Macromolecules 35 (2002) 1336 -1341.

Quantitative Characterization of Microscopic Variations in the Cross-Link Density of Gels

G. E. Mitchell,* L. R. Wilson,# M. T. Dineen,* S. G. Urquhart,+ F. Hayes,* E. G. Rightor,* A. P. Hitchcock,$ and H. Ade+

* Analytical Sciences Laboratory, The Dow Chemical Company, 1897 Building, Midland, Michigan 48667
# Superabsorbent Products R&D, The Dow Chemical Company, 1603 Building, Midland, Michigan 48667
+ Department of Physics, North Carolina State University, Raleigh, North Carolina 27695
$ Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario L8S 4M1, Canada

Received May 14, 2001 Revised Manuscript Received September 24, 2001

Abstract: We report the visualization and quantitative analysis of the cross-link structure in model core/shell hydrogel polymers on the microscopic scale, in a fully swollen state, using soft X-ray microscopy. The cross-link density in these materials and their microscopic or even nanoscopic variation critically influence materials characteristics, yet the cross-link density is difficult to characterize by conventional methods. By the use of soft X-ray microscopy, one can investigate these materials in a fully swollen state and thus directly visualize and quantitatively determine the cross-link structure on a microscopic scale. Materials that were cross-linked by different methods were shown to give rise to differently shaped profiles. Abrupt and gradient cross-link density profiles have been investigated, and the spatial variation in their cross-link density has been determined quantitatively.

10.1021/ma010840d S0024-9297(01)00840-3 2001 American Chemical Society

Current address: Chemistry, U. Saskatchewan