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Carboranes have been previously noted to distinctively affect the luminescent properties of semiconducting polymers when incorporated into the conjugated backbone. In this report, we use carborane-based poly(fluorene) derivatives as active materials for polymer light-emitting diodes and transistors. Optoelectronic analysis unequivocally shows that carborane does not participate in the π-conjugated network, yet their presence causes major red-shifting in device electroluminescence as well as in thin film photoluminescence. In field effect transistors, they also improve charge carrier mobility by an order of magnitude despite disrupting π-conjugation. This use of carborane-containing conjugated polymers in active devices holds promise as new responsive materials in electronic polymer applications.

Wearable sweat biosensors offer compelling opportunities for improved personal health monitoring and non-invasive measurements of key biomarkers. Inexpensive device fabrication methods are necessary for scalable manufacturing of portable, disposable, and flexible sweat sensors. Furthermore, real-time sweat assessment must be analyzed to validate measurement reliability at various sweating rates. Here, we demonstrate a "smart bandage" microfluidic platform for cortisol detection and continuous glucose monitoring integrated with a synthetic skin. The low-cost, laser-cut microfluidic device is composed of an adhesive-based microchannel and solution-processed electrochemical sensors fabricated from inkjet-printed graphene and silver solutions. An antibody-derived cortisol sensor achieved a limit of detection of 10 pM and included a low-voltage electrowetting valve, validating the microfluidic sensor design under typical physiological conditions. To understand effects of perspiration rate on sensor performance, a synthetic skin was developed using soft lithography to mimic human sweat pores and sweating rates. The enzymatic glucose sensor exhibited a range of 0.2 to 1.0 mM, a limit of detection of 10 μM, and reproducible response curves at flow rates of 2.0 μL min

Incorporation of o-carborane into the backbone of poly(dihexylfluorene)s drastically affects emission properties due to an intramolecular charge-transfer state (ICT) that forms between the fluorene...

Thin hydrogel films containing the acid sensitive cross-linker 2,5-dimethyl-2,5-hexanediol dimethacrylate (DHDMA) were synthesized as part of a larger project to create protective layers against chemical and biological (CB) threats. In order to operate efficiently as fabric coatings, the mechanical and moisture vapor transport properties of these materials must be understood. The hydrogels were composed primarily of poly(ethylene glycol) dimethacrylate (PEGDMA) and 2-hydroxyethyl methacrylate (HEMA) and were prepared by free radical cross-linking polymerization. The influence of different compositions of DHDMA, PEGDMA, and HEMA on the moisture vapor transmission rate (MVTR), mechanical properties, and swelling properties of PEGDMA/DHDMA/HEMA copolymer hydrogels has been investigated. The characterization by Fourier transform infrared (FTIR) spectroscopy confirmed the presence of all monomers used in the gel structure. The hydrogels showed high MVTR, which are comparable to the widely accepted breathable m...

Within molecular electronics, the molecular-scale transistor provides a compelling and central device. While substantial efforts have been expended on this subject, current embodiments typically involve cumbersome gating with nonintuitive routes for integration. In this theoretical study, we examined the efficacy of combining a new molecular architecture with the well-established atomic resolution of the Si(100)2 × 1 hydride-terminated surface to provide a molecular-scale modulation scheme that is conceptually easier to integrate. A series of alkyl-substituted carbazoles: ethylcarbazole, butylcarbazole, hexylcarbazole, and decylcarbazole, operating in the σ–π motif provided the transport conduit through extended conjugation of π–π stacking upon assembly along the Si(100)2 × 1 dimer row. It was found that alkyl substituent lengths greater than four methylene units (butylcarbazole) effectively isolated the extended π-conjugation from the underlying substrate by preventing tunneling due to breakdown at termi...

Fabrication of detection elements with ultrahigh surface area is essential for improving the sensitivity of analyte detection. Here, we report a direct patterning technique to fabricate three-dimensional CeO2 nanoelectrode arrays for biosensor application over relatively large areas. The fabrication approach, which employs nanoimprint lithography and a CeO2 nanoparticle-based ink, enables the direct, high-throughput patterning of nanostructures and is scalable, integrable, and of low cost. With the convenience of sequential imprinting, multilayered woodpile nanostructures with prescribed numbers of layers were achieved in a “stacked-up” architecture and were successfully fabricated over large areas. To demonstrate application as a biosensor, an enzymatic glucose sensor was developed. The sensitivity of glucose sensors can be enhanced simply by increasing the number of layers, which multiplies surface area while maintaining a constant footprint. The four-layer woodpile nanostructure of CeO2 glucose sensor ...

Soft UV-imprint lithography at sub-micron dimensions was achieved in thin films of photopolymer resist. The imprinting was enabled by overcoming resist absorption by polydimethylsiloxane (PDMS) through surface treatment with a layer of (heptadecafluoro-1,1,2,2-tetrahydrodecyl)dimethylchlorosilane. Characterization of the composite molds was done by X-ray photoelectron spectroscopy, nanoindentation, and contact angle measurements. PDMS molds treated with fluoroalkylsilane layer were used to imprint into thin films (70–630 nm) of UV curable resins consisting of either polyurethanes or acrylates, replicating with high fidelity features over the surface of wafer substrates. The use of these highly conformal PDMS molds allowed the patterning of functional materials including gold and aluminium by a simple imprint lithographic technique. This is the first report of the use of modified PDMS surfaces in an imprint process that enables the transfer of sub-micron patterns to underlying layers for device structure fabrication. The patterned features were studied with atomic force microscopy, scanning electron microscopy, and optical microscopy.

