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The topographical features on the individual particles in a powder and the surfaces with which they interact affect the powder adhesion. An experimental and modelling framework called the Enhanced Centrifuge Method (ECM) maps particle and surface properties onto 'effective' Hamaker constant distributions that describe the van der Waals (vdW) adhesion between a powder and a surface. The ECM was used to study the adhesion between polystyrene powder and silica surfaces to exemplify the 'effective' Hamaker constants quantify the effects of particle and surface properties on adhesion. Silica surfaces were polished to alter their surface roughness profiles to reveal levels of roughness in which the adhesion was controlled by either the powder or surface properties. This study revealed surface roughness height descriptions are inadequate descriptors of adhesion, and instead the frequency of roughness peaks to the particle size must be considered. This result was verified using an existing particle adhesion simulator.

The modification of the surface chemistry of a film is a key strategy to enhance the binding of molecules of interest in various sensing and detection applications. For example, the adhesion of explosive residues to a swab is critical for the detection of trace explosives in air transportation environments, and it can be enhanced by increasing the affinity of the swab to target molecules through favored chemical interactions. Here, the surface chemistries of polypyrrole (PPy) films were systematically tuned through the electropolymerization of thin layers of N-substituted pyrrole monomers to evaluate their interactions with a model explosive compound, trinitrotoluene (TNT). The surface groups examined included carboxylic acid, methyl, and amino-phenyl groups, in order to address a wide range of chemical functionalities. The interaction between the functionalized PPy films with TNT was compared with the interactions between TNT and commercial swabbing materials in a vapor deposition process. The amount of TNT deposited from the vapor phase on each of the different films was quantified by the ultraviolet–visible (UV–vis) light absorbance of the Meisenheimer complex formed from the interaction of TNT with a basic solution. The PPy films with surface functionalities that allowed for hydrogen bonding displayed the highest deposition of TNT, while Teflon-coated commercial materials had the lowest interaction with TNT. Thus, this work provides insight into the surface groups of interest for the enhanced collection of trace explosives as well as the critical design criteria for the next generation of swabbing materials.

The detection of trace amounts of explosive materials is critical to the security at mass transit centers (e.g., airports and railway stations). In a typical screening process, a trap is used to probe a surface of interest to collect and transfer particulate residue to a detector for analysis. The collection of residues from the surface being probed is widely viewed as the limiting step in this process. A multi-institutional study was performed to establish a methodology for the evaluation of sampling media collection efficiencies. Dry deposited residues of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), C-4 (an RDX-based explosive), and pentaerythritol tetranitrate (PETN) were harvested from acrylonitrile butadiene styrene (ABS) plastic, ballistic nylon (NYL), and uncoated aluminum surfaces using muslin, Texwipe cotton, and stainless-steel mesh traps. Transfer and collection efficiencies of the sample media were calculated based on liquid chromatography-mass spectrometry analysis. Dry transfer efficiencies (DTE%) to all tested surfaces were greater than 75%, with transfer to ABS plastic being the lowest. Collection efficiency (CE%) varied significantly across the traps and the surfaces, yet some conclusions can be drawn; nylon had the lowest CE% for all cases (∼10%), and the stainless steel mesh had the lowest CE% for the evaluated traps (∼20%). Though the testing parameters have been standardized among the participants to establish a framework for an independent comparison of contact sampling media and surfaces, substantial variations in the DTE% and the CE% were observed, suggesting that other variables can affect contact sampling.

Amorphous solid dispersions are a highly relevant pharmaceutical formulation strategy increasingly employed to enhance the dissolution performance of drugs with poor aqueous solubility. Formulation additives are known to play an important role in the phase behavior of such pharmaceutical products, as they can potentially promote or inhibit solid-state crystallization of drug molecules in the dispersion matrix as well as crystallization from supersaturated solutions. Considerably less is known about the potential role of dissolved additives on the fate of amorphous drug-rich interfaces which can arise due to liquid–liquid phase separation during dosing. In this study, amorphous drug films are crystallized in buffer containing various polymeric formulation additives and analyzed via atomic force and scanning electron microscopy methods to explore the effect of additives on the evolution of surface crystals. A 2D lattice Monte Carlo model further examines the polymer systems to determine important modes of polymer action. Results demonstrate adsorbed polymer competitively inhibits crystal growth by preferential interaction with high energy sites.

