Publications by authors named "James J Watkins"

37 Publications

Roll-to-roll nanoimprint lithography using a seamless cylindrical mold nanopatterned with a high-speed mastering process.

Nanotechnology 2021 Apr;32(15):155301

Smart Material Solutions, Inc. Raleigh, NC 27607, United States of America.

The advanced optical and wetting properties of metamaterials, plasmonic structures, and nanostructured surfaces have been repeatedly demonstrated in lab-scale experiments. Extending these exciting discoveries to large-area surfaces can transform technologies ranging from solar energy and virtual reality to biosensors and anti-microbial surfaces. Although photolithography is ideal for nanopatterning of small, expensive items such as computer chips, nanopatterning of large-area surfaces is virtually impossible with traditional lithographic techniques due to their exceptionally slow patterning rates and high costs. This article presents a high-throughput process that achieves large-area nanopatterning by combining roll-to-roll (R2R) nanoimprint lithography (NIL) and nanocoining, a process that can seamlessly nanopattern around a cylinder hundreds of times faster than electron-beam lithography. Here, nanocoining is used to fabricate a cylindrical mold with nanofeatures spaced by 600 nm and microfeatures spaced by 2 μm. This cylindrical drum mold is then used on a R2R NIL setup to pattern over 60 feet of polymer film. Microscopy is used to compare the feature shapes throughout the process. This scalable process offers the potential to transfer exciting lab-scale demonstrations to industrial-scale manufacturing without the prohibitively high cost usually associated with the fabrication of a master mold.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1361-6528/abd9f1DOI Listing
April 2021

Bimodal Mesoporous Carbon Spheres with Small and Ultra-Large Pores Fabricated Using Amphiphilic Brush Block Copolymer Micelle Templates.

ACS Appl Mater Interfaces 2020 Dec 11;12(51):57322-57329. Epub 2020 Dec 11.

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

We report the self-assembly of amphiphilic polystyrene--poly(ethylene oxide) (PS--PEO) brush block copolymers (BBCPs) into spherical micelles in an ethanol/water mixture as an efficient templating approach to fabricate mesoporous carbon spheres using polydopamine as a carbon source. Mesopore sizes of up to 25 nm are well controlled and are dependent on the molecular weight () of the BBCP. Such large pores are difficult to obtain using traditional linear block copolymers templates. Furthermore, bimodal mesoporous carbon spheres with two populations of pore sizes (24.5 and 6.5 nm) are obtained using a BBCP coassembled with a small molecule surfactant (Pluronic F127). An oxygen reduction reaction is used to demonstrate that electrocatalytic performance can be tuned by controlling the carbon sphere morphologies. This work provides a novel and versatile method to fabricate carbon spheres with broadly tunable bimodal pore sizes for potential applications in catalysis, separations, and energy storage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.0c16566DOI Listing
December 2020

Gradient Photonic Materials Based on One-Dimensional Polymer Photonic Crystals.

Macromol Rapid Commun 2020 Apr 13;41(8):e2000069. Epub 2020 Mar 13.

Department of Macromolecular Chemistry I and Bavarian Polymer Institute, University of Bayreuth, Bayreuth, 95440, Germany.

In nature, animals such as chameleons are well-known for the complex color patterns of their skin and the ability to adapt and change the color by manipulating sophisticated photonic crystal systems. Artificial gradient photonic materials are inspired by these color patterns. A concept for the preparation of such materials and their function as tunable mechanochromic materials is presented in this work. The system consists of a 1D polymer photonic crystal on a centimeter scale on top of an elastic poly(dimethylsiloxane) substrate with a gradient in stiffness. In the unstrained state, this system reveals a uniform red reflectance over the entire sample. Upon deformation, a gradient in local strain of the substrate is formed and transferred to the photonic crystal. Depending on the magnitude of this local strain, the thickness of the photonic crystal decreases continuously, resulting in a position-dependent blue shift of the reflectance peak and hence the color in a rainbow-like fashion. Using more sophisticated hard-soft-hard-soft-hard gradient elastomers enables the realization of stripe-like reflectance patterns. Thus, this approach allows for the tunable formation of reflectance gradients and complex reflectance patterns. Envisioned applications are in the field of mechanochromic sensors, telemedicine, smart materials, and metamaterials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/marc.202000069DOI Listing
April 2020

Ordered Nanoporous Carbons with Broadly Tunable Pore Size Using Bottlebrush Block Copolymer Templates.

