Fig. 5.

A potential explanation of how pNIPAAm chains are retained is presented: (A) some APTES molecules are retained during spin coating (the molecular structure of fully hydrolyzed APTES, having three -SiOH groups, is sketched to the right), (B) evaporation (black arrows) and segregation (purple arrows) of APTES during annealing under vacuum to result in a gradient distribution of the APTES within the film, and (C) formation of the APTES network and APTES oligomers within the film during curing. The red circles represent the polymerized APTES, forming siloxane bonds by condensing the –SiOH groups between APTES molecules. When all three of the –SiOH groups within one APTES molecules are all condensed, cross-linking would result (see the enlarged circle of (iii)).