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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Towards ternary binders involving limestone additions — A review

The review summarises literature to examine the transition from portland limestone cement system to composite ternary binder systems involving limestone. Interest in limestone addition as an ideal component in multicomponent binder systems has surged as evident from the large volume of literature published in the recent past. A ternary blended system, with co-substitution of limestone, has the potential to complement the reaction of the supplementary cementitious materials (SCMs). The direct addition of limestone powder helps to attain higher substitution levels of portland cement clinker, improve early age properties, and supplement SCM's reactivity. However, the dilution of hydrates could hamper the long-term benefits. In this review, the interaction of fine limestone is classified and elaborated under two broad umbrellas: physical and chemical interactions. The physical interactions can manifest in three ways, namely, filler action, shearing action and improved packing, which alters reaction rate and extent at early ages. The chemical interactions also modify the reaction kinetics and phase assemblage due to nucleation of C-S-H on calcite surfaces, preservation of the ettringite phase and formation of carboaluminates. Two different forms of carboaluminate hydrates — hemicarboaluminate and mono-carboaluminate can be present in the hydrate matrix depending on the balance between carbonate ions and aluminates in the pore solution. Several factors such as replacement level, particle size, choice of SCM, its reactivity and reactive aluminates content, sulphate levels, curing temperature, and duration of curing can control the carboaluminate formation, reaction degree of SCMs and chemical interaction from limestone additions. A combination of physical and chemical effects makes fine limestone a potential material for co-substitution with aluminosilicate based SCMs, mainly fly ash, slag, and calcined clay. In this review, the factors affecting limestone-SCM composites are summarised based on a detailed literature survey. The effects of SCM-limestone cement composites on hydration kinetics, reaction chemistry, the reactivity of SCMs, the stability of hydrated phases, and contribution to the physical structure development and macroscopic properties by evaluating hydration and mechanical properties are discussed. The importance of AFm (Al{sub 2}O{sub 3}–Fe{sub 2}O{sub 3}-mono) phases in various deterioration mechanisms in concrete and their influence on performance characteristics in different exposure environment is critically appraised.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Improving Proton Conductivity by Navigating Proton Trapping in High Scandium-Doped Barium Zirconate Electrolytes

Proton-conducting oxides are used in intermediate-temperature (300 °C < T < 700 °C) applications of fuel cells, electrolyzers, membrane reactors, hydrogen pumps, and sensors. The proton conductivity of doped ABO 3 perovskites is partly dependent on the proton concentration and hence on the level of material hydration. However, how the material hydration ability is affected by differences in doping is not fully understood. Here, we show the prospect of proton trapping and detrapping that influences material hydration and dehydration. The proton-trapping influence is significant for Sc-doped BaZrO 3 compared to Y-doped BaZrO 3 . Here, our work offers a perspective to understand how defect interaction/associations influence the hydration ability of proton-conducting oxides. Furthermore, positron annihilation lifetime spectroscopy was revealed to be a valuable technique for studying the proton-trapping phenomena and the defect chemistry of dense proton conductors. Density functional theory calculations also showed that a high hydration level in Sc-doped BaZrO 3 boosts proton migration. In contrast, the effect of boosting the proton migration due to increased hydration is limited for Y-doped BaZrO 3 . This effect, in turn, might explain the trend of conductivity with dopant concentration in doped BaZrO 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Ion and Water Dynamics in the Transition from Dry to Wet Conditions in Salt-Doped PEG

The influence of the water content on ion and water transport mechanisms in polymer membranes under low to moderate hydration conditions remains poorly understood. In this study, we combine ion and water diffusivity (PFG-NMR) measurements with atomistic molecular dynamics simulations to better understand transport processes in hydrated salt-doped poly(ethylene glycol). Above the water percolation threshold, the experimental and simulated diffusivities are in good agreement with the free volume transport models. At low hydration levels, unlike dry systems, ion diffusion cannot be described by polymer segmental dynamics alone. We rationalize such observations by the interplay between ion–water and ion–polymer solvation of cations and between ion–water and cation–anion interactions for anions. Further, we demonstrate that a two-state model combining ion–water solvation and free volume transport can describe water dynamics across the entire hydration range of interest. Here, our findings provide a more encompassing analysis of ion and water transport in hydrated polyelectrolytes, specifically in the low hydration regime.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Evaluation of a Robust, In-Situ Surface Treatment for Pipeline Solids Deposition Mitigation in Flowing Systems

