(686h) Combined Quartz Crystal Microbalance with Dissipation and Generalized Ellipsometry to Characterize the Deposition of Titanium Dioxide Nanoparticles on Model Rough Surfaces

Titanium dioxide nanoparticles (TiO₂NPs) are the most extensively manufactured engineered nanomaterials, and understanding of their interactions with soil and sandy aquifer materials is necessary for effective natural resource management [1]. Quartz crystal microbalance with dissipation monitoring (QCM-D) has been widely used to study TiO₂NPs at water-metal oxide interfaces as model systems for soils and aquifers. However, natural sands and sediments exhibit various degrees of surface roughness, and the effects of surface roughness are not accounted for in current QCM-D studies of nanoparticle adsorption, which use the Voigt-Kelvin model [2].

A new mechanical model that considers both viscoelastic and surface roughness effects [3] is described to analyze QCM-D measurements. Obtained parameters include adsorbate areal mass density, adsorbate viscoelastic properties, the vertical roughness length, and the permeability length. Silicon slanted columnar thin films (SCTFs) were deposited onto QCM-D sensors by electron-beam glancing angle deposition and conformably coated with an alumina film via atomic layer deposition to act as model rough surfaces. The adsorption of polyacrylate-stabilized TiO₂NPs onto flat surfaces and the SCTFs was measured by QCM-D and generalized ellipsometry (GE), an optical reference technique.

We report that the surface-roughness-modified mechanical model excludes water that is retained by the SCTF surface roughness and instead considers the surface mass density of TiO₂NPs and water coupled to the TiO₂NPs [4]. GE is also sensitive to the attachment of the TiO₂NPs. When the results of both techniques are combined, new information, the hydration of the polyacrylate-stabilized TiO₂NPs, can be evaluated.

[1] B. Kim et al. J. Environ. Monit., 14, 1128 (2012).

[2] M.V. Voinova et al. Phys. Scr., 59, 391 (1999).

[3] L. Daikhin et al. Anal. Chem., 74, 554 (2002).

[4] N. Kananizadeh et al. J. Hazard. Mater., In press. dx.doi.org/10.1016/j.jhazmat.2016.03.048