Chemical and mechanical control of liesegang patterns in polyacrylamide hydrogels

Abstract

Self-assembly of molecular components have attracted attention of scientific community in the past decades because of their great potential in designing functional devices in material science. Formed by simultaneous diffusion and precipitation reaction of co-precipitating chemicals in gel media, Liesegang patterns (LPs) are one of the examples of spontaneous pattern formation. LPs have been an attractive topic since their discovery in 1896, due to their wide occurrence in nature and potential applications in sensors, surface sciences, MEMS, bioengineering and microfluidics and fabrication of microstructured materials. Yet, mystery behind formation mechanism of LPs has not been completely solved. More parameters and conditions are needed to be investigated to understand the mechanism. In this study, we show that formation of Liesegang patterns in polyacrylamide hydrogels can be chemically and mechanically controlled. Firstly, we changed the chemical composition of the hydrogels and monitored the changes in the LPs formed at different locations. Then, we demonstrated that mechanical stress can alter LP formation both in terms of geometry of the rings and of their ‘appearance times’. Without any mechanical input, in (pseudo-) 2D gels, LPs form in circular shape. However, when mechanical stress is applied on gels, LPs appear as concentric ovals, the aspect ratio of which increases as applied mechanical stress increases. In this thesis, for the first time in the literature, we have provided mechanical manipulation of LPs. The time-dependent formation of the patterns and their significant alteration by mechanical input can help us build elastic deformation sensor through the visible patterns.