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High-fidelity aerodynamic analysis has been demonstrated for mean performance and unsteady dynamics in a sCO2 compressor designed by Hanwha Power Systems Americas for a 10 MWe Concentrating Solar Power plant. Simulations were performed with CRUNCH CFD® software tool that was matured to accurately model near critical real fluid effects in sCO2. Pre-test predictions for mean performance were validated with test data collected later. Performance predictions were accurate and captured sensitivity of the efficiency to inlet temperature of CO2 as well as steep drop-off at high flow rates due to condensation in the inlet throat. Detailed analysis was performed to understand the source of these performance losses at near critical conditions. Unsteady dynamic effects in the compressor at off-design conditions were also identified and quantified. In particular a system wide “condensation surge” condition was detected at high flow coefficients that results in large amplitude pulsations with accompanying mass flow fluctuations at low frequencies and has potential to cause damage in closed loop systems.

Seven copolymers of maleic anhydride were hydrolyzed and impregnated into sheets of bleached softwood kraft pulps to enhance market pulp properties. Drying the impregnated pulps at 120 °C for 10 minutes, attached to the fiber surfaces up 0.16 meq of carboxyl groups per gram of dry pulp. Heating the impregnated pulps regenerates succinic anhydride moieties which can then form stable ester linkages with cellulosic hydroxyls. The pH of the impregnation solution is important. Impregnation with solutions at pH 8 gave polymer contents without repulping issues. By contrast, impregnation at pH 4 gave dried pulp sheets that were too strong to enable repulping in a paper mill. Although most of the seven copolymers were fixed to cellulose, poly(ethylene-alt-maleic anhydride) gave the highest density of carboxyl groups. The simplicity of waterborne polymers and mild drying temperatures suggests maleic anhydride copolymer treatment could be implemented in a conventional market pulp mill.

Heating bleached kraft pulps treated with poly(ethylene-alt-maleic acid) (PEMAc) can lead to high yields of carboxylated polymer grafted to fibers. However, in many cases, the cured, dry pulp cannot be effectively repulped (redispersed in water) because the wet strength is too high. Impregnation with PEMAc solutions at pH 4 followed by high temperature (120-180 °C), catalyst-free curing for short times can give fixation yields >85% while maintaining repulpability. The combination of high fixation yields with low wet strength is possible because the extent of curing required for high grafting yields is less than the curing requirement for high wet strength. Two challenges in moving this technology to practicable applications are (1) identifying the optimum laboratory pulp curing conditions and (2) translating laboratory curing conditions to industrial processes. A modeling tool was developed to meet these challenges. The model is based on the observation that for curing conditions giving high fixation yields the wet tensile indices of grafted pulp sheets showed a power-law dependence on the βΓ product where β is the conversion of the succinic acid moieties in PEMAc to the corresponding succinic anhydride groups in the curing step and Γ is the amount of polymer applied to the pulp. For two PEMAc molecular weights and two pulp types, the power-law slopes were 0.6; however, the pre-exponential terms depended upon the specific polymer and pulp type combination. We propose that the relationships between the wet tensile index and βΓ, from polymer-treated, laboratory pulp handsheets, can be used to predict if proposed curing conditions for larger-scale processes will produce a repulpable product.

Development and commercial acceptance of sCO2 Brayton cycles for power generation applications are growing rapidly as they offer performance advantages over other cycles. To maximize the cycle performance, the compressors are designed to operate near the critical point of the working fluid. At the critical point the fluid properties change rapidly with variations in inlet conditions. This makes it challenging to both accurately predict the performance and guarantee the operability of the compressor, as the behavior is affected by these slight variations in inlet conditions. A full scale 1st stage main compressor for a 10MWe-Class recompression Brayton cycle was built and tested to validate performance and operability in this unique operating range. The compressor was tested in a laboratory environment with additional instrumentation, beyond what is required by PTC-10, to minimize the uncertainty in the measured performance. Complete constant speed characteristics were collected at multiple supercritical points, operating at constant inlet conditions for each speed line covering a range of compressor inlet densities from 400 to 600 kg/m3. Variations in the compressor stage efficiency and choke margin were observed, and the overall operability and stability of the compressor in response to changes in operating condition were also monitored. The compressor was shown to have excellent performance that closely matched the original design prediction. The performance at various inlet conditions showed minimal change in isentropic head coefficient at the design flow, but did show some variation in efficiency and choke margin across the map. These changes in performance were observed to be minimal, and did not affect the stable operation of the compressor. The results demonstrate that a commercial scale sCO2 compressor can operate near the critical point and achieve the high levels of performance and stability required for power generation applications.

Various supercritical carbon dioxide (sCO2) power cycles are an emerging bottoming cycle technology for gas turbine waste heat recovery with potential advantages relative to Organic Rankine Cycle (ORC) systems, including improved performance, compactness, improved economics, nonhazardous working fluids, and faster ramp capabilities. This work compares a waste heat recovery system based on an integrally geared compander in a sCO2 preheat cycle configuration with split recuperator with a recuperated ORC in the literature. The integrally geared system is comprised of an 1800 rpm generator with high-pressure and low-pressure pinions splitting a two-stage compressor and expander. Cycle constraints and design drivers, and optimization of the sCO2 system are described, along with current technology readiness and full-pressure full-temperature opera ting experience of the various components including compressors, expanders, heat exchangers, and other system components. Both cycles are paired with a commercial 15 MW gas turbine, and the resulting system costs, performance, and other attributes are presented. The cycles are compared with an cold-side temperature of 35 °C, showing an ORC system output of 5066 kW and an sCO2 system output of 5660 kW, i.e. an 11.7 % performance benefit for sCO2. Additionally, cost and size requirements and costs for the sCO2 and ORC-based systems are compared, indicating comparable nominal costs for both systems and a potentially lower cost for sCO2 systems, particularly when an indirect heat transfer loop is needed.

