Absence Of PVP Research Articles

Kinetic inhibitor effects on methane/propane clathrate hydrate-crystal growth at the gas/water and water/ n-heptane interfaces

The influence of the kinetic inhibitor poly( N-vinylpyrrolidone) or PVP on hydrate methane/propane hydrate formation was studied in pre-saturated liquid water with and without the presence of heptane under different undercooling conditions. It was found that when the inhibitor concentration was 0.1 wt%, hydrate formation started as a film at the gas/water interface similar to the crystal behavior without inhibitor. When the inhibitor concentration was 0.5 wt% hydrate formation started at the wall above the gas/water interface and the hydrate film at the gas/water interface was observed as well. However, for inhibitor concentration 1.0 wt%, the hydrate started forming from water droplets attached to the wall above the gas/liquid interface and grew catastrophically. When the inhibitor concentration was 0.1 wt% and undercooling was 13.7 or 8.1 K whiskery or fiber-type hydrate crystals, respectively, were seen within the liquid pool. This morphology was not observed in the absence of PVP. When inhibitor concentration was 0.5 or 1.0 wt% or undercooling was 3.2 K, there was no crystal growth within the liquid pool. Floating crystals were also observed, but were needle-type and thus different from the equiaxed floating crystals found in the system without the inhibitor.

Effects of Polymer Adsorption on Stabilities and CMP Performance of Ceria Abrasive Particles

In this paper we present that the effects of polymer adsorption on stabilities and CMP performance of ceria abrasive particles. Characterization of ceria abrasive particles in the presence of poly(vinyl pyrrolidone) (PVP) was performed by the measurements of adsorbed amounts of PVP, average sizes, and the back scattering intensities of the ceria abrasive particles as functions of PVP molecular weight and PVP concentration. The ceria abrasive particles in the presence of PVP were used to polish <TEX>$SiO_2\;and\;Si_3N_4$</TEX> films deposited on Si wafers in order to understand the effect of PVP adsorption on chemical mechanical polishing (CMP) performance, together with ceria abrasive particles without PVP. Adsorption of PVP on the ceria abrasive particles enhanced the stability of ceria abrasive particles due to steric stabilization of the thick adsorbed layer of PVP. Removal rates of the deposited <TEX>$SiO_2\;and\;Si_3N_4$</TEX> films by the ceria abrasive particles in the presence of PVP were much lower than those in the absence of PVP and their magnitudes were decreased with an increase in the concentration of free PVP chains in the dispersion media. This suggests that the CMP performance in the presence of PVP could be mainly controlled by the hydrodynamic interactions between the adsorbed PVP chains and the free ones. Moreover, the molecular weight dependence of PVP on the removal rates of the deposited films was hardly observed. On the other hand, high removal rate selectivity between the deposited films in the presence of PVP was not observed.

Polymer Adsorption Effects on Stabilities and Chemical Mechanical Polishing Properties of Ceria Particles

Characterization of ceria particles in the presence of poly(vinyl pyrrolidone) (PVP) was performed by the measurements of adsorbed amounts of PVP, average sizes, and back scattering intensities of the ceria particles as functions of PVP molecular weight and PVP concentration. Adsorption of PVP on the ceria particles enhanced the stability of ceria particles due to steric stabilization of the thick adsorbed layer of PVP. Moreover, SiO2 and Si3N4 films deposited on Si wafers were polished by the ceria particles in the presence of PVP in order to understand the effect of PVP adsorption on chemical mechanical polishing (CMP) technique, together with ceria particles without PVP and re-dispersed ceria particles adsorbed by PVP in water (re-dispersed ceria). Removal rates of the deposited SiO2 and Si3N4 films were decreased with an increase in the concentration of free PVP chains in the dispersion media, while the removal rates by the re-dispersed ceria were the same as those by the ceria particles in the absence of PVP.

Structural Investigation on the Poly(vinylpyrrolidone)−Water System in the Presence of Sodium Decyl Sulfate and Sodium Decanesulfonate: A Small Angle Neutron Scattering Study

Small angle neutron scattering (SANS) has been used to study the interaction of sodium decyl sulfate (C10OS) and sodium decanesulfonate (C10S) with poly(vinylpyrrolidone) (PVP). The measurements were performed on aqueous solutions of C10OS and C10S in the presence and absence of PVP. In all ternary systems the polymer concentration was kept constant at 1 wt %, and the surfactant molal concentration ranged from 0.002 to 0.150 mol kg-1. The analysis of the collected SANS profiles confirms the absence of any appreciable interaction between PVP and C10S in contrast with what observed for the PVP−C10OS−D2O system. In this latter system, in fact, a clear interaction peak in the scattering pattern appears well below the cmc of the surfactant, which suggests a complex formation between PVP and C10OS. The preferential interaction of poly(vinylpyrrolidone) toward sodium decyl sulfate with respect to sodium decanesulfonate reflects the difference in the chemical structure of the two surfactants that produces meaning...

