Broadband dielectric study of dynamics of polymer and solvent in poly(vinyl pyrrolidone)/normal alcohol mixtures

Broadband dielectric measurements of poly(vinyl pyrrolidone) (PVP)-monohydroxyl alcohol mixtures of various normal alcohols with the number of carbon atoms per molecule ranging from 1 to 9 were made in the frequency range of 20 Hz to 20 GHz at 25 degrees C. Two relaxation processes due to the reorientation of dipoles on the PVP and alcohol molecules were observed. The relaxation process at frequencies higher than 100 MHz is the primary process of alcohols, and that at frequencies lower than 10 MHz is attributed to the local chain motion of PVP. For mixtures of alcohol molecules that are smaller than propanol, the relaxation time of the alcohol increases with increasing PVP concentration, whereas for mixtures of alcohol molecules larger than butanol, the relaxation time of the alcohol decreases with increasing PVP concentration. The increase in the density of hydrogen-bonding sites upon the addition of PVP reduces the relaxation time of alcohol in the mixture, and vice versa. The relaxation time of the local chain motion of PVP increases with PVP concentration and solvent viscosity. Different time scales of the molecular motions of polymer and solvent coexist in homogeneous mixtures with hydrogen-bonded polar solvent and polymer.     

Broadband dielectric study of dynamics of poly(vinyl pyrrolidone)-ethylene glycol oligomer blends

Broadband dielectric measurements for blends of poly(vinyl pyrrolidone) (PVP) and ethylene glycol oligomer (EGO) from 0 to 40 wt % PVP were carried out at 25 degrees C in the frequency range from 20 Hz to 20 GHz. The EGOs used in this study were ethylene glycol (EG), diethylene glycol (2EG), and PEG400 (MW = 400). For the PVP-EG, -2EG, and -PEG400 blends, relaxation processes caused by the motion of EGO in the GHz range and the micro-Brownian motion of the PVP chain at 10 kHz-1 MHz were observed. Although the PVP-EGO blend is miscible, relaxation processes caused by the molecular motion of EGO and the local chain motion of PVP were observed individually. The relaxation time of the local chain motion of PVP showed a strong PVP concentration dependence and a solvent viscosity dependence, which are similar to those reported so far for the solutions in nonpolar solvents.     

Solvent effects on the dielectric dispersion of poly(vinyl pyrrolidone)-poly(ethylene glycol) blends

The complex relative dielectric function , loss tangent , complex electric modulus and alternating current electrical conductivity dispersion behaviour of liquid poly(vinyl pyrrolidone)-poly(ethylene glycol) (PVP–PEG) blends in water, ethyl alcohol and 1,4–dioxane solvent over the entire volume mixture concentration range has been investigated in the frequency range of 20 Hz to 1 MHz at 25 °C. The PVP–PEG blends show the dielectric dispersion corresponding to the micro-Brownian motion of the PVP chain in the upper frequency region, whereas in the lower frequency region, dielectric dispersion is due to ionic conduction and electrode polarization phenomena. Results show that the conductivity values of these blends in water and dioxane can be monitored with the change in the solvent concentration, whereas it has a small variation with ethyl alcohol concentration. The comparative dielectric dispersion shape study confirms that the chain dynamics of polymers blend is influenced by heterogeneous interactions and solvent polar strength.     

Interpolymer complexation and thermal behaviour of poly(styrene-co-maleic acid)/poly(vinyl pyrrolidone) mixtures

Polymer complexation between poly(styrene-co-maleic acid), (SMA28) and (SMA50) containing 28 and 50 mol% of maleic acid and poly(vinyl pyrrolidone) (PVP), has been investigated by differential scanning calorimeter (DSC), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). All results showed that the ideal complex composition of SMA28/PVP and SMA50/PVP leads, respectively, to 2:1 and 1:1 mole ratio of interacting components.For the investigated systems, the T_g versus composition curve does not follow any of the usual proposed models for polymer blends. Withal, a new model proposed by Cowie et al. is used to fit the T_g data and it is found to reproduce the experimental results more closely. According to n and q obtained values, it seems reasonable to conclude that the inter-associated hydrogen bonds dominate in SMA28/PVP (2:1) complexes. This effect is corroborated by the FTIR study as evidenced by the high displacement of the specific bands and ionic interactions have been clearly identified. Finally, a thermogravimetric study shows that ionic interactions increase the thermal stability of these complexes.     