Three-dimensional (3D) nanofabrication using the directed self-assembly of block copolymers (BCPs) holds great promise for the nanoscale device fabrication and integration into 3D architectures over large areas with high element densities. In this work, a robust platform is developed for building 3D BCP architectures with tailored functionality using 3D micron-scale woodpile structures (WPSs), fabricated by a multiphoton polymerization technique. By completely filling the spaces of the WPSs and using the interactions of the blocks of the BCPs with the struts of the WPS, well-developed 3D nanoscopic morphologies are produced. Metal ion complexation with one block of the copolymer affords a convenient stain to highlight one of the microdomains of the copolymer for electron microscopy studies but also, with the reduction of the complexing salt to the corresponding metal, a simple strategy is shown to produce 3D constructs with nanoscopic domain resolution.

Conjugated polymers of diketopyrrolopyrrole (DPP) and thiophene, especially 2,5-di-2-thienyl-thieno[3,2-b]thiophene, were characterized based on their molecular packing orientation, and they showed a π–π stacking distance of 3.6 A and a high field-effect hole mobility on the order of 10−2 cm2/Vs. Perovskite solar cells fabricated with the genuine or both oxidant- and salt dopant-free polymer as the hole-transporting layer displayed high photoconversion efficiencies of 16.3% as well as high durability. Conjugated polymers of diketopyrrolopyrrole (DPP) and thiophene, especially 2,5-di-2-thienyl-thieno[3,2-b]thiophene, were characterized by their molecular packing orientation with a π-π stacking distance of 3.6 A and a high field-effect hole mobility on the order of 10−2 cm2/Vs. A perovskite solar cell, fabricated with the genuine or both oxidizing and salt dopant-free polymer as a hole-transporting layer, displayed a high photo-conversion efficiency of 16.3% with high durability.

Cellulose nanocrystals (CNCs) were grafted with poly(2-ethynylene-9,9-dihexyl fluorene) via Sonogashira cross-coupling chemistry to yield environmentally friendly, composite nanoparticles. CNCs were first surface functionalized with 4-bromobenzoyl chloride to provide aryl halide tethering sites for Sonogashira cross-coupling. Poly(ethynylene fluorene) was then grafted-from the bromide functionalized CNC (s-Br-CNC) surface. The intermediate product, s-Br-CNC, was characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS), validating the success of the esterification reaction and giving an approximate degree of substitution. The grafted product, g-PEF-CNC, was analyzed and validated using XPS, showing the expected trends in C1s deconvolutions with addition of solely carbon based polymer. Grafted chains were cleaved via acid hydrolysis and were revealed to be n = 2–4 short chain oligomers thru analysis by matrix assisted laser desorption/ionization-time of flight mass spectrometry. A number of the potential end group pairs were observed. As such, the authors have successfully demonstrated and analyzed a novel grafted composite nanomaterial based on renewable nanocellulose substrates and semiconductive conjugated polymers.

Solvent-assisted soft nanoimprint lithography of cellulose nanocrystals (CNCs) has been applied to easily fabricate nano-/microscale structured cellulose films of various structures, including line gratings and pillar patterns. The cellulose-based ink consisted of CNCs, citric acid, and sodium hypophosphite monohydrate. After imprinting with a crosslinked poly(dimethylsiloxane) stamp (PDMS), the patterned CNC films were crosslinked via the citric acid present under mild heat treatment. In order to obtain well-defined ultra-small structures, two different modification methods were applied to optimize the wettability between the CNC dispersions and the PDMS stamp. With this modification, CNC films could be patterned on various substrates by either direct imprint or reversal imprint methods. The dimensions of the patterned features in the cellulose films was as small as 140 nm.

The trend of device downscaling drives a corresponding need for power source miniaturization. Though numerous microfabrication methods lead to successful creation of submillimeter-scale electrodes, scalable approaches that provide cost-effective nanoscale resolution for energy storage devices such as on-chip batteries remain elusive. Here, we report nanoimprint lithography (NIL) as a direct patterning technique to fabricate high-performance TiO2 nanoelectrode arrays for lithium-ion batteries (LIBs) over relatively large areas. The critical electrode dimension is below 200 nm, which enables the structure to possess favorable rate capability even under discharging current densities as high as 5000 mA g–1. In addition, by sequential imprinting, electrodes with three-dimensional (3D) woodpile architecture were readily made in a “stack-up” manner. The height of architecture can be easily controlled by the number of stacked layers while maintaining nearly constant surface-to-volume ratios. The result is a propo...

