Crystallization and aggregation behaviors of calcium carbonate in the presence of poly(vinylpyrrolidone) and sodium dodecyl sulfate

An anionic surfactant interacts strongly with a polymer molecule to form a self-assembled structure, due to the attractive force of the hydrophobic association and electrostatic repulsion. In this crystallization medium, the surfactant-stabilized inorganic particles adsorbed on the polymer chains, as well as the bridging effect of polymer molecules, controlled the aggregation behavior of colloidal particles. In this presentation, the spontaneous precipitation of calcium carbonate (CaCO3) was conducted from the aqueous systems containing a water-soluble polymer (poly(vinylpyrrolidone), PVP) and an anionic surfactant (sodium dodecyl sulfate, SDS). When the SDS concentrations were lower than the onset of interaction between PVP and SDS, the precipitated CaCO3 crystals were typically hexahedron-shaped calcite; the increasing SDS concentration caused the morphologies of CaCO3 aggregates to change from the flower-shaped calcite to hollow spherical calcite, then to solid spherical vaterite. These results indicate that the self-organized configurations of the polymer/surfactant supramolecules dominate the morphologies of CaCO3 aggregates, implying that this simple and versatile method expands the morphological investigation of the mineralization process.     

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.     

Titration microcalorimetry of poly(vinylpyrrolidone) and sodium dodecylbenzenesulphonate in aqueous solutions

Microcalorimetric titrations are carried out on solutions containing the anionic surfactant sodium dodecylbenzenesulphonate (SDBS), and mixtures of SDBS and the uncharged polymer poly(vinylpyrrolidone) (PVP). Measurements are taken at different temperatures. Micellisation of SDBS is driven by hydrophobic bonding. The interaction enthalpy of mixed PVP/SDBS systems shows clearly a consecutive endothermic and exothermic region with increasing surfactant concentration. The endothermic part can be looked upon as an incremental binding isotherm and reflects the number of surfactant molecules involved in the association process. The exothermic region features inverse hydrophobic bonding behaviour. This is related to the flexible nature of the adsorbent, i.e. the polymer. Electrostatic repulsion between neighbouring surfactant molecules causes at increased surfactant concentrations structural rearrangements of the polymer-surfactant complexes. This is accompanied by losing inter- and intrachain linking and entropy gain since the expanded complexes can move more freely. Additional surfactants continue to adsorb on the vacant hydrophobic adsorption sites. The influence of the initial amount of polymer and the electrolyte concentration support our proposals.     

Effect of ethanol on the interaction between poly(vinylpyrrolidone) and sodium dodecyl sulfate

The effect of ethanol on the interaction between the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic polymer poly(vinylpyrrolidone) (PVP) has been investigated using a range of techniques including surface tension, fluorescence, electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS), and viscosity. Surface tension and fluorescence studies show that the critical micelle concentration (cmc) of the surfactant decreases to a minimum value around 15 wt % ethanol; that is, it follows the cosurfactant effect. However, in the presence of PVP, the onset of the interaction, denoted cmc(1), between the surfactant and the polymer is considerably less dependent on ethanol concentration. The saturation point, cmc(2), however, reflects the behavior of the cmc in that it decreases upon addition of ethanol. This results in a decrease in the amount of surfactant bound to the polymer [C(bound) = cmc(2) - cmc] at saturation. The viscosity of simple PVP solutions depends on ethanol concentration, but since SANS studies show that ethanol has no effect on the polymer conformation, the changes observed in the viscosity reflect the viscosity of the background solvent. There are significant increases in bulk viscosity when the surfactant is added, and these have been correlated with the polymer conformation extracted from an analysis of the SANS data and with the amount of polymer adsorbed at the micelle surface. Competition between ethanol and PVP to occupy the surfactant headgroup region exists; at low ethanol concentration, the PVP displaces the ethanol and the PVP/SDS complex resembles that formed in the absence of the ethanol. At higher ethanol contents, the polymer does not bind to the ethanol-rich micelle surface.     

Physico-chemical and structural properties of hydrogels formed by chitosan, in the presence and absence of poly(vinylpyrrolidone) and sodium decylsulfate

The structure of chemically-crosslinked chitosan and chitosan-poly(vinylpyrrolidone) (PVP) hydrogels is investigated by means of the combined use of small-angle neutron scattering (SANS), electron paramagnetic resonance spectroscopy (EPR), intradiffusion, and swelling degree measurements. These hydrogels may be described in terms of an inhomogeneous structure composed by polymer-rich and polymer-poor regions. The polymer-rich regions, whose correlation distance zeta is ranged between approximately 600 and approximately 850 A, are, in turn, characterized by the presence of a network formed by the chemical crosslinks, with a mean correlation distance xi approximately 90 A. The structures of chitosan and chitosan-PVP hydrogels have also been analyzed in the presence of sodium decylsulfate micelles that could provide a multidomain system useful, in principle, for drug delivery applications. Both SANS and EPR measurements show that sodium decylsulfate micelles do not significantly interact with both the gels. Finally, intradiffusion and swelling degree measurements show an improved hydrophilicity of chitosan-PVP gels, even further magnified by the presence of C10OS surfactant.     