Miscibility and orientation behavior of poly(vinyl alcohol) / poly(vinyl pyrrolidone) blends

The miscibility of poly(viny1 alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) blends is investigated by differential scanning calorimetry (DSC) and wide-angle x-ray diffraction (WAXD). The molecular orientation induced by uniaxial stretching of the blends is also examined by WAXD and birefringence measurements. It is shown by the DSC thermal analysis that the polymer pair is miscible, since a single glass transition temperature (T_g) is situated between the T_gs of the two homopolymers at every composition. The T_g versus composition curve does not follow a monotonic function but exhibits a cusp point at a PVP volume fraction of a little under 0.7, as in a case predicted by Kovacs' theory. The presence of a specific intermolecular interaction between the two polymers is suggested by an observed systematic depression in the melting point of the PVA component. A negative value of the polymer-polymer interaction parameter, χ₁₂ = 0.35 (at 513 K), is estimated from a thermodynamic approach via a control experiment using samples crystallized isothermally at various temperatures. The extent of optical birefringence (Δn) of the drawn blends decreases drastically with increasing PVP content up to 80 wt %, when compared at a given draw ratio, and ultimately Δn is found to change from positive to negative at a critical PVP concentration of a little over 80 wt %. Discussion of the molecular orientation behavior takes into consideration a birefringence compensation effect in the miscible amorphous phase due to positive and negative contributions of oriented PVA and PVP, respectively.     

Interaction of collagen and poly(vinyl pyrrolidone) in blends

The interaction between collagen and poly(vinyl pyrrolidone) (PVP) in blends has been studied by viscometry, differential scanning calorimetry (DSC) and by Fourier transform infrared spectroscopy (FTIR). It was found that the amide A and amide I bands position in FTIR spectra of collagen were shifted after blending with PVP to higher wavenumbers. DSC measurements showed different melting temperature, glass transition temperature and enthalpy for the blends and for the single components. Viscosity measurements showed interaction between collagen and PVP also in a dilute water solution.The results have shown, that the interactions between collagen and PVP exist due to the strong interactions between the synthetic and biological component, mainly by hydrogen bonds. These interactions caused that collagen and PVP are miscible at molecular level. The blending of collagen with PVP may give the possibility of producing new materials for potential biomedical applications.     

Interactions between cationic mixed micelles and poly(vinyl pyrrolidone)

 The conductances of trimethyltetradecylammonium bromide (TTAB) + trimethylhexa decylammonium bromide (HTAB) and TTAB + trimethyldodecylammonium bromide (DTAB) mixtures over the entire mole fraction range were measured in aqueous poly(vinyl pyrrolidone) (PVP) containing 1–10 wt% PVP at 30 °C. Each conductivity (κ) curve for the TTAB + HTAB mixtures showed two breaks corresponding to two aggregation processes over the whole mole fraction range, except in the case of pure TTAB, where a single break corresponding to the conventional critical micelle concentration (cmc) was observed. In the case of TTAB + DTAB mixtures, each κ curve at a particular mole fraction of TTAB showed only one break, which was quite close to a similar one in pure water. In TTAB + HTAB mixtures, the first break is called the critical aggregation concentration. It is close to the conventional cmc and is attributed to the polymer-free micelle formation, whereas the second break is due to the polymer-bound micellar aggregates. However, no polymer-bound micellar aggregation process was observed in the case of TTAB + DTAB mixtures. Therefore, the presence of micelle–PVP interactions in the TTAB + HTAB case have been attributed to the stronger hydrophobicity of HTAB or TTAB + HTAB micelles in comparison to that of single or mixed micelles of TTAB + DTAB mixtures. From the conductivity data, various micelle parameters in the presence of PVP have been computed and discussed in terms of micelle–polymer interactions. The mixing behavior of TTAB +  HTAB corresponding to the first break, and that of TTAB + DTAB mixtures in the presence of PVP, is close to ideal and is also identical to that in pure water. Received: 26 August 1999 Accepted: 6 November 1999     

Electrospinning of poly(vinyl pyrrolidone)-iodine complex and poly(ethylene oxide)/poly(vinyl pyrrolidone)-iodine complex - a prospective route to antimicrobial wound dressing materials

New nanofibers containing poly(vinyl pyrrolidone)-iodine complex (PVP-iodine) were obtained by electrospinning in order to prepare materials suitable for wound dressings. Different approaches were used: a one-step method based on electrospinning of PVP-iodine or poly(ethylene oxide)/PVP-iodine solutions and a three-step method based on electrospinning of PVP or poly(ethylene oxide)/PVP mixed solutions followed by photo-mediated crosslinking of the obtained nanofibers and subsequent complexation with iodine. The average diameters of the fibers were in the range 150-470 nm depending on the composition and on the applied field strength (AFS) and increased with increasing the amount of PEO in the spinning solutions. Higher AFS resulted in greater fiber diameter and in size distribution broadening. Photo-mediated crosslinking in the presence of 4,4′-diazidostilbene-2,2′-disulfonic acid disodium salt successfully stabilized the electrospun PVP and PEO/PVP nanofibers against water and water vapor.     

