Charged Polystyrene Nanoparticles Near a SiO2/Water Interface
Journal article, 2019

Quartz crystal microbalance with dissipation (QCM-D) monitoring is used to investigate the adsorption processes at liquid-solid interfaces and applied increasingly to characterize viscoelastic properties of complex liquids. Here, we contribute new insights into the latter field by using QCM-D to investigate the structure near the interface and the high-frequency viscoelastic properties of charge-stabilized polystyrene particles (radius 37 nm) dispersed in water. The study reveals changes with increasing ionic strength and particle concentration. Replacing water with a dispersion is usually expected to give rise to a decrease in frequency, f. Increases in both f and dissipation, D, were observed on exchanging pure water for particle dispersions at a low ionic strength. The QCM-D data are well-represented by a viscoelastic model, with viscosity increasing from 1.0 to 1.3 mPa s as the particle volume fraction changes from 0.005 to 0.07. This increase, higher than that predicted for noninteracting dispersions, can be explained by the charge repulsion between the particles giving rise to a higher effective volume fraction. It is concluded that the polystyrene particles did not adhere to the solid surface but rather were separated by a layer of pure dispersion medium. The QCM-D response was successfully represented using a viscoelastic Kelvin-Voigt model, from which it was concluded that the thickness of the dispersion medium layer was of the order of the particle-particle bulk separation, in the range of 50-250 nm, and observed to decrease with both particle concentration and addition of salt. Similar anomalous frequency and dissipation responses have been seen previously for systems containing weakly adherent colloidal particles and bacteria and understood in terms of coupled resonators. We demonstrate that surface attachment is not required for such phenomena to occur, but that a viscoelastic liquid separated from the oscillating surface by a thin Newtonian layer gives rise to similar responses.

Separation

Silica

Polystyrenes

Quartz crystal microbalances

Ionic strength

Viscoelasticity

Volume fraction

Liquids

Author

Maja S. Hellsing

RISE Research Institutes of Sweden

Adrian R. Rennie

Uppsala University

Michael Rodal

Biolin Scientific AB/Q-Sense

Fredrik Höök

Chalmers, Physics, Biological Physics

Langmuir

07437463 (ISSN) 15205827 (eISSN)

Vol. 35 1 222-228

Subject Categories

Physical Chemistry

Materials Chemistry

Other Chemistry Topics

DOI

10.1021/acs.langmuir.8b03361

More information

Latest update

2/19/2019