A self-aligned double patterning approach using a dopamine chemistry-inspired coating technique has been developed for the fabrication of sub-20 nm patterns. Poly(methyl methacrylate) (PMMA) films were patterned by nanoimprint lithography to form relief features. A thin layer of polydopamine (PDA) was conformally deposited on the surface of the PMMA pattern sidewalls to form a spacer layer. After etching the surface of the PDA layer from the horizontal surfaces and subsequently removing the PMMA template, free-standing PDA sidewall patterns remained that essentially doubled the original PMMA pattern density with decreased feature dimensions as compared to the initial PMMA template structures. The critical dimension of the PDA patterns can be tuned to ∼20 nm by controlling the PDA deposition conditions and further reduced to ∼13 nm by thermal carbonization of the PDA. Both simple lines and more complex rhombic ring features were fabricated by this technique to demonstrate its capacity for replicating arbitrary patterns. This work represents a simple and scalable strategy for preparing well-defined nanostructures with feature sizes usually only accessible via complex leading edge lithographic methods.

Herein we examine the end-capping efficacy of several end-capping reagents (ECRs) in the Stille polymerization of 2,7-dibromo-9,9-bis(2-ethylhexyl)fluorene (Fl) and 2,5-bis(trimethylstannyl)-thieno[3,2-b]thiophene (TT). Polymerizations were carried out in a one-pot fashion where the molar ratio of TT relative to Fl was biased, ideally generating bis(trimethylstannyl) macromolecules. Various ECRs (bromobenzene, 4-bromotoluene, 4-(trifluoromethyl) bromobenzene, 4,4′-bromobiphenyl, 2-bromo-9,9-dimethylfluorene, iodobenzene, 4-iodotoluene, and 4,4′-iodobiphenyl) differing in reactivity were employed in the one-pot reaction. Polymers were characterized using GPC, 1H NMR, and end-capping efficacy was evaluated with MALDI-ToF MS. The iodo derivatives were found to disrupt propagation, severely inhibiting molecular weight. The bromo ECRs varied in end-capping efficiency: bromofluorene ∼ bromobiphenyl > trifluoromethylbromobenzene ∼ bromobenzene > bromotoluene. Additionally, we demonstrate a strong efficiency dependence on initial monomer concentration and demonstrate this method's superiority over post-polymerization end-capping.

Cellulose-based aerogels are reported that were generated using cellulose nanofibril (CNF) gels in an ambient drying process. These nancellulose aerogels were inspired by the preparation of a traditional Chinese food, frozen tofu, which undergoes significant toughening after freezing and thawing. It is this toughening mechanism that allows for the formation of nanocellulose aerogels which ordinarily would collapse upon ambient drying. By freezing hydrated CNF gel dispersions, solvent exchanging, and drying at ambient pressure, monolithic nanocellulose aerogels with high porosity (>98%), low density (as low as 0.018 g cm–3), and high surface area (>30 m2 g–1) were readily generated. Moreover, since no special reactors are required, these structures can be easily created over large areas. For example, a hydrated CNF gel was frozen at −72 °C, and then, the frozen gel was immersed directly in a 2-propanol bath to allow solvent exchange. The resulting alcohol-infused gel was dried at ambient pressure to fabric...

A simple and robust method has been developed for the generation of macroscopically ordered hexagonal arrays from the directed self-assembly (DSA) of cylinder-forming block copolymers (BCPs) based on minimal trench patterns with solvent vapor annealing. The use of minimal trench patterns allows us to probe the guided hexagonal arrays of cylindrical microdomains using grazing incidence small angle X-ray scattering (GISAXS), where the sample stage is rotated on the basis of the six-fold symmetry of a hexagonal system. It is found that the (10) planes of hexagonal arrays of cylindrical microdomains are oriented parallel to the underlying trench direction over macroscopic length scales (∼1 × 1 cm2). However, there are misorientations of the hexagonal arrays with short-range ordering. GISAXS patterns show that the hexagonal arrays on the minimal trench pattern are distorted, deviating from a perfect hexagonal lattice. This distortion has been attributed to the absence of topographic constraints in the unconfined direction on the 1-D minimal trench pattern. Also, the frustration of BCP microdomains, arising from the incommensurability between the trench pitch and natural period of the BCP at the base of the trench, influences the distortion of the hexagonal arrays.

A series of rubrene derivatives were synthesized and the influence of the side group in enhancing photo-oxidative stability was evaluated. Photo-oxidation half-lives were determined via UV-vis absorption spectroscopy, which revealed thiophene containing derivatives to be the most stable species. The electron affinity of the compounds did not correlate with stability as previously reported in literature. Our work shows that shorter excited-state lifetimes result in increased photo-oxidative stability in these rubrene derivatives. These results confirm that faster relaxation kinetics out-compete the formation of reactive oxygen species that ultimately degrade linear oligoacenes. This report highlights the importance of using molecular design to tune excited-state lifetimes in order to generate more stable oligoacenes.

