Intrinsically Fluorescent Polymer Blends

Some of the most relevant applications of fluorescence spectroscopy to the characterization of intrinsically fluorescent polymer blends are discussed in the following subsections. 

Straightforward as it cannot be considered that the point dipole description is adequate in view of the delocalized nature of the excited states. 

Based on the above-described study, Lidzey et al. concluded that in films with a better mixing of the two components there is a more effective energy transfer. In films deposited from chloroform solutions, a content of only 5 wt% F8BT was sufficient to allow a virtually complete energy transfer from PFO to F8BT. 

Note that the fluorescence was generated following laser excitation into the PFO component of the blend. Reproduced with permission from Ref [26] 2005, Elsevier. 

Cadby et al. [28] have used time-resolved SNOM to study the fluorescence emission lifetime of the polymers PFO and F8BT in a phase-separated blend. It was shown that the fluorescence lifetime and quantum efficiency of F8BT varied significantly between the different phase-separated domains, an effect which resulted from the relative efficiency of exciton diffusion to non-radiative defects. Measurements of the PFO emission lifetime indicated that both the PFO- and the F8BT-rich phases contained nanoscale volumes that approximated pure PFO. The PFO decay-lifetime measurements also confirmed the concentration of F8BT to be lower at the interface region between the PFO- and F8BT-rich phases. 

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Fluorescent additives may be studied in the same way as UV absorbers. The results are very similar but slightly more care is required in quantitative interpretation since self-quenching effects can lead to non-linearity in the concentration dependence of fluorescence intensity. UV microscopy has been used to follow the distribution of fluorescent additives (such as Uvitex OB) during isothermal crystallisation and cooling of isotactic PP [64]. Billingham et al. [58] have observed diffusion of Uvitex OB in a PP/rubber blend using UV fluorescence microscopy. UV microscopy can be very useful in the analysis of multilayer films where one layer of polymer is intrinsically fluorescent (e.g. PVDC). 

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