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Stretchable electronics are being used in applications such as wearable electronics, robotic skin, wearable health-monitoring devices, and smart textiles due to their excellent mechanical conformability through stretching, flexing, twisting, and folding. This work focuses on creating printable stretchable substrates based on butyl rubber (IIR), combined with a ferroelectric filler, barium strontium titanate (BST). BST has unique properties, including the ability to tune the dielectric properties by applying a bias to the substrate. A high loading of BST was incorporated to tailor the dielectric properties of the substrate. This work investigated the effect of three different cure systems on the properties, including interaction with a silver ink. For all cure systems, cure and scorch time decreased with increases in BST loading. A phenolic cure did not affect the ink conductivity, whereas the sulfur-cured systems resulted in nonconductive ink. For the phenolic-cured substrate, the tensile strength increased and the elongation decreased with increasing filler loading. The elastomer could be filled with up to 40 vol. % BST while still maintaining elongation greater than 200%.

Protein fouling on critical biointerfaces causes significant public health and clinical ramifications. Multiple strategies, including superhydrophobic (SHP) surfaces and coatings, have been explored to mitigate protein adsorption on solid surfaces. SHP materials with underwater air plastron (AP) layers hold great promise by physically reducing the contact area between a substrate and protein molecules. However, sustaining AP stability or lifetime is crucial in determining the durability and long-term applications of SHP materials. This work investigated the effect of protein on the AP stability using model SHP substrates, which were prepared from a mixture of silica nanoparticles and epoxy. The AP stability was determined using a submersion test with real-time visualization. The results showed that AP stability was significantly weakened by protein solutions compared to water, which could be attributed to the surface tension of protein solutions and protein adsorption on SHP substrates. The results were further examined to reveal the correlation between protein fouling and accelerated AP dissipation on SHP materials by confocal fluorescent imaging, surface energy measurement, and surface robustness modeling of the Cassie-Baxter to Wenzel transition. The study reveals fundamental protein adsorption mechanisms on SHP materials, which could guide future SHP material design to better mitigate protein fouling on critical biointerfaces.

Purpose Rapid tooling has numerous advantages when prototyping injection molded components, but the effects of the tooling on the resulting part properties are often overlooked. The purpose of this paper is to consider the effect of tooling on the final part properties and morphology. Design/methodology/approach Digital polyacrylonitrile-butadiene-styrene (ABS) tooling and aluminum tooling were used to mold test specimens from isotatic polypropylene (iPP). Tensile behavior, impact strength, shrinkage, surface roughness and porosity were evaluated for both sets of samples. Additionally, differential scanning calorimeter (DSC) and wide-angle X-ray scattering (WAXS) were used to assess the crystallinity of the samples. Findings Characterization of the molded parts showed that slower cooling rates in the Digital ABS inserts promoted the formation of ß-PP, while this crystal structure was not found in the parts molded using aluminum tooling. Additionally, parts molded on the digital ABS inserts exhibited higher mold shrinkage and SEM images identified microscopic shrinkage voids within the material. The change in morphology and the presence of voids significantly affected the tensile behavior with the parts molded in Digital ABS, which broke with little cold drawing and exhibited higher tensile moduli and higher yield strengths. Practical implications The results show that the choice of rapid tooling technique plays an important role on determining the properties of the final parts. Originality/value Previous studies have not characterized the effect of rapid tooling on the morphology of the molded articles fully or over a variety of processing conditions. This study builds on prior work by using both WAXS and DSC to characterize morphological changes over a wide range of processing conditions and comparing results to mechanical property and shrinkage data.

