Neutron reflection studies of copolymers at the hexane/water interface

Abstract

The conformations of three copolymers at the hexane/water interface have been studied using neutron reflection. The experiment is made possible by using a specially-designed apparatus in which a thin (~10 Mm) layer of hexane is spread on a water surface, thus allowing acceptable transmission of a neutron beam incident at a grazing angle to the surface. Since none of the polymers used was deuterated, sensitivity to the polymer structure was achieved using contrast variation of the two solvents. A triblock copolymer of polyethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (F127 of the Pluronic series) is shown to adopt a conformation that extends beyond the micellar radius in water and, thus, appears quite stretched. A random copolymer of poly(vinyl alcohol-co-acetate) is shown to adopt a very flat conformation at the interface, forming a dense layer no more than 20 Á thick. While both of these polymers have hydrophobic moieties, hexane is not a good solvent for either. In contrast, the hydrophobic block of a diblock copolymer of poly(dimethylsiloxane)-poly(2-vinylpyridine N-oxide) is very soluble in hexane, and in this case the hexane appears to have a much greater influence over the polymer structure. A substantial proportion of the polymer is found on the hexane side of the interface. University of Bristol. * I.C.I. Chemicals and Polymers.

Small-Molecule Surfactant Adsorption, Polymer Surfactant Adsorption, and Surface Solubilization: An Overview

“…Polymer conformation for a number of copolymers at the hexane/water interface has been studied by neutron reflection (42). In the case of poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) or PEO-PPO-PEO triblock, the adsorbed layer was diffuse and thicker than the micellar radius, suggesting some stretching of the molecule.…”

The use of block copolymer stabilizers for controlling dispersion stability

“…The ABA butylene oxide polymer was prepared at Manchester University [3]. Further details of the experimental procedures have been published elsewhere [4].…”

Dynamics of amphiphilic diblock copolymers at the air–water interface

“…We can now compare our experimental observations with an interfacial transition reported for PEO-PPO-PEO copolymers. For these multiblock systems, a structural transition at the air-water interface at around c = 0.1-1 mg L −1 was associated to the formation of a compact interfacial polymer layer with PEO chains extending into the water subphase or folding around the hydrophobic blocks [10,44]. The corresponding surface concentration Γ= 0.4 mg m −2 [11] and surface pressure Π = γ 0 − γ= 10-20 mN m −1 for this transition were also reported [9].…”

“…This concentration is usually controlled by varying the interfacial area in a Langmuir trough, in which a non-aqueous polymer solution is spread on the top of the water surface. These layers are known as "Langmuir layers"and their structural conformations have been studied by tensiometry, rheology, neutron/x-ray reflectivity, capillary wave scattering, electrocapillary waves and oscillating barrier experiments [8,9,10,11,12,13,14,15].…”