Diffusion fronts and gradient percolation: A survey

Twenty years ago, Bernard Sapoval suggested that the solders obtained by inter-diffusion of two metals, could have a fractal structure. He, then, initiated simulation calculations based on a lattice gas model, describing the diffusion of non-interacting particles on a square lattice. These ideas are nowadays a mainstream field of research, developing in various domains including topics as different as fractal etching, imbibition experiments, fractal structures of polymer interfaces, image treatment, fracture surfaces, urban growth, predatory-prey interaction, etc.