J Am Chem Soc 2019 Oct 11;141(42):17006-17014. Epub 2019 Oct 11.

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

We report the preparation of ordered porous carbon materials with tailored pore sizes selected between 16 and 108 nm using bottlebrush block copolymers (BBCPs) as templates. The nanoporous carbons are prepared via the cooperative assembly of polydimethylsiloxane--poly(ethylene oxide) (PDMS--PEO) BBCPs with phenol-formaldehyde resin yielding ordered precursor films, followed by carbonization. The assembly of PDMS--PEO BBCPs with the resin leads to films exhibiting a spherical morphology (PDMS as the minor domain) with uniform domain sizes between 18 and 150 nm in the bulk. The assembled PDMS sphere diameters scale linearly with BBCPs molecular weights, allowing precise control of domain size. Access to very large ordered domains is an enabling hallmark of BBCPs self-assembly, but reports of well-ordered spherical domains are not common. Carbonization of the ordered precursor films yields nanoporous carbon with uniform and tunable pore size. These nanoporous carbons are shown to exhibit excellent performance as supercapacitor electrodes with capacitance reaching up to 254 F g at a current density of 2 A g.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.9b09572DOI Listing
October 2019

Low-cost, durable master molds for thermal-NIL, UV-NIL, and injection molding.

Nanotechnology 2020 Jan 16;31(1):015302. Epub 2019 Sep 16.

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

Mold cost and mold lifetime are essential concerns for mass production of micro/nano-patterned surfaces by nanoimprint lithography or micro/nanoinjection molding. Master molds are typically produced by subtractive processing using wafer-based clean room techniques. For imprint lithography, polymer copies of such molds can often be employed, but the durability of such molds is quite limited. The conditions of high temperature and pressure for injection molding require use of the durable masters created in stainless steel, nickel or other robust materials, but such approaches are challenged by the high cost of patterning these substrates and limited lifetime. Here, we report the fabrication of durable crystalline zirconium dioxide (ZrO) masters via a simple direct imprint technique. ZrO nanoparticles (NPs) were formulated into an ink and imprinted on a variety of substrates using a solvent-assisted patterning technique and subsequently annealed to increase the mechanical durability of the mold. The hardness and modulus values of the ZrO coatings reached 11 ± 2 GPa and 120 ± 10 GPa, respectively after annealing. The hard ZrO mold was then employed for precision patterning of polymer surfaces by thermal and UV nanoimprinting lithography (NIL) techniques, and by injection molding. High fidelity pattern transfer continued throughout 115 000 injection molding cycles, there was no evidence of delamination, breakage or wear in the ZrO mold. Our simple imprint patterning technique using ZrO NPs inks enable us to fabricate robust molds with excellent thermal and mechanical properties as easily as imprinting simple polymer replicas. This simple and low-cost approach to mold preparation can enable a large variety of high throughput or large area nano-replication technologies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1361-6528/ab4507DOI Listing
January 2020

Copolymer Solid-State Electrolytes for 3D Microbatteries via Initiated Chemical Vapor Deposition.

ACS Appl Mater Interfaces 2019 Feb 30;11(6):5668-5674. Epub 2019 Jan 30.

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

Reliable integration of thin film solid-state polymer electrolytes (SPEs) with 3D electrodes is one major challenge in microbattery fabrication. We used initiated chemical vapor deposition (iCVD) to produce a series of nanoscale copolymer films comprising hydroxyethyl methacrylate and ethylene glycol diacrylate. Conformal copolymer coatings were applied to a variety of patterned 3D electrodes and subsequently converted into ionic conductors by lithium salt doping. Broad tunability in ionic conductivity was achieved by optimizing the copolymer cross-linking density and matrix polarity, resulting in a room-temperature conductivity of (6.1 ± 2.7) × 10 S cm, the highest value reported for conformal, nanoscale SPEs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.8b19689DOI Listing
February 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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.8b16985DOI Listing
January 2019

Bioinspired Photocatalytic Shark-Skin Surfaces with Antibacterial and Antifouling Activity via Nanoimprint Lithography.

ACS Appl Mater Interfaces 2018 Jun 1;10(23):20055-20063. Epub 2018 Jun 1.

