Search

The ability of polystyrene nanoparticles to facilitate the froth flotation of glass beads was correlated to the hydrophobicity of the nanoparticles. Contact angle measurements were used to probe the hydrophobicity of hydrophilic glass surfaces decorated with hydrophobic nanoparticles. Both sessile water drop advancing angles, θa, and attached air bubble receding angle measurements, θr, were performed. For glass surfaces saturated with adsorbed nanoparticles, flotation recovery, a measure of flotation efficiency, increased with increasing values of each type of contact angle. As expected, the advancing water contact angle on nanoparticle-decorated, dry glass surfaces increased with surface coverage, the area fraction of glass covered with nanoparticles. However, the nanoparticles were far more effective at raising the contact angle than the Cassie–Baxter prediction, suggesting that with higher nanoparticle coverages the water did not completely wet the glass surfaces between the nanoparticles. A series of polystyrene nanoparticles was prepared to cover a range of surface energies. Water contact angle measurements, θnp, on smooth polymer films formed from organic solutions of dissolved nanoparticles were used to rank the nanoparticles in terms of hydrophobicity. Glass spheres were saturated with adsorbed nanoparticles and were isolated by flotation. The minimum nanoparticle water contact angle to give high flotation recovery was in the range of 51° < θnpmin≤ 85°. [ABSTRACT FROM AUTHOR]

This is the first report describing a new technology where hydrophobic nanoparticles adsorb onto much larger, hydrophilic mineral particle surfaces to facilitate attachment to air bubbles in flotation. The adsorption of 46 nm cationic polystyrene nanoparticles onto 43 μm diameter glass beads, a mineral model, facilitates virtually complete removal of the beads by flotation. As little as 5% coverage of the bead surfaces with nanoparticles promotes high flotation efficiencies. The maximum force required to pull a glass bead from an air bubble interface into the aqueous phase was measured by micromechanics. The pull-off force was 1.9 μN for glass beads coated with nanoparticles, compared to 0.0086 μN for clean beads. The pull-off forces were modeled using Scheludko’s classical expression. We propose that the bubble/bead contact area may not be dry (completely dewetted). Instead, for hydrophobic nanoparticles sitting on a hydrophilic surface, it is possible that only the nanoparticles penetrate the air/water interface to form a three-phase contact line. We present a new model for pull-off forces for such a wet contact patch between the bead and the air bubble. Contact angle measurements of both nanoparticle coated glass and smooth films from dissolved nanoparticles were performed to support the modeling. [ABSTRACT FROM AUTHOR]

Described is a new, greener approach to increasing adhesion between wet cellulose surfaces. Polyvinylamine (PVAm) with grafted TEMPO spontaneously adsorbs onto cellulose and oxidizes the C6 hydroxyl to aldehyde groups that react to form covalent bonds with primary amines on PVAm. Grafted TEMPO offers two important advantages over solutions of low-molecular-weight water-soluble TEMPO derivatives. First, the oxidation of porous cellulose wood fibers is restricted to the exterior surfaces accessible to high-molecular-weight PVAm. Thus, fibers are not weakened by excessive oxidation of the interior fiber wall surfaces. The second advantage of tethered TEMPO is that the total dose of TEMPO required to oxidize dilute fiber suspensions is much less than that required by water-soluble TEMPO derivatives. PVAm-TEMPO is stable under oxidizing conditions. The oxidation activity of the immobilized TEMPO was demonstrated by the conversion of methylglyoxal to pyruvic acid. [ABSTRACT FROM AUTHOR]

The tensile and fracture properties of cross-linked paper were investigated at low and high relative humidity by cross-linking the joints formed between fibers. Cationic acetal dextran served as a model cross-linking agent, as it can be prepared to adsorb specifically to the fiber surface. Thus, cross-linking occurs only in the joints between fibers. The kinetics of hydrolysis was investigated to optimize the stock preparation, such that the resulting aldehyde groups react as the paper is dried. The effect of the cross-link density on the tensile and fracture properties was studied by varying the amount of acetal groups adsorbed to the pulp fibers. At low humidity, cross-linking improved the tensile and fracture properties of paper, although lower cross-link densities yielded better properties. Cross-linking was not effective at high relative humidty, as the tensile strength and stiffness were not improved. However, the fracture properties were significantly improved. [ABSTRACT FROM AUTHOR]

