Skip to main content
eScholarship
Open Access Publications from the University of California

UC Berkeley

UC Berkeley Previously Published Works bannerUC Berkeley

Wettability Reversal of Hydrophobic Pigment Particles Comprising Nanoscale Organosilane Shells: Concentrated Aqueous Dispersions and Corrosion-Resistant Waterborne Coatings.

  • Author(s): Mishra, Manish K;
  • Schöttle, Christian;
  • Van Dyk, Antony;
  • Beshah, Kebede;
  • Bohling, James C;
  • Roper, John A;
  • Radke, Clayton J;
  • Katz, Alexander
  • et al.

Published Web Location

https://pubs.acs.org/doi/10.1021/acsami.9b14898
No data is associated with this publication.
Abstract

We demonstrate the synthesis of polysiloxane-modified inorganic-oxide nanoparticles comprising a TiO2-based pigment (Ti-Pure R-706), which undergo drastic wettability reversal from a hydrophilic wet state to a hydrophobic state upon drying. Furthermore, the dry hydrophobic pigment particles can be reversibly converted back to a hydrophilic form by the application of high shear aqueous milling. Our synthetic approach involves first condensing the cross-linking monomer CH3Si(OH)3 onto the surface of Ti-Pure R-706 at pH 9.5 ± 0.2 in an aqueous suspension. After drying this surface-modified material in the presence of a polyanionic dispersant so as to preserve the primary particle size via dynamic light scattering, it is trimethylsilyl-capped with (CH3)3SiOH, which consumes some residual Si-OH functionalities, and washed to remove all dispersant and excess reagents. Transmission electron microscopy demonstrates a ∼6 nm polysiloxane coating uniformly surrounding the surface of the pigment particle. A 70 wt % (37 vol %) concentrated aqueous slurry of the hydrophobically modified pigment particles prepared in the absence of dispersant exhibits rheological characteristics that are nearly the same as an aqueous dispersion of native unmodified hydrophilic Ti-Pure R-706 comprising an optimal amount of the organic anionic dispersant. It is also possible to synthesize dispersions without the use of an added surfactant and/or dispersant at even higher solid concentrations of up to 75 wt % (43 vol %) in water, conditions at which even the hydrophilic native Ti-Pure R-706 oxide pigment yields a gel-like paste in the absence of a dispersant. Films prepared by drying an aqueous suspension of these pigment particles exhibited a hydrophobic contact angle of ∼125°. When acrylic-based waterborne coatings were prepared comprising these surface-modified Ti Pure R-706 pigments, they showed excellent corrosion protection of a mild steel substrate. These data point to a wettability reversal in which the particles change from hydrophobic to hydrophilic upon high-shear aqueous milling and vice versa upon drying. 29Si CP/MAS NMR spectroscopy highlights the importance of flexibility of the polysiloxane coating for achieving this wettability reversal, a result that emphasizes the importance of surface reconstruction.

Many UC-authored scholarly publications are freely available on this site because of the UC's open access policies. Let us know how this access is important for you.

Item not freely available? Link broken?
Report a problem accessing this item