Carborane-containing poly(dihexylfluorene)s experience drastic solvatochromism in both the solution and solid states, a characteristic that is advantageous for use in environmental and biological sensing applications. Understanding the intrinsic decay mechanisms that give rise to such sensitive emission properties is important for designing responsive sensors. The solution-state photophysical properties of homopolymer, poly(9,9-dihexyl(bisfluorenyl)carborane) (PFCY), and alternating copolymer, poly(9,9-dihexyl-2,7-fluorene- alt-9,9-dihexyl(bisfluorenyl)carborane) (PFCS), were deciphered using steady-state, electrochemical, spectroelectrochemical, and time-resolved spectroscopic methods. From these techniques, it was discovered that following excitation the conjugated fluorene local excited state (LES) donates an electron to the carborane molecule, forming an intramolecular charge transfer (ICT) state between a radical cation on the fluorene moiety and a radical anion on the carborane moiety. From the global analysis of transient absorption data, it was discovered that the rate of electron transfer from the fluorene to the carborane is heavily influenced by solvent polarity and is significantly faster in more polar solvents. Once formed, the ICT state can decay through radiative or nonradiative mechanisms and is more likely to undergo radiative decay in nonpolar solvents, due to an intramolecular restriction of the polar ICT state. This study elucidates the effects that polarity has on the excited-state formation and subsequent decay mechanisms of fluorene-carborane systems, conclusively explaining the solvatochromism and steady-state emission properties exhibited by this system.

Fabrication of detection elements with ultrahigh surface area is essential for improving the sensitivity of analyte detection. Here, we report a direct patterning technique to fabricate three-dimensional CeO

We demonstrate that a minimal topographic pattern with a confinement depth (D) much less than the domain spacing of block copolymers (L0) can be used to achieve highly ordered hexagonal arrays or unidirectionally aligned line patterns over large areas. Cylinder-forming poly(styrene-b-ethylene oxide) (PS-b-PEO) thin films were prepared on a series of minimal single trench patterns with different widths (W) and D. Upon thermal annealing, hexagonal arrays of cylindrical microdomains propagated away from the edges of a single trench, providing insight into the minimum pitch (P) of the trench necessary to fully order hexagonal arrays. The confinement trench D of 0.30L0, the W in the range of 1.26L0 to 2.16L0, and the P as long as 18.84L0 were found to be effective for the generation of laterally ordered hexagonal arrays with the density amplification up by a factor of 17, within the minimally patterned trench surfaces of 100 μm by 100 μm. Furthermore, we produced line patterns of cylindrical microdomains by using solvent vapor annealing on the minimally patterned trench surfaces. However, highly aligned line patterns could be achieved only on the patterned surface with P = 5.75L0, W = 1.26L0, and D = 0.30L0 because the influence of the minimally patterned trench surface on the lateral ordering decreased as the P and W increase at the fixed D, resulting in poor ordering. These findings suggest that the minimal topographic pattern is more effective in guiding hexagonal arrays than in guiding line patterns.

We present a strategy for tuning physical properties of P3HT-based copolymers by incorporating a fluorinated thiophene repeat unit. The synthesis and characterization of a series of fluorinated polythiophene P(3HT-co-3H4FT) materials are described, where the percentage of fluorinated repeat units in the polymer backbone is systematically varied from 0 to 100%. These P(3HT-co-3H4FT)s (P0, P25, P50, P75, and P100) were synthesized via direct arylation polymerization (DArP) methods. By varying the feed ratio of the two monomers, the percent of fluorinated repeat units (3H4FT) could be precisely controlled. As fluorination is increased, there is a strong effect on the electronic properties of the polymers, evidenced by a 0.4 eV drop in the EHOMO level for P100 when compared to P0. GIWAXS and TEM were used to determine the crystallinity and morphology. TEM analysis of thin film polymer/PCBM bulk-heterojunction blends indicates that increased fluorination does not result in stronger phase separation. Organic ph...

We demonstrate the generation of block copolymer (BCP) line patterns oriented orthogonal to a very small (minimal) topographic trench pattern over arbitrarily large areas using solvent-vapor annealing. Increasing the thickness of BCP films induced an orthogonal alignment of the BCP cylindrical microdomains, where full orthogonal alignment of the cylindrical microdomains with respect to the trench direction was obtained at a film thickness corresponding to 1.70L0. A capillary flow of the solvent across the trenches was a critical factor in the alignment of the cylindrical microdomains. Grazing incidence small-angle X-ray scattering was used to determine the orientation function of the microdomains, with a value of 0.997 being found reflecting a nearly perfect orientation. This approach to produce orthogonally aligned BCP line patterns could be extended to the nanomanufacturing and fabrication of hierarchical nanostructures.