The chlorophyll derivative copper chlorophyllin and related chlorins have promise as environmentally friendly agricultural chemicals, however, spray application is hindered by the propensity of dried spray deposits to wash off leaf surfaces during rain or irrigation. Hypothesis Polyelectrolyte complexes formed between anionic carboxymethyl cellulose and cationic polyamidoamine-epichlorohydrin can prevent the release of copper chlorophyllin from dried spray deposits on leaf surfaces when exposed to water. Experiments Sessile drops on parafilm and containing polyelectrolyte complex and copper chlorophyllin or Brilliant Sulfaflavine, an anionic water-soluble dye, were dried to form deposits that were physical models for crop spray drop deposits on hydrophobic leaf surfaces. Larger buffer drops were placed on the dried deposits and the release of copper chlorophyllin or the dye were measured. Findings Copper chlorophyllin showed some immediate (burst) release upon exposure to buffer whereas the remainder was immobilized on the parafilm. By contrast, Brilliant Sulfaflavine displayed rapid release following square root time dependence, typical of a diffusion-controlled process. The unusual behavior of copper chlorophyllin is attributed to the presence of CuChl nanoparticles when dispersed in water. The nanoparticles are encased in the polyelectrolyte complex that adheres to parafilm. The fraction of the added copper chlorophyllin lost in the burst release can be controlled by varying the polyelectrolyte complex composition and concentration.

Fiber-fiber adhesion, called “bonding” in the old paper physics literature, is a critical component of the overall strength of dry paper. With freshly formed very wet pulp fiber webs, all evidence suggests there are no fiber-fiber crossings with significant adhesive joint strength. With water removal, a point will be reached where fiber-fiber adhesion starts to contribute to the overall wet-web strength. The literature reveals very few examples of polymers that increase fiber-fiber joint strength in freshly formed webs. Here, we summarize the literature and explain why it is so difficult to promote fiber-fiber wet adhesion with polymers. Nevertheless, ongoing research in areas as diverse as tissue engineering scaffolds and biomimetic adhe-sives gives clues to future developments. Advances in paper machine engineering have lessened the importance of wet-web strength. By contrast, a critical issue in many of the evolving nanocellulose technologies is the strength of objects first formed by aqueous processing, the green strength—the strength of wet bodies before drying. For exam-ple, 3-D printed nanocellulose objects and ultralow density cellulosic aerogels can be destroyed by capillary forces during drying. There is a need for adhesives that strengthen freshly formed, wet lignocellulosic joints.

The dramatic loss of strength upon exposure to water is one of the challenges preventing the widespread substitution of plastic packaging with paper and paperboard. Although treatment with conventional wet strength resins and other adhesive polymers can strengthen wet paper, it is at the expense of green credentials, including easy recycling or rapid composting. The goal of this work was to demonstrate the adhesive requirements for strong, wet cellulose-cellulose joints that can be recycled easily because the joint strength can be destroyed by the presence of a weak reducing agent. Cellulose membrane surfaces were first treated with a bound layer of carboxymethyl cellulose, modified to have covalently tethered hydrazide groups. Joints were fabricated by laminating two hydrazide-modified membranes with a polymeric adhesive bearing aldehyde functionality. Aldehydes spontaneously condense with hydrazide to give hydrazone bonds. When the adhesive was oxidized dextran, the wet laminates had an intermediate strength. Upon exposure to a reducing agent, the joint strength was reduced to nearly zero because every hydrazone moiety connecting two cellulose surfaces included a cleavable disulfide linkage. By contrast, glyoxalated cationic polyacrylamide gave very strong wet joints. However, the wet adhesion was dominated by polyelectrolyte complexation, and the presence of hydrazone linkages had little influence on the wet adhesion. We conclude that robust joint degradability will require cleavable linkages in the adhesive backbone while minimizing polyelectrolyte complexation.

Traditional materials for lateral flow devices (cellulose, nitrocellulose) are typically produced in large batches with relatively thick membranes and a uniform pore size, making it challenging to ...

The wet strength of cellulose-cellulose joints, reinforced with PAE-loaded microgels, was decreased by nearly a factor of two when the labile disulfide crosslinks on the supporting microgels were exposed to a reducing agent. The supporting microgels were temperature and pH sensitive poly(N-isopropylmethacrylamide-co-acrylic acid) microgels, prepared with a disulfide crosslinker. The level of PAE loading increased with the microgel carboxyl content. This work illustrates a new approach to increasing the recyclability and compostability of wet-strength papers made with PAE wet-strength resin.

