Switchable surface approaches

To conclude, the results obtained with helical polymer stmctures at surfaces pave the way toward new approaches not only for the construction of new chiral materials, such as chiral selectors and catalysts, but also for the rational design of novel switchable chiral surfaces based on inversion of helicity of macromolecules. 

A purely physical approach based on an entrapment procedure was developed by Guo and Ulbricht (2011) to fabricate thermo-responsive polypropylene membranes. The polypropylene surface was exposed to solutions of an amphiphilic block copolymer of polyNiPAAm (PNiPAAm) with a hydrophobic poly(butylacrylate) block. After treatment under optimised conditions (i.e., solvent, concentration, temperature, exposure time), a hydrophilisation as well as a switchable wettability were achieved. 

Figure 90. Surface-stabilized configuration with less than optimum efficiency, switchable between two symmetric states with low optical contrast. The surface pretilt angle has been chosen equal to the smectic tilt angle 0in this example. For a strong boundary condition with zero pretilt, a different extreme limiting condition with approaching zero at the boundary is also conceivable, without any essential difference in the performance of the cell.

In this chapter, a series of recent results in surface modification of various surfaces employing the macromolecular anchoring layer approach was overviewed. It was demonstrated that the approach could be used as a virtually universal method for grafting of functional polymer brushes. The properties of the bmshes can be controlled by polymer nature, structural and morphological factors, and external stimuli. The polymer grafting technique developed can be readily applied to surface modification of fibers and textiles, leading to generation of hydrophobic, hydrophilic and switchable fibrous materials. 

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