Temperature responsive behavior of polymer brush/polyelectrolyte multilayer composites

Abstract

aThe complex interaction of polyelectrolyte multilayers (PEMs) physisorbed onto end-grafted polymer brushes with focus on the temperature-responsive behavior of the system is addressed in this work. The investigated brush/multilayer composite consists of a poly(styrene sulfonate)/poly(diallyldimethylammonium chloride) (PSS/PDADMAC) multilayer deposited onto the poly(N-isopropylacrylamide-bdimethylaminoethyl methacrylate) P(NIPAM-b-DMAEMA) brush. Ellipsometry and neutron reflectometry were used to monitor the brush collapse with the thickness decrease as a function of temperature and the change in the monomer distribution perpendicular to the substrate at temperatures below, across and above the phase transition, respectively. It was found that the adsorption of PEMs onto polymer brushes had a hydrophobization effect on PDMAEMA, inducing the shift of its phase transition to lower temperatures, but without suppressing its temperature-responsiveness. Moreover, the diffusion of the free polyelectrolyte chains inside the charged brush was proved by comparing the neutron scattering length density profile of pure and the corresponding PEM-capped brushes, eased by the enhanced contrast between hydrogenated brushes and deuterated PSS chains. The results presented herein demonstrate the possibility of combining a temperature-responsive brush with polyelectrolyte multilayers without quenching the responsive behavior, even though significant interpolyelectrolyte interactions are present. This is of importance for the design of multicompartment coatings, where the brush can be used as a reservoir for the controlled release of substances and the multilayer on the top as a membrane to control the diffusion in/out by applying different stimuli.

Effect of Architecture of Thermoresponsive Copolymer Brushes on Switching of Their Adsorption Properties

“…Thus, random PNIPAM–PDMAEMA copolymer brushes with low PDMAEMA fraction show switching of the zeta potential (inversion of charge sign) that can be explained by switching of the polymer chain conformation which resulted in change of the accessibility of charged. Block copolymer brushes, as it is reported in literature, also demonstrate thermoresponsive behavior with transition temperatures close to that of PNIPAM …”

“…Block copolymer brushes, as it is reported in literature, also demonstrate thermoresponsive behavior with transition temperatures close to that of PNIPAM. [51] We observed strong adsorption of PAA-modified 200 nm large SiO2 particles onto PDMAEMA brushes at elevated and room temperatures (Figure 3), which is due to electrostatic attraction between PAA and PDMAEMA. The surface density of adsorbed particles was found to be independent of the temperature.…”

Responsive Adsorption of N-Isopropylacrylamide Based Copolymers on Polymer Brushes

“…The physisorption of diblock copolymers containing a surface-anchoring block and the block of interest has the disadvantage of limited applications due to the reversibility of the physical interactions. To covalently end-attach polymer chains, the "grafting from" method-usually based on surface-initiated controlled radical polymerization-is a broadly used method [23][24][25][26][27][28][29]. The "grafting onto" method, which we chose, does not give access to very high grafting densities, but it has the great advantage of simplicity and allows the synthesis of brushes of very well-controlled chain distribution [30,31].…”

PDADMAC/PSS Oligoelectrolyte Multilayers: Internal Structure and Hydration Properties at Early Growth Stages from Atomistic Simulations

“…The usage of polyanions and polycations as building blocks in LbL processes is a choice largely explored experimentally in recent years. The resulting coatings, known as polyelectrolyte multilayers (PEMs) [8][9][10], have shown a great potential for many application fields, including the creation of biosensors and non-linear optical materials [11][12][13], catalysis and filtration membranes [14][15][16][17][18], protective and biocompatible coatings [19,20], or nanocapsules and drug delivery systems [21,22], to mention some examples. This considerable growth of experimental studies, stimulated by the generality and relative simplicity of the LbL procedure, has been accompanied by large research efforts on the fundamental understanding of PEMs assembly mechanisms.…”