title: Radical-initiator-Induced solid-state polymerization of butadiyne nanocrystals in water and their dispersion stabilization.
abstract: Butadiyne nanocrystals in water are usually polymerized by UV or gamma-ray irradiation to give polydiacetylene (PDA) nanocrystals. In this study, we confirmed that solid-state polymerization of 1,6-di(N-carbazolyl)-2,4-hexadiyne (DCHD) and 5,7-dodecadiyn-1,12-diyl bis[N-(butoxycarbonyl-methyl)carbamate] (4BCMU) could be stimulated by water-soluble radical initiators. The radical initiators used were potassium peroxodisulfate, three kinds of azo-type compounds and a redox initiator. In all cases, the solid-state polymerization was confirmed by color change into blue indicating that PDA modified by the radical residues at the end was formed. However, nanocrystal cohesion occurred especially when the concentration of the initiators was high or the dispersion was kept for a long time. In order to improve the dispersion stability, two kinds of surfactants, i.e., sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTMAC), were added to the DCHD nanocrystal aqueous dispersion. As a result, when anionic SDS was added, the solid-state polymerization of nanocrystals proceeded without coagulation and quantitative conversion was confirmed for all initiators. Cationic DTMAC has no effect on dispersion stabilization. PDA nanocrystal surfaces in water are negatively charged in nature and electric interaction of nanocrystals with the cations results in decrease of surface charge and aggregation of nanocrystals.
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510, Japan.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Kato
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kinemuchi
authors.forename: Yoko
authors.initials: Y
authors.lastname: Tatewaki
authors.forename: Shuji
authors.initials: S
authors.lastname: Okada
authors.forename: Akito
authors.initials: A
authors.lastname: Masuhara
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Kasai
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Oikawa
mesh_terms: D002070:Butadienes / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D004655:Emulsions / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D044367:Phase Transition; D012995:Solubility; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D002070:Butadienes; D004655:Emulsions; D046911:Macromolecular Substances; D014867:Water