Ionic strength responsive brushes

Figure 5.7 Schematic illustration of conformation changes of an ionic strength-responsive polymer brush.

All polyelectrolyte brushes, both weakly and strongly charged, are responsive to the ionic strength in (aqueous) solution (Balastre et al., 2002 Borisov et al., 1994 Israels, Leermakers, Fleer, 1994). At a low salt concentration (the osmotic brush regime),... 

SI-IMP has been used for synthesis of different types of stimuli-responsive polymer brushes that are responsive to several external stimuli, such as pFI, temperature, and ionic strength [28,58-65]. Because materials interact with their surroundings via their interfaces, the ability to fashion soft interfacial layers and tune the range, extent, and type of physicochemical interactions across interfaces is central to a variety of applications. Rahane et al. carried out sequential SI-IMP of two monomers to create bilevel poly(methacrylic acid)-Woc/c-poly(N-isopropylacrylamide) (PMAA-b-PNIPAM) block copolymer brushes that can respond to multiple stimuli [28]. They observed that each strata in the bilevel PMAA-b-PNIPAM brush retained its customary responsive characteristics PMAA being a "weak" polyelectrolyte swells as pH is increased and the thermoresponsive PNIPAM block collapses as temperature is raised through the volume phase transition temperature due to its lower critical solution temperature (LCST) behavior. As a result of ions added to make buffer solutions of various pH and because of the effect of surface confinement, the swollen-collapse transition of the PNIPAM layer occurs at a... 

The responsiveness of mixed polyelectrolyte brushes is modified by electrostatic interactions which can be used to regulate the mechanism of the phase segregation. Weak mixed poly electrolyte brushes are of special interest since the electrostatic interactions can be affected by pH and ionic strength of aqueous environment and the surface composition of the mixed polyelectrolyte brush can be switched just by a change of external pH. ... 

Another example of multiresponsive brushes shows response to magnetic fields and pH (Yu et al., 2013). Imidazole group-modified PEG-polypeptides were grafted onto silica-coated Fe304 NPs. The Fe304 responded to external magnetic fields while the polymeric shell responded to pH. SPB assembled by PEO-g-PDMAEMA, a copolymer synthesized by ATRP, responded to shear, ionic strength, and pH (Fig. 4.14) (Sui et al., 2011). 

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