The nanopatterning of a stimulus-responsive polymer by thermal dip-pen nanolithography

We demonstrate that poly(N-isopropylacrylamide) (PNIPAAm) nanostructures can be directly and reproducibly written from the melt using thermal dip-pen nanolithography. Whereas previous research examined polymer brushes where the strands were oriented normal to the surface, here the polymer strands are aligned parallel to the surface. Alignment parallel to the surface allows ultrathin films to be formed while still completely masking the substrate from the solution. Moreover, the aligned PNIPAAm retains its unique ability to reversibly bind and release proteins when driven through a hydrophobic-hydrophilic phase transition by a change in temperature. Unlike the conventional brush form, the phase transition in the aligned form is not associated with a change in height, retaining its dimensional stability.