Characterization of Pentacosa-10,12-Diynoic Acid - Poly(styrene-butyl acrylate) Latex for Radiation Sensitive Indicator

Full-text: Radiation including ionizing types are generally invisible, have no weight and charge (except alpha and beta particles) or odour. Although some of them do emit light and heat, the radiation can only be detected with special instrumentation made from inorganic or organic material. Conjugated polymer such as polydiacetylene is one of the organic material that has the ability to indicate ionizing radiation by colour change upon exposure. The colour change mechanism is related to availability of pi-electrons in its molecule structure which allows for pi-conjugation upon ionization. Ionization on the monomerics triple bonds may induce 1,4-addition which eventually form covalent bonds between adjacent molecules and turn the colour of the material from colourless to violet-blue (conjugation). The conjugated structure, however has restricted the molecules movement thus resulted in extremely brittle polymer which is also difficult to form continuous film. In order to overcome the issue, addition of low glass transition (T_g) polymer to polydiacetylene is required to aid its film forming capability while retain its colour change properties. Therefore, polystyrene-butylacrylate (PSBA) latex of T_g∼20 degree Celsius has been used in this study, to hold pentacosa-10,12-diynoic acid (PCDA), a monomer from polydiacetylene group. To ensure pi-electrons in PCDA do not lose its function prior to end application, any possible chemical interaction between PCDA and PSBA or any chemical residue from PSBA synthesis had to be avoided. Radiation-induced PSBA synthesis made the work easier where no chemical initiator was used for the reaction. Not only that, combination of hydrophobic and ionic interactions has been used for deposition of PCDA on PSBA surface. By this way, PCDA molecules are free to organize and self-assembled on the particles surface before conjugation and while conjugation occurs. Effect of surface charge density on PSBA that attracts the PCDA has also been investigated. Poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethyl-ammonium chloride) (PDADMAC) were used to alter PSBA charges by multiple layers up to five layers. PCDA was then added to the final layer and evaluated. Evaluation on the final latexes were carried out using gamma ray (Cs-137) at range between 5 Gy to 7 kGy and gamma ray (Co-60) at range between 5 to 50 kGy. Total colour differences (dE^*) of every samples were measured using colorimeter for comparison. Result from the analysis confirms that PSBA-filled PCDA is responsive against gamma radiation. Not only that, difference of colour measured for PSBA-filled PCDA was 50 % higher than non-filled PCDA. The colour change however comes to its limit at 10 kGy. (author)