Miniaturization on nm scale plays an important role not only for the electronics industry but also for questions of transport and sensor applications such as for the lab-on-a-chip approach. For example, ion channels, which can regulate the transport of ions with high selectivity due to their complex structure and functionality, represent an as yet unattained model in the research and fabrication of synthetic materials with nanoporous structures. A major challenge for mimicking the complexity of biological nanopores, is the requirement to be able to selectively place multiple functionalities in a nanopore at different positions. Common functionalization strategies for synthetic nanopores have so far allowed only two functional components to be placed locally. However, local multifunctionalization of nanopores is essential for a high degree of control over transport or pore accessibility for many applications and sensory questions.
This work is aimed at developing a model concept for multifunctional and local functionalization of nanopores. Based on orthogonal surface chemistry and wetting control, inverse colloidal monolayers with gold coating are provided with three different functionalities as a model system. In the first functionalization step, the silica pore wall is selectively addressed with ring-opening metathesis polymerization to achieve pore hydrophobicity. Due to the hydrophobization of the pores by the polymer, the outer gold surface can be selectively functionalized from an aqueous solution in the second step. The functionalization takes place via self-assembly of thiols. In the third and final functionalization step, the inner gold surfaces in the pore bottom can be selectively functionalized, as the outer gold surface is already covered with a monolayer of thiols. A polymerization initiator with a thiol end group is dissolved in ethanol, which can infiltrate the pore, and introduced to the pore bottom via self-assembly. Surface-initiated polymerization can subsequently be conducted.
To address sensory questions, Schiff bases are investigated as colorimetric chemosensors in nanoporous silica films and for wetting switching of inverse opals. For this purpose, different Schiff bases are synthesized and investigated in solution for their sensing potential for different metal cations. The most promising candidates are attached to the nanoporous silica films by thiol-ene click chemistry and investigated by UV-vis spectroscopy and contact angle measurements.
For many applications of nanopores, diffusion of molecules or water transport also play an important role. In this work, the mass transport of redox active test molecules through mesoporous silica films is quantitatively investigated with electrochemical impedance spectroscopy to determine the charge transfer resistance and diffusion coefficient as a function of wetting and pretreatment.
Water transport through mesoporous silica films can be studied using imbibition. For this purpose, photoiniferter-mediated polymerization is used to provide the mesoporous silica films with a polyelectrolyte that can interact with counter ions of the Hofmeister series. The parameter measured is the imbibition distance as a function of the imbibition time and allows conclusions to be made regarding the transport behavior of water as a function of the counter ions that influence the conformation of the polyelectrolyte. | English |