Dimethacrylate or divinyl-functionalized acetal-based crosslinkers were synthesized as building elements of acid-sensitive crosslinked hydrogels. Each crosslinker was prepared under catalytic acidic conditions with different functional groups installed at the acetal position. The hydrophilicity of the crosslinkers was tuned to control acidic-hydrolysis rate. We report the synthesis of hydroxyethyl dimethacrylate-functionalized dimethyl ketal (CL1), meta- or para-methoxybenzaldehyde based acetals (CL2m and CL2p), poly(ethylene glycol) dimethacrylate-functionalized dimethyl ketal-based crosslinker (CL3), and divinyl-functionalized meta-methoxybenzaldehyde-based acetal crosslinker (V-CL2m). An examination of acetal hydrolysis kinetics of the monomers was performed in aqueous buffer solutions using 1H NMR (proton nuclear magnetic resonance) and UV–Vis (ultraviolet–visible) spectroscopy at various pH ranges. The hydrolysis rates were strongly dependent on the structure of the acetal. Network films containing CL2m were prepared by thermally initiated polymerization with either hydroxyethylmethacrylate (HEMA) or methylmethacrylate (MMA). A study of the hydrolysis kinetics of these crosslinked films was performed using GC–MS (gas chromatography and mass spectroscopy) to understand the effect of monomer hydrophilicity, crosslinking density, and polymerization mechanism at different pHs. The crosslinked films composed of the hydrophilic monomer, HEMA, show faster hydrolysis than those containing more hydrophobic monomers (e.g. MMA). The hydrolysis rate decreases as the crosslinking density increases. In the case of thiol-ene networks formed by reacting pentaerythritol tetrakis(3-mercaptopropionate) and V-CL2m, each repeating unit is composed of an acid-degradable acetal-moiety. Hydrolysis of the thio-ene network films results in depolymerization into two lower molecular weight components, pentaerythritol tetrakis(3-(6-hydroxyhexylthio)propanoate) and meta-methoxybenzaldehyde.

We describe the synthesis and characterization of three new alternating copolymers containing fluorene and a dually dopable benzimidazole moiety. Poly(2-n-heptyl-benzimidazole-alt-9,9-di-n-octylfluorene) (PBIF), poly(2-n-heptyl-benzimidazole-vinylene-9,9-di-n-octylfluorene) (PBIF-VL), and poly(2-n-heptyl-benzimidazole-ethynylene-9,9-di-n-octylfluorene) (PBIF-EL) were synthesized from Suzuki, Heck, and Sonogashira cross-coupling reactions in reasonable yield. The materials were characterized through ultraviolet–visible spectroscopy, photoluminescence, and cyclic voltammetry. The vinyl and ethynyl bridges in PBIF-VL and PBIF-EL were incorporated to separate benzimidazole and fluorene units while retaining conjugation. This allowed us to differentiate between steric and electronic contributions to the band gap (Eg) changes that occur upon acid/base doping of these materials. We demonstrate that the blue shift arising from acid doping PBIF is due to steric torsion, while the red shift found upon base doping P...

A pragmatic method to deposit silver nanoparticles on polydopamine-coated nanoimprinted pillars for use as surface-enhanced Raman scattering (SERS) substrates was developed. Pillar arrays consisting of poly(methyl methacrylate) (PMMA) that ranged in diameter from 300 to 500 nm were fabricated using nanoimprint lithography. The arrays had periodicities from 0.6 to 4.0 μm. A polydopamine layer was coated on the pillars in order to facilitate the reduction of silver ions to create silver nucleation sites during the electroless deposition of sliver nanoparticles. The size and density of silver nanoparticles were controlled by adjusting the growth time for the optimization of the SERS performance. The size of the surface-adhered nanoparticles ranged between 75 and 175 nm, and the average particle density was ∼30 particles per μm(2). These functionalized arrays had a high sensitivity and excellent signal reproducibility for the SERS-based detection of 4-methoxybenzoic acid. The substrates were also able to allow the SERS-based differentiation of three types of bacteriophages (λ, T3, and T7).

Thiol–ene photo-click chemistry is used to cross-link poly(fluorene) derivatives incorporating varying length alkene side-chains into conjugated thin film networks with tunable network architecture, offering a systematic handle on network architecture in cross-linked conjugated polymers. Newly reported poly(fluorene)s with 5- and 11-carbon length thiol–ene compatible side-chains are cross-linked using difunctional and tetra-functional thiol cross-linkers to afford networks of varying connectivity which are tracked by FTIR, contact profilometry, and photo calorimetry. Fluorenone “defects” are additionally incorporated into the poly(fluorene) networks and act as a uniquely effective colorimetric indicator of electronic communication within the conjugated network. This provides a novel method for the systematic investigation of the effects of network architecture on cross-linked conjugated polymer films, which opens the door for controlling the optoelectronic properties of organic semiconductor networks as d...

Novel light emitting electrochemical cells (LECs) are fabricated using CdSe-CdS (core-shell) quantum dots (QDs) of tuned size and emission blended with polyvinylcarbazole (PVK) and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6). The performances of cells constructed using sequential device layers of indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), the QD/PVK/IL active layer, and Al are evaluated. Only color saturated electroluminescence from the QDs is observed, without any other emissions from the polymer host or the electrolyte. Blue, green, and red QD-LECs are prepared. The maximum brightness (≈1000 cd m-2) and current efficiency (1.9 cd A-1) are comparable to polymer LECs and multilayer QD-LEDs. White-light QD-LECs with Commission Internationale d'Eclairage (CIE) coordinates (0.33, 0.33) are prepared by tuning the mass ratio of R:G:B QDs in the active layer and voltage applied. Transparent QD-LECs fabricated using transparent silver nanowire (AgNW) composites as the cathode yield an average transmittance greater than 88% over the visible range. Flexible devices are demonstrated by replacing the glass substrates with polyethylene terephthalate (PET).