This article describes the study of the topography effect of superhydrophobic surfaces on the corrosion protection performance of steel through the air plastron behavior when subjected to an underwater environment. A random superhydrophobic surface was fabricated using spray coating and characterized for morphology and wettability by scanning electron microscopy (SEM) and goniometer measurements, respectively. By comparing the coated surfaces both with and without air plastron, it was found that superhydrophobicity postponed the corrosion of the coated steel specimens. This increase in corrosion protection of the superhydrophobic surface was due to the air plastron created by the superhydrophobicity in underwater immersion. Since different areas showed differing air plastron lifetimes (wetting behavior), it was assumed that the underlying topography of the superhydrophobic coating controlled the air plastron lifetime. To investigate this behavior, the micron scale topography of the different areas was studied using the technique of laser confocal microscopy over the specific areas and correlating with air plastron lifetime. Using the theoretical analysis based on superhydrophobic robustness and assuming the solid fraction is the same for different locations, it was demonstrated that the feature size [extracted by roughness analysis as root-mean-square (RMS)] correlated with the air plastron lifetime. It was confirmed from the plot of RMS and air plastron lifetime that smaller feature sizes could extend the air plastron lifetime and provide better anticorrosion performance.

Vascular surgery trainees participate in the vascular surgery in-training examination (VSITE) during each year of their training. Although the VSITE was developed as a low-stakes, formative examination, performance on that examination might correlate with the pass rates for the Vascular Surgery Board written qualifying examination (VQE) and oral certifying examination (VCE) and might, therefore, guide both trainees and program directors. The present study was designed to examine the ability of the VSITE to predict trainees' performance on the VQE and VCE.All first-time candidates of the Vascular Surgery Board VQE and VCE were analyzed from 2016 to 2020, including those from both the integrated and independent training pathways. VSITE scores from the final year of training were associated with the VQE scores and the probability of passing the VQE and VCE both. Linear and logistic regression models were used to determine the ability of VSITE results to predict the VQE scores and the probability of passing each board examination.VSITE scores available for the 559 candidates (69.3% male; 30.7% female) who had completed the VQE and 369 candidates (66.7% male; 33.3% female) who had completed both the VQE and the VCE. The linear regression model results for the final year of training showed that the VSITE scores explained 34% of the variance in the VQE scores (29% for the integrated and 37% for the independent trainees). Logistic regression demonstrated that the final year VSITE scores were a significant predictor of passing the VQE for both integrated and independent trainees (P .001). A VSITE score of 500 during the final year of training predicted a VQE passing probability of90% for each group of candidates. The probability of passing the VQE decreased to 73% for candidates from integrated programs, 61% for candidates from independent programs, and 64% for the whole cohort when the score was 400. The VSITE scores were a significant predictor of passing the VCE only for the candidates from independent programs (odds ratio, 1.01; 95% confidence interval, 1.00-1.02; P .01), for whom a VSITE score of 400 correlated with an 82% probability of passing the VCE.VSITE performance is predictive of passing the VQE for trainees from both integrated and independent training paradigms. Vascular surgery trainees and training programs should optimize their preparation and educational efforts to maximize performance on the VSITE during their final year of training to improve the likelihood of passing the VQE. Further analysis of the predictive value of VSITE scores during the earlier years of training might allow the board certification examinations to be administered earlier in the final year of training.

In this work the drag reduction performance of superhydrophobic composite coatings was investigated. The drag reduction behavior for both short-term and long-term use was studied using a parallel p...

Many surfaces in nature such as the lotus leaf, cicada wings, water spider legs and gecko feet have attracted attention due to their inherent superhydrophobicity and self-cleaning properties. These surfaces are characterized by water contact angles greater than 150° and contact angle hysteresis

Roll-to-roll hot embossing could revolutionize the manufacturing of multifunctional polymer films with the ability to process large area at a high rate with reduced cost. The continuous hot embossing of the films, however, has been hindered due to the lack of durable and flexible molds, which can replicate micro and nanofeatures with reliability over several embossing cycles. In this work, we demonstrate for the first time the fabrication of a flexible polymer (polyimide) mold from the commercially available sheet by a maskless photolithography approach combined with inductively coupled plasma etching and its potential application to the roll-to-roll hot embossing process. The flexible polyimide mold consisted of holes with controlled dimensions: diameter: 14 μm, spacing: 16.5 μm, and depth: 6.8 μm. The reliability of flexible polyimide mold was tested and implemented by embossing micron-sized features on a commercial thermoplastic polymer, polyamide, and thermoplastic elastomer (TPE) sheet. The polyimide mold replicated micron-sized features on polymer substrates (polyamide and TPE) with excellent fidelity and was durable even after numerous embossing cycles.