The conditions are elucidated whereby strong adhesive joints between two wet cellulose surfaces can be achieved with a polyelectrolyte adhesive. Adhesion results were obtained with wet, TEMPO oxidized, regenerated cellulose membranes that were laminated with polyvinylamine (PVAm) adhesive. Wet adhesion was determined as the 90° wet-peel delamination force. Aldehyde groups on the oxidized cellulose form imine and aminal covalent linkages with PVAm, covalently grafting PVAm onto the cellulose surfaces. From these results we conclude that the adhesive polymer must be covalently grafted to the cellulose surface—physically adsorbed polymers give weak polymer/cellulose interfaces in water. There are two cases which are remarkably different—never-dried joints versus dried and rewetted joints, we call once-dried. The strength of never-dried joints is important in paper manufacturing and is likely to be critical in the manufacture of the new nanocellulose composites and foams described in the recent literature. Only one adhesive joint architecture gave significant never-dried strength—joints with only a monolayer of polyelectrolyte adhesive sandwiched between two cellulose surfaces. We propose that polymeric chains are simultaneously covalently grafted onto both cellulose surfaces. In the usual case of bringing together two polymer coated cellulose surfaces in water, there is no never-dried wet adhesion because electrosteric stabilization inhibits significant molecular contact between opposing adsorbed polymers. By contrast, high once-dried wet adhesion is easier to achieve because polymer–polymer molecular contact is promoted by water removal. The requirements for once-dried wet adhesion are polyelectrolyte grafting to cellulose and cohesion within polymer layers, either due to covalent crosslinking, or attractive physical interactions.

Poly(ethylene-alt-maleic acid), PEMAc, is a linear polymer that, along with its isomer polyacrylic acid, has the highest carboxylic acid content of any polymer. The goal of this work was to elucidate the mechanisms that control the amount of PEMAc that is permanently fixed on pulp fibers after the impregnation of dry pulp with a dilute PEMAc solution followed by drying/heating (curing). Two mechanisms by which PEMAc is fixed to cellulose fibers were discovered, chemical, and physical fixation. With room temperature drying only physical fixation is operative. Evidence supports the explanation that physical fixation is a consequence of the slow swelling and dissolution of thick dried PEMAc deposits on fiber surfaces. Chemical fixation includes grafting to cellulose plus enhanced cohesion within thick PEMAc layers, possibly due to interchain crosslinking. The pH of the PEMAc impregnation solution determines the fixation mechanism for curing temperatures above 100 o C. Physical fixation dominates when pH > 8 whereas chemical fixation dominates for impregnation pH values < 7, suggesting the curing reactions require partial or complete protonation of the succinic acid moieties. The yield of impregnated polymer fixed to the fibers after washing depends upon the fixation mechanism. When chemical fixation dominates, the yields for low and high molecular weight PEMAc doses less than 0.1 meq/g (6.3 kg PEMA/tonne dry pulp) were close to or equaled 100%. By contrast, when the primary mechanism is physical fixation, yields are ~50% for high molecular weight PEMAc and 0-20% for low MW PEMAc. These results show that high PEMAc fixation yields can be achieved under curing conditions that could be implemented in pulp drying machines producing dry market pulp.

Protein A affinity chromatography, which is the standard method for monoclonal antibodies (mAbs) purification is expensive and involves elution at acidic pH, which could degrade the mAb. Moreover, it cannot be used to fractionate charge variants or to remove mAb aggregates. In this study, we examine the purification of Trastuzumab by cation-exchange z2 laterally-fed membrane chromatography (or z2LFMC). It has been shown that z2LFMC is suitable for carrying out high-speed, high-resolution protein purification. The results discussed in this paper demonstrate that the purity of Trastuzumab obtained by the z2LFMC process was comparable to that obtained by protein A chromatography (i.e., >95% with both methods), while the mAb recovery was significantly greater with z2LFMC (90.4% as opposed to 81.7%). Also, the z2LFMC process was faster, did not require acidic pH conditions for elution, and the mAb was eluted in a smaller pool (2.24 bed volumes as opposed to 2.74 bed volumes). The mAb productivity obtained with the z2LFMC process was more than 3 times higher than that obtained with the column-based purification processes. The z2LFMC device is significantly cheaper than its equivalent protein A affinity column, and earlier studies have shown to be suitable for separating mAb charge variants and aggregates. Therefore, the z2LFMC process could potentially be explored as a cheaper and more efficient alternative to protein A affinity chromatography.

The properties of dried deposits formed by placing drops of a commercial turf grass fungicide spray formulation on smooth, waxy PARAFILM® M surfaces were measured as functions of formulation variables. The deposit structure reveals the extent to which dispersed active ingredient particles are bound to oil droplets in agricultural spray dispersions, before drying. The dilute spray dispersion (herein called Green Emulsion) was a suspoemulsion, which is a mixed dispersion of large (2–50 μm) mineral oil drops and small (∼430 nm) polychlorinated Cu (II) phthalocyanine (PG7) pigments, also known as Green 7. The distribution of PG7 pigment in the dried spray drop deposit depended upon the partitioning of PG particles in the suspension before drying. Individually dispersed PG7 particles in the aqueous phase mainly ended up in the annulus (coffee ring), whereas PG7 particles adsorbed on the oil emulsion droplets ended up as a central oily deposit (the dome). After most of the water evaporated, some oil migrated beyond the dome and slowly beyond the annulus. Increasing the oil-soluble surfactant concentration inhibited PG7 binding to the oil/water interface, giving a very small dome area and a wide annulus after drying. The deposit structure is sensitive to the mixing intensity when spray concentrates are diluted in a mix-tank. Increased intensity of mixing the suspoemulsion gives smaller oil droplets, more PG7 bound to the oil/water interface and a smaller dome. The ASTM E2044 “Standard Test Method for Spreading of Liquid Agricultural Spray Mixtures” involves placing a drop of crop spray dispersion on PARAFILM® and measuring the dimensions of the resulting sessile drop. This work demonstrates that allowing the sessile drops on PARAFILM® to dry and analyzing the resulting deposit structure gives a direct measure of the extent to which active ingredient particles, initially dispersed in water, are transferred on or into oil drops in suspoemulsions.

