Direct observation of wetting behavior of water drops on single micro-scale roughness surfaces of rose petal effect
Journal
Journal of Colloid and Interface Science
Journal Volume
603
Pages
539-549
Date Issued
2021
Author(s)
Lin H.-P
Abstract
Hypothesis: It has been verified that a surface of single micro-scale structures with certain roughness could exhibit petal effect. That is, water drops with a contact angle larger than 150° would pin on the petal effect surface. It is conjectured that the water drop could pin on the single micro-scale roughness petal effect surface by totally infiltrating into spaces (or grooves) between micro-pillars. Experiments: An inverted optical microscopy system is synchronically applied in the process of advancing/receding contact angle (ACA/RCA) measurements to directly observe the wetting behavior of water droplets on hydrophobic patterned surfaces with regular arrays of square micro-pillars. Findings: A sequence of wetting behavior evolution, Wenzel → petal → pseudo-lotus → lotus, is observed on the hydrophobic patterned surfaces along with increasing surface roughness. It is interesting to observe a Cassie-Wenzel transition for water drops on a petal substrate during the ACA measurement (embedded needle method), leading to two ACAs, one before (in Cassie state) and one after the transition (in Wenzel state). Thus, the petal substrates have large contact angle hysteresis (CAH) (with both ACA and RCA in Wenzel state) to pin the water drop in Wenzel state. A Cassie-Wenzel transition is consistently observed during the evaporation process of water drops on pseudo-lotus substrates, leading to two RCAs: one in Cassie state and one in Wenzel state. The pseudo-lotus substrates have CAH (with both ACA and RCA in Cassie state) small enough to make water drops easily slide off. ? 2021 Elsevier Inc.
Subjects
Advancing contact angle
Cassie-Wenzel transition
Petal effect
Receding contact angle
Superhydrophobic surface
Contact angle
Drops
Hydrophobicity
Substrates
Surface roughness
Cassie-wenzel transitions
Contact angle hysteresis
Direct observations
Evaporation process
Micro-scale structures
Patterned surface
Roughness surfaces
Wetting behavior
Wetting
water
Article
contact angle
controlled study
evaporation
measurement
microscopy
nonhuman
petal
rose
surface property
wettability
biophysics
Biophysical Phenomena
Rosa
Surface Properties
Water
Wettability
SDGs
Type
journal article