Synthesis and characterization of poly(vinyl pyrrolidone)-capped bismuth nanospheres

Poly(vinyl pyrrolidone)-capped bismuth nanospheres were synthesized by a simple and convenient wet chemical method. In the process, bismuth nitrate was reduced by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) at 185 °C in air. PVP was used as a protecting agent to prevent oxidation of the sperical bismuth particles. PVP molecules were absorbed on the surface of bismuth nanospheres through the interaction of O–Bi bond which was confirmed by Fourier transform infrared (FT-IR) measurement. The thermal analysis shows the samples contained about 73 wt.% metallic bismuth. The optical absorption spectrum of poly(vinyl pyrrolidone)-capped bismuth nanosphere shows a strong absorption band at 275 nm.     

Grafting of poly(vinyl pyrrolidone) onto gelatin and its application as synthetic plasma expander

Grafting of N-vinyl pyrrolidone onto gelatin is reported using α,α'-azobisisobutyronitrile as initiator. The effects of various variables like initiator concentration, monomer concentration, time and temperature are reported. These variables appreciably affect the percentage grafting, grafting efficiency and molecular weight of the grafted chain. The graft copolymers were characterized by i.r. spectroscopy and ninhydrin tests. Sulphathiazole was coupled to these graft copolymers using a diazotization technique. Blood compatibility of these graft copolymers of different side chain molecular weight was found to be satisfactory.     

Silver nanoparticles stabilized by crosslinked poly(vinyl pyrrolidone) and its application for facilitated olefin transport

Positively polarized silver nanoparticles by poly(vinyl pyrrolidone) (PVP) have been demonstrated for use as stable olefin carriers for facilitated olefin transport membranes. The formation and size of silver nanoparticles stabilized by PVP were monitored using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Nanocomposite membranes consisting of polymer and silver nanoparticles stabilized by PVP exhibited the high separation performance for olefin/paraffin mixtures. X-ray photoelectron spectroscopy (XPS) showed that silver nanoparticles stabilized by PVP exhibited a high positive polarity, resulting in the reversible interaction between the surface of silver nanoparticles and olefin molecules.     

Viscoelasticity and tack of poly(vinyl pyrrolidone)–poly(ethylene glycol) blends

The adhesive properties of blends of high molecular weight poly(vinyl pyrrolidone) (PVP) and low molecular weight poly(ethylene glycol) (PEG) were systematically investigated with a probe test and correlated with their viscoelastic properties. The material parameters that were varied were the PEG content (31–41 wt %) and the hydration rate. The 36% PEG showed the best balance of properties for a pressure‐sensitive adhesive. At low debonding rates, the debonding took place through the formation of a fibrillar structure, whereas at high debonding rates, the debonding was brittle. This transition was attributed to the breakage and reformation of hydrogen bonds between PVP units and OH groups on PEG during the large strain of the polymer chains in elongation. This transition was observed, albeit shifted in frequency, for all three compositions, and the characteristic relaxation times of the hydrogen‐bonded network were estimated. A comparison between the tack properties of the adhesives and their linear viscoelastic properties showed a very strong decoupling between the small‐strain and large‐strain properties of the adhesive, which was indicative of a pronounced deviation from rubber elasticity in the behavior of the blends. This deviation, also seen during tensile tests, was attributed to the peculiar phase behavior of the blends. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2395–2409, 2002     

Dynamic structure of poly(vinyl pyrrolidone)/ethyl alcohol mixtures studied by time domain reflectometry