Thiol-ene chemistry is used for the surface grafting of vinyl-functionalized poly(fluorene) derivatives onto substrates containing free surface thiol groups. The grafting reaction proceeds in a matter of minutes under UV irradiation without photoinitiator, and the resulting surface-bound, solvent-impervious conjugated polymers retain their characteristic optoelectronic properties. End-chain grafted poly(fluorene)s reach greater surface densities than their side-chain grafted counterparts and show less blue-shifting of photoluminescence upon grafting, suggesting that chain end-grafted conjugated polymers experience less disruption of their extended conjugation and adopt a more brush-like surface conformation. Surface grafted poly(fluorene)s showed facile photopatterning, and thin film transistors with semiconducting polymers directly grafted to the dielectric layer showed performances directly comparable to conventional self-assembled layers of performance-improving alkylsilanes.

Sensors sensitive to infrared radiation based on multiwall carbon nanotubes (MWCNTs) are prepared. The physical suspension and thermal isolation needed for bolometric sensing are achieved by suspending the MWCNTs on polymer gratings fabricated by roll-to-roll (R2R) methods. The physical suspension of MWCNTs on nanoimprinted polymer gratings reduced the thermal link of tubes to the substrate and resulted in an enhanced bolometric photoresponse for the suspended devices. The performance of the R2R fabricated sensor is in the same range as those made by other previously reported wafer batch mode nanofabrication processes and the approximate detectivity of the IR sensor is found to be 4 × 106 cm Hz1/2/W. The successful R2R sensor fabrication process developed in the present work opens up a new low cost, high volume manufacturing technique for the production of sensors based on 1D nanomaterials.

This work reports the creation of superhydrophobic wrinkled surfaces with hierarchical structures at both the nanoscale and microscale. A nanoscale structure with 500 nm line gratings was first fabricated on poly(hydroxyethyl methacrylate) films by nanoimprint lithography while a secondary micro-scale structure was created by spontaneous wrinkling. Compared with random wrinkles whose patterns show no specific orientation, the hierarchical wrinkles exhibit interesting orientation due to confinement effects of pre-imprinted line patterns. The hierarchically wrinkled surfaces have significantly higher water contact angles than random wrinkled surfaces, exhibiting superhydrophobicity with water contact angles higher than 160° and water sliding angle lower than 5°. The hierarchically structured wrinkled surfaces exhibit tunable wettability from hydrophobic to superhydrophobic and there is an observed transition from anisotropic to isotropic wetting behavior achievable by adjusting the initial film thickness.

The mixed substituent cyclophosphazene monomers N3P3Cl4(OCHCH2)(OCH2CF3) (2) and N3P3Cl3(OCHCH2) (OCH2CF3)2 (3) undergo polymerization under radical initiation conditions to yield the mixed substituent poly[(vinyloxy)cyclotriphosphazenes] [CH2CH(ON3P3Cl4(OCH2CF3))]n(5) and [CH2CH(ON3P3Cl3(OCH2CF3)2)]n (6), respectively. A significant, progressive reduction in molecular weight compared to the parent polymer of the series [CH2CH(ON3P3Cl5)]n (4) was observed and attributed to increased chain transfer. The thermal decomposition of 5 and 6 is similar to that observed for 4 with an exothermic elimination of HCl at modest temperatures. An alternative synthetic pathway involving nucleophilic substitution reactions of 4 provided [CH2CH(ON3P3(OCH2CF3)5)]n (7), [CH2CH(N3P3Cl2(OC6H5)3)]n (8A), [CH2CH(ON3P3Cl1.7(OC6H5)3.3)]n (8B), [CH2CH(ON3P3Cl1.5(NHCH3)3.5)]n (9), [CH2CH(ON3P3Cl3.8 (N(CH2CH3)2)1.2]n (10A), [CH2CH(ON3P3Cl3.4(N(CH2CH3)2)1.6)]n (10B), and [N3P3Cl2(OCHCH2)(N(CH3)2)]n, (11). The thermal behaviors of all of the new polymers were examined by TGA, DTA, DSC, and pyrolysis mass spectrometry. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013

The electrochemical deposition of ZnO hierarchical nanostructures directly from PHEMA hydrogel coated electrodes has been successfully demonstrated. A variety of hierarchical ZnO nanostructures, including porous nanoflakes, nanosheets and nanopillar arrays were fabricated directly from the PHEMA hydrogel coated electrodes. Hybrid ZnO-hydrogel composite films were formed with low zinc concentration and short electrodeposition time. A dual-layer structure consisting of a ZnO/polymer and pure ZnO layer was obtained with zinc concentration above 0.01 M. SEM observations and XPS depth profiling were used to investigate ZnO nanostructure formation in the early electrodeposition process. A growth mechanism to understand the formation of ZnO/hydrogel hybrid hierarchical nanostructures was developed. The I-V characteristics of the ZnO-hydrogel composite films in dark and under ultraviolet (UV) illumination demonstrate potential applications in UV photodetection., 9 pages, 11 figures

