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We apply a machine learning (ML) technique to the multiobjective design of polymer blend electrolytes. In particular, we are interested in maximizing electrolyte performance measured by a combinati...

Recent experimental results have demonstrated that polymeric ionic liquids doped with Li salts exhibit enhanced ionic mobilities and lithium ion transference numbers with increasing salt concentrat...

Lower critical solution behavior in binary blends of hydrophobic polyethers with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]) exhibited a difference in lower critica...

Block copolymers self-assemble into a variety of morphologies that can serve as templates for preparing conductive or porous materials such as batteries and membranes. These morphologies can be eit...

We study ternary polymer-polymer-salt blend electrolytes using coarse-grained molecular dynamics. We specifically examine the influence of the polymer hosts’ incompatibility and polarity contrast o...

We used atomistic molecular dynamics simulations to study ion mobilities and the molecular mechanisms of transport in blends of poly(1-butyl-3-vinylimidazolium hexafluorophosphate) electrolytes with 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquids. We characterized the structural and dynamical properties of the blend electrolyte systems through radial distribution functions, diffusivities, conductivities, and different time scales of relaxation and probed the correlations underlying such characteristics. Our results indicate that many features of ion transport in such blend systems mirror those observed in our earlier study of pure polymerized ionic liquids [Mogurampelly et al. J. Am. Chem. Soc. 2017, 139, 9511]. Explicitly, we observe that the anions associated with the polymerized cation move along the polymer backbone via the formation and breakup of ion pairs involving polymerized cationic monomers of different polymer chains. Interestingly, for all blend systems excepting pure polymeric ...

We modulated the grafting density (σ) and chain length of polystyrene (PS) brushes on substrates to probe their effect on the glass transition temperature (Tg) in overlaying PS thin films. The Tg of PS films was analyzed as a function of brush thickness (or σRg2), where Rg is the radius of gyration of PS brushes. Our results indicate that PS films below 90 nm exhibit a nonmonotonic dependence of Tg on grafting density with the maximum Tg occurring near the regime of wetting–dewetting transition of the overlaying melt. The maximum Tg was found to be higher than the value of bulk PS system. Computer simulation results suggest that such trends arise as a consequence of the environment of enhanced friction presented by the brush layer and the overlap between the polymer film and the grafted layer.

Coarse-grained molecular dynamics simulations were carried out to identify the conditions under which the nanorods (NRs) side-grafted with polymer chains can assemble in end-to-end configurations in a homopolymer matrix, a structure of significant importance for optimal property characteristics. Our results demonstrate that by adjusting the grafting density and the grafted chain length, three different NR morphologies can be obtained, viz., side-by-side aggregation, end-to-end alignment and homogeneous dispersion. To understand the underlying mechanism, the chain characteristics around the NRs were systematically investigated. We find that the transition of NR morphologies from side-by-side aggregation to others is correlated to the mushroom-to-brush transition of the grafted chain configurations. At high grafting densities corresponding to the brush regime, the entropic steric repulsions between the polymer brushes prevent the NRs from approaching in side-by-side configurations. Instead, end-to-end assem...

An understanding of the structure–property relationship in polymer/nanorod (NR) nanocomposites is of fundamental importance in designing and fabricating polymer nanocomposites (PNCs) with desired properties. Here, we study the structural, mechanical, and viscoelastic properties of polymer-grafted NR filled PNCs, using coarse-grained molecular dynamics simulation. The mechanical reinforcement efficiency is found to be determined by the NR/polymer interfacial properties, which are in turn modulated by the grafting density, the grafted chain length, and the graft–matrix interaction strength. By systematically analyzing the evolution of the polymer-grafted NRs during mechanical deformation, we find that the NRs aligning side by side with each other do not contribute much to the mechanical reinforcement. Simulation results also indicate that the strain-dependent viscoelastic behavior (the Payne effect) originates from the failure of the local filler network and, especially, NR clusters constructed via site-to-...

