Liquid-Liquid Phase Separation Induced by Vapor Transfer in Evaporative Binary Sessile Droplets

Drying of binary sessile droplets consisting of ethanol and octamethyltrisiloxane on a high-energy surface is investigated. During the process of evaporation, the droplets undergo liquid-liquid phase separation, resulting in the appearance of microdroplets at the liquid-air interface, which subsequently violently burst. This phase separation is attributed to water vapor transfer into the droplet, which modifies the solubility and leads to the formation of a ternary mixture. The newly formed ternary mixture may undergo nucleation and growth or spinodal decomposition, depending on the droplet composition path. By control of the relative humidity of air, phase separation can be mitigated or even eliminated. The droplets also display high mobility and complex wetting behavior due to phase separation, with two contracting and two spreading stages. The mass loss experiments reveal that the droplets undergo three distinct drying stages with an enhanced evaporation rate observed during the phase separation stage. A modified diffusion-limited model was employed to predict the evaporation rate, accounting for the physiochemical changes during evaporation and proved to be consistent with experimental observations. The findings of this work enhance our understanding of a coupled fundamental process involving the evaporation of multicomponent mixtures, wetting, and phase separation.

Recent advances in mixing-induced nanoprecipitation: from creating complex nanostructures to emerging applications beyond biomedicine

Mixing-induced nanoprecipitation (MINP) is an efficient, controllable, scalable, versatile, and cost-effective technique for the preparation of nanoparticles. In addition to the formulation of drugs, MINP has attracted tremendous interest in other fields. In this review, we highlight recent advances in the preparation of nanoparticles with complex nanostructures via MINP and their emerging applications beyond biomedicine. First, the mechanisms of nanoprecipitation and four mixing approaches for MINP are briefly discussed. Next, three strategies for the preparation of nanoparticles with complex nanostructures including sequential nanoprecipitation, controlling phase separation, and incorporating inorganic nanoparticles, are summarized. Then, emerging applications including the engineering of catalytic nanomaterials, environmentally friendly photovoltaic inks, colloidal surfactants for the preparation of Pickering emulsions, and green templates for the synthesis of nanomaterials, are reviewed. Furthermore, we discuss the structure-function relationships to gain more insight into design principles for the development of functional nanoparticles via MINP. Finally, the remaining issues and future applications are discussed. This review will stimulate the development of nanoparticles with complex nanostructures and their broader applications beyond biomedicine.

Aggregation of carboxyl-modified polystyrene nanoplastics in water with aluminum chloride: Structural characterization and theoretical calculation

Nanoplastics (NPs) pollution of aquatic systems is becoming an emerging environmental issue due to their stable structure, high mobility, and easy interactions with ambient contaminants. Effective removal technologies are urgently needed to mitigate their toxic effects. In this study, we systematically investigated the removal effectiveness and mechanisms of a commonly detected nanoplastics, carboxyl-modified polystyrene (PS-COOH) via coagulation and sedimentation processes using aluminum chloride (AlCl₃) as a coagulant. PS-COOH appeared as clearly defined and discrete spherical nanoparticles in water with a hydrodynamic diameter of 50 nm. The addition of 10 mg/L AlCl₃ compressed and even destroyed the negatively charged PS-COOH surface layer, decreased the energy barrier, and efficiently removed 96.6% of 50 mg/L PS-COOH. The dominant removal mechanisms included electrostatic adsorption and intermolecular interactions. Increasing the pH from 3.5 to 8.5 sharply enhanced the PS-COOH removal, whereas significant loss was observed at pH 10.0. High temperature (23 °C) favored the removal of PS-COOH compared to lower temperature (4 °C). High PS-COOH removal efficiency was observed over the salinity range of 0 - 35‰. The presence of positively charged Al₂O₃ did not affect the PS-COOH removal, while negatively charged SiO₂ reduced the PS-COOH removal from 96.6% to 93.2%. Moreover, the coagulation and sedimentation process efficiently removed 90.2% of 50 mg/L PS-COOH in real surface water even though it was rich in inorganic ions and total organic carbon. The fast and efficient capture of PS-COOH by AlCl₃ via a simple coagulation and sedimentation process provides a new insight for the treatment of NPs from aqueous environment.