The performance of hydrophobic surfaces under hydraulic pressures is critical to a wide range of practical applications such as drag reduction of seaboard vessels and design of microfluidic devices. This research focuses on the evaluation of drag reduction and velocity slip of hydrophobic surfaces and coatings under external hydrostatic pressures using an acoustic wave device (i.e., quartz crystal microbalance, QCM). The correlation between the resonant frequency shift of a QCM device and drag reduction of hydrophobic surface coated on the QCM was theoretically developed and the model was validated by comparing the measurement results of the drag reduction of an epoxy-based superhydrophobic coating with those measured by a rheometer. The QCM device was further employed to study the wetting state transition and drag reduction of water on a micropillar array based superhydrophobic surface under elevated hydrostatic pressures. It was found that the transition from Cassie to Wenzel states occurred at a critical hydrostatic pressure which was indicated by a sudden frequency drop of the QCM device. In addition, the effective heights of the meniscus at the liquid/air interface increased with the external pressure before the transition took place. The drag reduction induced by the micropillar surface decreased with the increasing hydrostatic pressures. It was demonstrated that the developed QCM based technology provides a low cost, simple, and reliable tool for evaluating hydrophobic performance of various surfaces under external hydrostatic pressures.

The use of microfeature-enabled devices, such as microfluidic platforms and anti-fouling surfaces, has grown in both potential and application in recent years. Injection molding is an attractive method of manufacturing these devices due to its excellent process throughput and commodity-priced raw materials. Still, the manufacture of micro-structured tooling remains a slow and expensive endeavor. This work investigated the feasibility of utilizing additive manufacturing, specifically a Digital Light Processing (DLP)-based inverted stereolithography process, to produce thermoset polymer-based tooling for micro injection molding. Inserts were created with an array of 100-&mu, m wide micro-features, having different heights and thus aspect ratios. These inserts were molded with high flow polypropylene to investigate print process resolution capabilities, channel replication abilities, and insert wear and longevity. Samples were characterized using contact profilometry as well as optical and scanning electron microscopies. Overall, the inserts exhibited a maximum lifetime of 78 molding cycles and failed by cracking of the entire insert. Damage was observed for the higher aspect ratio features but not the lower aspect ratio features. The effect of the tool material on mold temperature distribution was modeled to analyze the impact of processing and mold design.

Tehila Nahum,1 Hanna Dodiuk,2 Samuel Kenig,2 Artee Panwar,1 Carol Barry,1 Joey Mead,1 1Department of Plastics Engineering, University of Massachusetts Lowell, Lowell, MA, USA; 2Department of Polymers and Plastics Engineering, Shenkar College of Engineering Design and Art, Ramat Gan, Israel Abstract: Durable superhydrophobic coatings were synthesized using a system of silica nanoparticles (NPs) to provide nanoscale roughness, fluorosilane to give hydrophobic chemistry, and three different polymer binders: urethane acrylate, ethyl 2-cyanoacrylate, and epoxy. Coatings composed of different binders incorporating NPs in various concentrations exhibited different superhydrophobic attributes when applied on polycarbonate (PC) and glass substrates and as a function of coating composition. It was found that the substrate surface characteristics and wettability affected the superhydrophobic characteristics of the coatings. Interfacial tension and spreading coefficient parameters (thermodynamics) of the coating components were used to predict the localization of the NPs for the different binders’ concentrations. The thermodynamic analysis of the NPs localization was in good agreement with the experimental observations. On the basis of the thermodynamic analysis and the experimental scanning electron microscopy, X-ray photoelectron spectroscopy, profilometry, and atomic force microscopy results, it was concluded that localization of the NPs on the surface was critical to provide the necessary roughness and resulting superhydrophobicity. The durability evaluated by tape testing of the epoxy formulations was the best on both glass and PC. Several coating compositions retained their superhydrophobicity after the tape test. In summary, it was concluded that thermodynamic analysis is a powerful tool to predict the roughness of the coating due to the location of NPs on the surface, and hence can be used in the design of superhydrophobic coatings. Keywords: superhydrophobic coating, durability, thermodynamics, silica nanoparticles, morphology

