Effects on wettability by surfactant accumulation/depletion in bulk polydimethylsiloxane (PDMS)

• Published in: Sensors and actuators. B, Chemical Vol. 119; no. 1; pp. 192 - 198
• Main Authors: Seo, Jeonggi, Lee, Luke P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 24.11.2006
• Subjects: Aqueous solutions; Contact angle; Contact angle measurement; Depletion; Immersion; Microfluidics; Nanostructure; Polydimethylsiloxane (PDMS); Silicone resins; Surface modification; Surfactants; Triton X-100; Wettability; Surface modification; Microfluidics; Contact angle measurement; Polydimethylsiloxane (PDMS); Triton X-100
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2005.12.019

Polydimethylsiloxane (PDMS) is an appealing silicone elastomer as a base material for microfluidic biomedical applications. Its ability to easily cross-link as well as its favorable physical and chemical properties has enabled a large number of micro- and nano-cast applications. However, PDMS’ hydrophobic surface can be problematic. Two methods presented here address the wettability of PDMS by accumulating or depleting surfactant in PDMS. The surfactant in the cross-linked PDMS matrix is released and activated upon contacting with an aqueous solution and assists the solution wetting of PDMS. Wettability was enhanced as a function of surfactant concentration. With the addition of 3% Triton TX-100 (a nonionic surfactant), the contact angle of deionized water on PDMS decreased up to 40° in 90 s, compared with a decrease of only 3° on unmodified PDMS. Dynamic measurements of contact angle and contact line radii showed wettability change due to the transfer of surfactant to the interface of the aqueous solution/PDMS. The stability of the modified PDMS was quantified by contact angle measurements over a 30-day duration. Immersing the modified PDMS in water for long time periods before the measurement depletes the surfactant; the resulting wettability becomes a function of immersion duration. The surface wettability can also be controlled with a function of immersion duration even after the PDMS is cured.