Formation process of silver-polypyrrole coaxial nanocables synthesized by redox reaction between AgNO3 and pyrrole in the presence of poly(vinylpyrrolidone)

We have recently demonstrated a one-step process to fabricate silver-polypyrrole (PPy) coaxial nanocables (Chen, A.; Wang, H.; Li, X. Chem. Commun. 2005, 14, 1863). The formation process of silver-PPy coaxial nanocables is discussed in this article. It was found from the results of TEM and SEM images that large numbers of silver atoms were formed when AgNO3 was added to a pyrrole solution. Then silver atoms transform to silver-PPy nanosheets with regular morphology, which will connect together to be more stable. Silver-PPy nanocables will be able to grow at the expense of the silver-PPy nanosheets. Poly(vinylpyrrolidone) (PVP) plays crucial roles in this process: as a capping agent to form silver nanowires, and as a dispersant of pyrrole monomers, which can influence the site at which pyrrole monomer exists. On the basis of experimental analysis, the possible mechanism was proposed. Because of the effect of PVP, silver ions and pyrrole monomers are apt to be adsorbed at the [111] and [100] facets of silver nanosheets, respectively. Obvious polymerization will take place on the boundary of the [111] and [100] facets. The PPy layer stays stable on the [100] facets. Meanwhile, newly formed silver atoms and silver nanosheets will further ripen and grow on the [111] facets. In a word, the morphology of final products and the formation process are determined by the reaction site between AgNO3 and the pyrrole monomer, which is influenced by PVP.     

CF bond activation in the reaction of BiCl3 with sodium 2,4,6-tris(trifluoromethyl)phenoxide

BiCl₃ reacts with sodium 2,4,6-tris(trifluoromethyl)phenoxide (NaOR_4f) in ether solution to produce an unusual condensation product in which three OR_f functions have been coupled with the elimination of three fluorine atoms. The product is R_fOC₆H₂(CF₃)₂C(O)OR_f, which has been characterized spectroscopically and by X-ray crystallography (triclinic space group P 1; a = 8.958(1), b = 12.652(2), c = 13.722(2)Å, α = 89.596(8)°, β = 75.92(1)°, γ = 71.412(7)°, V = 1425.6(3)ų, Z = 2). Bi(OR_f)₃ is believed to be an intermediate in this process. The carbonfluorine bond activation is not observed in the absence of BiCl₃.     

Studies of the antenna effect in polymer molecules. XVII. Synthesis and photocatalytic activity of poly(sodium styrenesulfonate-co-N-vinylcarbazole) and poly[sodium styrenesulfonate-co-N-(acryloyloxyhexyl)carbazole]

Two new antenna polyelectrolytes, poly(sodium styrenesulfonate-co-N-vinylcarbazole) (PSSS–VCz) and poly[sodium styrenesulfonate-co-N-(acryloyloxyhexyl)carbazole](PSSS–AHCz) have been synthesized. Both polymers were found to solubilize large hydrophobic compounds such as perylene in aqueous solution, but PSSS–AHCz was much more efficient than PSSS–VCz. The distribution coefficients of perylene between the polymer pseudophase and water was determined to be (2.9 ± 0.1) × 10⁶ and (4.0 ± 0.2) × 10⁴ in PSSS–AHCz and PSSS–VCz, respectively. The greater solubilizing ability of PSSS–AHCz is attributed to the higher content of hydrophobic monomer units in the polymer. Both copolymers displayed photocatalytic activity, absorbing light in the UV-visible spectral region. Energy can then be transferred to a solubilized molecule or dissolved oxygen and induce photochemical reactions. The model reaction used in this study was the photosensitized oxidation of perylene solubilized in aqueous polymer solutions. PSSS–AHCz was found to be a much more efficient photocatalyst than PSSS–VCz. The enhanced photocatalytic activity of PSSS–AHCz is attributed to the greater concentration of carbazole chromophores, the higher local concentration of probe in the polymeric pseudophase and possibly to the elimination of the low-energy excimer.     

