Multitechnique characterization of fatty acid-modified microgels.

The structure of fatty acid-modified hydrogel objects (microgels) created within microfluidic devices for controlled-release or sensory applications was characterized by various imaging and spectroscopic methods. Imaging with scanning electron microscopy revealed that the surface was rough and irregular on the micrometer scale. Examination of planar model systems analogous to the modified microgels with X-ray photoelectron spectroscopy and secondary ion mass spectroscopy showed that a fatty acid coating formed when the reaction conditions were conducive to covalent-bond formation. Visualization of the selectively stained lipophilic coating with laser scanning confocal microscopy while the microgel was positioned within a microfluidic channel demonstrated that the coating was confined to the microgel's periphery. Finally, using transmission electron microscopy, the thickness of the region functionalized with fatty acids was determined to be around 9 microm on samples very similar to those integrated into microfluidic devices. By using transmission electron microscopy to monitor the thickness of the fatty acid coating produced with different reaction conditions, it may be possible to customize these hybrid materials for specific sensory or controlled-release applications.