Digital holographic microscopy of spiropyran-based dynamic materials

Spiropyran (SP)-based dynamic materials undergo structural changes in response to external stimuli. In this paper, we show that digital holographic microscopy (DHM) is an effective candidate for characterisation of SPs (embedded in polymer matrices) and for monitoring of their dynamical changes. The polymer matrices are polylactic acid (PLA) and poly(methyl methacrylate) (PMMA) films, which are decorated with SPs and immobilised on graphene quantum dots (GQDs). GQDs are modified by benzylamines prior to the loading of SP species because of the enhancement of hydrophobic characteristics. UV irradiation is used as the external stimulus and the dynamical changes of the samples before and after UV irradiation are measured. DHM is arranged on a novel self-referencing setup, which substantially reduces the sensitivity of DHM to environmental vibrations. Morphometric information for characterisation of the samples is obtained by analysis of the recorded digital holograms. The experimental results demonstrate the potential of the presented technique to serve as an alternative technique for surface measurement methodologies such as atomic force microscope and stylus profiler for surface characterisation of similar materials.