Advanced synthesis for monodisperse polymer nanoparticles in aqueous media with sub-millimolar surfactants

Haruyuki Ishii, Motohiro Ishii, Daisuke Nagao, Mikio Konno

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)


Highly monodisperse polystyrene nanoparticles with mean diameters of less than 100 nm are synthesized via aqueous emulsion polymerization using an amphoteric initiator (VA-057) in the presence of sub-millimolar concentrations of anionic surfactant. Since the net charge on the initiator is almost zero at neutral pH, the resultant latex particle size is mainly determined by surfactant adsorption. Polymerizations were performed in the presence of a range of anionic surfactants with differing critical micelle concentrations (CMC) by varying the concentrations of surfactant, initiator and monomer, and also the ionic strength. Sodium dodecyl benzene sulfonate (SDBS), sodium hexadecyl sulfate (SHS), and sodium octadecyl sulfate (SOS) have relatively low CMCs and so enable formation of highly monodisperse nanoparticles at relatively low (sub-millimolar) surfactant concentrations, CS (i.e. below the CMC in each case). Empirically, it was found that the particle number, Np, and coefficient of variation of the particle size, CV, were strongly dependent on the CS/CMC ratio: Np increased almost in proportion with the square of this ratio, while the CV exhibited a minimum at approximately CS/CMC = 0.20. Higher ionic strength reduced the particle size, which is consistent with the above relationship because the addition of salt lowers the CMCs of ionic surfactants. Polymer latex particles produced using such formulations form highly regular, close-packed colloidal arrays.

Original languageEnglish
Pages (from-to)2772-2779
Number of pages8
Issue number12
Publication statusPublished - 2014 Jun 6


  • Aqueous emulsion polymerization
  • Monodisperse polymer nanoparticle
  • Sub-millimolar surfactant


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