Temperature controlled shape change of grafted nanofoams.

We demonstrated that nanoscale-level actuation can be, in principle, achieved with grafted polymer nanofoams by forces associated with conformational changes of stretched macromolecular chains. The nanofoams are fabricated via a two-step procedure. First, the "grafting to" technique is used to obtain a 20-200 nm anchored and cross-linked poly(glycidyl methacrylate) film. Second, the film is swollen in solvent and freeze dried until the solvent is sublimated. The grafted nanofoam possesses the behavior of a shape-memory material, exhibiting gradual mechanical contraction at the nanometer scale as temperature is increased. Both the thickness and shape-recovery ratio of the nanofoam have a close to linear dependency on temperature. We also demonstrated that by modification of the poly(glycidyl methacrylate) nanofoam with grafting low molecular weight polymers, one can tune an absolute nanoscale mechanical response of the porous polymer film.