Abstract The formation/precipitation and deposition of pipeline solids, such as gas hydrates, asphaltenes, and waxes have long plagued production fields. Given the vast differences in chemistries of these solids, any current prevention or mitigation strategy, particularly for cases where multiple issues are a concern, is likely to involve an extensive assortment of undefined chemical additives that are both costly and add complexity to the system. Surface treatments (coatings), on the other hand, present a relatively new viable option for management strategies. A chemically and physically robust surface treatment with the ability to address deposition issues for multiple pipeline solids could not only decrease the operating expenditures for a field through material cost savings and obviation of downstream separation, but could also simplify produced fluids by eliminating additional chemicals from the mixture. The purpose of this study is to explore the feasibility of a particular surface treatment as part of a solids management strategy. This work utilizes an omniphobic surface treatment to probe its effects on gas hydrate, asphaltene, and wax deposition. Specifically, high pressure rocking cells are employed to study gas hydrate nucleation and deposition. A bench-scale flowloop filled with crude oil and heptane is used to quantify the deposition of crude oil and asphaltenes after a set time period. Lastly, a mechanical shear device measures the adhesion force of wax deposits on untreated/treated surfaces. The gas hydrate rocking cell tests demonstrate an increase in induction time and occasional elimination of hydrate nucleation with the surface treatment. Moreover, the same apparatus indicates that the critical shear to avoid hydrate deposition may be lowered in the presence of the surface treatment compared to untreated pristine carbon steel coupons. A custom-built asphaltene flowloop then establishes that this surface treatment is effective in dramatically reducing the deposition of the aliphatic components of a crude oil, with a moderate reduction in the asphaltene fraction. Finally, mechanical adhesion force measurements for solidified paraffin wax display trends in agreement with the asphaltene results. The surface treatment on both pristine and corroded surfaces is able to reduce the adhesion of wax deposits to values below a pristine, untreated surface.

03 NATURAL GAS↗
DOE OSTI2024

Natural carbonation of portland cement with synthetic zeolite Y as a supplementary cementitious material

Risks associated with carbonation are a key limitation to greater replacement levels of ordinary portland cement (OPC) by supplementary cementitious materials (SCMs). The addition of pozzolanic SCMs in OPC alters the hydrate assemblage by forming phases like calcium-(alumina)-silicate-hydrate (C-(A)-S-H). The objective of the present study was to elucidate how such changes in hydrate assemblage influence the chemical mechanisms of carbonation in a realistic OPC system. Here, in this paper, we show that synthetic zeolite Y (faujasite) is a highly reactive pozzolan in OPC that reduces the calcium content of hydration products via prompt consumption of calcium hydroxide from the evolving phase assemblage prior to CO 2 exposure. Suppression of portlandite at moderate to high zeolite Y content led to a more damaging mechanism of carbonation by disrupting the formation of a passivating carbonate layer. Without this layer, carbonation depth and CO 2 uptake are increased. Binders containing 12–18% zeolite Y by volume consumed all the calcium hydroxide from OPC during hydration and reduced the Ca/(Si+Al) ratio of the amorphous products to near 0.67. In these cases, higher carbonation depths were observed after exposure to ambient air with decalcification of C-(A)-S-H as the main source of CO 2 buffering. Binders with either 0% or 4% zeolite Y contained calcium hydroxide in the hydrated microstructure, had higher Ca/(Si+Al) ratios, and formed a calcite-rich passivation layer that halted deep carbonation. Although the carbonated layer in the samples with 12% and 18% zeolite Y contained 70% and 76% less calcite than the OPC respectively, their higher carbonation depths resulted in total CO 2 uptakes that were 12x greater than the OPC sample. Passivation layer formation in samples with calcium hydroxide explains this finding and was further supported by thermodynamic modeling. High Si/Al zeolite additives to OPC should be balanced with the calcium content for optimal carbonation resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Reaction Layer Formation on MgO in the Presence of Humidity

