title: Water activity in lamellar stacks of lipid bilayers: "Hydration forces" revisited.
abstract: Water activity and its relationship with interactions stabilising lamellar stacks of mixed lipid bilayers in their fluid state are investigated by means of osmotic pressure measurements coupled with small-angle X-ray scattering. The (electrically neutral) bilayers are composed of a mixture in various proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic cosurfactant with an ethoxylated polar head. For highly dehydrated samples the osmotic pressure profile always exhibits the "classical" exponential decay as hydration increases but, depending on Simulsol to lecithin ratio, it becomes either of the "bound" or "unbound" types for more water-swollen systems. A simple thermodynamic model is used for interpreting the results without resorting to the celebrated but elusive "hydration forces".
authors.affiliation: Instituto de Física-GFCx, Universidade de São Paulo, P.O.B. 66318, SP 05314-970, São Paulo, Brazil.|Centre de recherche Paul-Pascal-CNRS, Université de Bordeaux, 115 avenue du Docteur-Schweitzer, F-33600, Pessac, France.
authors.forename: R
authors.initials: R
authors.lastname: Leite Rubim
authors.affiliation: Instituto de Física-GFCx, Universidade de São Paulo, P.O.B. 66318, SP 05314-970, São Paulo, Brazil.
authors.forename: B B
authors.initials: BB
authors.lastname: Gerbelli
authors.affiliation: Instituto de Física-GFCx, Universidade de São Paulo, P.O.B. 66318, SP 05314-970, São Paulo, Brazil.|Centre de recherche Paul-Pascal-CNRS, Université de Bordeaux, 115 avenue du Docteur-Schweitzer, F-33600, Pessac, France.
authors.forename: K
authors.initials: K
authors.lastname: Bougis
authors.affiliation: Instituto de Física-GFCx, Universidade de São Paulo, P.O.B. 66318, SP 05314-970, São Paulo, Brazil.
authors.forename: C L
authors.initials: CL
authors.lastname: Pinto de Oliveira
authors.affiliation: Centre de recherche Paul-Pascal-CNRS, Université de Bordeaux, 115 avenue du Docteur-Schweitzer, F-33600, Pessac, France.
authors.forename: L
authors.initials: L
authors.lastname: Navailles
authors.affiliation: Centre de recherche Paul-Pascal-CNRS, Université de Bordeaux, 115 avenue du Docteur-Schweitzer, F-33600, Pessac, France. nallet@crpp-bordeaux.cnrs.fr.
authors.forename: F
authors.initials: F
authors.lastname: Nallet
authors.affiliation: Instituto de Física-GFCx, Universidade de São Paulo, P.O.B. 66318, SP 05314-970, São Paulo, Brazil.
authors.forename: E
authors.initials: E
authors.lastname: Andreoli de Oliveira
mesh_terms: D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry*; D009997:Osmotic Pressure; D013501:Surface-Active Agents / Q000737:chemistry; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D008051:Lipid Bilayers; D013501:Surface-Active Agents; D014867:Water
keywords: Soft Matter: Self-organisation and Supramolecular Assemblies