The well-established atomic force microscopy (AFM)-based colloidal probe technique (CPT) and optical tweezers (OT) are combined to measure the interaction forces between blank SiO2 surfaces in aqueous ionic solutions (CaCl2) of varying concentration at pH 7. Spherical colloids (SiO2, diameter 4.63 ± 0.05 μm) taken out of the same batch are used by both methods. In the case of CPT, a single colloid is glued to a cantilever, and the interaction forces with a plain SiO2 surface are determined in dependence on the concentration of the surrounding medium. For the OT studies, two colloids (one fixed to a micropipet by capillary action, the other held with the optical trap) are approached to each other in nanometer steps, and the resulting forces are measured for the same media as in the CPT experiment. Both techniques fit well to each other and enable one to cover interaction energies ranging from 10−5 to 1 mN/m. The experimental data are well described by the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory revealing that the effective surface charge density changes slightly with concentration.
Tuesday, November 24, 2009
Forces between Blank Surfaces As Measured by the Colloidal Probe Technique and by Optical Tweezers − A Comparison
Mahdy M. Elmahdy, Astrid Drechsler, Christof Gutsche, Alla Synytska, Petra Uhlmann, Friedrich Kremer and Manfred Stamm
The well-established atomic force microscopy (AFM)-based colloidal probe technique (CPT) and optical tweezers (OT) are combined to measure the interaction forces between blank SiO2 surfaces in aqueous ionic solutions (CaCl2) of varying concentration at pH 7. Spherical colloids (SiO2, diameter 4.63 ± 0.05 μm) taken out of the same batch are used by both methods. In the case of CPT, a single colloid is glued to a cantilever, and the interaction forces with a plain SiO2 surface are determined in dependence on the concentration of the surrounding medium. For the OT studies, two colloids (one fixed to a micropipet by capillary action, the other held with the optical trap) are approached to each other in nanometer steps, and the resulting forces are measured for the same media as in the CPT experiment. Both techniques fit well to each other and enable one to cover interaction energies ranging from 10−5 to 1 mN/m. The experimental data are well described by the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory revealing that the effective surface charge density changes slightly with concentration.
The well-established atomic force microscopy (AFM)-based colloidal probe technique (CPT) and optical tweezers (OT) are combined to measure the interaction forces between blank SiO2 surfaces in aqueous ionic solutions (CaCl2) of varying concentration at pH 7. Spherical colloids (SiO2, diameter 4.63 ± 0.05 μm) taken out of the same batch are used by both methods. In the case of CPT, a single colloid is glued to a cantilever, and the interaction forces with a plain SiO2 surface are determined in dependence on the concentration of the surrounding medium. For the OT studies, two colloids (one fixed to a micropipet by capillary action, the other held with the optical trap) are approached to each other in nanometer steps, and the resulting forces are measured for the same media as in the CPT experiment. Both techniques fit well to each other and enable one to cover interaction energies ranging from 10−5 to 1 mN/m. The experimental data are well described by the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory revealing that the effective surface charge density changes slightly with concentration.
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment