Controlling Charge Percolation in Solutions of Metal Redox Active Polymers: Implications of Microscopic Polyelectrolyte Dynamics on Macroscopic Energy Storage.

Soluble redox-active polymers (RAPs) enable size-exclusion nonaqueous redox flow batteries (NaRFBs) which promise high energy density. Pendants along the RAPs not only store charge but also engage in electron transfer to varying extents based on their designs. Here, we explore these phenomena in Metal-containing Redox Active Polymers (M-RAPs, M = Ru, Fe, Co).

Effect of penetrant-polymer interactions and shape on the motion of molecular penetrants in dense polymer networks.

The diffusion of dilute molecular penetrants within polymers plays a crucial role in the advancement of material engineering for applications such as coatings and membrane separations. The potential of highly cross-linked polymer networks in these applications stems from their capacity to adjust the size and shape selectivity through subtle changes in network structures. In this paper, we use molecular dynamics simulation to understand the role of penetrant shape (aspect ratios) and its interaction with polymer networks on its diffusivity.

Direct-ink-write cross-linkable bottlebrush block copolymers for on-the-fly control of structural color.

Additive manufacturing capable of controlling and dynamically modulating structures down to the nanoscopic scale remains challenging. By marrying additive manufacturing with self-assembly, we develop a UV (ultra-violet)-assisted direct ink write approach for on-the-fly modulation of structural color by programming the assembly kinetics through photo-cross-linking. We design a photo-cross-linkable bottlebrush block copolymer solution as a printing ink that exhibits vibrant structural color (i.

Effect of Hydrodynamic Interactions and Flow on Charge Transport in Redox-Active Polymer Solutions.

Redox-active polymers (RAPs) are a subclass of polyelectrolytes that can store charge and undergo redox self-exchange reactions. RAPs are of great interest in the field of redox flow batteries (RFBs) due to their ability to quickly charge and discharge, their chemical modularity, and their molecular size. However, designing RAPs for efficient charge transport at the molecular level requires a fundamental understanding of the charge transport mechanisms that occur in RFBs.

Brownian dynamics simulations of bottlebrush polymers in dilute solution under simple shear and uniaxial extensional flows.

We study the dynamics of bottlebrush polymer molecules in dilute solutions subjected to shear and uniaxial extensional flows using Brownian dynamics simulations with hydrodynamic interaction (HI). Bottlebrush polymers are modeled using a coarse-grained representation, consisting of a set of beads interacting pairwise via a purely repulsive potential and connected by finitely extensible nonlinear springs. We present the results for molecular stretching, stress, and solution viscosity during the startup of flow as well as under steady state as a function of side chain length while keeping the backbone length fixed.

Modeling the competition between phase separation and polymerization under explicit polydispersity.

The dynamics of phase separation for polymer blends is important in determining the final morphology and properties of polymer materials; in practical applications, this phase separation can be controlled by coupling to polymerization reaction kinetics a process called 'polymerization-induced phase separation'. We develop a phase-field model for a polymer melt blend using a polymerizing Cahn-Hilliard (pCH) formalism to understand the fundamental processes underlying phase separation behavior of a mixture of two species independently undergoing linear step-growth polymerization. In our method, we explicitly model polydispersity in these systems to consider different molecular-weight components that will diffuse at different rates.

Simulation study of the effects of polymer network dynamics and mesh confinement on the diffusion and structural relaxation of penetrants.

The diffusion of small molecular penetrants through polymeric materials represents an important fundamental problem, relevant to the design of materials for applications such as coatings and membranes. Polymer networks hold promise in these applications because dramatic differences in molecular diffusion can result from subtle changes in the network structure. In this paper, we use molecular simulation to understand the role that cross-linked network polymers have in governing the molecular motion of penetrants.

Effect of Polypeptide Complex Coacervate Microenvironment on Protonation of a Guest Molecule.

Complex coacervate droplets formed by the liquid-liquid phase separation of polyelectrolyte solutions capture several important features of membraneless organelles including their ability to accumulate guest molecules and to provide distinct microenvironments. Here, we examine how polyions in complex coacervates can influence localized guest molecules, leading to a shifted protonation state of the guest molecule in response to its electrostatic environment. A fluorescent ratiometric pH indicator dye was used as a model guest molecule able to report its protonation state in the coacervate phase.

