Sep 6 2010
Unlike most biological membranes, polymeric, nanometer-thin membranes are very stable and can withstand considerable pressure.
This is an essential requirements for separation processes such as in water purification and desalination. Because their mechanical stability can be combined with flexibility and chemical functionality, polymer nanomembranes are also intensely researchers as materials for actuators and microsensors. They have also entered the biomedical field as artificial nacre and as a novel material used in surgery.
Among the techniques developed for fabricating defect-free and mechanically robust nanomembranes are layer-by-layer (LbL) assembly of polyelectrolyte multilayers; crosslinking of Langmuir–Blodgett; and self-assembled monolayers (SAMs). A more recent approach for the preparation of mechanically stable nanomembranes is the 'high-density crosslinking' of a spin-coated precursor solution. Due to their extraordinary sensitivity and dynamic range, highly crosslinked nanomembranes are regarded for next-generation pressure, thermal, tactile, and acoustic sensors.
However, the high crosslinking reduces the interactions between the polymer chains and the environment and thus impairs the sensitivity and flexibility of the films – a significant disadvantage for the fabrication of chemical- or bioresponsive polymer-based nanomembranes. For that reason, soft and stimuli-responsive polymer brushes have been the system of choice for the development of adaptive layers as actuators and sensors. These brushes react more quickly and has a higher sensitivity towards external stimuli.
Researchers in Germany have now developed the first freestanding polymer brush, grafted from a crosslinked monolayer (nanosheet) that provides mechanical stability and structural integrity. Because of the morphological similarity, they refer to this structure as a polymer carpet.
Reporting their findings in a recent issue of Small ("Polymer Carpets"), the groups of Armin Gölzhäuser at the University of Bielefeld and Rainer Jordan at the Technical University of Dresden, working with a team from the WACKER-Chair of Macromolecular Chemistry at the Technical University of Munich, have shown for the first time the preparation of supported and freestanding polymer carpets, which are brushes directly grafted from crosslinked nanosheets.
Source: http://www.inf.tu-dresden.de/