Hydrogel science — Published
Crosslink density
Crosslinks are the bridges between polymer chains. Fewer crosslinks let the network stretch further, so it absorbs more but forms a softer gel. More crosslinks make a firmer gel that absorbs less. Surface crosslinking — a harder shell on each particle — is used in hygiene grades to keep absorption high under pressure.
Gel strength and gel blocking
A soft gel can collapse into a layer that stops liquid reaching the particles behind it. This is gel blocking. In hygiene cores and in soil, firmer gel keeps pathways open.
Particle size
Fine particles swell faster but are dusty and more prone to gel blocking. Coarse granules swell more slowly and suit soil application and broadcasting equipment. Specify a size range (for example 0.5–2.0 mm) rather than a single value, and ask for the distribution on the CoA.
How these are measured
Common measures you will see on a data sheet:
Free swell capacity — total absorption without load (g/g).
Centrifuge retention capacity (CRC) — water kept after spinning (g/g).
Absorption under load (AUL) — absorption against a weight, e.g. 0.3 or 0.7 psi.
Particle size distribution — share of particles in each sieve fraction.