Primary surface measurement reported
Water contact angles (WCAs) were measured on the adaxial surface of refoliated quaking aspen leaves during the 2021 refoliation period.
Client Citation Analysis
Superhydrophobicity mechanism of refoliated quaking aspen leaves after complete defoliation by LDD (gypsy, spongy) moth caterpillars
This paper tracks the wetting behavior of refoliated quaking aspen leaves after complete LDD moth defoliation by measuring water contact angle over time and relating it to leaf surface structure development.
At-a-Glance Summary
Dropometer attribution in the paper
The Methods attribute WCA measurements to a “contact angle measurement system (Droplet Lab Dropometer).”
How the contact angle data were used in the study
WCA data were presented as a function of time during the refoliation period and compared against previously reported seasonal wettability datasets to discuss how refoliated leaves develop and maintain non-wettability after budbreak. The WCA results were also discussed alongside SEM observations of evolving microscale papillae and nanoscale epicuticular wax features.
Replication / reliability statement
At least 9 contact angle measurements were conducted per sample, and averages with standard deviations were reported.
Paper Details
Title
Superhydrophobicity mechanism of refoliated quaking aspen leaves after complete defoliation by LDD (gypsy, spongy) moth caterpillars
Authors
Xin Sui; Jason Tam; Harald Keller; Wenyan Liang; Uwe Erb
Journal
Plant Science
Year
2023
Volume
330
Pages / Article
111659
License
© 2023 Elsevier B.V. All rights reserved.
What Was Measured
Primary surface / interfacial measurement
Water contact angles (WCAs) on the adaxial (upper) leaf surface, measured using deionized water droplets and reported as averages with standard deviations.
Supporting measurements
Leaf size was quantified in two directions (parallel and perpendicular to the midrib) using image-based measurement. Leaf surface morphology development during refoliation was characterized by SEM, including measurements of papillae and epicuticular wax (ECW) feature sizes.
Water contact angle (WCA)
contact angle measurement system (Droplet Lab Dropometer)
Leaf size
ImageJ
Leaf surface morphology (SEM)
scanning electron microscope (Hitachi SU7000)
Role of the Dropometer
The “contact angle measurement system (Droplet Lab Dropometer)” was used to measure water contact angles on the adaxial surface of refoliated quaking aspen leaves. Leaves were mounted on 2 × 2 × 0.5 cm plexiglass coupons using double-sided tape, and 10 μL deionized water droplets were dispensed on the leaf surface to obtain WCA values reported as averages with standard deviations. The roll-off angle could not be obtained. The Methods state: "The roll-off angle of the water droplets could not be measured accurately. This was due to the poor adhesion of the droplets to the surface which caused the droplets to immediately roll off with the slightest disturbance, e.g. the engagement of the tilt stage on the contact angle measurement system." The leaf surface was too non-adhesive for the tilt stage to produce a usable measurement, which the authors attribute to the poor adhesion of the droplets to the leaf surface.
In this study, Dropometer-derived WCA data function as the quantitative wetting metric used to track refoliated leaf non-wettability over time and to support comparisons against prior seasonal wettability datasets discussed by the authors.
The 2012 comparison series plotted in Figs. 3 and 4 are from Tranquada & Erb (2014), a prior publication. The remaining columns of Table 1 (papillae base diameter, peak-valley height, ECW height, length and platelet thickness) are SEM measurements.
Bring This Measurement Into Your Lab
If you need water contact angles on leaves or other highly water repellent surfaces, we can show you a sessile drop measurement on your samples.
Key Findings
High-WCA non-wettability during refoliation
During the July 18–August 26, 2021 study period, the paper reports average WCA values ranging from 139.7° ± 3.5° to 150.1° ± 1.9° (summarized in Supplementary Materials S7, Table S2).
Evidence of a superhydrophobic wetting state in mid-to-late July
The Results describe Fig. 2(b–c) as evidence that the leaf surface attained a superhydrophobic wetting state, with a measured WCA > 145°.
