Publications by authors named "Kenneth R Carter"

47 Publications

Short Excited-State Lifetimes Enable Photo-Oxidatively Stable Rubrene Derivatives.

J Phys Chem A 2019 Sep 26;123(35):7558-7566. Epub 2019 Aug 26.

Department of Polymer Science and Engineering, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, United States.

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.
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http://dx.doi.org/10.1021/acs.jpca.9b04203DOI Listing
September 2019

Excited State Characterization of Carborane-Containing Poly(dihexyl fluorene)s.

J Phys Chem A 2019 Mar 25;123(9):1701-1709. Epub 2019 Feb 25.

Department of Polymer Science and Engineering , University of Massachusetts-Amherst , 120 Governors Drive , Amherst , Massachusetts 01003 , United States.

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.
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http://dx.doi.org/10.1021/acs.jpca.8b07955DOI Listing
March 2019

Three-Dimensional CeO Woodpile Nanostructures To Enhance Performance of Enzymatic Glucose Biosensors.

ACS Appl Mater Interfaces 2019 Jan 4;11(2):1821-1828. Epub 2019 Jan 4.

Department of Polymer Science and Engineering , University of Massachusetts Amherst , Amherst , Massachusetts 01003 , United States.

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 nanoelectrode arrays for biosensor application over relatively large areas. The fabrication approach, which employs nanoimprint lithography and a CeO 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 CeO glucose sensor exhibited enhanced sensitivity (42.8 μA mM cm) and good selectivity. This direct imprinting strategy for three-dimensional sensing architectures is potentially extendable to other electroactive materials and other sensing applications.
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http://dx.doi.org/10.1021/acsami.8b16985DOI Listing
January 2019

Guided Assembly of Block Copolymers in Three-Dimensional Woodpile Scaffolds.

ACS Appl Mater Interfaces 2018 Dec 30;10(49):42933-42940. Epub 2018 Nov 30.

Polymer Science and Engineering Department , University of Massachusetts Amherst , 120 Governors Drive , Amherst , Massachusetts 01003 , United States.

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.
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http://dx.doi.org/10.1021/acsami.8b17172DOI Listing
December 2018

Fabrication of sub-20 nm patterns using dopamine chemistry in self-aligned double patterning.

Nanoscale 2018 Nov;10(44):20779-20784

Department of Polymer Science and Engineering, University of Massachusetts - Amherst, 120, Governors Drive, Massachusetts 01003, USA.

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.
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http://dx.doi.org/10.1039/c8nr04040kDOI Listing
November 2018

Orthogonally Aligned Block Copolymer Line Patterns on Minimal Topographic Patterns.

ACS Appl Mater Interfaces 2018 Mar 27;10(9):8324-8332. Epub 2018 Feb 27.

Department of Polymer Science and Engineering , University of Massachusetts Amherst , 120 Governors Drive , Amherst , Massachusetts 01003 , United States.

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 1.70 L. 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.
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http://dx.doi.org/10.1021/acsami.7b17713DOI Listing
March 2018

Direct Imprinting of Scalable, High-Performance Woodpile Electrodes for Three-Dimensional Lithium-Ion Nanobatteries.

ACS Appl Mater Interfaces 2018 Feb 1;10(6):5447-5454. Epub 2018 Feb 1.

Department of Polymer Science and Engineering, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.

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 TiO 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. 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 proportional increase of areal capacity with the number of layers. The structure-processing combination leads to efficient use of the material, and the resultant specific capacity (250.9 mAh g) is among the highest reported. This work provides a simple yet effective strategy to fabricate nanobatteries and can be potentially extended to other electroactive materials.
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http://dx.doi.org/10.1021/acsami.7b14649DOI Listing
February 2018

Macroscopically ordered hexagonal arrays by directed self-assembly of block copolymers with minimal topographic patterns.

Nanoscale 2017 Oct;9(39):14888-14896

Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, MA 01003, USA.