This research presents a comprehensive analysis of the design and validation of a cross-flow microfiltration device for separation of microspheres based on size. Simulation results showed that pillar size, pillar shape, incorporation of back-flow preventers, and rounding of pillar layouts affected flow patterns in a cross-flow microfiltration device. Simulation results suggest that larger pillar sizes reduce filtration capacity by decreasing the density of microfiltration gaps in the device. Therefore, 10 μm rather than 20 μm diameter pillars were incorporated in the device. Fluid flow was not greatly affected when comparing circular, octagonal, and hexagonal pillars. However, side-channel fluid velocities decreased when using triangular and square pillars. The lengths of back-flow prevention walls were optimized to completely prevent back flow without inhibiting filtration ability. A trade-off was observed in the designs of the pillar layouts; while rounding the pillars layout in the channels bends eliminated stagnation areas, the design also decreased side-channel fluid velocity compared to the right-angle layout. Experimental separation efficiency was tested using polydimethylsiloxane (PDMS) and silicon microfluidic devices with microspheres simulating white and red blood cells. Efficiencies for separation of small microspheres to the side channels ranged from 73 to 75%. The silicon devices retained the large microspheres in the main channel with efficiencies between 95 and 100%, but these efficiencies were lower with PDMS devices and were affected by sphere concentration. Additionally, PDMS devices resulted in greater agglomeration of spheres when compared to silicon devices. PDMS devices, however, were easier and less expensive to fabricate.

National Science Foundation under the Nanoscale Science and Engineering Centers program; contract grant number: EEC-0832754.

As nanocomposite materials enter the marketplace, it is critical to consider the entire life cycle of those products, including end of life and reuse of scrap. While recycling of polymer based materials is widely accepted for manufacturing and consumer scrap, the influence of the nanoscale filler on the recycling process has received little attention and may pose some unique challenges, such as the potential for human exposure to carbon nanotubes (CNTs) during the recycling process. In this work, the impact of recycling on CNT-filled polypropylene (PP) properties and exposures was studied by repeated injection molding and granulation up to twenty cycles, while simultaneously monitoring exposures. Characterization of chemical structure, melt rheology, mechanical properties, and morphology were performed on recycled materials. Both the neat and filled materials showed a reduction in viscosity with recycling, but the changes were greater for the neat materials. The mechanical properties (such as modulus, strength, toughness) were also affected by recycling. The Young's modulus, yield strain and stress for both neat PP and CNT-filled PP were found to be little affected by recycling. Strain and stress at break for neat PP decreased with recycling, but only slight changes were found for the CNT-filled PP. The CNT-filled PP showed an increase in toughness with recycling due to changes in the crystallization behaviour. This offers potential for addition of CNTs for the purpose of improving recycling resistance. However, recycling should be performed under proper exposure controls because grinding generated high exposures to nanoparticles and CNT-containing respirable fibers.

This paper focuses on the effect of composite interface morphology on the wetting behavior of a nanocomposite coating based on an organosilane binder. Experimental results supported by modeling demonstrated that a sharp change in contact angle hysteresis occurred at air fractions in the range of 40–60%, as controlled by particle loading. The air-liquid interface evolution with particle loading was visualized using the fluorescent dye staining method. A correlation between topography and this air-liquid-solid interface was done by overlapping the optical images and fluorescence dye stained images of the stained superhydrophobic surface, which allowed the visualization of microscale features. The results showed the structures supporting solid-liquid contacts were 20 to 40 μm in size and had an edge-to-edge spacing that decreased with increasing particle loading. In this system a critical spacing to transition from the Wenzel to the Cassie-Baxter state was found to be approximately five times the average width of these microscale structures. Identification of critical surface topography can aid in the development of coatings that provide anti-corrosive and/or anti-icing features for marine vessels, bridges, and buildings.

