Surface modification of polytetrafluoroethylene thin films by non-coherent UV light and water treatment for electrowetting applications

Abstract

The electrowetting on dielectric or EWOD phenomenon is used in a wide range of applications, such as Liquid Lenses, Lab-on-Chip devices, or EWOD displays, among others. Its chemical resistance, electrical stability, ease of application, and low cost make polytetrafluoroethylene (PTFE) the preferred hydrophobic dielectric layer for such applications. However, the hydrophobic behaviour represents a challenge for spin coating other layers over its surface. As a consequence, several techniques are implemented to modify the surface of PTFE. These methods are complex, time-consuming, and produce morphology changes over the surface that are difficult and sometimes impossible to recover. In this work, we propose a new surface modification method that is based on a non-coherent UV light exposition method and a specific water treatment, that lead to a change from hydrophobic to hydrophilic, and a perfect recovery from hydrophilic to hydrophobic behaviour. Experiments: In this work, the fabrication of the hydrophobic layer treatment starts with the creation of a thin layer of alumina (Al O 2 3) over a glass substrate using an atomic layer deposition technique (ALD). A mixture of 10:1 FC40 solvent and Teflon Dupont AF1600 was coated over the alumina layer. The Teflon film was exposed to UV light produced by a low-pressure mercury (Hg) lamp for a period that ranges from 3−6 min. The results were analysed by scanning electron microscopy, x-ray spectroscopy, and static deionized water contact angle measurements. Findings: Contact angles dependent on UV light exposure time were observed. From the scanning electron microscopy analysis, it was confirmed that the UV treatment does not produce morphology changes over the surface. Nevertheless, the x-ray spectroscopy revealed that the UV exposed samples react when they are brought into contact with deionized water, improving the adhesion of the surface. The original hydrophobic behaviour of the surface is recovered (up to 98 %) after 3 h of thermal treatment. Furthermore, the thermal recovery analysis reveals a correlation between the recovery percentage and the applied temperature.

Rapid Transformation in Wetting Properties of PTFE Membrane Using Plasma Treatment

“…Even a short period of plasma treatment (a few seconds to a maximum of 1 min) is sufficient to bring about changes in surface wettability [9,12,[27][28][29][30][31][32]. By optimizing the operating parameters (such as pressure, power, time, and gas flow rate) and by varying the plasma gas (such as Ar, N 2 , O 2 , Ar+H 2 , CO 2 , and NH 3 ) different type of functionalization will be imparted on the surface of the material [33,34]. Liu et al [35] studied the effects of dielectric barrier discharge (DBD) plasma surface treatment on three different polymer surfaces, viz., polytetrafluoroethylene (PTFE), polyimide (PI), and poly(lactic acid) (PLA).…”

Hydrophilic Nature of Polytetrafluoroethylene through Modification with Perfluorosulfonic Acid-Based Polymers

“…'Supherhydrophobic surfaces' with lotus effect, repel water droplets and are used as self-cleaning, anti-icing and antibacterial surfaces [4][5][6][7], whereas 'superhydrophilic surfaces', with excellent water wettability are used as biocompatible and antifogging materials. In addition to these two surfaces, 'gecko surfaces', also called as 'adhesive hydrophobic surfaces' with a high contact angle that can pin water droplets to the surface are used to transfer small volumes of liquid from one place to another [8][9][10].…”

Rapidly Transforming PTFE from Hydrophobic to Hydrophilic through Plasma Treatment

“…of 1 minute) is sufficient to bring about changes in surface wettability. By optimizing the operating parameters (such as pressure, power, time and gas flow rate) and by varying the plasma gas (such as Ar, N2, O2, Ar+H2, CO2 and NH3) different type of functionalization can be imparted on the surface of the material [20,21]. Liu et al [22] studied the effects of dielectric barrier discharge (DBD) plasma surface treatment on three different polymer surfaces, viz., polytetrafluoroethylene (PTFE), polyimide (PI) and poly(lactic acid) (PLA).…”