Forces between Blank Surfaces As Measured by the Colloidal Probe Technique and by Optical Tweezers − A Comparison

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• 作者：Mahdy M. Elmahdy ; Astrid Drechsler ; Christof Gutsche ; Alla Synytska ; Petra Uhlmann ; Friedrich Kremer ; Manfred Stamm
• 刊名：Langmuir
• 出版年：2009
• 出版时间：November 17, 2009
• 年：2009
• 卷：25
• 期：22
• 页码：12894-12898
• 全文大小：769K
• 年卷期：v.25,no.22(November 17, 2009)
• ISSN：1520-5827

文摘

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.