We propose that a testing procedure we call wet-peel significantly augments conventional wet paper testing when comparing wet-strength resin efficacy or the influence wood pulp fiber surface treatments on wet paper strength. A thin layer of wet-strength resin is sandwiched between a pair of thin, wet regenerated cellulose membranes to form a laminate, which is a physical model for fiber-fiber joints in paper. In the wet-peel method, the ninety-degree wet-delamination force gives a direct measure of adhesion in the wet cellulose-cellulose joint. Wet-peel measurements offer: 1) comparisons of wet-strength polymers at the same content of polymer in the laminate joint without the influences of varying fines contents, formation or paper density; 2) measurements of both the wet-strength of cured, dried joints, and the strength of never-dried joints (i. e. analogous to wet-web strength); 3) demonstrations of the influence of fiber surface chemistry modifications including oxidation and the presence of firmly bound polymers; and, 4) the evaluation of more exotic joint structures including layer-by-layer assemblies, microgels and colloidal polyelectrolyte complexes.

The inkjet printing of biocompatible silica sols has gained popularity, both for biosensor production and development of holographic devices. However, there still remain significant issues related to premature clogging of inkjet printheads when printing aqueous silica sols. To better understand the causes of clogging of piezoelectric inkjet nozzles, printing studies were coupled with studies of colloidal stability along with silica deposition on surfaces, both under normal flow and piezoelectrically driven oscillating flow through an inkjet cartridge. Our studies show that clogging most likely results from deposition of silica colloids onto the internal surfaces of the printhead, followed by displacement of micron-sized pieces of the deposited material upon piezoelectric deformation of the printhead surface, which then block the nozzles of the printhead. Based on this result, we formulated a low-pH sol derived from sodium silicate and evaluated its colloidal stability, binding to silica surfaces and resistance to clogging of inkjet nozzles under normal and voltage-driven oscillating flow. We show that silica sols with a pH of 3.1 provide optimal printing behavior while allowing reproducible printing of spatially controlled silica patterns on paper to produce enzyme-based biosensing devices.

Demonstrated is a new method for stamping nanoscale polymeric patches (footprints) onto surfaces. Cationic core-shell nanoparticles with hard polystyrene (PS) cores and soft poly( n -butyl methacrylate) (PB) shells spontaneously adsorbed on glass beads suspended in water. With mixing, the bead-bead collisions removed the adsorbed polymer particles, leaving PB footprints. The footprint density on the bead surfaces mirrored the initial density of adsorbed nanoparticles. The footprint thicknesses, measured by AFM, were 10–20 nm. Our motivation for this research was developing nanoparticles that promoted glass bead flotation (i.e. nanoparticle flotation collectors). Whereas the adsorbed nanoparticles did promote flotation, glass beads coated only with footprints gave poor flotation recoveries in spite of the hydrophobic nature of PB. We propose that footprint-coated spherical bead surfaces are too smooth for efficient bead attachment to air bubbles. Janus particles with one hard PS lobe and a soft PB lobe were more strongly adhering and more effective at promoting bead flotation, presumably because of high bead/nanoparticle adhesion. Beyond the flotation application, footprint formation could be a simple approach to modifying dispersed particle surfaces in a wide range of applications.

Demonstrated is a new approach to cellulose fiber-based materials that are strong when wet, yet can be recycled after exposure to a weak reducing agent. Poly(N-isopropylacrylamide-co-acrylic acid) microgels were transformed into wet cellulose adhesives by incorporation of hydrazide groups that can form hydrazone linkages to oxidized cellulose. Reductant responsivity was obtained by introducing cleavable disulfide linkages, either in the chains tethering the adhesive hydrazide groups, or by using disulfide cross-links in the microgels. Both types of disulfide derivatives gave about 75% reduction in cellulose wet adhesion after exposure to a reductant. Truly sustainable wood-fiber replacements for plastic packaging must be insensitive to water while being fully recyclable; this work demonstrates two routes to reversible wet cellulose adhesives, facilitating recycling.

An environmentally friendly procedure for the surface modification of cellulose nanocrystals (CNCs) in water is presented. Tannic acid (TA), a plant polyphenol, acts as the primer when mixed with CNCs in suspension, which are then reacted with decylamine (DA), the hydrophobe. Schiff base formation/Michael-type addition covalently attaches primary amines with long alkyl tails to CNC-TA, increasing the particle hydrophobicity (contact angle shift from 21 to 74°). After modification, the CNC-TA-DA particles in the water phase separate, allowing for easy collection of modified material. The dried product is readily redispersible in toluene and other organic solvents, as demonstrated by turbidity measurements, dynamic light scattering, optical microscopy, and liquid crystal self-assembly behavior. Electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, solid-state 13C NMR, and X-ray diffraction support the successful surface modification and indicate that CNC particle mo...

Layer-by-layer (LbL) assemblies of polyvinylamine with grafted TEMPO moieties (PVAm-T) with sodium polystyrenesulfonate (PSS) were prepared on gold-sulfonate surfaces, and the redox properties were measured by cyclic voltammetry. LbL compositions were probed by quartz crystal microbalance (wet) and ellipsometric (dry) film measurements. Approximately 30% of the TEMPO moieties in the LbL assemblies were redox-active when the total TEMPO coverage was varied up to 6 μmol/m2, by either varying the TEMPO content in PVAm-T or by varying the number of LbL bilayers. Three non-redox-active PVAm/PSS blocking bilayers were required to prevent the electrode from oxidizing PVAm-T in the exterior LbL layer. This suggests significant intermixing between the layers in the LbL film. In addition to contributing to the small but growing body of work on redox polymers based on grafted TEMPO, this work serves as a reference point for understanding the redox properties of colloidal PVAm-T-laccase complexes in future work.

