Block copolymers containing polymeric ionic liquids (PILs) can potentially combine high ionic conductivity and mechanical robustness. However, recent work demonstrates that the ionic conductivity of a model lamellar material is significantly depressed relative to expectations based on the measured properties of a PIL homopolymer (Coote et al., ACS Polymers Au, 3, 2023). Herein, the factors that control the ionic conductivity of this block copolymer chemistry are interrogated through systematic variations in morphology, where ionic conductivity is measured with a configuration that is insensitive to restructuring of the block copolymer at the electrode surface. The principal reason for the depressed ionic conductivity of lamellar phases at intermediate-to-strong segregation strength is defects that disrupt the long-range continuity of ionic domains, and a secondary reason is the elevated glass transition temperature (T g) of the PIL domains due to the high-T g nonionic domains. Transport-blocking defects are reduced by decreasing the molecular weight to achieve a weakly segregated state or by increasing the molecular weight to suppress diffusion and trap a morphology with only short-range order. We further show that transport-blocking defects are largely absent from PIL-rich morphologies having nonionic cylindrical or spherical domains embedded in a PIL matrix. The methodology outlined in this work offers a simple approach to identify the physics that control the bulk ionic conductivity of block copolymeric ionic liquids, providing critical information that can guide the design of such materials for target applications.

Abstract Polymer-grafted nanoparticles (PGNPs) combine the flexible conformation and chemical diversity of polymer brushes with the modifiable properties of inorganic cores, offering a versatile platform for constructing advanced nanostructures. Compared to traditional hard NPs, PGNPs show unique assembly behavior driven by their adaptable polymer brush conformations and tunable surface properties. Introducing three-dimensional (3D) soft confinement further expands the structural diversity of PGNP assemblies. In this Perspective, we explore how 3D soft confinement within oil-in-water emulsions directs PGNP assembly through complex enthalpic and entropic interactions at interfaces, resulting in unique self-assembled structures. First, we discuss how polymer brush-driven entropic and enthalpic interactions guide film assemblies, which similarly affect PGNP organization in 3D systems. Then, we examine 3D confined oil-in-water emulsion systems, where interfacial interactions at droplet surfaces create structural complexity by manipulating the conformation and orientation of PGNPs and other assembly constituents. Finally, this Perspective presents new opportunities and future directions for designing multifunctional materials through 3D confined PGNP assembly, with applications in optics, catalysis, and biomedicine.

Chemical doping has been widely used to enhance the electrical performance of conjugated polymer thin films for organic electronic devices with specific attention given to dopant molecule selection, modifications of copolymer design to enhance dopant interactions, and the doping process itself. Here, a set of expanded core thiophene-based copolymers are doped via solution, sequential, or "serial" doping processes. Serial doping, which utilizes solution and sequential doping methods in succession, was utilized to investigate how the use of a two-step doping method impacts the doping efficiency, thin film conductivity, and morphology. Results show that serial doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) increases the conductivity of all of the thiophene-based copolymers relative to either one-step solution or sequential doping processes. This increase in conductivity of serial-doped films is not attributed to greater levels of incorporation of F4TCNQ; rather, the serial-doped thin films display more ordered crystalline microstructures, despite the pristine films having amorphous character. This indicates that serial doping enhances the conductivity by inducing crystallization. This study also shows that as the spacing length between alkyl side chains of the expanded core copolymers is increased, the conductivity and the ordering of crystallites increases. Overall, this work provides insight into how copolymer design and the doping method impact conductivity through complex and intertwined relationships between dopant integration, effective electron transfer, and thin film microstructure.