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 cm). 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.
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http://dx.doi.org/10.1039/c7nr05394kDOI Listing
October 2017

Surface Grafting of Functionalized Poly(thiophene)s Using Thiol-Ene Click Chemistry for Thin Film Stabilization.

ACS Appl Mater Interfaces 2016 Nov 31;8(44):30543-30551. Epub 2016 Oct 31.

Conte Polymer Center for Polymer Research, University of Massachusetts-Amherst , 120 Governors Drive, Amherst, Massachusetts 01003, United States.

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 cm V s, which are consistent with poly(thiophene) monolayer devices.
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http://dx.doi.org/10.1021/acsami.6b08667DOI Listing
November 2016

Underwater Superoleophobic Surfaces Prepared from Polymer Zwitterion/Dopamine Composite Coatings.

Adv Mater Interfaces 2016 Mar 18;3(6). Epub 2016 Jan 18.

Department of Polymer Science & Engineering, Conte Center for Polymer Research, 120 Governors Drive, University of Massachusetts, Amherst, MA 01003, USA.

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 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.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5074057PMC
http://dx.doi.org/10.1002/admi.201500521DOI Listing
March 2016

Directed Self-Assembly of Block Copolymer Thin Films Using Minimal Topographic Patterns.

ACS Nano 2016 08 18;10(8):7915-25. Epub 2016 Jul 18.

Department of Polymer Science and Engineering, University of Massachusetts Amherst , 120 Governors Drive, Amherst, Massachusetts 01003, United States.

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.
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http://dx.doi.org/10.1021/acsnano.6b03857DOI Listing
August 2016

Scaling Up Nature: Large Area Flexible Biomimetic Surfaces.

ACS Appl Mater Interfaces 2015 Oct 16;7(42):23439-44. Epub 2015 Oct 16.

Department of Polymer Science and Engineering, ‡Department of Chemical Engineering, University of Massachusetts , Amherst, Massachusetts 01003, United States.

The fabrication and advanced function of large area biomimetic superhydrophobic surfaces (SHS) and slippery lubricant-infused porous surfaces (SLIPS) are reported. The use of roll-to-roll nanoimprinting techniques enabled the continuous fabrication of SHS and SLIPS based on hierarchically wrinkled surfaces. Perfluoropolyether hybrid molds were used as flexible molds for roll-to-roll imprinting into a newly designed thiol-ene based photopolymer resin coated on flexible polyethylene terephthalate films. The patterned surfaces exhibit feasible superhydrophobicity with a water contact angle around 160° without any further surface modification. The SHS can be easily converted into SLIPS by roll-to-roll coating of a fluorinated lubricant, and these surfaces have outstanding repellence to a variety of liquids. Furthermore, both SHS and SLIPS display antibiofouling properties when challenged with Escherichia coli K12 MG1655. The current article describes the transformation of artificial biomimetic structures from small, lab-scale coupons to low-cost, large area platforms.
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http://dx.doi.org/10.1021/acsami.5b04957DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4957525PMC
October 2015

Nanoimprinted Patterned Pillar Substrates for Surface-Enhanced Raman Scattering Applications.

ACS Appl Mater Interfaces 2015 Oct 24;7(39):22106-13. Epub 2015 Sep 24.

Department of Food Science, University of Massachusetts , 102 Holdsworth Way, Amherst, Massachusetts 01003, United States.

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).
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http://dx.doi.org/10.1021/acsami.5b07879DOI Listing
October 2015

UV-nanoimprint lithography as a tool to develop flexible microfluidic devices for electrochemical detection.

Lab Chip 2015 Jul;15(14):3086-94

Department of Food Science, University of Massachusetts, 102 Holdsworth Way, Amherst, MA 01003, USA.