Piezoelectric inkjet printing is susceptible to printhead clogging when printing with inks that contain dispersed particles. This paper investigates the mechanisms by which 28-530 nm nanoparticle dispersions induce printhead clogging without forming large aggregates or thick deposited layers on printhead surfaces. Printing experiments were combined with nanoparticle deposition studies and with experiments where inks were pumped through printheads at a constant flow rate with a syringe pump. Submonolayer coverages of hydrophobic cationic polystyrene nanoparticles adhering to printhead surfaces promote rapid clogging by trapped air that enters from the nozzle opening. We propose that the deposited particles distort the shape of the ink/air meniscus, possibly causing air entrainment, and promote air bubble adhesion to the interior printhead surfaces. The printer's purge-blot cleaning procedure removes air clogs, but the clogs quickly reform when printing is resumed because the adsorbed nanoparticles are not removed by the cleaning procedure. Nondepositing anionic hydrophobic nanoparticles cause much less clogging, possibly because of filtration of trace large aggregates. Colloidal stability is a necessary but not sufficient criterion for ink dispersions; the ink particles must not adsorb onto the printhead surfaces. Thus, alternate surface chemistries for the printhead and ink particle surfaces may be required to print hydrophobic ink materials.

Forming an adhesive joint between two wet cellulose surfaces before a drying step is important when manufacturing paper, foams, aerogels, other novel materials from wood pulp fibers, and various types of nanocellulose. This paper reviews the literature with an emphasis on the role of adhesive polymers on wet cellulose adhesion. Linkages between the organization of adhesives between the bonded surfaces and the strength of joints are emphasized. Relevant adhesion results from the surface forces apparatus, colloidal probe atomic force microscopy, paper wet-web strength, and wet-peeling of laminated regenerated cellulose membranes are considered.

Cationic polystyrene-core-poly(n-butyl methacrylate)-shell (PS–PB) nanoparticles perform as flotation collectors as they spontaneously adsorb onto 43 μm glass beads in water, promoting glass bead attachment to air bubbles. Under our flotation conditions at room temperature, polystyrene is a hard plastic, whereas, with glass transition near room temperature, poly(n-butyl methacrylate) is a soft polymer. Colloidal probe atomic force microscopy measurements revealed that the pull-off forces and the work of adhesion of PS–PB nanoparticles to glass were significantly higher than observed with harder PS particles. Glass bead recovery in laboratory flotation experiments increased significantly with thickness of the soft PB shells on the PB–PS core/shell nanoparticles. Ninety-two nm Janus particles consisting of one PS and one PB lobe were also very effective collectors. We propose that high nanoparticle/glass bead adhesion minimizes nanoparticle removal by bead/bead collisions (nanoscale ball milling) during mix...

A library of 32 polystyrene copolymer latexes, with diameters ranging between 53 and 387 nm, was used to develop and demonstrate a high-throughput assay using a 96-well microplate platform to measure critical coagulation concentrations, a measure of colloidal stability. The most robust assay involved an automated centrifugation–decantation step to remove latex aggregates before absorbance measurements, eliminating aggregate interference with optical measurements made through the base of the multiwell plates. For smaller nanoparticles (diameter

Many biodetection systems employ labile enzymes and substrates that need special care, making it hard to routinely use them for point-of-care or field applications. In this work we provide a simple solution to this challenging problem through the creation of all-inclusive pullulan assay tablets. The proposed tablet system not only enhances the long-term stability of both enzymes and organic substrates, but also simplifies the assay procedure. The enhanced stability is attributed to two factors: the restriction of the molecular motion of proteins and impermeability to molecular oxygen afforded by the tables. These tablets dissolve rapidly upon addition to testing samples, making the test very easy to perform. Using the ATP-detecting luciferase–luciferin system as an example, we show that the tablet-based assay can achieve highly sensitive detection of ATP in biological samples and that the activity of the assay tablets remains unchanged for over a month at room temperature.

Successful implementation of sCO2 power cycles requires high compressor efficiency at both the design-point and over a wide operating range in order to maximize cycle power output and maintain stable operation over a wide range of transient and part-load operating conditions. This requirement is particularly true for air-cooled cycles where compressor inlet density is a strong function of inlet temperature that is subject to daily and seasonal variations as well as transient events. In order to meet these requirements, a novel centrifugal compressor stage design was developed that incorporates multiple novel range extension features, including a passive recirculating casing treatment and semi-open impeller design. This design, presented and analyzed for CO2 operation in a previous paper, was fabricated via direct metal laser sintering and tested in an open-loop test rig in order to validate simulation results and the effectiveness of the casing treatment configuration. Predicted performance curves in air and CO2 conditions are compared, resulting in a reduced diffuser width requirement for the air test in order to match design velocities and demonstrate the casing treatment. Test results show that the casing treatment performance generally matched CFD predictions, demonstrating an operating range of 69% and efficiency above air predictions across the entire map. The casing treatment configuration demonstrated improvements over the solid wall configuration in stage performance and flow characteristics at low flows, resulting in an effective 14% increase in operating range with a 0.5-point efficiency penalty. The test results are also compared to a traditional fully shrouded impeller with the same flow coefficient and similar head coefficient, showing a 42% range improvement over traditional designs.

