Microstructure of Dispersions of Lamellar Droplets Carrying Anchoring Hydrophobically Endcapped Poly(sodium acrylate)s as Novel Steric Stabilizers

Abstract

Microstructure of dispersions of lamellar droplets carrying anchoring hydrophobically endcapped poly(sodium acrylate)s as novel steric stabilizers Kevelam, J; Martinucci, S.; Engberts, J.B.F.N.; Blokzijl, W.; van de Pas, J.C.; Blonk, H.; Versluis, P.; Visser, Antonie J.W.G. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. We have studied the influence of anchoring hydrophobically single-endcapped poly(sodium acrylate)s on the microstructure and colloidal stabilization of self-assembled lamellar droplets formed from a mixture of anionic and nonionic surfactants in concentrated aqueous electrolyte solutions. A fluorescently labeled hydrophobically endcapped poly(sodium acrylate) has been synthesized and characterized using timeresolved fluorescence spectroscopic techniques; it appears that the fluorophore has considerable freedom of internal rotation. Using this labeled poly(sodium acrylate), the presence of an adsorbed polymer layer bound to the surface of the droplets was imaged by confocal scanning laser microscopy, providing visual evidence that the droplets are sterically stabilized. Laser diffraction and refractive index measurements were employed to determine average particle sizes of the colloidal particles, and it was established that increasing the molecular weight of the hydrophilic (pendant) backbone at a constant (hydrophobic) anchor density, or increasing the concentration of polymer in the dispersion at constant molecular weight, results in a decrease of the average droplet size. This is in agreement with theoretical predictions that an increased lateral pressure in the adsorbed layer, due to a higher polymer segment density near the surface, is relieved by increasing the curvature of the lamellar droplets. Finally, the adsorption of hydrophobically endcapped polymers to lamellar droplets has been described in terms of a Freundlich isotherm, reflecting the degressive increase of the amount of polymer adsorbed onto the surface of the droplets with increasing polymer concentration. Again, an increase of lateral pressure with surface coverage is held responsible for this effect.

Aggregation Behavior of Mono-endcapped Hydrophobically Modified Poly(sodium acrylate)s in Aqueous Solution

“…Mono-endcapped hydrophobically modified poly (sodium acrylate)s were prepared by radical polymerization using an initiator and chain transfer agent. The procedure has been described previously (19). The initiator, ditridecanoyl peroxide, was prepared from tridecanoic acid chloride using sodium hydroxide and hydrogen peroxide (20).…”

Effect of Hydrophobic Modification on the Properties of Polymer‐Blended Microemulsion Gels

“…Stabilization via association appears to proceed through the adsorption of the amphiphilic polymer through the surface of the bilayers followed by the penetration of the hydrophobic portion (dodecyl chains) of the amphiphilic polymer to the bilayer. These “hydrophobes” act as stickers, and they hold several bilayers in close vicinity (Kevelam et al, ). Thus the penetration of the hydrophobic chain of HMHEC into several lamellar bilayers leads to the assembly of microlamellar units close to the periphery.…”

Rheology of Concentrated Dispersions of Sterically Stabilized Polydisperse Lamellar Droplets

“…Hydrophobical ly S ingle-Endcapped Stabilizing Polymers. The synthesis and characterization of the hydrophobically single-endcapped stabilizing poly(sodium acrylate)s (Scheme ) have been described before . The chemical structures of the polymers have been abbreviated for clarity.…”

“…These studies have yielded many important insights into the relationships between dispersion microstructure and bulk rheological properties, and the aim of this study is to apply the obtained insights to the rheological investigation of a much more complex system, where the particle size is polydisperse, and in which case added polymer not just increases the grafting density but also decreases the average particle size. The microstructural features of the lamellar dispersion, as a function of both polymer concentration and molecular weight, have been described before, and serve as a starting point for the present rheological investigation. Thus, we will investigate lamellar dispersions with added hydrophobically endcapped poly(sodium acrylate)s having a molecular weight ranging between 750 and 30 000.…”