Research in microfluidic biosensors has led to dramatic improvements in sensitivities. Very few examples of these devices have been commercially successful, keeping this methodology out of the hands of potential users. In this study, we developed a method to fabricate a flexible microfluidic device containing electrowetting valves and electrochemical transduction. The device was designed to be amenable to a roll-to-roll manufacturing system, allowing a low manufacturing cost. Microchannels with high fidelity were structured on a PET film using UV-NanoImprint Lithography (UV-NIL). The electrodes were inkjet-printed and photonically sintered on second flexible PET film. The film containing electrodes was bonded directly to the channel-containing layer to form sealed fluidic device. Actuation of the multivalve system with food dye in PBS buffer was performed to demonstrate automated fluid delivery. The device was then used to detect Salmonella in a liquid sample.
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http://dx.doi.org/10.1039/c5lc00515aDOI Listing
July 2015

Intrinsic and extrinsic parameters for controlling the growth of organic single-crystalline nanopillars in photovoltaics.

Nano Lett 2014 Oct 29;14(10):5547-54. Epub 2014 Sep 29.

Department of Polymer Science and Engineering, University of Massachusetts , Amherst, Massachusetts 01003, United States.

The most efficient architecture for achieving high donor/acceptor interfacial area in organic photovoltaics (OPVs) would employ arrays of vertically interdigitated p- and n- type semiconductor nanopillars (NPs). Such morphology could have an advantage in bulk heterojunction systems; however, precise control of the dimension morphology in a crystalline, interpenetrating architecture has not yet been realized. Here we present a simple, yet facile, crystallization technique for the growth of vertically oriented NPs utilizing a modified thermal evaporation technique that hinges on a fast deposition rate, short substrate-source distance, and ballistic mass transport. A broad range of organic semiconductor materials is beneficial from the technique to generate NP geometries. Moreover, this technique can also be generalized to various substrates, namely, graphene, PEDOT-PSS, ZnO, CuI, MoO3, and MoS2. The advantage of the NP architecture over the conventional thin film counterpart is demonstrated with an increase of power conversion efficiency of 32% in photovoltaics. This technique will advance the knowledge of organic semiconductor crystallization and create opportunities for the fabrication and processing of NPs for applications that include solar cells, charge storage devices, sensors, and vertical transistors.
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http://dx.doi.org/10.1021/nl501933qDOI Listing
October 2014

Spatially mapping charge carrier density and defects in organic electronics using modulation-amplified reflectance spectroscopy.

Adv Mater 2014 Jul 30;26(26):4539-45. Epub 2014 May 30.

Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Dr., Amherst, MA, 01003, USA.

Charge-modulated optical spectroscopy is used to achieve dynamic two-dimensional mapping of the charge-carrier distribution in poly(3-hexylthiophene) thin-film transistors. The resulting in-channel distributions evolve from uniformly symmetric to asymmetrically saturated as the devices are increasingly biased. Furthermore, physical, chemical, and electrical defects are spatially resolved in cases where their presence is not obvious from the device performance.
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http://dx.doi.org/10.1002/adma.201400859DOI Listing
July 2014

Enhancing adhesion of elastomeric composites through facile patterning of surface discontinuities.

ACS Appl Mater Interfaces 2014 May 25;6(9):6845-50. Epub 2014 Apr 25.

Department of Polymer Science and Engineering, University of Massachusetts , 120 Governors Drive, Amherst, Massachusetts 01003-9265, United States.

Patterning interfaces can provide enhanced adhesion over a projected area. However, careful consideration of the material properties and geometry must be applied to provide successful reversible adhesives. We present a simple method to use patterned, elastomeric fabric composites to enhance the shear adhesion strength by nearly 40% compared to a non-patterned sample. We describe how this enhancement depends on the pattern geometry, the velocity dependence of the adhesive materials, and the controlled displacement rate applied to the interface. Through these observations, we discuss strategies for improving reversible adhesives.
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http://dx.doi.org/10.1021/am5006546DOI Listing
May 2014

Surface grafting of vinyl-functionalized poly(fluorene)s via thiol-ene click chemistry.

Langmuir 2014 Apr 11;30(15):4427-33. Epub 2014 Apr 11.

