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Microplastics and per- and polyfluoroalkyl substances (PFAS) are two of the most notable emerging contaminants reported in the environment. Micron and nanoscale plastics possess a high surface area-to-volume ratio, which could increase their potential to adsorb pollutants such as PFAS. One of the most concerning sub-classes of PFAS are the perfluoroalkyl carboxylic acids (PFCAs). PFCAs are often studied in the same context as other environmental contaminants, but their amphiphilic properties are often overlooked in determining their fate in the environment. This lack of consideration has resulted in a diminished understanding of the environmental mobility of PFCAs, as well as their interactions with environmental media. Here, we investigate the interaction of PFCAs with polyethylene microplastics, and identify the role of environmental weathering in modifying the nature of interactions. Through a series of adsorption–desorption experiments, we delineate the role of the fluoroalkyl tail in the binding of PFCAs to microplastics. As the number of carbon atoms in the fluoroalkyl chain increases, there is a corresponding increase in the adsorption of PFCAs onto microplastics. This relationship can become modified by environmental weathering, where the PFCAs are released from the macro and microplastic surface after exposure to simulated sunlight. This study identifies the fundamental relationship between PFCAs and plastic pollutants, where they can mutually impact their thermodynamic and transport properties. 

Colloidal suspensions are an ideal model for studying crystallization, nucleation, and glass transition mechanisms, due to the precise control of interparticle interactions by changing the shape, charge, or volume fraction of particles. However, these tuning parameters offer insufficient active control over interparticle interactions and reconfigurability of assembled structures. Dynamic control over the interparticle interactions can be obtained through the application of external magnetic fields that are contactless and chemically inert. In this work, we demonstrate the dual nature of magnetic nanoparticle dispersions to program interactions between suspended nonmagnetic microspheres using an external magnetic field. The nanoparticle dispersion simultaneously behaves as a continuous magnetic medium at the microscale and a discrete medium composed of individual particles at the nanoscale. This enables control over a depletion attractive potential and the introduction of a magnetic repulsive potential, allowing a reversible transition of colloidal structures within a rich phase diagram by applying an external magnetic field. Active control over competing interactions allows us to create a model system encompassing a range of states, from large fractal clusters to low-density Wigner glass states. Monitoring the dynamics of colloidal particles reveals dynamic heterogeneity and a marked slowdown associated with approaching the Wigner glass state. 

Competition between attractive and repulsive interactions drives the formation of complex phases in colloidal suspensions. A major experimental challenge lies in decoupling independent roles of attractive and repulsive forces in governing the equilibrium morphology and long-range spatial distribution of assemblies. Here, we uncover the ‘dual nature’ of magnetic nanoparticle dispersions, particulate and continuous, enabling control of the short-range attraction and long-range repulsion (SALR) between suspended microparticles. We show that non-magnetic microparticles suspended in an aqueous magnetic nanoparticle dispersion simultaneously experience a short-range depletion attraction due to the particulate nature of the fluid in competition with an in situ tunable long-range magnetic dipolar repulsion attributed to the continuous nature of the fluid. The study presents an experimental platform for achieving in situ control over SALR between colloids leading to the formation of reconfigurable structures of unusual morphologies, which are not obtained using external fields or depletion interactions alone.

 

Solvent evaporation in unpinned droplets of colloidal suspensions leads to the formation of porous shells which buckle under the pressure differential imposed by drying. We investigate the role of aspect ratio of rod-shaped particles in suppressing such buckling instabilities. Longer, thinner rods pack into permeable shells with consequently lower Darcy's pressure and thus avoid buckling.