The glass transition temperature (T g ), in-plane diffusivity (D), and effective viscosity (η eff ) were measured for the same thin film system of poly(isobutyl methacrylate) supported by silica (PiBMA/SiOx). We found that both the T g and D were independent of the film thickness (h 0 ), but η eff decreased with decreasing h 0 . We envisage the different h 0 dependencies to be caused by T g , D, and η eff being different functions of the local T g 's (T g,i ) or viscosities (η i ), which vary with the film depth. By assuming a three-layer model and that T g (h 0 ) = ⟨T g,i ⟩, D(h 0 ) ∼ k B T/⟨η i ⟩, and η eff (h 0 ) = h 0 3 /3M tot (η i ), where ⟨...⟩ denotes spatial averaging and M tot is the mobility of the films, we were able to account for the experimental data. By extending these ideas to the analogous data of polystyrene supported by silica (PS/SiOx), a resolution was found for the long-standing inconsistency regarding the effects of confinement on the dynamics of polymer films.

Predicting the interactions between a semiconducting polymer and dopant is not straightforward due to the intrinsic structural and energetic disorder in polymeric systems. Although the driving force for efficient charge transfer depends on a favorable offset between the electron donor and acceptor, we demonstrate that the efficacy of doping also relies on structural constraints of incorporating a dopant molecule into the semiconducting polymer film. Here, we report the evolution in spectroscopic and electrical properties of a model conjugated polymer upon exposure to two dopant types: one that directly oxidizes the polymeric backbone and one that protonates the polymer backbone. Through vapor phase infiltration, the common charge transfer dopant, F 4 -TCNQ, forms a charge transfer complex (CTC) with the polymer poly(3-(2′-ethyl)hexylthiophene) (P3EHT), a conjugated polymer with the same backbone as the well-characterized polymer P3HT, resulting in a maximum electrical conductivity of 3 × 10 −5 S cm −1 . We postulate that the branched side chains of P3EHT force F 4 -TCNQ to reside between the π-faces of the crystallites, resulting in partial charge transfer between the donor and the acceptor. Conversely, protonation of the polymeric backbone using the strong acid, HTFSI, increases the electrical conductivity of P3EHT to a maximum of 4 × 10 −3 S cm −1 , 2 orders of magnitude higher than when a charge transfer dopant is used. The ability for the backbone of P3EHT to be protonated by an acid dopant, but not oxidized directly by F 4 -TCNQ, suggests that steric hindrance plays a significant role in the degree of charge transfer between dopant and polymer, even when the driving force for charge transfer is sufficient.

Marangoni forces drive a fluid to flow in response to positional differences in surface energy. In thin polymer films, a difference in surface energy between two coincident liquid polymers could offer a useful route to manufacture topographically patterned surfaces via the Marangoni effect. Previously, we have demonstrated a photochemical method using the Marangoni effect for patterning thin polystyrene films. To generalize the approach, a theoretical model that gives the underlying physics of this process was also developed, which further revealed that low viscosities, low diffusivities, and large surface energy gradients favor rapid evolution of large film thickness variations. However, as described by the Stokes−Einstein equation or the Rouse model, low viscosity is generally correlated with high diffusivity in a single-component system. Herein, we report a strategy to decouple film viscosity and diffusivity by co-casting a high molecular weight surface energy gradient creating copolymer (low diffusivity) with a low molecular weight majority homopolymer (high diffusivity and low viscosity), which are miscible with each other. Patterned light exposure through a photomask imposes a patterned surface energy gradient between light-exposed and unexposed regions due to photochemical reactions involving only the low diffusivity component. Upon heating the film to the liquid state, the film materials (primarily the low viscosity homopolymer component) flow from the low to high surface energy regions. This strategy either eliminates or greatly slows dissipation of the prepatterned surface energy gradient while maintaining rapid feature formation, resulting in formation of ca. 500 nm high features within only 30 min of thermal annealing. Furthermore, the formed features are stable upon extended thermal annealing for up to one month. It is found that a ratio of Marangoni forces to capillary forces can provide a predictive metric that distinguishes which scenarios produce features that dissipate or persist.

Nature has engineered universal, catechol-containing adhesives which can be synthetically mimicked in the form of polydopamine (PDA). In this study, PDA was exploited to enable the formation of block copolymer (BCP) nanopatterns on a variety of soft material surfaces. While conventional PDA coating times (1 h) produce a layer too rough for most applications of BCP nanopatterning, we found that these substrates could be polished by bath sonication in a weakly basic solution to form a conformal, smooth (root-mean-square roughness ∼0.4 nm), and thin (3 nm) layer free of large prominent granules. This chemically functionalized, biomimetic layer served as a reactive platform for subsequently grafting a surface neutral layer of poly(styrene-random-methyl methacrylate-random-glycidyl methacrylate) to perpendicularly orient lamellae-forming poly(styrene-block-methyl methacrylate) BCP. Moreover, scanning electron microscopy observations confirmed that a BCP nanopattern on a poly(ethylene terephthalate) substrate was not affected by bending with a radius of ∼0.5 cm. This procedure enables nondestructive, plasma-free surface modification of chemically inert, low-surface energy soft materials, thus overcoming many current chemical and physical limitations that may impede high-throughput, roll-to-roll nanomanufacturing.

We report that the fractions of “bonded” or “unbonded” monomers at a filler interface dictate the composition dependence of the glass transition temperatures (T g) of polyhedral oligomeric silsesquioxane (POSS)-containing nanocomposites. T g is arguably the single most important material property; however, predicting T g in nanocomposites is often challenging because of confounding interfacial effects. To this end, we design a model nanocomposite to systematically study T g of nanocomposites by leveraging the “all-interfacial” nature of ultrasmall POSS fillers loaded into random copolymers of styrene and 2-vinylpyridine (2VP). The amine-functionalized POSS forms hydrogen bonds only with 2VP, which behaves as a “bonded” monomer. The influence of copolymer composition and POSS loading on the T g of this model composite is successfully explained by a Fox equation framework. This model also captures the T g increase of other POSS-based polymer composites and potentially directs the future design of nanocomposite materials with tailored T g.