In this study, a paper-based point-of-care (POC) colorimetric biosensor was developed for the detection of lactate dehydrogenase in serum using a nonporous, oxygen impermeable reversibly gelling polysaccharide material based on pullulan. The pullulan could be printed onto paper surfaces along with all required assay reagents, providing a means for high-stability immobilization of all reagents on paper. Serum containing lactate dehydrogenase (LDH) was directly spotted on to the pullulan-coated bioactive paper and provided quantitative colorimetric data that was comparable to that obtained with a conventional plate-reader method. The paper strip was found to be highly stable and could be stored at 4 °C for at least 10 weeks with no loss in performance, as compared to a complete loss in performance within 1 day when the reagents were printed without the stabilizing polysaccharide. The ease of fabrication coupled with the high stability of the printed reagents provides a facile platform for easily manufactured POC sensors.

The effect of water-soluble polymers on the properties of Pickering emulsions stabilized by cellulose nanocrystals (CNCs) was investigated. Pretreatment of CNCs with excess adsorbing polymer, hydroxyethyl cellulose (HEC) or methyl cellulose (MC), gave smaller and more stable dodecane-in-water emulsion droplets compared to either polymer or CNCs alone, i.e., synergistic stabilization. By contrast, dextran, which does not adsorb on CNCs, gave unstable emulsions, with or without CNCs. CNCs with HEC or MC produced emulsions that showed no significant creaming or phase separation over several months. Interfacial tension, quartz crystal microbalance and confocal laser scanning microscopy measurements indicate that both HEC and MC are surface active and adsorb onto CNCs. 75% of the oil–water interface is covered by CNC particles coated with HEC or MC and the remaining interface is stabilized by HEC or MC chains not bound to cellulose. Viscoelastic emulsion gels were also produced by adding excess MC to the CNC-H...

Polystyrene nanoparticles can promote froth flotation of mineral particles if the nanoparticles are sufficiently hydrophobic and are colloidally stable in the high ionic strength solutions typical of commercial flotation operations. A library of 80 unique polystyrene nanoparticle types was prepared with click chemistry and used to determine if particles that were sufficiently hydrophilic to be colloidally stable in high ionic strength and high pH solutions, were also capable of promoting flotation. The conflicting requirements of colloidal stability and hydrophobicity can be achieved in 9 mM sodium carbonate, a very challenging environment. Instead of testing all 80 samples with laborious flotation testing, automated assays measuring colloid stability and nanoparticle hydrophobicity were employed. The colloid stability assay measured the critical coagulation concentrations (CCC). Nanoparticle hydrophobicity was characterized by water contact angle, measurements (CA). A smaller cohort of the most promising nanoparticle candidates for detailed flotation testing were identified by mapping nanoparticle properties on the CA versus CCC plain – a “Flotation Domain Diagram”. We believe that this work was the first time that combinatorial synthesis and high throughput screening have been used in the development of flotation chemicals. Finally, based on the accumulated evidence, effective nanoparticle flotation collectors are likely to be ∼50 nm in diameter, with a soft hydrophobic polymer shell and with surface functional group densities in the order of magnitude of 0.1 nm−2.

The structure and electrochemical properties of adsorbed complexes based on mixtures of polyvinylamine-g-TEMPO (PVAm-T) and laccase were related to the ability of the adsorbed complexes to oxidize cellulose. PVAm-T10 with 10% of the amines bearing TEMPO moieties (i.e., DS = 10%), adsorbed onto gold sulfonate EQCM-D sensor surfaces giving a hydrogel film that was 7 nm thick, 89% water, and encasing laccase (200 mM) and TEMPO moieties (33 mM). For DS values10%, all of the TEMPOs in the hydrogel film were redox-active in that they could be oxidized by the electrode. With hydrogel layers made with lower-DS PVAm-Ts, only about half of the TEMPOs were redox-active; 10% DS appears to be a percolation threshold for complete TEMPO-to-TEMPO electron transport. In parallel experiments with hydrogel complexes adsorbed onto regenerated cellulose films, the aldehyde concentrations increased monotonically with the density of redox-active TEMPO moieties in the adsorbed hydrogel. The maximum density of aldehydes was 0.24 μmol/m

In order to maintain viability as a future power-generating technology, concentrating solar power (CSP) must reduce its levelized cost of electricity (LCOE). The cost of CSP is assessed with the System Advisor Model (SAM) from the National Renewable Energy Laboratory (NREL). The performance of an integrally geared compressor-expander recuperated recompression cycle with supercritical carbon dioxide (sCO2) as the working fluid is modeled. A comparison of the cycle model to the integrated SAM cycle performance is made. The cycle model incorporates innovative cycle control methods to improve the range of efficiency, including inventory control. The SAM model is modified to accommodate the predicted cycle performance. The ultimate goal of minimizing the LCOE is targeted through multiple approaches, including the cost of the power block, the impact of system scale, the sizing of the thermal system relative to the power block system, the operating approach for changes in ambient temperature and availability of sunlight. Through reduced power block cost and a detailed cycle model, the LCOE is modeled to be 5.98 ȼ/kWh, achieving targeted techno-economic performance. The LCOE of the CSP system is compared to the cost of hybrid solar and fossil-fired systems. An analysis is made on the efficacy of a fossil backup system with CSP and how that relates to potential future costs of carbon dioxide emissions.