Tunable platinum–ruthenium nanoparticle properties using microwave synthesis

Stable polymer coated platinum–ruthenium nanoparticles were prepared. The effects of several preparation parameters have been studied in view of optimizing the particles' composition and structure characteristics. Solutions of hexachloroplatinic acid and ruthenium chloride in ethylene glycol were reduced at 173 °C in the presence of poly(N-vinyl-2-pyrrolidone) with rapid refluxing in a commercial microwave system. These nanoparticles form stable colloidal solutions in ethanol for several months without any precipitation. Transmission electron microscopy (TEM) analysis revealed the presence of metallic clusters with a uniform size of about 2–3 nm. Photo-correlation spectroscopy (PCS) measurements revealed an average hydrodynamic particle size of about 10 nm. X-Ray photoelectron spectroscopy (XPS) indicates that most of the Pt and Ru atoms are in reduced metallic state. X-Ray diffraction (XRD) revealed alloyed single-crystal clusters with diameters barely smaller than corresponding TEM measurements. The above TEM, PCS, XPS and XRD observations converge on a simple picture of monodisperse, uniformly alloyed Pt–Ru nanoparticles with uniform diameters in the range of 2–3 nm for the PVP-coated samples. Their compositions are comparable with the metal content of the reactants. The PVP layer is less than 7 nm thick, and probably very porous. In the absence of PVP, agglomerated, larger nanoparticles were obtained with a Pt-rich core and Ru-rich shell.

Complex Formation between Poly(vinylpyrrolidone) and Sodium Decyl Sulfate Studied through NMR

Recent experimental studies have shown a preferential interaction of poly(vinylpyrrolidone) (PVP) toward the alkyl sulfate surfactants rather than toward those belonging to the alkyl sulfonate series. To gain information on the complex formation between PVP and the alkyl sulfate surfactants, we have performed 1H and 13C NMR and NOESY measurements on aqueous solutions of sodium decyl sulfate (C10OS) in the presence and absence of PVP at 1wt %. The results show that C10OS interacts with PVP, forming micelle-like clusters bound onto the polymer, and furthermore suggest that the PVP−C10OS complex formation implies the synergic effects of the electrostatic attractions between the surfactant headgroup and the nitrogen and oxygen atoms in the pyrrolidone ring of PVP and of the hydrophobic interaction between the surfactant alkyl moiety and the ring carbons of PVP.

Mixed adsorption of poly(vinylpyrrolidone) and sodium dodecylbenzenesulfonate on kaolinite

The mixed adsorption of the nonionic polymer poly(vinylpyrrolidone) (PVP) and the anionic surfactant sodium dodecylbenzenesulfonate (SDBS) on kaolinite has been studied. Both components adsorb from their mixture onto the clay mineral. The overall adsorption process is sensitive to the pH, the electrolyte concentration, and the amounts of polymer and surfactant. Interpretation of the experimental data addresses also the patchwise heterogeneous nature of the clay surface. In the absence of PVP, SDBS adsorbs on kaolinite by electrostatic and hydrophobic interactions. However, when PVP is present, surfactant adsorption at 10 −2 M NaCl is mainly driven by charge compensation of the edges. The adsorption of PVP from the mixture shows similar behavior under different conditions. Three regions can be distinguished based on the changing charge of polymer–surfactant complexes in solutions with increasing SDBS concentration. At low surfactant content, PVP adsorbs by hydrogen bonding and hydrophobic interactions, whereas electrostatic interactions dominate at higher surfactant concentrations. Over the entire surfactant concentration range, polymer–surfactant aggregates are present at the edges. The composition of these surface complexes differs from that in solution and is controlled by the surface charge.

