Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 5: New Materials

CPP 5.1: Vortrag

Montag, 25. Februar 2008, 10:00–10:15, C 230

Shear stable colloidal crystals as pH- and pressure sensors. — Roy Goldberg and •Hans Joachim Schöpe — Johannes Gutenberg-Universität Mainz, Institut für Physik, Staudinger Weg 7, 55099 Mainz, Deutschland

Opaline hydrogels were produced as polycrystalline bulk material with bcc-structure by immobilization of self-ordered charged colloidal particles crystallized under equilibrium conditions in a poly(acrylamide) matrix. The final size of a polycrystalline sample is about 7 qcm, a single crystal is up to several mm in length. The crystal size is tunable by varying the amount of photoinitiator and the hydrogel volume-change due to swelling. The resulting photonic crystals are of high quality showing high order reflections. These hydrogels show a reversible shift of the diffraction Bragg-peak wavelength in dependence of external conditions due to swelling or shrinking as funczion of the pH and under applied mechanical stress. The wavelength of the photonic band gap can be shifted over the entire spectrum of visible light (500nm). Bulk material offers the possibility to shift the position of the main Bragg reflection to smaller and to larger wavelength simultaneously: under compression the wavelength of the (110)-reflection parallel to the direction of compression decreases while perpendicular to the direction of compression it increases.