Nanostructured membranes from polymer-surfactant films

• Main Author: Jaber, Robben
• Other Authors: Edler, Karen
• Published: University of Bath 2014
• Subjects: 541
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642053

A new method of preparing solid nanostructured polyelectrolyte films through self-assembly at the air/solution interface was discovered by our group. These films form spontaneously through interactions between water-soluble polymers with polarisable groups, and surfactant micelles with a positive charge. The films have an ordered mesostructure consisting of a surfactant liquid-crystalline phase in a polymer hydrogel matrix. In initial work, micellization of a variety of cationic surfactants in the presence of the film-forming polymer, polyethylenimine, was investigated. Surfactants, which formed robust, well-ordered films, were selected for the subsequent experiments. The main aim of this thesis was to exploit the mesostructures in these films as templates for polymerization of styrene. The replication of ordered surfactant liquid-crystalline structures into mechanically and chemically stable nanostructured polymer materials could provide a rapid, cheap method to generate intricate nanostructures. As a first step of this project, encapsulation of styrene into cationic surfactant/polymer films was investigated. Deuterated and hydrogenated styrene were used to probe the structure and location of styrene in the micelles and films using small-angle neutron scattering and neutron reflectivity experiments. The results showed that styrene was most effectively encapsulated in the films prepared from cetylpyridinium bromide (CPBr) and benzyldimethylhexadecylammonium bromide (BDHAB). In the films, the high viscosity hydrogel surrounding the swollen surfactant micelles prevents diffusion and micelle rearrangement on short timescales, making them an ideal host for styrene polymerisation to create solid polymer nanostructures within the water-soluble polymer film. Both thermal methods and UV-irradiation were used to initiate polymerization of the encapsulated styrene. The nanostructured polystyrene produced was characterised using a range of techniques. In the second part of this project, the species 1-(2-Pyridylazo)-2-naphthol (PAN) and pyrene were incorporated in the micelles in the nanostructured hydrogel films to prepare metal ion sensors. PAN is a well-known chelating agent for transition metal ions. When used with pyrene in micellar systems the fluorescence response of pyrene is modified in a quantitative manner when PAN is bound to metal ions. The response of the micellar solution can thus be calibrated and used as a fluorescence sensor. Unfortunately the optical response of the films was poor, but the films were used in an electrochemical cell, demonstrating selective and sensitive detection of metal ions.