Stability of Polyaniline Aqueous Dispersions Prepared in the Presence of Surfactant Mixtures

Aqueous dispersions of doped polyaniline were synthesized in the presence of mixtures of a carboxylcontaining polymeric surfactant with low- and high-molecular-mass stabilizers. Polyaniline aqueous dispersions obtained using a mixture of carboxyl-containing polymeric and low-molecular-mass surfactants are characterized by high dispersity and narrow particle-size distribution but low sedimentation stability. The doping agent influences the stability of the dispersions prepared in the presence of polymeric and low-molecular-mass surfactants. The dispersions obtained using a mixture of macromolecular surfactants are characterized by larger particle size but higher sedimentation stability due to increased viscosity of the system.     

The Effect of Poly(methyl vinyl ether-alt-maleic acid) Stabilizer on the Stability of Polyaniline-Poly(methyl vinyl ether-alt-maleic acid) Dispersions

The polyaniline (PANI) dispersions have been prepared in acidic aqueous media by oxidative dispersion polymerization in the presence of a polymeric stabilizer. The polymeric stabilizer used in this study is the poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) which contains acid groups (-COOH). The PANI-PMVEMA particles have a uniform size and a spherical shape. The PANI-PMVEMA dispersions show almost no desorption of the PMVEMA, even though the sonication at 500 W for 20 min and the centrifugation at 500 rpm for 60 min are performed 10 times. The existence of the PMVEMA on the surface is confirmed by X-ray photoelectron spectroscopy. The dispersion stability of the PANI-PMVEMA dispersions is extensively influenced by zeta potential which was governed by the acid group (-COOH) of the PMVEMA on the PANI-PMVEMA particle surface. Copyright 2000 Academic Press.     

Thin wetting films from aqueous solutions of surfactants and phospholipid dispersions

The microscopic thin wetting film method was used to study the stability of wetting films from aqueous solution of surfactants and phospholipid dispersions on a solid surface. In the case of tetradecyltrimethylammonium bromide (C(14)TAB) films the experimental data for the receding contact angle, film lifetime, surface potential at the vapor/solution and solution/silica interface were used to analyze the stability of the studied films. It is shown that with increasing C(14)TAB concentration charge reversal occurs at both (vapor/solution and solution/silica) interfaces, which affects the thin-film stability. The spontaneous rupture of the thin aqueous film was interpreted in terms of the earlier proposed heterocoagulation mechanism. The presence of the mixed cationic/anionic surfactants was found to lower contact angles and suppresses the thin aqueous film rupture, thus inducing longer film lifetime, as compared to the pure amine system. In the case of mixed surfactants hetero-coagulation could arise through the formation of ionic surfactant complexes. The influence of the melting phase-transition temperature T(c) of the dimyristoylphosphatiddylcholine (DMPC) on the stability of thin films from dispersions of DMPC small unilamellar vesicles on a silica surface was studied by measuring the film lifetime and the TPC expansion rate. The stability of thin wetting films formed from dispersions of DMPC small unilamellar vesicles was investigated by the microinterferometric method. The formation of wetting films from diluted dispersions of DMPC multilamellar vesicles was studied in the temperature range 25-32 degrees C. The stability of thin film of lipid vesicles was explained on the basis of hydrophobic interactions. The results obtained show that the stability of wetting films from aqueous solutions of single cationic and mixed cationic-anionic surfactants has electrostatic origin, whereas the stability of the phospholipid film is due to hydrophobic interaction.     

On the structure and electrical conductivity of polyaniline/polystyrene blends prepared by an aqueous‐dispersion blending method

This article describes electrically conductive polymer blends containing polyaniline‐dodecyl benzene sulfonic acid (PANI‐DBSA) dispersed in a polystyrene (PS) matrix or in crosslinked polystyrene (XPS). Melt blending of previously mixed, coagulated, and dried aqueous dispersions of PANI‐DBSA and PS latices lead to high conductivities at extremely low PANI‐DBSA concentrations (∼0.5 wt % PANI‐DBSA). In these blends, the very small size of the PANI‐DBSA particles and the surface properties (with surfactants used) of both the PANI and polymer particles play a major role in the PANI‐DBSA particle structuring process. The PANI‐DBSA behavior is characteristic of a unique colloidal polymeric filler with an extremely high surface area and a strong interaction with the matrix, evidenced by a significantly higher glass‐transition temperature of the matrix. The effect of the shear level on the conductivity and morphology of the PS/PANI‐DBSA blends was studied by the production of capillary rheometer filaments at various shear rates. An outstanding result was found for XPS/PANI‐DBSA blends prepared by the blending of aqueous XPS and PANI‐DBSA dispersions. Some of these blends were insulating at low shear levels; however, above a certain shear level, smooth surface filaments were generated, with dramatically increased and stable conductivities. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 611–621, 2001     

