A low-voltage pulsed electron beam has been constructed that demonstrates energy efficiency and enhances the overall polymerization of acrylic monomers when compared to traditional, continuous low-voltage electron beams. The novelty of this equipment and the need to evaluate different configurations and explore operating ranges required frequent and cost-effective dosimetry. Two types of dosimetry were used: electronic dosimetry, relying on the

The responses of viscoelastic solids indented by flat-ended cylindrical and spherical tip indenters are analyzed in this paper. The viscoelastic solid is a semi-infinite medium described by a standard three-element model. The theoretical relaxation and creep solutions are derived for a viscoelastic half-space using the method of functional equations. These solutions can apply to the responses of compressible as well as incompressible coatings to flat-ended cylindrical punch and spherical tip indentation. They establish a fundamental basis for probing mechanical properties of polymeric coatings with micro- and nanoindentation tests. To obtain the strain and stress distributions, an explicit finite difference method is employed to solve a viscoelastic indentation problem. The experimental creep and relaxation tests are conducted on both bulk polystyrene and polyurethane coatings. The viscoelastic properties are derived by fitting the theoretical solutions with the experimental data measured.

Misting of Newtonian liquids, in the film-split region of two counter rotating rigid and deformable cylinders was visualized with standard and high-speed cameras. Flow instabilities begin with ribbing and eventually lead to generation of air-borne droplets called mist. As speed was raised, a uniform film thickness evolved into one with ribs, which evolved into continuous sheets of liquid extending downstream of the gap between the cylinders. The edge of each sheet formed a rim whose two ends were attached to the ribs on the cylinders. Still images via high-speed photography revealed a new mechanism for mist generation: the sheets extended downstream, became unstable and ruptured to produce air-borne droplets. A droplet time-of-flight measurement technique quantified the effect of process settings (speed and speed ratio) and material properties (viscosity and surface tension) on droplet size, count, and mass concentration of mist.

Frequency responses to the slot die coating process is analyzed using empirical modal analysis to predict the effects of periodic process disturbances such as gap oscillation and variations in vacuum pressure, web velocity, and flow rate. A type of empirical modal analysis known as an experimental modal approach was used, and an oscillator basis model was assumed by using a linearized governing equation, and the coefficient of the basis model was determined by curve-fitting. By completing the process, we were able to decompose each mode, during which process it was found that the modes are of two types: a squeeze mode related to viscous characteristics and sinuous modes that are identical to capillary waves. Observation of the meniscus shapes of each mode revealed, in the third mode near the lip edge, significant fluctuations that can induce other coating defects. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 2268-2279, 2010

In order to avoid undesired effects from vortices in many industrial processes, it is important to know the set of operating parameters at which the flow does not have recirculation. The map of these conditions in the parameter space is called vortex-free operating window. Here, we propose an efficient way to construct such window automatically without expensively checking every possible flow states. The proposed technique is based on tracking a path in the parameter space at which the local kinematic condition at a stagnation point for vortex birth is satisfied. This multiparameter continuation is performed by solving an augmented Navier–Stokes system. In the augmented system, the birth condition and the governing equations was represented in Galerkin’s finite element context. We used the proposed method in two important coating flows with free surfaces: single-layer slot coating and forward roll coating.

Nanoporous, adhesive latex coatings and ink-jet deposited latex microstructures containing concentrated, viable, but nongrowing microorganisms may be useful smart coatings. When rehydrated, these bioactive coatings can be used for multi-step oxidations, reductions, as biosensors, in biofuel cells, or high intensity industrial biocatalysts. Engineering coating microstructure, preservation of microbe viability during drying at ambient temperature and the stability of these coatings following rehydration is investigated in 5 mu m to 75 mu m thick coatings of microbes concentrated 10(2) to 10(3)-fold on polyester, metals or electrode substrates. Nanoporosity is essential for preserving microbial viability in dry coatings and bioreactivity following rehydration. Non-toxic (low biocide or biocide-free) latex emulsions contain carbohydrate porogens which vitrify to arrest polymer particle coalescence during film formation generating nanopores. However, the molecular mechanism of how vitrified carbohydrates function as osmoprotectants and preserve microbial viability by formation of glasses in the pore space during film formation is unknown. Coating nanoporosity in hydrated films is estimated by tracer diffusivity and visualized by cryogenic-SEM. Emulsion composition, drying conditions and coating thickness