Regioregular poly[(3-hexylthiophene)-ran-(3-undecenylthiophene)] (pP3HT) and vinyl terminated poly(3-hexylthiophene) (xP3HT) were synthesized by the McCullough method and surface grafted to thiol modified silicon dioxide wafers using thiol–ene click chemistry. Utilizing this method, semiconducting, solvent impervious films were easily generated. Thiol–ene click chemistry is convenient for film stabilization in electronics because it does not produce side products that could be inimical to charge transport in the active layer. It was found through grazing incidence wide-angle X-ray scattering (GIWAXS) that there is no change in microstructure between as-spun films and thiol–ene grafted films, while there was a change after the thiol–ene grafted film was exposed to solvent. Organic field-effect transistors (oFETs) were fabricated from grafted films that had been swelled with chloroform, and these devices had mobilities on the order of 10–6 cm2 V–1 s–1, which are consistent with poly(thiophene) monolayer dev...

In working towards the goal of mimicking multiple features of the extracellular matrix (ECM), we developed a strategy to create adhesive protein patterns on polymer films with tunable viscous characteristics. The block copolymer films are generated by interfacial self-assembly with the presentation of dopant homopolymer, since the concentration of the latter is known to affect the lateral mobility of the film. The supported polymer films are subsequently surfacemodified by microcontact printing using fibronectin (FN), yielding material surfaces which can potentially display independent control over mechanical and adhesive properties. This work demonstrates a new method for the design of materials with the potential to recapitulate the viscous component of the ECM in future in vitro studies.

Hydration is central to mitigating surface fouling by oil and microorganisms. Immobilization of hydrophilic polymers on surfaces promotes retention of water and a reduction of direct interactions with potential foulants. While conventional surface modification techniques are surface-specific, mussel-inspired adhesives based on dopamine effectively coat many types of surfaces and thus hold potential as a universal solution to surface modification. Here, we describe a facile, one-step surface modification strategy that affords hydrophilic, and underwater superoleophobic, coatings by the simultaneous deposition of polydopamine (PDA) with poly(methacryloyloxyethyl phosphorylcholine) (polyMPC). The resultant composite coating features enhanced hydrophilicity (i.e., water contact angle of ~10° in air) and antifouling performance relative to PDA coatings. PolyMPC affords control over coating thickness and surface roughness, and results in a nearly 10 fold reduction in Escherichia coli adhesion relative to unmodified glass. The substrate-independent nature of PDA coatings further promotes facile surface modification without tedious surface pretreatment, and offers a robust template for codepositing polyMPC to enhance biocompatibility, hydrophilicity and fouling resistance.

A series of cross-linked thin films were prepared via thiol–ene click chemistry from 4-phenylethenyl end-capped tunable band gap conjugated polymers with different photoemission. We demonstrate that the emissive color of PLED devices can be successfully tuned from blue to orange via the use of networks prepared using the thiol–ene click reaction. Electrochemical and optical properties were studied by using cyclic voltammetry, UV–vis absorption, and fluorescence spectroscopy, respectively. PLEDs with configuration of ITO/PEDOT:PSS/x-polymer/Ca:Al were fabricated. The devices had turn-on voltages below 8 V and exhibited multicolor emission. Multilayer devices that demonstrated effective color separation and improved color characteristics compared to blended devices were also prepared.

Graphical abstractDisplay Omitted Highlights? We report a powerful new route to fabricate air gap dielectrics with well-defined pore geometries. ? Method utilizes the combination of nanoimprint lithography and a sacrificial template approach. ? Successful fabrication of defect free mechanically robust air gap films (ultra-low k value of 1.9). ? Attractive candidates as interlayer dielectrics for next-generation integrated circuit applications. We report a simple and high-resolution method to fabricate air gap dielectrics with well-defined geometries. This method utilizes nanoimprint lithography to pattern a thermally labile organic polymer, poly (2-hydroxyethyl methacrylate) (PHEMA), subsequently used as a sacrificial template to form air gap nanochannels in a low-k spin-on-glass, poly(methylsilsesquioxane) (PMSSQ). The morphology and dimensions of obtained structures were characterized by cross-sectional SEM, revealing well-defined, continuous and uniform nanochannels. Dielectric constant measurements showed that introduction of these air gap nanochannels into the PMSSQ layer decreased the dielectric constant value from 2.8 to 1.9, while nanoindentation experiments confirmed that the nanochannels were mechanically robust as the air gap films retained the hardness of 1GPa. Infusion with a fluorescent dye solution and subsequent quenching with gold nanoparticles demonstrated continuous nature and uniform distribution of the nanochannels throughout the sample.

In this study, a novel approach is demonstrated to fabricate hierarchically structured cadmium selenide (CdSe) layers with size-tunable nano/microporous morphologies achieved using polystyrene (PS) bilayered templates (top layer: colloidal template) via potentiostatic electrochemical deposition. The PS bilayer template is made in two steps. First, various PS patterns (stripes, ellipsoids, and circles) are prepared as the bottom layers through imprint lithography. In a second step, a top template is deposited that consists of a self-assembled layer of colloidal 2D packed PS particles. Electrochemical growth of CdSe crystals in the voids and selective removal of the PS bilayered templates give rise to hierarchically patterned 2D hexagonal porous CdSe structures. This simple and facile technique provides various unconventional porous CdSe films, arising from the effect of the PS bottom templates.

