A combined theoretical and experimental study is presented to investigate the interplay of forces in the spin-dewetting process in order to achieve enhanced control over droplet generation. In this regard, toluene–polystyrene (PS) film is spin dewetted on a solid substrate to generate an array of droplets. The underlying mechanisms of the spin dewetting of the films into the droplets are explained with the help of a theoretical model followed by a long-wave linear stability analysis (LWLSA). Stabilizing forces like solution viscosity and surface tension play essential roles. The study uncovers that the centripetal force stretches the film radially outward, before it becomes ultrathin and undergoes dewetting under the influence of van der Waals forces, while the surface tension force acts as a stabilizing influence. On the other hand, the viscous force kinetically stabilizes the system to expedite or delay drop formation on the substrate. An imbalance of these factors ultimately decides the droplet spacing, which leads to interesting morphologies such as singlet, doublet, triplet, and clusters of droplets at specific PS concentrations in the range 0.0001–0.0005%, with a ~10–14 nm average droplet height. The experimental data revealed that, at ~3000 rpm, PS (0.01–0.1%) results in critical droplet spacings of λ_max~98–172 μm, leading to immediate dewetting and uniform droplet formation. Our theoretical predictions are in close agreement with the experimental results, validating the present model. The insights gained in this work provide a foundation by presenting a robust framework for controlled droplet generation by optimizing process parameters to achieve the desired droplet size, distribution, and uniformity. The findings have broad applications in material science, biomedical engineering, and related disciplines.

The growing contamination of water bodies by micro- and nanoplastics (MNPs) and oil pollutants poses a critical challenge to environmental sustainability, public health, and the efficiency of present-day wastewater treatment technologies. Because conventional separation techniques generally target only a single class of pollutants and often rely on petroleum-based materials or toxic fabrication routes, there is a pressing need for sustainable, multifunctional purification systems. This study addresses that gap by developing an environmentally benign cellulose acetate (CA)-based composite membrane capable of simultaneously removing both MNPs and oil contaminants from water. A biodegradable CA membrane was fabricated using a modified non-solvent induced phase separation (NIPS) technique. To enhance adsorption capabilities and broaden pollutant selectivity, the CA matrix was functionalized with tannic acid (TA), chitosan (CH), and activated charcoal (AC) in a single-step synthesis. These natural and carbonaceous additives create hierarchical porosity, reduce hydrophobicity, and introduce multiple interaction sites, allowing the membrane to operate by synergistic mechanisms rather than single-mode filtration. Comprehensive morphological and chemical characterizations—FESEM, EDX, MATLAB image analysis, and FTIR—verified uniform dispersion of TA, CH, and AC throughout the CA matrix. Structural analysis showed an average pore radius of ~33 nm, enabling both size-based and adsorption-based capture. Chemical spectroscopy confirmed strong interfacial bonding, including hydrogen bonding, π–π stacking, hydrophilic interactions, and electrostatic coupling between CA and the incorporated additives. The separation performance of the CA–TA–CH–AC membrane was evaluated under flow-through conditions for both microplastic (30 µm) and nanoplastic (200 nm) polystyrene particles. Removal efficiencies exceeded 90% at higher membrane bed heights, driven by extended contact time and increased interaction pathways. FESEM imaging provided direct visual evidence of captured plastics embedded within membrane pores and adhered across the surface, confirming robust adhesion and mechanical stability during continuous filtration. The synergy of TA (π–π and hydrogen bonding), CH (electrostatic attraction and hydrophilicity), and AC (surface adsorption and van der Waals forces) is reflected in the high capture efficiency across particle sizes. In addition to plastic remediation, the composite membrane also demonstrated >90% demulsification efficiency for olive-oil-in-water emulsions. The dominant mechanisms include hydration-layer-mediated oil rejection through hydrophilic TA and CH domains, and droplet adsorption on the high-surface-area AC microstructure. These results confirm that both oil and polymeric contaminants can be passively removed in a single step without requiring surfactants or external energy inputs. Building upon these outcomes, the work proposes a layered membrane filtration device incorporating gradient functionality—pristine CA, CA–TA, CA–CH, and CA–AC—to sequentially achieve size exclusion, hydrophobic/π–π binding, electrostatic capture, and final adsorption polishing. This modular approach enables targeted contaminant removal, ease of regeneration, and long-term durability, establishing a scalable pathway toward advances in broad-spectrum water purification. In conclusion, this research presents a green, scalable, and multifunctional CA-based membrane platform capable of simultaneous MNP and oil contaminant separation using synergistic physicochemical interactions. The developed system aligns with principles of sustainable materials engineering and offers potential for expansion toward the removal of dyes, heavy metals, pharmaceuticals, and other emerging pollutants.

This research examines partial dewetting and labyrinthine morphologies in thin polystyrene (PS) films using a ternary solvent mixture of water, acetone, and methyl ethyl ketone (MEK) (15:3:7 by volume). The films are initially glassy but destabilize due to the solvent into mixed structures containing labyrinth-like patterns and holes, not droplets. Morphological changes result from solvent–nonsolvent interactions. MEK is a good solvent that swells the film, lowers the glass transition temperature, and increases chain mobility, while acetone, as a cosolvent, provides uniform solvent uptake, and water as a nonsolvent reduces film–substrate affinity and promotes spreading-driven dewetting. The opposing influence of these factors leads to viscosity gradients that drive heterogeneous nucleation of holes, their growth to large size, and partial coalescence. The process ends before equilibrium is reached as rapid evaporation of MEK balances driving forces with viscosity, and traps intermediate structures. The physics behind the existence or a mechanical pathway to intermediate structures is provided by studies of the spreading coefficient and hole growth. This work demonstrates engineering solvent mixtures for controlled non-equilibrium surface patterning in polymer thin films.