While the phase separation of binary mixtures of chemically different polymer-grafted nanoparticles (PGNPs) is observed to superficially resemble conventional polymer blends, the presence of a “soft” polymer-grafted layer on the inorganic core of these nanoparticles qualitatively alters the phase separation kinetics of these “nanoblends” from the typical pattern of behavior seen in polymer blends and other simple fluids. We investigate this system using a direct immersion annealing method (DIA) that allows for a facile tuning of the PGNPs phase boundary, phase separation kinetics, and the ultimate scale of phase separation after a sufficient “aging” time. In particular, by switching the DIA solvent composition from a selective one (which increases the interaction parameter according to Timmerman’s rule) to an overall good solvent for both PGNP components, we can achieve rapid switchability between phase-separated and homogeneous states. Despite a relatively low and non-classical power-law coarsening exponent, the overall phase separation process is completed on a time scale on the order of a few minutes. Moreover, the roughness of the PGNP blend film saturates at a scale that is proportional to the in-plane phase separation pattern scale, as observed in previous blend and block copolymer film studies. The relatively low magnitude of the coarsening exponent n is attributed to a suppression of hydrodynamic interactions between the PGNPs. The DIA method provides a significant opportunity to control the phase separation morphology of PGNP blends by solution processing, and this method is expected to be quite useful in creating advanced materials.

Designing next-generation lightweight pulsed power devices hinges on understanding the factors influencing the energy storage performance of dielectric materials. Polymer dielectric films have a quadratic dependence of energy storage on the voltage breakdown strength, and strategies to enhance the breakdown strength are expected to yield a path toward high energy storage densities. Highly stratified lamellar block copolymer (L-BCP) films of model polystyrene-b-polymethylmethacrylate (PS-b-PMMA) exhibited as much as ∼50% enhancement in breakdown voltage (E BD) (225% increase in stored energy density, U ∼ E BD 2) compared to unordered as-cast L-BCP films. Such an energy density using amorphous polymer is on par with industry-standard semicrystalline biaxially oriented polypropylene (BOPP) and as such a notable development in the field. This work develops a deeper understanding of the molecular mechanisms of E BD enhancement in L-BCP films, relating E BD directly to molecular weight (M n), with interpretation to effects of chain-end density and distribution, interface formation, layer thickness, and their relative contributions. As-cast disordered L-BCP films show decreasing E BD with decreasing M n similar to homopolymer studies because of the increase of homogeneously distributed chain ends in the film. E BD increases significantly in parallel ordered L-BCP films because of the combination of interface formation and spatial isolation of the chain ends into segregated zones. We further confirm the role of chain ends in the breakdown process blending a low M n L-BCP with matched M n homopolymers to attain the same layer spacing as neat L-BCP of higher M n. E BD shows a significant decrease at low homopolymer fractions because of increased net chain-end density within swollen ordered L-BCP domains in wet-brush regime, followed by increased E BD because of layer thickness increase via segregated “interphase layer” formation by excess homopolymers. Notably, E BD of homopolymer swollen L-BCPs is always lower than that of neat L-BCPs of the same domain spacing because of overall adverse chain-end contribution from homopolymers. These findings provide important selection rules for L-BCPs for designing next-generation flexible electronics with high energy density solid-state BCP film capacitors.

Previous studies have shown that the degree of ordering and alignment in block copolymer (BCP) films can be enhanced by increasing the thermodynamic driving force for microphase separation, χN, where χ is the Flory–Huggins interaction parameter between the polymer components and N is the number of statistical segments in the BCP. In practice, this strategy for controlling the microstructure of any BCP film normally involves reducing the temperature T and/or increasing N. However, both of these methods have the drawback of leading to a corresponding slowing down of the rate of ordering and dynamic-heterogeneity-associated defect formation in the material, related to both glass formation and entanglement. In the present work, we explore the use of an ionic liquid (IL) having a high cohesive interaction strength with a relatively low volatility to increase the cohesive interaction parameter χ, while at the same time keeping the molecular mobility high. In particular, we show that IL-driven enhancement of χ and higher molecular mobility, coupled with the poly­(methyl methacrylate) (PMMA) surface wetting interaction strength, induces enhanced substrate-driven stratification of parallel lamellae in polystyrene-b-poly­(methyl methacrylate) BCP (PS–PMMA) films over much larger distances than without IL. We anticipate that this method can be used to prepare relatively defect-free multilayer films wherein the IL is mostly removed under vacuum annealing during the short processing time while preserving the intrinsic lamellar morphology despite the initial high-IL mass fraction. This approach should be extremely useful in applications like barrier materials and batteries, solid-state dielectric capacitors, optical waveguides, and other applications where substrate-parallel multilayer films of controlled thickness are required.

Surface-textured polymer nanocomposite (PNC) films are utilized in many device applications, and therefore understanding the relaxation behavior of such films is important. By extending an in situ wrinkle relaxation method, we observed that the thermal stability of wrinkled PNC films, both above and below the glass transition temperature (T g ), is proportional to a film's nanoparticle (polymer grafted and bare) concentration, with a slope that changes sign at a compensation temperature (T comp ) that is determined to be in the vicinity of the film's T g . This provides unambiguous confirmation of entropy−enthalpy compensation (EEC) as a general feature of PNC films, implying that the stability of PNC films changes from being enhanced to becoming diminished by simply passing through this characteristic temperature, a phenomenon having evident practical ramifications. We suggest EEC will also arise in films where residual stresses are associated with the film fabrication process, which is relevant to nanotech device applications.

The template-free unidirectional alignment of lamellar block copolymers (l-BCPs) for sub-10 nm high-resolution patterning and hybrid multicomponent nanostructures is important for technological applications. We demonstrate a modified soft-shear-directed self-assembly (SDSA) approach for aligning pristine l-BCPs and l-BCPs with incorporated polymer-grafted nanoparticles (PGNPs), as well as the l-BCP conversion to aligned gold nanowires, and hybrid of metallic gold nanowire and dielectric silica nanoparticle in the form of line-dot nanostructures. The smallest patterns have a half-pitch as small as 9.8 nm. In all cases, soft-shear is achieved using a high-molecular-mass polymer topcoat layer, with support on a neutral bottom layer. We also show that the hybrid line-dot nanostructures have a red-shifted plasmonic response in comparison to neat gold nanowires. These template-free aligned BCPs and nanowires have potential use in nanopatterning applications, and the line-dot nanostructures should be useful in the sensing of biomolecules and other molecular species based on the plasmonic response of the nanowires.