Ambient: Measurements in Liquids
Capillary force is a major problem in tensile force measurements since it effectively strengthens the tip-surface interaction. It is usually caused by adsorbed moisture on substrates from ambient environment. To eliminate this additional force, measurements in liquids can be conducted. With X-terminated tip and substrate in liquid L, the addition to Fad is calculated using Eq 1 with WXLX = 2γLL; that is, the extra force comes from the attraction of liquid molecules to each other. This is ~10 pN for EtOH which still allows for the observation of even the weakest polar/nonpolar interactions (~20 pN). The choice of liquid is dependent on which interactions are of interest. When the solvent is immiscible with functional groups, larger than usual tip-surface bonding exists. Therefore, organic solvents are appropriate for studying van der Waals and hydrogen bonding while electrolytes are best for probing hydrophobic and electrostatic forces.
Read more about this topic: Chemical Force Microscopy