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The local, nanoscale organization of crystallites in conjugated polymers is often critical to determining the charge transport properties of the system. Block copolymer geometries, which offer controlled nanostructures with tethering of chains at interfaces, are an ideal platform to study the local organization of conjugated polymer crystallites. The model conjugated polymer poly(3-(2'-ethyl)hexylthiophene) (P3EHT) features a depressed melting temperature relative to the widely studied poly(3-hexylthiophene) (P3HT), which allows it to robustly form microphase-separated domains that confine the subsequent P3EHT crystallites. Importantly, P3EHT crystallization in confinement is coupled to a rubbery second block via interfacial tethering, mechanical properties, and chain stretching. Here, the impact of thermal processing on the diblock copolymer structure is examined to elucidate the key driving forces controlling the final coupled diblock copolymer and crystalline structures. Surprisingly, the diblock copolymer domain size is significantly impacted by the temperature at which the conjugated domain is crystallized. Decreasing amounts of domain extension are observed with increasing crystallization temperatures. This temperature-dependent domain structure appears to be correlated with the crystallization processes; these processes are inferred from precise changes in the lamellar structure across melting. By carefully tracking the changes in domain structure across melting, this work identifies three distinct regimes. We suggest a structural model of the conjugated block melting processes consisting of (I) excluded-chain relaxation, followed by (II) chain interdigitation during melt-recrystallization, and finally (III) complete melting that is independent of the initial crystallization conditions. These results suggest that P3EHT crystallization processes associated with temperature-dependent chain diffusion and nucleation are primarily responsible for the unexpected temperature-dependent crystallization behavior. They also emphasize that less perfect conjugated polymer crystals may actually be associated with a poorly interdigitated structure. Furthermore, this work demonstrates the utility of leveraging a diblock copolymer structure with a rubbery second block in order to precisely track changes in the crystallite structure. [ABSTRACT FROM AUTHOR]

Abstract: Rod–coil block copolymers are an increasingly important class of molecules for the self-assembly of functional polymer systems, many of which have rodlike chain conformations due to rigid secondary structures, extended π-conjugation, or aromatic groups along the polymer backbone. Examples of these polymers are helical proteins, polyisocyanates, main-chain semiconducting polymers, and aromatic polyesters, polyamides, or polyimines. Many hindered or liquid crystalline systems self-assembled from block copolymers, including dendronized polymers and mesogen-jacketed liquid crystalline polymers, also form rod–coil block copolymers. In these cases, steric crowding of the bulky or mesogenic side chains causes the polymer backbone to become quasi-linear. The incorporation of rigid rod polymers into the block copolymers results in extremely rich self-assembly behavior that differs markedly from that of traditional block copolymers due to the interplay between microphase separation of the rod and coil components and liquid crystalline alignment. The combination of these effects results in novel structures both in solution and melts. This review discusses in detail the self-assembly and thermodynamics of rod–coil diblock and triblock copolymers. After summarizing the applications of these materials, their aggregation and gelation in solution is discussed. Our knowledge of their bulk phase behavior is thoroughly reviewed both from the experimental and theoretical perspectives, and the self-assembly of these materials in thin film geometries that are critical to many applications in organic electronics and functional surface patterning is treated. Finally, the outlook for the future of these systems is summarized along with current knowledge gaps and exciting areas for the advancement of the field. [Copyright &y& Elsevier]

Abstract: The nanometer-scale architectures in thin films of self-assembling block copolymers have inspired a variety of new applications. For example, the uniformly sized and shaped nanodomains formed in the films have been used for nanolithography, nanoparticle synthesis, and high-density information storage media. Imperative to all of these applications, however, is a high degree of control over orientation of the nanodomains relative to the surface of the film as well as control over order in the plane of the film. Induced fields including electric, shear, and surface fields have been demonstrated to influence orientation. Both heteroepitaxy and graphoepitaxy can induce positional order on the nanodomains in the plane of the film. This article will briefly review a variety of mechanisms for gaining control over block copolymer order as well as many of the applications of these materials. Particular attention is paid to the potential of perfecting long-range two-dimensional order over a broader range of length scales and the extension of these concepts to functional materials and more complex architectures. [Copyright &y& Elsevier]

Solid-solid junctions with an interfacial self-assembled monolayer (SAM) are a class of interfaces with very low thermal conductance. Au–SAM–GaAs junctions were made using alkanedithiol SAMs and fabricated by nanotransfer printing. Measurements of thermal conductance using the 3ω technique were very robust and no thermal conductance dependence on alkane chain length was observed. The thermal conductances using octanedithiol, nonanedithiol, and decanedithiol SAMs at room temperature are 27.6±2.9, 28.2±1.8, and 25.6±2.4 MW m-2 K-1, respectively. [ABSTRACT FROM AUTHOR]

A new type of a positive tone chemically amplified photoresist based on well‐defined, sequence‐controlled polypeptoids with ten repeat‐units are synthesized and their potential for extreme‐UV lithography (EUVL) is demonstrated, resulting in line‐space patterns of 70 nm pitch. The synthesized samples contain 4‐(ethyl) phenol (Eph) and propyne (Ppy) side chains, while their change in solubility upon exposure is induced by the deprotection of 4‐(ethyl) phenol side groups. The resist performance is evaluated using deep UV and extreme‐UV lithography. While all samples are developable in isopropyl alcohol, the content, and the sequence of hydrophobic alkyne side chains lead to a detectable change in solubility, dissolution rate, and resist performance. [ABSTRACT FROM AUTHOR]

The article discusses the development in directing self-assembly of block copolymers. This study focused on the nanoscale features of block copolymers as means of turning a pattern media in microelectronic applications. Researches are under way for a new route to nanopatterning which is very significant in optical lithography. The semiconductor industry needs intrinsic technology to answer for the demands in high-density features for data storage and computing speed. New applications are tested for further developments.