Microstructured surfaces injection molded from thermoplastic elastomers have emerging applications as superhydrobic surfaces and patterned adhesives, but there is a limited understanding of the factors affecting replication with these materials. This work investigates the interactions of the tooling aspect ratio and feature orientation (negative and positive tooling) and thermoplastic elastomer hard segment content on microfeature replication. Electroformed nickel tooling having positive and negative features with different geometries and aspect ratios of 0.02:1 to 2:1 were molded from three copolyester thermoplastic elastomers with similar chemistry and different hardness values. The tooling and part features were characterized for feature depth and height as well as feature definition using scanning electron microscopy and optical profilometry. Results were correlated with elastomer properties.

Incorporation of nanoclays in vulcanized rubber can enhance the barrier and mechanical properties, with the aid of intercalation, exfoliation, or both. Achieving a high degree of dispersion such as intercalation and exfoliation is critical for obtaining optimal properties. In this work, a stepwise approach was developed to disperse the natural montmorillonite (MMT) clay modified with a quaternary ammonium salt in brominated butyl rubber (BIIR). The solvent intercalation method followed by mechanical shear was used to effectively intercalate/exfoliate the MMT bundles. Special consideration was given to effectively remove the solvent from the solvent intercalated master batch. The nanocomposites fabricated using this technique showed a high degree of intercalation and exfoliation along with improved barrier, dynamic mechanical, and mechanical properties. This improvement in properties offers an opportunity for this material to be used in high-end applications requiring improved mechanical as well as barrier properties; an example is a thinner tire inner liner with reduced hysteresis, lower running temperatures, and reduced fuel consumption.

Injection molding of thermoplastic resins is well known to produce volatile organic compounds which can adversely affect operator health, but there is little understanding of particulate emissions. Recent molding of nanocomposites produced no emission of carbon nanotubes, but emission of organic nanoparticulates of unknown composition. This work is an investigation of those particulates with the gaseous phase emissions of airborne nanoparticles collected during injection molding of neat and additive-filled polypropylene and polycarbonate compounds. The starting materials, collected nanoparticles, and molded parts were analyzed using thermogravimetric analysis, thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy, differential scanning calorimetry, and gas chromatography-mass spectrometry. The results were analyzed to determine the composition of the nanoparticulates and compounds lost from the polypropylene and polycarbonate during injection molding. Characterizing these emissio...

The electrical percolation threshold of different polyethylene/carbon nanotube nanocomposites was studied as a function of chain structure, matrix viscosity, and the effect of compatibilizer. The lower the viscosity of the matrix the lower is the percolation threshold, regardless of the chain architecture and degree of crystallization. To improve dispersion a series of acrylic acid copolymer are introduced into the system. The highest concentration of acid co-monomer that maintain miscibility with the polyethylene matrix is 5 wt.%. The compatibilizer in its pristine form does not have a significant effect on dispersion and on volume resistivity. When the acidic copolymer was modified with aminomethylpyridine, in order to facilitate π–π interaction with the nanotubes, a 4-decade reduction was recorder for the high viscosity matrices at 10 wt.% compatibilizer loading. Copyright © 2014 John Wiley & Sons, Ltd.

Electrophoretic deposition from viscous media has the potential to produce in-mold assembly of nanoparticles onto three-dimensional parts in high-rate, polymer melt-based processes like injection molding. The effects of the media's molecular weight on deposition behavior were investigated using a model system of carbon black and polystyrene in tetrahydrofuran. Increases in molecular weight reduced the electrophoretic deposition of the carbon black particles due to increases in suspension viscosity and preferential adsorption of the longer polystyrene chains on the carbon black particles. At low deposition times (≤5 s), only carbon black deposited onto the electrodes, but the deposition decreased with increasing molecular weight and the resultant increases in suspension viscosity. For longer deposition times, polystyrene codeposited with the carbon black, with the amount of polystyrene increasing with molecular weight and decreasing with greater charge on the polystyrene molecules. This deposition behavior suggests that use of lower molecular polymers and control of electrical properties will permit electrophoretic deposition of nanoparticles from polymer melts for high-rate, one-step fabrication of nano-optical devices, biochemical sensors, and nanoelectronics.

