Understanding the kinetic mixing between liquid crystalline nanoparticles and agrochemical actives.

The use of liquid crystalline nanoparticles as potential agrochemical delivery agents or adjuvant systems is gaining traction due to the possibility that the systems can enhance penetration of the active and increase adhesion of the formulation to the leaf, increasing overall efficacy and decreasing the harmful environmental impact. However the interaction between liquid crystalline nanoparticles and active products is not well understood. Using small angle X-ray scattering we investigated the structural changes that occur to liquid crystalline nanoparticles upon addition of three common herbicides, 2,4-D 2-ethylhexyl ester, bromoxynil octanoate and haloxyfop-p-methyl ester active agrochemicals in the form of emulsions. It was found that the hydrophobic herbicides induced structural changes to varying degrees when pre-mixed with liquid crystalline forming lipids (phytantriol and glycerol monooleate) and also during dynamic mixing as emulsions.

Tristearin as a Model Cuticle for High-Throughput Screening of Agricultural Adjuvant Systems.

The widely varied compositions and structures of plant cuticles create problems in the identification of suitable model systems for laboratory testing of adjuvants. We have compared the behavior of an extracted cuticle wax with tristearin, a well characterized crystalline triglyceride, which we propose as a model cuticle for ranking new adjuvant systems for their propensity to disrupt the cuticle barrier. The interaction of adjuvant products and their components with the extracted cuticle wax and tristearin was determined using differential scanning calorimetry and small angle X-ray scattering approaches. The interaction of the additive with tristearin caused a concentration-dependent change in the crystallite level, and correlated between the extracted wax and tristearin. Tristearin was subsequently used to compare the effectiveness of a range of adjuvant products and their major components. This approach has utility to quantify the effects of adjuvant components and enable more judicious selection of adjuvant candidates to progress to plant trials.

Kinetic Resolution of the Interactions between Agrochemical Products and Adjuvant Systems upon Mixing.

The addition of an adjuvant to a pesticide usually occurs in a mix-tank, before spray application to the crop. Their interaction is potentially crucial to overall efficacy but has received little attention from a physical-chemical perspective. Study was undertaken by laser diffraction, Raman spectroscopy, and small-angle X-ray scattering to resolve these physical processes. It was shown that migration of the pesticide into the adjuvant droplet occurred in all cases studied. The level of transfer was dependent upon adjuvant level, adjuvant solubility, and surfactant level. For suspension pesticides, dissolution of crystallites within the droplet occurred to a degree limited by solubility. The results directly demonstrate the transfer of the pesticide into the adjuvant carrier. This indicates that for emulsion-based pesticides, application to the target is likely as a homogeneously mixed droplet, whereas for suspension pesticides, solubility may limit transfer and dissolution, leading to heterogeneity in the applied particles.

Tailoring liquid crystalline lipid nanomaterials for controlled release of macromolecules.

Lipid-based liquid crystalline materials are being developed as drug delivery systems. However, the use of these materials for delivery of large macromolecules is currently hindered by the small size of the water channels in these structures limiting control over diffusion behaviour. The addition of the hydration-modulating agent, sucrose stearate, to phytantriol cubic phase under excess water conditions incrementally increased the size of these water channels. Inclusion of oleic acid enabled further control of swelling and de-swelling of the matrix via a pH triggerable system where at low pH the hexagonal phase is present and at higher pH the cubic phase is present. Fine control over the release of various sized model macromolecules is demonstrated, indicating future application to controlled loading and release of large macromolecules such as antibodies.