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A Comparative Study of Force Measurements in Solution Using Micron and Nano Size Probe

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Document pages: 14 pages

Abstract: Atomic force microscopy (AFM) is a device that isused for not only high-resolution imaging butalso used for measuring forces. It is possible to quantify the surface density change for both colloid and nano probe as well as silica surface. By changing the quantity of ions withina potassium chloride solution, it then becomes possible to evaluate thequantity of ions that attach themselves to AFM colloid probe, nano probe and silica samples. In this study, the force was measured between AFM probes and silica surface in differentionic concentrations. Two different types of AFM probe were used: a colloidprobe with a radius of 500 nano-meters and a nano probe with a radius of 10 nano-meters. This study is focused on measuring how the force magnitude, especially electricaldouble layer force, varied between the twotypes of probes by changing ionic concentrations. For all test trials, the resultsagreed with the electrical double layer theory. Although the micron probe wasalmost an exact match for all ranges, the nano probe was closest within its short-range forces. This is attributed tothe formula use when analyzing the electrical double layer force. Because theformula was originally calculated for the micron probe, the shape and size ofthe nano probe created too many variables for an exact match. Along withquantifying the forces, this experiment allowed for an observation of Van derWaals force making it possible to calculate the Hamaker constant. Conclusively,all results show that the obtained surface charge density increases as theionic concentration increases. In addition, through the comparison of theresults obtained from the nano-sized probe and the micron-sized probe, it was concluded that nano size probe mapped higher surfacecharge density above the silica surface than the micron-sized probe under the same conditions.

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