Self-consistent hopping theory of activated relaxation and diffusion of dilute penetrants in dense crosslinked polymer networks.

We generalize a microscopic statistical mechanical theory of the activated dynamics of dilute spherical penetrants in glass-forming liquids to study the influence of crosslinking in polymer networks on the penetrant relaxation time and diffusivity over a wide range of temperature and crosslink fraction (fn). Our calculations are relevant to recent experimental studies of a nm-sized molecule diffusing in poly-(n-butyl methacrylate) networks. The theory predicts the penetrant relaxation time increases exponentially with the glass transition temperature, Tg(fn), which grows roughly linearly with the square root of fn due to the coupling of local hopping to longer-range collective elasticity.

How Segmental Dynamics and Mesh Confinement Determine the Selective Diffusivity of Molecules in Cross-Linked Dense Polymer Networks.

The diffusion of molecules ("penetrants") of variable size, shape, and chemistry through dense cross-linked polymer networks is a fundamental scientific problem broadly relevant in materials, polymer, physical, and biological chemistry. Relevant applications include separation membranes, barrier materials, drug delivery, and nanofiltration. A major open question is the relationship between transport, thermodynamic state, and penetrant and polymer chemical structure.

Concentration-Driven Self-Assembly of PS--PLA Bottlebrush Diblock Copolymers in Solution.

Bottlebrush polymers are a class of semiflexible, hierarchical macromolecules with unique potential for shape-, architecture-, and composition-based structure-property design. It is now well-established that in dilute to semidilute solution, bottlebrush homopolymers adopt a wormlike conformation, which decreases in extension (persistence length) as the concentration and molecular overlap increase. By comparison, the solution phase self-assembly of bottlebrush diblock copolymers (BBCP) in a good solvent remains poorly understood, despite critical relevance for solution processing of ordered phases and photonic crystals.

Interaction potential for coarse-grained models of bottlebrush polymers.

Bottlebrush polymers are a class of highly branched macromolecules that show promise for applications such as self-assembled photonic materials and tunable elastomers. However, computational studies of bottlebrush polymer solutions and melts remain challenging due to the high computational cost involved in explicitly accounting for the presence of side chains. Here, we consider a coarse-grained molecular model of bottlebrush polymers where the side chains are modeled implicitly, with the aim of expediting simulations by accessing longer length and time scales.

Transfer Matrix Model of pH Effects in Polymeric Complex Coacervation.

Oppositely charged polyelectrolytes can undergo an associative phase separation, in a process known as polymeric complex coacervation. This phenomenon is driven by the electrostatic attraction between polyanion and polycation species, leading to the formation of a polymer-dense coacervate phase and a coexisting polymer-dilute supernatant phase. There has been significant recent interest in the physical origin and features of coacervation; yet notably, experiments often use weak polyelectrolytes the charge state of which depends on solution pH, while theoretical or computational efforts typically assume strong polyelectrolytes that remain fully charged.

Recent progress in the science of complex coacervation.

Complex coacervation is an associative, liquid-liquid phase separation that can occur in solutions of oppositely-charged macromolecular species, such as proteins, polymers, and colloids. This process results in a coacervate phase, which is a dense mix of the oppositely-charged components, and a supernatant phase, which is primarily devoid of these same species. First observed almost a century ago, coacervates have since found relevance in a wide range of applications; they are used in personal care and food products, cutting edge biotechnology, and as a motif for materials design and self-assembly.

100th Anniversary of Macromolecular Science Viewpoint: Opportunities in the Physics of Sequence-Defined Polymers.

Polymer science has been driven by ever-increasing molecular complexity, as polymer synthesis expands an already-vast palette of chemical and architectural parameter space. Copolymers represent a key example, where simple homopolymers have given rise to random, alternating, gradient, and block copolymers. Polymer physics has provided the insight needed to explore this monomer sequence parameter space.

Micro- to macro-phase separation transition in sequence-defined coacervates.

Phase separation can be driven by the association of oppositely charged polyelectrolytes in solution, a process known as complex coacervation. This can manifest as macrophase separation, which arises when both polymer species are homopolyelectrolytes, or can lead to microphase separation when one or both of the charged species are block copolyelectrolytes. This is not a strict dichotomy; recently, macrophase separation was observed for a number of copolymers containing sequence-defined patterns of neutral vs charged monomers, including patterns with lengthy blocks.

