Long-Term Reduction in Poly(dimethylsiloxane) Surface Hydrophobicity via Cold-Plasma Treatments

Abstract

Poly(dimethylsiloxane), PDMS, a versatile elastomer, is the polymer of choice for microfluidic systems. It is inexpensive, relatively easy to pattern, and permeable to oxygen. Unmodified PDMS is highly hydrophobic. It is typically exposed to an oxygen plasma to reduce this hydrophobicity. Unfortunately, the PDMS surface soon returns to its original hydrophobic state. We present two alternative plasma treatments that yield long-term modification of the wetting properties of a PDMS surface. An oxygen plasma pretreatment followed by exposure to a SiCl4 plasma and an oxygen-CCl4 mixture plasma both cause a permanent reduction in the hydrophobicity of the PDMS surface. We investigate the properties of the plasma-treated surfaces with X-ray photoelectron spectroscopy (XPS) and contact angle measurements. We propose that the plasma treated PDMS surface is a dynamic mosaic of high- and low-contact-angle functionalities. The SiCl4 and CCl4 plasmas attach polar groups that block coverage of the surface by low-molecular-weight groups that exist in PDMS. We describe an application that benefits from these new plasma treatments, the use of a PDMS stencil to form dense arrays of DNA on a surface.

Investigation of the surface microstructure evolution of silicone rubber during corona discharge via slow positron beam and electrochemical impedance spectroscopy

“…As shown in Figure b, the 1,260 cm −1 ( group) peak area decreases with the increasing corona treatment time, indicating the same decreasing trend of the other two. The reduction of these three peaks indicates a rupture of the Si–C bond and C–H bond in PDMS, and the formation of a relatively hydrophilic surface state in silicone rubber . Additional evidence for the decrease in surface hydrophobicity is the broadened peak located at 3,380 cm −1 , as shown in Figure a, which is attributed to the vibration of hydrogen bonding .…”

Study on surface structure of plasma‐treated polydimethylsiloxane (PDMS) elastomer by slow positron beam

“…To return the surface to its pretreatment hydrophobic character, the LMW siloxanes will diffuse through silica‐like layer covering the sample surface. () Due to the blocking effect of silica‐like layer, a number of LMW species accumulates beneath the inorganic layer, resulting in an increased S t value . Compared with 3‐min–treated sample, the 5‐minute one forms a thicker silica‐like layer, of which the blocking effect on migration of LMW species is more remarkable.…”

“…Normally, based on Zhu et al, Si(−O) 1 : 101.5 ± 0.1 eV, Si(−O) 2 : 102.1 ± 0.1 eV, Si(−O) 3 : 102.7 ± 0.1 eV, and Si(−O) 4 : 103.4 ± 0.1 eV can be detected on a PDMS composite surface. Usually, Si2 p subpeaks at 101.5 eV and 102.1 eV are assigned to an organic silicone phase, ie, uncrosslinked LMW siloxanes or PDMS backbone,() while these subpeaks at 102.7 and 103.4 eV are associated with an inorganic silica‐like (SiO x ) phase. () The peak‐split results of each subpeak area percentage are shown in Table .…”

“…To return the surface to its pretreatment hydrophobic character, the LMW siloxanes will diffuse through silica-like layer covering the sample surface. 15,38 Due to the blocking effect of silica-like layer, 14…”

Toward the Development of a Versatile Functionalized Silicone Coating

“…Due to their commercial availability, low cost and chemical inertness, SEs have been applied in diverse biomedical technologies, including contact lenses and human implants, which require that the surface of PDMS be hydrophilic to minimize factors such as corneal discomfort and platelet adhesion, respectively. 9 Increasing the surface energy of intrinsically hydrophobic PDMS 10 can be achieved by chemical modification, physical alteration, 11,12,13,14,15,16 a combination of both chemical 17,18,19,20,21,22,23,24,25 and physical treatment, 26,27,28 or simple physisorption. 29,30,31,32 In spite of these efforts, achieving stable PDMS-modified surfaces remains a challenging task.…”