The BSF reaction system displayed photoinduction and photoinhibition behavior under flow conditions. The oscillatory period decreased as the light irradiation mainly enhanced the negative process and affected the positive feedback.

Nonlinear chemical reactions produce interesting chemohydrodynamic patterns in an unstirred medium, which act as interesting demonstrations to display the novel phenomena in a nonequilibrium chemical system. Here, we report new outreach experiments: pH chemohydrodynamic patterns modulated by sodium polyacrylate in the bromate–sulfite–ferrocyanide (BSF) reaction system. In an unstirred Petri dish, transient pH stripe patterns for a bromate–sulfite–ferrocyanide reaction system driven by proton autocatalysis and isothermal density-induced flow can be initiated in the center of approximately two-dimensional Petri dishes by adding a small amount of sulfuric acid solution with a certain concentration. Finally, the transient patterns are restored to the homogeneous high pH state due to proton negative feedback. The addition of sodium polyacrylate can not only lead to horizontal Marangoni flow for forming filamentary pH patterns but also decreases the diffusion of hydrogen ions, which results in a monotonic relationship between the pattern lifetime and polyacrylate concentration. Through these simple, lively and interesting experimental demonstrations, undergraduate students majoring in chemistry can realize the effect of transportations such as diffusion, density-induced flow, and Marangoni flow on complex pattern formation driven by a simple inorganic clock reaction.