The interactions between counterions and electronic carriers in electrically doped semiconducting polymers are important for delocalization of charge carriers, electronic conductivity, and thermal stability. The introduction of a dianions in semiconducting polymers leads to double doping where there is one counterion for two charge carriers. Double doping minimizes structural distortions, but changes the electrostatic interactions between the carriers and counterions. Polymeric ionic liquids (PIL) with croconate dianions are helpful to investigate the role of the counterion in p‐type semiconducting polymers. PILs prevent diffusion of the cation into the semiconducting polymers during ion exchange. The redox‐active croconate dianions undergo ion exchange with doped semiconducting polymers depending on their ionization energy. Croconate dianions are found to reduce doped films of poly(3‐hexyl thiophene), but undergo ion exchange with a polythiophene with tetraethylene glycol side chains, P(g42T‐T), that has a lower ionization energy. The croconate dianion maintains crystalline order in P(g42T‐T) and leads to a lower activation energy for the electrical conductivity than PF6− counterions. The control of the doping level with croconate allows optimization of the thermoelectric performance of the semiconducting polymer. The thermal stability of the doped films of P(g42T‐T) is found to depend strongly on the nature of the counterion. [ABSTRACT FROM AUTHOR]

Understanding the transport properties of water in self-assembled block copolymer morphologies is important for furthering the use of such materials as water-purifying membranes. In this study, we used coarse-grained dissipative particle dynamics simulations to clarify the influence of pore morphology on the self-diffusion of water in linear-triblock-copolymer membranes. We considered representative lamellar, cylindrical, and gyroid morphologies and present results for both the global and local diffusivities of water in the pores. Our results suggest that the diffusivity of water in the confined, polymer-coated pores differs from that in the unconfined bulk. Explicitly, in confinement, the mobility of water is reduced by the hydrodynamic friction arising from the hydrophilic blocks coating the pore walls. We demonstrate that in lamella and cylindrical morphologies, the latter effects can be rendered as a universal function of the pore size relative to the brush height of the hydrophilic blocks. [ABSTRACT FROM AUTHOR]

Review: 151 refs. [ABSTRACT FROM AUTHOR]

Block copolymer (BCP) self‐assembly‐assisted doping for semiconductors is used to achieve discrete doping with nanometer‐scale junction depth, high throughput, and large area coverage. As devices become smaller and more sophisticated, spatial control of dopants becomes more critical. A variety of doping methods, such as monolayer doping and δ‐doping, have been developed to replace the conventional doping method, ion‐implantation; however, lateral patterning of dopants relies on photo‐ or e‐beam lithography. To address these challenges, a self‐assembling dopant (boron)‐containing BCP is designed to directly pattern dopants on the nanometer scale. This method skips the lithography step and is compatible with directed self‐assembly approaches. The effect of the boron concentration in the BCP on the doping performance is systematically studied by changing the volume fraction of the boron‐containing block while keeping the domain spacing and the mesoscale morphology constant. Successful self‐assembly of the BCP into a hexagonally packed cylindrical morphology is confirmed by small‐angle X‐ray scattering and resonant soft X‐ray scattering with a 26 nm cylinder‐to‐cylinder distance. Doping silicon using these BCPs enables discrete doped areas with shallow (7–13 nm) junction depth as demonstrated by the depth profile of boron, and supported by a sheet resistance study. [ABSTRACT FROM AUTHOR]

We report a method to determine the thermal conductivities of polymer composites with single-walled carbon nanotubes (SWNTs) using time-domain thermoreflectance. Both through-plane and in-plane thermal conductivities were determined. Two types of CPEs used in these studies are of the same conjugated backbone but with either cationic (CPE-PyrBIm4) or anionic (CPE-Na) pendant functionalities. The CPE-Na/SWNT composites are p-type conductors, whereas the CPE-PyrBIm4/SWNT counterparts exhibit n-type charge transport. The CPE/SWNT films were prepared through a filtration method that preferentially aligns the SWNTs in the in-plane direction. Attaching the composites onto glass substrates with a precoated heat transducer allows one to measure the through-plane thermal conductivity of materials with rough surfaces. The in-plane thermal conductivity can be measured by embedding thick samples into epoxy followed by microtoming to expose the relatively smooth cross sections. The thermal conductivity along the in-plane direction is found to be higher than that along the through-plane direction. Indeed, the anisotropy factor of thermal conductivity in these composites is approximately an order of magnitude, favoring in-plane direction. [ABSTRACT FROM AUTHOR]

Amphiphilic polypeptoids can be designedwith specific sequencesof hydrophilic and hydrophobic units, which determine their surfaceproperties for antifouling/fouling release purposes. Although thesequence-dependent surface structures of polypeptoids have been extensivelyinvestigated, e.g., with X-ray spectroscopy, their molecular structuresunder the aqueous conditions relevant to marine fouling have not beenstudied. In this work, we applied sum frequency generation (SFG) vibrationalspectroscopy to study the surface structures and hydration of a seriesof amphiphilic polypeptoid coatings with different sequences in airand water. SFG spectra, in agreement with X-ray spectroscopy studies,revealed that the surface coverage of the hydrophilic N-(2-methoxyethyl)glycine (Nme) units in air is affected by both thenumber and position of the hydrophobic N-(heptafluorobutyl)glycine(NF) units in the peptoid chain and is negatively correlated withthe surface concentration of the fluorine element. Our ability toprobe the SFG signals of water molecules at the peptoid surface providesnew information on the hydrated film properties. From these SFG signalsand the time evolution of water contact angles on the polymers, wesee that the hydrated film properties are also dependent upon thepeptoid sequence. This work indicates that the surface presence ofthe Nme groups and the ability of the polymers to order and stronglyhydrogen bond with interfacial water molecules determine their antifoulingproperties, whereas the surface restructuring rate upon contact withwater affects their fouling release behaviors. [ABSTRACT FROM AUTHOR]