Influence of Nucleoid-Associated Proteins on DNA Supercoiling.

DNA supercoiling, where the DNA strand forms a writhe to relieve torsional stress, plays a vital role in packaging the genetic material in cells. Experiment, simulation, and theory have all demonstrated how supercoiling emerges due to the over- or underwinding of the DNA strand. Nucleoid-associated proteins (NAPs) help structure DNA in prokaryotes, yet the role that they play in the supercoiling process has not been as thoroughly investigated.

Correction: Transfer matrix theory of polymer complex coacervation.

Correction for 'Transfer matrix theory of polymer complex coacervation' by Tyler K. Lytle et al., Soft Matter, 2017, 13, 7001-7012.

Simulation of semidilute polymer solutions in planar extensional flow via conformationally averaged Brownian noise.

The dynamics and rheology of semidilute polymer solutions in strong flows are of great practical relevance. Processing applications can in principle be designed utilizing the relationship between nonequilibrium polymer conformations and the material properties of the solution. However, the interplay between concentration, flow, hydrodynamic interactions (HIs), and topological interactions which govern semidilute polymer dynamics is challenging to characterize.

Force-Dependent Facilitated Dissociation Can Generate Protein-DNA Catch Bonds.

Cellular structures are continually subjected to forces, which may serve as mechanical signals for cells through their effects on biomolecule interaction kinetics. Typically, molecular complexes interact via "slip bonds," so applied forces accelerate off rates by reducing transition energy barriers. However, biomolecules with multiple dissociation pathways may have considerably more complicated force dependencies.

Ring polymer dynamics and tumbling-stretch transitions in planar mixed flows.

The properties of dilute polymer solutions are governed by the conformational dynamics of individual polymers which can be perturbed in the presence of an applied flow. Much of our understanding of dilute solutions comes from studying how flows manipulate the molecular features of polymer chains out of equilibrium, primarily focusing on linear polymer chains. Recently there has been an emerging interest in the dynamics of nonlinear architectures, particularly ring polymers, which exhibit surprising out-of-equilibrium dynamics in dilute solutions.

Tip-Patched Nanoprisms from Formation of Ligand Islands.

We apply the concept of "island formation" established for planar substrates, where ligands laterally cluster as they adsorb, to preparing nanoparticles (NPs) with precisely sized surface patches. Using gold triangular nanoprisms and 2-naphthalenethiols (2-NAT) as a prototypical system, we show that the preferential adsorption of 2-NAT on the prism tips leads to formation of tip patches. The patches are rendered visible for direct transmission electron microscopy and atomic force microscopy imaging upon attaching polystyrene--poly(acrylic acid).

Mapping the phase behavior of coacervate-driven self-assembly in diblock copolyelectrolytes.

Oppositely-charged polymers can undergo an associative phase separation process known as complex coacervation, which is driven by the electrostatic attraction between the two polymer species. This driving force for phase separation can be harnessed to drive self-assembly, via pairs of block copolyelectrolytes with opposite charge and thus favorable coulombic interactions. There are few predictions of coacervate self-assembly phase behavior due to the wide variety of molecular and environmental parameters, along with fundamental theoretical challenges.

Designing Electrostatic Interactions via Polyelectrolyte Monomer Sequence.

Charged polymers are ubiquitous in biological systems because electrostatic interactions can drive complicated structure formation and respond to environmental parameters such as ionic strength and pH. In these systems, function emerges from sophisticated molecular design; for example, intrinsically disordered proteins leverage specific sequences of monomeric charges to control the formation and function of intracellular compartments known as membraneless organelles. The role of a charged monomer sequence in dictating the strength of electrostatic interactions remains poorly understood despite extensive evidence that sequence is a powerful tool biology uses to tune soft materials.

Dilute solution structure of bottlebrush polymers.

Bottlebrush polymers are a class of macromolecules that have recently found use in a wide variety of materials, ranging from lubricating brushes and nanostructured coatings to elastomeric gels that exhibit structural colors. These polymers are characterized by dense branches extending from a central backbone and thus have properties distinct from linear polymers. It remains a challenge to specifically understand conformational properties of these molecules, due to the wide range of architectural parameters that can be present in a system, and thus there is a need to accurately characterize and model these molecules.