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: Nano-fibrous mats have been successfully prepared by electrospinning of the blend solutions of cationic cellulose derivatives (PQ-4) and polyvinyl alcohol (PVA). Effects of the blending ratio and applied voltage on the morphology and diameter of the electrospun nano-fibers were investigated. The average diameter of the PQ-4/PVA blend fibers was in the range of 150-250 nm. The electrospinning process became instable and the fiber diameter distribution broadened with increasing PQ-4 content and applied voltage. The antibacterial activity of electrospun PQ-4/PVA blend mats against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus indicated potential for biomedical use.Carbohydrate research 08/2011; 346(11):1337-41. · 2.03 Impact Factor
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ABSTRACT: Stimulus-responsive polyelectrolyte particles are used in a wide array of scientific and technological applications, such as foods, personal care products, pharmaceutics, and separation processes. Depending on their method of preparation, they range from tens of nanometers to millimeters in size, assume a variety of morphologies, and respond to a range of external stimuli. Despite their broad utility, however, literature describing their preparation and properties remains fragmented. To this end, this article presents a broad and unifying review on their formation and properties. Specifically, it surveys the molecular mechanisms by which polyelectrolytes associate and methods by which their assemblies are shaped into particulate matter. It also discusses how particle properties can be tuned by varying their preparation methods and the molecular properties of their constituents, and review some of their applications.Journal of Dispersion Science and Technology 08/2011; 32(8):1119-1128. · 0.60 Impact Factor
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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