Phase behavior of cationic hydroxyethyl cellulose-sodium dodecyl sulfate mixtures: effects of molecular weight and ethylene oxide side chain length of polymers.
ABSTRACT Novel cationic hydroxyethyl cellulose (HEC) polymers with different molecular weights (1.1 x 10(5) to 1.7 x 10(6) g/mol) and ethylene oxide (EO) side chain lengths (1.5-2.9 EO units) were mixed with sodium dodecyl sulfate (SDS) in aqueous solutions. The phase diagrams of cationic HEC-SDS complexes were determined in the dilute polymer concentration regime (< 0.5 wt %) with gradual addition of SDS molecules. The viscosity and structures of the complexes during the phase evolution were studied using rheometry and dynamic light scattering. The gradual addition of SDS first induced interchain associations with the bound SDS aggregates serving as cross-linkers to form an open network structure, producing a very broad size distribution and high viscosities of the complex solutions, and then condensed the network and induced a structure reorganization, resulting in globular aggregates with narrow size distributions. The growth of these globular aggregates in size eventually led to macroscopic sedimentation near charge neutralization. Further addition of SDS randomly broke the sedimentary aggregates into small particles and SDS micelles with low solution viscosities. The effects of molecular weight and EO side chain length of polymers on the phase boundary, viscosity, and structure of cationic HEC-SDS complexes were discussed.
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ABSTRACT: Here we relate the adsorption from mixtures of well-defined poly(amidoamine) (PAMAM) dendrimers of generation 4 and 8 with sodium dodecyl sulfate (SDS) at the air-water interface to the bulk solution properties. The anionic surfactant shows strong attractive interactions with the cationic dendrimers at pH 7 and electrophoretic mobility measurements indicate that the association is primarily driven by electrostatic interactions. Optical density measure-ments highlight the lack of colloidal stability of the formed bulk aggregates at compositions close to charge neutrality, the timescale of which is dependent on the dendrimer generation. Adsorption at the air-water interface was followed from samples immediately after mixing using a combination of surface tension, neutron reflectometry and ellipsometry measurements. In the phase separation region for dendrimers of generation 4 we observed high surface tension corresponding to a depleted surfactant solution, but only when the aggregates carried an excess of surfactant. Interestingly, these depleted adsorption layers contained spontaneously-adsorbed macroscopic aggregates, and these embedded particles do not rearrange to spread monomeric material at the interface. These findings are discussed in relation to the interfacial properties of mixtures involving dendrimers of generation 8 as well as polydisperse linear and hyperbranched polyelectrolytes where there is polyelectrolyte bound to a surfactant monolayer. The results presented here demonstrate the capability of dendrimers to sequester anionic surfactants in a controllable manner, with potential applications as demulsification and antifoaming agents.Langmuir 04/2014; · 4.38 Impact Factor
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ABSTRACT: Mixtures of oppositely charged surfactants and polyelectrolytes are commonplace in household products, whose performance depends on surfactant/polyelectrolyte binding. Many of these formulations contain multiple surfactant species. Although polyelectrolyte interactions with ionic/nonionic surfactant mixtures have been characterized in detail, literature on polyelectrolyte interactions with mixtures of anionic or cationic surfactants remains limited. To address this, we used UV–vis spectroscopy and gel swelling experiments to study the competitive binding of two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS), to a cationically derivatized hydroxyethyl cellulose gel (JR-125TM). Because SDBS absorbs UV radiation and SDS does not, UV–vis spectroscopy allowed the effect of SDS on the SDBS binding to be elucidated. The competitive binding of SDBS and SDS to the gel was modeled using a simple, two-species Langmuir isotherm, which yielded fair agreement with the experimental data. Additionally, to address the need for effective separation processes, we demonstrated the use of cationic hydroxyethyl cellulose gels in the removal (and recovery) of surfactants from water. This revealed that densely-crosslinked polyelectrolyte gels are advantageous for surfactant removal because they: (1) increase the surfactant/polyelectrolyte binding strength, and (2) increase the binding capacity of the gel by reducing swelling. The gel-bound surfactant can be recovered and recycled by extraction into a 50/50 water/ethanol mixture.Colloids and Surfaces A Physicochemical and Engineering Aspects 12/2010; 372(1 - 3):196–203. · 2.35 Impact Factor
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ABSTRACT: In this work, the interactions between cationic cellulose (PQ-10) and anionic surfactant (SDBS) in aqueous media were investigated by turbidity, electric conductivity, steady-state fluorescence, shear rheology and transmission electron microscopy (TEM) analyses. Results indicated that precipitation appeared near the charge neutrality point, and the size of precipitation region widened with increasing PQ-10 concentration (0.57–1.72 mM for 0.05% PQ-10, and 2.30–17.22 mM for 0.5% PQ-10). The specific conductivity values of SDBS in the presence of PQ-10 were higher than that of pure SDBS over the whole concentration range under current experimental conditions. The aggregation number of SDBS kept constant in the flat region of the micropolarity curve (0.86 mM–1.43 mM). The structural transformation of the mixtures was monitored visually by TEM. As SDBS concentration increased, the morphologies of the mixtures changed gradually from branched wormlike aggregates to interconnected networks, finally the networks collapsed.Carbohydrate Polymers 03/2012; 88(1):139–145. · 3.92 Impact Factor