Polymer-modified Mesoporous hybrid thin films: perm-selective membranes by chemical tuning of pore surface and volume

A. CALVO; A. BUNSEN; B. YAMEEN; M. C. FUERTES; F. J. WILLIAMS; O. AZZARONI; G. J. A. A. SOLER-ILLIA

Strasbourgo

Conferencia; Hybrid Materials 2011; 2011

Hybrid Materials

Rational design of hybrid “smart materials” able to react to external solicitations represents a challenge in current materials science. The chemical processes that take place in constrained environments such as membranes, micelles or nanopores are greatly modified by short-range physical-chemical properties. Mesoporous thin films (MTF) with monodisperse, ordered pores in the 2-50 nm range, constitute a robust functional scaffold with tailored cavity size, shape, interconnectivity and surface properties. Inclusion of functional polymers (either adsorbed or grafted) permits to obtain confined polyelectrolyte-surface systems that are nanoscale designed to respond to external solicitations such as pH, temperature, etc. The combination of these two building blocks leads to a “nanotoolbox” of spatially located functions with well-defined chemical functionality.   In this work, we present the chemical routes leading to two families of polymer-modified mesoporous thin films. Functional polyelectrolyte brushes were grafted to the pore walls of hybrid MTF (silica, titania, zirconia or hybrid oxides) in two steps. First, an initiator group was attached to dangling amino organic groups; subsequent polymerization led to smooth inclusion of anionic, cationic or zwitterionic brushes within the pores. The second strategy implies the adsorption of polyelectrolites (PAAH, PSS, or SAMs) into the 3D framework of MTF under controlled temperature, concentration and ionic strength conditions. Exhaustive characterization by FE-SEM, SAXS, XRR and ellipsoporosimetry permits to quantify mesostructure and pore filling.   The macromolecules significantly modify the properties of the pore system, by modifying the surface or volume of the mesoporous matrix. Perm-selectivity towards electrochemical probes can be switched by modifying the mesopore surface functions with the polyelectrolyte. When a zwitterion is grafted, ion gating is achieved. Cationic polyelectrolytes permit to locally produce gold nanoparticles in the mesopores by pre-concentrating the metal precursor. The integration of mesoporous films and polymer brushes provides a core concept to design complex architectures with synergic properties.