Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 44: P9: Crystallization, Nucleation and Self Assembly

CPP 44.13: Poster

Wednesday, March 18, 2015, 10:00–13:00, Poster A

Photonic materials from hydrogel-coated gold nanocrystals: Effect of cross-linker density, temperature and volume fraction — •Astrid Rauh and Matthias Karg — Physical Chemsitry I, University of Bayreuth, Germany

The self-assembly of soft polymer colloids allows the preparation of photonic materials with responsive bandgap behavior. To increase the refractive index of a polymer material and thus the diffraction, the implementation of inorganic cores can be useful. We synthesized a series of single gold nanoparticle cores encapsulated in a cross-linked poly-N-isopropylacrylamide (PNIPAM) shell. To investigate the influence of the thermoresponsive hydrogel shell morphology on the crystallization behavior, the shell thickness and cross-linker density were varied. The cross-linker density influences the softness and the swelling capacity of the polymer network.

The crystallization behavior was investigated in dependence of volume fraction and temperature. We found crystalline structures with diffraction in the visible for a broad range of concentrations. A lower crosslinking density supported the crystal formation. Increasing the temperature, the volume fraction of the core-shell particles is lowered.[1] Therefore, a melting of the crystals in a certain concentration range can be achieved. Upon cooling the crystalline structures exceed the critical volume fraction and form again colloidal crystals. This indicates the reversibility of the structure formation.

[1] M. Karg, T. Hellweg, P. Mulvaney, Adv. Funct. Mater. 2011, 21, 4668-4676