While polymer materials possess significantpromise as components in large-area organic electronic devicessuchas thin-film transistors or photovoltaic devicesthe abilityto improve the performance of these materials is critically linkedto understanding and controlling the morphology, namely control ofcrystallinity, crystallite size, and texture. In this context, conjugatedpoly(3-alkylthiophenes) are a model system for studying the structure–propertyrelationships in conjugated polymers. Herein, we examine P3EHT asa model polymer for exploring crystallization in P3ATsas ithas a final melting transition well below degradation in contrastto the more common P3HTusing differential scanning calorimetry(DSC) and wide-angle X-ray scattering. Notably, examination of themelting endotherms following isothermal crystallization of P3ATsnamelypoly(3-hexylthiophene) (P3HT) and poly(3-(2′ethyl)hexylthiophene)(P3EHT)reveals a bimodal final melting peak. Differentialscanning calorimetry reveals a shift in the lower temperature peakto higher temperatures as the isothermal crystallization temperatureis raised and convergence into a single observed endothermic peakat high crystallization temperatures. Complementary wide-angle X-rayscattering experiments reveal an increase in crystallite perfectionalong the π–π stack direction at higher crystallizationtemperatures. Thus, properties of the P3EHT crystallite populations,average size and/or perfection, can be deliberately manipulated throughcontrol of the isothermal crystallization temperature. We furtherdetermine that the bimodal nature of P3EHT’s melting behavioris a consequence of a melt-recrystallization mechanism and observeperfection of the π–π stack direction during themelt-recrystallization process. Lastly, we utilize the obtained finalmelting temperatures to elucidate values for ΔHm0and Tm0, 20 ± 4 J/g and 92 °C, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] The polymeric cations of polymeric ionic liquids (PILs) can adsorb from the bulk of a conventional ionic liquid (IL) to the Au(1 1 1) electrode interface and form a boundary layer. The interfacial properties of the PIL boundary layer may be tuned by potential. Atomic force microscopy has been used to investigate the changes of surface morphology, normal and lateral forces of a 5 wt% PIL/IL mixture as a function of potential. Polymeric cations adsorb strongly to Au(1 1 1) and form a polymeric cation-enriched boundary layer at −1.0 V. This boundary layer binds less strongly to the surface at open circuit potential (OCP) and weakly at + 1.0 V. The polymeric cation chains are compressed at −1.0 V and OCP owing to electrical attractions with the electrode surface, but fully stretched at + 1.0 V due to electrical repulsions. The lateral forces of the 5 wt% PIL/IL mixture at −1.0 V and OCP are higher than at + 1.0 V as the polymeric cation-enriched boundary layer is rougher and has stronger interactions with the AFM probe; at + 1.0 V, the lateral force is low and comparable to pure conventional IL due to displacement of polymeric cations with conventional anions in the boundary layer. [ABSTRACT FROM AUTHOR]

In organic mixed ionic–electronic conductors (OMIECs), it is critical to understand the motion of ions in the electrolyte and OMIEC. Generally, the focus is on the movement of net charge during gating, and the motion of neutral anion–cation pairs is seldom considered. Uptake of mobile ion pairs by the semiconductor before electrochemical gating (passive uptake) can be advantageous as this can improve device speed, and both ions can participate in charge compensation during gating. Here, such passive ion pair uptake in high‐speed solid‐state devices is demonstrated using an ion gel electrolyte. This is compared to a polymerized ionic liquid (PIL) electrolyte to understand how ion pair uptake affects device characteristics. Using X‐ray photoelectron spectroscopy, the passive uptake of ion pairs from the ion gel into the OMIEC is detected, whereas no uptake is observed with a PIL electrolyte. This is corroborated by X‐ray scattering, which reveals morphological changes to the OMIEC from the uptake of ion pairs. With in situ Raman, a reorganization of both anions and cations is then observed during gating. Finally, the speed and retention of OMIEC‐based neuromorphic devices are tuned by controlling the freedom of charge motion in the electrolyte. [ABSTRACT FROM AUTHOR]

Polymers have many desirable propertiesfor engineering systems–e.g., low mass density, chemical stability,and high strength-to-mass ratio–but applications of polymersin situations where heat transfer is critical are often limited bylow thermal conductivity. Here, we leverage the enormous researchand development efforts that have been invested in the productionof high-modulus polymer fibers to advance understanding of the mechanismsfor thermal transport in this class of materials. Time-domain thermoreflectance(TDTR) enables direct measurements of the axial thermal conductivityof a single polymer fiber over a wide temperature range, 80 < T< 600 K. Relaxation of thermoelastic stress in theAl film transducer has to be taken into account in the analysis ofthe TDTR data when the laser spot size is small because the radialmodulus of the fiber is small. This stress relaxation is controlledby the velocity of the zero-order symmetric Lamb mode of a thin Alplate. We find similarly high thermal conductivities of Λ ≈20 W m–1K–1in crystalline polyethyleneand liquid crystalline poly(p-phenylene benzobisoxazole).For both fiber types, Λ(T) ∝ 1/Tnear room temperature, suggesting an intrinsic limit tothe thermal conductivity governed by anharmonicity, not structuraldisorder. Because of the high degree of elastic anisotropy, longitudinalacoustic phonons with group velocities directed along fiber axis arelikely to be the dominate carriers of heat. [ABSTRACT FROM AUTHOR]

Tunability of polymer surface properties depends cruciallyon boththe chemical composition of the polymer and the physics of the chains(e.g., surface segregation, chain shape, etc.). Polypeptoids, whichare non-natural biomimetic polymers based on an N-substituted glycinebackbone, provide a flexible model system in which monomer sequence,chain shape, and self-assembled structure can easily be controlledto understand their influence on surface properties. We demonstratethe influence of the amount and sequence of hydrophobic monomers ina predominantly hydrophilic peptoid chain on the surface propertiesof a hybrid block copolymer, poly(peptoid-b-styrene).Just three fluorinated groups in peptoid sequences consisting of upto 45 hydrophilic monomers in length were needed to lower the surfaceenergy of the peptoid and allow for its maximal surface segregation.Positioning these fluorinated groups in the middle of a chain as opposedto the chain ends resulted in a change in chain conformation at thesurface as evidenced by near-edge X-ray absorption fine structurespectroscopy (NEXAFS). Surface reconstruction of polymers containingonly three fluorinated monomers occurred within seconds but couldbe slowed by an order of magnitude when five fluorinated monomerswere incorporated. [ABSTRACT FROM AUTHOR]