This paper presents the selection of a system configuration and off-design control method for an integrally geared compander based on cycle modeling and optimization. The goal of the cycle modeling was to determine a cycle configuration that would reach an efficiency of 50% at design conditions and to optimize off-design control to maintain high efficiencies. The compander is being developed for use in a concentrated solar power supercritical carbon dioxide power plant with expected turbine inlet temperatures of 705°C and utilizing dry cooling leading to compressor inlet temperature varying between 35°C and 55°C. The compander is unique as it consists of eight turbomachinery stages on four pinions all being driven by a single bull gear. The separate stages offer the opportunity to consider a variety of flow splits and cycle configurations including intercooling and multiple stages of reheat. Cycle modeling was conducted in two stages: on-design and off-design. On-design modeling was simulated with all components operating at their design point. This was used to compare the performance of different cycle configurations and design temperatures. Off-design modeling was then performed to investigate the temperature dependence of the cycle efficiency and power output and to develop a control strategy. Strategies considered and discussed include: turbine bypass, compressor recycle, inlet guide vanes, and inventory control. To determine the best operating conditions for each configuration and control strategy, a genetic algorithm was implemented to optimize the cycle performance across the range of operating temperatures being considered. The final selection of cycle configuration, design temperature and control strategy is also presented.

Supercritical carbon dioxide (sCO2) power cycles require high compressor efficiency at both the design-point and over a wide operating range. Increasing the compressor efficiency and range helps maximize the power output of the cycle and allows operation over a broader range of transient and part-load operating conditions. For sCO2 cycles operating with compressor inlets near the critical point, large variations in fluid properties are possible with small changes in temperature or pressure. This leads to particular challenges for air-cooled cycles where compressor inlet temperature and associated fluid density are subject to daily and seasonal variations as well as transient events. Design and off-design operating requirements for a wide-range compressor impeller are presented where the impeller is implemented on an integrally-geared compressor-expander (IGC) concept for a high temperature sCO2 recompression cycle. In order to satisfy the range and efficiency requirements of the cycle, a novel compressor stage design incorporating a semi-open impeller concept with a passive recirculating casing treatment is presented that mitigates inducer stall and extends the low flow operating range. The stage design also incorporates splitter blades and a vaneless diffuser to maximize efficiency and operating range. These advanced impeller design features are enabled through the use of direct metal laser sintering (DMLS) manufacturing. The resulting design increases the range from 45% to 73% relative to a conventional closed impeller design while maintaining high design point efficiency.

Flotation of 43μm diameter, hydrophilic glass beads with hydrophobic cationic polystyrene nanoparticle flotation collectors revealed that bead-bead collisions during conditioning and flotation caused the irreversible abrasion of the adsorbed nanoparticles. The abraded particles were present in the suspension as large aggregates. Nanoparticle abrasion explains why small polystyrene particles are more effective than larger ones, and why, much higher dosages of larger nanoparticles are required for the same flotation performance. These behaviors also were demonstrated with a phenomenological model of the abrasion dynamics.

We describe a versatile and simple method to perform sequential reactions on paper analytical devices by stacking dry pullulan films on paper, where each film contains one or more reagents or acts as a delay layer. Exposing the films to an aqueous solution of the analyte leads to sequential dissolution of the films in a temporally controlled manner followed by diffusive mixing of the reagents, so that sequential reactions can be performed. The films can be easily arranged for lateral flow assays or for spot tests (reactions take place sequentially in the z-direction). We have tested the general feasibility of the approach using three different model systems to demonstrate different capabilities: 1) pH ramping from low to high and high to low to demonstrate timing control; 2) rapid ready-to-use two-step Simon's assays on paper for detection of drugs of abuse utilizing a 2-layer stack containing two different reagents to demonstrate the ability to perform assays in the z-direction; and 3) sequential cell lysing and colorimetric detection of an intracellular bacterial enzyme, to demonstrate the ability of the method to perform sample preparation and analysis in the form of a spot assay. Overall, these studies demonstrate the potential of stacked pullulan films as useful components to enable multi-step assays on simple paper-based devices.

This initial study shows that hydrophobic modification of guar polymers used in eye drops forms weak gels with human serum albumin (HSA), suggesting that modified guar may offer advantages for treatment of dry eye diseases that lead to elevated HSA concentrations in tears. Specifically, hydroxypropyl guar samples were oxidized and derivatized with linear alkyl amines to give a series of modified guar polymers (MGuar) bearing hydroxypropyl, N-alkylamide, and carboxyl moieties. MGuar interactions with lysozyme and HSA were measured by binding and rheological methods as functions of the alkyl chain length and the extent of hydrophobic modification. HSA binds MGuar, giving weak gels, whereas lysozyme shows little tendency to bind MGuar or to interfere with HSA binding. Six mole percent substitution of decyl hydrophobes gave the strongest gels in the presence of HSA.

Poly( N -isopropylacrylamide) (PNIPAM) core/poly( N -isopropylmethacrylamide) (PNIPMAM) shell microgels react with dilute alkaline bleach, forming chloramides primarily in the PNIPAM core. The resulting microgels are colloidally stable in PBS (phosphate buffered saline) at body temperature because the PNIPMAM shell provides steric stabilization. Selective chloramide formation of the PNIPAM cores reflects the low tendency of the PNIPMAM shell to react with hypochlorite. The chlorinated core/shell microgels can be cleaned and stored. Because PNIPAM chloramide can oxidize 2-mercaptoethanol and glutathione, the chlorinated core/shell microgels may have applications in targeted cell death.

