Aqueous dispersions of lipid nanoparticles wet hydrophobic and superhydrophobic surfaces

Effects of tank-mix adjuvants on physicochemical properties and dosage delivery at low dilution ratios for unmanned aerial vehicle application in paddy fields

BACKGROUND

Unmanned aerial vehicles (UAVs) have been developed to improve the efficiency of pesticide applications, and they are now widely utilized in Asia. The deposition and retention periods of pesticides on plant surfaces present serious challenges for modern precision agriculture, as these factors directly affect pesticide bioavailability, efficacy, and loss. Tank-mix adjuvants have been utilized to improve pesticide performance, but their effects on physicochemical properties and dosage delivery at low dilutions are not well understood.

RESULTS

We found that different tank-mix adjuvants affected droplet impact behavior, the wetting and spreading of spray dilutions, and pesticide deposition on rice leaves by changing the physicochemical properties of spray dilutions. The adjuvant methyl oxirane polymer with oxirane, mono (3,5,5-trimethylhexyl) ether (adjuvant c) significantly reduced the dynamic surface tension of the spray dilution and inhibited the rebound of large droplets (D₀  = 2 ± 0.2 mm) and spray droplets (0.2 MPa with a LU-01 nozzle) on rice leaves, and improved the wetting and spreading performance of the spray dilution on rice leaves. Field tests showed that adjuvant c could significantly increase the deposition of chlorantraniliprole on rice leaves.

CONCLUSION

Overall, the use of appropriate tank-mix adjuvants at low dilution ratios for UAV application in paddy fields can improve the performance of spray dilutions, increase the effective deposition and wetting spread of pesticides on rice leaves, further reduce the dosage of pesticide products and improve pesticide utilization. © 2022 Society of Chemical Industry.

Eco-friendly Water-Based λ-Cyhalothrin Polydopamine Microcapsule Suspension with High Adhesion on Leaf for Reducing Pesticides Loss

Recently, innovations of nano/microcarrier formulations have been focused on improving application efficiencies and retention time. In this study, a water-based 2.5% λ-cyhalothrin (LC) microcapsule suspension (CS) was developed by orthogonal test with biodegradable and adhesive polydopamine (PDA) microcapsules (MCs) as carriers. The obtained LC-PDA CS had good suspension properties, flow behavior, storage stability, and rheological properties. LC-PDA CS had higher retention, wettability, and decreased rainwater washing out on the leaves than commercial CS. LC-PDA CS displayed higher insecticidal activity against Lipaphis erysimi compared to commercial CS. LC-PDA CS reduced the toxicity of LC to the aquatic organism Danio rerio compared to LC. The above results demonstrated that LC-PDA CS would be eco-friendly water-based pesticides carrier system for prolonging the retention time on target leaf and reducing toxicity to aquatic organisms.

Multifunctionalized Cellulose Nanofiber for Water-Repellent and Wash-Sustainable Coatings on Fabrics

A new synthetic route was developed to modify cellulose nanofiber for water-repellent coatings with great sustainability after multiple washing cycles. Multiple functional groups were grafted on 2,2,6,6-tetramethylpiperidine 1-oxyl radical (TEMPO)-oxidized cellulose nanofibers (TOCN) to achieve superhydrophobic performance and strong adhesion on cotton cloth. First, hexadecylamine (HDA) was used to modify TOCN surface into hydrophobic derivatives via amidation. The amidation-modified TOCN (AMT) were then grafted with a polyisocyanate cross-linking agent (PCA). The final multimodified TOCN (MMT) had hydrophobic alkyls and isocyanate groups on the surface. These surface functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). After spraying the MMT suspension on cotton fabrics, the isocyanate groups would react with hydroxyl groups on cotton fibers, leading to a uniform conformal layer of MMT on fabric surfaces. The MMT coating showed great water repellence and washing sustainability. A large contact angle of 150° and a small sliding angle of ∼10° were observed. The superhydrophobic performance retained even after 10 laundry washing cycles. Several examples were also demonstrated to show the capability and the possibility of applying this coating material for water-repellent applications.

Difunctional Fluorescence Nanoparticles for Accurate Tracing of Nanopesticide Fate and Crop Protection Prepared by Flash Nanoprecipitation

Facile fabrication of difunctional nanoparticles (NPs) for pesticide delivery and imaging is still a fascinating challenge. Here, water-dispersible difunctional NPs were developed using flash nanoprecipitation (FNP) where self-assembling amphiphilic block copolymers were used to encapsulate a highly hydrophobic model pesticide, Lambda-cyhalothrin, and the fluorescent dye Nile red. The particle size (ranging from 158 to 280 nm) and fluorescence property of NPs could be controlled by varying the flow rate or Nile red feed concentration. The aggregation state and rearrangement of the dye molecules in the NPs were also investigated. IVIS imaging and confocal laser scanning microscopy analysis demonstrated that the resulting difunctional nanopesticide particles could allow accurate in situ tracking of the pesticide on the leaf surface, while effectively avoiding interference from chlorophyll autofluorescence. The difunctional NP suspension maintained high insecticidal activity and stability. This work demonstrates the feasibility and great potential of the FNP method in universal fabrication of multifunctional NPs with in situ pesticide tracing and crop protection capabilities.

Interaction Forces between Water Droplets and Solid Surfaces across Air Films

Wetting of solid surfaces occurs when the intervening air film between a water droplet and a solid surface ruptures. Although this rupturing phenomenon is well known, the underlying mechanism has not yet been well understood. In this work, the rupture of intervening air films is systematically studied by measuring the spatiotemporal thickness profiles of the air films between droplets of deionized water and flat solid surfaces using a synchronized triwavelength reflection interferometry microscope. It has been shown that the critical rupture thickness of the air film (h _c) depends on the surface hydrophobicity of solid surfaces. The h _c value was increased from 50 nm on a hydrophobic surface having an equilibrium water contact angle (θ_w) of 96° to 1.42 μm on a hydrophilic surface having a θ_w of 25°. In addition, an increase in the critical rupture thickness with decreasing surface hydrophobicity was found to be applicable not only to chemically treated quartz surfaces but also to a variety of natural mineral surfaces. By determining the pressure within the air films, we have shown that a strong attractive force is present between water droplets and hydrophilic surfaces, thereby accelerating the draining of air films. The measured forces might be of electrostatic origin, and the forces become less attractive with increasing hydrophobicity of solid surfaces. The present result provides a fundamental insight into the rupture of air films from the perspective of surface forces.

Fabrication of Hydrophobic Coatings Using Sugarcane Bagasse Waste Ash as Silica Source

Eco-friendly hydrophobic coatings were fabricated on tiles via the drop-casting process. Sugarcane bagasse waste ash (SBA) was used as a silica source and dimethyldiethoxysilane (DMDEOS) was used as a surface functionalizing agent. The elemental composition of SBA was measured using X-ray fluorescence (XRF) and energy-dispersive spectroscopy (EDS) techniques. The surface morphology of SBA was analyzed through the field-emission scanning electron microscopy (FESEM) technique. The surface wettability of SBA coated tiles was evaluated by determining the static water contact angle (WCA). XRF studies showed that the impurities were removed, and the silica content was enriched by the acid treatment. SBA coated tiles showed good hydrophobicity with a WCA of 135°. The high hydrophobicity of the coated tiles may be attributed to the increase of surface roughness by SBA. Moreover, the SBA coating was successfully tested on various substrates such as tiles, brick, glass, and cotton cloth. SBA coated glass substrate was more durable compared to other substrates at normal room temperature.