We modulated the grafting density (σ) of a random copolymer brush of poly(styrene-r-methyl methacrylate) on substrates to probe its effect on the formation of perpendicularly aligned lamellae of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA). Supported by coarse-grained simulation results, we hypothesized that an increase in σ will allow us to systematically tune the block copolymer interfacial interactions with the substrates from being preferential to one of the blocks to being neutral toward both blocks and will thereby facilitate enhanced regimes of perpendicularly aligned lamellae. We verified such a hypothesis by using a simple grafting-to approach to modify the substrates and characterized the thickness window for perpendicular lamellae as a function of brush thickness (or σ) on the grafted substrates using scanning force microscopy (SFM) images and grazing incidence small-angle X-ray scattering (GISAXS) measurements. The experimental results validated our hypothesis and suggested that the σ o...

We report the results of atomistic simulations of the structural equilibrium properties of PS–PEO block copolymer (BCP) melt in the ordered lamellar phase doped with LiPF6 salt. A hybrid simulation strategy, consisting of steps of coarse-graining and inverse coarse-graining, was employed to equilibrate the melt at an atomistic resolution in the ordered phase. We characterize the structural distributions between different atoms/ions and compare the features arising in BCPs against the corresponding behavior in PEO homopolymers for different salt concentrations. In addition, the local structural distributions are characterized in the lamellar phase as a function of distance from the interface. The cation–anion radial distribution functions (RDF) display stronger coordination in the block copolymer melts at high salt concentrations, whereas the trends are reversed for low salt concentrations. Radial distribution functions isolated in the PEO and PS domains demonstrate that the stronger coordination seen in B...

In recent works, we demonstrated that donor-b-acceptor block copolymer compatibilizers can be utilized in donor–acceptor blends of conjugated homopolymer donors and PCBM acceptors to target equilibrium morphologies containing the interconnected, cocontinuous structures that are desired for efficient bulk heterojunction devices. In this article, we utilize a combination of morphology and device-level simulations to demonstrate that by tuning the photoelectronic properties of the block copolymer additives, the device characteristics of such ternary blend systems can be made to outperform the idealized morphologies envisioned in donor–acceptor systems. Explicitly, we propose that by appropriately choosing the HOMO and LUMO energy levels of the block copolymer additives, an energy cascade can be exploited to reduce charge recombination and increase fill factors. The resulting device performance of such ternary blends reflects the combined influence of morphology and energy cascades, and in some instances, ter...

We use molecular dynamics simulations to study the normal mode dynamics and frequency dependent dielectric relaxation spectra of diblock copolymers in lamellar phases. In contrast to previous works which have relied on the applicability of Rouse modes, we effect an explicit normal-mode analysis of the chain dynamics in the ordered phases in the directions parallel and perpendicular to the lamellar plane. We considered two models to isolate the specific effects arising from the morphological ordering and mobility disparities between the blocks. For systems with no mobility disparity between the blocks, our analysis demonstrates that both the normal modes and their relaxation dynamics in the planes parallel and perpendicular to the lamella exhibit deviations from the Rouse modes. For systems in which the mobility of one of the blocks was frozen in the lamellar phase, the normal modes closely resembled the Rouse modes for tethered polymers. However, the relaxation dynamics of such modes exhibited deviations ...

Use of block copolymer thin films in lithographic applications requires orientation of domains perpendicular to a substrate. Algebraic models were used to predict conditions that are favorable for perpendicular versus parallel domain orientation in films confined between two interfaces. The free energy of each orientation was evaluated, yielding response surface plots as a function of film thickness and the preferential interaction strength at each interface. The model predicts that perpendicular orientation is generally favored for thinner films and at thicknesses incommensurate with the bulk periodicity, L0. If either the top or bottom interfaces are preferential for one block, the favorable thickness windows shift depending on the interface wetting behavior. An extensive body of thin film experimental work corroborated the analytical predictions. The algebraic model has predictive value, and it demonstrates the complexity of the dependence of block copolymer orientation on the wetting behavior of the i...