By combining antifouling shark-skin patterns with antibacterial titanium dioxide (TiO) nanoparticles (NPs), we present a simple route toward producing durable multifunctional surfaces that decrease microbial attachment and inactivate attached microorganisms. Norland Optical Adhesive, a UV-crosslinkable adhesive material, was loaded with 0, 10, or 50 wt % TiO NPs from which shark-skin microstructures were imprinted using solvent-assisted soft nanoimprint lithography on a poly(ethylene terephthalate) (PET) substrate. To obtain coatings with an exceptional durability and an even higher concentration of TiO NPs, a solution containing 90 wt % TiO NPs and 10 wt % tetraethyl orthosilicate was prepared. These ceramic shark-skin-patterned surfaces were fabricated on a PET substrate and were quickly cured, requiring only 10 s of near infrared (NIR) irradiation. The water contact angle and the mechanical, antibacterial, and antifouling characteristics of the shark-skin-patterned surfaces were investigated as a function of TiO composition. Introducing TiO NPs increased the contact angle hysteresis from 30 to 100° on shark-skin surfaces. The hardness and modulus of the films were dramatically increased from 0.28 and 4.8 to 0.49 and 16 GPa, respectively, by creating ceramic shark-skin surfaces with 90 wt % TiO NPs. The photocatalytic shark-skin-patterned surfaces reduced the attachment of Escherichia coli by ∼70% compared with smooth films with the same chemical composition. By incorporating as low as 10 wt % TiO NPs into the chemical matrix, over 95% E. coli and up to 80% Staphylococcus aureus were inactivated within 1 h UV light exposure because of the photocatalytic properties of TiO. The photocatalytic shark-skin-patterned surfaces presented here were fabricated using a solution-processable and roll-to-roll compatible technique, enabling the production of large-area high-performance coatings that repel and inactivate bacteria.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.8b05066DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6013830PMC
June 2018

Photonic Resins: Designing Optical Appearance via Block Copolymer Self-Assembly.

Macromolecules 2018 Mar 15;51(6):2395-2400. Epub 2018 Mar 15.

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

Despite a huge variety of methodologies having been proposed to produce photonic structures by self-assembly, the lack of an effective fabrication approach has hindered their practical uses. These approaches are typically limited by the poor control in both optical and mechanical properties. Here we report photonic thermosetting polymeric resins obtained through brush block copolymer (BBCP) self-assembly. We demonstrate that the control of the interplay between order and disorder in the obtained photonic structure offers a powerful tool box for designing the optical appearance of the polymer resins in terms of reflected wavelength and scattering properties. The obtained materials exhibit excellent mechanical properties with hardness up to 172 MPa and Young's modulus over 2.9 GPa, indicating great potential for practical uses as photonic coatings on a variety of surfaces.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.macromol.7b02288DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5905989PMC
March 2018

Direct Printing of Graphene Electrodes for High-Performance Organic Inverters.

ACS Appl Mater Interfaces 2018 May 26;10(18):15988-15995. Epub 2018 Apr 26.

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

Scalable fabrication of high-resolution electrodes and interconnects is necessary to enable advanced, high-performance, printed, and flexible electronics. Here, we demonstrate the direct printing of graphene patterns with feature widths from 300 μm to ∼310 nm by liquid-bridge-mediated nanotransfer molding. This solution-based technique enables residue-free printing of graphene patterns on a variety of substrates with surface energies between ∼43 and 73 mN m. Using printed graphene source and drain electrodes, high-performance organic field-effect transistors (OFETs) are fabricated with single-crystal rubrene (p-type) and fluorocarbon-substituted dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDIF-CN) (n-type) semiconductors. Measured mobilities range from 2.1 to 0.2 cm V s for rubrene and from 0.6 to 0.1 cm V s for PDIF-CN. Complementary inverter circuits are fabricated from these single-crystal OFETs with gains as high as ∼50. Finally, these high-resolution graphene patterns are compatible with scalable processing, offering compelling opportunities for inexpensive printed electronics with increased performance and integration density.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.8b01302DOI Listing
May 2018

Wavelength-Selective Three-Dimensional Thermal Emitters via Imprint Lithography and Conformal Metallization.

ACS Appl Mater Interfaces 2018 Mar 23;10(9):8173-8179. Epub 2018 Feb 23.

