Fabrication of Anisotropic Super Hydrophobic/Hydrophilic Nanoporous Membranes by Plasma Polymerization of C[sub 4]F[sub 8] on Anodic Aluminum Oxide

Abstract

Freestanding anodic aluminum oxide ͑AAO͒ membranes were fabricated using a two-step anodization procedure, voltage reduction method, and inductively coupled plasma polymerization. The fabrication process was monitored with electrochemical and spectroscopic ellipsometry measurements, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. Static contact angle measurements demonstrated that the two surfaces of the fabricated AAO membranes have dramatically different degrees of hydrophobicity. The contact angle of water on the side modified with the fluorocarbon film was 150°, whereas the contact angle on the hydrophilic side, which was initially attached to the aluminum substrate, was less than 5°. The fabricated freestanding AAO membranes with only one hydrophobic surface are expected to find applications in the design of new systems for separation and filtration and as gas and liquid transport devices such as gas-diffusion electrodes for miniature power sources and sensors.Nanoporous anodic aluminum oxide ͑AAO͒ membranes and nanopore arrays attached to aluminum substrates have great potential for numerous applications in the rapidly developing nanotechnology field. 1,2 Both freestanding membranes and arrays, having hexagonally ordered pores, have been extensively used in the fabrication of a variety of nanostructures. The modification of pores with metals or semiconductor materials is primarily motivated by the numerous possibilities to fabricate novel materials and nanodevices ͑e.g., magnetic recording media, optical and electroluminescent display devices͒. 3 This modification can be accomplished by a number of methods, including electro-and electroless deposition, 3-8 chemical vapor deposition, 9 and sol-gel deposition. 10 The potentially useful optical, photoelectrochemical, electrical, and transport properties of modified AAO arrays make them very promising for application in design of new nanotechnology products such as: sensing devices, adsorbants, preconcentrators, gas and liquid separation and transportation devices, and membranes in microreactors or micropower sources.The highly ordered AAO arrays are typically fabricated using a two-step anodization procedure. 11 This method involves porous-type anodization of aluminum in acidic electrolytes and sequential chemical etching of resulting porous and barrier aluminum oxide layers. The second anodization leads to formation of highly ordered AAO arrays. 11-13 The preparation of freestanding AAO membranes requires the underlying aluminum substrate to be removed. This can be accomplished, for example, by dissolving the whole aluminum substrate in a mercuric chloride solution. Alternatively, the separation of the AAO membrane from the aluminum substrate can be achieved by the voltage reduction method. 14 The application of this method results in gradual thinning and complete dissolution of the barrier oxide layer, which connects porous aluminum oxide and aluminum. [14][15][16] The focus of recent research has ...

Nanoporous Anodic Alumina Photonic Crystals for Optical Chemo- and Biosensing: Fundamentals, Advances, and Perspectives

“…Nonetheless, polymer plasma deposition cannot achieve sufficient penetration depth to coat the inner surface of nanoporous materials such as NAA, being limited to surface-based applications [ 106 ]. Modification of NAA platforms with plasma polymer deposition enables the tuning of the hydrophobicity of the surface by polymerizing fluorocarbon monomers using argon or oxygen plasma [ 215 ]. Plasma polymer deposition also changes the chemical and geometrical properties of NAA as platform material in drug delivery systems, where drug release from NAA can be controlled and extended over longer periods of time [ 216 , 217 ].…”

Nanoporous Anodic Alumina Platforms: Engineered Surface Chemistry and Structure for Optical Sensing Applications

“…Brenov et al for the first time, reported on the modification of NAA by plasma polymerization [41]. They prepared Janus-type NAA membranes by depositing hydrophobic fluorocarbon polymer from plasma polymerization of C 4 F 8 on one side of the NAA membranes while the other side was left unmodified.…”

Soft and Hard Surface Manipulation of Nanoporous Anodic Aluminum Oxide (AAO)

“…This technique is particularly efficient and convenient because the ultrathin polymer films of various functionalities can be deposited on any surfaces without the need of surface pre-modification [121]. It is well-established by the first report of plasma treatment on AAO membrane from Brevnov et al [122], who prepared Janus-type membranes with a hydrophilic and hydrophobic side. This approach reported that a super-hydrophobic surface is obtained on AAO membranes using inductively coupled plasma polymerization of fluorocarbon (C 4 F 8 ) monomer, with a water contact angle (WCA) of 150°.…”