The management of proton conductivity in the protic ionic liquidimidazolium bis(trifluoromethylsulfonyl)imide ([Im][TFSI]) is investigatedvia the use of quasi-elastic neutron scattering (QENS) and pulsed-fieldgradient NMR. The introduction of excess neutral imidazole to [Im][TFSI]leads to enhanced conductivity. We find that proton dynamics in [Im][TFSI]with excess imidazole are characterized by proton hopping that isencompassed in the slower of two translational processes, as identifiedby QENS. This relatively slow process contributes to long-range diffusionmore than the faster process. NMR diffusion measurements show thatproton hopping decreases with increasing temperature, but significantproton hopping persists even at the maximum experimental temperatureof 120 °C. This, in combination with minimal ion aggregation,leads to high proton conductivity and a high proton transference numberover a wide temperature range. [ABSTRACT FROM AUTHOR]

A series of oligothiophene-perfluoro-9-heterofluorene donor-acceptor (DA) compounds was synthesized via a combination of nucleophilic aromatic substitution (SNArP) and palladium coupling reactions. These compounds arc of interest as possible building blocks for materials with useful electron transport properties, since they possess relatively low LUMO energy levels of -3.3 to -3.6 eV (as determined by differential pulse voltammetry). The HOMO-LUMO energy gaps, as determined by UV-vis spectroscopy, range between 2.4 and 2.5 eV, and photoluminescence emission spectra reveal λems values in the range of 480-600 nm (corresponding to yellow-orange emission). Dilute solution-state photoluminescence quantum yields were signiOcantly lower than those of the pure acceptor heterofluorenes (0.02-0.38 for the DA compounds vs ~1 for the pure acceptors), and notable solvatochromism in the fluorescence suggests emission from a charge-separated state. Theoretical calculations show that HOMO-level electron density is more localized on the thiophene fragment, while the LUMO level electron density is mostly associated with the electron-deficient portion of the molecule. Photovoltaic (PV) devices based on DA/poly-3-hexylthiophene (P3HT) blends exhibit improved performance over P3HT-only devices, suggesting the ability of these DA compounds to transport electrons in the solid state. [ABSTRACT FROM AUTHOR]

By trapping molecules between two gold electrodes with a temperature difference across them, the junction Seebeck coefficients of 1,4-benzenedithiol (BDT), 4,4′-dibenzenedithiol, and 4,4″-tribenzenedithiol in contact with gold were measured at room temperature to be +8.7 ± 2.1 microvolts per kelvin (μV/K), +12.9 ± 2.2 μV/K, and +14.2 ± 3.2 μV/K, respectively (where the error is the full width half maximum of the statistical distributions). The positive sign unambiguously indicates p-type (hole) conduction in these heterojunctions, whereas the Au Fermi level position for Au-BDT-Au junctions was identified to be 1.2 eV above the highest occupied molecular orbital level of BDT. The ability to study thermoelectricity in molecular junctions provides the opportunity to address these fundamental unanswered questions about their, electronic structure and to begin exploring molecular thermoelectric energy conversion. [ABSTRACT FROM AUTHOR]

Polymers that simultaneously transport electrons and ions are paramount to drive the technological advances necessary for next-generation electrochemical devices, including energy storage devices and bioelectronics. However, efforts to describe the motion of ions or electrons separately within polymeric systems become inaccurate when both species are present. Herein, we highlight the basic transport equations necessary to rationalize mixed transport and the multiscale material properties that influence their transport coefficients. Potential figures of merit that enable a suitable performance benchmark in mixed conducting systems independent of end application are discussed. Practical design and implementation of mixed conducting polymers require an understanding of the evolving nature of structure and transport with ionic and electronic carrier density to capture the dynamic disorder inherent in polymeric materials. [ABSTRACT FROM AUTHOR]

Polymeric ionic liquids (PILs) have attracted considerable attention as electrolytes with high stability and mechanical durability. Light‐responsive materials are enabling for a variety of future technologies owing to their remote and noninvasive manipulation, spatiotemporal control, and low environmental impact. To address this potential, responsive PIL materials based on diarylethene units were designed to undergo light‐mediated conductivity changes. Key to this modulation is tuning of the cationic character of the imidazolium bridging unit upon photoswitching. Irradiation of these materials with UV light triggers a circa 70 % drop in conductivity in the solid state that can be recovered upon subsequent irradiation with visible light. This light‐responsive ionic conductivity enables spatiotemporal and reversible patterning of PIL films using light. This modulation of ionic conductivity allows for the development of light‐controlled electrical circuits and wearable photodetectors. [ABSTRACT FROM AUTHOR]

Polymeric ionic liquids (PILs) have attracted considerable attention as electrolytes with high stability and mechanical durability. Light‐responsive materials are enabling for a variety of future technologies owing to their remote and noninvasive manipulation, spatiotemporal control, and low environmental impact. To address this potential, responsive PIL materials based on diarylethene units were designed to undergo light‐mediated conductivity changes. Key to this modulation is tuning of the cationic character of the imidazolium bridging unit upon photoswitching. Irradiation of these materials with UV light triggers a circa 70 % drop in conductivity in the solid state that can be recovered upon subsequent irradiation with visible light. This light‐responsive ionic conductivity enables spatiotemporal and reversible patterning of PIL films using light. This modulation of ionic conductivity allows for the development of light‐controlled electrical circuits and wearable photodetectors. [ABSTRACT FROM AUTHOR]

An obituary for professor Edward J. Kramer, of Department of Materials Science and Engineering at Cornell University is presented.

