Effect of Molecular Architecture of PDMAEMA–POEGMA Random and Block Copolymers on Their Adsorption on Regenerated and Anionic Nanocelluloses and Evidence of Interfacial Water Expulsion

Abstract

Block copolymers of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) with varying block sizes were synthesized by consecutive reversible addition-fragmentation chain transfer (RAFT) polymerization and then exposed to cellulose substrates with different anionic charge density. The extent and dynamics of quaternized PDMAEMA-b-POEGMA adsorption on regenerated cellulose, cellulose nanofibrils (CNF), and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF) was determined by using electromechanical and optical techniques, namely, quartz crystal microbalance (QCM-D) and surface plasmon resonance (SPR), respectively. PDMAEMA-b-POEGMA equilibrium adsorption increased with the anionic charge of cellulose, an indication of electrostatic interactions. Such an observation was further confirmed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Depending on their architecture, adsorption on TOCNF of some of the PDMAEMA-b-POEGMA copolymers produced a significant reduction in QCM frequency, as expected from large mass uptake, while surprisingly, other copolymers induced the opposite effect. This latter, remarkable behavior was ascribed to coupled water expulsion from the interface upon charge neutralization of anionic surface sites with adsorbing cationic polymer segments. These observations were further investigated with SPR and QCM-D measurements using deuterium oxide solvent exchange to determine the amount of coupled water at the TOCNF-block copolymer interface. Finally, random copolymers with similar composition adsorbed to a larger extent compared to the respective block copolymers, revealing the effect of adsorbed loops and tails as well as hydration.

Tailoring adhesion of anionic surfaces using cationic PISA-latexes – towards tough nanocellulose materials in the wet state

“…Previously in our group, we have shown examples of cellulose modification using PISA-inspired latex systems, comprising a cationic poly(2-dimethyl aminoethyl methacrylate) PDMAEMA-based corona. 21,22 Despite the interesting adsorption properties of PDMAEMA, [46][47][48][49] one of the observed challenges is the hydrolysis of the monomer in aqueous media, even at neutral pH, resulting in methacrylic acid-residues along the polymer backbone. 22 Anionic residues in the backbone give rise to lower cationic charge, thus resulting in lower adsorption to anionic surfaces.…”

Understanding Toughness in Bioinspired Cellulose Nanofibril/Polymer Nanocomposites

“…[17][18][19][20] In such a colloidal preparation route it is important to consider the long-range electrostatic interactions between the (typically negatively) charged CNFs and the polymer of choice during nanocomposite formation. [21][22][23] For instance, strongly interacting polymers that lead to flocculation with CNF will not allow to make ordered, nanostructured composites, and thus, quantitative structure/property relationships based 4 on nano-/mesoscale structures and interactions are overruled by microscale structures (flocculates). 6,9,23 This imposes great constraints on the selection of polymers to derive detailed structure/property relationships in order to progress fundamentally and substantially in the understanding of the behavior of such bioinspired, highly reinforced CNF/polymer nanocomposites.…”

Polymers and biopolymers at interfaces

“…Similarly, detailed QCM-D analysis can be used to explore the interaction of water with molecules at the test surface, and the influence of molecular architecture upon that interaction, such as in the case of synthetic hydrophilic random and block copolymers on different nanocellulose fibril-coated surfaces, which explored the possibility of water expulsion from the interface as a result of copolymer deposition and the driving forces behind that interaction (in this case, predicted to be of an electrostatic nature) [349]. In some cases this too can be linked to pH responsivity, such as in the case of mycolic acid monolayers [109].…”