Controlling local physico-chemical properties of colloidal particles and their self-assembled structures

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In this thesis the physico-chemical properties of colloids and their self-assembled structures are investigated in detail. The focus lies on the fundamental investigation of colloids, their interfacial behavior during self-assembly processes and the influence of the colloid´s local environment on the physico-chemical properties. A novel, versatile entrapment technique was developed to investigate colloids and their interfacial equilibrium position directly at the air-water interface. The entrapment enables to investigate the contact angle position ex situ in an scanning electron microscope (SEM), allowing determining local contact angles even for single nanoparticles. The crystallization of nanoparticles into highly crystalline close-packed architectures is well-understood. But as the structure of such colloidal monolayers is limited to hexagonal geometry new techniques have to be developed to create new and more complex architectures. Here, the amphiphile-driven self-assembly approach at the air-water interface of a Langmuir trough is introduced to create reproducibly network- or chainlike packing as well as colloidal assemblies with a pseudo-square lattice. This technique provides the advantage of not using any additional special equipment or pre-treated template substrates as it is commonly used to yield anisotropic self-assembly of colloids. The influence of polymer composition, concentration and manipulation of the electrostatic environment on the chain-like and square arrangements is investigated in detail. The self-assembly of colloids at the air-water interface is also used to create highly functional two-dimensional colloidal monolayers. The approach of the binary co-assembly of template and functional photoswitchable colloids into complex binary monolayers is used to create locally separated light-responsive nano-pixels as a model system for optical data storage application. Moreover, functional and trigger responsive nanoparticles are also useful for drug delivery applications in nanomedicine as presented in this work. By functionalization of nanoparticles with a pH responsive dye the path of nanoparticles or nanocapsules through cells can be monitored. Again, localized properties of the nanoparticles and their direct environment can be investigated in detail. Based on the results, drug carriers such as nanocapsules can be designed to release their payload at a distinct position inside the cell upon change of the pH value.

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