## Abstract

We have measured the interaction forces versus distance between pairs of 2-µm diameter polystyrene spheres immersed in electrolytes containing up to 1 M KCl. A reproducible long-range repulsion was observed for concentrations below 0.01 M. Adhesion varied considerably from measurement to measurement (values ranged from 3.5 to 140 nN) and showed no systematic trend as a function of electrolyte strength. Data for repulsion in 0.001 M KCl are well fitted by a simple result based on the Derjaguin approximation and the linearized Poisson-Boltzmann equation. This fit yields a surface potential (ψ_{0}) of 87 mV and a Debye length of 7.7 ±0.1 nm, in reasonable agreement with the expected Debye length (9.5 nm) and the measured ζ potential (83 ± 2 mV). A full numerical solution of the Poisson-Boltzmann equation shows that the simple theory works reasonably in these conditions, despite the fact that ψ_{0}/k_{B}T > 1. Measurements made in pure water and measurements of the interaction between a sphere and a mice surface gave results that varied from run to run, none of which agreed with theoretical calculations.

Original language | English (US) |
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Pages (from-to) | 637-641 |

Number of pages | 5 |

Journal | Langmuir |

Volume | 9 |

Issue number | 3 |

DOIs | |

State | Published - Jan 1 1993 |

## ASJC Scopus subject areas

- Materials Science(all)
- Condensed Matter Physics
- Surfaces and Interfaces
- Spectroscopy
- Electrochemistry