A novel method named tin-assisted transfer of nanoscale electroplated metal structures was introduced for the fabrication of flexible devices. With the addition of a tin releasing layer, electroplated metal structures, which were achieved on rigid substrates using a combination of electron beam lithography and electroplating, were successfully transferred to flexible substrates. Using this method, various metal (Ag, Au, and Pt) structures were patterned onto flexible substrates. To demonstrate the utility of this process for fabrication of flexible devices, a mid-infrared flexible metamaterial with chiral structures was successfully produced.

Poly(methyl methacrylate-co-methacrylic acid) was modified with 4-aminomethyl pyridine, in order to facilitate π–π interactions with carbon nanotubes. The π–π * transitions of both the carbon nanotubes and the pyridine modified copolymer were observed by X-ray photoelectron and UV–vis spectroscopy, respectively. The π-interactions themselves were evident by UV–vis absorbance quenching and red shift and also by fluorescence emission quenching and blue-shift. Those spectroscopic evidences suggested that the nanotubes were wrapped by the modified copolymer through π–π interactions. Introducing the pyridine modified copolymer as a compatibilizer in polymethyl methacrylate composites enabled improved nanotube dispersion, which led to reductions in volume resistivity and increases in composite storage modulus. Those results indicated that this novel compatibilizer could be suitable for a variety of carbon nanotube/poly(methyl methacrylate) composite based applications, where improved nanotube dispersion is desirable without damaging the nanotubes inherent properties.

Rubber/clay nanocomposites (RCNs) have many applications because of their improved properties. The dispersion of clay in a rubber matrix, which plays an important role in the properties of RCNs, is a challenge. In this article, a solvent-free approach to produce the styrene butadiene rubber (SBR)/clay nanocomposites by using liquid rubber/clay master batches was introduced. The liquid/rubber master batches were first prepared using a high-speed centrifugal mixer and then compounded with neat SBR using conventional rubber compounding equipment. Compared with the composites prepared by melt mixing, this approach resulted in a better dispersion of the clay in the rubber matrix and improvements in tensile strength (4.98 MPa at 10 phr clay loading) and elongation at break (>1000% at 10 phr clay loading). The improved dispersion was confirmed by X-ray diffraction. The effect of clay loading on the tensile properties, dynamic mechanical properties, and the Payne effect was also investigated. The increase in clay loading resulted in a steady increase in the tensile properties up to a loading of 15 phr. The reinforcement in the RCN modulus using clay was compared with five models, including the Guth and Halpin-Tsai equations. This solvent-free approach offers benefits in dispersion of clay for industrial applications of rubber nanocomposites.

An hierarchical structure, composed of a ternary cocontinuous polymer blend, where carbon nanotubes are mostly localized in one of the phases through π–π interactions, is fabricated by direct melt mixing of polyamide 12 and polypropylene, as the two major components of the ternary blend, together with pyridine-modified poly(ethylene-co-methacrylic acid) as the minor component that can form strong interactions with the CNTs via π–π interactions and confined the percolated network at the polyamide/polypropylene interface. The hierarchical structure was designed by means of surface energies, and the obtained morphology was verified using electron microscopy. This ternary structure has lower electrical resistivity as compared to cocontinuous binary composites. Different polymer viscosities were used in this study in order to emphasize the importance of kinetics during cocontinuous morphology formation.

Patterning of conducting polymer into sub-micron patterns over large areas at high rate and low cost is significant for commercial manufacturing of novel devices. Electrophoretic and dielectrophoretic assembly provide an easily scaled approach with high fabrication rates. In this work, electrophoretic and dielectrophoretic assembly were used to assemble polyaniline (PANi) into multiscale sub-micron size patterns in less than 1 min. The process was controlled by assembly time, amplitude, and frequency of the electric field. Dielectrophoretic assembly is preferable for manufacturing as it reduces damage to the templates used to control the assembly. Using this method, sub-micron patterns with dimensions of the assembled PANi down to 100 nm were fabricated over large areas in short times. The assembled PANi was further transferred to other flexible polymer substrates by a thermoforming process, providing a fast, easily controlled and promising approach for fabrication of nanoscale devices.

In this work, we demonstrate the development of a flexible, high-dielectric-constant substrate based on barium strontium titanate (BST)/thermoplastic cyclic olefin copolymer (COC) nanocomposites suitable for fully printable phased array applications. This functionalized BST/COC substrate is demonstrated to possess tunability as a function of an applied DC bias. This tunable substrate is implemented for a tunable frequency selective surface in the X-band frequency range.

