The surface properties of polymers are important in a wide range of contexts, including adhesion, gas transport and bio-compatibility. At the same time it is often vital to retain the desirable bulk properties of the polymer, such as tear resistance, modulus and tensile strength

Surface specific chemical modification of polymer films can be achieved by careful control of the reaction parameters, and confocal Raman microscopy, a powerful, non-destructive technique for characterising the modifier depth profile, can be used to enhance the development of surface modified polymers that will be much more versatile in their commercial applications.

In collaboration with the Instituto de Cienncia y Tecnologia de Polimeros (Madrid) we have also examined the extent of the surface modification of a polymeric membrane. The polymer (PVC) was modified according to the following reaction scheme.

Raman microscopy

Raman microscopy is a technique that provides useful information about the vibrations that molecules undergo when they are subjected to a monochromatic light source (eg a laser). The Raman microscope can be used in confocal mode by focusing the laser beam through a normal optical microscope to particular depths within the polymer film, and it provides information on the depth, type and amount of modification present.

One complication of the confocal Raman technique is that the apparent depth of analysis, is not the actual depth of analysis due to differences in the refractive index of the sample. This problem can be overcome by using equation 1 once the refractive index of the film has been measured.

Where = the apparent focal point of the laser and NA (the numerical aperture) requires the refractive index (n) to be calculated.