Department of Polymer Science and Engineering, University of Massachusetts Amherst , 120 Governors Dr., Amherst, Massachusetts 01003, United States.

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.
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http://dx.doi.org/10.1021/la5000588DOI Listing
April 2014

Large-area, continuous roll-to-roll nanoimprinting with PFPE composite molds.

Nanotechnology 2013 Dec 27;24(50):505307. Epub 2013 Nov 27.

Department of Polymer Science and Engineering, University of Massachusetts-Amherst, Amherst, MA 01003, USA. Center for Hierarchical Manufacturing, University of Massachusetts-Amherst, Amherst, MA 01003, USA.

Successful implementation of a high-speed roll-to-roll nanoimprinting technique for continuous manufacturing of electronic devices has been hindered due to lack of simple substrate preparation steps, as well as lack of durable and long lasting molds that can faithfully replicate nanofeatures with high fidelity over hundreds of imprinting cycles. In this work, we demonstrate large-area high-speed continuous roll-to-roll nanoimprinting of 1D and 2D micron to sub-100 nm features on flexible substrate using perfluoropolyether (PFPE) composite molds on a custom designed roll-to-roll nanoimprinter. The efficiency and reliability of the PFPE based mold for the dynamic roll-to-roll patterning process was investigated. The PFPE composite mold replicated nanofeatures with high fidelity and maintained superb mold performance in terms of dimensional integrity of the nanofeatures, nearly defect free pattern transfer and exceptional mold recovering capability throughout hundreds of imprinting cycles.
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http://dx.doi.org/10.1088/0957-4484/24/50/505307DOI Listing
December 2013

Superhydrophobic surfaces from hierarchically structured wrinkled polymers.

ACS Appl Mater Interfaces 2013 Nov 4;5(21):11066-73. Epub 2013 Nov 4.

Department of Polymer Science and Engineering, University of Massachusetts , 120 Governors Drive, Amherst, Massachusetts 01003-9263, United States.

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.
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http://dx.doi.org/10.1021/am403209rDOI Listing
November 2013

Patterned polymer films via reactive silane infusion-induced wrinkling.

Langmuir 2013 Apr 29;29(14):4632-9. Epub 2013 Mar 29.

Polymer Science and Engineering Department, University of Massachusetts - Amherst, Conte Center for Polymer Research, 120 Governors Drive, Amherst, Massachusetts 01003, USA.

A method for simultaneously patterning and functionalizing thin poly(2-hydroxyethyl methacrylate) films through a reactive silane infusion based wrinkling is developed. Wrinkled patterns with tunable wavelengths on submicrometer size are easily produced over large area surfaces and can express a wide variety of chemical functional groups on the surface. The characteristic wavelength of wrinkling scales linearly with initial film thickness, in agreement with a gradationally swollen film model. Results from X-ray photoelectron spectroscopy confirm that the wrinkled film is composed of two layers: a gradient cross-linked top layer and a uniform un-cross-linked bottom layer. The surface chemical properties of wrinkles can be easily tuned by infusion of different functional silanes. Hierarchical wrinkled patterns with micro/nano structure can be achieved by combining wrinkling with other simple lithography methods. Wrinkled nanopatterns can be used as a mold to transfer the topology to a variety of other materials using nanoimprint lithography.
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http://dx.doi.org/10.1021/la400155dDOI Listing
April 2013

Facile colloidal lithography on rough and non-planar surfaces for asymmetric patterning.

Small 2013 Sep 28;9(18):3037-42. Epub 2013 Feb 28.

Department of Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, MA 01003-9263, USA.

Free-standing colloidal arrays can be easily transferred to supported fibers. These films conform and provide the template to have consistent submicrometer and nanometer features transferred to the periphery of rough, 7 μm diameter fibers. This technique is adjustable to a number of fiber surfaces and colloidal template sizes.
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http://dx.doi.org/10.1002/smll.201202821DOI Listing
September 2013

Opportunities with fabric composites as unique flexible substrates.