In blends of chemically distinct polymers, the surface is usually enriched by the polymer with the lowest surface energy. Herein, we show that when "high energy" bottlebrush copolymers having an approximately equimolar mixture of polystyrene (PS) and poly(2-vinylpyridine) (P2VP) side chains are blended with "low energy" linear PS, the bottlebrush copolymer can enrich the free surface despite an estimated 15% gain in surface energy. This wetting reversal process is mediated by a strong entropic preference for the highly branched bottlebrush architecture at the surface of the blend. The high-energy surface forms spontaneously during film casting when the linear PS chains are much longer than the bottlebrush side chains and is stable through thermal annealing when the lengths of PS side chains, P2VP side chains, and linear PS are optimized. This work demonstrates that for a given commodity polymer, the library of candidate chemistries for the design of surface-active polymer additives is much broader than previously known.

The ionic conductivity in lamellar block copolymer electrolytes is often anisotropic, where the in-plane conductivity exceeds the through-plane conductivity by up to an order of magnitude. In a prior work, we showed significant anisotropy in the ionic conductivity of a lamellar block copolymer based on polystyrene (PS) and a polymer ionic liquid (PIL), and we proposed that the through-film ionic conductivity was depressed by layering of lamellar domains near the electrode surface. In the present work, we first tested that conclusion by measuring the through-plane ionic conductivity of two model PIL-based systems having controlled interfacial profiles using impedance spectroscopy. The measurements were not sensitive to changes in interfacial composition or structure, so anisotropy in the ionic conductivity of PS-block-PIL materials must arise from an in-plane enhancement rather than a through-plane depression. We then examined the origin of this in-plane enhancement with a series of PS-block-PIL materials, a P(S-r-IL) copolymer, and a PIL homopolymer, where impedance spectra were acquired with a top-contact electrode configuration. These studies show that enhanced in-plane ionic conductivities are correlated with the formation of an IL-rich wetting layer at the free surface, which presumably provides a low-resistance path for ion transport between the electrodes. Importantly, the enhanced in-plane ionic conductivities in these PS-block-PIL materials are consistent with simple geometric arguments based on properties of the PIL, while the through-plane values are an order of magnitude lower. Consequently, it is critical to understand how surface and bulk effects contribute to impedance spectroscopy measurements when developing structure-conductivity relations in this class of materials.

We examine the effects of solvent composition and solution-casting protocol on the structure of a lamellar sulfonated pentablock copolymer (SPC) membrane. Films are prepared by a layering process, wherein the film is built up through sequential bar-coating steps. Process variables include bar gap height, which controls drying time and layer thickness, and solvent selectivity toward each block in the SPC, which controls solution-state structure and biases the domain orientations at the surface. We find that irrespective of solvent selectivity, one-layer films have poorly ordered structures in the bulk with minimal restructuring near the surface. However, when the process involves sequential deposition of two or more layers, then the bulk structure of dry films can be well-predicted by the solution-state structure, and domain orientations at the surface are templated by polymer-solvent interactions. Consequently, processing conditions strongly influence through-plane transport properties of the SPC films. When the casting process generates disordered lamellae in bulk with a perpendicular lamellar orientation at the surface, both water and protons can move across the film. However, when the process generates highly ordered lamellae in bulk and parallel lamellar orientations at the surface, transport of both water and protons is inhibited by limited pathways. Significantly, the methodology outlined in this work can be extended to other ionic block copolymer platforms, allowing researchers to tailor bulk and surface morphologies for optimization of critical transport properties.

The most effective antifouling coatings are designed to slowly release biocides that target a broad spectrum of marine organisms. However, as biocides have a deleterious effect on marine life, there is demand for environmentally friendly coatings that resist fouling through physical interactions. We propose a simple platform for the development of such coatings based on bottlebrush-modified elastomers. The bottlebrush additives were synthesized to have side chain chemistries that are known to be fouling-resistant, and these were incorporated in a commercial elastomer through blending and/or covalent attachment. The fouling performance of these coatings was highly variable, with area coverages of hard and soft foulants ranging from 1.4% to 7.2% and 29.1% to 64.0%, respectively, across a set of eight materials. The origin of these differences was explained by examining the structure of the coating surface through chemical imaging by time-of-flight secondary ion mass spectrometry (TOF-SIMS) and topographic imaging by atomic force microscopy (AFM). We found that fouling by certain soft and hard fouling organisms was primarily influenced by surface composition, which was controlled by both the chemistry and loading level of the bottlebrush additive, and was independent of the inherent surface roughness. While no type of coating could resist all soft and hard foulants, a formulation based on a bottlebrush copolymer additive with both siloxane and fluorinated monomers was effective against nearly all organisms encountered in the study.