Hydrogel characteristics of electron-beam-immobilized poly(vinylpyrrolidone) films on poly(ethylene terephthalate) supports

A novel strategy for the preparation of thin hydrogel coatings on top of polymer bulk materials was elaborated for the example of poly(ethylene terephthalate) (PET) surfaces layered with poly(vinylpyrrolidone) (PVP). PVP layers were deposited on PET foils or SiO2 surfaces (silicon wafer or glass coverslips) precoated with PET and subsequently cross-linked by electron beam treatment. The obtained films were characterized by ellipsometry, X-ray photoelectron spectroscopy, infrared spectroscopy in attenuated total reflection, atomic force microscopy (AFM), and electrokinetic measurements. Ellipsometric experiments and AFM force-distance measurements showed that the cross-linked layers swell in aqueous solutions by a factor of about 7. Electrokinetic experiments indicated a strong hydrodynamic shielding of the charge of the underlying PET layer by the hydrogel coatings and further proved that the swollen films were stable against shear stress and variation of pH. In conclusion, electron beam cross-linking ofpreadsorbed hydrophilic polymers permits a durable fixation of swellable polymer networks on polymer supports which can be adapted to materials in a wide variety of shapes.     

Synthesis of aramides in solutions of poly(vinylpyrrolidone)

Results on polycondensation of poly(1.4 benzamide) (PBA) and 2.5.DCIPDAcoTPA in solutions of poly(vinylpyrrolidone) (PVP) will be presented. For polycondensation, the method of OGATA, using triphenylphosphine and hexachloroethane, and the low-temperature solution polycondensation of dicarboxylic acid dichlorides and diamines, were applied. It is shown that the molar mass of PBA depends strongly on the PVP:PBA ratio. To explain this dependence, one has to take into account the phase behavior of the ternary rigid rod polymer/flexible coil polymer/solvent system and the influence of the matrix polymer. An enhancement of the molar mass of the PBA produced can be observed when the PVP:PBA is high enough to prevent an association of the PBA, i.e. when one stays in the isotropic one-phase area of the phase diagram. Under these circumstances, it is possible to obtain one-phase systems in nonsolvents for the aramides.     

Solubility of silybin in aqueous poly(vinylpyrrolidone) solution

Silybin is a main component in silymarin, which is an antihepatotoxic polyphenolic substance isolated from the milk thistle plant, Silybum marianum. A major problem in the development of an oral solid dosage form of this drug is the extremely poor aqueous solubility. In present work, the solubility of silybin in aqueous poly(vinylpyrrolidone) (PVP k30) solution at the temperature range from 293.15 to 313.15 K was measured by a solid–liquid equilibrium method. Experimental results reveal that the solubility of silybin increases with the increase both in PVP's concentration and temperature. With the increase in PVP's concentration, the transfer enthalpy for silybin from water to aqueous PVP solution decreases within a negative region, and the transfer entropy increases slightly first in a positive region and then decreases to a negative region. The transfer enthalpy is lower than the entropy term. A modified UNIQUAC model was used to correlate solubility data.     

Sorption and diffusion of water in poly(vinylpyrrolidone)

The effect of molecular mass, thermal prehistory, physical state, and three-dimensional chemical crosslinked structure of a polymer on dissolution and diffusion in the PVP-water system has been studied. The kinetic dependences of sorption that correspond to the Fickian or pseudonormal type have been measured. In a certain concentration range, sorption is accompanied by transition of the system to the rubbery state. In the glassy state, the negative concentration dependence of the diffusion coefficient related to the nonequilibrium state of the polymer sorbent is observed. Sorption isotherms are described by S-shaped curves. It has been shown that the thermal prehistory of the polymer sorbent has the most pronounced effect on its sorption behavior. The effect of molecular mass is insignificant, while three-dimensional chemical crosslinks in PVP manifest themselves only in the region of the rubbery state. In accordance with the double sorption model, the experimental isotherms are represented as the superposition of two isotherms described by the Langmuir and Flory-Huggins equations. For the glassy state of the polymer sorbent, the degree of the nonequilibrium state has been estimated. With due regard for the excess free volume, the detailed thermodynamic analysis of isotherms has been performed; namely, the pair interaction parameters and the free energy of mixing have been calculated. The state of water in the polymer has been examined within the framework of hydrate contributions and clusterization theory.     

Intramolecular mobility of spin labelled poly(vinylpyrrolidone) and poly(vinylcaprolactam) in solutions

The intramolecular (segmental) mobilities of poly(vinylpyrrolidone) and poly(vinylcaprolactam) in solutions have been investigated using the spin label technique. The rotational correlation times for the segments do not depend on the spin label used for their determination. The rotational correlation times and the effective segmental dimensions for poly(vinylcaprolactam) are greater than those for poly(vinylpyrrolidone), the difference being due to different dimensions of the side-groups of the macromolecules. Near the temperature of phase separation in an aqueous solution of poly(vinylcaprolactam), the hydrophobic interaction of macromolecular side-groups leads to the compression of the molecular coil. As a result, the segmental mobility diminishes, and the spatial limitations on the rotation of a spin label surrounded by bulky side-groups become more severe.     

