Pyranine

PAAm-κC composite gels are prepared by free-radical copolymerization using 0.71 g of AAm, 0.01 g of BIS (N, N’-methylenebisacrylamide), 0.008 g of APS (ammonium persulfate) and 2 µl of TEMED (tetramethylethylenediamine) are dissolved in 5 mL of distilled water (pH 6.5) by heating. The heated mixture solution is held at 80°C. Then different amounts of κ-carrageenan (0.5, 1, 1.5, 2, 2.5 and 3 (w/v) % κC) are added. Pyranine (Py) is used in the PAAm–κC composites as a fluorescence probe, which is a derivative of pyrene possessing three SO₃^- groups, which can form bonds with positive charges on the gel. Pyranine (Py) concentration is kept constant at 4×10^-4 M, for all experiments. The solution is stirred (200 rpm) for 15 min to achieve a homogenous sample solution. All samples are deoxygenated by bubbling nitrogen for 10 min just before the polymerization process. The drying and swelling experiments of disc-shaped PAAm–κC composite gels prepared are performed in air and in water, respectively, at various temperatures (30, 40, 50, and 60°C). A model LS-50 spectrometer equipped with a temperature controller is used for fluorescence intensity measurements, which are made at a 90° position and spectral bandwidths are kept at 5 nm. Disc-shaped gel samples are placed on the wall of a 1-cm path-length square quartz cell filled with air and/or water for the drying and swelling experiments^[3].

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