Feasibility of Kelvin Probe Force Microscopy to Measure the Surface Potential Decay of Polystyrene Film Due to Relative Humidity

The feasibility of measuring the surface potential decay of polystyrene (PS) film is investigated at room temperature by using Kelvin probe force microscopy (KPFM). The PS film was charged by an ion injection method utilizing Bruker's atomic force microscope (AFM) Nanoman module with a pulse duration of 1 ms, SCM-PIT electrically conductive probe, and a voltage pulse of -250 mV. The surface potential decayed linearly on a semi-log scale with time, where the time decay constant was quantified for relative humidity (RH) = 5% by KPFM at room temperature. The surface potential decayed due to the interaction of the PS film with the hydronium ions available in the environment. Furthermore, the effect of the material forms (film vs. microspheres) on the time decay constant at RH = 5% was investigated. The time decay constants measured using different methods exhibited excellent correlation with the AFM-KPFM. This also confirmed that the results are independent of the material form (microspheres vs. film form). As a result, the proposed method can be used to measure the effect of RH for any PS surface (i.e., particles of various sizes and films) exposed to these environmental conditions.