Dielectric studies of poly(vinyl pyrrolidone)/ethyl alcohol (PVP–E) binary mixtures with concentration variations were carried out in the frequency range of 10 MHz to 10 GHz by time domain reflectometry at 15, 25, 35, and 45 °C. One relaxation process, corresponding to ethyl alcohol molecules in the poly(vinyl pyrrolidone) (PVP) matrix, was observed in this frequency range for all the mixtures. The static dielectric constant of the PVP–E mixtures decreased linearly with an increase in the weight fraction of PVP. The observed anomalous increase in the value of the relaxation time (τ) of these mixtures was interpreted by the consideration of the variation in the local structure of self‐associated ethyl alcohol molecules and also the PVP behavior as a geometric constraint for the rotational motion of ethyl alcohol molecules. Furthermore, the τ values of these mixtures were independent of the viscosity. The energy parameters for the dielectric relaxation process (the free energy, enthalpy, and entropy of activation for the dipolar orientation) were determined to confirm the transient behavior of the heterogeneous species due to the breaking and re‐forming of hydrogen bonds with the internal rotation of ? OH groups in the ordered structure of the PVP–E mixtures. On the basis of the evaluated dielectric parameters, the formation of supermolecular structure in the PVP–E mixtures in dynamic equilibrium was sketched and examined by the consideration of the hydrogen bonding between the terminal hydroxyl groups of self‐associated ethyl alcohol flexible chains and the carbonyl groups of monomer units of PVP coiled chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1134–1143, 2005     

Solubilization and stabilization of fullerene C60 in presence of poly(vinyl pyrrolidone) molecules in water

Solubilizing C₆₀ molecules in an aqueous medium is highly imperative in processing them in different forms of ionic or nonionic liquids, nanofluids, films and other derivatives. In this investigation, we report a facile chemical route using polymer molecules of poly(vinyl pyrrolidone) (PVP) which mediate C₆₀ molecules dissolving in water in a stable solution at room temperature. Poly(vinyl pyrrolidone) molecules, soluble in water as well as many organic liquids such as n-butanol, ethanol, or DMF, can be useful for transferring C₆₀ molecules from a non-aqueous to an aqueous system. A broad optical absorption arises over 270–520 nm when C₆₀ molecules are dissolved in water, 0.001–0.065 g/L in presence of 20–120 g/L PVP molecules. It consists of a strong π → π* absorption band (relatively sharp) lying at 294 nm in C(sp²) electrons from PVP-surface modified C₆₀ molecules followed by a broad charge transfer band which extends up to 520 nm. Upon a suitable surface modification, the C₆₀ molecules conquer enhanced optical absorption in both kinds of the bands. Dynamic light scattering reveals an average hydrodynamic length 181.5 nm and a polydispersity index 0.506 after a typical loading 0.065 g/L C₆₀. A zeta potential ?8.3 mV with a surface conductivity 0.064 mS/cm at 6.5 pH describes a negatively charged surface structure, showing an n-electron transfer from C=O (PVP) to a nanosurface in surface modified C₆₀ molecules in a weak donor–acceptor complex. Water soluble C₆₀ in presence of a biocompatible compound like PVP is useful for biological, medicinal, and other applications.     

Rheological behaviour of irradiated wound dressing poly(vinyl pyrrolidone) hydrogels

The use of hydrogels as biomaterials has increased lately. Poly(vinyl pyrrolidone) (PVP) is an example of polymer hydrogels applied for the synthesis of hydrogel to be used in different biomedical applications. This paper describes a study on rheological properties of PVP hydrogels obtained by gamma radiation techniques. PVP hydrogels were obtained by gamma radiation of PVP water solutions with different radiation doses. It was studied the influence of additives such as poly(ethylene glycol) (PEG), poly(ethylene oxide) (PEO) and glycerol on the rheological behaviour of the gel. The rheological behaviour of hydrogel samples was characterized by measuring the shear storage modulus (G′) under dynamic shear loading. Besides this, sterility and cytotoxicity tests were performed. The study on rheological behaviour of hydrogels showed that G′ of PVP gels change according to the additive used. Glycerol increases the fluidity of the gel. The influence of PEG depends on the amount and on its molecular mass. The increase on PEG amount and molecular mass cause a decrease of G′ and an increase in the crosslinking density of PVP hydrogel network. The use of high molecular weight PEO allows the increase of the elasticity of the PVP gels.     

