Effects of structural and chemical anisotropy of nanostructures on droplet spreading on a two dimensional wicking surface

Abstract

When a liquid droplet is deposited onto an array of nanostructures, a situation may arise in which the liquid wicks into the space between the nanostructures surrounding the droplet, forming a thin film that advances ahead of the droplet edge. This causes the droplet to effectively spread on a flat, composite surface that is made up of the top of the nanostructures and the wicking film. In this study, we examined the effects of structural and chemical anisotropy of the nanostructures on the dynamics of droplet spreading on such two-dimensional (2D) wicking surfaces. Our results show that there are two distinct regimes to the process, with the first regime characterized by strong anisotropy in the droplet spreading, following the asymmetric structural or chemical cues provided by the nanostructures. The trend reverses in the second regime, however, as the droplet adopts an increasingly isotropic shape with which it eventually comes to rest. Based on these findings, we formulated a quantitative model that accurately describes the behaviour of droplet spreading on 2D wicking surfaces over a wide range of conditions.

Bacterial Attachment, Aggregation, and Alignment on Subcellular Nanogratings

“…Analysis of the results was then carried out with a semi-empirical quantitative model that separated the effects of physicochemical surface interactions and biological responses. The procedure for the fabrication of Si nanogratings in this study is similar to that previously reported for the synthesis of nanostructures on silicon (Si) and polymeric substrates [16][17][18][19] . Briefly, P-type (100) Si wafers were first cleaned with acetone and dipped in HF for 60 s to remove the native oxide.…”

“…The procedure for the fabrication of Si nanogratings in this study is similar to that previously reported for the synthesis of nanostructures on silicon (Si) and polymeric substrates. − Briefly, P-type (100) Si wafers were first cleaned with acetone and dipped in hydrofluoric acid (HF) for 60 s to remove the native oxide. Four hundred nanometers of Ultra-i-123 positive photoresist was then spin coated onto the surface and baked at 110 °C for 90 s. The wafers were diced into 1 cm × 1 cm samples and exposed to interference lithography using a He–Cd laser with a wavelength of 365 nm.…”