Chapter 4: Non-linear Characterizations of Surface Charge and Interfacial Morphology

This Chapter discusses a special technique for the measurement of surface and subsurface charge in electrically modified biomaterials. In addition, it also describesthe laser scanning microscopy technique used in surface and interfacial characterisation of biomaterials and biological materials. Corona poling/charging is a very useful method for introducing polarization into polar materials and space charge in non-polar ones. The apparatus required is relatively inexpensive and a large number of parameters can be varied. The laser intensity modulation method (LIMM) is an excellent technique for analysis of the polarization/space charge deposited in regions near the surface of the materials by corona charging. Preliminary experiments were conducted to show the effects of corona polarity, charging time and temperature, and charge loss by storage in different media. Laser scanning microscopy based on second harmonic (SH) imaging represents a very useful tool for investigating the surface structure and the interfacial properties of the biological samples. The combined strong scattering and absorption of ultraviolet and visible light in the case of confocal microscopy lead to a rapid loss of both intensity and contrast when the penetration depth in the tissues is higher than a few tens of microns into tissue. Unlike in confocal microscopy, in the case of the SH imaging the scanning light is able to penetrate much deeper inside the sample's volume.