Polymer PVP

As discussed earlier the whole process is a redox reaction. Selenium is reduced using sodium borohydride to give selenide ions. In the above reaction, the metal ion reacts with the polymer (PVP or PVA) solution to form the polymer-metal ion solution. Addition of the selenide ion solution to the polymer-metal ion solutions resulted in instantaneous change in the colour of the solutions from colourless to orange (PVA) and orange red (PVP). This indicates the formation of CdSe nanoparticles. The addition of the selenide solution to the polymer - metal ion solution resulted in gradual release of selenide ion (Se -) upon hydrolytic decomposition in alkaline media (equation 4). The released selenide ions then react with metal ion to form seed particles (nucleation). 

Recently, Somorjai, Yang et al. [143] examined this reaction over lwt.% Pt/SBA-15 utilizing an elaborate preparation protocol. Preformed Pt nanoparticle sols of five different mean sizes, obtained by alcohol reduction in the presence of a protecting polymer (PVP) were combined with SBA-15 silica exhibiting 9nm pores. After 3h low-power ultrasonic treatment, the Pt particles were evenly distributed throughout the pores of the support (Figure 12 (a)-(e)). 

Recently, Chaudhari compared the activity of dispersed nanosized metal particles prepared by chemical or radiolytic reduction and stabilized by various polymers (PVP, PVA or poly(methylvinyl ether)) with the one of conventional supported metal catalysts in the partial hydrogenation of 2-butyne-l,4-diol. Several transition metals (e.g., Pd, Pt, Rh, Ru, Ni) were prepared according to conventional methods and subsequently investigated [89]. In general, the catalysts prepared by chemical reduction methods were more active than those prepared by radiolysis, and in all cases aqueous colloids showed a higher catalytic activity (up to 40-fold) in comparison with corresponding conventional catalysts. The best results were obtained with cubic Pd nanosized particles obtained by chemical reduction (Table 9.13). 

VNfeuts, I., D. Kempen, A. Decode, G. Verreck, J. Peeters, M. Brewster, and G. Van den Mooter. 2005. Physical stability of the amorphous state of loperamide and two fragment molecules in solid dispersions with the polymers PVP-K30 and PVP-VA6Sur J Pharm ScE5 313-320. 

In 1998 the commercially available polymer PVP (Mw 20,000) was introduced as a dielectric layer for organic TFTs by the Philips group [19]. It is soluble in common organic solvents (e.g. acetone, n-butanol, propylene glycol monomethyl ether ace-... 

The effect of the interdigitation between the polymer chains of two brushes on the interaction force profile is plotted in Fig. 8 for three polymers PVP-PI 69-39, PVP-PI 38-69, and PS-X (140 K). The solid curves present the results in which the interdigitation was taken into account, while the dashed ones those in which the interdigitation was neglected. For the former, the chain conformational partition function [Eq. (5)] involves a 2mX2m supermatrix G for which the chain free ends can be located in any lattice layer between the two surfaces. For the latter, the conformational partition function involves a m X in supermatrix G with chains con-... 

In the context of the model presented above, the microscopic relaxation time of a water molecule is equal to the cutoff time of the scaling in time domain To-For the most hydrophilic polymer, PVA, the strong interaction between the polymer and the water molecule results in the greatest value of microscopic relaxation time To, only 10% less than the macroscopic relaxation time of the bulk water. The most hydrophobic polymer, PVP, has the smallest value of a single water molecule microscopic relaxation time, which is almost equal to the microscopic relaxation time of bulk water (see Table III). Therefore, weakening the hydrophilic properties (or intensifying the hydrophobic properties) results in a decreasing of interaction between the water and the polymer and consequently in the decrease of To-... 

We summarize here the features of the UPS and UVA data which lead to the molecular ion concept for these aromatic pendant group polymers. First, the spectra of the polymers PVP and PS are essentially identical to those of condensed model molecular moieties 2-vinyl pyridine and ethyl benzene, respectively. Second, the solid-state spectra are related to the gas-phase spectra of these model moieties by an essentially constant shift to higher energy (lower binding energy) of all the ionization peaks by = 1.5 0.1 eV. Third, the width in energy of the solid-state ionization peak is Air = 1.0 0.1 for both polymers... 

We now consider the effect of electrostatics on initial adsorption rates. Our first example [26] is again for the polycationic polymer PVP+ adsorbing at pH 8 on Ti02, which is negatively charged under these conditions see Figure 5. It is the same system as considered in Figure lb. Two sets of... 

An advantage of radiochemical induced cross-linking is the possibility to combine polymers with different properties. For that purpose, the polymers were separately dissolved in water. The solutions were mixed and irradiated. (Gottlieb et al. 2005) describes the synthesis of temperature-sensitive hydrogel blends of PVME (as thermo-sensitive polymer) and the radiation-cross-linkable polymer PVP (a polymer that is applied in pharmaceutics). The experiments show that the gelation dose of the blend is between the gelation doses of the two pure polymers. 