TiO2is commonly used as a brightening agent for paper, but may also be used on paper as a photocatalyst. The TiO2aggregates that typically form in/on paper are inefficient both for brightening or photooxidation. We describe, for the first time, the preparation of homogeneously distributed, non-aggregated TiO2particles on cellulose fibers using explicit bioconjugation with the fusion protein of CBM2a-Strep-tag II/streptavidin/biotinylated TiO2. The maximum absorption of proteins and nanoparticles onto paper were determined to be ca.6.22 × 10−2nm−2for CBM2a-Strep-tag II, 1.93 × 10−2nm−2for streptavidin, and 58 µm−2for TiO2nanoparticles, respectively. The efficiency of photocatalysis of the TiO2-containing paper prepared by this bioconjugation method was demonstrated by the decolorization of UV sensitive dye (reactive black dye 5). Immobilized TiO2efficiently degraded the dye within about 10 hours. Only after extensive photolysis (12 hours) did sufficient degradation of the bioconjugating linkers occur such that free TiO2particles and cellulose fibers were found in the supernatant. These experiments demonstrate that bioconjugation of TiO2to paper leads to an effective, supported photocatalyst system. [ABSTRACT FROM AUTHOR]

The phase behavior and surface tension of aqueous, linear polyvinylamine (PVAm) bearing pendant phenylboronic acid moieties (PBA) were measured as functions of pH and the degree of PBA substitution. Coupling of PBA with 4% of the nitrogen on low molecular weight (15 kDa) PVAm gave water-soluble copolymer from pH 1 to 12. By contrast, derivatives of 150 kDa PVAm phased separated at pH 9 with as little as 4% derivatization. The pH ranges over which phase separation occurred increased with PBA substitution. The copolymer based on 51% substitution was insoluble over most of the pH range. Electrophoresis and potentiometric titration confirmed that the copolymers were amphoteric with isoelectric points around pH 9.5. The hydrophobicity of the copolymers was reflected in the significant lowering of surface tension, particularly at high pH. Finally fructose, which binds to borate, influenced the titration curves but did not influence surface tension. [ABSTRACT FROM AUTHOR]

Cationic polystyrene latex was flocculated with mixtures of hydroxypropyl guar (HPG) and boric acid, which form an anionic polyelectrolyte HPG−borate. Flocculation could be reversed by either lowering pH or by adding fructoseboth procedures remove labile borate ions weakly bound to the HPG chains. Mixtures of phenyl boronic acid (PBA) and HPG also flocculate latex although the range of HPG−PBA concentrations, giving flocculation was much narrower than HPG−borate. The differences were explained by the tendency of borate ion to cross-link HPG chains, whereas PBA is monofunctional and cannot cross-link HPG. [ABSTRACT FROM AUTHOR]

AbstractPolyelectrolyte complexes are routinely used as adhesives to strengthen fiber-fiber contacts in paper. This work evaluates different approaches to putting the polyelectrolyte complexes into the adhesive joint. Instead of conventional wet paper mechanical testing, a wet cellulose film delamination technique was employed permitting direct comparison of different approaches to applying the polymeric adhesive to the cellulose-cellulose joint. The adhesion strengths of layer-by-layer polyelectrolyte complexes assembled on wet cellulose films and the adhesion strengths of the corresponding polyelectrolyte complex coated on wet cellulose films are compared. The wet adhesion strengths were measured by peel delamination. The polyelectrolyte complexes were based on mixtures of cationic polyvinylamine (PVAm) and anionic carboxymethyl cellulose (CMC). The layer-by-layer assemblies of PVAm and CMC yielded stronger wet adhesion than did coated films of the corresponding colloidal complexes or pure PVAm at the same coverage (mass of polymer/joint area). The role of CMC was to give ionic crosslinks with PVAm which increase the cohesive strength of thick PVAm layers. PVAm gives much stronger wet adhesion to cellulose compared to the oxidized silicon wafer surfaces. It is proposed that imine and aminal bonds can form between the polyamine and hemiacetals in the regenerated cellulose films which cannot form with silica. [ABSTRACT FROM AUTHOR]

Amphoteric, poly( N-isopropylacrylamide)-based microgels are functionalized with aminophenylboronic acid (PBA) functional groups to produce colloidally stable, glucose-responsive gel nanoparticles that exhibit glucose-dependent swelling responses at physiological temperature, pH, and ionic strength. Up to 2-fold volumetric swelling responses are observed in response to physiological glucose concentrations, the first such physiological response reported for a colloidally stable microgel. Amphoteric microgels can also be designed to both swell and deswell in response to glucose according to the pH of the medium, the concentration of PBA groups grafted to the microgel, and the relative concentrations of the cationic and anionic functional groups in the platform microgel. The increasing anionic charge density on the microgels observed at higher glucose binding fractions can be applied to switch the net charge of the microgels from cationic to anionic as the glucose concentration increases. Preliminary experiments suggest that such amphoteric PBA−microgels have a high capacity for insulin uptake and can selectively release more insulin at higher glucose concentrations under physiological conditions via glucose-induced, “on−off” switching of electrostatic attractions between insulin and the microgel. [ABSTRACT FROM AUTHOR]