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

Metallic photonic crystals (MPCs) exhibit wavelength-selective thermal emission enhancements and are promising thermal optical devices for various applications. Here, we report a scalable fabrication strategy for MPCs suitable for high-temperature applications. Well-defined double-layer titanium dioxide (TiO) woodpile structures are fabricated using a layer-by-layer soft-imprint method with TiO nanoparticle ink dispersions, and the structures are subsequently coated with high purity, conformal gold films via reactive deposition from supercritical carbon dioxide. The resulting gold-coated woodpile structures are effective MPCs and exhibit emissivity enhancements at a selective wavelength. Gold coatings deposited using a cold-wall reactor are found to be smoother and result in a greater thermal emission enhancement compared to those deposited using a hot-wall reactor.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.7b16902DOI 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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.7b14649DOI Listing
February 2018

Poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] Oligomer Single-Crystal Nanowires from Supercritical Solution and Their Anisotropic Exciton Dynamics.

J Phys Chem Lett 2017 Jul 16;8(13):2984-2989. Epub 2017 Jun 16.

Department of Physics, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.

Supercritical fluids, exhibiting a combination of liquid-like solvation power and gas-like diffusivity, are a relatively unexplored medium for processing and crystallization of oligomer and polymeric semiconductors whose optoelectronic properties critically depend on the microstructure. Here we report oligomer crystallization from the polymer organic semiconductor, poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) in supercritical hexane, yielding needle-like single crystals up to several microns in length. We characterize the crystals' photophysical properties by time- and polarization-resolved photoluminescence (TPRPL) spectroscopy. These techniques reveal two-dimensional interchromophore coupling facilitated by the high degree of π-stacking order within the crystal. Furthermore, the crystals obtained from supercritical fluid were found to be similar photophysically as the crystallites found in solution-cast thin films and distinct from solution-grown crystals that exhibited spectroscopic signatures indicative of different packing geometries.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.jpclett.7b01128DOI Listing
July 2017

Graphene Ink as a Conductive Templating Interlayer for Enhanced Charge Transport of C-Based Devices.

ACS Appl Mater Interfaces 2016 Nov 20;8(43):29594-29599. Epub 2016 Oct 20.

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

We demonstrate conductive templating interlayers of graphene ink, integrating the electronic and chemical properties of graphene in a solution-based process relevant for scalable manufacturing. Thin films of graphene ink are coated onto ITO, following thermal annealing, to form a percolating network used as interlayer. We employ a benchmark n-type semiconductor, C, to study the interface of the active layer/interlayer. On bare ITO, C molecules form films of homogeneously distributed grains; with a graphene interlayer, a preferential orientation of C molecules is observed in the individual graphene plates. This leads to crystal growth favoring enhanced charge transport. We fabricate devices to characterize the electron injection and the effect of graphene on the device performance. We observe a significant increase in the current density with the interlayer. Current densities as high as ∼1 mA/cm and ∼70 mA/cm are realized for C deposited with the substrate at 25 °C and 150 °C, respectively.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.6b05536DOI Listing
November 2016

Rapid, Large-Area Synthesis of Hierarchical Nanoporous Silica Hybrid Films on Flexible Substrates.

J Am Chem Soc 2016 Oct 7;138(41):13473-13476. Epub 2016 Oct 7.

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

We report a simple strategy for the creation of large-area nanoporous hybrid films of silica, carbon, and gold on polyethylene terephthalate via photothermal processing. This method enables the selective heating of light-absorbing thin films on low-temperature substrates using sub-millisecond light pulses generated by a xenon flash lamp. The film contains gold nanoparticles as the nanoheaters to convert light energy to heat, a sacrificial block copolymer surfactant to generate mesopores, and cross-linked polyhedral oligomeric silsesquioxane as the silica source to form the skeleton of the porous structure. Hierarchical porous structures are achieved in the films after photothermal treatment, with uniform mesopores (44-48 nm) on the surface and interconnected macropores (>50 nm) underneath resulting from a foaming effect during release of gaseous decomposition products. The loading of gold nanoparticles is up to 43 wt % in the product, with less than 2 wt % organic residue. This rapid and large-area process for the synthetis of porous structures is compatible with roll-to-roll manufacturing for the fabrication of flexible devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.6b06947DOI Listing
October 2016

Block Copolymer Nanocomposites with High Refractive Index Contrast for One-Step Photonics.

ACS Nano 2016 Jan 5;10(1):1216-23. Epub 2016 Jan 5.

