Wetting and surface properties of (modified) fluoro-silanised glass

Performance matching between the surface structure of cucumber powdery mildew in different growth stages and the properties of surfactant solution

BACKGROUND

Understanding performance matching of pesticide droplets on the surface of cucumber leaves modified by powdery mildew is of practical importance for the agricultural sector. Here, the surface texture and wettability of cucumber leaves covered by powdery mildew were systematically examined using parameters such as micromorphology, physicochemical properties, and liquid droplet contact angle measurements.

RESULTS

Our results show that powdery mildew growth can be divided into four distinct stages according to the surface texture characteristics of the diseased cucumber leaves. The three-dimensional (3D) surface structures of powdery mildew layers on cucumber leaves had individual characteristics at different mildew growth stages, among which powdery mildew was more easily spread in the last growth stage, and powdery mildew height was greatest in the NO. 2 growth stage (S_a  = 425.35 μm). Surface free energy values, static contact angle, and contact angle hysteresis all correlated strongly with the surface characteristics of powdery mildew layers at different growth stages. When the concentration of surfactant reached the critical micelle concentration, the wetting state of AEO-5 solution droplets on the surface of cucumber powdery mildew leaves reached the Wenzel state more easily. The wettability of a droplet on the leaf surface depends on the state of the monomer and micelle in the surfactant solution and the surface characteristics of the powdery mildew-covered leaf.

CONCLUSION

The 3D structure and relative dielectric constant of powdery mildew-covered leaves influenced surface texture characteristics, which in turn controlled the wetting and matching ability of surfactant droplets on diseased leaves. This work provides valuable new insights into the matching of the structure of powdery mildew-covered plant leaves with the properties of surfactant solutions. © 2021 Society of Chemical Industry.

Microfabrication and Surface Functionalization of Soda Lime Glass through Direct Laser Interference Patterning

All-purpose glasses are common in many established and emerging industries, such as microelectronics, photovoltaics, optical components, and biomedical devices due to their outstanding combination of mechanical, optical, thermal, and chemical properties. Surface functionalization through nano/micropatterning can further enhance glasses’ surface properties, expanding their applicability into new fields. Although laser structuring methods have been successfully employed on many absorbing materials, the processability of transparent materials with visible laser radiation has not been intensively studied, especially for producing structures smaller than 10 µm. Here, interference-based optical setups are used to directly pattern soda lime substrates through non-lineal absorption with ps-pulsed laser radiation in the visible spectrum. Line- and dot-like patterns are fabricated with spatial periods between 2.3 and 9.0 µm and aspect ratios up to 0.29. Furthermore, laser-induced periodic surface structures (LIPSS) with a feature size of approximately 300 nm are visible within these microstructures. The textured surfaces show significantly modified properties. Namely, the treated surfaces have an increased hydrophilic behavior, even reaching a super-hydrophilic state for some cases. In addition, the micropatterns act as relief diffraction gratings, which split incident light into diffraction modes. The process parameters were optimized to produce high-quality textures with super-hydrophilic properties and diffraction efficiencies above 30%.

Electrografting of alkyl films at low driving force by diverting the reactivity of aryl radicals derived from diazonium salts

Alkyl and partial perfluoroalkyl groups are strongly attached to carbon surfaces through (i) the abstraction of the iodine atom from an iodoalkane by the sterically hindered 2,6-dimethylphenyl radical and (ii) the reaction of the ensuing alkyl radical with the carbon surface. Since the 2,6-dimethylphenyl radical is obtained at -0.25 V/Ag/AgCl by reducing the corresponding diazonium salt, the electrografting reaction is facilitated by ∼1.7 V by comparison with the direct electrografting of the iodo compounds. Layers of various thicknesses, including monolayers, are obtained by controlling the time duration of the electrolysis. The grafted films are characterized by electrochemistry, IR, XPS, ellipsometry, and water contact angles.

Quantification of physical (roughness) and chemical (dielectric constant) leaf surface properties relevant to wettability and adhesion

BACKGROUND

Spray droplet adhesion is dependent not only on formulation and droplet parameters but also on the surface properties (physical and chemical) of the leaf. Quantifying these leaf surface properties would aid understanding and modelling of adhesion, helping to optimise spray formulations. Fractal dimensions (FDs) were used to quantify the relative leaf surface roughness of ten plant species. Static droplet contact angles were measured on each leaf surface, and wetting tension was calculated. Chemical profiles of the leaf surfaces were developed by evaluating contact angle behaviour relative to solution dielectric constants.

RESULTS

The FDs of Cryo-SEM micrographs taken at 300× magnification gave the best correlation with adhesion. The wetting tension intercept had a strong relationship with mean adhesion, and successfully accounted for the wettability of the outlier species.

CONCLUSIONS

The microroughness of the leaf surface, as revealed by Cryo-SEM, can be quantified by fractal dimension analysis. However, the wetting tension intercept is a more useful universal measure of the surface properties of the leaf (including roughness) as they pertain to adhesion. The slope of the wetting tension versus dielectric constant plot allowed preliminary quantification of the chemical contribution of leaf surface dielectric behaviour to adhesion.

High extinction polarimeter for the precision measurement of the in-plane optical anisotropy of molecular monolayers

A polarimeter using selected Glan-Thompson polarizers, a spatially filtered probe laser beam, precision polarizer orientation, and spatially filtered output coupling into an optical fiber achieves a static extinction ratio between crossed and parallel polarizer and analyzer orientations of I(perpendicular)/I(parallel) approximately = 2 x 10(-10). This instrument allows the detection of retardance as small as 0.0015 nm to better than 1%, enabling the first detailed study of the in-plane birefringence of molecular monolayers. We demonstrate the performance of the polarimeter with measurements of the photoinduced birefringence of azobenzene-based monolayers self-assembled on glass.