Abstract  X-ray Photoelectron Spectroscopy (XPS) was used to characterize the functional groups present on regenerated cellulose films after mild oxidation with TEMPO–NaBr–NaClO and the results were correlated with the adhesion forces holding together two wet cellulose films laminated with a thin (i.e. less than 10 mg/m2) layer of polyvinylamine (PVAm). There was no correlation between adhesion and carboxyl content, whereas wet adhesion was proportional to the total content of aldehyde and hemiacetal groups on the cellulose. It is proposed that aldehyde groups react with neighboring cellulose chains to form hemiacetals which serve as crosslinks strengthening the cellulose surface. The hemiacetals can also be attacked by primary amines to give imine and aminal covalent linkages to the PVAm adhesive layer. [ABSTRACT FROM AUTHOR]

Photoactive TiO2can be used to mediate a variety of disinfection processes. It was postulated that TiO2particles could be directed to specific targets of interest using biotin/streptavidin linkages. Biotinylated TiO2nanoparticles (anatase) were obtained by treating TiO2nanoparticles with 3-aminopropyltriethoxysilane (APTS) in anhydrous DMSO, followed by reaction with N-hydroxysuccinimidobiotin. 29Si CP-MAS NMR, 13C CP-MAS NMR, and FTIR spectra showed that biotin was covalently bound to the TiO2surface. Transmission electron microscopy (TEM) demonstrated that prolonging the silanization reaction times led to increasingly thick silsesquioxane coating layers of up to approximately 10 nm. The specific surface area (SSA) of the TiO2particles decreased from 16 m2g-1before treatment to 9.1 m2g-1after aminosilanization and to 8.4 m2g-1after biotinylation, as measured by nitrogen adsorption. Amino surfaces modified for 4, 16, and 26 h had total amino group densities ranging from 2.9 to 26 to 66 nm-2, respectively, whereas accessible surface amino group densities ranged from 2.7 to 10 to 17 nm-2as shown from nitrogen adsorption, polyelectrolyte titration, conductiometric titration, and biotin assays. Not all the amino groups were accessible for biotinylation:  the densities of active biotin were found to be 2.1, 7.0, and 11.5 nm-2. The ability of the attached biotin to bind to streptavidin was demonstrated by confocal microscopy with the use of fluorescently labeled streptavidin−FITC. Although streptavidin was readily able to bind to biotinylated TiO2particles, it did not act as a strong flocculating agent for the biotinylated TiO2particles. The implications of these observations, with respect to particle accessibility to tethered streptavidin, are discussed. [ABSTRACT FROM AUTHOR]

The reactivity ratios for the aqueous free‐radical copolymerization of diallyldimethylammonium chloride and N‐vinylformamide were found to be 0.13 and 1.92, respectively, from a Fineman–Ross analysis of a series of batch polymerizations. Because batch polymerization could not give a uniform product in a high yield with two monomers of such different reactivities, a semibatch procedure was developed in which the more reactive N‐vinylformamide was added in 10 steps over the course of the copolymerization. The poly(diallyldimethyl‐ ammonium chloride‐co‐N‐vinylformamide) copolymers were hydrolyzed to give poly(diallyldimethylammonium chloride‐co‐vinylamine). The utility of the vinylamine/diallyldimethylammonium chloride copolymers was demonstrated by the preparation and characterization of three derivatives: (1) a copolymer with coupled dansyl groups for fluorescence detection; (2) a copolymer with coupled dabsyl groups for ultraviolet–visible detection; and (3) an ultra‐high‐molecular‐weight (1.6 × 106 Da) poly(diallyldimethylammonium chloride) by chain extension (coupling) with glycerol diglycidyl ether. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1068–1075, 2007 [ABSTRACT FROM AUTHOR]