A fundamental understanding of charge transport in polymeric semiconductors requires knowledge of how the electrical conductivity varies with carrier density. The thermopower of semiconducting polymers is also a complex function of carrier density making it difficult to assess structure-property relationships for the thermoelectric power factor. We examined the thermoelectric properties of poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (pBTTT-C14) by measurements of an electrochemical transistor using a polymeric ionic liquid (PIL) gate dielectric that can modulate the carrier concentration from 4 × 1018 to 3 × 1020 cm-3. As carrier density increases, so does the concentration of associated counterions, leading to a greater degree of energetic disorder within the semiconductor. Using thermopower measurements, we show experimentally that the electronic density-of-states broadens with increasing carrier density in the semiconducting polymer. The origin of a commonly observed power law relationship between thermopower and electrical conductivity is discussed and related to the changes in the electronic density-of-states upon doping. [ABSTRACT FROM AUTHOR]

The development of high-performance ion conducting polymers requires a comprehensive multiscale understanding of the connection between ion--polymer associations, ionic conductivity, and polymer mechanics. We present polymer networks based on dynamic metal--ligand coordination as model systems to illustrate this relationship. The molecular design of these materials allows for precise and independent control over the nature and concentration of ligand and metal, which are molecular properties critical for bulk ion conduction and polymer mechanics. The model system investigated, inspired by polymerized ionic liquids, is composed of poly(ethylene oxide) with tethered imidazole moieties that facilitate dissociation upon incorporation of nickel(II) bis(trifluoromethylsulfonyl)imide. Nickel--imidazole interactions physically cross-link the polymer, increase the number of elastically active strands, and dramatically enhance the modulus. In addition, a maximum in ionic conductivity is observed due to the competing effects of increasing ion concentration and decreasing ion mobility upon network formation. The simultaneous enhancement of conducting and mechanical properties within a specific concentration regime demonstrates a promising pathway for the development of mechanically robust ion conducting polymers. [ABSTRACT FROM AUTHOR]

Controlling the self-assembly of block copolymers with variable chain shape and stiffness is important for driving the self-assembly of functional materials containing nonideal chains as well as for developing materials with new mesostructures and unique thermodynamic interactions. The polymer helix is a particularly important functional motif. In the helical chain, the traditional scaling relationships between local chain stiffness and space-filling properties are not applicable; this in turn impacts the scaling relationships critical for governing self-assembly. Polypeptoids, a class of sequence-defined peptidomimetic polymers with controlled helical secondary structure, were used to systematically investigate the impact of helical chain shape on block copolymer self-assembly in a series of poly(n-butyl acrylate)-b-polypeptoid block copolymers. Small-angle X-ray scattering (SAXS) of the bulk materials shows that block copolymers form hexagonally packed cylinder domains. By leveraging sequence control, the polypeptoid block was controlled to form a helix only at the part either adjacent to or distant from the block junction. Differences in domain size from SAXS reveal that chain stretching of the helix near the block junction is disfavored, while helical segments at the center of cylindrical domains contribute to unfavorable packing interactions, increasing domain size. Finally, temperature-dependent SAXS shows that helix-containing diblock copolymers disorder at lower temperatures than the equivalent unstructured diblock copolymers; we attribute this to the smaller effective N of the helical structure resulting in a larger entropic gain upon disordering. These results emphasize how current descriptions of rod/coil interactions and conformational asymmetry for coil polymers do not adequately address the behavior of chain secondary structures, where the scalings of space-filling and stiff--elastic properties relative to chain stiffness deviate from those of typical coil, semiflexible, and rodlike polymers. [ABSTRACT FROM AUTHOR]

A conjugated polyelectrolyte (poly[2,6-(4,4-bis-potassium butanylsulfonate-4H-cyclopenta-[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT-SO3K) assembles into a novel, hierarchical hydrogel structure with all structural evidence indicating dominant electrostatic rather than aromatic or mesogen interactions. PCPDTBT-SO3K forms an entangled polymer mesh, where polymer chains are tied together by ionic cross-links, comprising microgel clusters that percolate to form a macroscopic three-dimensional network. With increasing temperature, ions gain mobility to move toward the exterior of the microgel clusters, dissolving the ionic cross-links and inhibiting network percolation through electrostatic repulsion. While π-π stacking interactions may be present in a disorganized fashion, no long-range π-π stacking is evident in X-ray scattering. Soft materials based on PCPDTBT-SO3K remain semiconducting and exhibit elevated ionic conductivity at the structural reorganization temperature. [ABSTRACT FROM AUTHOR]

Electronic and optical properties of conjugated polymers are strongly affected by their solid-state microstructure. In nematic polymers, mesoscopic order and structure can be theoretically understood using Maier-Saupe (MS) models, motivating us to apply them to conjugated macromolecular systems and consider the problem of their material-specific parametrization. MS models represent polymers by worm-like chains (WLC) and can describe collective polymer alignment through anisotropic MS interactions. Their strength is controlled by a phenomenological temperature-dependent parameter, ν(T). We undertake the challenging task of estimating material-specific ν(T), combining experiments and Self-Consistent Field theory (SCFT). Considering three different materials and a spectrum of molecular weights, we cover the cases of rod-like, semiflexible, and flexible conjugated polymers. The temperature of the isotropic-nematic transition, TIN, is identified via polarized optical microscopy and spectroscopy. The polymers are mapped on WLC with temperature-dependent persistence length. Fixed persistence lengths are also considered, reproducing situations addressed in earlier studies. We estimate ν(T) by matching TIN in experiments and SCFT treatment of the MS model. An important conclusion is that accounting explicitly for changes of persistence length with temperature has significant qualitative effects on ν(T). We moreover correlate our findings with earlier discussions on the thermodynamic nature of phenomenological MS interactions. [ABSTRACT FROM AUTHOR]

The mechanical and conductive properties of a polymeric ionic liquid (PIL) are decoupled through the addition of a fraction of trivalent anions to a chloride single-ion conductor. Trivalent phosphate ions strongly coordinate with polymer-bound imidazoliums, producing an increase in both the ionic conductivity and the polymer viscosity. Both the viscosity and the ionic conductivity increase with phosphate content, and the conductivity is superior to that of the neat PIL at larger trivalent anion concentrations. The interaggregate spacing (determined by X-ray scattering), glass transition temperature (measured by calorimetry), and free volume (estimated by rheology) are each sensitive to the presence of trivalent ions but not to changes in the phosphate concentration. Thus, the presence of a fraction of trivalent anions qualitatively changes the structure and interaction of ions, resulting in modified macroscopic properties of the PIL. We hypothesize that this step change in properties upon introducing phosphate ions is due to a densification of ion aggregates by the trivalent ion, which strongly binds to imidazolium ions. This provides a new mechanism for creating PILs with tailored conductive and rheological behavior. [ABSTRACT FROM AUTHOR]