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

Photonic crystals (PhCs) prepared using the self-assembly of block copolymers (BCPs) offer the potential for simple and rapid device fabrication but typically suffer from low refractive index contrast (Δn ≤ 0.1) between the phase-segregated domains. Here, we report the simple fabrication of BCP-based photonic nanocomposites with large differences in refractive index (Δn > 0.27). Zirconium oxide (ZrO2) nanoparticles coated with gallic acid are used to tune the optical constants of the target domains of self-assembled (polynorbornene-graft-poly(tert-butyl acrylate))-block-(polynorbornene-graft-poly(ethylene oxide)) (PtBA-b-PEO) brush block copolymers (BBCPs). Strong hydrogen-bonding interactions between the ligands on ZrO2 and PEO brushes of the BBCPs enable selective incorporation and high loading of up to 70 wt % (42 vol %) of the ZrO2 nanoparticles within the PEO domain, resulting in a significant increase of refractive index from 1.45 to up to 1.70. Consequently, greatly enhanced reflection at approximately 398 nm (increases of ∼250%) was observed for the photonic nanocomposites (domain spacing = 137 nm) relative to that of the unmodified BBCPs, which is consistent with numeric modeling results using transfer matrix methods. This work provides a simple strategy for a wide range tuning of optical constants of BCP domains, thereby enabling the design and creation of high-performance photonic coatings for various applications. The large refractive index contrast enables high reflectivity while simultaneously reducing the coating thickness necessary, compared to pure BCP systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsnano.5b06525DOI Listing
January 2016

Large-Volume Self-Organization of Polymer/Nanoparticle Hybrids with Millimeter-Scale Grain Sizes Using Brush Block Copolymers.

J Am Chem Soc 2015 Oct 23;137(39):12510-3. Epub 2015 Sep 23.

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

We report that an exceptionally large volume of highly ordered arrays (single grains) on the order of millimeters in scale can be rapidly created through a unique innate guiding mechanism of brush block copolymers (BBCPs). The grain volume is over 10(9) times larger than that of typical self-assembled linear BCPs (LBCPs). The use of strong interactions between nanoparticles (NPs) and BBCPs enables high loadings of functional materials, up to 76 wt % (46 vol %) in the target domain, while maintaining excellent long-range order. Overall, this work provides a simple method to precisely control the spatial orientation of functionalities at nanometer length scales over macroscopic volumes, thereby enabling the production of hybrid materials for many important applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.5b08632DOI 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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5lc00515aDOI Listing
July 2015

Low-Temperature Fabrication of Mesoporous Titanium Dioxide Thin Films with Tunable Refractive Indices for One-Dimensional Photonic Crystals and Sensors on Rigid and Flexible Substrates.

ACS Appl Mater Interfaces 2015 Jun 11;7(24):13180-8. Epub 2015 Jun 11.

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

Highly transparent mesoporous titanium dioxide (TiO2; anatase) thin films were prepared at room temperature via ultraviolet (UV) irradiation of hybrid polymer-TiO2 nanoparticle thin films. This approach utilized a UV-curable polymer in conjunction with the photocatalytic activity of TiO2 to form and degrade the organic component of the composite films in one step, producing films with well-controlled porosity and refractive index. By adjustment of the loading of TiO2 nanoparticles in the host polymer, the refractive index was tuned between 1.53 and 1.73. Facile control of these properties and mild processing conditions was leveraged to fabricate robust one-dimensional photonic crystals (Bragg mirrors) consisting entirely of TiO2 on silicon and flexible poly(ethylene terephthalate) substrates. The mesoporous Bragg mirrors were shown to be effective chemical vapor sensors with strong optical responses.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.5b03240DOI Listing
June 2015

Controlled supramolecular self-assembly of large nanoparticles in amphiphilic brush block copolymers.

J Am Chem Soc 2015 Mar 17;137(11):3771-4. Epub 2015 Mar 17.

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

To date the self-assembly of ordered metal nanoparticle (NP)/block copolymer hybrid materials has been limited to NPs with core diameters (D(core)) of less than 10 nm, which represents only a very small fraction of NPs with attractive size-dependent physical properties. Here this limitation has been circumvented using amphiphilic brush block copolymers as templates for the self-assembly of ordered, periodic hybrid materials containing large NPs beyond 10 nm. Gold NPs (D(core) = 15.8 ± 1.3 nm) bearing poly(4-vinylphenol) ligands were selectively incorporated within the hydrophilic domains of a phase-separated (polynorbornene-g-polystyrene)-b-(polynorbornene-g-poly(ethylene oxide)) copolymer via hydrogen bonding between the phenol groups on gold and the PEO side chains of the brush block copolymer. Well-ordered NP arrays with an inverse cylindrical morphology were readily generated through an NP-driven order-order transition of the brush block copolymer.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.5b01050DOI Listing
March 2015

Strain-tunable one dimensional photonic crystals based on zirconium dioxide/slide-ring elastomer nanocomposites for mechanochromic sensing.

