Characterization by UV-Visible Spectrophotometry

Spectrophotometry is one of the most widespread analytical techniques employed to characterize the optical properties of polymeric nanocomposites. 

The spectrophotometry is a technique based on Lambert-Beer law, which is the math support for measurement of the absorption of radiation by solid, liquid, or gaseous samples. The absorption can occur in the ultraviolet, visible, and infrared regions of the electromagnetic spectrum [21]. 

For measurements of the absorption of radiation in a determined wavelength the equation (6.1) is used  

The results of the analysis are reported as absorbance or transmittance. Some examples of the use of spectrophotometry in the characterization of optical properties of nanocomposites with polymer matrix and different nanoparticles are discussed in the following sections. 

The UV-visible absorption of nanocomposites of poly(L-lysine) and single walled carbon nanotubes was studied by Kim et al. [22]. The carbon nanotubes in water showed an absorption peak at 254 nm, which is typical for this kind of material. For the carbon nanotubes dispersed in the polymer the absorbance occurred at 207 and 266 nm, while the pure poly(L-lysine) showed an absorbance maximum at 219 nm. The peaks of nanocomposite were shifted to shorter wavelengths due to the wrapping of the polymer. The authors suggested that this support the existence of significant van der Waals interactions between the polymer and the nanotubes. 

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These tables provide simple examples of commonly encountered compounds, but of course there are a huge number of complex biomolecules that can be characterized by UV/visible spectrophotometry. Such characterization is primarily based on the presence of distinct functional groups. 

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