Understanding the Structure and Dynamics of Nanocellulose-Based Composites with Neutral and Ionic Poly(methacrylate) Derivatives Using Inelastic Neutron Scattering and DFT Calculations

Abstract

Bacterial nanocellulose (BC)-based composites containing poly(2-hydroxyethyl methacrylate) (PHEMA), poly(methacroylcholine chloride) (PMACC) or poly(methacroylcholine hydroxide) (PMACH) were characterized by inelastic neutron scattering (INS) spectroscopy, combined with DFT (density functional theory) calculations of model systems. A reasonable match between calculated and experimental spectral lines and their intensities was used to support the vibrational assignment of the observed bands and to validate the possible structures. The differences between the spectra of the nanocomposites and the pure precursors indicate that interactions between the components are stronger for the ionic poly(methacrylate) derivatives than for the neutral counterpart. Displaced anions interact differently with cellulose chains, due to the different ability to compete with the O-H···O hydrogen bonds in cellulose. Hence, the INS is an adequate technique to delve deeper into the structure and dynamics of nanocellulose-based composites, confirming that they are true nanocomposite materials instead of simple mixtures of totally independent domains. Keywords: bacterial nanocellulose; nanocomposites; poly(2-hydroxyethyl methacrylate); poly(methacroylcholine chloride); poly(methacroylcholine hydroxide); inelastic neutron scattering; DFT calculations IntroductionA tour through the kaleidoscopic portfolio of materials developed in the last decades, clearly shows that composite materials based on cellulose [1], and bacterial nanocellulose (BC) in particular [2], are quite relevant for myriad domains of applications [3][4][5]. In fact, the exopolysaccharide BC, which is biosynthesized by several non-pathogenic bacteria in the form of membranes with a tree-dimensional network of cellulose nanofibrils [6], has shown potential for drug delivery [7-9], wound healing [10,11], bone tissue engineering [12], antimicrobial materials [13], food and food packaging [14,15], water remediation [16,17] and fuel cells [5,18,19], just to mention some fields of application.In terms of production, BC-based nanocomposites can be prepared by in situ and ex situ methodologies [20], which already enabled the combination of BC with a vast array of synthetic polymers Molecules 2020, 25, 1689 2 of 16 (e.g., polyaniline [21] and Nafion [22]) and biopolymers (e.g., lactoferrin [23] and fucoidan [24]), as well as hybrid materials with metal oxides, metal sulphides and metal nanoparticles [4], and graphene and derivatives [25,26], with the aim of enhancing or adding novel properties to the ensuing materials [2]. Among the available methodologies, the in situ polymerization of monomers with, for instance, (metha)acrylate functional groups, is a simple top-down method that promotes the use of BC without altering its valuable and unique three-dimensional structure [2]. Acrylamide [27], acrylic acid [28], glyceryl monomethacrylate [29], 2-ethoxyethyl methacrylate [29], 2-aminoethyl methacrylate [30], methacryloyloxyethyl phosphate [31], N-methacryloyl glycine [7] and bis[2-(me...

Natural Polymers-Based Materials: A Contribution to a Greener Future

“…Engineering natural polymers-based materials derived from polysaccharides and proteins is the main objective of the work carried out by the BioPol4fun research group. In the last decade, we have been intensively exploiting cellulose [ 63 , 64 ], nanocelluloses (e.g., bacterial nanocellulose (BNC) [ 61 , 65 , 66 ], nanofibrillated cellulose (CNFs) [ 67 , 68 ] and cellulose nanocrystals (CNCs) [ 69 ]), chitosan [ 70 , 71 , 72 , 73 ], pullulan [ 71 , 74 , 75 , 76 ], starch [ 68 ], hyaluronic acid [ 77 , 78 ], alginate [ 79 ], fucoidan [ 80 , 81 ], agar [ 82 ], lysozyme [ 83 , 84 , 85 , 86 ], and gelatin [ 87 ] ( Figure 1 ) to fabricate films [ 85 , 88 , 89 , 90 , 91 ], membranes [ 81 , 92 , 93 , 94 , 95 ], (nano)composites reference [ 64 , 96 , 97 , 98 , 99 ], coatings [ 100 , 101 , 102 , 103 ], nanosystems [ …”

New Insights on the Vibrational Dynamics of 2-Methoxy-, 4-Methoxy- and 4-Ethoxy-Benzaldehyde from INS Spectra and Periodic DFT Calculations

“…This is particularly valuable for amorphous systems, for which the experimental INS spectrum can be matched to a combination of proposed model structures whose spectral contributions are determined from discrete DFT. This methodology has been comprehensively described in the influential work on doped poly(hexylthiophene) [ 10 ] and it has been used by some of us to experimentally assess the random nature of 2,4-poly(ethylene furanoate) [ 11 ] and to interpret the structure of bacterial cellulose composites [ 12 ]. It can also be advantageous to validate proposed crystal structures, namely those derived from periodic DFT calculations.…”

Water in Deep Eutectic Solvents: New Insights From Inelastic Neutron Scattering Spectroscopy

“…Upon hydration, τ 1 mode is red-shifted while the ratio τ 3 /τ 2 decreases. The red-shift of τ 1 mode has been observed for situations in which there are competitive hydrogen bond donors for the chloride anion [28,50]. In pure ChCl, all the methyl groups of choline are hydrogen-bonded to chloride anions (CCDC database, RefCode:CHOCHL01), and the methyl torsional motions are restricted.…”

“…In pure ChCl, all the methyl groups of choline are hydrogen-bonded to chloride anions (CCDC database, RefCode:CHOCHL01), and the methyl torsional motions are restricted. In the presence of alternative hydrogen bond donors, such as urea [28] or matrix donors [50], chloride anions are displaced and some methyl groups became freer. Consequently, methyl torsions move to lower wavenumbers.…”