Hollow latex particles are used as white pigments for paints and paper coatings. In the coating dispersion, each hollow particle is filled with water. As the coating dries, water vacates the latex, leaving an air-filled void sized to scatter light (~0.5 μm) within each particle. Examinations of dried coatings reveal that hollow particles can collapse, decreasing their light scattering efficiency. Cryogenic scanning electron microscopy (cryoSEM) was used to characterize the microstructure of coatings containing hollow latex during drying. Images suggest latex voids empty after air invades into the coating interstitial space and collapse occurs late in the drying process. The effects of temperature (10–60°C), humidity (20–80%), and binder concentration (0–30 wt%) on particle collapse were also studied through SEM of dried coating surfaces. High drying temperature, high humidity, and low binder concentrations promoted collapse. For hollow latex particles with porous shell walls, temperature and humidity had little effect, whereas binder increased collapse. From these results, a theoretical model is proposed. During drying, diffusion of water from the particle creates a vacuum inside the latex. The vacuum is either relieved by nucleation of a gas bubble from the dissolved air in the water-filled particle or it causes the particle to collapse by buckling.

Nanoparticle films coated on smooth substrates by convective assembly from dilute suspensions in dip-coating configuration are known to have discrete film morphologies. Specifically, the film morphology is characterized by alternating bands of densely packed particles and bands of bare substrate. Convective assembly is a frontal film-growth process that occurs at the three-phase contact line formed by the substrate, the suspension in which it is submersed, and the surrounding air. The bands are parallel to this contact line and can be either monolayered or multilayered. Monolayered bands result whenever the substrate is withdrawn from the suspension at a rate too high for particles to assemble into a continuous film. We report a new insight to the mechanism behind this banding phenomenon, namely, that inter-band spacing is strongly influenced by the constituent particle size. We therefore propose a geometric model relating the inter-band spacing to the particle size. By making banded films with systematically varied particle sizes (silica/zeolite, 20 to 500 nm), we are able to quantitatively validate our model. Furthermore, the model correctly predicts that multilayered banded films have higher inter-band spacings than monolayered banded films comprising the same particles.

We simulate evaporation-driven self-assembly of colloidal crystals using an equivalent network model. Relationships between a regular hexagonally close-packed array of hard, monodisperse spheres, the associated pore space, and selectivity mechanisms for face-centered cubic microstructure propagation are described. By accounting for contact line rearrangement and evaporation at a series of exposed menisci, the equivalent network model describes creeping flow of solvent into and through a rigid colloidal crystal. Observations concerning colloidal crystal growth are interpreted in terms of the convective steering hypothesis, which posits that solvent flow into and through the pore space of the crystal may play a major role in colloidal self-assembly. Aspects of the convective steering and deposition of high-Peclet-number rigid spherical particles at a crystal boundary are inferred from spatially resolved solvent flow into the crystal. Gradients in local flow through boundary channels were predicted due to the channels' spatial distribution relative to a pinned free surface contact line. On the basis of a uniform solvent and particle flux as the criterion for stability of a particular growth plane, these network simulations suggest the stability of a declining {311} crystal interface, a symmetry plane which exclusively propagates fcc microstructure. Network simulations of alternate crystal planes suggest preferential growth front evolution to the declining {311} interface, in consistent agreement with the proposed stability mechanism for preferential fcc microstructure propagation in convective assembly.

This article explores the influence of functional acid monomers incorporated into polymer latex dispersions for their ability to effectively disperse TiO(2) pigment particles in flat paint applications. The functional acid monomer type (i.e., vinylphosphonic acid, acrylic acid, methacrylic acid, and itaconic acid), the partitioning of acid monomer in the polymer or aqueous phase during the emulsion polymerization and the role of the latex polymer particle size were investigated. The model latex dispersions were then formulated into their corresponding paints. Through the use of Cryogenic Scanning Electron Microscopy (Cryo-SEM), it is possible to qualitatively observe the TiO(2) efficiency of the paints in the wet state. Furthermore, these results can be correlated with measurable performance properties (i.e., abrasion resistance/tint strength) of the same paints in the dry state. Finally, the sole interaction of these tailored latices with TiO(2) itself is investigated through Cryo-SEM to gain a comparative insight into how these particles orient themselves with one another dependent on the functional acid monomer employed.

