title: Electric Interfacial Layer of Modified Cellulose Nanocrystals in Aqueous Electrolyte Solution: Predictions by the Molecular Theory of Solvation.
abstract: The X-ray crystal structure-based models of Iα cellulose nanocrystals (CNC), both pristine and containing surface sulfate groups with negative charge 0-0.34 e/nm(2) produced by sulfuric acid hydrolysis of softwood pulp, feature a highly polarized "crystal-like" charge distribution. We perform sampling using molecular dynamics (MD) of the structural relaxation of neutral pristine and negatively charged sulfated CNC of various lengths in explicit water solvent and then employ the statistical mechanical 3D-RISM-KH molecular theory of solvation to evaluate the solvation structure and thermodynamics of the relaxed CNC in ambient aqueous NaCl solution at a concentration of 0.0-0.25 mol/kg. The MD sampling induces a right-hand twist in CNC and rearranges its initially ordered structure with a macrodipole of high-density charges at the opposite faces into small local spots of alternating charge at each face. This surface charge rearrangement observed for both neutral and charged CNC significantly affects the distribution of ions around CNC in aqueous electrolyte solution. The solvation free energy (SFE) of charged sulfated CNC has a minimum at a particular electrolyte concentration depending on the surface charge density, whereas the SFE of neutral CNC increases linearly with NaCl concentration. The SFE contribution from Na(+) counterions exhibits behavior similar to the NaCl concentration dependence of the whole SFE. An analysis of the 3D maps of Na(+) density distributions shows that these model CNC particles exhibit the behavior of charged nanocolloids in aqueous electrolyte solution: an increase in electrolyte concentration shrinks the electric interfacial layer and weakens the effective repulsion between charged CNC particles. The 3D-RISM-KH method readily treats solvent and electrolyte of a given nature and concentration to predict effective interactions between CNC particles in electrolyte solution. We provide CNC structural models and a modeling procedure for studies of effective interactions and the formation of ordered phases of CNC suspensions in electrolyte solution.
authors.affiliation: †National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada.|‡Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G8, Canada.
authors.forename: Olga
authors.initials: O
authors.lastname: Lyubimova
authors.affiliation: †National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada.|‡Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G8, Canada.|§Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
authors.forename: Stanislav R
authors.initials: SR
authors.lastname: Stoyanov
authors.affiliation: †National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada.
authors.forename: Sergey
authors.initials: S
authors.lastname: Gusarov
authors.affiliation: †National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada.|‡Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G8, Canada.
authors.forename: Andriy
authors.initials: A
authors.lastname: Kovalenko
mesh_terms: D002482:Cellulose / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D053758:Nanoparticles / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry; D012996:Solutions; D012997:Solvents / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D012996:Solutions; D012997:Solvents; D014867:Water; D012965:Sodium Chloride; D002482:Cellulose