Block copolymer (BCP) thermoplastics are used in a wide range of commercial products. It is well known that the mechanical performance of these materials depends on the BCP architecture and composition, and the introduction of non-covalent interactions via comonomers can be used to tune key properties. However, tailoring the mechanics of BCPs by blending with polymeric additives is rarely explored, as most BCP/polymer blends have limited miscibility. Here, we examine the structure, mechanics, and thermal stability of a commodity thermoplastic, poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS), with polymeric additives of either polystyrene (PS) or poly(methyl methacrylate-co-cyclohexyl methacrylate) (PrC, 70 mol % cyclohexyl methacrylate). PS and PrC are athermal and enthalpically compatible additives, respectively, for the PS end-blocks in SEBS. The SEBS/PS blends have a narrow miscibility window with respect to PS molecular weight and loading, where either an ordered lamellar morphology or a disordered morphology is observed. In contrast, the attractive interaction between PrC and PS end-blocks leads to complete miscibility of SEBS/PrC blends across the full range of PrC molecular weights (up to 63.8 kg/mol) and loadings (up to 40 vol %) that were studied, where an ordered lamellar morphology with continuity in the rubber phase was generally observed. Consequently, the PrC additives can increase the modulus and yield stress, as well as delay the onset of strain hardening, without loss of toughness. Additionally, PrC additives can elevate the glass transition temperature of the PS blocks and maintain a high modulus at elevated operating temperatures, expanding the service window for SEBS. The principles established in this research could be translated to other types of styrenic BCP thermoplastics.

Fundamental understanding of the physical processes controlling deprotection in chemical amplified resists (CARs) is critical to improve their utility for high-resolution lithography. We employ a combined experimental and computational method to examine the impacts of excess free volume generation, reaction byproducts, catalyst clustering, and catalyst counter-anion chemistry/size on deprotection rates in a model terpolymer CAR. These studies suggest that catalyst diffusion can be enhanced by a combination of excess free volume and reaction byproducts, and that counter-anion chemistry/size plays a key role in local reaction rates, which stems from differences in the rotational mobility of the catalyst.

The surface properties of polymeric materials govern interactions with the surroundings and are responsible for various application-relevant properties. Recent studies have shown that bottlebrush polymers can be used to modify the surface chemistry of the polymers because they spontaneously segregate to the interfaces when they are blended with the linear polymers, driven in large part by entropic effects that arise from the unique architecture of bottlebrush polymers. However, while prior work has largely focused on equilibrium segregation profiles, kinetic and processing effects can also drive bottlebrush additives to surfaces and interfaces. In solution-cast blends of polymers and colloids, vertical stratification is controlled by the relative Peclet (Pe) numbers of the constituents, i.e., the relative rates of solvent evaporation and solute diffusion. Herein, we studied processing effects that drive bottlebrush additives to interfaces when blended with linear polymers. We prepared blends of bottlebrush polystyrene (BBPS) and linear perdeuterated polystyrene (dPS), where the BBPS side-chain length was fixed at N-sc = 48, the BBPS backbone length ranged from N-b = 30-260, and the dPS chain length ranged from N-m = 40-548. The relative Pe numbers of BBPS and dPS were varied by changing the solvent and sizes of BBPS and dPS. In contrast to other binary blends where the constituents have disparate sizes (e.g., colloid/colloid, polymer/colloid, and polymer/polymer), we found that the relative Pe number cannot account for the degree of segregation observed in these bottlebrush and linear polymer blends. For a fixed BBPS side-chain length, we observe stronger surface segregation of bottlebrush additives when the blend is cast using lower boiling point solvents and/or for blends with longer bottlebrush polymers. We further show that solvent annealing of the film can increase the enrichment of bottlebrush additives near surfaces. This study provides insight into the interplay of processing effects and blend thermodynamics that govern surface segregation of bottlebrush polymer additives.