Rapid development of high water repellency after budbreak in the refoliation case
When comparing refoliated leaves (2021) to an initial growth-stage dataset from 2012 from Tranquada & Erb (2014), the paper states that leaves collected 2 days after budbreak (July 18, 2021) were already highly hydrophobic, and that the maximum average WCA after 13 days was 150.1° ± 1.9° (Table S2 in Supplementary Materials S7).
Different seasonal trend compared with a normal growth season comparison
In the comparison presented in Fig. 3, the paper reports that refoliated 2021 leaves maintained strong non-wettability until July 31, followed by a slight decrease of WCA in August; this is discussed alongside the seasonal “transition period” described for the 2012 dataset from Tranquada & Erb (2014)
WCA discussed alongside multi-scale surface structure development
The paper ties WCA behavior to surface structure development by discussing SEM-observed papillae and epicuticular wax (ECW) morphology through the refoliation period and presenting a correlation table (Table 1) linking micro/nano roughness metrics with wetting properties.
Figures & Visuals
What it shows
Shows example contact angles of individual water droplets on refoliated leaf surfaces for collection dates spanning July 18 through August 26, 2021.
What it shows
Compares average WCAs (with standard deviations) for the 2021 refoliation period against a same-calendar-window dataset from a normal growth season (2012).
What it shows
Compares average WCAs (with standard deviations) from the 2021 refoliation period against an initial growth and development phase dataset from 2012.
Why It Matters
In this paper, water contact angle is the primary quantitative metric used to assess non-wettability of refoliated aspen leaves and to track how that wetting behavior evolves across the refoliation period.
By combining Dropometer-based WCA measurements with SEM-based descriptions of papillae and epicuticular wax development, the authors connect wetting behavior to evolving dual-scale surface structure and use comparisons to prior seasonal datasets to frame how refoliation differs from a normal growth season.
Practical Takeaways
Leaf mounting approach for contact-angle testing
The Methods describe mounting leaves on 2 × 2 × 0.5 cm plexiglass coupons using double-sided tape to support WCA measurement on the adaxial surface.
Defined droplet volume and liquid for WCA
The paper reports dispensing 10 μL deionized water droplets for WCA measurements.
Replicate-based reporting of WCA
The paper reports at least 9 contact angle measurements per sample and presents averages with standard deviations.
Time-series wetting characterization during refoliation
WCA measurements were used to track refoliated leaf wetting behavior across multiple collection dates and to support comparisons to previously reported seasonal wettability datasets discussed in the Results.
Roll-off angle could not be measured on these surfaces
The paper reports that the roll-off angle could not be measured accurately on refoliated aspen leaves: droplets rolled off at the slightest disturbance, including engaging the tilt stage itself. If you are characterising very low-adhesion surfaces, expect roll-off angle to be the limiting measurement and plan a lower-disturbance approach.
Frequently Asked Questions
What did the Dropometer measure in this study?
The authors used a contact angle measurement system (Droplet Lab Dropometer) to measure water contact angles on the upper (adaxial) surface of refoliated quaking aspen leaves. Leaves were mounted on plexiglass coupons with double-sided tape, 10 μL deionized water droplets were dispensed, and at least 9 measurements per sample were averaged.
What water contact angles were reported for the refoliated leaves?
Average water contact angles over the July 18 to August 26, 2021 study period ranged from 139.7° ± 3.5° to 150.1° ± 1.9°. Leaves collected about 2 days after budbreak were already highly hydrophobic, and the authors report a superhydrophobic wetting state (above 145°) in late July, with leaves remaining highly non-wetting until the end of August.
How do the authors explain the high contact angles?
The authors relate the wetting behavior to SEM observations of microscale papillae covered with nanoscale epicuticular wax crystals, a hierarchical roughness that they say promotes Cassie-Baxter wetting. Table 1 sets the average water contact angle beside papillae and wax crystal dimensions for three dates in 2021.
Was the roll-off angle measured?
The authors report that the roll-off angle could not be measured accurately because droplets rolled off at the slightest disturbance, including engagement of the tilt stage. They attribute this to the poor adhesion of the droplets to the leaf surface.