Nanoscale adhesive forces between silica surfaces in aqueous solutions.
Nanoscale adhesive forces between a colloidal silica probe and a flat silica substrate were measured with an atomic force microscope (AFM) in a range of aqueous NaCl, CaCl2, and AlCl3 solutions, with concentrations ranging from 10(-)(6) to 10(-)(2) M at pH ∼5.1. Notably, the measured force curves reveal large pull-off forces in water which increase in electrolyte solutions, with jump-off-contact occurring as a gradual detachment of the probe from the flat substrate rather than as a sharp discontinuous jump. The measured force curves also show that the number and size of the steps increase with concentration and notably with electrolyte valence. For the higher concentration and valence the steps become jumps. We propose that these nanoscale adhesive forces between mineral surfaces in aqueous solutions may arise from newly born cavities or persistent subnanometer bubbles. Formation of cavities or nanobubbles cannot be observed directly in our experiments; however, we cannot disregard them as responsible for the discontinuities in the measured force data. A simple model based on several cavities bridging the two surfaces we show that is able to capture all the features in the measured force curves. The silica surfaces used are clean but not intentionally hydroxylated, as contact angle measurements show, and as such may be responsible for the cavities.
Chemical Engineering Department and Surface Analysis Laboratory (ASIF), University of Concepción, PO Box 160-C, Correo 3, Concepción, Chile.
Paula
P
Troncoso
Chemical Engineering Department and Surface Analysis Laboratory (ASIF), University of Concepción, PO Box 160-C, Correo 3, Concepción, Chile.
Jorge H
JH
Saavedra
Department of Food Engineering, University of Bio-Bio, PO Box 447, Chillán, Chile.
Sergio M
SM
Acuña
Chemical Engineering Department and Surface Analysis Laboratory (ASIF), University of Concepción, PO Box 160-C, Correo 3, Concepción, Chile.
Ricardo
R
Jeldres
Metallurgical Engineering Department, University of Concepción, PO Box 160-C, Correo 3, Concepción, Chile.
Fernando
F
Concha
Chemical Engineering Department and Surface Analysis Laboratory (ASIF), University of Concepción, PO Box 160-C, Correo 3, Concepción, Chile. Electronic address: petoledo@udec.cl.
Pedro G
PG
Toledo
D000269:Adhesives / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry; D006900:Hydroxylation; D012822:Silicon Dioxide / Q000737:chemistry*; D012996:Solutions; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
D000269:Adhesives; D003102:Colloids; D004573:Electrolytes; D012996:Solutions; D014867:Water; D012822:Silicon Dioxide
AFM; Adhesion; Cavitation; Contact surfaces; Dehydroxylation; Nanoscale forces; Silica