Starbursts are defects in wrinkled powder coatings wherein the typical random orientation of the wrinkles is disrupted. Instead, wrinkles orient radially around a central point creating a star-like pattern. The origin of the starburst defect was investigated by mechanical profilometry and elemental analysis by energy dispersive X-ray spectroscopy (EDS). Topographical measurements demonstrated that the centers of the stars almost always are at a higher elevation compared to their surroundings, suggesting the presence of non-dispersed extender particles or external impurities at the center. EDS analysis of the center of the stars confirmed the presence of external particles or impurities. Radial orientation of the wrinkles around the external particles can be explained by preferential pattern orientation due to directional stress relief.

Time-sectioning cryogenic scanning electron microscopy (cryo-SEM) was introduced in an earlier publication as a technique to directly visualize wet microstructures. In this work, the evolution of an asymmetric membrane microstructure of dry–wet cast (phase inversion) polysulfone solution coatings is methodically captured using cryo-SEM. The images show that the as-deposited, homogeneous coating (predecessor of the membrane) partially phase separates into a dispersion of droplets during the brief initial drying step, and then, on immersion in a coagulant, skins at the free surface and undergoes complete phase separation below, first by nucleation and growth, rapidly followed by partial coalescence into bicontinuous, open-celled structures. The phase-separated region is two-tiered consisting of an intermediate fine-scaled layer lying above a thicker and coarser layer. The membranes also display disproportionately large voids called macrovoids. Cryo-micrographs suggest that macrovoids in phase-separating coatings form due to a unique network instability triggered by successive tensile ruptures of the gelled polymer-rich network. In this wet cast process, a hypothesis is developed showing how (i) build-up of compressive pressure in pores and tensile stress in the network from overall swelling and local syneresis, (ii) vertical rupture (normal to substrate), (iii) stress localization, (iv) post-rupture relaxation and (v) plausible horizontal ruptures may cause this network instability and drive convective flows from adjacent pores into the growing void. Mathematical analysis of stress development and supporting cryo-micrographs of a dry cast process are also included in appendices.

Capillary pressure force and direct surface tension force are known to be sufficient though probably not necessary to drive the compaction stage of latex film formation. There is abundant evidence that van der Waals force can draw particles together progressively more around the perimeters of interparticle contacts, but their role in compaction remains unanswered. With the powerful technique of high-resolution cryogenic scanning electron microscopy (cryo-SEM), together with fast-freezing and freeze-drying followed by controlled annealing at temperatures below and around the nominal glass transition temperature, we have documented the role of van der Waals force in film formation in the water-free condition, i.e., with capillary pressure and surface tension forces absent. Results of imaging the freeze-dried and annealed coatings are fully consistent with the hypothesis that van der Waals force alone can compact a latex coating. The rate at which particles flatten and thus the coating compacts by annealing increases, as expected, with temperature and time. The results of rewetting tests of coatings annealed at various temperatures demonstrate that compacted coating is not necessarily coalesced, and that even full compaction of solid particles can be elastic, hence reversible, rather than viscoelastic or viscoplastic. Some of the results suggest that soluble ionic surfactant and oligomeric and grafted polymeric stabilizers at particle surfaces, collapse to undetectable dimensions during freeze-drying, yet reswell to detectable size during rewetting, if they have not dissolved into polymer particles during annealing.