Thermal annealing strongly impacts the nano- and microstructure of conjugated polymers. Despite the fundamental importance for the resulting optoelectronic behavior of this class of materials, the underlying crystallization processes have not received the same attention that is encountered in other disciplines of materials science. The question arises whether classical treatment of nucleation and growth phenomena is truly applicable to conjugated polymers? Here, the isothermal crystallization behavior of the conjugated polymer poly(3-(2'-ethyl)hexylthiophene) (P3EHT) is monitored with differential scanning calorimetry (DSC). Avrami analysis reveals growth- and nucleation-limited temperature regimes that are separated by the maximum rate of crystallization. The molecular weight of the polymer is found to strongly influence the absolute rate of crystallization at the same degree of undercooling relative to the melting temperature. A combination of optical microscopy and grazing-incidence wide-angle X-ray scattering (GIWAXS) confirms that the resulting nano- and microstructure strongly correlate with the selected isothermal annealing temperature. Hence, this work establishes that classical nucleation and growth theory can be applied to describe the solidification behavior of the semicrystalline conjugated polymer P3EHT. [ABSTRACT FROM AUTHOR]

Poly(dimethylsiloxane) (PDMS)- and poly(ethylene oxide) (PEO)-based block copolymer coatings functionalized with amphiphilic, surface-active, and sequence-controlled oligomer side chains were studied to directly compare the effects of hydrophilicity, hydrogen bonding, and monomer sequence on antifouling performance. Utilizing a modular coating architecture, structurally similar copolymers were used to make direct and meaningful comparisons. Amphiphilic character was imparted with non-natural oligopeptide and oligopeptoid pendant chains made from oligo-PEO and surface-segregating fluoroalkyl monomer units. Surface analysis revealed rearrangement for all surfaces when moved from vacuum to wet environments. X-ray photoelectron spectroscopy (XPS) spectra indicated that the polymer backbone and oligomer interactions play key roles in the surface presentation. Biofouling assays using the macroalga Ulva linza showed that the presence of peptoid side chains facilitated the removal of sporelings from the PDMS block copolymer, with removal matching that of a PDMS elastomer standard. The lack of a hydrogen bond donor in the peptoid backbone likely contributed to the lower adhesion strength of sporelings to these surfaces. Both the initial attachment and adhesion strength of the diatom Navicula incerta were lower on the coatings based on PEO than on those based on PDMS. On the PEO coating bearing the blocky peptoid sequence, initial attachment of N. incerta showed no measurable cell density. [ABSTRACT FROM AUTHOR]

Controlling crystallinity and molecular packing at nano- and macroscopic length scales in conjugated polymer thin films is vital for improving the performance of polymer-based electronic devices. Herein, the inherent amphiphilicity of rigid donor-acceptor copolymers used in high performance polymer electronics is leveraged to allow the formation of highly ordered lyotropic mesophases. By increasing the length and branching of solubilizing chains on cyclopentadithiophene-alt-thiadiazolopyridine-based alternating copolymers, amphiphilicity can be increased, and lyotropic liquid crystalline mesophases are observed in selective solvents. These lyotropic mesophases consist of chain extended polymers exhibiting close, ordered π-stacking. This is evidenced by birefringent solutions and red-shifted absorbance spectra displaying pronounced excitonic coupling. Crystallinity developed in solution can be transferred to the solid state, and thin films of donor-acceptor copolymers cast from lyotropic solutions exhibit improved crystalline order in both the alkyl and π-stacking directions. Because of this improved crystallinity, transistors with active layers cast from lyotropic solutions exhibit a significant improvement in carrier mobility compared to those cast from isotropic solution, reaching a maximum value of 0.61 cm² V-1 s-1. This approach of rational side chain design bridges the gap from solution structure to solid state structure and is a promising and general approach to allow the expression of lyotropic mesophases in rigid conjugated polymers. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses articles within the issue dedicated to professor Edward J. Kramer's work.

Elucidating the relationship between chemical structure, morphology, and ionic conductivity is essential for designing novel high-performance materials for electrochemical applications. In this work, the effect of lamellar domain spacing (d) on ionic conductivity (σ) is investigated for a model system of hydrated diblock copolymer based on a protic polymerized ionic liquid. We present a strategy that allows for the synthesis of a well-defined series of narrowly dispersed PS-b-PIL with constant volume fraction of ionic liquid moieties (fIL ≈ 0.39) and with two types of mobile charge carriers: trifluoroacetate anions and protons. These materials self-assemble into ordered lamellar morphologies with variable domain spacing (ca. 20-70 nm) as demonstrated by small-angle X-ray scattering. PS-b-PIL membranes exhibit ionic conductivities above 10-4 S/cm at room temperature, which are independent of domain spacing consistent with their nearly identical water content. The conductivity scaling relationship demonstrated in this paper suggests that a mechanically robust membrane can be designed without compromising its ability to transport ions. In addition, PIL-based membranes exhibit low water uptake (λ ≈ 10) in comparison with many proton-conducting systems reported elsewhere. The low water content of the materials described herein makes them promising candidates for electrochemical devices operating in aqueous electrolytes at low current densities where moderate ion conduction and low product crossover are required. [ABSTRACT FROM AUTHOR]

