Advance 1

The surface free energy of all materials was measured using highly polished surfaces (Sa <0.02 µm). Contact angle measurements were performed by a DSA25S (Krüss, Hamburg, Germany) using purified water and diiodomethane. Eight measurements were performed for each test liquid, each with a drop volume of 0.2 µl and a time interval of 30 s between application and measurement at 23 °C under air atmosphere [49 (link)]. The application was software-controlled using the manufacturer’s own DO3252 “Liquid Needle” dosing unit. Analyses were performed with the software “ADVANCE 1.11” (Krüss, Hamburg, Germany) by averaging the contact angles on both sides (fitting method: ellipse) and surface free energy (total, dispersive and polar parts) was calculated according to Owens and Wendt [50 (link)].

Sample surfaces were validated with confocal laser scanning microscopy (Keyence VK-X1000/1050, Keyence, Osaka, Japan) with a 50× objective (Nikon CF IC EPI Plan 50×; NA: 0.5; NIKON, Osaka, Japan) and a red laser (λ  =  661 nm). Five areas per sample were analyzed using the software “MultiFileAnalyzer” 2.1.3.89 (Keyence, Osaka, Japan), according to ISO 25178-2:2012 and appropriate filtering (S-Filter: 0.5 µm; F-Filter: 0.1 mm; Filter type: spline; end effect correction). For an analysis of the surface texture, the parameters of the arithmetical mean height (Sa), developed interfacial area ratio (Sdr), the auto-correlation length (Sal), and the skewness (Ssk) and the kurtosis (Sku) of the surface distribution were further surveyed.
The analysis of the surface free energy was performed on 15 samples via contact angle measurements. For this purpose, 0.5 µL each of purified water and diiodomethane was applied to the surface using a “DSA25S” with “Liquid Needle DO3252” and measured using “ADVANCE 1.11” (all KRÜSS, Hamburg, Germany) after a delay of 30 s (fitting method: ellipse). Following the advanced contact angle measurements, another 0.5 µL was added to the drops and measured again until a total volume of 2 µL was reached [31 (link)]. The total surface free energy as well as the polar and dispersive parts were calculated according to Owens and Wendt [32 (link)].

The hydrophobicity of root surfaces was determined by [25 (link),26 (link)], as follows: the cultivated rice root was placed on sterile filter paper until dry, followed by fixation onto the slide with double-sided tape. The contact angles were measured by the sessile drop method using a video-based optical contact angle measuring device DSA25 (Kruss, Germany). DDI water droplets (1.0 μL, n = 6) were deposited on the fixed roots in distances of a few millimeter. The shape of each drop was captured in a video sequence of which the contact angle after 5 s was evaluated using the Advance software (Kruss ADVANCE 1.7.2.1, Germany). Glass surfaces and polystyrene surfaces were evaluated as control.