Synthesis and gas permeation properties of poly(vinyl chloride)‐graft‐poly(vinyl pyrrolidone) membranes

A series of amphiphilic graft copolymers consisting of poly(vinyl chloride) (PVC) main chains and poly(vinyl pyrrolidone) (PVP) side chains, i.e. PVC‐g‐PVP, was synthesized via atom transfer radical polymerization (ATRP), as confirmed by ¹H NMR, FT‐IR spectroscopy, and gel permeation chromatography (GPC). Transmission electron microscope (TEM) and small angle X‐ray scattering (SAXS) analysis revealed the microphase‐separated structure of PVC‐g‐PVP and the domain spacing increased from 21.4 to 23.9 nm with increasing grafting degree. All the membranes exhibited completely amorphous structure and high Young's modulus and tensile strength, as revealed by wide angle X‐ray scattering (WAXS) and universal testing machine (UTM). Permeation experimental results using a CO₂/N₂ (50/50) mixture indicated that as an amount of PVP in a copolymer increased, CO₂ permeability increased without the sacrifice of selectivity. For example, the CO₂ permeability of PVC‐g‐PVP with 36 wt% of PVP at 35°C was about four times higher than that of the pristine PVC membrane. This improvement resulted from the increase of diffusivity due to the disruption of chain packing in PVC by the grafting of PVP, as confirmed by WAXS analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

An ESR study of polymer-Cu(II) complexes in poly(vinyl alcohol), polyacrylamide,and poly(vinyl pyrrolidone) films

Optical and ESR spectra of polymer-Cu(II) complexes in polymer films have been studied. The dependence on F₁ = [Cu²⁺]/[MU] and F₂ = [OH^?]/[Cu²⁺], where [MU] is the molar concentration of monomeric units of the polymer, has been obtained. Optical spectra and potentiometric titration curves in solution have also been studied. There exists a buffer region 0 ? F₂ ? 2. Optical spectra in films are slightly different from those in solutions. At least five different ESR signals, designated as A, B, C or D, and E, have been found in poly(vinyl alcohol)-Cu(II). These signals appear successively with increasing F₂. Assignments are proposed as follows. Signal A (F₂ ≈ 0), also found in poly(acrylamide)-Cu(II) and poly(vinyl pyrrolidone)-Cu(II), is due to a single Cu(II) coordinated with two water molecules and chelated with two oxygens or nitrogens attached to the polymer. A chain of Cu(II) ions singly and double bridged with OH^? ions is responsible for the B signal (F₂ ≈ 1). The C and D signals (F₂ ≈ 2) appear to be caused, respectively, by a dimeric Cu(II) complex singly or doubly bridged with OH^? ions. The E signal (F₂ ≈ 7) appears to be due to a monomeric Cu(II) complex, different from that responsible for the A signal.     

Water sorption and transport in blends of poly(vinyl pyrrolidone) and polysulfone

Water sorption and transport properties for a series of miscible blends of hydrophobic bisphenol A polysulfone and hydrophilic poly(vinyl pyrrolidone) are reported. Study was restricted to blends that remained homogeneous after exposure to liquid water. The solubility of water in the blend films increased with increasing hydrophilic polymer content. Equilibrium sorption isotherms show dual-mode behavior at low activities and swelling behavior at high activities. The sorption kinetics are generally Fickian for blends containing 20% poly(vinyl pyrrolidone) or less, but exhibit two-stage behavior in blends containing 40% poly(vinyl pyrrolidone). Diffusion coefficients extrapolated to zero concentration decrease with increasing poly(vinyl pyrrolidone) content, owing to a decrease in the fractional free volume. However, the diffusion coefficient becomes a greater function of activity as the composition of hydrophilic polymer in the blend is increased, due to plasticization of the material by large levels of sorbed water. Permeability coefficients generally decrease with increasing poly(vinyl pyrrolidone) content for blends containing 20% poly(vinyl pyrrolidone) or less because the decrease in the diffusion coefficient is greater than the increase in the solubility coefficient. Blends containing 40% poly(vinyl pyrrolidone) have permeability coefficients greater than those of polysulfone due to high water solubility. The permeability coefficients depend on water concentration in approximately the same way for all blends. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 655–674, 1997     

Electrospun nanofibers of poly（vinyl pyrrolidone）/Eu^3＋ and its photoluminescence properties

Nanofibers of poly（vinyl pyrrolidone） （PVP）/Eu^3＋ with diameters of 300-900 nm were prepared by using sol-gel processing and electrospinning technique. The products were characterized by scanning electron microscope （SEM）, Fourier transform infrared spectroscopy （FT-IR）, and photoluminescence （PL）. The results indicated that, Eu^3＋ was successfully embedded in the onedimensional hybrid nanofibers, and the PVP/Eu^3＋ hybrid nanofibers had favorable photoluminescence properties.