Granular compressive behavior has been evaluated with respect to particle size distribution. All granules were prepared with a polydimethylsiloxane (PDMS) binder with viscosity ranging from 12 to 2413 Pa·s. All granules were prepared with 90% particulates and 10% binder by mass. Granules were prepared using two unimodal particle size distributions (420–595 μm silica and 105–420 μm silica) and two bimodal particle size distributions. The bimodal size distributions were comprised of 420–595 μm silica and 0–63 μm silica in 75%/25% and 50%/50% mass fractions, where the first percentage refers to the amount of 420–595 μm silica particles included. The granules were compressed with 1, 10, and 100 mm/s velocities. The granules prepared with 420–595 μm silica particles were found to exhibit greater granular strength than those prepared with 105–420 μm particles. These results are uniquely different from those of previous studies which indicate that a smaller size fraction of particles will result in a stronger granule. The addition of a secondary particle size distribution in conjunction with the 420–595 μm silica particles results in a granule with significantly increased strength over the granule prepared with a unimodal distribution. It is suggested that the bimodal size distribution allows an increased number of interparticle contacts per unit volume to increase the granular strength.

In order to minimize the effects of surface roughness and deformation, a new method for estimating the Hamaker constant, A, of solids using the approach-to-contact regime of an atomic force microscope (AFM) is presented. First, a previous “jump-into-contact” quasi-static method for determining A from AFM measurements is analyzed and then extended to include various AFM tip-surface force models of interest. Then, to test the efficacy of the “jump-into-contact” method, a dynamic model of the AFM tip motion is developed. For finite AFM cantilever-surface approach speeds, a true “jump” point, or limit of stability, is found not to appear, and the quasi-static model fails to represent the dynamic tip behavior at close tip-surface separations. Hence, a new “quasi-dynamic” method for estimating A is proposed that uses the dynamically well-defined deflection at which the tip and surface first come into contact, dc, instead of the dynamically ill-defined “jump” point. With the new method, an apparent Hamaker const...

Powder behavior affects a wide variety of industries due to the use of solids in processing and manufacturing. As such, the prediction of powder behavior is advantageous to these industries and particle scale measurements that allow prediction of powder behavior can be very beneficial. The centrifuge technique was utilized experimentally with silica particles adhered to stainless steel to characterize the adhesion of the silica powder. To describe the observed adhesion force distributions, a simulated powder with a realistic size distribution, but assumed to be comprised of smooth spheres, was conceived. The adhesion between the real powder and the stainless steel was modeled using the idealized powder and assuming a simple sphere-flat plate adhesion model. During the model validation, an effective Hamaker constant distribution that allowed the simulated adhesion of the smooth spheres to match the experimentally-observed adhesion was developed. The effective Hamaker constant distribution captured the effects of the roughness and shape variations in the individual particle within the powder, and these effects were linked to the measured particle size distribution of the powder.

The compressive behavior of granular materials has been evaluated under a variety of conditions. Granules were formulated using two size fractions of two different particulate materials prepared with a polydimethylsiloxane binder ranging in viscosity from 12–2413 Pa·s. The solids content of the granules was maintained constant at 90% in all cases studied. Granules were compressed at three different velocities (1, 10, and 100 mm/s). At these high viscosities, characteristics of the binder appear to have the greatest impact on granular behavior. Through ~ 300 Pa·s, the granule strength increases with increasing viscosity. Above this critical viscosity, however, the granular strength remains approximately constant within a given set of test parameters. The compression velocity also impacts the granular strength, as do the size and shape of the particulate inclusions (though to a lesser extent).

peer-reviewed The dissolution or melting of a crystalline drug into a molten polymeric matrix underpins the fabrication of a number of drug delivery systems. However, little is known about how crystals dissolve in such viscous matrices. Herein, the heat-induced dissolution of indomethacin crystals into a molten polymer, copovidone, was evaluated, probing changes in crystal features at multiple length scales using various microscopy techniques. Diffusion of the drug into the polymer film was observed by elemental composition analysis (scanning electron microscopy with energy-dispersive X-ray analysis). Under polarized light microscopy, irregular dissolution patterns were observed, in which channels and holes were seen forming in the crystals, which then resulted in fragmentation. At shorter length scales by scanning and transmission electron microscopy (SEM and TEM), crystals demonstrated a range of channel formation and fragmentation behaviors. Defect sites intrinsic to the bulk crystals were hypothesized to be the origin of the dissolution-induced fragmentation process. A defect site-driven dissolution and fragmentation model was thus proposed. A Monte Carlo simulation of crystal dissolution under a range of surface energy configurations is also presented. This study has implications for modeling and understanding of dissolution kinetics and pathways of organic crystals in the context of processing operations such as hot melt extrusion.

