Hydrophobicity, Adhesion, and Friction Properties of Nanopatterned Polymers and Scale Dependence for Micro- and Nanoelectromechanical Systems

Abstract

Applications in micro/nanoelectromechanical systems generally require low adhesion and friction values between two materials of interest. By alteration of the material combinations and surface roughness, including nanopatterning, adhesion and friction can be tailored to meet a specific requirement. Surfaces found in nature, such as hydrophobic lotus leaves, provide a good example of this optimization. Recent models of hydrophobic leaf surfaces show a correlation between roughness and hydrophobicity, which can be mimicked by the presence of nanopatterned asperities on a polymer surface. In addition, by introducing nanopatterns on the polymer surface, the real area of contact decreases when another surface comes into contact with the patterned surface, which reduces adhesion and friction. This study explores the effect of nanopatterning on hydrophobicity, adhesion, and friction for two different hydrophilic polymers, poly(methyl methacrylate) (PMMA) and polyurethane acrylate (MINS), with two types of patterned asperities, low aspect ratio and high aspect ratio, investigated by use of an atomic/friction force microscope (AFM/FFM). In addition to the polymers, a hydrophobic coating was deposited on the surface of the patterned PMMA to study the effect of roughness on the contact angle, along with adhesion and friction. Relative contribution due to change in contact angle and real area of contact are explored. Scale dependence on adhesion and friction was also studied using AFM tips of various radii. Since applications of these surfaces will require operation in varying environments, the effect of relative humidity is investigated.

Wetting Transition Characteristics on Microstructured Hydrophobic Surfaces

“…[1][2][3][4] As one of the most important surface properties, wettability has been studied vigorously to control the contact angle by using surfaces roughness for variety of fields, such as in mechanical, electronic, and bio-technology. [5][6][7][8] Generally, wetting regimes have been classified into three distinct states such as the Cassie state, the Wenzel state, and the intermediate state.…”

Designing nanostructured block copolymer surfaces to control protein adhesion

“…Furthermore, because these block copolymer systems are relatively unexplored, it was important to characterize their morphology. The characterization of the block copolymer surface morphology has been performed by atomic force microscopy (AFM) [99][100][101][102]. AFM is commonly used to characterize block copolymer morphology and to confirm that the synthesized block copolymer phase-separated into nanodomains.…”

Controlling the Cassie-to-Wenzel Transition: an Easy Route towards the Realization of Tridimensional Arrays of Biological Objects

“…Thanks to their wetting properties, these surfaces are of increasing interest in a variety of fields including self-cleaning and antifouling surfaces, film coating, MEMS/BioMEMS and microfluidics [5][6][7][8].…”