Ru(r -C8Hio)(7] -C8Hi2) reacts rapidly with dihydrogen (1-3 atm) at room temperature in a hydrocarbon solvent to give ruthenium particles and cyclooctane. In the presence of a polymer (PVP nitrocellulose, NC cellulose acetate, CA), the reaction produces particles, the size of which depends upon the nature of the polymer and upon the relative concentration of the precursor in the polymer. In this way, monodisperse particles of 1 to 1.5 nm mean size have been... 

In model systems, the hydrophilic polymer PVP is frequently used as a stabilizing reagent for Au clusters. Here, to reduce computational costs, the PVP molecule shown in Fig. 19.5 was used as a model molecule to investigate the interactions between Au atoms and PVP. The optimized structure of Au-PVP is displayed in Fig. 19.5. The adsorption energy of this model was estimated to be 3.93 kcal/mol, and the Mulliken charge on the Au atom was —0.214. 

The influence of poly(N-vinylpyrrolidone) polymers (PVP) as electrolyte additives on the performance of lead—acid batteries has been studied, but controversial results are reported by different research groups depending on the molecular weight and concentration of the polymer used. The application of PVP as additive to the positive or negative active materials is probably more effective than if added to the electrolyte. 

A composite ceramic membrane was formed [77] by the graft polymerisation of a hydrophilic polymer, PVP, onto the surface of silica membranes (pore size = 3.0 pm). The flux of an unmodified UF membrane of an oil/water emulsion (4.7%) decreased with time as compared to the flux of the composite membrane. The dechne in flux was caused by fouling and/or the immediate formation of an oil gel layer on the surface of the unmodified membrane. The modified membrane, in contrast, was not only more resistant to adsorption of oil, but also had a higher oil rejection. The performance of the modified ceramic membrane depends upon the configuration of the grafted chains in response to solvent—polymer interactions. Thus, the hydrophific PVP polymer chains tend to expand or extend away from the surface in aqueous solutions, preventing oil adsorption on the membrane surface. Simultaneously, the hydrophific polymer allows the passage of water molecules preferentially over oil. 

PVP is a physiologically inert and biologically compatible polymer. PVP is known to reduce significantly the toxicity and irritant effects of many medications. PVP can form complexes with a variety of substances. For example, the PVP-iodine complex in the form of povidone or Betadine aqueous solution is the most widely used antiseptic in hospitals. It significantly reduces the toxicity and staining effect of the tincture of iodine solution but retains the germicidal activity of the iodine. 

FIG U RE 4.16 Surface tension as a function of SDS concentration in solutions of a charged polymer (PVP). The two T points can be seen. Reprinted from Lange (1971) with permission from Springer (copyright). 

D N- H HMQC experiments recorded at a 60kHz MAS rate were recently performed, in drugs (acetaminophen), polymer (PVP), and polymer-drug dispersions, to assess proximities between nitrogen and proton nuclei involved in H-bonds [44], This 2D N- H HETCOR NMR experiment considerably shortens the acquisition time required compared to a N-H HETCOR spectrum (6h vs 48h) [45]. The GIPAW-DFT approach was employed to calculate N ICSs and N EFG parameters (C and... 

FIGURE 134 Moisture uptake profiles as a function of relative humidity for a number of amorphous systems including polymers (PVP, HPMCAS, a PLA, X), amorphous indomethacin (IMC, ) and a 50% IMC-PVP amorphous mixture ( ) [42d, 46]. MD simulations for similar systems at selected water compositions are discussed in this chapter. The solid line represents the predicted moisture uptake profile for PLA from a recent MD simulation [12b], The structure shown adjacent to the sohd hne is the monomer unit within PLA. 

In solutions of polymers (PVP, PEG, PDDA) complete or partial neutralization of the negative charge of the anionic form of the initial metal complex was seem Similar behavior was observed for metal complexes comprising micelles (SDS). In the case of micellar system CTABr lanthanide bis-phthalocyanine predominantly existed in the anionic form. 

The QELS and adsorption studies of competitive adsorption and aggregation of macromolecules/ NP for polymers (PVP, PEG, PVA), gelatin, ovalbumin or BSA, and nanosilica are in agreement with the QCM data with respect to the effects of surface roughness, confinement space in pores, and the characteristics of macromolecules and their interactions in pre-adsorbed macromolecules and with partially coated solid surfaces. Proteins can more effectively displace smaller polymer molecules if the latter have only electron-donor groups (PEG, PVP). In the case of a pre-adsorbed... 

Before adsorption of polymers, nanosUica S =232 mVg) was heated in air at 450°C for several hours to remove adsorbed compounds. Certain amounts of the nanosilica powder and a polymer (PVP or PEG) solution were loaded into a glass reactor (2 dm ) with a mixer (>500 rpm) providing a pseudo-liquid state (PLSR) of a powder and agitated at room temperature for 0.5 h. Then certain amount of ethanol was dripped (one or two drops per second) in the reactor at room temperature and the mixture was agitated for 1-6 h, and then it was dried at room temperature (Gun ko et al. 2006i). 

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