With the highest content of primary amine functional groups of any polymer, polyvinylamine (PVAm) is a potent tool for the modification of macroscopic and nanoparticle surfaces. Based on the free radical polymerization and subsequent hydrolysis of N-vinylformamide, PVAm is prepared as linear polymers (0.8 kDa to >1 MDa), microgels, macrogels, and copolymers. The amine groups serve as reaction sites for grafting PVAm to surfaces and for the preparation of derivatives. Coupling low-molecular-weight molecules and oligomers gives PVAm-X, where X includes hydrophobes, carbohydrate oligomers, proteins, TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), phenylboronic acids, and fluorocarbons. This contribution highlights the use of PVAm and PVAm-X to modify solid surface properties. Where possible, the PVAm properties and applications as an interfacial agent are compared to those of linear polyethylenimine, polyallylamine, and chitosan.

Thermoresponsive microgels bearing primary amine groups were prepared by the Hofmann rearrangement of methacrylamide groups present in cross-linked NIPMAM (N-isopropylmethacrylamide) microgels. Most thermoresponsive microgels are based on NIPAM (N-isopropylacrylamide). By substituting NIPMAM for NIPAM, and methacrylamide for acrylamide, side reactions and the generation of carboxyl groups were prevented during the Hofmann reaction. The Hofmann rearrangement is sufficiently slow under our conditions (1 h for a 51% conversion) to permit fine control of the primary amine contents in the microgels. When starting with PNIPMAM microgels containing both methacrylamide and acrylic acid residues, we prepared a series of amphoteric microgels spanning a range of amine contents, all from a common parent microgel. Therefore, every microgel in the series had the same microstructure, cross-link density, and molecular weight.

A simple and inexpensive method is reported for the long-term stabilization of enzymes and other unstable reagents in premeasured quantities in water-soluble tablets (cast, not compressed) made with pullulan, a nonionic polysaccharide that forms an oxygen impermeable solid upon drying. The pullulan tablets dissolve in aqueous solutions in seconds, thereby facilitating the easy execution of bioassays at remote sites with no need for special reagent handling and liquid pipetting. This approach is modular in nature, thus allowing the creation of individual tablets for enzymes and their substrates. Proof-of-principle demonstrations include a Taq polymerase tablet for DNA amplification through PCR and a pesticide assay kit consisting of separate tablets for acetylcholinesterase and its chromogenic substrate, indoxyl acetate, both of which are highly unstable. The encapsulated reagents remain stable at room temperature for months, thus enabling the room-temperature shipping and storage of bioassay components.

A new poly(acrylic acid)-grafted TEMPO (PAA-T) is compared to polyvinylamine-grafted TEMPO and free TEMPO as oxidation mediators for cellulose. The polymer-immobilized mediators require lower overall TEMPO concentrations and they restrict oxidation to the exterior surfaces of porous cellulose. On the other hand, the resulting surfaces are coated with grafted polyvinylamine and laccase, if the enzyme is used as the primary oxidant. PAA-T is anionic and does not sufficiently adsorb onto anionic cellulose to give oxidation, whereas cellulose rendered cationic by an adsorbed layer of PVAm is oxidized by PAA-T + laccase. There is no clear “best choice” mediator/primary oxidant combination for cellulose oxidation subsequent to PVAm grafting; the advantages of each mediator are summarized.

Gelation of cellulose nanocrystal (CNC) dispersions was measured as a function of the presence of four nonionic polysaccharides. Addition of hydroxyethyl cellulose (HEC), hydroxypropyl guar (HPG), or locust bean gum (LBG) to CNC dispersions induced the gelation of dilute CNC dispersions, whereas dextran (DEX) did not. These behaviors correlated with adsorption tendencies; HEC, HPG, and LBG adsorbed onto CNC-coated quartz crystal microbalance sensors, whereas DEX did not adsorb. We propose that the adsorbing polysaccharides greatly increased the effective volume fraction of dilute CNC dispersions, driving more of the nanocrystals into anisotropic domains. SDS and Triton X-100 addition disrupted HEC-CNC gels whereas CTAB did not. Surface plasmon resonance measurements with CNC-coated sensors showed that SDS and Triton X-100 partially removed adsorbed HEC, whereas CTAB did not. These behaviors illustrate the complexities associated with including CNC dispersions in formulated products: low CNC contents can induce spectacular changes in rheology; however, surfactants and soluble polymers may promote gel formation or induce CNC coagulation.

We recently reported on the multilayer printing of sol–gel/enzyme bioinks onto porous filter paper to create bioactive paper test strips. The method involves printing of four inks: a polymer underlayer, a sol–gel-based silica layer, an acetylcholinesterase (AChE) enzyme layer, and finally a top layer of silica. To improve our understanding of the nature of these printed materials, filter paper printed with various ink components was characterized by activity assays (with and without protease treatment), confocal microscopy to assess the location and mixing of layers, and scanning electron microscopy of deposited inks to assess the morphology and ink location. Although the silica and enzyme solutions were printed sequentially, they formed a composite material within the porous paper network and coated only the fibers as a 35 ± 15 nm thin film without filling the macropores. The silica coating on the cellulose fibers was sufficiently flexible to allow bending of the paper substrate, unlike traditional silic...

Water soluble pullulan films were formatted into paper-based microfluidic devices, serving as a controlled time shutoff valve. The utility of the valve was demonstrated by a one-step, fully automatic implementation of a complex pesticide assay requiring timed, sequential exposure of an immobilized enzyme layer to separate liquid streams. Pullulan film dissolution and the capillary wicking of aqueous solutions through the device were measured and modeled providing valve design criteria. The films dissolve mainly by surface erosion, meaning the film thickness mainly controls the shutoff time. This method can also provide time-dependent sequential release of reagents without compromising the simplicity and low cost of paper-based devices.