Interaction of poly(vinylpyrrolidone) with cationic and nonionic surfactants in aqueous solution studied by 1H NMR

Aqueous solutions of surfactant at various concentrations with 0.2% poly(vinylpyrrolidone) (PVP) were studied by 1H NMR methods, including relaxation time and self-diffusion coefficient measurements and two-dimensional nuclear Overhauser enhancement spectroscopy. Two surfactants were concerned: cationic cetyltrimethylammonium bromide (CTAB) and nonionic Triton X-100 (TX-100). In the presence of 0.2% PVP, the variation of the T2 values of CTAB protons is similar to that in the absence of PVP. Relaxation times of PVP protons are not significantly affected by the increasing concentration of CTAB. This indicates that no interaction between PVP and CTAB could be detected. However, in the presence of 0.2% PVP, TX-100 micelles are formed at a concentration lower than its normal critical micellization concentration. According to the results of relaxation time measurement of water protons, the presence of 0.2% PVP also induces the contraction of the hydrophilic layer of the TX-100 micelle. This indicates some interaction between PVP and TX-100, but the mechanism of this interaction needs further investigation.

Simultaneous adsorption of sodium dodecyl sulfate and poly(vinyl pyrrolidone) on titanium dioxide with quaternary ammonium groups

Simultaneous adsorption of sodium dodecyl sulfate (SDS) and poly(vinyl pyrrolidone) (PVP) on titanium dioxide with quaternary ammonium groups (XN m, where m is the carbon number of the alkyl chain, 8 and 12) was investigated by measuring the amount of adsorbed SDS and PVP, ζ potential, and dispersion stability. The conformation of PVP adsorbed was also estimated using a spin-labeled polymer. The amount of SDS adsorbed on XN m in the presence of PVP was enhanced at low SDS concentrations, but was depressed at high SDS concentrations compared with that in the absence of PVP. Further, the amounts of SDS adsorbed on XN m in the presence and in the absence of PVP were greater than that on untreated titanium dioxide. The adsorption of PVP was remarkably enhanced at low SDS concentrations, followed by a dramatic decrease at high SDS concentrations for XN m and untreated titanium dioxide. The results of ESR measurements indicate that the PVP adsorbed on XN m in the absence and in the presence of SDS takes mainly train conformation, while the PVP adsorbed on untreated titanium dioxide in the absence of SDS takes loops or tails and converts to train conformation in the presence of SDS. In addition, the dispersion stability of XN m and untreated titanium dioxide suspensions increased at low SDS concentrations in the presence of PVP compared to that in the absence of PVP.

Adsorption of SDS and PVP at the air/water interface

The technique of specular reflection of neutrons has been used to investigate the adsorption from polyvinylpyrrolidone/sodium dodecyl sulphate (PVP/SDSI) solutions at the air/water interface. Isotropic substitution was used to highlight features of the adsorbed layer and to distinguish between solvent and solute in this layer. At low SDS concentrations the presence of the polymer causes an increase in the adsorption of surfactant (at 1 × 10 −4 M SDS, the area per molecule of SDS is 227A˚ 2 in the absence of polymer, 100A˚ 2 in 0.5% PVP and 85A˚ 2 in 2.0% PVP). On increasing the surfactant concentration this difference is reduced unit, at high SDS concentrations, the surface concentration of surfactant is higher in the absence of PVP (at 0.01 M SDS, the area per SDS molecule is 42A˚ 2, and 46a˚ 2 at 0%, 0.5% and 2.0% PVP respectively).

Effect of polyvinylpyrrolidone on the crystallinity and dissolution rate of solid dispersions of the antiinflammatory CI-987

Solid dispersions of CI-987 (5-{[3,5-bis(l,l-dimethylethyI)-4-hydroxyphcnyl]-methylene}-2,4-thiazolidinedione) having varying concentrations of polyvinylpyrrolidone (PVP K 28–32), were prepared in an attempt to improve the dissolution rate of CI-987. The physical characteristics of these solid dispersions were investigated by X-ray diffraction and dissolution rate studies. The dissolution rate of CI-987 can be significantly increased by increasing the weight fraction of PVP in the solid dispersions. The maximum dissolution rate occurred with the solid dispersion having a PVP weight fraction of 0.81 where the CI-987 dissolution rate is 15-times greater than that for CI-987 in the absence of PVP and where X-ray diffraction suggests that CI-987 exists in a totally amorphous state. As the PVP weight fractions decreased from 0.81, the dispersions displayed increasing degrees of crystallinity. The dissolution rate vs PVP weight fraction plot displayed three distinct regions: at low PVP (high drug) weight fractions, a drug-controlled region; at intermediate PVP weight fractions, a region where changes in the degree of crystallinity of CI-987 play a major role; and at high PVP (low drug) weight fractions, a PVP-controlled region.

