Mesostructured polymer/surfactant hydrogel films for encapsulation and release.

Matthew J. Wasbrough (U of Bath, UK)

We have investigated thin hydrogel films formed that form spontaneously at the air/solution interface of polymer/surfactant solutions. These films were first seen with hexadecyltrimethylammonium bromide (CTAB) and polyethylenimine (PEI).1, 2 In our earlier studies we found that it was possible to produce hydrogel films at the air/solution interface up to several tens of microns thick. The films are composed of surfactant micelles trapped in a network of polymer hydrogel. These films are not only much thicker than previously seen adsorption layers at the interface of polymer/surfactant solutions, they also show very strong mesoscale ordering throughout the structure.3 Recently we have been studying the effect of different surfactants on the mesostructure of the thin films using small angle neutron scattering and x-ray and neutron reflectometry. Here we will discuss how the variation in surfactant, and therefore micelle structure in solution, can be related to final structure within the thin films. Using three different surfactants, hexadecyltriethylammonium bromide (CTEAB), CTAB and didodecyldimethylammonium bromide (DDAB), it is possible to reliably create thin films with cubic, hexagonal and lamellar structures, which all show strong 3-dimensional ordering. One potential use for these films is as a storage or delivery device for drug molecules. This was previously studied with the original CTAB/PEI system and shown to be possible.4 Here we will report the extent of encapsulation of hydrophobic species in the different mesostructures generated using the surfactants above. Given the shape of micelles can affect the solubility of hydrophobic species and interconnected nature of the film structure will alter the release profile, being able to control the structure of these films is of great importance to any future application. We will also comment on the ability of these films to release the encapsulated species, which we have studied using UV/VIS spectroscopy and the dye Nile red. Grazing incidence x-ray diffraction images showing 3-dimensional structure in thin films of PEI with (from left to right) DDAB (lamellar), 1:2 ratio mixture DDAB:CTAB (hexagonal), 1:20 ratio mixture of DDAB:CTAB (hexagonal), and CTEAB (cubic).

1.B. M. D. O'Driscoll, C. Fernandez-Martin, R. D. Wilson, S. J. Roser and K. J. Edler, J. Phys. Chem. B, 2006, 110, 5330-5336.

2.B. M. D. O'Driscoll, E. Milsom, C. Fernandez-Martin, L. White, S. J. Roser and K. J. Edler, Macromolecules, 2005, 38, 8785-8794.

3.D. Taylor, R. K. Thomas and J. Penfold, Adv. Colloid Interface Sci., 2007, 132, 69-110.

4.B. M. D. O'Driscoll, A. M. Hawley and K. J. Edler, J. Colloid Interface Sci. , 2008, 317, 585-592.

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