title: Electrical conductance of hydrophobic membranes or what happens below the surface.
abstract: Nanoporous alumina membranes rendered hydrophobic by surface modification via covalent attachment of hydrocarbon or fluorocarbon chains conduct electricity via surface even when the pores are not filled with electrolyte. The resistance is many orders of magnitude higher than for electrolyte-filled membranes and does not depend on the electrolyte concentration or pH, but it does depend on the type of hydrophobic monolayer and its density. The corresponding surface resistance varies from greater than 10(18) Omega per square to less than 3 x 10(9) Omega per square. When the hydrophobic monolayer contains a small proportion of photoactive spiropyran that is insufficient to switch the surface to hydrophilic after spiropyran photoisomerization to the merocyanine form, the membrane resistance also becomes light-dependent with a reversible increase of surface resistance by as much as 15%. Surface conduction is ascribed to hydration and ionization of the alumina surface hydroxyls and the ionizable groups of the hydrophobic surface modifiers.
authors.affiliation: Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, USA.
authors.forename: Ivan
authors.initials: I
authors.lastname: Vlassiouk
authors.forename: Fabian
authors.initials: F
authors.lastname: Rios
authors.forename: Sean A
authors.initials: SA
authors.lastname: Vail
authors.forename: Devens
authors.initials: D
authors.lastname: Gust
authors.forename: Sergei
authors.initials: S
authors.lastname: Smirnov
mesh_terms: D001578:Benzopyrans / Q000737:chemistry; D004553:Electric Conductivity; D004563:Electrochemistry; D004573:Electrolytes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007211:Indoles / Q000737:chemistry; D007536:Isomerism; D008051:Lipid Bilayers / Q000737:chemistry*; D008566:Membranes / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D009574:Nitro Compounds / Q000737:chemistry; D010777:Photochemistry; D013141:Spiro Compounds / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors
chemical_list: D001578:Benzopyrans; D004573:Electrolytes; D007211:Indoles; D008051:Lipid Bilayers; D009574:Nitro Compounds; D013141:Spiro Compounds; C516131:spiro-merocyanine; C088184:spiropyran