We measure the static structure factor S(q) and the cooperative diffusion coefficient Dc of weakly charged poly(acrylic acid) gels as a function of temperature and salt concentration. The variations of S(q) with these parameters agree semi-quantitatively with a recent model that predicts the occurrence of mesophases in similar systems. We use the theoretical S(q) to derive Dc in a simplified approach. The obtained expression describes satisfactorily the experimental behaviour of Dc