Mineralization by MgO is an attractive potential strategy for direct air capture (DAC) of CO 2 due to its tendency to form carbonate phases upon exposure to water and CO 2 . Hydration of MgO during this process is typically assumed to not be rate limiting, even at ambient temperatures. However, surface passivation by hydrated phases likely reduces the CO 2 capture capacity. Here, we examine the initial hydration reactions that occur on MgO(100) surfaces to determine whether they could potentially impact CO 2 uptake. We first used atomic force microscopy (AFM) to explore changes in reaction layers in water (pH = 6 and 12) and MgO-saturated solution (pH = 11) and found the reaction layers on MgO are heterogeneous and nonuniform. To determine how relative humidity (R.H.) affects reactivity, we reacted samples at room temperature in nominally dry N 2 (~11–12% R.H.) for up to 12 h, in humid (>95% R.H.) N 2 for 5, 10, and 15 min, and in air at 33 and 75% R.H. for 8 days. X-ray reflectivity and electron microscopy analysis of the samples reveal that hydrated phases form rapidly upon exposure to humid air, but the growth of the hydrated reaction layer slows after its initial formation. Reaction layer thickness is strongly correlated with R.H., with denser reaction layers forming in 75% R.H. compared with 33% R.H. or nominally dry N 2 . The reaction layers are likely amorphous or poorly crystalline based on grazing incidence X-ray diffraction measurements. After exposure to 75% R.H. in air for 8 days, the reaction layer increases in density as compared to the sample reacted in humid N 2 for 5–15 min. Further, this may represent an initial step toward the crystallization of the reaction layer. Overall, high R.H. favors the formation of a hydrated, disordered layer on MgO. Based on our results, DAC in a location with a higher R.H. will be favorable, but growth may slow significantly from initial rates even on short timescales, presumably due to surface passivation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

SANS quantification of bound water in water-soluble polymers across multiple concentration regimes

Contrast-variation small-angle neutron scattering (CV-SANS) is a widely used technique for quantifying hydration water in soft matter systems, but it is predominantly applied in the dilute regime or for systems with a well-defined structure factor. Here, CV-SANS was used to quantify the number of hydration water molecules associating with three water-soluble polymers with different critical solution temperatures and types of water–solute interactions in dilute, semidilute, and concentrated solution through the exploration of novel methods of data fitting and analysis. Multiple SANS fitting workflows with varying levels of model assumptions were evaluated and compared to give insight into SANS model selection. These fitting pathways ranged from general, model-free algorithms to more standard form and structure factor fitting. In addition, Monte Carlo bootstrapping was evaluated as a method to estimate parameter uncertainty through simulation of technical replicates. The most robust fitting workflow for dilute solutions was found to be form factor fitting without CV-SANS ( i.e. polymer in 100% D 2 O). For semidilute and concentrated solutions, while the model-free approach can be mathematically defined for CV-SANS data, the addition of a structure factor imposes physical constraints on the optimization problem, suggesting that the optimal fitting pathway should include appropriate form and structure factor models. The measured hydration numbers were consistent with the number of tightly bound water molecules associated with each monomer unit, and the concentration dependence of the hydration number was largely governed by the chemistry-specific interactions between water and polymer. Polymers with weaker water–polymer interactions ( i.e. those with fewer hydration water molecules) were found to have more bound water at higher concentrations than those with stronger water–polymer interactions due to the increase in the number of forced water–polymer contacts in the concentrated system. This SANS-based method to count hydration water molecules can be applied to polymers in any concentration regime, which will lead to improved understanding of water–polymer interactions and their impact on materials design.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Cooperative Research and Development Agreement between National Energy Technology Laboratory and Korea Institute of Energy Research (KIER) [Abstract]

KIER and NETL will collaborate to study hydrate-based technologies to enhance desalination, gas separation, and hydrocarbon flow through pipelines and wellbores. With optimized selections of hydrate formers and reactors, gas hydrates can be effective and economic mechanisms of separation for solid-water and gas mixtures, and gas hydrate formation or dissociation can be significantly delayed or expedited with suitably selected additives. Comprehensive laboratory studies, including identifying novel hydrate formers or inhibitors to control temperature and pressure requirements and understanding their working mechanism or developing reactor systems for production of large quantities of hydrates, will be performed at both KIER and NETL either parallelly or serially.