ABSTRACT Charge transport in poly(3-alkylthiophene)s (P3AT)s is closely linked to the nanoscale organization of crystallites. Block copolymer morphologies provide an ideal platform to study crystallization as the chain ends are tethered at a known interface in a well-defined geometry. The impact of soft versus hard confinement on P3EHT crystallization was studied using poly(3-(2′-ethyl)hexylthiophene) (P3EHT) containing diblocks with both rubbery poly(methyl acrylate) (PMA) and glassy polystyrene (PS) blocks. Here, P3EHT's lower melting point relative to the commonly studied poly(3-hexylthiophene) (P3HT) facilitated its confined crystallization and makes it an ideal model system. While transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) revealed well-ordered lamellar morphologies both in the melt and post-crystallization for both sets of diblocks, the glassy blocks inhibit confined crystallization of P3EHT relative to rubbery matrix blocks. Analysis of aligned diblocks by both SAXS and wide angle X-ray scattering (WAXS) revealed that the P3EHT chain axis aligns perpendicular to domain interfaces, allowing preferential growth of the alkyl-chain and π-π stacking directions parallel to lamellae. Finally, it was shown that following diblock self-assembly in the melt, crystallite growth drives expansion of microdomains to match the P3EHT contour length. It was concluded that P3EHT chains adopted an extended conformation within confined crystallites due to the rigid nature of polythiophenes relative to flexible chain crystalline polymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 205-215 [ABSTRACT FROM AUTHOR]

We report the synthesis of a series of water-soluble anionic narrow band-gap conjugated polyelectrolytes with a varied density of the ionic functional groups. The charge density is modulated by incorporating the structural units with tetraethylene glycol (TEG) monomethyl ether side chains. These polymers are readily p-doped during dialysis in water. CPEs with TEG side chains exhibit tighter intermolecular packing in the solid state and higher electrical conductivity. [ABSTRACT FROM AUTHOR]

Side-chain engineering is increasingly being utilized as a technique to impact the structural order and enhance the electronic properties of semiconducting polymers. However, the correlations drawn between structural changes and the resulting charge transport properties are typically indirect and qualitative in nature. In the present work, a combination of grazing incidence X-ray diffraction and crystallographic refinement calculations is used to determine the precise molecular packing structure of two thiophene-based semiconducting polymers to study the impact of side-chain modifications. The optimized structures provide high-quality fits to the experimental data and demonstrate that in addition to a large difference in interchain spacing between the two materials, there exists a significant disparity in backbone orientation as well. The calculated structures are utilized in density functional theory calculations to determine the band structure of the two materials and are shown to exhibit a dramatic disparity in interchain dispersion which accounts for the large observed difference in charge carrier mobility. The techniques presented here are meant to be general and are therefore applicable to many other highly diffracting semicrystalline polymers. [ABSTRACT FROM AUTHOR]

Thermoelectricsare famously challenging to optimize, because ofinverse coupling of the Seebeck coefficient and electrical conductivity,both of which control the thermoelectric power factor. Inorganic–organicinterfaces provide a promising route for realization of the strongelectrical and thermal asymmetries required for thermoelectrics. Inthis work, transport properties of inorganic–organic interfacesare probed and understood at the molecular scale using the STM-break junction measurement technique, theory, and a class of newly synthesizedmolecules. We synthesized a series of disubstituted thiophene derivativesvarying the length of alkylthio-linkers and the number of thiophenerings. These molecules allow the systematic tuning of electronic resonanceswithin the junction. We observed that these molecules have a decreasingSeebeck coefficient with increasing length of the alkyl chain, whileoligothiophene junctions show an increasing Seebeck coefficient withlength. We find that thiophene–Au junctions have significantlyhigher Seebeck coefficients, compared to benzenedithiol (in the rangeof 7–15 μV/K). A minimal tight-binding model, includinga gateway state associated with the S–Au bond, captures andexplains both trends. This work identifies S–Au gateway statesas being important and potentially tunable features of junction electronicstructure for enhancing the power factor of organic/inorganic interfaces. [ABSTRACT FROM AUTHOR]

A study of the scope and limitations of varying the ligand framework around the dinuclear core of FvRu2 in its function as a molecular solar thermal energy storage framework is presented. It includes DFT calculations probing the effect of substituents, other metals, and CO exchange for other ligands on Δ Hstorage. Experimentally, the system is shown to be robust in as much as it tolerates a number of variations, except for the identity of the metal and certain substitution patterns. Failures include 1,1′,3,3′-tetra- tert-butyl ( 4), 1,2,2′,3′-tetraphenyl ( 9), diiron ( 28), diosmium ( 24), mixed iron-ruthenium ( 27), dimolybdenum ( 29), and ditungsten ( 30) derivatives. An extensive screen of potential catalysts for the thermal reversal identified AgNO3-SiO2 as a good candidate, although catalyst decomposition remains a challenge. [ABSTRACT FROM AUTHOR]

In this work, crystallization kinetics and aggregate growth of poly(3-ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X-ray diffraction and optical absorption show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time-dependent, field-effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of ≈2-3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter-aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics. [ABSTRACT FROM AUTHOR]

The chain shape of polymers affects many aspects of theirbehavior and is governed by their intramolecular interactions. Delocalizationof electrons along the backbone of conjugated polymers has been shownto lead to increased chain rigidity by encouraging a planar conformation.Poly(3-hexylthiophene) and other poly(3-alkylthiophenes) (P3ATs) areinteresting for organic electronics applications, and it is clearthat a hierarchy of structural features in these polymers controlscharge transport. While other conjugated polymers are very rigid,the molecular structure of P3AT allows for two different planar conformationsand a significant degree of torsion at room temperature. It is unclear,however, how their chain shape depends on variables such as side chainchemistry or regioregularity, both of which are key aspects in themolecular design of organic electronics. Small-angle neutron scatteringfrom dilute polymer solutions indicates that the chains adopt a randomcoil geometry with a semiflexible backbone. The measured persistencelength is shorter than the estimated conjugation length due to thetwo planar conformations that preserve conjugation but not backbonecorrelations. The persistence length of regioregular P3HT has beenmeasured to be 3 nm at room temperature and decreases at higher temperatures.Changes in the regioregularity, side chain chemistry, or syntheticdefects decrease the persistence length by 60–70%. [ABSTRACT FROM AUTHOR]