Cohesive Hamaker constants of solid materials are measured via optical and dielectric properties (i.e., Lifshitz theory), inverse gas chromatography (IGC), and contact angle measurements. To date, however, a comparison across these measurement techniques for common energetic materials has not been reported. This has been due to the inability of the community to produce samples of energetic materials that are readily compatible with contact angle measurements. Here we overcome this limitation by using physical vapor deposition to produce thin films of five common energetic materials, and the contact angle measurement approach is applied to estimate the cohesive Hamaker constants and surface energy components of the materials. The cohesive Hamaker constants range from 85 zJ to 135 zJ across the different films. When these Hamaker constants are compared to prior work using Lifshitz theory and nonpolar probe IGC, the relative magnitudes can be ordered as follows: contact angle > Lifshitz > IGC. Furthermore, the dispersive surface energy components estimated here are in good agreement with those estimated by IGC. Due to these results, researchers and technologists will now have access to a comprehensive database of adhesion constants which describe the behavior of these energetic materials over a range of settings.

Polymer inhibition of crystal growth from supersaturated solutions is an important area of study, particularly in the pharmaceutical field. Polymers can be used to modify crystal morphology or to slow crystal growth with the goal of enhancing oral drug absorption. In order to fully understand the effect of polymers on crystal growth, it is important to understand the kinetics of the integration step. In this study, a rotating disk apparatus is used to isolate the integration step from the mass transfer step so that the integration kinetics can be determined for growth rates in the absence and presence of polymers. The results indicate that the presence of polymers in solution greatly impacts the integration step and has no impact on the mass transfer kinetics.

Realistic descriptions of interfacial contact between rough, deformable surfaces under load are difficult to obtain; however, this contact is of great import in a wide range of applications. Here, we detail, through experiment and computational simulation, the interfacial contact between four common traps and five commonly investigated surfaces encountered in explosives detection applications associated with airport security. The Young's modulus and hardness of four traps and seven substrates were measured using nanoindentation. These properties determine how deformation occurs when traps are applied for contact sampling of explosives. The nanoindentation data were analyzed using the Oliver-Pharr method, and an indenter area function was created using silicon and gold as the reference materials. The Young's moduli of the traps ranged from 0.2 to 8 GPa, while those of the surfaces ranged from 0.5 to 4 GPa. The hardness values of the traps ranged from 0.005 to 0.22 GPa, while those of the surfaces ranged from 0.02 to 0.2 GPa. For each of 20 scenarios (4 traps, 5 surfaces), six contact simulations were performed. In these contact simulations, the Greenwood-Willliamson microcontact model was used to represent the behavior of the asperities on the traps, while the Timoshenko Beam model was used to describe the macroscopic behavior of the bulk trap materials spanning the space between asperities. This combination of feature- and trap-scale modeling provides a more realistic description of the interfacial contact than either model applied individually. The calculated distributions of separation distances between the traps and surfaces when the traps were contacted with the surfaces under a normal load were compared to estimate the relative effectiveness of the traps at interrogating the topography of the surfaces. This method is proposed as a tool to guide the development of trap materials for surface sampling and surface cleaning applications.

Controlling the rate of crystal growth from supersaturated solutions is a desirable capability in the pharmaceutical field. The biological absorption of poorly soluble drugs can be enhanced by inhibiting crystal growth and prolonging the duration of supersaturated solutions formed in vivo by dissolving supersaturating dosage forms. The use of polymeric additives to slow crystal growth is an emerging area of interest, yet the mechanisms of polymer inhibition are still being explored. In this study, the ability of a polymer to poison crystal growth and impact crystal morphology is assessed for felodipine crystallized from the amorphous material under different conditions. It was found that when polymers are present during crystal evolution from an amorphous solid exposed to water, they can impact the size and shape of the resulting crystals. This in turn influences the subsequent rate of crystal growth from supersaturated solutions. Therefore, when testing the ability of polymers to impact crystal growth, a...

Many types of manufacturing processes involve powders and are affected by powder behavior. During the development of new powder processes, it is common that only very small quantities of powder are available. It is highly desirable to implement tools that allow the behavior of bulk powder to be predicted based on the behavior of these small quantities. If the powder can be well-characterized, it is possible to improve the processing performance. In this work, an enhancement of the centrifuge technique was proposed as a means of powder characterization by using specially designed substrates with hemispherical indentations within the centrifuge. Simulations of the centrifuge technique were performed to test the viability of applying this enhancement experimentally. These simulations predicted the percentage of particles remaining as a function of centrifuge rotational speed, indentation size, and particle size, for spherical silica particles against indented substrates made from silicon. Particles that are smaller than an indentation complement that indentation, leading to an increase in the adhesion force. In comparison, particles that are larger than an indentation have a smaller relative adhesion force. These two types of particle–indentation interactions generate a unique set of residual adhering percentage (RAP) curves that can be used to determine the particle size distribution and Hamaker constant of the system. These simulation results for the specifically-designed substrates demonstrate the capability of the enhanced centrifuge technique for advanced powder characterization.