The activity, characterization and distribution of the nitrogen assimilation enzyme, glutamine synthetase, in jack pine seedlings.

The extraction of glutamine synthetase (GS) from jack pine (Pinus banksiana Lamb.) tissue was facilitated by solubilization of the tissue with 1% or more Nonidet P-40 detergent. In contrast with procedures commonly used to extract GS from other plant tissues, highest recovery of GS was obtained when jack pine tissues were subjected to ultrasonic homogenization in the absence of PVP. Chromatography on DEAE-Sephacel showed that jack pine needles possess two isoforms of GS. Isoform GS(1), which is generally associated with the cytoplasm, eluted at 90 mM KCl and accounted for 80% of total GS activity. Isoform GS(2), which eluted at 280 mM KCl, is generally associated with the chloroplast and is thought to be active in the primary assimilation of ammonium in leaves. Thus GS(2) activity may be important if conifers are to avoid ammonium toxicity under circumstances, such as exposure to nitrous oxides, where nitrate reductase activity is induced in needles. In June, 72% of total GS activity was located in needles. Near the end of the growing season in August, however, only 1% of total GS activity was found in needles whereas 79% was found in roots.

In vitro release of alpha 1-acid glycoprotein RNA sequences shows fidelity with the acute phase response in vivo.

The acute phase reaction of rat liver to subcutaneous turpentine challenge results in a 20- to 100-fold increase in alpha 1-acid glycoprotein (alpha AGP) mRNA. We utilized this response to establish conditions appropriate for study of RNA transport in vitro using hybridization with 32P-labeled exon and intron alpha AGP sequences. Contamination of nuclear preparations by membrane-absorbed cytoplasmic RNA was eliminated by detergent-rinsing. The in vitro incubation conditions that most reflected the in vivo state required RNase inhibitor (purified from placenta), polyvinylpyrrolidone to prevent nuclear swelling, and addition of ATP. Under these circumstances, alpha AGP sequences were transported only from turpentine-stimulated preparations, were found only in poly(A)+ RNA, and were the same size as authentic cytoplasmic mRNA. Omission of polyvinylpyrrolidone resulted in release of some alpha AGP sequences in smaller, more heterogeneous poly(A)- RNA, and leakage of some alpha AGP sequences was observed from control preparations. Omission of ATP resulted in restriction of mature alpha AGP mRNA to the nucleus. In contrast to alpha AGP mRNA, transport of albumin mRNA was decreased 3-4X in turpentine-treated preparations. The largest alpha AGP intron was not found in RNA transported from treated nuclei in complete medium. The intron-containing fragments remained in the nucleus, largely in poly(A)- RNA of a size consistent with free intron. Some hybridization of intron sequences was observed with cytoplasmic and nuclear membrane-associated poly(A)+ RNA preparations which may represent 3'-processing catabolites; leakage of these sequences was considerably greater in the absence of PVP. On the basis of densitometric estimates, a 5-fold increase in the amount of alpha AGP exon sequences was observed in nuclear RNA, comparing treated with control animals, but transport of alpha AGP exon sequences was detectable only from treated nuclei, indicating at least a 50-fold increase in abundance of alpha AGP sequences. This suggests that a selective gating mechanism may be operative at the level of post-transcriptional nucleocytoplasmic transport during induction of alpha AGP in the acute phase response.

Chlorothiazide-Polyvinylpyrrolidone (PVP) Interactions: Influence on Membrane Permeation (Everted Rat Intestine) and Dissolution

The permeation of chlorothiazide through the in vitro everted rat intestine was investigated from dilute, saturated and supersaturated solutions in the presence and absence of PVP. Although chlorothiazide clearance was lower than that of either hydrochlorothiazide or salicylic acid, the high dose to solubility ratio rather than excessive membrane impermeability, seemed the primary factor limiting chlorothiazide absorption. Reduced chlorothiazide membrane transport from dilute solutions containing PVP and enhanced dissolution from a drug:PVP (1:2) mechanical mixure were observed and could be explained by the formation of a soluble complex in solution. Chlorothiazide transport rates, from systems supersaturated relative to crystalline chlorothiazide, were enhanced in the presence of PVP. This effect together with increased dissolution from a chlorothiazide:PVP (1:2) coprecipitate were consistent with the ability of PVP to inhibit drug crystallization.