Abstract
We investigate the adsorption of pH- or temperature-responsive polymer systems by ellipsometry and neutron reflectivity. To this end, temperature-responsive poly (N-isopropylacrylamide) (PNIPAM) brushes and pH-responsive poly (acrylic acid) (PAA) brushes have been prepared using the “grafting onto” method to investigate the adsorption process of polymers and its reversibility under controlled environment. To that purpose, macromolecular brushes were designed with various chain lengths and a wide range of grafting density. Below the transition temperature (LCST), the characterization of PNIPAM brushes by neutron reflectivity shows that the swelling behavior of brushes is in good agreement with the scaling models before they collapse above the LCST. The reversible adsorption on PNIPAM brushes was carried out with linear copolymers of N-isopropylacrylamide and acrylic acid, P(NIPAM-co-AA). While these copolymers remain fully soluble in water over the whole range of temperature investigated, a quantitative adsorption driven by solvophobic interactions was shown to proceed only above the LCST of the brush and to be totally reversible upon cooling. Similarly, the pH-responsive adsorption driven by electrostatic interactions on PAA brushes was studied with copolymers of NIPAM and N,N-dimethylaminopropylmethacrylamide, P(NIPAM-co-MADAP). In this case, the adsorption of weak polycations was shown to increase with the ionization of the PAA brush with interactions mainly located in the upper part of the brush at pH 7 and more deeply adsorbed within the brush at pH 9.
Highlights
Polymer brushes are densely packed assemblies of polymer chains that are end-attached to a surface or interface [1,2]
We found that the brush was swollen below as temperature were investigated using neutron reflectivity
We found that the brushthe was swollen expected andLCST
Summary
Polymer brushes are densely packed assemblies of polymer chains that are end-attached to a surface or interface [1,2]. Water-immersed polymer brushes can be sensitive to changes of temperature [5], pH or ionic strength [6], and other stimuli depending on the nature of the polymer: Upon stimulus, the brushes adapt their conformation. Such change can be used to control the surface properties in order to design smart surfaces exhibiting responsive adsorption [7], specific.
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