Photoresponsive assemblies interactions

This chapter describes the non-LBL approaches of tandem assembly and interfacial stabilization for the formation of closed shell structures, with an emphasis on ensembles in which NPs constitute the shell. Tandem assembly is a versatile and environmentally friendly route to the formation of useful NP-shelled capsules. In contrast to sacrificial core templating and LBL assembly methods, tandem assembly has the important differentiating feature that it avoids the incineration or solvent dissolution step to generate the hollow interior of the capsule. Enhancements in optical, mechanical, catalytic, and release properties of such materials hold great promise for their application in photoresponsive delivery systems, catalysis, and encapsulation. Interfacial stabilization routes are found to yield NP-shelled structures in the form of emulsions and foams that have enhanced stability over those from conventional, surfactant-based approaches. Unusual interactions of the NP with fluid interfaces have made possible new structures, such as water-in-air foams, colloidosomes, and anisotropic particles. 

Supramolecular spherical assemblies of NPs with photoresponsive adhesion/dispersal behaviour were also obtained in a ternary system hierarchically combining the host-guest interaction of different types of CDs toward porphyrin and azobenzene. The inclusion complexation of an azobenzene modified water soluble porphyrin (1) with phthalo-cyanine-grafted permethyl (3-CDs (2) could be reversibly cross-linked to relatively larger nanospheres with naphthyl bridged bis(a-CD)s (3). The large spheres (12 -3) turned reversibly to small-sized particles (1 2) upon photoisomerization of the azoaromatic group in 1 (Fig. 13). 

The formation of vesicles can also be induced by electrostatic interaction or electrostatic self-assembly. Among others, it was shown that LUVs are obtained when a polycation is mixed with a polyanion-fc-poly(ethylene glycol). The vesicle size can be controlled by changing the polymer concentration. Vesicles are also obtained when a polyanion- -poly(ethylene glycol) is mixed with a cationic azobenzene surfactant. In that case, the vesicles are photoresponsive, that is, they dissemble if the azobenzene is isomerized from the irans form to the cis form. Finally, vesicles can also be prepared by mixing a cationic dendrimer and an anionic sulfonate dye. ... 

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