Amorphous solid dispersions are widely used to enhance the oral bioavailability of poorly water-soluble drugs. Polymeric additives are commonly used to delay crystallization of the drug from the supersaturated solutions formed upon ASD dissolution by influencing the nucleation and growth of crystals. However, there is limited evidence regarding the mechanisms by which polymers stabilize supersaturated drug solutions. The current study used experiments and computational modeling to explore polymer-drug interactions in aqueous solutions. Nucleation induction times for supersaturated solutions of nine drugs in the presence of five newly synthesized cellulose-based polymers were evaluated. The polymers had carboxylic acids substituents with additional variations in the side-chain structure: (1) one with a single side chain and a carboxylic acid termination, (2) three with a branched side chain terminated with a carboxylic and an alcohol group (varying the cellulose linkage and the length of the hydrocarbon side chain), and (3) one with a branched side chain with two carboxylic acid end groups. The polymers with a short side chain and one carboxylic acid were effective, whereas the polymers with the two carboxylic acids or a long hydrocarbon chain were less effective. Atomic force microscopy experiments, evaluating polymer adsorption onto amorphous drug films, indicated that the effective polymers were uniformly spread across the surface. These results were supported by molecular dynamics simulations of a polymer chain in the presence of a drug aggregate in an aqueous environment, whereby the effective materials had a higher probability of establishing close contacts and more negative estimated free energies of interaction. The insights provided by this study provide approaches to design highly effective polymers to improve oral drug delivery.

The bioavailability of orally administered drugs that exhibit poor aqueous solubility can be enhanced with the use of supersaturating dosage forms. Stabilization of these forms by preventing or inhibiting crystallization in solution is an important area of study. Polymers can be used to stabilize supersaturated systems; however, the properties that impact their effectiveness as crystal growth rate inhibitors are not yet fully understood. In this study, the impact of various polymers on the crystal growth rate of felodipine and the conformation of these polymers adsorbed to crystalline felodipine was investigated in order to gain a mechanistic understanding of crystal growth inhibition. It was determined that polymer hydrophobicity impacted polymer adsorption as well as adsorbed polymer conformation. Polymer conformation impacts its surface coverage, which was shown to directly correlate to the polymer's effectiveness as a growth rate inhibitor. By modeling this correlation, it is possible to predict polymer effectiveness given the surface coverage of the polymer.

Poor aqueous solubility is a major hindrance to oral delivery of many emerging drugs. Supersaturated drug solutions can improve passive absorption across the gastrointestinal tract membrane as long as crystallization can be inhibited, enhancing the delivery of such poorly soluble therapeutics. Polymers can inhibit crystallization and prolong supersaturation; therefore, it is desirable to understand the attributes which render a polymer effective. In this study, the conformation of a polymer adsorbed to a crystal surface and its impact on crystal growth inhibition were investigated. The crystal growth rate of a poorly soluble pharmaceutical compound, felodipine, was measured in the presence of hydroxypropyl methylcellulose acetate succinate (HPMCAS) at two different pH conditions: pH 3 and pH 6.8. HPMCAS was found to be a less effective growth rate inhibitor at pH 3, below its pKa. It was expected that the ionization state of HPMCAS would most likely influence its conformation at the solid-liquid interface. Further investigation with atomic force microscopy (AFM) revealed significant differences in the conformation of HPMCAS adsorbed to felodipine at the two pH conditions. At pH 3, HPMCAS formed coiled globules on the surface, whereas at pH 6.8, HPMCAS adsorbed more uniformly. Thus, it appeared that the reduced effectiveness of HPMCAS at pH 3 was directly related to its conformation. The globule formation leaves many felodipine growth sites open and available for growth units to attach, rendering the polymer less effective as a growth rate inhibitor.

During the manufacture of pharmaceuticals, it is desirable to modify the surface of powder particles to alter their adhesion characteristics without changing their dissolution rates or their chemical or biological characteristics. In this study, dry silica nanoparticle coatings were applied to spheroidal micron-scale aluminum host particles to alter their surface morphology and adhesion behavior. The host particles were coated with either hydrophobic or hydrophilic fumed nanosilica using a magnetically assisted impact coating technique. The adhesion between polished or unpolished stainless steel and all three particle types, including uncoated aluminum and aluminum coated with either hydrophobic or hydrophilic nanosilica, was examined at 30% relative humidity. On both steel surfaces, the measured adhesion force towards the uncoated aluminum was greater than towards either type of coated aluminum. The uncoated aluminum adhered more strongly to the polished substrate than to the unpolished one. The hydrophobic- and hydrophilic-coated particles adhered to both substrates with roughly the same force, such that there was no effect of either the substrate type or the coating type on the adhesion. To confirm that capillary forces had no influence on the measured adhesion, the adhesion behavior between the uncoated aluminum particles and the steel was measured at 15 and 30% RH, and no change in adhesion force was observed.