Using molecular dynamics (MD) simulations in conjunction with topological analysis algorithms, we investigate the changes, if any, in entanglement lengths of flexible polymers in ordered lamellar phases of diblock copolymers. Our analysis reveals a reduction in the average entanglement spacing of the polymers with increasing degree of segregation between the blocks. Furthermore, the results of the topological analysis algorithms indicate an inhomogeneous distribution of entanglement junctions arising from the segregated morphology of the block copolymer. To understand such trends, we invoke the packing arguments proposed by Kavassalis and Noolandi in combination with the framework of polymer self-consistent-field theory (SCFT) and Monte Carlo simulations. Such an analysis reveals qualitatively similar characteristics as our MD results for both the average entanglement spacing and the inhomogeneities in entanglements. Together, our results provide evidence for the changes in entanglement features arising f...

Using all atom molecular dynamics and trajectory-extending kinetic Monte Carlo simulations, we study the influence of Al2O3 nanoparticles on the transport properties of ions in polymer electrolytes composed of poly(ethylene oxide) (PEO) melt solvated with LiBF4 salt. We observe that the mobility of Li+ cations and BF4– anions and the overall conductivity decrease upon addition of nanoparticles. Our results suggest that the nanoparticles slow the dynamics of polymer segments near their surfaces. Moreover, the preferential interactions of the ions with the nanoparticles are seen to lead to an enhancement of ion concentration near the particle surfaces and a further reduction in the polymer mobilities near the surface. Together, these effects are seen to increase the residence times of Li+ cations near the polymer backbone in the vicinity of the nanoparticles and reduce the overall mobility and conductivity of the electrolyte. Overall, our simulation results suggest that both the nanoparticle-induced changes...

We use a numerical implementation of polymer self-consistent field theory to study the effective interactions between two spherical particles in polyelectrolyte solutions. We consider a model in which the particles possess fixed charge density and the polymers contain a prespecified amount of dissociated charges. We quantify the polymer-mediated interactions between the particles as a function of the particle charge, polymer concentrations and particle sizes. We study the interplay between depletion interactions, which arise as a consequence of polymer exclusion from the particle interiors, and the electrostatic forces which result from the presence of charges on the polymers and particles. Our results indicate that for weakly charged and uncharged particles, the polymer-mediated interactions predominantly consist of a short-range attraction and a long-range repulsion. When the particle charge is increased, the interactions become purely repulsive. A longer range, albeit weaker, bridging attraction was al...

Polymeric microemulsions are formed in a narrow range of phase diagram when a blend of immiscible homopolymers is compatibilized by copolymers. In this study, we consider the ternary blend system of A and B homopolymers mixed with block copolymers containing A and B segments and probe the efficacy of different copolymer configurations in promoting the formation of microemulsion phases. Specifically, we consider (a) monodisperse diblock copolymers (D), (b) diblock copolymers with bidisperse molecular weights (MW) (BDL), (c) block copolymers having MW polydispersity in one of the blocks (PD), (d) diblock copolymers having monodisperse MW but bidispersity in average composition (BDC), and (e) gradient copolymers exhibiting a linear variation in the average composition (G). Using single chain in mean field simulations effected in two dimensions, we probe the onset of formation and the width of the bicontinuous microemulsion channel in the ternary phase diagram of homopolymer blended with compatibilizer. We ob...

We present a strong stretching theory model for microphase segregation of AB + AC block copolymer blends in which the B and C segments possess strongly attractive (hydrogen bonding) interactions. In microphase separated morphologies, we demonstrate that the attraction between the B and the C segments causes a bending force toward the A layers. Such bending forces may induce transitions from lamellar and A-majority cylindrical morphologies in the pure component systems to “inverted” cylindrical and spherical morphologies in blends in which the B and C segments constitute the matrix phase. Similar driving forces may also drive transitions from A-majority spherical phases in pure component systems to highly asymmetric lamellar morphologies in blends. The predictions of our model are in excellent agreement with the trends observed in recent experimental results.

