Diffusion-limited electroless silver reduction on copper for "porous monocrystal"Part of:
We investigated the process of the electroless silver reduction on copper for the formation of “quasi” 2D morphological patterns of silver: “porous monocrystal”. Surprisingly, when we place the copper precursor inside a matrix of densely packed spheres of ion exchange resins—glass spheres containing transition metals—we observed silver patterns not on the copper bead but on the glass spheres. Initially we expected that silver dendritic 2D patterns can be formed below the spheres or 1D growth of silver. Surprisingly, we observed silver growth around spheres and following spreading of the different morphological patterns on spheres.
We modelled the diffusion-limited aggregation (DLA) in the petri dish for our “quasi” 2D morphological patterns of silver. The features are surprisingly similar to the experiments. In particular we analyzed morphology of pattern as a function of time. We recorded a video of silver pattern formation and made a time-space kymogram, using ImageJ, with following calculation of branching instability pattern.
The question is how we can affect the dendritic pattern growth kinetics. We demonstrated how to control morphological 2D silver patterns by controlling regimes of growth. We varied the shape of the copper precursor and as well as solution parameters (silver ions concentration and additives in solution, viscosity) in relation to the morphology of formed 2D patterns.
Moreover we did experiments to affect not just a diffusion, but chemical reaction in the system. One example of the reaction regulation with oligoethylene glycol. If oligoethylene glycol presents in reaction medium of AgNO3 initial stages of network development is slower, however, the diffusion limit comes later. Moreover the first stage of growth, when ratio area / perimeter increases, is longer and has sub-stages that formed Liesegang-like pattern, probably due to periodic interplay between reaction and diffusion processes.
Using theoretical model we show that Petri-dish size is important to explain the change between growth regimes. We have an instruments, nutrient concentration, additional chemicals in solution, local heating, etc. to affect the morphology and branching instabilities of formed patterns.