Investigation of the Uniformity of Gel Shrinkage by Imaging Tracer Particles Using X‐Ray Microtomography

Abstract

Mass transfer and structural changes in the polymer matrix need to be understood for a rational optimization of the biopolymer‐based aerogels production. Herein, the uniformity of changes that occur in the gel structure during the aerogel production by a newly developed method which is based on the imaging of metal tracer particles using X‐ray microtomography (X‐ray micro‐CT) alongside the application of point pattern techniques such as the K‐nearest‐neighbor (KNN) distances is studied. Agar is initially used as a system of validation for the developed method, after which other polysaccharide and protein‐based gels such as alginate, whey protein isolate (WPI), and gelatine are studied. The KNN distance is seen to reduce from hydrogel to aerogel. Furthermore, by means of the KNN distances, the biopolymers are observed to experience a nonuniform distribution of tracer particles correlating to nonuniform shrinkage. Densification at specific sites of the gel represented by lower KNN distance values could be distinguished for each biopolymer. Finally, the spatially resolved polymer network density profile is estimated from the KNN distance by correlating it to experimentally determined polymer network density.