03 NATURAL GAS↗
DOE OSTI2020

Cooperative Research and Development Agreement between National Energy Technology Laboratory and Raytheon Technologies Corporation [Abstract]

KIER and NETL will collaborate to study hydrate-based technologies to enhance desalination, gas separation, and hydrocarbon flow through pipelines and wellbores. With optimized selections of hydrate formers and reactors, gas hydrates can be effective and economic mechanisms of separation for solid-water and gas mixtures, and gas hydrate formation or dissociation can be significantly delayed or expedited with suitably selected additives. Comprehensive laboratory studies, including identifying novel hydrate formers or inhibitors to control temperature and pressure requirements and understanding their working mechanism or developing reactor systems for production of large quantities of hydrates, will be performed at both KIER and NETL either parallelly or serially.

02 PETROLEUM↗
DOE OSTI2024

Systems, methods, and compositions for purifying water

Systems for removing one or more contaminants from water are provided that can include a hydrate formation chamber assembly; a contaminated water diffusion assembly within the hydrate formation chamber assembly; a space between a wall of the hydrate formation chamber assembly and the diffusion assembly; and a guest compound conduit configured to provide a guest compound within the space and form a hydrate comprising water and the guest compound. Methods for removing one or more contaminants from water are provided that can include providing a contaminated water mixture and one or more guest compounds; forming a hydrate complex comprising water and the one or more guest compounds; and separating the water from the guest compounds to provide water with less contaminant. Mixtures are also provided that can include a liquid component comprising water and at least one contaminant, and a solid component comprising a hydrate complex. One embodiment of the system provides methods for production of excess electric power as a byproduct of the desalination process.

McGrail, Bernard P.↗
DOE OSTI2022

Time-resolved 3D characterisation of early-age microstructural development of Portland cement

Abstract Time-resolved in-situ synchrotron X-ray microtomography reveals new levels of detail about the chemical and physical processes that take place as Portland cement hardens. The conversion of a fluid paste into a hardened product can be monitored on a sub-minute time-scale, and with sample movement/settlement corrections applied to enable individual particles to be tracked as they react, hydrate, and become interconnected into a single strong monolith. The growth of the strength-giving hydrate phases surrounding cement grains, and of the fluid-filled pore network that surrounds them, is able to be directly viewed at the level of individual cement particles through the application of this tracking protocol. When cement is brought into contact with water, a layer which differs in density from the bulk of the cement grains becomes observable on the grain surfaces during the induction period (during which time the heat evolution from the paste is relatively low). As hydration continues, reaction products grow both from particle surfaces into the initially fluid-filled region, and also into the space originally occupied by the cement particles, forming a density gradient within the microstructure. As the reaction accelerates and larger volumes of solid phases precipitate, the newly-formed solid structure percolates via interconnection of agglomerated low-density outer hydrates, which then densify as hydration continues. This eventually leads to solidification of the structure into a hardened porous matrix. Graphical abstract

36 MATERIALS SCIENCE↗
DOE OSTI2024

Studying the Collective Functional Response of a Receptor in Alchemical Ligand Binding Free Energy Simulations with Accelerated Solvation Layer Dynamics

Ligand binding free energy simulations (LB-FES) that involve sampling of protein functional conformations have been longstanding challenges in research on molecular recognition. Particularly, modeling of the conformational transition pathway and design of the heuristic biasing mechanism are severe bottlenecks for the existing enhanced configurational sampling (ECS) methods. Inspired by the key role of hydration in regulating conformational dynamics of macromolecules, this report proposes a novel ECS approach that facilitates binding-associated structural dynamics by accelerated hydration transitions in combination with the lambda-exchange of free energy perturbation (FEP). Further, two challenging protein-ligand binding processes involving large configurational transitions of the receptor are studied, with hydration transitions at binding sites accelerated by Hamiltonian-simulated annealing of the hydration layer. Without the need for pathway analysis or ad hoc barrier flattening potential, LB-FES were performed with FEP/lambda-exchange molecular dynamics simulation at a minor overhead for annealing of the hydration layer. The LB-FES studies showed that the accelerated rehydration significantly enhances the collective conformational transitions of the receptor, and convergence of binding affinity calculations is obtained at a sweet-spot simulation time scale. Alchemical LB-FES with the proposed ECS strategy is free from the effort of trial and error for the setup and realizes efficient on-the-fly sampling for the collective functional response of the receptor and bound water and therefore presents a practical approach to high-throughput screening in drug discovery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Relationships between Water’s Structure and Solute Affinity at Polypeptoid Brush Surfaces