Carboranes have been previously noted to distinctively affect the luminescent properties of semiconducting polymers when incorporated into the conjugated backbone. In this report, we use carborane-based poly(fluorene) derivatives as active materials for polymer light-emitting diodes and transistors. Optoelectronic analysis unequivocally shows that carborane does not participate in the π-conjugated network, yet their presence causes major red-shifting in device electroluminescence as well as in thin film photoluminescence. In field effect transistors, they also improve charge carrier mobility by an order of magnitude despite disrupting π-conjugation. This use of carborane-containing conjugated polymers in active devices holds promise as new responsive materials in electronic polymer applications.

The use of thiol-ene click chemistry is demonstrated for the first time as a suitable method for cross-linking thin films of 4-phenylethenyl end-capped poly(fluorene). Cross-linking was accomplished by a simple, brief UV curing step at modest temperatures. This chemistry provides an advantage over similar schemes employed for cross-linking conjugated polymers since it does not require elevated temperature or produce potentially detrimental side products. Thiol-ene cross-linking was found to preserve the emissive color integrity of the poly(fluorene) films and allowed for facile photopatterning of the active polymer layer. Furthermore, the investigated cross-linking chemistry was shown to be fully compatible with fabrication of polymer light-emitting diodes (PLEDs) whose performance was comparable to noncross-linked devices. Multicolor PLEDs were also demonstrated by taking advantage of the photopatternability of the thiol-ene based system.

Easy soft imprint nanolithography (ESINL) is employed in the patterning of multiple olymer brushes. This new approach to soft lithography is found to be uniquely effective at patterning brushes both prior to and subsequent to grafting of the polymer chains. Silicon substrates are grafted with polystyrene, polymethylmethacrylate, and polyhydroxyethylmethacrylate using surface-initiated atom transfer radical polymerization assisted by activators generated by electron transfer (ARGET-ATRP) and characterized by contact angle measurements, infrared spectroscopy, and ellipsometry. Line grating features of 3 cm × 3 cm with critical dimensions in the range of 410-480 nm are imprinted directly over grafted brush layers or over assembled monolayers of initiator molecules and transferred to the active layer by reactive ion etching. In all cases the grating pattern is accurately reproduced in the brush layer as confirmed by atomic force microscopy, demonstrating the capability of the technique to generate large-area nanoscale patterns on a range of surface types and functionalities.

We introduce a novel method to easily fabricate nanopatterns at ambient conditions using solvent-assisted soft nanolithography. For this purpose, a P3HT/PCBM bilayer, one of well-known standard models of solar cell systems, was chosen to optimize bilayer solar cells using the new lithographic technique. The nanopatterns of P3HT made using this method have improved device efficiency compared to planar bilayer heterojunction of the solar cell. The new patterning process creates solar cell devices with a greater than 2-fold increase in power conversion efficiency (PCE) compared to an otherwise equivalent, flat device. This improvement in efficiency is due to the increased interfacial area created by the patterning process. This result demonstrates the feasibility of extensive applications toward nanolithography, relevant to device fabrication, such as electronic devices.

Highly crystalline, continuous parallel arrays of CdSe nanowires have been generated through electrodeposition using photoresist templates. Easy soft imprint nanolithography (ESINL) was used to pattern a commercially available photoresist, Norland Optical Adhesive 60 (NOA 60), deposited onto the ITO substrates, prior to electrodeposition. Using the exposed ITO layer as an electrode, a thin film of CdSe was electrodeposited from an electrolyte containing CdCl2, SeO2, and HCl on the substrate, and the resist was subsequently removed in an alkaline developer solution. The resulting CdSe nanowires were 100 nm in thickness, 300–500 nm in width, and several centimeters in length. Imprinted templates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDX). The SEM analysis confirmed the formation of parallel arrays of nanowires unaffected by the resist lift-...

Hybrid conjugated polymers containing carborane directly bonded in the aromatic backbone repeat structure have interesting electronic bonding structures and are potentially useful new materials in organic electronics. Conjugated polymers based on o-carborane are particularly interesting for applications in sensing and detection because of the cage's unique bonding scheme and its bent geometry. Poly(fluorene) containing o-carborane displays multiple emission pathways that can be modulated through interactions with small molecules. In this paper, we report that films of poly(fluorene) with o-carborane in the backbone function as vapochromatic photoluminescent sensors toward volatile organic molecules.

Conjugated polymers were grafted onto cellulose substrates in an effort to create a general method for the synthesis of conjugated polymer/cellulose hybrid materials. In this report, we describe the grafting of poly(fluorene), poly(fluorenevinylene), and a poly(fluorene-ethynylene-phenylene) onto modified cellulose paper substrates using Suzuki, Heck, and Sonogashira-type polymerizations, respectively. The application of these three widely used coupling chemistries to surface-grafted conjugated polymers on cellulose provides a general route to cellulose-based hybrid materials tunable with almost any aromatic repeat structure for specific applications.