pH‐Responsive Swelling of Poly(acrylic acid) Brushes Synthesized by the Grafting Onto Route

Abstract

International audienceThe swelling of poly(acrylic acid) brushes in aqueous solutions is studied by neutron reflectivity. The brushes are synthesized on silicon wafers using a grafting onto approach and their stretching is investigated at various pH, grafting densities, and chain lengths. Neutron reflectivity provides the average thickness and, more interestingly, the density profile of the brushes. The profiles obtained experimentally are in good agreement with theory. The swelling ratio of the poly(acrylic acid) brushes is compared with that of other polymer brushes formerly investigated using classic scaling laws. Owing to a new representation with the normalized thickness, it is demonstrated that there is a general behavior for all polymer brushes with a master curve for neutral polymer brushes and for polyelectrolyte brushes

Responsive Adsorption of N-Isopropylacrylamide Based Copolymers on Polymer Brushes

“…Neutron reflectivity measurements were performed at silicon-liquid interface on the reflectometer EROS at the Laboratoire Léon Brillouin (CEA, Saclay, France). The experimental procedure and setup were described in detail in previous publications [36,46]. Neutron reflectivity experiments were carried out with protonated polymer brushes (without and with protonated free copolymers) and deuterated water in order to determine the monomer density profile of the brushes (without and with the adsorbed copolymers).…”

“…Figure S1 shows an example of neutron reflectivity data and the profile of the volume fraction of monomers corresponding to the best fit of the experimental results. The analytical forms of the density profile of polymer brushes were investigated in detail in previous publications and in particular for poly (acrylic acid) brushes [36]. In the present work, we aim at comparing the density profiles of polymer brushes at different temperatures, with or without adsorbed polymers, a simple step model is well adapted.…”

“…Other studies have reported changes of properties at the coil-to-globule transitions using other experimental techniques [14,24,35]. In the case of PAA, the pH induced transition from the neutral brush to the polyelectrolyte brush has been studied by various groups using neutron reflectivity [36], AFM [6], or spectroscopic ellipsometry [37] in order to determine the different regimes of swelling which depend on pH, ionic strength, and grafting density. Other teams have investigated the dissociation behavior of the PAA brushes, for instance using infrared spectroscopy ellipsometry [38] or a combination of infrared spectroscopy and contact angle titration [39].…”

“…In this article, we investigate the adsorption behavior of such copolymers on temperature-responsive brushes of PNIPAM at pH 7 and on pH-responsive PAA brushes at ambient temperature. To this end, a careful analysis of the swelling behavior of the PAA brushes (published elsewhere [36]) and PNIPAM brushes was carried out by ellipsometry and neutron reflectivity. The combination of these techniques gives access to the amount of adsorbed polymer depending on the chain lengths and on the grafting densities of the PAA and PNIPAM brushes.…”

Synthesis of naringin‐based polymer brushes via seATRP

“…These polymerization methods include ring‐opening polymerization, click reaction, cationic polymerization, anionic polymerization, radical (co)polymerization, reversible addition‐fragmentation chain transfer polymerization (RAFT), nitroxide‐mediated polymerization (NMP), and atom transfer radical polymerization (ATRP), as well as combinations of different methods . Considering these techniques, macromolecular brushes can be synthesized via three main approaches: “grafting through”, “grafting onto”, or “grafting from” . Undoubtedly, “grafting from” is one of the most useful technique which involves attachment of initiator molecules to the backbone and growing of polymer chains via polymerization; therefore, macromolecular brushes with high grafting density can be prepared by using these tactics …”