functionality, may offer endless possibilities for engineering hierarchical solids. |
Thursday, March 17, 2022 9:36AM - 9:48AM |
S16.00009: Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface Ahmet Uysal, Srikanth Nayak, Raju R Kumal Amphiphilic lipid-ion interactions at aqueous interfaces drive the assisted ion transport in various biological and industrial systems. In chemical separations of heavy elements, lipids coordinate metal ions and solubilize them in an organic phase. Direct observation of lipid-metal interactions is highly difficult at the buried oil/water interface, and is accessible with limited experiments. Here, we demonstrate that inverted bilayer structures previously observed at oil/aqueous interfaces can also be formed at the air/aqueous interface. This facilitates the easier study of lipid-ion interactions over a wide range of parameters with multiple probes, including synchrotron X-ray reflectivity (XR), X-ray fluorescence near total reflection (XFNTR), and vibrational sum-frequency generation spectroscopy (VSFG). The formation of bilayers is highly sensitive to the metal ion charge density. While Lu3+ (115 C/mm3) led to bilayer formation, Nd3+ (82 C/mm3) and Sr2+ (33 C/mm3) led to monolayers. By introducing Lu3+ ions to preformed lipid monolayers, we extract kinetic parameters corresponding to monolayer to inverted bilayer conversion. Temperature-dependent studies show Arrhenius behavior with an energy barrier of 40 kcal/mol. The kinetics of monolayer to inverted bilayer conversion is also affected by the presence of background salts where thiocyanate accelerates the conversion more than nitrate does. Our results show the outsized importance of ion-specific effects on interfacial structure and kinetics, pointing to their role in chemical separation methods. Finally, this model system can be used to study a wide variety of lipid-ion interactions, opening a new avenue in molecular-scale understanding of these important systems. |
Thursday, March 17, 2022 9:48AM - 10:00AM |
S16.00010: Standalone 2-D Nanosheets and the Consequent Hydrogel and Coacervate phases formed by 2.5-nm Spherical U60 Molecular Clusters in Dilute Aqueous Solution Yuqing Yang, Yifan Zhou, Jiahui Chen, Tsuyoshi Kohlgruber, Travis Smith, Bowen Zheng, Jennifer Szymanowski, Peter C Burns, Tianbo Liu Comparing with simple ions and large colloidal suspensions, macroions exhibit completely different solution behaviors since the size disparity between them and their counterions, and the resulted counterion association and counterion-mediated attraction. Previously, hollow spherical blackberry structures from various macroions, e.g., polyoxometalates, metal-organic cages, functionalized fullerenes and dendrimers, are well reported. Nowadays, two unexpected phases, hydrogel and coacervate, are observed in dilute aqueous solution of fully hydrophilic nanoscale uranyl peroxide clusters with di- or tri-valent salts. Full phase diagrams are constructed and the mechanisms behind them are given which mainly associated with counterion-mediated attraction. The imbalance between macroions and small counterions leads to counterion association around macroions, the consequent counterion-mediated attraction as well as anisotropic nanosheets. These nanosheets further bend and enclose to form hollow, spherical blackberry-type structures with mono-valent counterions; while when introducing di/tri-valent counterions, the rigid nanosheets stand along in dilute aqueous solution, leading gelation with significant excluded volume. Coacervates and precipitates phenomena can be detected at higher ionic strengths as the result of the closer stacking of nanosheets. The fascinating phase behavior of nanoscale hydrophilic macroions are expected to be general for macroions, which indicates the unique features of soluble ions with nanoscale sizes, distinguishing them from simple ions and large colloids. |
Thursday, March 17, 2022 10:00AM - 10:12AM |
S16.00011: Landau analysis of a salt-free polyanion/polycation blends: a continuum approach Junhan Cho Recently, the combination of a molecular equation-of-state model from liquid state theory and a self-consistent mean-field theory has been made for analyzing the equilibrium phase behaviors of various mixtures containing charged polymer chains in a uniform dielectric medium. Here, we expand the free energy functional as a series in proper order parameters to obtain the 4-field Landau free energy targeting a salt-free blend of weakly charged polyanions and polycations. The ion-ion correlations are shown to convert the polymer blends of Ising class to a microphase separating Brazovskii class. Our theory, which is based on continuum-space integral equation approaches, possesses various features that is missing in the classical Voorn-Overbeek theory such as excluded volume, dispersion interactions, and chain connectivity. In particular, we focus on the systems with disparity in dispersion interactions between the constituents, which affects the critical behavior of the blend. The phase diagrams containing classical morphologies are to be determined in various situations of asymmetric dispersion interactions. It will also be mentioned how this Landau analysis for rather simple blend is generalized to more complicated mixtures with uncharged small components and also salts. |
Thursday, March 17, 2022 10:12AM - 10:24AM |
S16.00012: The breaking of electroneutrality in a phase separating polyelectrolyte gel Giulia L Celora, Matthew Hennessy, Andreas Muench, Barbara Wagner, Sarah L Waters A common assumption in models of polyelectrolyte gels that are surrounded by an ionic solution is that the electric double layer that forms at the gel-solution interface has a passive role in the dynamics and hence can be neglected. In this talk, I will revisit this assumption through the use of a novel phase-field model of a polyelectrolyte gel. I will first discuss non-homogeneous equilibrium solutions of the model and show that when the Debye and Kuhn lengths are comparable, a novel mode of phase separation emerges. While phase separation is initially localised in the double layer, eventually it propagates to the bulk of the gel leading to global breakdown of electroneutrality. I will then showcase a range of numerical simulations that illustrate how, by changing the concentration of ions in the surrounding solution, it is possible to transform the internal structure of the gel by producing a finite number of positively and negatively charged phases near the gel-solution interface. |
Thursday, March 17, 2022 10:24AM - 10:36AM |
S16.00013: Grafted Nanoparticle Penetration Barriers in Polymers: Effect of Entropy Aparna Swain Understanding the fundamentals of nanoparticle (NP) penetration into soft matter systems is indispensable for numerous applications ranging from targeted nanoparticle-based drug delivery to generating hybrid polymer nanocomposite materials. Hence, it is crucial to identify the parameters which control the extent of NP penetration. Here, we study the penetration of polystyrene-grafted Au nanoparticles (PGNPs) into an entropically/enthalpically coupled soft polymer film. The behaviour of penetration of NPs are two different way, in one case it's penetrating in dispersed manner and in another cases it penetrates in a intact manner. |
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