Patterning of wettability for controlling capillary-driven flow in closed channels

• Published in: Journal of colloid and interface science Vol. 402; pp. 259 - 266
• Main Authors: O’Loughlin, Muireann, Priest, Craig, Popescu, Mihail N., Ralston, John
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 15.07.2013; Elsevier
• Subjects: Capillaries; Capillary rise; Channels; Chemical heterogeneity; Chemistry; Contact angle; Devices; Exact sciences and technology; General and physical chemistry; glass; glycerol; hydrophilicity; hydrophobicity; nanoparticles; Patterning; Penetration; Photopatterning; Solid-liquid interface; Surface physical chemistry; Titanium dioxide; ultraviolet radiation; Walls; Wettability; Wettability; Contact angle; Capillary rise; Photopatterning; Chemical heterogeneity; Heterogeneity; Patterning
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2013.03.058

[Display omitted] •Photocatalytic patterning of wettability in TiO2-coated glass capillaries.•Different pattern periodicity at constant coverage shows distinct filling behaviour.•Filling behaviour departs from that predicted using the Cassie contact angle.•Convergence to theoretical predictions is observed for small periodicities. Glass capillaries are prepared with well-defined regions of tuneable wettability on the interior walls using an inexpensive and simple approach. A homogeneous layer of hydrophilic TiO2 nanoparticles is adsorbed on the capillary wall and chemically hydrophobized using octadecyltrihydrosilane (OTHS). The hydrophobic OTHS monolayer is then patterned by spatially-selective removal of the OTHS via TiO2-catalysed decomposition by ultraviolet irradiation. By patterning the capillaries with hydrophilic-hydrophobic rings, modulated penetration of a liquid (glycerol, in this study) can be achieved. For given wettability contrast, the penetration dynamics and equilibrium rise heights are very sensitive to the characteristic length-scale of the pattern, and may offer greater, time-dependent sampling control in fluidic devices.