Reversible Patterning Cross-Linked, Humidity-Responsive Polymer Films with Programmatically and Accurately Controlled Deformation

A series of novel humidity-responsive and photosensitive polymer films (PCA- PAA-PEG) are prepared. These films can be patterning cross-linked by the photodimerization of coumarin pendant groups. The humidity-induced deformation can be well controlled by the pattern because of the different modulus and hydrophilicity between cross-linked and un-cross-linked segments. In addition, the pattern can be erased and the deformation direction can be changed programmatically by the de-cross-linking-re-crosslinking approach due to the reversible photodimerization of coumarin groups. The cross-linking degree also affects the humidity responsiveness of the film. The deformation of the gradient patterning cross-linked film can be more accurately controlled. Moreover, the length and width ratio (L/W-s/W-h) of the un-crosslinked segment to the cross-linked segment affects the deformation of the films as well. When L/W-s/W-h is 5/2/1 or 5/3/1, the deformation is controllable, and when L/W-s/W-h is 5/1/1 or 5/4/1, the deformation is random at the initial stage, but the whole film will bend along the short axis in the end.

Automated summary

A series of novel humidity-responsive and photosensitive polymer films have been prepared, which can control humidity-induced deformation through patterned cross-linking and change deformation direction programmatically through reversible photodimerization. Additionally, the length and width ratio between un-crosslinked and cross-linked segments affects the deformation of the films.