Publications by authors named "Jakob Wohlert"

Wood, with its constituent building block cellulose, is by far the most common biomaterial on the planet and has been the most important material used by humans to establish civilization. If there is one single biomaterial that should be studied and used by materials scientists across disciplines to achieve a sustainable future, it is cellulose. This perspective provides insights for the general materials science community about the unique properties of wood and cellulose and how they may be used in advanced sustainable materials to make a substantial societal impact.

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Motivated by the limitations of conventional coarse-grained molecular dynamics for simulation of large systems of nanoparticles and the challenges in efficiently representing general pair potentials for rigid bodies, we present a method for approximating general rigid body pair potentials based on a specialized type of deep neural network that maintains essential properties, such as conservation of energy and invariance to the chosen origins of the particles. The network uses a specialized geometric abstraction layer to convert the relative coordinates of the rigid bodies to input more suitable to a conventional artificial neural network, which is trained together with the specialized layer. This results in geometric representations of the particles optimized for the specific potential.

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Interpolymer association in aqueous solutions is essential for many industrial processes, new materials design, and the biochemistry of life. However, our understanding of the association mechanism is limited. Classical theories do not provide molecular details, creating a need for detailed mechanistic insights.

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The improvement of properties in nanocomposites obtained by topochemical surface modification, e.g., acetylation, of the nanoparticles is often ascribed to improved between the nanoparticle and the matrix.

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The addition of urea in pre-cooled alkali aqueous solution is known to improve the dope stability of cellulose solution. However, its thermodynamic mechanism at a molecular level is not fully understood yet. By using molecular dynamics simulation of an aqueous NaOH/urea/cellulose system using an empirical force field, we found that urea was concentrated in the first solvation shell of the cellulose chain stabilized mainly by dispersion interaction.

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Capillary forces play an important role during the dewatering and drying of nanocellulosic materials. Traditional moisture removal techniques, such as heating, have been proved to be deterimental to the properties of these materials and hence, there is a need to develop novel dewatering techniques without affecting the desired properties of materials. It is, therefore, important to explore novel methods for dewatering these high-added-value materials without negatively influencing their properties.

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Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it.

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While strong water association with cellulose in plant cell walls and man-made materials is well-established, its molecular scale aspects are not fully understood. The thermodynamic consequences of having water molecules located at the microfibril-microfibril interfaces in cellulose fibril aggregates are therefore analyzed by molecular dynamics simulations. We find that a thin layer of water molecules at those interfaces can be in a state of thermal equilibrium with water surrounding the fibril aggregates because such an arrangement lowers the free energy of the total system.

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Chemical recycling of poly(L-lactic acid) to the cyclic monomer L-lactide is hampered by low selectivity and by epimerization and elimination reactions, impeding its use on a large scale. The high number of side reactions originates from the high ceiling temperature (T ) of L-lactide, which necessitates high temperatures or multistep reactions to achieve recycling to L-lactide. To circumvent this issue, we utilized the impact of solvent interactions on the monomer-polymer equilibrium to decrease the T of L-lactide.

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The elastic tensors of chitin and chitosan allomorphs were calculated using density functional theory (DFT) with and without the dispersion correction and compared with experimental values. The longitudinal Young's moduli were 114.9 or 126.

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Atomistic molecular dynamics simulation is an important complement to experimental techniques for investigating properties of hydrated carbohydrate polymers at the molecular scale. A critical problem is to determine whether or not a simulation has converged to thermal equilibrium before data collection can begin. In this work, simulations of xylan oligomers starting from random configurations at different levels of hydration are performed.

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Interaction between xylan and cellulose microfibrils is required to maintain the integrity of secondary cell walls. However, the mechanisms governing their assembly and the effects on cellulose surface polymers are not fully clear. Here, molecular dynamics simulations are used to study xylan adsorption onto hydrated cellulose fibrils.

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Methylated carbohydrates are important from both biological and technical perspectives. Specifically, methylcellulose is an interesting cellulose derivative that has applications in foods, materials, cosmetics, and many other fields. While the molecular dynamics simulation technique has the potential for both advancing the fundamental understanding of this polymer and aiding in the development of specific applications, a general drawback is the lack of experimentally validated interaction potentials for the methylated moieties.

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Hypothesis: Interfacial tensions play an important role in dewatering of hydrophilic materials like nanofibrillated cellulose, and are affected by the molecular organization of water at the interface. Application of an electric field influences the orientation of water molecules along the field direction. Hence, it should be possible to alter the interfacial free energies to tune the wettability of cellulose surface through application of an external electric field thus, aiding the dewatering process.