Excellent antifouling surfaces are generally thought to create a tightly bound layer of water that resists solute adsorption, and highly hydrophilic surfaces such as those with zwitterionic functionalities are of significant current interest as antifoulant strategies. Furthermore, despite significant proofs-of-concept, we still lack a fundamental understanding of how the nanoscopic structure of this hydration layer translates to reduced fouling, how surface chemistry can be tuned to achieve antifouling through hydration water, and why, in particular, zwitterionic surfaces seem so promising. Here, we use molecular dynamics simulations and free energy calculations to investigate the molecular relationships among surface chemistry, hydration water structure, and surface–solute affinity across a variety of surface-decorated chemistries. Specifically, we consider polypeptoid-decorated surfaces that display well-known experimental antifouling capabilities and that can be synthesized sequence specifically, with precise backbone positioning of, e.g., charged groups. Through simulations, we calculate the affinities of a range of small solutes to polypeptoid brush surfaces of varied side-chain chemistries. We then demonstrate that measures of the structure of surface hydration water in response to a particular surface chemistry signal solute–surface affinity; specifically, we find that zwitterionic chemistries produce solute–surface repulsion through highly coordinated hydration water while suppressing tetrahedral structuring around the solute, in contrast to uncharged surfaces that show solute–surface affinity. Based on the relationship of this structural perturbation to the affinity of small-molecule solutes, we propose a molecular mechanism by which zwitterionic surface chemistries enhance solute repulsion, with broader implications for the design of antifouling surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Polymorphism of Magnesium Chloride Decahydrate under High Pressures and Low Temperatures Found in Icy Moons

Magnesium chloride hydrates show a rich diversity of structural forms, with different hydration numbers ranging from 1 to 12. Here, we show that this structural versatility is also present within the same hydration numbers, with the formation of a new phase of magnesium chloride decahydrate (MgCl 2 ·10H 2 O-II) stable at the conditions of 0.03–0.40(14) GPa at 234(11) K and up to 2.11(3) GPa at 220(2) K, as determined by in situ single-crystal X-ray diffraction. The hydrogen bonding interactions of MgCl 2 ·10H 2 O-II are identified and the bulk modulus determined at B 0 = 18.9(12) GPa at 220(2) K. We discuss the implication of this high-pressure MgCl 2 hydrate for icy moon compositional investigations and showcase the structural and density changes between the various hydrates in MgCl 2 ·nH 2 O.

high pressure↗
DOE OSTI2026

Application of Ibuprofen Sodium Dihydrate for Thermochemical Energy Storage

Thermochemical energy storage (TCES) offers a transformative approach to address grid instability by harnessing reversible chemical reactions for efficient heat storage and release. Here, we introduce pharmaceutical organic salt hydrates as a class of materials with exceptional performance for low-grade waste heat recovery. We demonstrate ibuprofen sodium dihydrate (ISD) as an example organic hydrate exhibiting a dehydration temperature range of 60-110 °C and a remarkable dehydration enthalpy of up to 59.5 kJ/mol of water, ideally suited for capturing industrial and residential waste heat. Using rigorous multimodal characterization, including thermogravimetric analysis, differential scanning calorimetry, in-situ FTIR, in-situ PXRD, and NMR, we demonstrate ISD's superior thermal, chemical, and structural stability over 150 hydration-dehydration cycles, achieving an unprecedented cycling efficiency of ~99.9%. Compared to conventional inorganic salt hydrates like strontium chloride hexahydrate and calcium oxalate monohydrate, ISD showcases enhanced durability without deliquescence or pulverization, even under high-humidity conditions. In-situ analyses confirm the transition from ISD to ibuprofen sodium anhydrous (ISA) proceeds with structural reorganization, thereby combining the dehydration mechanism with phase transitions, resulting in higher energy storage capacity. Microstructural analyses reveal that repeated water intercalation and structural transitions aid in creating significant porosity that enhances water transport kinetics, further improving the hydration/dehydration performance. By combining the phase change and chemical dehydration mechanisms, ISD paves the way for designing a new class of organic salt hydrates, offering tunable properties to meet diverse thermal energy storage demands and supporting sustainable grid resilience.