Polymerized ionic-liquids (PILs) are promising materialswhoseionic properties can be tuned based on their chemistry. By incorporatingPILs into block copolymer (BCP) structures, it is possible to providecomplementary functionality (i.e., structural stability) and transporttunability to ion-conducting materials. In this study, we describethe self-assembly and conductivity of novel poly(styrene-block-histamine methacrylamide) diblock copolymers (PS-b-PHMA) and the resulting PS-b-PIL derivatives obtainedafter treatment with trifluoroacetic acid (TFA). These materials self-assembleinto ordered BCP structures with tunable domain sizes as demonstratedby small-angle X-ray scattering (SAXS) and transmission electron microscopy(TEM). PS-b-PHMA membranes show conductivities upto 2 × 10–4S/cm at room temperature, whichincrease byan order of magnitude in the presence of acid. In addition, both PHMA-and PIL-based membranes exhibit lower water uptake (λ = 4–6and 8–10, respectively) in comparison with most proton conductingmembranes reported elsewhere. The low water content in these membranestranslates into a stronger effect of morphology on transport behavior,resulting in a measurable increase in ion conductivity as a functionof conducting channel size. [ABSTRACT FROM AUTHOR]

Abstract: Block copolymer thin films with distinct morphologies are prepared by spin casting a nominally lamellar assay of poly(styrene-block-ethylene oxide) from a variety of solvents with and without salt doping. The 3-D morphologies of free-standing thin-film regions, which are obtained by casting directly onto holey substrates, are investigated in detail using various energy-filtering transmission electron microscopy techniques and by electron tomography. Surface characterization is achieved by atomic force microscopy. Our results demonstrate that in order to fully characterize the unique 3-D morphologies of the block copolymer thin films, a multi-method approach is required. When casting from a binary solvent, an unexpected layered honeycomb-type morphology is revealed, which likely results from an expansion of the poly(ethylene oxide) phase. A dramatic effect of selective cation coordination on the morphology of the as-cast block copolymer films is also directly observed. [Copyright &y& Elsevier]

We report on the synthesis and morphology of a block copolymer, poly(3-(2′-ethylhexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO), that conducts both electrons and ions. We show that in the melt state the P3EHT-b-PEO chains self-assemble to produce traditional nanoscale morphologies such as lamellae and gyroid. This is in contrast to a majority of previous studies on copolymers with electronically conducting blocks wherein a nanofibrillar morphology is obtained. Our approach enables estimation of the Flory–Huggins interaction parameter, χ. The segregation strength between the two blocks is controlled through the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). For the salt-free sample, the gyroid morphology, obtained in the melt state, is transformed into lamellae below the melting temperature of the P3EHT block. This is due to the "breaking out" of the crystalline phase. For the salt-containing sample, P3EHT-b-PEO has a lamellar morphology in both melt and crystalline states (confined crystallization). [ABSTRACT FROM AUTHOR]

A fluctuation X-ray scattering experiment has been carried out on platinum-coated gold nanoparticles randomly oriented on a substrate. A complete algorithm for determining the electron density of an individual particle from diffraction patterns of many particles randomly oriented about a single axis is demonstrated. This algorithm operates on angular correlations among the measured intensity distributions and recovers the angular correlation functions of a single particle from measured diffraction patterns. Taking advantage of the cylindrical symmetry of the nanoparticles, a cylindrical slice model is proposed to reconstruct the structure of the nanoparticles by fitting the experimental ring angular auto-correlation and small-angle scattering data obtained from many scattering patterns. The physical meaning of the refined structure is discussed in terms of their statistical distributions of the shape and electron density profile. [ABSTRACT FROM AUTHOR]

Block copolymers with tunable compositions offer theability todirectly control the interaction strength between the two blocks andtherefore polymer properties. The miscibility of an A–B blockcopolymer can be increased by introducing B or B-like comonomers intothe A block, and literature has shown that both the amount and thedistribution of these comonomers affect the compatibility of the twoblocks. Sequence-defined block copolymers in which one can exactlycontrol the composition and comonomer distribution provide a uniqueopportunity to control the overall strength of segregation. Here,sequence-defined block copolymers have been synthesized via azide–alkynecoupling using polystyrene and sequence-specific polypeptoids (N-substitutedglycines) with 2-methoxyethyl side chains. These polystyrene-polypeptoidblock copolymers readily self-assemble into hexagonally packed andlamellar morphologies. N-(2-phenylethyl)glycine residues,which have a styrene-like side chain, were introduced throughout thepolypeptoid block to increase the compatibility with the polystyreneblock. As the compatibility increased, the strength of segregationand therefore the block copolymer order–disorder transitionsdecreased. The polystyrene–polypeptoid block copolymers providea tunable platform for further studies on the effect of compositionand sequence design on self-assembly and block copolymer properties. [ABSTRACT FROM AUTHOR]

Understanding the driving forces for the collapse ofa polymerchain from a random coil to a globule would be invaluable in enablingscientists to predict the folding of polypeptide sequences into definedtertiary structures. The HP model considers hydrophobic collapse tobe the major driving force for protein folding. However, due to theinherent presence of chirality and hydrogen bonding in polypeptides,it has been difficult to experimentally test the ability of hydrophobicforces to independently drive structural transitions. In this work,we use polypeptoids, which lack backbone hydrogen bonding and chirality,to probe the exclusive effect of hydrophobicity on the coil-to-globulecollapse. Two sequences containing the same composition of only hydrophobic“H” N-methylglycine and polar “P” N-(2-carboxyethyl)glycine monomers are shown to have verydifferent globule collapse behaviors due only to the difference intheir monomer sequence. As compared to a repeating sequence with aneven distribution of H and P monomers, a designed protein-like sequencecollapses into a more compact globule in aqueous solution as evidencedby small-angle X-ray scattering, dynamic light scattering, and probingwith environmentally sensitive fluorophores. The free energy changefor the coil-to-globule transition was determined by equilibrium denaturanttitration with acetonitrile. Using a two-state model, the protein-likesequence is shown to have a much greater driving force for globuleformation, as well as a higher mvalue, indicatingincreased cooperativity for the collapse transition. This differencein globule collapse behavior validates the ability of the HP modelto describe structural transitions based solely on hydrophobic forces. [ABSTRACT FROM AUTHOR]