Polymers Nucleation and Growth Mechanism: Solubility, a Determining Factor

摘要

Temperature and ultrasound effect on the nucleation and growth mechanisms (NGM) of poly(ortho- toluidine) (POT) was investigated. Synthesis conditions at temperatures between 263 and 303 K wereoptimized with and without ultrasonic irradiation. The obtained i-t transient is complex and itsdeconvolution showed to be made up of three contributions that initially included a progressivenucleation with bidimensional growth (PN2D), along with two progressive nucleation contributionswith three-dimensional growth, one controlled by diffusion and the other by charge transfer, PN3Ddifand PN3Dct, respectively. Besides, as temperature decreases, a decrease of the charge associated toeach contribution was observed. At the same time the nucleation induction time increases, as occurswhen ultrasound is applied during the electro-polymerization. This effect was ascribed to kineticfactors rather than to film conductivity. Conductivity measurements of deposits obtained at differenttemperature corroborated this issue. In situ spectro-electrochemical studies were accomplished toanalyze differences between polymer films obtained by varying the temperature. The results enabledthe proposed electro-polymerization model to be validated: it was found that the electro-depositionprocess initially depends on oligomers solubility at the electrode-solution interface. When theseoligomers reach a chain length at which are insoluble, they precipitate on the electrode surface, givingrise to the nuclei that establish the onset of the polymer electro-deposition process. Also, these resultsexplain the important effect of temperature and ultrasound on the NGM, because these variablesdirectly affect solubility, a determining factor in electro-polymerization.