RESUMEN
The steric stability of inorganic colloidal particles in an apolar solvent is usually described in terms of the balance between three contributions: the van der Waals attraction, the free energy of mixing, and the ligand compression. However, in the case of nanoparticles, the discrete nature of the ligand shell and the solvent has to be taken into account. Cadmium selenide nanoplatelets are a special case. They combine a weak van der Waals attraction and a large facet to particle size ratio. We use coarse grained molecular dynamics simulations of nanoplatelets in octane to demonstrate that solvation forces are strong enough to induce the formation of nanoplatelet stacks and by that have a crucial impact on the steric stability. In particular, we demonstrate that for sufficiently large nanoplatelets, solvation forces are proportional to the interacting facet area, and their strength is intrinsically tied to the softness of the ligand shell.
RESUMEN
Capillary zone electrophoresis (CZE) of gold nanoparticles (Au NPs) was investigated in terms of dispersion stability during the analysis process. It was shown that CZE of Au NPs can be performed under dynamic coating conditions depending on the background electrolyte (BGE) composition. The influence of both the co-ion and counter-ion in the BGE was evaluated. It was proven that the application of relatively large buffering counter-ions provides steric stability to NPs during CZE. Among the investigated co-ions, citrate and MOPS were found to be advantageous for the CZE of Au NPs. On the other hand, the presence of zwitterionic substances and multiply charged counter-ions in BGE was shown to promote the aggregation and adsorption of the NPs to the capillary wall. A correlation between the particle stability in CZE and isotachophoresis (ITP) performance was observed and discussed. A sensitivity improvement by two orders of magnitude was achieved using the developed ITP methods.
RESUMEN
The utilization of increased dosage of insect repellents to overcome mosquito resistance has raised environmental concerns globally. In accord to this, we have formulated an efficacious, water-dispersive, nanometric formulation of a poor water-soluble insect repellent, diethylphenylacetamide (DEPA) by poly(ethylene glycol) (PEG) polymerization followed by PIT emulsification method. The critical micelle concentration of PEG in the spontaneously emulsified conventional DEPA droplets was determined, based on the droplets physical stability. Subjecting them to PIT emulsification yielded monodispersed polymeric nanomicelles of DEPA (Nano DEPA) with hydrodynamic mean diameter of 153.74 nm. The high-resolution scanning and transmission electron microscopic studies revealed the characteristic core-shell structure of micelle. The comparative efficacy of Bulk DEPA and Nano DEPA was evaluated by larvicidal and WHO cone bioassay against the Japanese encephalitis vector Culex tritaeniorhynchus. The median lethal concentrations (48 h) for 3rd instars C. tritaeniorhynchus larvae were found to be 0.416 mg/L for Bulk DEPA and 0.052 mg/L for Nano DEPA, respectively. The median knockdown concentrations (60 min) for the two to three-day-old, sucrose-fed, female adult mosquitoes were 5.372% (v/v) and 3.471% (v/v) for Bulk and Nano DEPA, respectively. Further investigation by histopathological and biochemical studies propound that Nano DEPA exerted better bioefficacy as comparative to its bulk form even at minimal exposure concentrations. Hence, Nano DEPA will serve as an effective alternate in controlling the vector expansion with reduced dosage.