A novel UV lithographic technique for the patterning of the block copolymer (Pluronic) thin films is developed. The present method is based on UV-induced water affinity changes in block copolymer films. By water vapor post-treatment of the film, a difference in water content is established between UV illuminated and unilluminated sections, which can induce an osmotic pressure at the interface. This osmotic pressure drives the migration of Pluronic molecules, resulting in formation of patterns on the block copolymer films. Remarkably, this patterning method requires neither initiators nor polymerizable moieties which are essential for a conventional photolithographic approach. Additionally, the etching process is bypassed, eliminating the use of destructive acids or organic solvents and making this an environmentally friendly patterning protocol. It is reported that Pluronic is photo-responsive to UV exposure, which causes the dehydration of the PEO-PPO-PEO backbone.