Direct Measurement of Double-Layer, van der Waals, and Polymer Depletion Attraction Forces between Supported Cationic Bilayers

Abstract

The interactions of supported cationic surfactant bilayers and the effects of nonadsorbing cationic polyelectrolytes on these interactions were studied using the surface forces apparatus (SFA) technique. Bilayers of the cationic surfactant di(tallow ethyl ester) dimethyl ammonium chloride (DEEDMAC) were deposited on mica surfaces using the Langmuir-Blodgett technique, and the interactions between the bilayers were measured in various salt, nonionic polymer (PEG), and cationic polyelectrolyte solutions at different polymer molecular weights and concentrations. The forces between the bilayers in CaCl(2) solution are purely repulsive and follow the DLVO theory quantitatively down to bilayer separations of ∼2 nm. Addition of nonadsorbing polymer or polyelectrolyte has a number of effects on the interactions including the induction of a depletion-attraction between the bilayers and screening of the double-layer repulsion due to the added ions in the solution from the polyelectrolyte. The experimental results are shown to agree well with standard theories of depletion attraction and double-layer screening associated with dissolved polyelectrolyte. We also observed significant time and rate effects on measuring the equilibrium bilayer-bilayer interactions possibly due to the unexpectedly long times (>1 min) associated with the charge regulation of the bilayer surfaces. Implications for the interactions and stability of vesicle dispersions, i.e., of free rather than supported bilayers, in polymer solutions are discussed.

Adhesive Interactions between Vesicles in the Strong Adhesion Limit

“…To implement our model, we require the values of $W_P^{(0)}$ and K a . A recent SFA study51 shows that the interactions between the cationic surfactant under study in the presence of polyDADMAC are well represented by a combination of van der Waals attraction, a modified electrostatic repulsion and the depletion-induced attraction. The calculations are identical to those presented in section 2.2, except that the electrostatic repulsion term has to be modified according to the approach of Tadmor et al 52.…”

Design of eco-friendly fabric softeners: Structure, rheology and interaction with cellulose nanocrystals

“…We surmise that crowding effects are triggered by the increase in overall volume fraction and/or by polymer induced depletion interactions [38,39]. Adding polymers to a colloidal dispersion is known to induce short-range attractive forces between particles above a threshold volume fraction [42,43]. It is also possible that other interaction types are present and also modify the vesicular organization.…”

Interaction of adsorbed polymers with supported cationic bilayers

“…DLVO theory can describe the interaction between vesicles in a dilute solution. [17][18][19] However, in a concentrated dispersion in the presence of polymer additives, no simple theory can accurately determine the interaction between vesicles. In the presence of adsorbing or non-adsorbing polymers, combined effects due to DLVO forces, steric repulsion, depletion attraction, hydration and hydrophobic forces, and forces due to mechanical deformation of the vesicle surface may all contribute to the overall interaction potential.…”

“…19 The effect of non-adsorbing charged and uncharged polymers on the forces between bilayers were explored experimentally. 19 Simulation of polymer graed lipid bilayers were performed 26 and experimental evidence of hydrophobic interaction between the protein molecules and lipid domains were investigated by X-ray diffraction technique. 8 The latter work showed that proteins and polymers adsorb to bilayer surfaces and causes an increase in the head group area of the lipid molecules while collapsing the thickness of the bilayer membrane, still maintaining the bilayer integrity.…”

“…Given enough time for equilibration (on the order of 10-30 s) 19 at a given distance, the counterion Cl À near the surface will adsorb to the positively charged DEEDMAC head groups of the bilayer thus reducing the net charge on the surface and resulting in a lower energy of interaction between the surfaces; in this case the force decay length, D 0 , equals the Debye length, k…”