  Although the pattern formation on polymer gels has been considered as a
result of the mechanical instability due to the volume phase transition, we
found a macroscopic surface pattern formation not caused by the mechanical
instability. It develops on gelation surfaces, and we consider the
reaction-diffusion dynamics mainly induces a surface instability during
polymerization. Random and straight stripe patterns were observed, depending on
gelation conditions. We found the scaling relation between the characteristic
wavelength and the gelation time. This scaling is consistent with the
reaction-diffusion dynamics and would be a first step to reveal the gelation
pattern formation dynamics.