A successful approach to calculating van der Waals (vdW) forces between irregular bodies is to divide the bodies into small cylindrical volume elements and integrate the vdW interactions between opposing elements. In this context it has been common to use Hamaker's expression for parallel plates to approximate the vdW interactions between the opposing elements. This present study shows that Hamaker's vdW expression for parallel plates does not accurately describe the vdW interactions for co-axial cylinders having a ratio of cylinder radius to separation distance (R/D) of 10 or less. This restricts the systems that can be simulated using this technique and explicitly excludes consideration of topographical or compositional variations at the nanoscale for surfaces that are in contact or within a few nm of contact. To address this limitation, approximate analytical expressions for nonretarded vdW forces between finite cylinders in different orientations are derived and are shown to produce a high level of agreement with forces calculated using full numerical solutions of the corresponding Hamaker's equations. The expressions developed here allow accurate calculation of vdW forces in systems where particles are in contact or within a few nm of contact with surfaces and the particles and/or surfaces have heterogeneous nanoscale morphology or composition. These calculations can be performed at comparatively low computational cost compared to the full numerical solution of Hamaker's equations.

Frankliniella fusca (Hinds) naturally disperses from winter weeds to crops in spring, causing direct and indirect damage. Field preparation before planting includes use of herbicides or cultivation to kill unwanted vegetation, which adversely affects F. fusca host plants and potentially influences F. fusca dispersal. Common chickweed, Stellaria media (L.), infested with F. fusca, was used as a model to study effects of timing and type of vegetation management on adult dispersal. Infested weeds were caged and F. fusca weekly dispersal was monitored using sticky traps. Weed management treatments performed at an early (14 April–11 May) or late (2 wk after early treatment) date consisted of glyphosate, paraquat, disking, hoeing, or untreated control. Late glyphosate and hoeing treatments resulted in cumulative dispersal statistically similar to or greater than from control plots. Compared with the control, significantly more F. fusca dispersed from the glyphosate and hoeing plots during the 3 wk afte...

The effects of surface film (coating) thickness, , on the adhesion of a particle to a surface are investigated. The model system in this work includes a pre-manufactured silicon nitride probe (initial radius of curvature ~15 nm) and a silicon substrate onto which gallium nitride films have been deposited via atomic layer deposition. The gallium nitride films have varying thicknesses (0, 5, 11, 12, 16, and 80 nm). We develop theory supporting the hypothesis that the coating material will appear transparent to the particle if is small in comparison to the particle-substrate separation distance, D. However, as increases a transition in the particle-substrate interaction will take place. This implies the existence of a critical coating thickness, *, beyond which the adhesion behavior of the coating material will be equivalent to bulk (see Fig. 1). We show * is a simple function of D and a parameter termed the permissible fractional error, . Taking D = 0.4 nm at contact, for = 0.05 (i.e. 5% permissible fractional error), * 28 nm. The adhesion between the model system particle and substrate is measured using contact mode atomic force microscopy (AFM). Experimental results confirm that for small (i.e. 5, 11, and 12 nm) , the interaction between the silicon nitride probe and underlying silicon is relatively unaffected by the presence of the gallium nitride film; for large (i.e. 80 nm) , the interaction parallels that between silicon nitride and bulk ( 5 µm) gallium nitride. The * for this model system is approximately 30 nm, which is in good agreement with our theoretical predictions.

The interactions between nanoparticles and rough surfaces are of great scientific and engineering importance and have numerous applications in surface science and biotechnology. Surface geometry and roughness play crucial roles in observed particle adhesion forces. We previously developed a model and simulation approach to describe adhesion between microscale bodies. This work provides detailed descriptions of the modeling framework, with associated experimental validation, applied to nanoscale systems. The physical systems of interest include nanoscale silicon nitride adhering to different surfaces in both dry and aqueous environments. To perform the modeling work, precise descriptions of the geometry of the particle and the roughness of the particle and substrate were generated. By superimposing the roughness and geometry models for the particle and the substrate, it was possible to precisely describe the spatial configurations of the adhering surfaces. The interacting surfaces were then discretized, and the adhesion force between the two surfaces was calculated by using Hamaker's additive approach, based on van der Waals interactions. In the experimental work, an atomic force microscope (AFM) was used to measure the adhesion force (pull-off force) between nanoscale silicon nitride cantilever tips and a range of substrates in different environments. The measured and predicted force distributions were compared, and good agreement was observed between theory and experiment.