We model the self-assembly of a diblock copolymer thin film in contact with a random copolymer brush using self-consistent field theory employing a quenched distribution for the brush chains. We focus on the regime of parameters where the diblock copolymers exhibit lamellar morphologies, and study the alignment behavior of the lamellar morphologies on the grafted substrates. Our results reveal a templating of the self-assembly morpology by the brush chains. We find two novel features of this templating behavior: The ends of the grafted chains rearrange themselves to create a more favorable interface, an effect which is present in both the parallel and perpendicular morphologies, and is enhanced with increasing blockiness of the sequences of the random copolymer. In addition, the brush chains may splay laterally in perpendicular morphologies and enrich the interface even further in the favorable component. The latter feature leads to nontrivial free energy differences between the parallel and perpendicular...

Phase behavior of binary blends consisting of high molecular weight polystyrene-block-poly(2-vinylpyridine) copolymer (PS-b-P2VP) and low molecular weight polystyrene-block-poly(4-hydroxystyrene) copolymer (PS-b-PHS) was investigated by using small-angle X-ray scattering and transmission electron microscopy. Both PS-b-P2VP and PS-b-PHS exhibited lamellar microdomain over the entire experimental temperatures up to 300 °C. When the weight fraction of PS-b-PHS in the blend was less than 0.1, the lamellar microdomains were maintained. However, with increasing amount of PS-b-PHS, the microdomains in the blends were transformed to hexagonally packed (HEX) cylindrical microdomains and body-centered cubic (BCC) spherical microdomains. On the other hand, when a relatively high molecular weight of PS-b-PHS was used, the BCC spherical microdomains were not observed even at a large weight fraction of PS-b-PHS in the blend, but HEX cylindrical microdomains were formed. The phase behaviors observed experimentally were ...

We present experimental results for the glass transition behavior of polystyrene (PS) films on grafted PS layers of the same chemical identity as a function of film thickness. Our results suggest t...

We present the results of a facilitated kinetic Ising model based investigation of the confinement and filler-induced changes in the glass transition, fragility, and aging dynamics of a model system. This work is motivated by the issue of relationships, if any, in the glass transition phenomena of polymer nanocomposites and polymer thin films. Our results suggest that addition of plasticizing fillers lower the Tg and increase the fragility of the system, while antiplasticizing fillers have an opposite effect. Confinement arising in freely suspended films of both filled and unfilled systems were seen to reduce the overall Tg of the system. Confinement and filler-induced shifts in the Tg were not found to be quantitatively equivalent when compared at the appropriate film thicknesses and interparticle spacings. However, the fragilities exhibited a trend that suggests a closer quantitative equivalence between the PNCs and thin films. In all the cases we examined, the aging dynamics and nonequilibrium relaxati...

We present results obtained using a drift-diffusion model for the structure−property correlations in photovoltaic devices based on self-assembly of rod−coil block copolymers. We use a self-consistent field theory model to generate the self-assembly morphologies of rod−coil block copolymers in confined situations. The density and orientational order parameter profiles so-obtained are then used as input to a recently proposed drift-diffusion model which predicts the photovoltaic device characteristics. The latter model allows for prescription of arbitrary morphologies of donor and acceptor phases while simultaneously incorporating the role of anisotropic charge transport of holes and excitons that arise in the ordered phases of rod−coil block copolymers. We present results elucidating the role of morphology of self-assembly, orientation of lamellar phases, domain widths, and the degree of phase separation and orientational ordering, upon the photovoltaic device characteristics.

