Abstract
Hydrophobicity is an important parameter for the risk assessment of chemicals, but standardised quantitative methods for the determination of hydrophobicity cannot be applied to nanomaterials. Here we describe a method for the direct quantification of the surface energy and hydrophobicity of nanomaterials. The quantification is obtained by comparing the nanomaterial binding affinity to two or more engineered collectors, i.e. surfaces with tuned hydrophobicity. In order to validate the concept, the method is applied to a set of nanoparticles with varying degrees of hydrophobicity. The technique described represents an alternative to the use of other methods such as hydrophobic interaction chromatography or water–octanol partition, which provide only qualitative values of hydrophobicity.
Highlights
That substantially means that the NP adsorption velocity is reduced by a factor eÀΔGmax=kT in the presence of an energy barrier as compared to the maximum velocity
In this work a method is presented for the quantitative characterisation of nanoparticles hydrophobicity by measuring their affinity towards functionalized surfaces
The determination of the affinity of NPs towards substrate surfaces with different hydrophobicity degrees enables the direct characterisation of the NPs having unknown surface functionalization and residual hydrophobicity in a direct manner
Summary
Silicon wafers (Si(100); diameter, 50 mm; resistivity, 1−20 Ω cm) supplied by ITME (Warsaw, Poland) were used as the substrate for the whole study. Before modification the wafers were washed with ethanol and water and dried under nitrogen flow. The silicon substrate was modified by different deposition processes in order to tune the surface hydrophobicity. Polytetrafluoroethylene (PTFE) coating was plasma deposited to generate a hydrophobic surface. The deposition was performed using pure octofluorocyclobutane (C4F8) as the gas precursor at a pressure of 3.5 Pa, applying a power of 142 W for 5 min[12]
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