Both sorbitan monolaurate (Span 20) and polyoxyethylene(
20) sorbitan monolaurate (Tween 20)
nonionic surfactants are sorbitan fatty acid esters
with the same cyclic structure. The main structural
difference is the additional polyoxyethylene
units in Tween 20, giving it higher molecular
weight and HLB value (Table 2).