Multifunctional TiO2 -based particles : the effect of fluorination degree and liquid surface tension on wetting behavior

Abstract

A systematic investigation into the influence of the degree of fluorination on the static and dynamic wetting behavior of TiO2-based nanobelt (TNB) particles with various liquids is described. The effect of the degree of fluorination and the surface tension of the liquid on the occurrence and stability of liquid marbles, foams or dispersions are studied and the wetting behavior and arrangement of particles at the air–liquid surface are observed. Using contact angle (θ) measurements, the relation between the type of particle-stabilized material and θ is established. For liquids of relatively high tension like water or formamide which do not wet the fluorinated particles, a powder-like material (marble) is formed. For polar oils of intermediate tension (35–50 mN m−1), which partially wet the fluorinated particles, stable air-in-oil foams can be prepared in which particles form a close-packed layer enveloping air bubbles. Liquids of relatively low tension, e.g., ethanol or polydimethylsiloxane, wet the particles forming a uniform dispersion and partial sedimentation. By contrast, the as-prepared hydrophilic TNB particles are rapidly wetted by all the liquids as expected due to their high surface energy. The stable cross-stacked TNB particles with fluoroalkylsilane (FAS) modification could be a versatile platform in a wide range of applications, especially for fluidic devices (e.g., biofluids, gas sensing, and lab-on-a-chip devices). In a proof-of-concept study, the oil–water separation performance of fabrics with chemically stable TNB/FAS coating and the liquid isolation by a TNB/FAS shell for highly sensitive gas sensing or reagent assays are investigated.