Dynamic instability and light-induced spatial bifurcation of mercuric iodide and external electric field experiments in two-dimensional gel media

Formation of Liesegang patterns in the presence of an electric field

“…Concerning the motion of the front, it is experimentally found to be diffusive in [21], [22] (with a slight decrease in the diffusion coefficient with increasing field intensity), and [23] (for a 2D geometry), in agreement with our theoretical predictions [32] for a forward field. Other exper- [25,26,27], present a motion of the front with a small drift component (that increases with increasing field intensity [21]).…”

“…Experiments on Liesegang patterns in the presence of an electric field have been going on quite a while since the pioneering works of Happel et al [18] and Kisch [19], see [20,21,22,23,24,25,26,27,28,29,30,31]. As already mentioned in [32], with the exception of [21,28,29], these experiments were carried on for a single polarity of the electric field (i.e., either a 'forward', or a 'reverse' field according to our terminology).…”

“…The methods of control described above are somewhat rigid since the parameters cannot be changed during the process while, ideally, one requires an easily tuned, flexible external field for control. In principle, the electric field provides such an external control and, indeed, there is experimental evidence [18,19,20,21,22,23,24,25,26,27,28,29,30] that an electric field significantly alters the emerging pattern (see Fig. 1 for a schematic experimental setup).…”

Morphology of a 2D Mg2+/NH4OH Liesegang pattern in zero, positive and negative radial electric field

“…In Liesegang landscapes, the morphological appearance of the bands is governed by the coupling between diffusion, chemical reactions and the field response of the co-precipitate ions. A diversity of wave propagation features were demonstrated in the presence of an electric field, in HgI 2 [7,8], Cr(OH) 3 [9], Ag 2 Cr 2 O 7 [10,11] and Co(OH) 2 [12,13] precipitate systems. A wealth of wave structures and exotic behavior was also obtained from the conjecture of the dynamics of diffusion-precipitation patterning media subjected to applied electric fields [11,[14][15][16].…”

Complex motion of precipitation bands

“…In contrast to removing material to construct a structure (top-down processing), controlled precipitation is suggested as means to generate a prescribed bulk design (bottom-up processing). In order to understand how to guide and locate precipitation regions, it is instrumental to investigate cases where, in addition to precipitation in the reaction zone, redissolution in the wake of the moving front also takes place [7,8,9,10,11,12,13,14,15]. The resulting virtual motion of a precipitation pulse (or more complicated pattern) is easily visualized and its dynamics can be studied in detail.…”