In chemically amplified resists (CARs), it is known that catalyst diffusion is accelerated by the deprotection reaction. However, the mechanisms that drive this enhancement are not yet known as it is difficult to probe local changes in polymer chemistry and density during the reaction, as well as their effects on catalyst diffusion, through experiments alone. We examine catalyst diffusion in a model terpolymer CAR, both in the presence and absence of reaction, using a combination of experiments and atomistic simulations. From experiments, we find that deprotection rates are faster than film densification, and that reaction enhances long-time catalyst diffusion lengths by a factor of four. From simulations, we find evidence that catalyst mobility is enhanced in recently reacted regions of the terpolymer. These results provide insight into the origins of accelerated catalyst diffusion during reaction, and will be utilized in the development of physics-informed models of CAR systems.

Polymeric chemically amplified resists (CARs) are critical materials for high-throughput lithographic processes. A photoactivated acid-anion catalyst changes the polymer's solubility via a deprotection reaction, which enables pattern development through selective dissolution. To capture observed reaction kinetics, reaction-diffusion models employ a catalyst diffusivity that is accelerated by reaction. However, the microscopic origin and factors contributing to this phenomena remain unclear. Herein, we employ detailed atomistic molecular dynamics simulations to examine the impact of protecting group removal and material relaxation on catalyst mobility. We report data on polymer density, catalyst dispersion, excess free volume, and segmental dynamics with increasing time/extent of deprotection. We then propose simple kinetic Monte Carlo algorithms that can describe both molecular dynamics simulations of deprotection reactions and experimental data.

Bottlebrush polymers are complex macromolecules with tunable physical properties dependent on the chemistry and architecture of both the side chains and the backbone. Prior work has demonstrated that bottlebrush polymer additives can be used to control the interfacial properties of blends with linear polymers but has not specifically addressed the effects of bottlebrush side chain microstructures. Here, using a combination of experiments and self-consistent field theory (SCFT) simulations, we investigated the effects of side chain microstructures by comparing the segregation of bottlebrush additives having random copolymer side chains with bottlebrush additives having a mixture of two different homopolymer side chain chemistries. Specifically, we synthesized bottlebrush polymers with either poly(styrene-ran-methyl methacrylate) side chains or with a mixture of polystyrene (PS) and poly(methyl methacrylate) (PMMA) side chains. The bottlebrush additives were matched in terms of PS and PMMA compositions, and they were blended with linear PS or PMMA chains that ranged in length from shorter to longer than the bottlebrush side chains. Experiments revealed similar behaviors of the two types of bottlebrushes, with a slight preference for mixed side-chain bottlebrushes at the film surface. SCFT simulations were qualitatively consistent with experimental observations, predicting only slight differences in the segregation of bottlebrush additives driven by side chain microstructures. Specifically, these slight differences were driven by the chemistries of the bottlebrush polymer joints and side chain end-groups, which were entropically repelled and attracted to interfaces, respectively. Using SCFT, we also demonstrated that the interfacial behaviors were dominated by entropic effects with high molecular weight linear polymers, leading to enrichment of bottlebrush near interfaces. Surprisingly, the SCFT simulations showed that the chemistry of the joints connecting the bottlebrush backbones and side chains played a more significant role compared with the side chain end groups in affecting differences in surface excess of bottlebrushes with random and mixed side chains. This work provides new insights into the effects of side chain microstructure on segregation of bottlebrush polymer additives.

