Nanostructured polymer-surfactant films for encapsulation/release

Self-assembly phenomena can be exploited to design materials with tailored nanostructures for a variety of applications. Solutions of polyelectrolytes with surfactants are known to show a variety of adsorption behaviours at interfaces. We have recently been exploiting this phenomenon to create novel solid films of polyelectrolyte and surfactant at the air-solution interface, from solutions where the polyelectrolyte is essentially uncharged. In these systems, a self-supporting film (Fig 1a,b), containing highly ordered 2D or 3D surfactant mesostructures, in a hydrogel matrix several hundred nanometres thick forms spontaneously at the solution surface.1 Our initial investigations focused on films made from solutions of polyethylenimine (PEI) and cationic surfactants but we have extended these to a number of other surfactants and polymers, allowing detailed control of film mesostructure and thickness.2, 3 More recently we have also prepared films with similar structures to those of films grown at the air-solution interface by spray coating of the same aqueous synthesis solutions (Fig 1c). The encapsulation and release of hydrophobic and amphiphilic species in the films has been studied as a function of the degree of crosslinking and type of nanoscale ordering present in these hydrogel films. Also, in order to improve the biocompatibility of our membranes, we have investigated the use of zwitterionic surfactants such as myristyl sulphobetaine (SB3-14) which are less toxic than cationic surfactants. We have found that these species require the presence of calcium ions to allow ordered mesostructures to form in the films. We are continuing work to develop these membranes for potential applications in a system for controlled release4 and as a responsive support for sensor species. In this presentation I will describe our studies on the structure and formation of these films, in particular our work to improve control of nanostructure in the films, encapsulation efficiency and the biocompatibility of our materials.


Figure 1: (a) Photograph of a PEI-surfactant film recovered on a plastic mesh of edge size 1cm, with schematic showing ordered arrays of micelles inside the film encapsulating hydrophobic material for release. Grazing incidence diffraction from (b) PEI-cationic surfactant film at the air-solution interface and (c) a DNA film templated with zwitterionic surfactant, SB3-14, spray coated on a silicon wafer, both with a cubic close packed micellar mesostructure.

References:
1 K. J. Edler, A. Goldar, T. Brennan, and S. J. Roser, Chem. Commun., (2003) 1724.
2 B. M. D. O'Driscoll, E. A. Nickels, and K. J. Edler, Chem. Commun., (2007) 1068.
3 K. J. Edler, M. J. Wasbrough, J. A. Holdaway and B. M. D. O'Driscoll, Langmuir (2009) 25(7), 4047.
4 B. M. D. O'Driscoll, A. M. Hawley, and K. J. Edler, J. Colloid Interface Sci. (2008) 317(2), 585.