A trifluoroacetic acid-based etchant is described that can remove a sacrificial component of a multi-component polymer, e.g., a self-assembled block copolymer. The etchant can operate at a high etch rate and with excellent selectivity. The etchant can remove a hydrolysable sacrificial component such as a polylactide block from a self-assembled block copolymer. The etchant enables the macroscopic preservation of the nanostructure morphologies of self-assembled copolymers (e.g., poly(styrene-block-lactide) copolymers) and can yield pristine porous films of the non-hydrolysable component of the starting multi-component polymer.