Surface Charge Measurements on Biomaterials in Dry and Wet Conditions
The most commonly used charge measurement methods in dry and wet condition are discussed in this Chapter. A number of methods [thermally stimulated depolarization current (TSDC), induction probe, field mill, electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM)] for electrostatic charge measurement in dry conditions have been reviewed. The TSDC method is capable of measuring the integral charge at the surface, as well as in the volume of the sample, but the charge is destroyed by the measurement. On the other hand, induction techniques are sensitive only to the surface charge, but they are usually non-contact and non-destructive. In particular, scanning probe microscopy (SPM) techniques allow the measurement of surface charge with high lateral (tens of nanometres) and potential (∼mV) resolution. In wet conditions, the streaming potential technique is most commonly used for surface potential measurements, although KPFM can also be employed in certain cases.