SANS study on the surfactant effect on nanophase separation in epoxy-based hydrogels prepared from alpha,omega-diamino terminated polyoxypropylene and polyoxyethylene bis(glycidyl ether)
Abstract
Effect of a cationic surfactant (myristyltrimethylamrhonium bromide, Ci4TAB) on swelling behaviour of epoxy network containing polyoxyethylene (POE) and polyoxypropylene (POP) and structure of resulting hydrogels was studied using small-angle neutron scattering (SANS). Nanophase separated structure of hydrogel prepared by swelling of the network in pure water was revealed.
Characteristic length scale of the structure as measured by Bragg's distance is ca 78 angstrom. The structure consists of water-poor and water-rich nanodomains separated by a diffuse interface of effective thickness ca 5 angstrom.
Presence of the surfactant in swelling solution has a strong effect on swelling behaviour of the epoxy network and structure of resulting hydrogels. At the macroscopic level, both, the swelling degree and surfactant uptake bythe network increase considerably with growing surfactant concentration in swelling solution.
At the microscopic level, the two-phase nanophase separated structure is preserved, however, it becomes finer as expressed by a continuous decay of Bragg's distance from 78 angstrom (in absence of the surfactant) to 61 angstrom (highest surfactant concentration). Effective thickness of interface varies between ca 3-6 angstrom.
Presence of the surfactant also induces variation of the neutron scattering length density at much longer length scale of ca 200-1200 angstrom. Strong binding of the surfactant to POP chains in epoxy network is responsible for the effects observed.