ACS Appl Mater Interfaces 2015 Feb 3;7(6):3641-6. Epub 2015 Feb 3.

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

We demonstrate the fabrication and performance of tunable, elastic organic/inorganic composite one-dimensional photonic crystals (1DPCs) in the visible spectrum. By controlling the composition of high refractive index metal oxide nanoparticle/polymer composites, a refractive index difference of 0.18 between the filled and unfilled polymer layers can be achieved while maintaining desirable flexibility and elasticity. This index contrast is achieved with a loading of 70 wt % zirconium dioxide nanoparticles within a slide-ring elastomer matrix, which is composed of topologically cross-linked polyrotaxane polyols. The large refractive index contrast enables high reflectivity while simultaneously minimizing the number of layers necessary, compared to purely polymer systems. Because the films are both flexible and elastic, these nanocomposite 1DPCs can function as colorimetric strain sensors. We demonstrate the sensing behavior of these 1DPCs by applying over 40% strain, resulting in a visible color shift across the visible spectrum from red to blue. 1DPCs of just 6 periods maintain reflectance of 40% throughout the visible spectrum, with a tensile mechanochromic sensitivity (Δλ/Δεmax) as high as -6.05 nm/%.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/am5079946DOI Listing
February 2015

Synthesis and controlled self-assembly of UV-responsive gold nanoparticles in block copolymer templates.

J Phys Chem B 2014 Nov 27;118(44):12788-95. Epub 2014 Oct 27.

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

We demonstrate the facile synthesis of gold nanoparticles (GNPs) functionalized by UV-responsive block copolymer ligands, poly(styrene)-b-poly(o-nitrobenzene acrylate)-SH (PS-b-PNBA-SH), followed by their targeted distribution within a lamellae-forming poly(styrene)-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer. The multilayer, micelle-like structure of the GNPs consists of a gold core, an inner PNBA layer, and an outer PS layer. The UV-sensitive PNBA segment can be deprotected into a layer containing poly(acrylic acid) (PAA) when exposed to UV light at 365 nm, which enables the simple and precise tuning of GNP surface properties from hydrophobic to amphiphilic. The GNPs bearing ligands of different chemical compositions were successfully and selectively incorporated into the PS-b-P2VP block copolymer, and UV light showed a profound influence on the spatial distributions of GNPs. Prior to UV exposure, GNPs partition along the interfaces of PS and P2VP domains, while the UV-treated GNPs are incorporated into P2VP domains as a result of hydrogen bond interactions between PAA on the gold surface and P2VP domains. This provides an easy way of controlling the arrangement of nanoparticles in polymer matrices by tailoring the nanoparticle surface using UV light.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp508212fDOI Listing
November 2014

Controlled integration of oligo- and polythiophenes at the molecular scale.

Phys Chem Chem Phys 2015 Oct;17(40):26525-9

Department of Polymer Science and Engineering, Conte Research Center, University of Massachusetts, 120 Governors Drive, Amherst, MA 01002, USA.

High molecular weight PBTTT-C12 is blended with the pure trimer, BTTT-3, to enhance intergrain connectivity and charge transport. Analysis of the morphology and crystallinity of the blends shows that the polymer and oligomer are well-integrated, leading to high hole mobilities, greater than 0.1 cm(2) V(-1) s(-1), in films that contain as much as 83% oligomer.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c4cp02944eDOI Listing
October 2015

Simple ligand exchange reactions enabling excellent dispersibility and stability of magnetic nanoparticles in polar organic, aromatic, and protic solvents.

Langmuir 2014 Feb 3;30(6):1514-21. Epub 2014 Feb 3.

