Synthesis and characterisation of pentacosa-10,12-diynoic Acid – poly (styrene-butyl acrylate) latex for gamma radiation indicator

Abstract

Pentacosa-10,12-diynoic acid (PCDA) is one of the most highly used polymeric materials in radiation sensing applications. It is quintessential for its ability to indicate ionising radiation by colour transition. The PCDA monomer forms lipid vesicles in aqueous mediums that closely align themselves. This alignment enables polymerisation of the monomer upon irradiation. The polymerisation is visibly identified by the polymer colour transition from colourless to bluish-violet. However, the indication of radiation is hampered by the vesicle’s instability and low colour reflectance from its transparent body. Therefore, an opaque polystyrene-butyl acrylate (PSBA) latex was fused into the transparent PCDA vesicles to promote the stability while simultaneously enhancing the colour reflectance. The PSBA was copolymerised using the radiation route to avoid the presence of unwanted chemical residues, especially from the initiator. The fusion of PCDA and PSBA was accomplished by the hydrophobic-hydrophobic interaction. The effect of ionic layers on the PSBA surface against the effectiveness of PCDA immobilisation was also investigated. The ionic layers from polyelectrolytes (PEL), namely, poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethyl-ammonium chloride) (PDADMAC), were applied layer-bylayer onto the PSBA surface for up to five layers prior to PCDA adsorption. The performance of all stable latexes (PCDA/PSBA-PEL0,1,3,5) as radiation indicators was evaluated using gamma ray source from Cesium 137 (0.662 MeV) and Cobalt 60 (1.17 MeV). Colour transitions demonstrated by the latex were measured and reported as total colour difference (dE*). Results from the analysis confirm that PSBA-filled PCDA is responsive against gamma radiation from 1 to 50 kGy. The optimum colour transition response by irradiated samples compared to unirradiated samples is noted after 7 kGy of 137Cs and 10 kGy of 60Co. Moreover, the difference of colour measured for PSBA-filled PCDA is 50% higher than non-filled PCDA, suggesting that high colour reflectance was achieved by the presence of the opaque PSBA. All latex particles were stable during pre and post-irradiation up to 60 days of storage. Variation of colours was noted on the irradiated non-filled PCDA. However, the variation reduced with the presence of PSBA core inside PCDA envelope due to less available room between PCDA and PSBA, which usually allows for PCDA molecule relaxation.