The mechanical properties of chemical-mechanical planarization (CMP) pads are very important to their performance. In this paper, pads are described in terms of their bulk properties and the properties of their asperity layer for applications in copper CMP. In particular, the elastic properties of these layers are studied. Pads were soaked in a copper polishing slurry or water for specified times and changes in their elastic moduli were measured. In general, pad immersion in water reduced the bulk modulus because the water penetrated the pads and disrupted hydrogen bonds between adjacent polyurethane chains. In addition, it was found that surface grooving affected the pad elastic modulus, especially that of the asperity layer. To evaluate the effect of use in copper CMP on the pad properties, the elastic moduli of the bulk and asperity layers on a pad were measured following pad use in a commercial polisher. The periodic loads during CMP were believed to facilitate the penetration of water into the pads, lowering their bulk elastic moduli. A slight increase in the elastic modulus of the asperity layer was seen as a result of pad use in copper CMP. The inherent variations in modulus measurements for dry pads were also measured.

Work performed to study the scalability of continuum force models to describe particle adhesion from the micro- to the nano-scale is described. This work employed silicon nitride particles with nominal diameters on the micrometer scale and silicon nitride atomic force microscope cantilevers with nanometer-scale radii of curvature to determine adhesion interaction forces to substrates relevant to advanced lithography applications in the semiconductor industry. The force required to dislodge the particles or cantilevers from the substrates was taken to be the adhesion force. For all systems studied, a distribution of adhesion forces was observed resulting from roughness on the particles and/or substrates and geometry variations on the particles. Previously developed adhesion models that included van der Waals (vdW) and electrostatic (ES) interactions, and that also included the geometry and morphology of the interacting surfaces, were used to describe the force distributions. In air, the ES forces were foun...

Reduction of the nonspecific serum protein adsorption on a gold surface to levels low enough to allow the detection of biomarkers in complex media has been achieved using the N-hydroxysuccinimide (NHS) ester of 16-mercaptohexadecanoic acid. Carboxymethylated dextran (CM dextran), which is widely used, nonspecifically adsorbs enough proteins to mask the signal from target biomarkers in complex solutions such as serum or blood. The use of short-chain thiols greatly reduces the amount of nonspecific protein adsorption. Mixed layers of 11-mercaptoundecanoic acid or the NHS ester of 11-mercaptoundecanoic acid mixed layers with either 11-mercaptoundecanol or undecanethiol, and 16-mercaptohexadecanoic acid or the NHS ester of 16-mercaptohexadecanoic acid with hexadecanethiol, were also investigated for nonspecific protein binding properties as well as for biomarker signal response. The NHS ester of 16-mercaptohexadecanoic acid exhibits the largest signal for the biomarker myoglobin (including CM dextran) while offering a significantly diminished amount of nonspecific binding. The sensor has also been shown to detect interleukin-6 in cell culture media containing protein concentrations of at least 4 mg/mL.

In this work, parylene-C is exposed to the effluent from a microwave ammonia plasma with a goal of producing primary amine groups on the parylene-C. These amine groups are desired as sites for the attachment of various biomolecules that will influence the biocompatibility of the parylene-C. Ammonia plasma treatment is an effective approach for creating amine species on polymers. In this work, attenuated total reflectance infrared spectroscopy studies showed that no primary amine groups resulted from this treatment of parylene-C. Instead, reactive nitrogen-bearing radicals from the plasma appear to have been complexed by chlorine in the polymer. The formation of these complexes scavenged nitrogen-bearing radicals from the plasma and prevented the formation of nitrogenous species, such as the desired primary amines, on the parylene-C. These results are consistent with results of ammonia plasma treatment of other chlorinated polymers and suggest that alternative approaches are required to create nitrogen-bearing species on parylene-C.

The elimination or minimization of non-specific protein adsorption from serum is critical for the use of surface plasmon resonance (SPR) sensors for in vitro and in vivo analysis of complex biological solutions. The ultimate goals in this application are to minimize non-specific adsorption of protein and to maximize analyte signal. A reduction of the non-specific protein adsorption from serum of up to 73% compared to carboxymethylated-dextran 500kDa (CM-dextran) was achieved following a survey of eight biocompatible polymers and 10 molecular weights of CM-dextran. These coatings minimize non-specific adsorption on the sensor while also serving as immobilization matrices for antibody fixation to the probes. Polymers including polysaccharides: CM-dextrans, CM-hyaluronic acid, hyaluronic acid, and alginic acid were investigated. Humic acid, polylactic acid, polyacrylic acid, orthopyridyldisuldfide-polyethyleneglycol-N-hydroxysuccinimide (OPSS-PEG-NHS), and a synthesized polymer; polymethacrylic-acid-co-vinyl-acetate (PMAVA) were also used. The non-specific protein adsorption reduction was measured over a 14 day period at 0 degrees C for each polymer. Calibration curves using some of these polymers were constructed to show the performance and low detection limit possibilities of these new antibody supports. For many of the polymers, this is the first demonstration of employment as an antibody support for an optical or surface active sensor. CM-dextran is the polymer offering the largest signal for the antigen detection. However, the biocompatible polymers demonstrate a greater stability to non-specific binding in serum. These biocompatible polymers offer different alternatives for CM-dextran.