Ceramic nanoparticle/monodisperse latex coatings with a nanoparticle-rich surface and a latex-rich body were created by depositing aqueous dispersions of monodisperse latex, approximately 550 nm in diameter, and nanosized ceramic particles onto substrates and drying. On the top surface of the dried coating, the latex particles are closely packed with nanoparticles uniformly occupying the interstitial spaces, and along the cross section, nanoparticles fill the spaces between the latex particles in the near surface region; a compacted latex structure, nearly devoid of nanoparticles, lies beneath. Cryogenic scanning electron microscopy images of partially dried coatings at successive drying stages reveal two important steps in forming this structure: top-down consolidation of latex particles and accumulation of nanoparticles in interstitial spaces among latex particles near the surface. A systematic study of the effect of processing conditions, including nanoparticle concentration, nanoparticle size, latex glass transition temperature, and drying conditions, on the final microstructure was carried out. The unique microstructure described above forms when the monodisperse latex is large enough to create pore channels for the transport of nanosized particles and the drying conditions favor "top-down" as opposed to "edge-in" drying.

The phase behavior of poly(ethylene oxide)−poly(butadiene) (PEO-PB) diblock copolymers mixed with water was studied using small-angle X-ray scattering (SAXS), cryogenic scanning electron microscopy (cryo-SEM), cryogenic transmission electron microscopy (cryo-TEM), and dynamic mechanical spectroscopy. Two sets of diblocks were synthesized by adding different lengths of PEO to hydroxy terminated PB with degrees of polymerization NPB = 46 and 170. Two-component mixtures were investigated as a function of block composition and copolymer molecular weight, between 1 and 100 wt % polymer content. Melt phase behavior is consistent with established theory and known experimental behavior for diblock copolymers. Various lyotropic liquid crystalline structures, notably lamellae (L), hexagonally packed cylinders (H), and spheres (S) arranged on cubic (body-centered cubic, face-centered cubic) lattices, were documented as a function of water content. At the higher molecular weights (NPB = 170), a random network phase (...

Silica nanoparticles with a narrow particle size distribution and controlled diameters of 10-20 nm are synthesized via hydrolysis and hydrothermal aging of tetraethylorthosilicate in an aqueous L-lysine solution. Cryo-transmission electron microscopy (cryo-TEM) reveals that the silica nanoparticles assemble to form close-packed nanoparticle crystals over short length scales on carbon-coated grids. Evaporative drying of the same sols results in nanoparticle stability and remarkable long-range facile ordering of the silica nanoparticles over scales greater than 10 microm. Whereas small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) discount the possibility of a core (silica)-shell (lysine) structure, the possibility remains for lysine occlusion within the silica nanoparticles and concomitant hydrogen bonding effects driving self-assembly. Facile ordering of the silica nanoparticles into multilayer and monolayer coatings over square-centimeter areas by evaporation-induced self-assembly is demonstrated using a novel dip-coating device.

Latex biocatalytic coatings containing ∼50% by volume of microorganisms stabilize, concentrate and preserve cell viability on surfaces at ambient temperature. Coatings can be formed on a variety of surfaces, delaminated to generate stand‐alone membranes or formulated as reactive inks for piezoelectric deposition of viable microbes. As the latex emulsion dries, cell preservation by partial desiccation occurs simultaneously with the formation of pores and adhesion to the substrate. The result is living cells permanently entrapped, surrounded by nanopores generated by partially coalesced polymer particles. Nanoporosity is essential for preserving microbial viability and coating reactivity. Cryo‐SEM methods have been developed to visualize hydrated coating microstructure, confocal microscopy and dispersible coating methods have been developed to quantify the activity of the entrapped cells, and FTIR methods are being developed to determine the structure of vitrified biomolecules within and surrounding the cells in dry coatings. Coating microstructure, stability and reactivity are investigated using small patch or strip coatings where bacteria are concentrated 10 2 ‐ to 10 3 ‐fold in 5–75 μm thick layers with pores formed by carbohydrate porogens. The carbohydrate porogens also function as osmoprotectants and are postulated to preserve microbial viability by formation of glasses inside the microbes during coat drying; however, the molecular mechanism of cell preservation by latex coatings is not known. Emerging applications include coatings for multistep oxidations, photoreactive coatings, stabilization of hyperthermophiles, environmental biosensors, microbial fuel cells, as reaction zones in microfluidic devices, or as very high intensity (>100 g·L ‐1 coating volume·h ‐1 ) industrial or environmental biocatalysts. We anticipate expanded use of nanoporous adhesive coatings for prokaryotic and eukaryotic cell preservation at ambient temperature and the design of highly reactive “living” paints and inks.