Depletion Forces Induced by Mixed Micelles of Nonionic Block Copolymers and Anionic Surfactants

Abstract

Depletion forces were measured between a silica sphere and a silica plate in solutions containing nonionic Pluronic P123 poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymers and anionic sodium dodecyl sulfate (SDS) surfactants using colloidal probe atomic force microscopy. Prior research established synergistic depletion force enhancement in solutions containing SDS and unimeric Pluronic F108 block copolymers via formation of large pseudo-polyelectrolyte complexes. The current work addresses a more complex system where the polymer is above its critical micelle concentration, and surfactant binding alters not only the size and charge of the micelles but also the number of polymers per micelle. Force profiles were measured in 10 000 ppm P123 (1 wt %, corresponding to 1.72 mM based on average molar mass) solutions containing SDS at concentrations up to 64 mM and compared to micellar P123 solutions and to P123-free SDS solutions. Whereas force profiles in the SDS-free micellar P123 solutions were purely repulsive, P123/SDS complexation produced synergistic depletion force enhancement for SDS concentrations between 2 and 32 mM. The synergism that occurred within a finite SDS concentration range was explained by comparing the hydrodynamic size, molar mass, charge, and concentration of depletants in P123/SDS mixtures and their respective single-component solutions obtained with the aid of dynamic light scattering, static light scattering, and dodecyl sulfate ion-selective electrode measurements. These measurements showed that complexation produced effects that would be mutually counteracting with respect to depletion forces: decreasing the mixed micelle hydrodynamic diameter relative to SDS-free P123 micelles would tend to weaken depletion forces, while adding charge and decreasing the aggregation number of polymers per micelle (thereby increasing the number concentration of micellar depletants) would tend to strengthen depletion forces.

Effects of Modification Degrees on the Colloidal Stability of Amphiphilic Janus Graphene Oxide in Aqueous Solution with and without Electrolytes

“…C-DLVO theory describes the stability of nanoparticles as the balance between van der Waals (vdW) attractive forces and electrostatic (EL) repulsive forces . Meanwhile, e-DLVO theory is more suitable for stability description of systems that contain other interaction forces, such as depletion forces, steric interaction, and hydrophobic interaction. , …”

“…C-DLVO theory describes the stability of nanoparticles as the balance between van der Waals (vdW) attractive forces and electrostatic (EL) repulsive forces. 24 Meanwhile, e-DLVO theory is more suitable for stability description of systems that contain other interaction forces, such as depletion forces, 25 steric interaction, 26 and hydrophobic interaction. 23,27 Amine-functionalized GO was a quite common group of the modified GO, which showed multiple applications in the biomedical field, 28 catalysis, 29 heavy-metal detection, 30 and enhanced oil recovery (EOR).…”

Different Agglomeration Processes Induced by the Varied Interaction of Fe–Fe Analogues with Differently Charged Surfactants

“…Moreover, the excess osmotic pressure in the solution forces particles to close up from their overlapping depletion zone. 30,41 However, the negative surface charge of the particles increased markedly, increasing the activation energy of methanol, causing much lower reaction rate. From the previous study, it is known that the methanol activation is the limiting step when PBAs were used for PC transesterification.…”

Preparation of Mesoporous Aluminosilicates with Decreased Dosage of Organic Template and Water: Insights into the HLB Effect of the Cotemplate

“…Therefore, obtaining dispersed micelles in high template concentration is highly desirable. Incorporation of the cotemplate with strong hydrophilicity may lead to the dispersity of composite micelles. − The HLB value can be used to describe the hydrophilicity of the introduced amphiphilic surfactants. In this sense, cotemplates with a high HLB value would be expected to favor the dispersity of composite micelles.…”