title: Fabrication of surface charge gradients in open-tubular capillaries and their characterization by spatially resolved pulsed streaming potential measurements.
abstract: Surface charge gradients have been formed on the inside surface of 75 μm i.d. silica capillaries via controlled rate infusion using 3-aminopropyltriethoxysilane as the reactive precursor. These 400 mm length gradients have been characterized using spatially resolved streaming potential measurements, from which the zeta potential as a function of distance was determined. The gradient capillaries exhibited a gradual variation in zeta potential from top to bottom, whereas uniformly modified and as-received capillaries were relatively homogeneous along their length. For a gradient prepared with a relatively high concentration of aminosilane, the zeta potential changed over 60 mV from one end of the capillary to the other, yielding a variation in the magnitude of the apparent surface charge of ~7 fold. By changing the concentration of the aminoalkoxysilane and/or the rate of infusion, both the value of the zeta potential (and hence surface charge) and its spatial profile (i.e., rate of change with distance) could be manipulated.
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284-2006, United States.
authors.forename: Balamurali
authors.initials: B
authors.lastname: Kannan
authors.forename: Kenji
authors.initials: K
authors.lastname: Nokura
authors.forename: Julio C
authors.initials: JC
authors.lastname: Alvarez
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Higgins
authors.forename: Maryanne M
authors.initials: MM
authors.lastname: Collinson