Carol Barry

Antibody orientation enhanced by selective polymer–protein noncovalent interactions

A unique interaction has been found between protein G’ (a truncated recombinant bacterial “alphabet” protein which aligns by noncovalent attachment to the antibody stem) and poly(methyl methacrylate), a thermoplastic polymer substrate, which can be easily fabricated using high-rate processes. Significantly improved orientation efficiency with traditional passive adsorption for this system (termed ALYGNSA) has been achieved as compared to the same assay performed on a polystyrene substrate with protein G’. Results were consistent with an average alignment of 80% of the human immunoglobulin G capture antibody which translated into a 30% to 50% improved alignment over an array of industry standards tested. Laser scanning confocal microscopy confirmed the immunological results. Studies of additional poly(methyl methacrylate) polymer derivatives and protein biolinker (A and AG) combinations have been conducted and have revealed different degrees of antibody alignment. These findings may lead to additional novel noncovalent methods of antibody orientation and greater sensitivity in immunological assays.

Directed Assembly of Polymer Blends Using Nanopatterned Templates

The direct assembly of polymer blends on chemically functionalized surfaces is shown to produce a variety of nonuniform complex patterns. This method provides a powerful tool for easily producing nonuniform patterns in a rapid (30 s), one-step process with high specificity and selectivity for a variety of applications, such as nanolithography, polymeric optoelectronic devices, integrated circuits, and biosensors.

Numerical simulation of phase separation of immiscible polymer blends on a heterogeneously functionalized substrate

The spinodal phase decomposition of an immiscible binary polymer blend system is investigated with numerical models in two-dimensional and three-dimensional (3D). The effect of the elastic energy is included. The mechanism of the evolution of the phase separation is studied and the characteristic length R(t) is shown to be proportional to t(13). In the case when the phase separation is directed by a heterogeneously functionalized substrate, the increase in the characteristic length is divided into two stages by a critical time. The R(t) approximately t(13) diagram can be fitted with a straight line in both the first and second stages. The slope of the fitting line significantly decreases after the critical time. The compatibility of the resulting pattern to the substrate pattern is also measured by a factor C(S). It is observed that there is also a critical time in the evolution of the compatibility for the cases with and without elastic energy. The critical time of C(S) is identical with the respective critical time of R(t). The lateral and vertical composition profiles functionalized substrate is observed with the 3D model. The difference mechanism of the cases with and without elastic energy is discussed.

Heat Resistant Elastomers

Abstract This paper reviews the different types of heat resistant elastomers and the effects of compounding on the high temperature performance of these materials. Degradation mechanisms and testing procedures are discussed briefly. New developments in improving high temperature resistance are presented.

The effects of recycling on the properties of carbon nanotube-filled polypropylene composites and worker exposures

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 Youngs 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.

Evaluation of Vacuum Venting for Micro-injection Molding

Abstract 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).

Evaluation of novel tooling for nanoscale injection molding

Injection molding technology is one of the most promising candidates for the economically viable manufacturing of nanoscale parts, but the composition and surface properties of tooling materials become more critical as the size of the molded features decreases. In the study, the effect of novel tooling with micro and nanoscale features was investigated by employing this tooling as inserts for micro injection molding of polycarbonate. Parts molded from etched silicon wafers with pattern depths of 300 nm and widths of 200 to 980 nm showed a significant decrease in replication quality with the size the features, probably because polymer adhered to the tooling surface. Silicon tooling from a different source and titanium-coated gallium arsenide tooling produced higher quality replication. The replication quality from the silicon tooling, however, was constant over 3000 molding cycles and coated gallium arsenide inserts survived the molding pressures; (the uncoated gallium arsenide fractured). These findings suggest that modifications to the insert surfaces will allow for viable tooling for injection molding of plastic parts with nanoscale features.

Precise pattern replication of polymer blends into nonuniform geometries via reducing interfacial tension between two polymers.

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.

Enhanced protein binding on femtosecond laser ablated poly(methyl methacrylate) surfaces

Poly(methyl methacrylate) (PMMA) substrates were ablated through a fast femtosecond (fs) laser scanning process to create patterns for enhanced protein binding. Typically, two patterns with lines and grids were produced and the protein binding was evaluated by studying the adsorption of fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA). It was found that the adsorption of FITC-BSA was increased up to tenfold on both patterns compared with the untreated PMMA surface, indicating the potential application of the fs laser ablated PMMA surfaces as protein assay substrates.

Critical factors for nanoscale injection molding

Injection molding technology offers the most competitive potential to meet the growing demand for cost-effective manufacturing of components with micro and nanoscale features due to its far greater production rates than the other techniques. Since conventional mold tooling materials and techniques are not suitable for sub-micron scale molding, mature silicon processing technology were evaluated as tooling for these features. Simple pattern geometries of trench lines were employed to simplify the analysis and all parts were molded using optical grade high-flow polycarbonate. Replication quality was evaluated in terms of depth ratio (height of molded feature/depth of corresponding tooling feature) and root-mean-square roughness. Although perfect replication has not been achieved with the given system, several factors including surface adhesion and feature aspect ratio were found to be critical for replication of nanoscalefeatures. Of four factors possibly affecting replication, adhesion of the polymer to silicon surface during ejection was found to be critical and is influenced by processing temperatures, cooling times, tooling mounting systems, and tooling surface roughness. Trapped of air in tooling trenches, damage to the silicon tooling during molding, and shrinkage of polymer during cooling may also have contributed to less-than-perfect replication. All factors seem synergistic and the effects are greater for small feature geometries.