The phase behaviors of polyelectrolyte complexes formed from dilute solutions of poly(vinyl amine) (PVAm) and carboxymethyl cellulose (CMC) were determined as a function of overall composition and pH. The phase diagram included regions with soluble complexes, colloidal complexes, and macroscopic precipitates. Colloidal complexes were stable when either polymer was in sufficient excess to give electrosteric stabilization. The polymer mixing ratios giving complexes with an isoelectric point of 7 could be predicted from a simple model using the degree of ionization vs pH data for PVAm and CMC. The model failed at extreme pH values because not all added polymer was incorporated into the complexes. At pH 7, essentially all the added polymer was incorporated into the colloidal complex or precipitate, as long as the mixing ratio was within ±10% of charge stoichiometry. The interaction of PVAm and CMC at pH 7 was endothermic, supporting the generally accepted viewpoint that the interaction of oppositely charged polyelectrolytes is entropy-driven. Although the colloidal complexes had a broad particle size distribution, the average particle size was rather insensitive to mixing ratio. By contrast, complex size was sensitive to electrolyte concentration with no complex formation when the NaCl concentration was ≥2 M. [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry (DSC) is used to investigate the thermal phase transitions of a range of N-isopropylacrylamide (NIPAM)-based, carboxylic acid-functionalized microgels with well-defined radial and chain functional group distributions. The transition enthalpies of protonated microgels can be correlated with the hydrophobicity of the functional comonomer, while the transition enthalpies for ionized microgels can be correlated with the degree of microgel deswelling achieved across the thermal phase transition. The peak widths at half-height vary inversely with the average length of NIPAM blocks in each of the microgels, as calculated using a kinetic copolymerization model. Deconvolution of the asymmetric DSC thermograms is accomplished using a two-transition model, thought to relate to core−shell-type transitions induced by the significant local heterogeneities within the functionalized microgels. The ratio between the two transition temperatures of these deconvoluted peaks is a useful quantitative probe of the radial functional group distribution. An additional, low-temperature transition is also observed in the thermogram of the vinylacetic acid-functionalized microgel, indicative of the occurrence of local chain rearrangements prior to the macroscopic phase transition in this microgel. Complementary light scattering analysis suggests that microphase separation may account for this additional transition peak. [ABSTRACT FROM AUTHOR]

Poly(N-isopropylacrylamide) (PNIPAM) microgels are functionalized with aminophenyboronic acid (APBA) to produce nanoparticles which swell in response to increases in the glucose concentration. A “graft-to” approach was used to synthesize a range of microgels with different physical properties from the same base microgel. Higher APBA graft yields are achieved as the −COOH groups in the platform microgel become more localized on the surface and more highly spaced within the subchains. The glucose swelling response of the graft microgels is enhanced as the PBA functional groups become more localized in the outer shell of the microgel and more randomly distributed within the gel network subchains. The glucose-induced VPTT shift observed in the PBA−microgel conjugates can be exploited to produce microgels that exhibit on−off glucose swelling as a function of temperature or enhanced swelling responses over specific glucose concentration ranges at a single, tunable temperature. The “secondary” thermal phase transition is thus applied to effect an order-of-magnitude enhancement or suppression of the “primary” glucose-induced phase transition. Both linear and nonlinear microgel glucose sensors are subsequently designed which are active within targeted glucose concentration ranges. [ABSTRACT FROM AUTHOR]

Abstract  Regenerated cellulose films were laminated using very thin layers of the protein Bovine Serum Albumin (BSA) as an adhesive. The wet delamination strength was measured as functions of pH, lamination time, temperature and pressure, as well as cellulose oxidation. Drying at elevated temperature (120 °C) was required for strong adhesion. Oxidation of the cellulose membranes to introduce surface carboxyl/aldehyde groups increased the wet delamination strength by 60%, implying that the peel failures happened at the protein/cellulose interface. The wet delamination force was independent of the pH and ionic strength of solutions used to apply the BSA; whereas adhesion decreased with increasing pH of the rewetting solution. Furthermore, the swelling of the BSA interplay region was also increased at high pH. It is proposed that covalent grafting of BSA onto the oxidized cellulose, and disulfide crosslinking within the protein layer contributed to wet adhesion. [ABSTRACT FROM AUTHOR]

Paper strips containing DNA-conjugated microgels (MG) are used to achieve sensitive DNA detection in three steps: target DNA promoted ligation of a DNA primer to the MG-bound DNA, rolling circle amplification (RCA) between the primer and a circle DNA, and hybridization of the RCA products and a fluorescent DNA probe. [ABSTRACT FROM AUTHOR]

We demonstrate that DNA oligonucleotides covalently coupled to colloidal microgel can be manipulated by T4 DNA ligase for DNA ligation and by Phi29 DNA polymerase for rolling circle amplification (RCA). We also show that the long single-stranded RCA product can generate intensive fluorescence upon hybridization with complementary fluorescent DNA probe. We believe DNA–microgel conjugates can be explored for the development of DNA based bioassays and biosensors. [ABSTRACT FROM AUTHOR]