Synthesis of CdS, ZnS and Ag2S nanoparticles stabilized by sodium bis(2-ethylhexyl)sulfosuccinate and polyoxyethylenesorbitan monooleate in aqueous medium

The effect of synthesis conditions (molar ratio between precursors, concentration of surfactants, synthesis temperature) on the size of CdS, ZnS and Ag₂S nanoparticles (NPs) stabilized by sodium bis(2-ethylhexyl)succinate and polyoxyethylenesorbitan monooleate was studied. It was established that stabilization by polyoxyethylenesorbitan results in formation of smaller NPs (～8 nm) as compared to that in the presence of sodium bis(2-ethylhexyl)sulfosuccinate (14–60 nm), which is due to the difference between the adsorption rates of these surfactants onto the surface of synthesized NPs. The resulting aqueous dispersions of CdS, ZnS and Ag₂S NPs exhibit long-term stability to sedimentation. The nanoparticle size increases insignificantly with temperature increasing to 65–70°C and rises abruptly at higher temperatures. The increase in the ratio between concentrations of precursors (sulfide and metal ions) also results in an increase in NP size, allowing one to synthesize nanoparticles of prescribed sizes. The optical properties of the resulting nanoparticles were studied. The positions of the exciton peaks and the luminescence intensity peaks of the dispersions of synthesized CdS and ZnS NPs were determined.     

Effect of peroxide depolymerization of chitosan on properties of chitosan sulfate particles produced from this substance

Effect of the oxidative destruction of chitosan on the rate at which a dispersed phase is formed in its dilute solutions in the presence of sulfate ions and on the composition, size and ζ-potential of submicrometer chitosan sulfate particles being formed was studied. It was found that the particle size steadily decreases as the molecular mass of chitosan becomes smaller, and the sedimentation stability of aqueous dispersions increases in the absence of surfactants. The \(\nu _{SO_4 } :\nu _{NH_2 }\) molar ratio in chitosan sulfate particles is independent of the molecular mass of chitosan and varies within the range 0.45–0.46. A pH-dependence of the sign of the ζ-potential with isoelectric point at pH 5.0 was found for particles based on destructed chitosan.     

Emulsion polymerization of styrene and methyl methacrylate using a hydrophobically modified inulin and comparison with other surfactants

The use of a new class of graft polymer surfactants, based on inulin, in emulsion polymerization of poly(methyl methacrylate) (PMMA) and polystyrene (PS) particles is described. PS and PMMA were synthesized by emulsion polymerization, and stable particles with a high monomer content (50 wt %) were obtained with a very small amount of polymeric surfactant ([surfactant]/[monomer] = 0.0033). The latex dispersions were characterized by dynamic light scattering and by transmission electron microscopy to obtain the average particle size and the polydispersity index, and the stability was determined by turbidimetry measurements and expressed in terms of critical coagulation concentration. The last section gives a comparison of PMMA particles prepared by emulsion polymerization using classical surfactants from different types as emulsifiers with that obtained using the copolymer surfactant. It shows the superiority of INUTEC SP1 as it is the only one that allows stable particles at 20 wt % monomer content, with a smaller ratio [surfactant]/[monomer] = 0.002.     

The effect of polyoxyethylene glycol monoethers ofn-hexadecanol on the stability of a polystyrene latex dispersion

The influence of nonionic surface active agents, a series of polyoxyethylene glycol monoethers ofn-hexadecanol, on the stability of dispersions of 2m diameter polystyrene latices has been investigated.Adsorption and microelectrophoretic studies showed the presence of looped monolayers of surface active agent at plateau adsorption.Examination of sedimentation volumes and redispersibility, correlated with potential energy calculations, showed that the stability of the dispersions depended on the characteristics of the adsorbed layer and on added electrolyte.     

二甲基聚硅氧烷阴离子型乳液的稳定性

作为织物柔软剂,二甲基聚硅氧烷阴离子型稀乳液的耐电解质稳定性对实际应用有着重要的意义。然而有关这方面的报道极少,而关于非离子型和阴离子型表面活性剂对它的电解质凝聚稳定性的影响至今未见报道。     

The Effect of Mechanical Activation of the Surface of Inorganic Pigments on the Stability of Their Aqueous Dispersions in the Presence of Ethylhydroxyethyl Cellulose

