1,721,082 research outputs found
PHASE EQUILIBRIA IN A WATER-BLOCK COPOLYMER SYSTEM
No full textMixts. contg. water and poly(oxyethylene-b-oxypropylene-b-oxyethylene) were studied and the phase boundaries detd. The phase diagram shows similarities with non-ionic surfactant systems of the n-alkyl-polyoxyethylene glycol family, with occurrence of different lyotropic liq. cryst. phases and of upper consolute boundaries. Added sodium salts have a pronounced effect on the crit. soln. boundaries, which can be shifted upwards (downwards), depending on the counterion. A qual. explanation of the above effects is given in terms of adsorption and/or depletion of the electrolytes at the polar-apolar interface of the aggregates formed by block copolymers
Polymer-Surfactant and Protein-Surfactant Interactions
No full textphase behaviour, thermodynamic properties, anionic polyelectrolyt
Supra-molecular association in bile salts.
No full textA review on the supramolecular association modes of bile salts in solution
WATER-TRIFLUOROETHANOL MIXTURES: SOME PHYSICOCHEMICAL PROPERTIES
No full textThe physicochem. properties of water-2,2,2 trifluoroethanol mixts. have been investigated, at 25 °C, by d., viscosity, surface tension, and relative permittivity. An anal. based on the Kirkwood theory for the dielec. polarization of mixts. has been performed and the gK correlation factor has been related to the occurrence of hydrogen bonding networks. Data on the above system have been analyzed and compared to literature data on water-ethanol mixts., to obtain information on the role that partial fluorination plays in the interactions of alcs. with water mols. As inferred from excess properties, nonideality contributions are smaller than in the corresponding water-ethanol solns. Accordingly, the extension of hydrogen bond networks and/or van der Waals contributions to the overall system stability are less significant than in simple alcs
Dispersability of carbon nanotubes in biopolymer-based fluids and their potential biotechnological applications
No full textThe dispersability of carbon nanotubes in aqueous solutions containing proteins or nucleic acids is discussed. In the
mentioned systems different dispersion modes occur, depending on the type and concentration of biopolymer, and on
the amount of dispersed nanotubes, as well. The phase behavior depends on how much biopolymers are adsorbing, and,
naturally, on their molecular details. Modulation of the nanotube/biopolymer interactions helps switching between
repulsive and attractive regimes between surface-functionalized particles. Accordingly, dispersion or phase separation
take place, and the formation of nematic phases, or gels, may prevail with respect to dispersions. We report on systems
containing DNA-stabilized and lysozyme-stabilized carbon nanotubes, since the two cases are representative of largely
different adsorption modes. In the former case, ss-DNA uniformly rolls around CNTs and ensures significant surface
coverage; conversely, lysozyme poorly, randomly and non-cooperatively adsorb onto nanotubes. A fine tuning of
temperature, nano-tube content, added polymer, pH and/or ionic strength conditions induces the formation of different
dispersion modes and different phases, as well
Hybrid nano-composites made of ss-DNA/wrapped carbon nanotubes and titania
No full textMulti-walled carbon nanotubes, MWCNTs, are stabilized thanks to the surface wrapping of single-strand DNA, ss-DNA; the resulting adducts are kinetically and thermodynamically stable Such entities build up nano-hybrids with titania, TiO2, nano-particles, in presence of surfactant as an adjuvant. The conditions leading to TiO2 adsorption onto ss-DNA/CNTs were investigated, by optimizing the concentration of adducts, nano-particles (NPs), and of the cationic surfactant (CTAB). Controlling the working conditions makes possible to get homogeneously organized hybrids. Characterization by DLS, electro-phoretic mobility, SEM and AFM clarified the surfactant-assisted association modes between adducts and CTAB-functionalized TiO2. Nano-particles’ clustering onto DNA-wrapped adducts gives hybrids trough electrostatic interactions. Surface coverage by TiO2 is significant and homogeneous. It is expected that the reported hybrids can be useful for applications in heterogeneous catalysis. © 201
Attempts to control depletion in the surfactant-assisted stabilization of single-walled carbon nanotubes
No full textSingle-walled carbon nanotubes were stabilized by an anionic surfactant, sometimes in mixture with a nonionic one (Triton TX-100), and/or in presence of salt. The stabilizing activity of sodium dodecylsulfate is poor, with occurrence of phase separation at moderate surfactant content; even lower is the one ascribed to TX-100. We quantified the stabilization in terms of surface coverage by the adsorbing species; the effect is counteracted by the presence of micelles present in the surrounding medium. A chemical approach accounted for the competition between surface adsorption and micelle formation.Destabilization of the dispersions is due to unbalanced osmotic effects and is related to depletion. The above phenomenon occurs when the volume fraction of micellar aggregates reaches a certain threshold, whose value is related to micelle size. Depletion was avoided by selecting the maximum possible amounts of sodium dodecylsulfate, NaCl and/or Triton TX-100. In mixed systems the stabilization is active for longer times compared to dodecylsulfate, although depletion occurs at lower surfactant content. © 2013
Polymer-Surfactant Interactions
No full textAqueous solutions containing poly(vinyl-pyrrolidone) and sodium caprylate, or poly(vinyl-pyrrolidone) and tetraethylammonium perfluorooctanesulfonate, respectively, have been investigated by volumetric, ionic conductivity and surface tension methods. The presence of an interaction region has been determined from conductivity and surface tension. The width of such a region depends on the amount of polymer in the mixture, temperature, surfactant content and added electrolyte (NaCl). The observed behaviour was explained in terms of the combined effects played by the alkyl-chain hydophobicity, polar head group(s) and counter-ions.
An approximate solution to a mass action model for the binding of surfactants onto polymers has been introduced. It allows determining the width of the interaction region as a function of polymer mass percent in the mixture
Rheological Properties of Protein-Surfactant based gels
No full textWater-based protein-surfactant gels, formed by mixing bovine serum albumin (BSA) and sodium dodecyl sulfate in water, were investigated by rheological methods. The measurements were performed for many different protein-to-surfactant ratios as a function of the applied frequency, stress, or strain, as well as by changing the temperature, in the range between 15 and 65 degrees C. The rheological behavior of the gels as a function of applied frequency is interpreted in terms of the overlapping of at least two viscoelastic relaxation processes. The rheological results indicate the presence of thermal transitions from essentially viscous to mainly elastic regimes, in analogy with the thermal gelation processes observed in polymer solutions. The thermal gelation threshold in the present system is modulated by the protein/surfactant ratio. Differential scanning calorimetry measurements were also performed to determine whether thermal gelation is somehow concomitant to protein denaturation. The results indicate that the thermal denaturation of BSA in protein-surfactant based gels occurs at slightly higher temperatures than in the bulk. Scanning electron microscopy indicates the occurrence in the gel structure of globules formed by the arrangement of fibrils
BINDING OF SURFACTANTS ONTO POLYMERS. A KINETIC MODEL
No full textThe kinetics of surfactant binding onto polymers is discussed by taking into account recent investigation performed in some water-polymer-surfactant systems. The links between the obsd. kinetic parameters, i.e. relaxation times, and the thermodn. quantities controlling polymer-surfactant interactions are considered. A model for the kinetics of surfactant binding onto polymers is presented and discussed
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