We present experimental results quantifying the dewetting behavior of poly(methyl methacrylate) (PMMA) melt on polymer brushes of polystyrene (PS) molecules. Our studies indicate contact angles which display a brush molecular weight dependence similar to that expected for autophobic dewetting situation. We use strong segregation theory calculations to model the interfacial tension behavior in our observations and delineate the interplay between enthalpic and entropic effects in polymer wetting upon polymer brushes.

Efficient strategies for dispersion of carbon nanotubes in polymeric and solvent matrices constitutes an area of active interest. In this article, we examine from a theoretical perspective the hypo...

The Flory−Huggins interaction is measured for a model rod−coil block copolymer system, poly(alkoxyphenylenevinylene-b-isoprene), by fitting the interfacial segregation of block copolymer to a homopolymer interface and by using the random phase approximation (RPA) for block copolymers. The measured interfacial segregation of a block copolymer to the interface between homopolymers, fit with a self-consistent field theory (SCFT) simulation using χ as a variable parameter, gives a functional form χ = 34.8/T − 0.091. When RPA is applied to neutron scattering curves for the rod−coil system above the order−disorder transition, the theoretical structure factors are inconsistent with observed scattering curves due to complex aggregated structures formed in the nematic and isotropic states. Using the Flory−Huggins parameter and a previously measured value of the Maier−Saupe parameter, the PPV-b-PI phase diagram may be converted from system-specific variables to dimensionless parameters. Under the assumptions that t...

We present a new model based on self-consistent field theory (SCFT) approach and complement it by strong segregation theory (SST) based calculations to characterize the self-assembly behavior in si...

Poly(methyl methacrylate) (PMMA)−C60 nanocomposites, with compositions in the range 0 ≤ φC60wt ≤ 0.05, are shown to exhibit systematic increases in dynamic shear moduli, in glass transition temperature (Tg), and in the longest relaxation time of the polymer (τR) with increasing fullerene concentration. We show that while the φC60wt dependence of the plateau modulus can be reconciled with a conventional “filler” effect, the systematic increases in Tg and in τR are associated with specific interactions between the C60 and the polymer segments. In the melt, these segment−C60 interactions are proposed to reduce polymer segmental mobility in the vicinity of the particle surface and ultimately suppress polymer dynamics, as measured mechanically, in a manner consistent with an increase in the polymer segmental friction coefficient.

The addition of homopolymers to a self-assembling rod-coil block copolymer is demonstrated to be a flexible route toward domain size control. Molecular weight matched rod-like homopolymers interdigitate with the rod-blocks within their respective lamellae. As a result of the interdigitation, the coil blocks must rearrange to occupy more interfacial area resulting in an unprecedented decrease in domain spacing with increasing rod homopolymers. Conversely coil homopolymers were locally solubilized within the coil microdomain resulting in an increase of domain spacing with increasing coil homopolymers. The mechanisms of homopolymers solubilization are in qualitative agreement with predictions made by self-consistent mean-field theory (SCFT) calculations.

We study the effective pair interaction potentials and the resulting phase behavior, percolation transitions of nanorods dispersed in solutions of adsorbing polymers. We use polymer self-consistent-field theory in conjunction with the Derjaguin approximation to compute the polymer-mediated orientation-dependent pair interaction potential between cylindrical nanorods. A modified Flory theory and a simple analytical model are used to delineate the different equilibrium phases and the onset of percolation for nanorods in polymer solutions. Our results suggest that the topology of the phase diagram of a mixture of polymer and rods is highly dependent on the anisotropy of the rods, relative sizes of the rods and polymers, concentration of the polymer, and the strength of adsorption. For the case of nonadsorbing polymers, the polymer depletion-induced attractive interactions result in a large two-phase region which widens with an increase in the polymer concentration. Addition of adsorbing polymers is observed ...