The effect of mechanical activation of the surfaces of TiO₂ and Fe₂O₃ inorganic pigments on the stability of their aqueous dispersions in the presence of a nontoxic water-soluble polymer, ethylhydroxyethyl cellulose (EHEC), was investigated. The mechanical activation of dispersions was performed under the action of ultrasonic field and in a laboratory disintegrator. Intense mechanical action on aqueous dispersions of TiO₂ and Fe₂O₃ in the absence of polymer leads to their fast coagulation. In the presence of EHEC, a weak stabilizing effect was observed which was enhanced significantly upon the mechanical treatment of the dispersions. It is shown that the ultrasonic treatment of aqueous dispersions of inorganic pigments results in a significant narrowing of particle size distributions for both pigments. It is found that the interaction of EHEC with the pigment surface proceeding through the adsorption mechanism is accompanied by conformational transformations and changes in the configuration of adsorbed macromolecules. Vigorous mechanical action results in the activation of the processes of polymer adsorption on freshly formed surfaces of the pigments and in the formation of solvated adsorption layers of EHEC which determine the sedimentation stability of the systems.     

Development of radioligands for the dopamine transporter

The extraction of Penicillin G (Pen G) and its conversion to 6-aminopenicillin acid (6-APA) and phenylacetic acid (PAA) was performed by means of Penicillin G Amidase immobilised in the emulsion liquid membranes. Using various surfactants as emulsifiers and an appropriate carrier it is possible to obtain different extraction rates of Pen G as well as back transfer rates of the hydrolysis products. The surfactants with polyoxyethylene chain facilitate the back transfer through the membrane phase, whereas the more hydrophobic surfactants, e.g., Paranox 100, tend to accumulate Pen G hydrolysis products in the internal aqueous phase.     

Mg-Al-CO3水分散液的稳定性及流变性

水滑石;水分散体系;层状结构;Mg-Al-CO3水分散液的稳定性及流变性     

Polyurethane anionomers synthesised with aromatic, aliphatic or cycloaliphatic diisocyanates, polyoxyethylene glycol and 2,2-bis(hydroxymethyl)propionic acid

Taking advantage of the step-growth polyaddition method, which has been developed earlier, and applying it in the reaction of aromatic, cycloaliphatic and aliphatic diisocyanates with polyoxyethylene glycol, 2,2-bis(hydroxymethyl)propionic acid and 1,6-hexamethylene-diamine, a few polyurethane anionomers were synthesised, which were recovered from aqueous dispersions in the form of thin polymeric films. Analytical chemistry methods, like gel permeation chromatography with N,N-dimethylacetamide as the polar eluent and high-resolution nuclear magnetic resonance and IR spectroscopy, were employed to confirm their chemical structures, to find molecular weights and their distribution and to characterise the polarity of the chemical structure of the polyurethane chain formed.     

Effects of Various Additives on the Cloud Point of Dodecyl Polyoxyethylene Polyoxypropylene Ether

Effects of various additives, including electrolytes, alcohols and organic acids, polymers, and ionic and nonionic surfactants, on the cloud point of dodecyl polyoxyethylene (5) polyoxypropylene (4) ether nonionic surfactant aqueous solutions are investigated. The salting-out electrolytes decrease the cloud point while salting-in electrolytes increase it. Most alcohols and organic acids can lower the cloud point except for methanol and ethanol. The polymers form complexes with the surfactant and decrease the cloud point. The added surfactants can be inserted into the micelles of the nonionic surfactant and form mixed micelles, thus raising the cloud point.     

The temperature dependence of the stability of aqueous kraft lignin dispersions in the near-isoelectric state of its particles

The stability of dilute aqueous kraft lignin dispersions in a near-isoelectric state of its particles (pH 2) is studied in the temperature range of 0?C20°C. An extremal temperature dependence with a minimum in the region of 10°C is revealed for the stability. It is assumed that, in the examined temperature range, the observed effect is due to variations in the surface forces and a possible influence of the morphology of aggregates being formed on their sedimentation.     

Influence of surfactant addition on the stability of concentrated alumina dispersions in water

The goal of this study was to assess the effects of surfactant addition on the stability and viscosity of concentrated alumina dispersions. The stabilizing effects of several candidate surfactants were investigated for concentrated dispersions of two different pseudoboehmite aluminas at pH 4 and 7. The stabilities of concentrated alumina dispersions treated by pH adjustment alone and by pH adjustment combined with surfactant addition were compared to assess the degree to which the surfactant enhanced stability. The initial rate of mass removal from a sedimenting alumina dispersion was used as a measure of stability.

