Light-induced brushes

A spiropyran derivative with an amine linker was synthesized and coupled to grafted brushes of PGMA and of PMAA activated with perfluorophenyl trifluoroacetate. Exposure of the modified brushes to UV light, which converts the attached moieties from the uncharged transparent spiropyran to the zwitterionic merocyanine form, rendered the brushes deep purple in color, fluorescent, and hydrophilic. The properties switched back by thermal or visible light-induced relaxation. The kinetics of the switching was found to be dependent on the chemical environment provided by the polymer brushes as well as on the polarity of added solvent. 

There is a host of other intriguing phenomena associated with the structure and dynamics of stars, which we only list here. The inhomogeneous monomer density distribution in Fig. 2 is responsible for temperature and/or solvency variation in analogy to polymer brushes attached on a flat solid surface [198]. In fact, multiarm star solutions display a reversible thermoresponsive vitrification (see also Sect. 5) which, in contrast to polymer solutions, occurs upon heating rather than on cooling [199]. Another effect is the organization of multiarm stars in filaments induced by weak laser light due to action of electrostrictive forces [200]. This effect was recently attributed [201] to local concentration fluctuations which provide localized-intensity dependent refractive index variations. Hence, the structure factor speciflc to the particular material plays a crucial role in the pattern formation. 

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