Effect of trace sodium polystyrene sulfonate on the solubility, nucleation and crystallization of thiourea from metastable zone width data

The nucleation parameters from two deterministic approaches; the self-consistent Nývlt-like approach (SCA) and the linearized integral nucleation-only (NO) approach, were used to examine the effect of sodium polystyrene sulfonate (NaPSS) on the metastable zone width (MSZW) of Thiourea (TU) in aqueous solution. The addition of NaPSS enhanced the interfacial tensions, γ, of TU (2.52–3.27 mJ.m⁻² for SCA model and 1.91–2.95 mJ.m⁻² for NO model) leading to increased apparent nucleation progression, m, (1.54–3.44). The MSZW and growth of TU crystals in the presence of NaPSS occurs by instantaneous and heterogeneous nucleation. NaPSS delayed the nucleation of TU, a factor which correlates with increased TU crystal size distribution (38.1 μm in water to ∼ 88.36 μm). High values of m also correspond to observed lower solubility of TU in the presence of NaPSS. Finally, molecular modelling shows NaPSS strongly binds to the TU crystal surfaces during crystallization, inhibiting the nucleation.