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

The use of magnetic nanoparticles (MNPs) in real-world applications is often limited by the lack of stable solutions of monodisperse NPs in appropriate solvents. We report a facile one-pot ligand exchange reaction that is fast, efficient, and thorough for the synthesis of hydrophilic MNPs that are readily dispersed in polar organic and protic solvents (polarity index = 3.9-7.2) including alcohols, THF, DMF, and DMSO for years without precipitation. We emphasize the rational selection of small-molecule ligands such as 4-hydroxybenzoic acid (HBA), 3-(4-hydroxyphenyl)propionic acid (HPP), and gallic acid (GAL) that provide strong bonding with the MNP (FePt and FeOx) surfaces, hydrophilic termini to match the polarity of target solvents, and offer the potential for hydrogen-bonding interactions to facilitate incorporation into polymers and other media. Areal ligand densities (Σ) calculated based on the NP core size from transmission electron microscopy (TEM) images, and the inorganic fractions of NPs derived from thermogravimetric analysis (TGA) indicated a significant (2-4 times) increase in the ligand coverage after the exchange reactions. Fourier transform infrared spectrometry (FTIR) and (1)H nuclear magnetic resonance (NMR) studies also confirmed anchoring of carboxyl groups on NP surfaces. In addition, we demonstrate a facile one-step in situ synthesis of FePt NPs with aromatic ligands for better dispersibility in solvents of intermediate polarity (polarity index = 1.0-3.5) such as toluene, chlorobenzene, and dichloromethane. The creation of stable dispersions of NPs in solvents across the polarity spectrum opens up new applications and new processing widows for creating NP composites in a variety of host materials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la404757qDOI Listing
February 2014

Platinum electrodeposition at unsupported electrochemically reduced nanographene oxide for enhanced ammonia oxidation.

ACS Appl Mater Interfaces 2014 Feb 17;6(3):2137-45. Epub 2014 Jan 17.

Department of Chemistry and Center for Advanced Nanoscale Materials, University of Puerto Rico, Río Piedras Campus , P.O. Box 23346, San Juan, Puerto Rico 00931-3346, United States.

The electrochemical reduction of highly oxidized unsupported graphene oxide nanosheets and its platinum electrodeposition was done by the rotating disk slurry electrode technique. Avoiding the use of a solid electrode, graphene oxide was electrochemically reduced in a slurry solution with a scalable process without the use of a reducing agent. Graphene oxide nanosheets were synthesized from carbon platelet nanofibers to obtain highly hydrophilic layers of less than 250 nm in width. The graphene oxide and electrochemically reduced graphene oxide/Pt (erGOx/Pt) hybrid materials were characterized through different spectroscopy and microscopy techniques. Pt nanoparticles with 100 facets, clusters, and atoms at erGOx were identified by high resolution transmission electron microscopy (HRTEM). Cyclic voltammetry was used to characterize the electrocatalytic activity of the highly dispersed erGOx/Pt hybrid material toward the oxidation of ammonia, which showed a 5-fold current density increase when compared with commercially available Vulcan/Pt 20%. This is in agreement with having Pt (100) facets present in the HRTEM images of the erGOx/Pt material.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/am4052552DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3985924PMC
February 2014

Solution processable high dielectric constant nanocomposites based on ZrO2 nanoparticles for flexible organic transistors.

ACS Appl Mater Interfaces 2013 Dec 12;5(24):13096-103. Epub 2013 Dec 12.

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

A solution-based strategy for fabrication of high dielectric constant (κ) nanocomposites for flexible organic field effect transistors (OFETs) has been developed. The nanocomposite was composed of a high-κ polymer, cyanoethyl pullulan (CYELP), and a high-κ nanoparticle, zirconium dioxide (ZrO2). Organic field effect transistors (OFETs) based on neat CYELP exhibited anomalous behavior during device operation, such as large hysteresis and variable threshold voltages, which yielded inconsistent devices and poor electrical characteristics. To improve the stability of the OFET, we introduced ZrO2 nanoparticles that bind with residual functional groups on the high-κ polymer, which reduces the number of charge trapping sites. The nanoparticles, which serve as physical cross-links, reduce the hysteresis without decreasing the dielectric constant. The dielectric constant of the nanocomposites was tuned over the range of 15.6-21 by varying the ratio of the two components in the composite dielectrics, resulting in a high areal capacitance between 51 and 74 nF cm(-2) at 100 kHz and good insulating properties of a low leakage current of 1.8 × 10(-6) A cm(-2) at an applied voltage of -3.5 V (0.25 MV cm(-1)). Bottom-gate, top-contact (BGTC) low operating voltage p-channel OFETs using these solution processable high-κ nanocomposites were fabricated by a contact film transfer (CFT) technique with poly(3-hexylthiophene) (P3HT) as the charge transport layer. Field effect mobilities as high as 0.08 cm(2) V(-1) s(-1) and on/off current ratio of 1.2 × 10(3) for P3HT were measured for devices using the high-κ dielectric ZrO2 nanocomposite. These materials are promising for generating solution coatable dielectrics for low cost, large area, low operating voltage flexible transistors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/am404129uDOI Listing
December 2013

Relating chemical structure to device performance via morphology control in diketopyrrolopyrrole-based low band gap polymers.