ACS Appl Mater Interfaces 2012 Dec 21;4(12):6640-5. Epub 2012 Nov 21.

Department of Polymer Science and Engineering, University of Massachusetts, 120 Governors Dr. Amherst, Massachusetts 01003-9265, USA.

Flexible substrates enable new capabilities in applications ranging from electronics to biomedical devices. To provide a new platform for these applications, we investigate a composite material consisting of rigid fiber fabrics impregnated with soft elastomers, offering the ability to create load bearing, yet flexible substrates. We demonstrate an integrated and facile one-step imprint lithographic patterning method on a number of fabrics and resins. Furthermore, the bending and tensile properties were examined to compare the composites to other flexible materials such as PET and cellulose paper. Carbon fiber composites possess a higher tensile modulus than PET while retaining almost an order of magnitude lower bending modulus. Fabric composites can also have anisotropic mechanical properties not observed in homogeneous materials. Finally, we provide a discussion of these anisotropic mechanical responses and their potential use in flexible applications.
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http://dx.doi.org/10.1021/am3017812DOI Listing
December 2012

Hierarchically structured porous cadmium selenide polycrystals using polystyrene bilayer templates.

Langmuir 2012 Sep 4;28(37):13149-56. Epub 2012 Sep 4.

Polymer Science and Engineering Department, University of Massachusetts-Amherst, Conte Center for Polymer Research, 120 Governors Drive, Amherst, Massachusetts 01003, USA.

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.
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http://dx.doi.org/10.1021/la3020805DOI Listing
September 2012

Electroluminescent networks via photo "click" chemistry.

J Am Chem Soc 2011 Dec 22;133(50):20546-51. Epub 2011 Nov 22.

Department of Polymer Science and Engineering, University of Massachusetts Amherst, Conte Center for Polymer Research, 120 Governors Drive, Amherst, Massachusetts 01003, USA.

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.
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http://dx.doi.org/10.1021/ja2088579DOI Listing
December 2011

One-pot synthesis of hybrid TiO2-polyaniline nanoparticles by self-catalyzed hydroamination and oxidative polymerization from TiO2-methacrylic acid nanoparticles.

Chem Commun (Camb) 2011 Oct 5;47(38):10710-2. Epub 2011 Sep 5.

Department of Polymer Science and Engineering, University of Massachusetts Amherst, Conte Center for Polymer Research, 120 Governors Drive, Amherst, Massachusetts 01003, USA.

A simple self-catalyzed hydroamination method for creating hybrid TiO(2)-polyaniline core-shell nanoparticles (NP) has been shown. Hybrid NPs with a range of possible sizes are afforded in high yield under mild reaction conditions and simultaneously show improved charge transport and electrochromic behavior compared to either polyaniline alone or physically blended with TiO(2).
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http://dx.doi.org/10.1039/c1cc13137kDOI Listing
October 2011

Functionally decoupled soft lithography for patterning polymer brushes.

Small 2011 Sep 5;7(18):2669-74. Epub 2011 Aug 5.

Polymer Science and Engineering Department, University of Massachusetts Amherst, Conte Center for Polymer Research, 120 Governors Drive, Amherst, Massachusetts 01003, USA.

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.
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http://dx.doi.org/10.1002/smll.201100895DOI Listing
September 2011

Solvent-assisted soft nanoimprint lithography for structured bilayer heterojunction organic solar cells.

Langmuir 2011 Sep 29;27(17):11251-8. Epub 2011 Jul 29.

Polymer Science and Engineering, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, USA.

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.
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http://dx.doi.org/10.1021/la201809gDOI Listing
September 2011

Carborane-containing poly(fluorene): response to solvent vapors and amines.

ACS Appl Mater Interfaces 2011 Jun 26;3(6):1796-9. Epub 2011 May 26.

Polymer Science and Engineering Department, University of Massachusetts-Amherst, 120 Governors Drive, Amherst, Massachusetts 01003-9263, USA.

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.
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http://dx.doi.org/10.1021/am2000856DOI Listing
June 2011