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Cell walls of so-called “wood-materials” are constituted by a complex, highly anisotropic and hierarchically organized nanocomposite, characterized by stiff crystalline cellulose nano-fibers, parallel to each other, and embedded in a softer and less anisotropic matrix of hemicelluloses, lignin and water. This matrix is hygroscopic, and therefore swells with increasing humidity. Consequently, wood cells undergo large dimensional changes. A minimal model of wood secondary cell walls to predict water absorption has recently been developed by Bertinetti and co-workers [1] in the form of an Equation of State (EOS) that represents equivalently the water sorption versus relative humidity, as considered in chemical engineering, or the relation between osmotic pressure and volume of solutes, in the physical chemistry equation of state approach initiated by Jean Perrin. We extend hereby this model to the presence of electrolytes adsorbed in the gel part wood cell wall and compare compression wood cell walls to the extreme case of coir.

The interaction between surfaces displaying end-grafted hydrophilic polymer brushes plays important roles in biology and in many wet-technological applications. In this context, the conformation of the brushes upon their mutual approach is crucial, because it affects interaction forces and the brushes' shear-tribological properties. While this aspect has been addressed by theory, experimental data on polymer conformations under confinement are difficult to obtain. Here, we study interacting planar brushes of hydrophilic polymers with defined length and grafting density. Via ellipsometry and neutron reflectometry we obtain pressure–distance curves and determine distance-dependent polymer conformations in terms of brush compression and reciprocative interpenetration. While the pressure–distance curves are satisfactorily described by the Alexander-de-Gennes model, the pronounced brush interpenetration as seen by neutron reflectometry motivates detailed simulation-based studies capable of treating brush interpenetration on a quantitative level.

Aqueous alkyltrimethylammonium bromides, or dialkyldimethylammonium ones, were mixed with sodium alkyl sulfates and dialkanesulfonates. Depending on the overall surfactant concentration, charge and/or mole ratios, cat-anionic vesicles were formed by mixing nonstoichiometric amounts of oppositely charged species. The resulting vesicles are thermodynamically and kinetically stable. ζ-potential and dynamic light scattering characterized the systems. As a rule, cat-anionic vesicles have sizes in the 10(2)-10(3) nm range and bear significant amounts of surface charges. At fixed surfactant concentration, the vesicle surface charge density scales with mole ratios and tends to zero as the latter approach unity. Conversely, the hydrodynamic radius diverges when the cationic/anionic mole ratio is close to 1. The double-layer thickness and surface charge density are controlled by mole ratios and addition of NaBr, which plays a role in vesicle stability. The salt screens the surface charge density and modulates both vesicle size and double-layer thickness. Slightly higher concentrations of NaBr induce the transition from vesicles toward lamellar phases. The electrokinetic properties of cat-anionic dispersions were analyzed by dielectric relaxation experiments. The measured properties are sensitive to vesicle size distributions. In fact, the relaxation frequency shifts in proportion to vesicle polydispersity. Model calculations proposed on that purpose supported the experimental findings.

Nonstoichimetric mixtures of two oppositely charged surfactants, such as sodium dodecylsulfate and hexadecyltrimethylammonium bromide or tetradecyltrimethylammonium bromide and tetraethylammonium perfluorooctanesulfonate, a fluorinated species, form vesicles in dilute concentration regimes of the corresponding phase diagrams. Vesicles size and charge density are tuned by changing the mole ratio between oppositely charged species, at fixed overall surfactant content. They are also modulated by adding neutral electrolytes, or raising T. In the investigated regions, mixtures made of sodium dodecylsulfate/hexadecyltrimethylammonium bromide show ideality of mixing, the other non ideality and phase separation. The formation of unilamellar vesicles occurs in the sodium dodecylsulfate/hexadecyltrimethylammonium bromide mixture, but not in the other. DLS, viscosity, and electrophoretic mobility quantified the above effects. Surface charge density, surface tension, elasticity, and osmotic pressure concur to the stability of unilamellar vesicles and a balance between the above contributions is demonstrated. The results are relevant for practical applications of vesicles as carriers in biomedicine.