An important strategy for realizing flexible electronics is to use solution-processable materials that can be directly printed and integrated into high-performance electronic components on plastic. Although examples of functional inks based on metallic, semiconducting and insulating materials have been developed, enhanced printability and performance is still a challenge. Printable high-capacitance dielectrics that serve as gate insulators in organic thin-film transistors are a particular priority. Solid polymer electrolytes (a salt dissolved in a polymer matrix) have been investigated for this purpose, but they suffer from slow polarization response, limiting transistor speed to less than 100 Hz. Here, we demonstrate that an emerging class of polymer electrolytes known as ion gels can serve as printable, high-capacitance gate insulators in organic thin-film transistors. The specific capacitance exceeds that of conventional ceramic or polymeric gate dielectrics, enabling transistor operation at low voltages with kilohertz switching frequencies.

Advances in synthetic polymer chemistry have unleashed seemingly unlimited strategies for producing block polymers with arbitrary numbers (n) and types (k) of unique sequences of repeating units. Increasing (k,n) leads to a geometric expansion of possible molecular architectures, beyond conventional ABA-type triblock copolymers (k = 2, n = 3), offering alluring opportunities to generate exquisitely tailored materials with unparalleled control over nanoscale-domain geometry, packing symmetry, and chemical composition. Transforming this potential into targeted structures endowed with useful properties hinges on imaginative molecular designs guided by predictive theory and computer simulation. Here, we review recent developments in the field of block polymers.

In a miscible polymer blend the local environment of a monomer of type A will, on average, be rich in A compared to the bulk composition, φ, and similarly for B; this is a direct consequence of chain connectivity. As a result, the local dynamics of the two chains may exhibit different dependences on temperature and overall composition. By assigning a length scale (or volume) to particular dynamic mode, the relevant “self-concentration” φs can be estimated. For example, we associate the Kuhn length of the chain, l K, with the monomeric friction factor, ζ, and thus the composition and temperature dependences of ζ should be influenced by φs calculated for a volume V ∼ l K 3. An effective local composition, φeff, can then be calculated from φs and φ. As lower T g polymers are generally more flexible, the associated φ s is larger, and the local dynamics in the mixture may be quite similar to the pure material. The higher T g component, on the other hand, may have a smaller φs, and thus its dynamics in the mixture would be more representative of the average blend composition. An effective glass transition temperature for each component, T g eff, can be estimated from the composition-dependent bulk average T g as T g(φeff). This analysis provides a direct estimate of the difference in the apparent T g's for the two components in miscible blends, in reasonable agreement with those reported in the literature for four different systems. Furthermore, this approach can reconcile other features of miscible blend dynamics, including the asymmetric broadening of the calorimetric T g, the differing effects of blending on the segmental relaxation times of the two components, and the failure of time−temperature superposition.

Here we summarize recent progress in the development of electrolyte-gated transistors (EGTs) for organic and printed electronics. EGTs employ a high capacitance electrolyte as the gate insulator; the high capacitance increases drive current, lowers operating voltages, and enables new transistor architectures. Although the use of electrolytes in electronics is an old concept going back to the early days of the silicon transistor, new printable, fast-response polymer electrolytes are expanding the potential applications of EGTs in flexible, printed digital circuits, rollable displays, and conformal bioelectronic sensors. This report introduces the structure and operation mechanisms of EGTs and reviews key developments in electrolyte materials for use in printed electronics. The bulk of the article is devoted to electrical characterization of EGTs and emerging applications.

By combining three mutually immiscible polymeric components in a mixed-arm star block terpolymer architecture, we have observed the formation of a previously unknown class of multicompartment micelles in dilute aqueous solution. Connection of water-soluble poly(ethylene oxide) and two hydrophobic but immiscible components (a polymeric hydrocarbon and a perfluorinated polyether) at a common junction leads to molecular frustration when dispersed in aqueous solution. The incompatible hydrophobic blocks form cores that are protected from the water by the poly(ethylene oxide) blocks, but both are forced to make contact with the poly(ethylene oxide) by virtue of the chain architecture. The structures that emerge depend on the relative lengths of the blocks and can be tuned from discrete multicompartment micelles to extended wormlike structures with segmented cores.

Self-assembled nanostructures obtained from natural and synthetic amphiphiles serve as mimics of biological membranes and enable the delivery of drugs, proteins, genes, and imaging agents. Yet the precise molecular arrangements demanded by these functions are difficult to achieve. Libraries of amphiphilic Janus dendrimers, prepared by facile coupling of tailored hydrophilic and hydrophobic branched segments, have been screened by cryogenic transmission electron microscopy, revealing a rich palette of morphologies in water, including vesicles, denoted dendrimersomes, cubosomes, disks, tubular vesicles, and helical ribbons. Dendrimersomes marry the stability and mechanical strength obtainable from polymersomes with the biological function of stabilized phospholipid liposomes, plus superior uniformity of size, ease of formation, and chemical functionalization. This modular synthesis strategy provides access to systematic tuning of molecular structure and of self-assembled architecture.