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The adsorption of nonionic polymers to cellulose is of large importance both in the plant cell wall during synthesis and for the development of sustainable materials from wood. Here, the thermodynamics of adsorption of the polysaccharide xyloglucan (XG) to both native and chemically modified cellulose with carboxyl groups was investigated using molecular dynamics simulations. The free energy of adsorption was calculated as the potential of mean force between an XG oligomer and model cellulose surfaces in a range of temperatures from 298 K to 360 K.

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Inspired by the Bogolanfini dyeing technique, we report how flexible nanofibrillated cellulose (CNF) films can be functionalized and patterned by surface-bound nanoparticles of hydrolyzable tannins and multivalent metal ions with tunable colors. Molecular dynamics simulations show that gallic acid (GA) and ellagic acid (EA) rapidly adsorb and assemble on the CNF surface, and atomic force microscopy confirms that nanosized GA assemblies cover the surface of the CNF. CNF films were patterned with tannin-metal ion nanoparticles by an in-fibre reaction between the pre-impregnated tannin and the metal ions in the printing ink.

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Cellulose nanofibers (CNFs) have interesting physicochemical and colloidal properties that have been recently exploited in novel drug-delivery systems for tailored release of poorly soluble drugs. The morphology and release kinetics of such drug-delivery systems heavily relied on the drug-CNF interactions; however, in-depth understanding of the interactions was lacking. Herein, the interactions between a poorly soluble model drug molecule, furosemide, and cationic cellulose nanofibers with two different degrees of substitution are studied by sorption experiments, Fourier transform infrared spectroscopy, and molecular dynamics (MD) simulation.

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Macromolecular dynamics in biological systems, which play a crucial role for biomolecular function and activity at ambient temperature, depend strongly on moisture content. Yet, a generally accepted quantitative model of hydration-dependent phenomena based on local relaxation and diffusive dynamics of both polymer and its adsorbed water is still missing. In this work, atomistic-scale spatial distributions of motional modes are calculated using molecular dynamics simulations of hydrated xyloglucan (XG).

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Xylan is tightly associated with cellulose and lignin in secondary plant cell walls, contributing to its rigidity and structural integrity in vascular plants. However, the molecular features and the nanoscale forces that control the interactions among cellulose microfibrils, hemicelluloses, and lignin are still not well understood. Here, we combine comprehensive mass spectrometric glycan sequencing and molecular dynamics simulations to elucidate the substitution pattern in softwood xylans and to investigate the effect of distinct intramolecular motifs on xylan conformation and on the interaction with cellulose surfaces in Norway spruce ().

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The adsorption of urea on cellulose at room temperature has been studied using adsorption isotherm experiments and molecular dynamics (MD) simulations. The immersion of cotton cellulose into bulk urea solutions with concentrations between 0.01 and 0.

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Article Synopsis
  • The shape and structure of polysaccharides in plant materials affect how they interact with each other and perform in different uses.
  • Scientists studied how flexible the connections (glycosidic linkages) between sugar units are in hemicelluloses using simulations and experiments.
  • They found that different types of connections have different levels of stiffness and flexibility, which impacts how these materials work in plant cell walls and in products we use.
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Room temperature ionic liquids (ILs) of the imidazolium family have attracted much attention during the past decade for their capability to dissolve biomass. Besides experimental work, numerous compuational studies have been concerned with the physical properties of both neat ILs and their interactions with different solutes, in particular, carbohydrates. Many classical force fields designed specifically for ILs have been found to yield viscosities that are too high for the liquid state, which has been attributed to the fact that the effective charge densities are too high due to the lack of electronic polarizability.

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The disaccharide trehalose (TRH) strongly affects the physical properties of lipid bilayers. We investigate interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH using NMR spectroscopy and molecular dynamics (MD) computer simulations. We compare dipolar couplings derived from DMPC/TRH trajectories with those determined (i) experimentally in TRH using conventional high-resolution NMR in a weakly ordered solvent (bicelles), and (ii) by solid-state NMR in multilamellar vesicles (MLV) formed by DMPC.

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Empirical force fields for computer simulations of carbohydrates are often implicitly assumed to be valid also at temperatures different from room temperature for which they were optimized. Herein, the temperature dependence of the hydroxymethyl group rotamer populations in short oligosaccharides is investigated using molecular dynamics simulations and NMR spectroscopy. Two oligosaccharides, viz.

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Differences in tensile properties between cellulose crystal allomorphs cannot be rationalized by simply counting hydrogen bonds. From molecular dynamics computer simulations the cooperative nature of energy contributions to axial cellulose crystal modulus becomes apparent. Using a decomposition of inter and intramolecular forces as a function of tensile strain, the three allomorphs show dramatic differences in terms of how the contributions to elastic energy are distributed between covalent bonds, angles, dihedrals, electrostatic forces, dispersion and steric forces.

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