Synthetic Vesicles at Hydrophobic Surfaces

Abstract

Determinations of surface tension (γ) at the air−water interface, contact angles (θ), and in and ex situ ellipsometric mean thickness (d) were used to study the interaction between dioctadecyldimethylammonium bromide (DODAB) small vesicles and spin-coated polystyrene sulfate (PSS) films on silicon wafers. Upon the addition of NaCl (50 mM final concentration) to a 0.2 mM DODAB dispersion, adsorption from vesicles on PSS films immediatly yielded a DODAB layer 6.0 nm thick which remained stable as a function of time. However, in water, in situ DODAB adsorption monotonically increased reaching at most 1.6−1.8 nm as a function of time (from 15 min of interaction), which were not values consistent with bilayer deposition. At early stages in pure water, DODAB adsorption linearly increased with the square root of time, indicating a vesicle diffusion controlled process with ca. 1.0 × 10-11 m2 s-1 as the vesicle diffusion coeficient (D) in nice agreement with reported D for similar vesicles. In contrast, adding 50 mM salt, resulted in a very fast adsorption kinetics determined by the hydrophobic attraction between salt-induced defects on the bilayer and the film surface. Ex situ measurements of DODAB adsorption were difficult because wetting/drying cycles of the PSS film increased its mean thickness. From 0.1 up to 1.0 mM DODAB, the adsorbed DODAB film in air was more hydrophobic (advancing contact angle, θa, = 84 ±3°) than the bare PSS film (θa = 71 ± 4). Air−water surface tension for a DODAB dispersion in pure water rapidly decreased upon salt addition (7−50 mM NaCl), suggesting salt-induced vesicle fusion with the air−water interface occurred, in nice agreement with salt-induced vesicle fusion at the hydrophobic polymer−water surface.

Hybrid Materials from Intermolecular Associations between Cationic Lipid and Polymers

“…However, in pure water, the electrostatic attraction was not enough to deposit a DODAB bilayer on polystyrene sulfate films. 53 Therefore, the mechanical approach described in this work for immobilization of the antimicrobial DODAB lipid in a polymeric network certainly represents a significant improvement regarding its applications to produce antimicrobial coatings.…”

“…Films of PMMA or PS were previously produced by spin-coating onto Si wafers from toluene solutions at 10.0 mg/mL. 52, 53 In the second set of experiments, solutions containing DODAB and PS or PMMA were prepared in chloroform, a good solvent for both polymers and DODAB. The solutions were prepared at fixed final concentration of polymer (10 mg/mL) and DODAB concentration varying from 0.1 mg/mL to 6.0 mg/mL.…”

Competitive Adsorption of Cationic Bilayers and Chitosan on Latex: Optimal Biocidal Action

“…Previously, other types of hydrophobic defects leading to vesicle fusion upon salt addition had been identified in DODAB dispersions composed only of large and closed bilayer vesicles which decreased their colloid stability. 54,55 Consistently, at high particle number densities such as 10 12 particles/mL, DODAB was more effective in flocculating (increasing mean particle size) the latices than was chitosan, a flocculant agent for which the hydrophobic attraction between macromolecule and surface is absent (Figures 5 and 6). Again, consistently, particle flocculation kinetics by DODAB was attenuated upon increasing the hydrophilic character of the latex surface by using PMMA instead of PSS ( Figure 5B,D, Figure 6B,D).…”

Biomimetic Systems in Nanomedicine

“…For example, we calculated numerically the electrostatic interaction energy as a function of the separation distance in between charged spherical vesicles or bilayer-covered polystyrene microspheres interacting in water solutions of monovalent electrolyte. [13][14][15] The calculation of total interaction energies between interacting flat surfaces or particles taking this energy as the sum of the repulsive double layer energy and the attractive van der Waals energy, is the basis of the DLVO theory. 11,16 This theory is successful for many interacting systems but fails for systems where other interaction forces are present such as the solvation forces resulting in structural repulsion at short distances (<1 nm).…”