Surface Deposition and Phase Behavior of Oppositely Charged Polyion–Surfactant Ion Complexes. Delivery of Silicone Oil Emulsions to Hydrophobic and Hydrophilic Surfaces

Abstract

The adsorption from mixed polyelectrolyte–surfactant solutions at hydrophobized silica surfaces was investigated by in situ null-ellipsometry, and compared to similar measurements for hydrophilic silica surfaces. Three synthetic cationic copolymers of varying hydrophobicity and one cationic hydroxyethyl cellulose were compared in mixtures with the anionic surfactant sodium dodecylsulfate (SDS) in the absence or presence of a dilute silicone oil emulsion. The adsorption behavior was mapped while stepwise increasing the concentration of SDS to a polyelectrolyte solution of constant concentration. The effect on the deposition of dilution of the bulk solution in contact with the surface was also investigated by gradual replacement of the bulk solution with 1 mM aqueous NaCl. An adsorbed layer remained after complete exchange of the polyelectrolyte/surfactant solution for aqueous NaCl. In most cases, there was a codeposition of silicone oil droplets, if such droplets were present in the formulation before dilution. The overall features of the deposition were similar at hydrophobic and hydrophilic surfaces, but there were also notable differences. SDS molecules adsorbed selectively at the hydrophobized silica surface, but not at the hydrophilic silica, which influenced the coadsorption of the cationic polymers. The largest amount of deposited material after dilution was found for hydrophilic silica and for the least-hydrophobic cationic polymers. For the least-hydrophobic polyions, no significant codeposition of silicone oil was detected at hydrophobized silica after dilution if the initial SDS concentration was high.

Characterization of Cationic Polyelectrolytes Adsorption to an Anionic Emulsion via Zeta‐Potential and Microcalorimetry

“…The congruence between the visual phase behavior visual study and f-potential measurements enables deducing that PE-surfactant coacervation is the dominant mechanism for the emulsion flocculation. These observations and this deduction are consistent with literature reports for PE interactions with surfactants on flat surfaces in aqueous solution, where the bulk phase separation is found to control the interfacial adsorption [5,12,[16][17][18][19][20]. The phase behavior and fpotential measurements are schematically summarized as follows: as PE is added to initially stable anionic emulsion droplets, the electrostatic interaction of the oppositely charged PE and anionic surfactant results in coacervation and encapsulation/aggregation of the emulsion droplets and phase separation.…”

“…A decrease in solubility (e.g., the formation of gel-like polymer-surfactant complexes, PSCs) drives the adsorption to a surface. The work of Nylander et al and Linse and Kallrot [5,12,[16][17][18][19][20][21][22] has contributed significantly to the experimental and theoretical investigations of the PE adsorption behavior onto a silica substrate in the presence or absence of anionic surfactants. In most of their studies, the surfactant is depleted from the surface due to non-favorable electrostatic repulsion; consequently coacervate complexes preferentially form in the bulk solution before interacting with the surface.…”

“…We will examine this charge density effect in this study by fixing both the ionic strength and the colloid charge density, while varying the polymer linear charge density. Other factors, such as the hydrophobicity of the polymer [12,27] or surface [17,19,20], also modify the adsorption behavior; however, these factors are not explicitly considered in this study.…”

Forces between oil drops in polymer-surfactant systems: Linking direct force measurements to microfluidic observations

“…The PS complex and resultant attractive interaction is influenced by many factors including surfactant concentration, added electrolytes, polymer backbone flexibility, polymer charge, and surfactant-polymer associations (often based on charge or hydrophobic interaction). This sensitivity and flexibility is one of the reasons why PS complexes are used so widely in formulated products (40). This has led to an extensive understanding of PS complex behaviour in the bulk (25,37,39,41).…”

Water-Insoluble Surface Coatings of Polyion–Surfactant Ion Complex Salts Respond to Additives in a Surrounding Aqueous Solution

“…9−12 Another protocol used to deposit films from mixed polymer−surfactant solutions is "coacervation by dilution", commonly employed in hair care applications. 2,13 The drawback with the latter technique is again that quite thin surface layers are typically produced, especially at high dilution of the solution. 13 A new approach to producing CS films on solid substrates was introduced by Antonietti et al 14,15 and Thunemann et al, 16 who showed that it was possible to cast CS films from certain organic solvents.…”