Drying dissipative patterns of biological polyelectrolyte solutions

Drying dissipative structural patterns of aqueous solutions of biological polyelectrolytes, sodium poly (α, L-glutamate; NaPGA) and poly (-L-lysine hydrobromide; PLL.HBr), were studied on a cover glass. Below the critical polymer concentration, m* (ca. 0.003 and ca. 0.01 monoM for NaPGA and PLL.HBr, respectively), the dried patterns shrank only around the center of the initial solution area wetted on a cover glass. Above the m* values, on the other hand, the drying pattern extended throughout the initial solution area. The m* values agreed excellently with the critical polymer concentrations, where the surface tensions started to decrease sharply as the polymer concentrations increased. The broad rings were always observed in the drying patterns of any solutions examined. The spoke-like cracks appeared at the polymer concentrations above the m* values and only in the area of the broad rings. Microscopic structures such as cross-like, rod-like, and block-like patterns formed irrespective of polymer concentrations. Especially, the city-road-like microscopic pattern was observed for PLL.HBr solutions, which strongly supports the formation of crystal structures of PLL.HBr that remain in the whole processes of dryness. These patterns were correlated deeply with the crystal-like orientation of the biological polyelectrolytes at the air–solution interfaces.