J Am Chem Soc 2013 Dec 12;135(51):19248-59. Epub 2013 Dec 12.

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

We investigated the structure-morphology-performance relationship of diketopyrrolopyrrole (DPP)-based low band gap polymers with different donor cores in organic field effect transistors (OFETs) and organic photovoltaics (OPVs). The change in the chemical structure led to strong physical property differences, such as crystalline behavior, blend morphology, and device performance. In addition, the choice of solvents and additives enabled one to fine tune the properties of these materials in the condensed state. For instance, when thin films were processed from solvent mixtures, both in the pure polymer and in a blend, we observed an enhanced edge-on orientation and the formation of thinner and longer polymer fibrils. In the BHJ blends, processing from a solvent mixture reduced the size scale of the phase separation and promoted the formation of a fibrillar network morphology, having a polymer-PCBM mixture filling the interfibrillar regions. The characteristic length scale of the fibrillar network dictated the specific inner surface area, which directly correlated to the performance in the OPV devices. When the BHJ mixture was processed from a single solvent, a large-scale phase separated morphology was observed that was stratified, normal to the film surface. A strong scattering anisotropy was observed in the resonant soft X-ray scattering of the blends that provided insight into the packing of the polymer chains within the fibrils. The morphology and performance trend in OPVs paralleled the performance in an OFET, suggesting that similar processing conditions should be considered in OFET fabrication.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ja408923yDOI Listing
December 2013

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0957-4484/24/50/505307DOI Listing
December 2013

Hydrophobization of inorganic oxide surfaces using dimethylsilanediol.

Langmuir 2013 Feb 22;29(5):1329-32. Epub 2013 Jan 22.

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

Dimethylsilanediol is a stable crystalline solid that was described in 1953. As the monomer of an important class of commercial products (poly(dimethylsiloxanes)-silicones, PDMS) and as a simple molecule in its own right (the silicon analog of acetone hydrate), it has been neglected by several fields of fundamental and applied research including the hydrophobization of inorganic oxide surfaces. We report that dimethylsilanediol is a useful reagent for the surface modification (hydrophobization) of oxidized silicon and other oxidized metal surfaces and compare the wetting properties of modified solids with those of conventionally modified surfaces. That water is the only byproduct of this modification reaction suggests that this and likely other silanediols are useful surface-modification agents, particularly when substrate corrosion or the competitive adsorption of byproducts is an issue. We note that dimethylsilanediol is volatile with a significant vapor pressure at room temperature. Vapor-phase surface modifications are also reported.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la303963qDOI Listing
February 2013

Photoinduced disorder in strongly segregated block copolymer composite films for hierarchical pattern formation.

ACS Nano 2013 Feb 18;7(2):1513-23. Epub 2013 Jan 18.

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

Submicrometer patterns of adjacent, well-ordered and disordered domains were obtained using optical lithography by area-selective, photoinduced disordering transitions within block copolymer composite films. Enantiopure tartaric acid was blended with poly(ethylene oxide-block-tert-butyl acrylate), PEO-b-PtBA, copolymers to yield well-ordered films. In the presence of triphenylsulfonium triflate, a photoacid generator, photoinduced disorder was achieved upon UV-exposure by deprotection of the PtBA block to yield poly(acrylic acid). Poly(acrylic acid) is compatible with both PEO and tartaric acid and deprotection yields a phase mixed material and disorder within seconds. Tartaric acid performs two additional functions in this system. First, it increases segregation strength in PEO-b-PtBA, enabling well-ordered systems at low BCP molecular weights, small domain sizes, and rapid disordering kinetics. Second, the presence of tartaric acid suppresses PEO crystallization, resulting in smooth films and eliminating the influence of PEO crystallization on film morphology.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nn3052956DOI Listing
February 2013