Thangaraj, Kavin C.↗
DOE OSTI2026

Protonation Dynamics of Confined Ethanol–Water Mixtures in H-ZSM-5 from Machine Learning-Driven Metadynamics

Zeolites are indispensable heterogeneous catalysts in industrial chemical processes, valued for their strong Brønsted acidity, well-defined microporous frameworks, and tunable pore structures. Their catalytic activity arises primarily from Brønsted acid sites (BAS), typically present as bridging hydroxyl groups (Si–OH–Al). Under aqueous reaction conditions, these protons interact dynamically with water and alcohol molecules, leading to complex solvation and protonation behavior within confined pores. In this study, we investigate the protonation equilibrium occurring between ethanol and water at the BAS of acidic zeolites under varying hydration levels, i.e., C2H5OH–(H2O)n, n=1–4. Local structure was analyzed through an adaptive-learning global optimization algorithm, while enhanced sampling molecular dynamics simulations with Well-Tempered Metadynamics (WMetaD) and machine learning interatomic potentials (MLPs) provide free-energy surfaces (FES) at variable hydration levels. The results reveal a strong dependence of proton localization on the degree of hydration. At low hydration (1 water molecule), the proton resides predominantly on ethanol; with 2 water molecules, it shifts toward water, and at higher hydration (3 or more water molecules), it becomes extensively delocalized over the water cluster. These findings underscore the critical role of solvation in modulating acid site behavior and suggest that a minimum of three water molecules is necessary to fully stabilize the proton on water within the zeolite framework. This solvation threshold has significant implications for catalytic processes, particularly in biomass conversion reactions where alcohol protonation is a key step in dehydration mechanisms.

machine learning↗
DOE OSTI2021

The chemical and physical origin of incineration ash reactivity in cementitious systems

Incorporating industrial byproducts and waste in concrete is the key to reducing landfill usage as well as lowering the environmental footprint of cement industry. An emerging industrial byproduct which can partly replace cement is the Municipal Solid Waste Incinerator Ash (MSWI ash: residue that is left after incineration of municipal solid waste in a Waste-to-Energy facility). These ashes are predominantly calcium-rich; however, they also contain additional elements whose speciation is not known. These elements can significantly alter the hydration characteristics of a cementitious system. Here, our results suggest these ashes can accelerate as well as retard cement hydration. Specifically, Pb, Br, S, Ca, and Cl appear to accelerate cement hydration, whereas Cu, Fe, Al, Ti, Si, K, Zn, and Sr appear to retard cement hydration. Changes in hydration characteristics can have a strong bearing on the physical characteristics of cementitious systems incorporating incineration ashes. Thus, to selectively screen ashes that synergistically enhance the physical characteristics, we introduce a novel “Incineration Ash Coefficient (IAC),” which shows a strong correlation with the compressive strength (R 2 =0.79) of cement-ash binary mixtures.

42 ENGINEERING↗
DOE OSTI2023

Diffusion in intact secondary cell wall models of plants at different equilibrium moisture content

Secondary plant cell walls are composed of carbohydrate and lignin polymers, and collectively represent a significant renewable resource. Leveraging these resources depends in part on a mechanistic understanding for diffusive processes within plant cell walls. Common wood protection treatments and biomass conversion processes to create biorefinery feedstocks feature ion or solvent diffusion within the cell wall. X-ray fluorescence microscopy experiments have determined that ionic diffusion rates are dependent on cell wall hydration as well as the ionic species through non-linear relationships. In this work, we use classical molecular dynamics simulations to map the diffusion behavior of different plant cell wall components (cellulose, hemicellulose, lignin), ions (Na + , K + , Cu2 + , Cl - ) and water within a model for an intact plant cell wall at various hydration states (3-30 wt% water). From these simulations, we analyze the contacts between different plant cell wall components with each other and their interaction with the ions. Generally, diffusion increases with increasing hydration, with lignin and hemicellulose components increasing diffusion by an order of magnitude over the tested hydration range. Ion diffusion depends on charge. Positively charged cations preferentially interact with hemicellulose components, which include negatively charged carboxylates. As a result, positive ions diffuse more slowly than negatively charged ions. Measured diffusion coefficients are largely observed to best fit piecewise linear trends, with an inflection point between 10 and 15% hydration. These observations shed light onto the molecular mechanisms for diffusive processes within secondary plant cell walls at atomic resolution.

09 BIOMASS FUELS↗