Fig. 8. Complex coacervation model of foam cement formation. (A) Macroanion (red) and macrocation (blue), pH 5. Mg²⁺ and Ca²⁺ are pumped in to neutralize excess polyanion charges. (B) Neutralization leads to phase separation of the coacervate (CO) from the equilibrium solution (E). CO is an enriched blend of anion, cation and Mg²⁺. Both phases are fluid although CO is viscous. (C) As volume of CO phase increases and CO desolvation proceeds, more vacuoles of E form within CO instead of diffusing to E phase. (D) Upon secretion into seawater at pH 8, electrostatic interaction of Mg²⁺ and Ca²⁺ with phosphate groups becomes ionic due to low solubility, increasing the viscosity of CO. (E) Oxidation of Dopa to quinones leads to cement solidification by cross-linking.