Prior work suggests that rubber-containing polymers like impact modified polystyrene (HIPS) and thermoplastic vulcanizates (TPVs) exhibit unusual behavior when injection molded to create parts with microstructured surfaces. This work was an in-depth investigation of the effects of material composition, including matrix stiffness, rubber content, and rubber domain size, on replication of injection molded microstructured surfaces. Multiple grades of HIPS, poly(acrylonitrile-butadiene-styrene), and TPVs allowed for a range of material properties. The polymers were molded using a range of processing conditions (melt and mold temperatures, packing pressures, and cooling times) and replication was measured using scanning electron microscopy. Microfeature replication (feature definition and depth ratios) was correlated with matrix stiffness, rubber content, and rubber domain size in the polymer materials and with the processing parameters.

Patterned polymer structures with different functionalities have many potential applications. Directed assembly of polymer blends using chemically functionalized patterns during spin-coating has been used to fabricate the patterned polymer structures. For bridging the gap between laboratorial experiments and manufacturing of nanodevices, the polymer blends structures are required to be precisely patterned into nonuniform geometries in a high-rate process, which still is a challenge. In this Article, we demonstrated for the first time that by decreasing the interfacial tension between two polymers polystyrene and poly(acrylic acid) via adding a compatibilizer (polystyrene-b-poly(acrylic acid) ), a polystyrene/poly(acrylic acid) blend was precisely patterned into nonuniform geometries in a high-rate fashion. The patterned nonuniform geometries included angled lines with angles varied from 30° to 150°, T-junctions, square arrays, circle arrays, and arbitrary letter-shaped geometries. The reduction in the interfacial tension improved the line edge roughness and the patterning efficiency of the patterned polymer blends. In addition, the commensurability between characteristic length and pattern periodicity for well-ordered morphologies was also expanded with decreasing interfacial tension. This approach can be easily extended to other functional polymers in a blend and facilitate the applications of patterned polymer structures in biosensors, organic thin-film electronics, and polymer solar cells.

While the effect of vacuum venting has been reported for injection molding of micro and nanoscale features, the limited research has produced conflicting results. To clarify the positive effect of vacuum venting on replication of microscale features, this work focused on the interactions between vacuum venting and (1) feature size, (2) material type in terms of melt viscosity and wettability, and (3) injection velocity and mold temperature. A metal-polymer hybrid tooling with a range of positive microscale features was employed to mold polystyrene and polymethylmethacrylate parts. Overall, vacuum venting always effective in feature definition (sharpness of edges) enhancement, but provided increases in depth ratio that depended on material (melt viscosity and wettability) and processing conditions (i.e., injection velocity, and mold temperature).

In this paper, the electrical conductivity and mechanical properties such as elastic modulus of multiwalled carbon nanotubes (MWCNTs) reinforced polypropylene (PP) nanocomposites were investigated both experimentally and theoretically. MWCNT-PP nanocomposites samples were produced using injection mold at different injection velocities. The range of the CNT fillers is from 0 up to 12 wt%. The influence of the injection velocity and the volume fraction of CNTs on both electrical conductivity and mechanical properties of the nanocomposites were studied. The injection speed showed some effect on the electrical conductivity, but no significant influence on the mechanical properties such as elastic modulus and stress-strain relations of the composites under tensile loading. Parallel to the experimental investigation, for electrical conductivity, a percolation theory was applied to study the electrical conductivity of the nanocomposite system in terms of content of nanotubes. Both Kirkpatrick (Rev Mod Phys 45:574–588, 1973) and McLachlan et al. (J Polym Sci B 43:3273–3287, 2005) models were used to determine the transition from low conductivity to high conductivity in which designates as percolation threshold. It was found that the percolation threshold of CNT/PP composites is close to 3.8 wt%. For mechanical properties of the system, several micromechanical models were applied to elucidate the elastic properties of the nanocomposites. The results indicate that the interphase between the CNT and the polymers plays an important role in determining the elastic modulus of the system.