The anionic surfactants Surfine WNT-A and DOWFAX 3B2 were identified as effective in enhancing the stability of concentrated alumina dispersions. The optimal doses of these surfactants for stabilizing 15% by weight VERSAL™ 250 alumina dispersions at pH 4 were determined to be about 4.6 × 10⁻⁵ mol g⁻¹ for both surfactants. On the basis of the initial rate of mass removal, surfactant-stabilized 15 wt.% suspensions were found to be approximately 2.5 and 10.6 times more stable than similar dispersions stabilized electrostatically by pH adjustment alone. These more stable dispersions exhibited lower viscosities than observed for the alumina dispersions not subjected to surfactant addition. The results indicate that the stability of concentrated alumina dispersions can be enhanced by anionic surfactant addition, and that such surfactants may therefore help to control the rheology of concentrated dispersions of alumina in water.     

Production and stabilization of fullerene dispersions in liquid media in the presence of nonionic surfactants

Dispersion of C₆₀ fullerenes in water and ethanol in the presence of nonionic surfactants, ethylene oxide derivatives, was studied. It was found that the quality of the dispersion process and the stability of dispersions depend on the structure, degree of oxyethylation, and concentration of surfactants. The optimal conditions are found in which stable fullerene dispersions are obtained as ingredients of cosmetic preparations with antioxidant properties.     

阿维菌素水乳剂的稳定性

首先将辛基酚聚氧乙烯醚(OP10)、苯乙烯基酚聚氧乙烯醚(602)和蓖麻油聚氧乙烯(40)醚(EL-40)分别与蓖麻油聚氧乙烯(20)醚(EL-20)复配制备阿维菌素水乳剂,从亲水亲油平衡(HLB)值、临界胶束浓度(cmc)、表面张力等方面分析了二元表面活性剂复配对乳液稳定性的影响;其次,在EL-40与EL-20复配基础上,将苯乙烯基酚聚氧乙烯聚氧丙烯醚(1601),嵌段共聚物(L64)和辛基酚聚氧乙烯醚磷酸酯(A)分别添加到乳液中,从粒径、表面张力和zeta电势等方面考察三元表面活性剂复配对乳液稳定性的影响.结果表明:EL-40与EL-20复配具有较低的表面张力,可制备较稳定的乳液.添加1601和L64对乳液稳定性有一定提高;而添加A大大提高了乳液的稳定性,这是由于A显著降低了液滴粒径和表面张力,增加了zeta电势.     

Understanding mercapto ligand exchange on the surface of FePt nanoparticles

Tailoring the surface of nanoparticles is essential for biological applications of magnetic nanoparticles. FePt nanoparticles are interesting candidates owing to their high magnetic moment. Established procedures to make FePt nanoparticles use oleic acid and oleylamine as the surfactants, which make them dispersed in nonpolar solvents such as hexane. As a model study to demonstrate the modification of the surface chemistry, stable aqueous dispersions of FePt nanoparticles were synthesized after ligand exchange with mercaptoalkanoic acids. This report focuses on understanding the surface chemistry of FePt upon ligand exchange with mercapto compounds by conducting X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies. It was found that the mercapto end displaces oleylamine on the Pt atoms and the carboxylic acid end displaces the oleic acid on the Fe atoms, thus exposing carboxylate and thiolate groups on the surface that provide the necessary electrostatic repulsion to form stable aqueous dispersions of FePt nanoparticles.     

Characterization of latex particles for aqueous polymeric coating by electroacoustic method

Concentrated dispersions are used as coating dispersions for aqueous polymeric coatings, and characterization of the actual concentrated dispersions is an important in the pharmaceutical industry. The commonly used aqueous coating polymers are acrylic polymers and cellulose derivatives. We conducted a characterization study of polymethacrylate-based aqueous polymeric latex for aqueous coating, Eudragit L30D-55 (A-latex) and Eudragit RL30D (C-latex), by electroacoustic method. Colloidal Vibration Current (CVI) is one of the most important parameters relating to dynamic electrophoretic mobility and zeta potential, so we evaluated this parameter first. Volume fractions var of the latex in concentrated dispersions affect the CVIs according to the theory of Dukhin et al. The A-latex and C-latex CVI(*)s which were corrected with regard to the effect of volume fraction by the theoretical equation were nearly constant independent of phi in the ranges >0.04 and >0.03, respectively. The zeta potentials and colloidal stabilities of the concentrated dispersions were evaluated using an electroacoustic method by altering the pH and salt concentration. A-latex strongly aggregated at and below pH 2.5 and at and beyond 0.06 mol/L of electrolyte concentration. Regarding C-latex, instable dispersion was observed at 0.3 and 1 mol/L of NaCl concentration. The total potential energy of interaction between pairs of latex particles was changed by altering the salt concentration in this dispersion based on DLVO theory. The experimental results of stability in the concentrated latex dispersions can be explained by the total interaction energies.