Rapid coagulation of Langmuir-Blodgett mesoscopic bands on mica by monovalent ions

Masahito Sano, Ayumi Kamino, Seiji Shinkai

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

Langmuir-Blodgett films of 4-heptoxy-4'-carboxyazobenzene on mica transferred from pure water exhibit novel strip structures consisting of mono-molecular thick straight bands 80 nm wide and more than 100 μm long. To examine a possibility that these bands are self-organized structures of small monolayer clusters, the effects of monovalent ions are investigated. The monovalent ions caused the mesoscopic bands to coagulate. The fraction of coagulated bands was measured as a function of ion concentrations at pH 7.0 by atomic force microscopy. K+ and Cs+ are shown to interact with the mica surface strongly and destabilize the bands by developing the hydration force. Na+ and Li+ cause critical coagulation without destabilization and have the critical concentrations at 3.0 and 1.6 mM, respectively. UV-vis reflection spectroscopy demonstrates that no molecular reorientation deviating from an H-aggregate-like state occurs during coagulation. X-ray photoelectron spectroscopy was used to obtain an adsorption isotherm of Na+. A comparison with a model monolayer described by Poisson-Boltzmann-Stern theory shows that the unusually large Na+ binding occurs prior to the coagulation. A comment is made on the importance of the characteristically large perimeter regions of monolayer clusters making up the band.

Original languageEnglish
Pages (from-to)24-30
Number of pages7
JournalJournal of Colloid and Interface Science
Volume220
Issue number1
DOIs
Publication statusPublished - Dec 1 1999
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Colloid and Surface Chemistry

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