The effect of the thermodynamic selectivity of a solvent on the self-assembly of a styreneisoprene (SI) diblock copolymer with block molecular weights of 1.1 × 10 4 and 2.1 × 10 4 g/mol is investigated. We explore the phase behavior from the melt state to dilute solution in solvents that are of varying selectivities for the two blocks. Bis(2-ethylhexyl) phthalate (DOP) is a neutral good solvent for SI. Di-n-butyl phthalate (DBP) and diethyl phthalate (DEP) are good solvents for PS but marginal and poor, respectively, for PI. Tetradecane (C14) is utilized as a complementary solvent that is good for PI but poor for PS. Small-angle X-ray scattering (SAXS) and static birefringence are used to locate and identify order-order (OOT) and order-disorder transitions (ODT). Dynamic and static light scattering were used to characterize the dilute solution micellar behavior. The neat polymer forms the gyroid (G 1) morphology at low temperature, an OOT to hexagonal-packed cylinders (C1) occurs at 185°C, and the ODT is located at 238°C. Dilution with DOP decreases the OOT temperature in agreement with the dilution approximation, i.e., OOT ∼ φ -1 , but the ODT follows a stronger dependence of ODT ∼ φ -1.4 . The slightly selective solvent DBP stabilizes the ordered state relative to DOP. Rich lyotropic and thermotropic behavior is observed among regions of lamellae (L), inverted gyroid (G2), inverted hexagonal-packed cylinders (C2), and inverted body-centered-cubic spheres (S2 bcc ). Solutions in DEP display similar morphological behavior, along with significantly increased ODT temperatures. Because of the asymmetric block copolymer composition, the phase behavior in the isoprene-selective solvent C14 is markedly different, as only G1, C1, and S1 bcc phases are observed. The overall sequence of phases with dilution and/or heating is rationalized on the basis of diagonal trajectories across the phase map (temperature vs composition) for undiluted block copolymers: addition of a neutral solvent corresponds to increasing the temperature and thus a "vertical" trajectory, whereas the partitioning between microdomains of a selective solvent amounts to a "horizontal" trajectory to a renormalized block volume composition. However, a variety of novel features are observed in DEP: the formation of face-centered-cubic packed micelles, a reentrant thermotropic ODT, and a large window of L + C 2 coexistence. The dependence of the principal length scale, d*, on φ, T, and structure is also considered. The strongly temperature-dependent selectivity produces a crossover in the scaling of d* vs φ for the lamellar phase: the addition of a selective solvent increases d*, but as the solvent becomes neutral, d* decreases. This phenomenon is captured by selfconsistent mean-field calculations.

The phase behavior of six poly(styrene-b-isoprene) (SI) diblock copolymers has been mapped out in the styrene-selective solvents di-n-butyl phthalate (DBP), diethyl phthalate (DEP), and dimethyl phthalate (DMP). The polymer molecular weights were chosen to make the melt order−disorder transition (ODT) experimentally accessible, and the styrene compositions f ranged from 0.23 to 0.70, to access the full range of melt morphologies. For each polymer a phase diagram was constructed, with polymer volume fractions, φ, ranging from 0.01 to 1.0 and temperatures, T, from 0 to 250 °C. Phase assignments were based on small-angle X-ray scattering (SAXS), and the ODTs and order−order transitions (OOTs) were located by a combination of SAXS, rheology, and static birefringence. The critical micelle temperatures (cmt) in dilute solution were determined by dynamic light scattering. In this manner the full “phase cube” was mapped out in each solvent, enabling generation of phase maps (φ,f) at constant T and (f,T) at constant φ. The solvents range from slightly to strongly selective, in the sequence DBP, DEP, and DMP, and in each case the selectivity diminishes with increasing T. This property gives rise to a plethora of thermally induced OOTs, and several solutions exhibit four distinct equilibrium phases upon heating. In addition to the eight phases well established for SI copolymers in the melt (a body-centered-cubic (bcc) array spheres of styrene or isoprene, hexagonally packed cylinders of styrene or isoprene, gyroid with isoprene or styrene matrix, lamellae, disordered), broad regions of lamellae + cylinder coexistence and face-centered-cubic (fcc) isoprene spheres were observed. The sequence of phases could be broadly understood in terms of changes in spontaneous interfacial curvature arising from differential swelling of the two microdomains. For a given polymer and solvent, the ODT varied smoothly with φ from the melt value down toward the dilute solution critical micelle temperature (cmt); at about φ ≈ 0.2 the ordered phases gave way to a solution of micelles. In some cases solutions near φ ≈ 0.2 exhibit reentrant ODTs, as they evolved from a solution of micelles to an fcc (and/or bcc) lattice, to a solution of chains, upon heating. The origins of these various phenomena are discussed, and the results are compared and contrasted with other measurements on SI copolymers in the literature.