The acid-catalyzed deprotection of glassy polymer resins is an important process in semiconductor lithography. Studies have shown that the reaction kinetics in these materials is controlled by slow diffusion of the acid-anion catalyst, but trends deviate from models of a first-order reaction coupled to a composition-invariant Fickian diffusivity. We present a concerted experimental and computational effort to examine catalyst diffusion in a model resin of poly(4-hydroxystyrene-co-tert-butyl acrylate-co-styrene), or P(HOSt-tBA-St), which is deprotected in the presence of an acid catalyst to poly(4-hydroxystyrene-co-acrylic acid-co-styrene), or P(HOSt-AA-St). We employed an inert catalyst analogue to examine long-time ion dynamics in both terpolymers with atomistic molecular dynamics simulations and compared the calculated Fickian diffusivities with direct measurements of ion diffusion fronts using time-of-flight secondary ion mass spectrometry. Our results demonstrate that ion diffusivities in P(HOSt-tBA-St) and in P(HOSt-AA-St) are similar near and below the glass transition, consistent with a diffusion process that is dominated by interactions with the polar HOSt units. We then compared the bulk reaction kinetics measured by Fourier-transform infrared spectroscopy with reaction kinetics obtained using mesoscopic reaction-diffusion models. We found that initial reaction kinetics is significantly accelerated compared to predictions based on the long-time ion diffusivities of our inert system. This study highlights the potential of atomistic modeling coupled with targeted experiments for interrogating the physical and chemical processes that control pattern formation in next-generation lithographic materials.

Catalyst diffusion is a critical component of the pattern formation process in chemically amplified resists (CARs). In this study, we used a concerted experimental and modeling effort to examine diffusion of an inert catalyst analogue (sodium triflate) in a hydroxystyrene-based ESCAP terpolymer resin. First, atomistic simulations at high temperatures reveal an order-of-magnitude enhancement of the Fickian diffusivity in the protected reactant versus the fully deprotected product, while time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements at temperatures near the glass transition show no appreciable differences. The data from simulations and experiments conform to a unified curve, enabling estimates of the Fickian diffusivity at relevant post-exposure bake (PEB) temperatures through extrapolation. Second, acid-catalyzed reaction kinetics were measured with Fourier-transform infrared spectroscopy and compared with reaction-diffusion models based on the estimated Fickian diffusivities. The initial kinetics in experiments is orders-of-magnitude faster than predictions, demonstrating that models of catalyst transport should capture effects beyond Fickian diffusion. Finally, the simulations examined ion-ion and polymer-ion interactions at the atomistic level, features that are difficult to probe by experimental investigations. These data show that ion pair clustering in the protected and deprotected materials is similar as temperature is reduced, and ion pair dynamics in both materials is dominated by interactions with hydroxystyrene repeat units. These trends explain the experimental observations that ion diffusion is similar in the protected and deprotected polymers.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used for chemical analysis of surfaces. ToF-SIMS is a powerful tool for polymer science because it detects a broad mass range with good mass resolution, thereby distinguishing between polymers that have similar elemental compositions and/or the same types of functional groups. Chemical labeling techniques that enhance contrast, such as deuterating or staining one constituent, are generally unnecessary. ToF-SIMS can generate both two-dimensional images and three-dimensional depth profiles, where each pixel in an image is associated with a complete mass spectrum. This Review begins by introducing the principles of ToF-SIMS measurements, including instrumentation, modes of operation, strategies for data analysis, and strengths/limitations when characterizing polymer surfaces. The sections that follow describe applications in polymer science that benefit from characterization by ToF-SIMS, including thin films and coatings, polymer blends, composites, and electronic materials. The examples selected for discussion showcase the three standard modes of operation (spectral analysis, imaging, and depth profiling) and highlight practical considerations that relate to experimental design and data processing. We conclude with brief comments about broader opportunities for ToF-SIMS in polymer science.

Substituents were introduced onto addition polynorbornenes to modify their thermal properties. The resultant materials displayed depressed glass-transition temperatures, high decomposition temperatures, and could be melt-processed.