A critical particle Reynolds number approach for analyzing the hydrodynamic removal of micron-scale particles from surfaces was presented and tested experimentally. A model system involving polydisperse polystyrene spheres adhering to a quartz surface and subject to laminar channel flow of an aqueous solution was considered. An experimentally validated adhesion model was used to predict an adhesion force distribution for the adherent spheres based on the size of the spheres and the morphological characteristics of the spheres and quartz. This force distribution was combined with the critical particle Reynolds number approach to predict particle removal and the predictions were compared to experimental observations. Results indicate that when variations in particle size, adhesion force, and point around which rolling occurs are taken into account, particle removal from surfaces can be described quantitatively.

To control the interactions between surfaces and biological systems, it is common to attach polymers, proteins, and other species to the surfaces of interest. In this case, surface modification of polydimethylsiloxane (PDMS) was performed by exposing PDMS films to the effluent from a microwave ammonia plasma, with a goal of creating primary amine groups on the PDMS. These amine sites were to be used as binding sites for polymer attachment. Chemical changes to the surface of the PDMS were investigated as a function of treatment time, microwave power, and PDMS temperature during plasma treatment. Functional groups resulting from this treatment were characterized using attenuated total reflectance infrared spectroscopy. Plasma treatment resulted in the incorporation of oxygen- and nitrogen-containing groups, including primary amine groups. In general, increasing the treatment time, plasma power and substrate temperature increased the level of oxidation of the films, and led to the formation of imines and nitriles. PDMS samples treated at 100 W and 23 °C for 120 s were chosen for proof-of-concept dextran coating. Samples treated at this condition contained primary amine groups and few oxygen-containing groups. To test the viability of the primary amines for attachment of biopolymers, functionalized dextran was successfully attached to primary amine sites on the PDMS films.

The preparation and use of multiple polymers attached to a surface plasmon resonance (SPR) sensor for optimization of signal enhancement and minimization of fouling during sensing of biological species has been achieved. These polymers are advantageous compared to the current practice of carboxymethylated-dextran (CM-dextran). The polymers offer a wide range of functionalities and different molecular weights. Using these polymers, the SPR sensors can be fabricated as fast or faster than the CM-dextran sensor. In this study, we investigated the use of nine polymers for SPR biosensors. Polysaccharides, including CM-dextran, CM-hyaluronic acid, hyaluronic acid, and alginic acid, were investigated. Humic acid, polylactic acid, polyacrylic acid, orthopyridyldisulfide-polyethyleneglycol-N-hydroxysuccinimide (OPSS-PEG-NHS) and a synthesized polymer; polymethacrylic-acid-co-vinyl-acetate (PMAVA), were also used. The polymers were chemically attached to a thiol monolayer on the SPR biosensor using carbodiimide chemistry. The polymers were functionalized for binding of anti-myoglobin (anti-MG). The sensor performance was measured using myoglobin (MG) at 25 ng ml−1, a biologically relevant level for myocardial infarction detection. Most polymers offered similar performance to CM-dextran for MG detection in HEPES buffer saline pH 7.4 (HBS). In preliminary studies in bovine serum, each of the candidate polymers demonstrated better performance than CM-dextran.

Parylenes belong to a family of polymers that have been investigated for use in electronic and medical applications. The photooxidation of these materials is of interest both to prevent degradation and to induce targeted chemical changes. This article describes a transport and reaction model for the photooxidation of parylenes. This model is based on existing polymer photooxidation mechanisms that have been adapted to this system. The model has been compared with existing parylene photooxidation data for this system and shows qualitative agreement with surface oxidation profiles and oxidation depth profiles. On the basis of the results of the model comparison, it has been determined that the key parameters that appear to affect the photooxidation of parylenes are the diffusion coefficient of oxygen in these films and the concentration of oxygen initially present in these films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2666–2677, 2004

During the copper electrowinning process, sulfuric acid mist is released into the air above the electrowinning tanks. This mist causes health problems for the operators in the electrowinning plant. Therefore, the Occupational Safety and Health Administration (OSHA) has mandated that electrowinning tanks comply with new stringent regulations. This has sparked an interest by copper mines to develop new techniques to reduce acid mist. Foam blankets have been employed as a possible solution. Through designed experiments, a range of surfactant concentrations and space velocities that reduced the acid mist were identified. In this paper, foam blankets using a BASF Pluronic F67 nonionic surfactant were proven to be a viable technique for acid mist reduction. The foam blankets examined may be effective in facilities that operate at evolved gas space velocities around 2.0 cm/min. This method leads to over a 90% reduction of sulfuric acid mist, thus, providing one option for putting the electrowinning system in compliance with OSHA's regulations.