Oxiranylidene intermediate in the reaction of trans-2-chloro-3- tert-butyloxirane with sodium phenoxide.

The reaction of trans-2-chloro-3-(t-butyl)oxirane with sodium phenoxide in acetonitrile to give trans-2-phenoxy-3-(t-butyl)oxirane involves α-elimination to give an oxiranylidene which undergoes a stereoselective stepwise addition of phenol to give product.     

On the effect of copper (II) and chloride ions on the iodate-hydrogen peroxide reaction in the presence and absence of manganese (II)

The effect of copper (II) and chloride ions on the manganese (II) catalyzed iodate-peroxide reaction has been examined with reference to the hydrogen peroxide-iodic acid-manganese (II)-organic species oscillatory reaction. The observations are considered to provide evidence for iodine dioxide as the key intermediate in the manganese (II) catalyzed reaction. Kinetic data for the copper (II) catalyzed reaction are reported.     

Complex formation of daunomycin with poly(vinylpyrrolidone) and poly(ethylene glycol)

Russian Journal of General Chemistry - Complexes of the anthracycline antitumor antibiotic daunomycin with biocompatible polymer carriers, poly(vinylpyrrolidone) and poly(ethylene glycol), have...     

Effective luminescence quenching of tris(2,2-bipyridine)ruthenium(II) by methylviologen on clay by the aid of poly(vinylpyrrolidone)

Electron-transfer quenching of tris(2,2-bipyridine)ruthenium(II) by methylviologen in an aqueous suspension of clay in the presence of poly(vinylpyrrolidone) was investigated. The quenching behavior of the excited tris(2,2-bipyridine)ruthenium(II) on clay by the coadsorbed methylviologen indicated the homogeneous distribution of the adsorbed dyes. The quenching rate was high when the clay with larger particle size was used as the host. The adsorption of poly(vinylpyrrolidone) on clay resulted in the coadsorption of the tris(2,2-bipyridine)ruthenium(II) and methylviologen without segregation.     

Interdiffusion at the interface between poly(vinylpyrrolidone) and epoxy

Electron microprobe analysis (EMP) was used to study interdiffusion in bilayer films of thermoplastic poly(vinylpyrrolidone) (PVP) and a thermoset epoxy. The bilayer films were prepared by casting a stoichiometric mixture of the uncured diglycidyl ether of bisphenol A epoxy (DGEBA) and 4,4′-diaminodiphenylsulfone (DDS) on the PVP film and then curing the system in a two-step process under a nitrogen atmosphere. For the EMP studies, the sulfur signal was used as a probe for DDS, while the nitrogen signal served as a probe for both DDS and PVP. The addition of brominated DGEBA to the conventional DGEBA in a 1: 1 weight ratio allowed the bromine signal to be used as a probe for the epoxy phase. It was found that the interfacial thickness was much larger for the film prepared from low molecular weight PVP than that from high molecular weight PVP. Interdiffusion was suppressed when the initial cure temperature in the two-step cure cycle was 130°C compared to 170°C, in which the first stage of the cure reaction dominated the interdiffusion process. More importantly, it was demonstrated that the diffusion front of the curing agent was located closer to the thermoplastic polymer phase as compared to that of the thermoset polymer in the interface region. This tendency was more significant in the system with the larger interfacial thickness. These results have important consequences on interphase structures and properties. They suggest that crosslinking of the epoxy in the interphase may be suppressed because of an insufficient amount of curing agent and that the not-fully-reacted curing agent in the PVP phase may act to plasticize this phase. © 1997 John Wiley & Sons, Inc.     

Effects of inorganic salts on the properties of aqueous poly(vinylpyrrolidone) solutions

Cloud point curves and temperatures have been determined for aqueous solutions of poly(vinylpyrrolidone) at several concentrations for a variety of inorganic salts (phosphates, monohydrogen phosphates, sulfates, carbonates, dihydrogen phosphates and fluorides). The resulting dependency of the critical temperatures (mostly between 289 and 350 K) on the molar concentration can be expressed as sequences showing the decreasing effect of anion species or cation species in salting out the polymer. The decreasing order of effectiveness of the anions in reducing the temperatures is PO ₄ ^3– >HPO ₄ ^2– >SO ₄ ^2– CO ₃ ^2– >H₂PO ₄ ^– >F^–. The order for cation is Na⁺>K⁺. The changes brought about in temperatures by the salts were found to be the results of the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and additive salts and of the change of water structure by structure making or structure breaking ions, and of the influence of salts on the hydration sheath of the polymer.Deceased