Analysis of the Spatial Variation of Crosslink Density in Superabsorbent Polymers

Abstract Superabsorbent polymers are often designed with increased density of crosslinking in the outer layer of the particles in order to improve liquid retention under load. For efficient product design, it is desirable to directly measure the spatial variation in crosslink density. Typically employed techniques (such as solvent uptake or measuring the changes in various mechanical properties such as the modulus) do not provide spatially resolved crosslink density information. We have applied Scanning Transmission X-ray Microscopy to examine the swelling of inhomogenously crosslinked superabsorbent polymers in deionized water and salt water solution. Scanning Transmission X-ray Microscopy (STXM) is an effective way to study the chemical and morphological character of polymers on a sub micron spatial scale.1 STXM image contrast is based on core electron excitation by x-ray absorption; an interaction that has remarkable chemical sensitivity. Beam damage is less than in TEM microscopes and samples can be examined in wet and in ambient conditions.