Mechanical anisotropy of nanostructured parylene films during sliding contact

Abstract

Microscale sliding friction experiments were performed on nanostructured poly-chloro-p-xylylene (PPX-Cl, a.k.a, parylene) films. Oblique-angle vapour-phase deposition resulted in nanostructured columnar films tilted 57°–63° relative to the surface. The mechanical response to sliding was studied relative to the film structural anisotropy by examining contact friction and deformation in three sliding orientations: ‘with’, ‘against’ and ‘perpendicular’ to the tilt axis of the columns. Friction coefficients were uniformly high (0.5–1.5) for all orientations. Neither frictional anisotropy nor depth hysteresis was observed for sliding perpendicular to the column tilt axis. However, sliding ‘with’ and ‘against’ the column tilt axis resulted in measurable friction anisotropy as well as depth hysteresis, with larger contact depths and higher friction coefficients for sliding ‘with’ the column tilt. In comparison, planar films did not exhibit either frictional anisotropy or depth hysteresis. The depth hysteresis during sliding parallel to the tilt axis is attributed to the lateral force contribution to the total contact loading. Contacts formed when the sliding orientation was perpendicular to the column tilt axis were nominally Hertzian, allowing estimation of elastic moduli of the films from the load–displacement data during sliding. These films may have applications in the area of tissue engineering for directional cell sheet growth, MEMS developments for directional microfluidic pumps and sensors for deformation induced detection.

Neuronal alignment on asymmetric textured surfaces

“…15 Cell polarization (i.e., response to external cues such as chemical gradients and mechanical deformation) has been studied extensively on textured surfaces to understand cell fate. 16 However, unidirectional polarization in response to surface mechanical cues has not been demonstrated earlier.…”

Frictional Anisotropy of Oblique Nanocolumn Arrays Grown by Glancing Angle Deposition

“…The mechanism and qualitative behavior of frictional anisotropy is universal regardless of the presence of plastic deformation, since significant differences in frictional resistance are observed even in the early stage of scratching where only elastic deformation could occur in the experiments. So et al [12] have conducted friction experiments for polymeric oblique columns, and their results revealed that friction coefficients were almost the same or higher when sliding in the forward direction compared to the reverse direction. Since a blunt indenter tip (R = 17 lm) was used in their experiments, only the W-mode deformation could occur.…”

“…During the sliding of a solid object on an oblique nanocolumn array or an asymmetric periodic structure, anisotropic friction resistance arises due to the deformation anisotropy [8][9][10][11][12]. Using this feature, novel devices for moving solid objects in specific directions are anticipated to be developed.…”

“…Using this feature, novel devices for moving solid objects in specific directions are anticipated to be developed. Although a few previous studies have been conducted on investigating the friction of polymeric nanocolumn arrays [12] and aligned carbon nanotube arrays [13], the frictional anisotropy have not been well clarified yet. The objective of this study is to elucidate the friction and its anisotropy on oblique Ti nanocolumns grown by GLAD.…”

A fluidic device with polymeric textured ratchets

“…Ranging from templated and template-free deposition to photolithography to direct printing, numerous techniques for manufacturing textured surfaces have been developed. For example, a micro-scale smooth surface enables transporting droplets, micro-scale pumps, and adhesion [11]. Recently, bio-derived thermoplastics have also been used for fabrication of textured surfaces.…”