It was found previously that the Schiff base bonds in poly(allylamine hydrochloride)-g-pyrene (PAH-Py) microcapsules (MCs) are hydrolyzed at pH 2 within 1 h, leading to disassembly of the MCs and protrusion of pyrene aldehyde (Py) nanorods (NRs) on the capsule surface. Herein, we found a new way to modulate the protrusion of NRs by addition of 1-pyrenesulfonic acid sodium salt (PySO₃Na). Along with the increase in PySO₃Na to Py molar ratio in the MCs solution, the protrusion of NRs was progressively blocked and even inhibited at a ratio of 2.3, and at this condition, the microcapsules were stable under pH 2 for 24 h. After the composite microcapsules with excess PySO₃Na were washed with a pH 10 solution and then incubated in a pH 2 solution, the NRs could be protruded from the MCs again. The fluorescence peak position of the PAH-Py/PySO₃Na MCs gradually red-shifted with a decrease in pH value, and a sharp transition occurred at pH 3.6, demonstrating the formation of pyrene excimers between the PySO₃Na small molecules and the pendant Py groups on the PAH chain. The formed excimers take the role of blocking the self-assembly of cleaved Py molecules instead of inhibiting the hydrolysis of the Schiff base, whereas the MCs were stabilized by the charge interaction between PySO₃Na and PAH backbone and the hydrophobic interaction between the pyrene rings.

Schematic illustration showing the formation of PAH-Py microcapsules (a–c) and protrusion (c–e) and non-protrusion (c–d′ and e) of NRs without (d) and with (d′) the presence of PySO3Na, respectively.

Erjia Guan, Tianxiang Wang, Zhipeng Wang, Changyou Gao*

Journal of Colloid and Interface Science

http://www.sciencedirect.com/science/article/pii/S0021979713004827