PHOTOCHROMIC PROBES FOR THE ANALYSIS OF THE SIZE DISTRIBUTION OF LOCAL FREE VOLUME IN AMORPHOUS GLASSY PERFLUOROPOLYMERS OF HYFLON AD
M. Macchionea,b, G. De Lucaa, E. Driolia, J.C. Jansena
a Institute on Membrane Technology, ITM-CNR, c/o University of Calabria, Via P. Bucci, 87036 Arcavacata di Rende, (CS) – ITALY
bDepartment of Chemistry, University of Calabria, Via P. Bucci, 87036 Arcavacata di Rende, (CS) – ITALY
The phenomenon of photochromism can be used for the determination of the local free volume distribution in glassy polymers. Photo-isomerizable molecules are dispersed homogenously into the polymer matrices. Upon irradiation with UV or visible light the photochromic molecules undergo trans-cis isomerization. This can only occur when a sufficient amount of free volume is available for the rotation of the molecule in the polymer matrix. The aim of the present work is to use the photochromic probe technique to obtain the distribution of local free volume elements in Hyflon AD 60X and Hyflon AD 80X. In this contribution for the first time Quantum Mechanics calculations were used for estimating the extra volumes needed for the photoisomerization.
Results and discussion
Figure 1. Ratio of the cis isomer in the film and the cis isomer in solution as a function of the total isomerisation volume in Hyflon AD.
Six membranes were prepared with different photochromic probe molecules. The ratio between the amount of cis isomer in the film and in solution after the irradiation indicates the availability of free volume elements of sufficiently large size. A plot of this ratio as a function of the total isomerisation volume yields the size distribution of free volume elements in the polymeric material (Figure 1). The entire size distribution of free volume elements in Hyflon AD80X is clearly shifted to higher volume compared to Hyflon AD60X.
Photochromic probe method is a suitable method to evaluate the distribution of free volume elements in Hyflon AD polymers. This procedure is complementary to methods which only determine the overall free volume fraction. The method demonstrates that Hyflon AD80X has larger free volume elements than in Hyflon AD60X.