Measurement of the Transition Temperature Governing the Photoinduced Reversible Solid-to-Liquid Transition of Azobenzene-Containing Polymers

The ability to observe photoinduced reversible solid-to-liquidtransitions for some polymers bearing photo-active azobenzene groups(azopolymers) has become a competitive research field in materialsscience and technology because of their potential applications inphotocontrolled adhesives, photohealable materials, or soft lithography.Unfortunately, methods to accurately characterize this transitionare scarce and mainly qualitative, which limits the understandingof the parameters governing it. In the first part of this paper, wewill show that the photoinduced reversible solid-to-liquid transitioncan be associated to a transition temperature (named T (SL)). This transition temperature can be accurately measuredusing a scanning probe microscopy-based method. Then, the measurementof T (SL) on azopolymers with different chemicalstructures will allow us to understand why the experimental irradiationconditions to observe the solid-to-liquid transition were different.With the possibility to accurately characterize the photoinduced solid-to-liquidtransition, we believe that this work paves the way to the optimizationof azopolymer design for a better photocontrol of their mechanicalproperties.