Bottlebrush polymers can be used to introduce novel surface properties including hydrophilicity, stimuli-responsiveness, and reduced friction forces. However, simple, general, and efficient approaches to cross-linking bottlebrush polymer films and coatings are limited. Here, we report that bottlebrush polymers with an unsaturated polynorbornene backbone and thiol-terminated side chains can be cross-linked on demand by UV irradiation to produce uniform and insoluble bottlebrush polymer coatings. To quantify the kinetics and efficiency of cross-linking by UV exposure (254 nm), we measured the normalized residual thickness (NRT) of bottlebrush and linear polymer films after UV exposure and solvent washing. For bottlebrush polymers with thiol-terminated polystyrene (PS) side chains, the NRT exceeded 60% for a UV dose of 1.0 J/cm(2), while unfunctionalized linear PS required a dose of 7.9 J/cm(2) to achieve similar NRT values. Rapid UV-induced cross-linking of the bottlebrush PS was attributed to the thiol-ene coupling of the thiol-terminated side chains with the unsaturated polynorbomene backbones, as demonstrated through FTIR measurements and control studies involving bottlebrush polymers with saturated backbones. To establish the broader applicability of this approach, UV-induced cross-linking was demonstrated for thin films of bottlebrush polymers with thiol-terminated poly(methyl acrylate) (BB-PMMA-SH) side chains and those with poly(ethylene glycol) (BB-PEG) and poly(lactic acid) (BB-PLA) side chains which do not contain thiol end groups. UV-induced cross-linking of BB-PEG and BB-PLA films required the use of a multifunctional thiol additive. Finally, we demonstrated that bottlebrush polymer multilayers can be fabricated through sequential deposition and UV-induced cross-linking of different bottlebrush polymer chemistries. The cross-linking process outlined in this work is simple, general, and efficient and produces solvent-resistant coatings that preserve the unique properties and functions of bottlebrush polymers.

Discrete oligomers (i.e., highly monodisperse) can provide a deep understanding of chain-length-dependent properties of polymers and their self-assembly behaviors. Herein, discrete oligo(3-hexylthiophene)s (D-o3HTs) with a dispersity (D) of 1.0 and degree of polymerization (DP) between 6 and 18 were obtained through a simple synthetic procedure of 3-hexlythiophene trimer-based polymerizations and automated column chromatography purification. As the DP of D-o3HTs increases, longer conjugation lengths cause red shifts in their optical properties and yield tunable crystalline properties. Interestingly, D-o3HTs with DP = 12 assemble into a dominant edge-on Form I structure in thin films and show highly ordered fiber morphologies. In addition, Bragg rod patterns are observed in thin films by transmission electron microscopy and grazing incidence X-ray scattering with these patterns being distinctive when compared to those for conventional regioregular poly(3-hexylthiophene) with D = 1.1. Finally, the formation of 2-dimensional flowerlike nanostructures with overall micrometer dimensions is obtained from D-o3HTs via solvent-mediated self-assembly. These results offer an understanding of self-assembly behaviors of discrete conjugated polymers, leading to exquisite control over their crystallinity and nanoscale morphology.

Despite successful modeling of graphene as a 0.34-nm thick optical film synthesized by exfoliation or chemical vapor deposition (CVD), graphene induced shift of surface plasmon resonance (SPR) of gold films has remained controversial. Here we report the resolution of this controversy by developing a clean CVD graphene transfer method and extending Maxwell-Garnet effective medium theory (EMT) to 2D materials. A SPR shift of 0.24 is obtained and it agrees well with 2D EMT in which wrinkled graphene is treated as a 3-nm graphene/air layered composite, in agreement with the average roughness measured by atomic force microscope. Because the anisotropic built-in boundary condition of 2D EMT is compatible with graphene's optical anisotropy, graphene can be modelled as a film thicker than 0.34-nm without changing its optical property; however, its actual roughness, i.e., effective thickness will significantly alter its response to strong out-of-plane fields, leading to a larger SPR shift.