We present strong segregation approximation based analytical calculations and complementary computer simulation results on the ordering and structural characteristics of block copolymer−nanoparticle mixtures. We consider specifically the case of a symmetric block copolymer organized in a lamella phase, which is mixed with both selective and nonselective nanoparticles. We present results within the strong segregation approximation quantifying the density distribution of nanoparticles and the influence of the nanoparticles upon the lamella thickness and their elastic constants. The case of nonselective nanoparticles is treated in detail to account more accurately for both size effects and finite concentrations of nanoparticles. The latter results suggest the possibility of layer instabilities and morphological transitions resulting from the surfactant-like role of nonselective particles. Qualitative features of our model predictions are in agreement with our computer simulation results.

We use computer simulations to study the mechanisms governing the linear viscoelasticity behavior of composites of spherical nanofillers dispersed in polymer melt matrices. Our results suggest that particles can influence the viscoelastic properties of the system by a variety of different mechanisms. On one hand, the particle-induced effects on the dynamics of polymer segments modify the relaxation spectrum of the polymers. Second, particle jamming effects lead to slow relaxations and substantial enhancements in elasticity. Finally, our results suggest that the strain field distortion caused by the presence of rigid inclusions also affects the overall modulus of the composite. For our model system, we delineate the regimes and frequencies at which the different effects manifest and also suggest how the picture can be generalized for parametric conditions different from our simulations.

We apply a recently proposed multiscale simulation approach to study the dynamical properties of polymer blend interfaces. We use this approach to study the influence of the bulk rheological properties of the polymer blend components upon the slip at unentangled polymer interfaces. Our numerical results agree quite well with the predictions from scaling approaches and phenomenological theories. Moreover, these results also provide a microscopic explanation of the negatively deviating viscosities of polymer blends. We also present results elucidating the slip suppressing influence of block copolymer compatibilizers. Our results suggest that even trace fractions of compatibilizers can suppress slip at polymer interfaces. We study the influences of the molecular weight of the block copolymer and the coverage of block copolymers upon the dynamical properties of polymer blend interfaces, and we suggest some effects that might account for the effect of compatibilizers in the suppression of coalescence during po...

We present a Monte Carlo approach to incorporating the effect of thermal fluctuations in field theories of polymeric fluids. This method is applied to a field-theoretic model of a ternary blend of AB diblock copolymers with A and B homopolymers. We find a shift in the line of order-disorder transitions from their mean-field values, as well as strong signatures of the existence of a bicontinuous microemulsion phase in the vicinity of the mean-field Lifshitz critical point. This is in qualitative agreement with a recent series of experiments conducted with various three-dimensional realizations of this model system. Further, we also compare our results and the performance of the presently proposed simulation method to that of an alternative method involving the integration of complex Langevin dynamical equations., Comment: minor changes, references added

We examine the concept of entanglements and the associated entanglement lengths in polymer interfaces. Explicitly, we consider the influence of the compositional inhomogeneity and the manner in which it influences the entanglement lengths. We address this issue by adapting the packing model of entanglements proposed by Kavassalis and Noolandi. The effects of the compositional inhomogeneity are incorporated through a combination of Monte Carlo simulations and self-consistent-field theory computations. Our results mainly focus on the inhomogeneous variations of entanglements in the interfacial region of polymer blends. In this context, we elaborate upon the connections between our results and the experimentally measurable macroscopic properties like the slip, rheology, and the toughness of polymer−polymer interfaces.

We review a class of new computer simulation methods for polymeric fluids and other soft condensed matter systems that are based on an underlying field-theoretic description. These methods, while still in an early stage of development, show considerable promise for studying the equilibrium properties of many-component systems capable of intricate self-assembly, such as solutions and blends containing block and graft copolymers. Field-theoretic simulation methods also provide a great deal of flexibility in model building and coarse graining, and appear to be particularly well suited to treat systems with soft, long-range interactions, such as polyelectrolytes. We attempt to connect various related theoretical approaches, such as self-consistent field theory and dynamic density functional theory, within a common framework.