Drying dissipative patterns of aqueous solution of poly(methacrylic acid) and its salt neutralized half

Drying patterns of poly(methacrylic acid) (HPMA) and its salt neutralized half with sodium hydroxide (NaHPMA) were studied on a cover glass, a watch glass, and a glass dish. The patterns of HPMA and NaHPMA are compared with the previous observation of sodium salt of poly(methacrylic acid), NaPMA (Okubo et al. Colloid Polym Sci 287:1155–1165, 2009). HPMA and especially NaHPMA are hygroscopic, and only the macroscopic patterns were observed. However, microscopic patterns were not observed clearly especially for NaHPMA in the room atmosphere. The hygroscopy of the dried films was in the order NaPMA < HPMA < NaHPMA. Broad rings of HPMA formed only at the outside edge irrespective of polymer concentration. Simplified laurel crown-like patterns appeared on a cover glass, which supports the strong solute–substrate affinity. On the other hand, the broad ring size of NaHPMA decreased sharply at the lower polymer concentrations than the critical concentration, m*. The results of NaHPMA support that both the inter-solutes and solute–substrate affinity are rather weak, and the pattern size was determined with the excluded volume effects. Sharpness parameter, S, of the broad rings was in the order HPMA > NaHPMA > NaPMA. The magnitude of S values of NaPMA was similar to that of poly(ethylene glycol) (PEG). HPMA, NaHPMA, and NaPMA were grouped into E, A, and A, respectively, among six groups of solutes A to F.