Effect of Electrolytes and Temperature on the Structure of a Poly(ethylene oxide)−Poly(propylene oxide)− Poly(ethylene oxide) Block Copolymer Adsorbed to a Perfluorocarbon Emulsion

Abstract

We have used small-angle neutron scattering to study the detailed structure of the poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO) block copolymer Poloxamer 188 adsorbed at the interface in a perfluorodecalin in water emulsion and specifically to investigate the effect of electrolytes and of temperature. Low (<0.5 M) concentrations of 1:1 electrolyte caused the polymer layer to extend from the interface, apparently by desorption of loop contacts between the PEO chains and the perfluorocarbon−water interface. The extension of the polymer layer is accompanied by a reduction in the fraction of bound polymer segments. A similar effect was found with increasing temperatures. Higher concentrations of electrolyte caused the PEO chains to collapse slightly toward the surface, and it is suspected that this was due to the water becoming a poorer solvent for PEO as the ionic strength of the dispersion medium was increased. No corresponding collapse of the polymer chains was observed at higher temperatures, in the temperature range studied (25−55 °C), but this does not rule out collapse at higher temperatures; the cloud point of the polymer in 1% solution is 112 °C.

Extensive surface studies help to analyse zeta potential data: the case of cationic emulsions

“…The naked particles exhibited δ values of 0.60-0.66 nm similar to those reported by Kraayenhof et al (1993) for pure PC vesicles but significantly larger than the more widely adopted distance of about 0.2 nm (Eisenberg et al, 1979). The shift in the shear plane outwards from the surface produced by the Poloxamer itself was very inferior to the 2 nm reported by Washington (1997) for perfluorocarbon emulsions and can be due to its deep immersion in the thick interface, to a coiled conformation or to other interactions of the hydrophilic subunits with the surface as previously reported (Barnes and Prestidge, 2000).…”

Fluorine‐containing nanoemulsions for MRI cell tracking

“…F68 stabilizes the PFC oil droplets in aqueous phase mostly by steric effects 66. Previous structural studies have shown that block polymers adsorb onto the interface between the colloid PFC and the aqueous phase and that this adsorption is dependent on the electrolyte concentration in the solution 67–69…”

Polymer bristles: a SANS study

“…Highly collapsed layers, or layers in which the buoy blocks also adsorb, give rise to profiles that decay approximately exponentially. This latter type of profile is also encountered in the case of homopolymer adsorption, and even described the adsorbed layers formed by the POEpoly(oxypropylene)-POE triblock copolymers in our earlier work (Washington, 1996(Washington, & 1997. To determine which profile types best fit the experimental data we compared the values of Γ and σ characterising each profile type with the same values derived from the surface-Guinier analysis.…”

“…In this work we have used small-angle neutron scattering (SANS) to examine the structure of the adsorbed layers formed by a number of well characterised low molecular weight poly(oxyethylene)-bpoly(oxybutylene) (POE-b-POB) diblock copolymers at the perfluorocarbon-water interface in a submicron emulsion, a model colloidal system that we have used before (Washington, 1996(Washington, & 1997 and which provides a well characterised, impenetrable, locally flat, interface.…”