Parylene-N and parylene-C are polymers of interest for microelectronic and medical coating applications. Modifications for improved surface properties could make them even more useful in such applications. Parylene-N and parylene-C films were exposed to ultraviolet light in the presence of oxygen and analyzed with Rutherford backscattering spectrometry, secondary-ion mass spectroscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. This study shows that such exposure results in the formation of aldehyde and carboxylic acid groups near the surface of the films. At the maximum exposure dose, the concentration of oxygen in both parylene-N and parylene-C is about 13% at the film surface, and it decreases exponentially with increasing depth. Further modeling and optimization of this process would allow it to be used to tailor the surface concentration of oxygenated species in parylene for the optimization of adhesion and wettability or for the chemical binding of other moieties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1486–1496, 2003

A new method for determining Hamaker constants was examined for materials of interest in integrated circuit manufacture. An ultra-high vacuum atomic force microscope and an atomic force microscope operated in a nitrogen environment were used to measure the interaction forces between metals, dielectrics, and barriers used during the metalization portion of integrated circuit manufacturing. The materials studied included copper, silver, titanium nitride, silicon dioxide, poly(tetrafluoroethylene), and parylene-N. Spheres coated with a material of interest were mounted on AFM cantilevers and brought into contact with substrates of interest. The interaction force was measured as the cantilever approached the substrate but before the two surfaces came into contact, and also when the particle was pulled out of contact with the substrate. The Hamaker constant calculation from the contact measurement is based on an adhesion model that quantifies the contribution of geometrical, morphological and mechanical properties of materials to the measured adhesion force. Hamaker constants determined with this new approach were compared with values found by using the Derjaguin approximation for a sphere to describe the interaction force as the cantilever approaches the surface. Both approaches produced similar values for most of the systems studied, with variations of less than 10%.

The goal of this work was to evaluate the ability of photothermal induced resonance (PTIR) to measure the local infrared absorption spectra of crystalline organic drug nanoparticles embedded within solid matrices. Herein, the first reports of the chemical characterization of sub-100 nm organic crystals are described; infrared spectra of 90 nm griseofulvin particles were obtained, confirming the chemical resolution of PTIR beyond the diffraction limit. Additionally, particle size distributions via dynamic light scattering and PTIR image analysis were found to be similar, suggesting that the PTIR measurements are not significantly affected by inhomogeneous infrared absorptivity of this system. Thus as medical applications increasingly emphasize localized drug delivery via micro/nano-engineered structures, PTIR can be used to unambiguously chemically characterize drug formulations at these length scales.

A model was developed for the effect of van der Waals interactions between a rough, deformable, spherical colloid and a flat, smooth, hard surface in contact. The model demonstrates the significant effect of colloid roughness on removal force. Small changes in colloid roughness produce large changes in the predicted removal force. Several authors attribute discrepancies in the observed interaction force between particles and surfaces to colloid roughness, and our model supports their hypotheses. Experimental data documenting the force required to remove colloids of polystyrene latex from silica substrates in aqueous solution were collected during AFM studies of this system. When colloid roughness exists, as is the case in this work, our model bounds the observed removal force. The predicted range of removal forces is in better quantitative agreement with our removal force data than are forces predicted by classical DLVO theory. Copyright 2000 Academic Press.

Removal of platinum sidewall redepositions formed due to patterning of electrodes during reactive ion etching for an embedded dynamic random access memory project has been investigated. During etching of these devices, nonvolatile etch products commonly deposit onto the pattern sidewall. Removal of these residues without damaging other exposed materials is a challenging process. A mixture of argon and chlorine plasma was used to etch the platinum electrodes used in this study. Following the etching step the wafers were processed in an oxygen plasma (ashed) to remove the photoresist on the wafer. The effectiveness of various postash-cleaning methods was investigated. Results are presented for wafers that were heated at different temperatures for varying times in different ambients, wafers that were cleaned in aqueous hydrochloric acid of varying concentrations, and wafers that were cleaned in a 40 kHz ultrasonic bath in water, in aqueous hydrochloric acid, and in aqueous ammonium hydroxide. At the conditions studied, it was determined that dissolution of the residues was not the controlling removal mechanism. Rather, a combination of dissolution and physical displacement appeared to control the cleaning process. Specifically, the application of ultrasonic energy to baths of 6 M hydrochloric acid provided the best cleaning results.