Poly(laurylmethacrylate-block-styrene-block-laurylmethacrylate) gradient copolymers (PLMA-PS-PLMA) in a selective solvent for PLMA, self-assemble into spherical colloidal micelles. The structure and the dynamics of the solutions are investigated as a function of temperature and concentration using small angle X-ray scattering (SAXS) and rheology. When the temperature is increased, the micellar cores shrink and the coronas increase due to the gradual solubilization of the domains where S and LMA segments are mixed. The swelling of the micelles is perfectly correlated to the increase of the viscosity. The variations of the low-shear viscosity over a wide range of concentrations and temperatures are rescaled onto a universal curve and compared to those for other soft colloidal systems like star polymers, hairy particles and dendrimer solutions.