Boundary Lubrication of PEO-PPO-PEO Triblock Copolymer Physisorbed on Polypropylene, Polyethylene, and Cellulose Surfaces

Recent advances on microplastics pollution and removal from wastewater systems: A critical review

Microplastics (MPs) (plastic particles <5 mm) are globally acknowledged as a serious emerging micropollutant, which passes through various pathways in natural habitats and eventually ends up in our food chain. In this context, the present study critically reviews recent advances in MPs sampling and detection, occurrence, fate, and removal in wastewater treatment plants (WWTPs) by delineating their characteristics that manifest toxicity in the environment via effluent discharge. While there is currently no standard protocol in place, this work examined and compared the latest approaches adopted for improved sampling, sample processing, and characterization of MPs via fluorescence imaging and certified reference materials for method validation. MPs concentration from different sources in the WWTPs varies considerably ranging between 0.28 and 18285 MPs/L (raw wastewater), 0.004-750 MPs/L (effluent), and 0.00023-10380 MPs/kg (sludge). Assessment of MPs removal efficiency across different treatment stages in various in WWTPs has been performed and elucidated their removal mechanisms. The overall MPs removal efficiency in primary, secondary, and tertiary treatment stages in WWTPs reported to be around 57-99%, 78.1-99.4%, and 90-99.2%, respectively. Moreover, the review covers advanced treatment methods for removing MPs, including membrane bioreactors, coagulation/flocculation, ultrafiltration, rapid sand filtration, ozonation, disc filtration, and reverse osmosis, which have been found to be highly effective (>99%). Membrane bioreactors have been proclaimed to be the most reliable secondary treatment technique for MPs removal. Coagulation (92.2-95.7%) followed by ozonation (99.2%) as a tertiary treatment chain has been demonstrated to be the most efficient in removing MPs from secondary-treated wastewater effluent. Further, the review delineates the effect of different treatment stages on the physical and chemical characteristics of MPs, associated toxicity, and potential impact factors that can influence the MPs removal efficiency in WWTPs. Conclusively, the merits and demerits of advanced treatment techniques to mitigate MPs pollution from the wastewater system, research gaps, and future perspectives have been highlighted.

Effects of Ozone Fumigation on the Main Postharvest Pathogenic Fungi Penicillium sp. and the Storage Quality of Blueberry in Majiang County, China

In this study, the fungus Penicillium sp. was isolated from rotting postharvest blueberry fruits at different storage stages and identified into genera. Inoculation of this strain on the surface of fresh fruits was able to cause rotting. The strain was then used as a reference strain to test the chemical control effect of ozone fumigation during storage. The results showed that ozone fumigation had an obvious inhibitory effect on Penicillium sp. in a dose- and time-dependent manner. Meanwhile, ozone fumigation treatment could prevent the loss of fruit firmness, slow down the decrease of soluble solids, total phenolics, and anthocyanins, and maintain a lower activity of PPO and higher activities of POD and CAT. As far as we know, this is the first report on the effects of ozone fumigation on the postharvest pathogenic fungi Penicillium sp. and on the storage quality of postharvest blueberry collected from Majiang County, Guizhou province, China.

Hydroxyl Influence on Adsorption and Lubrication of an Ultrathin Aqueous Triblock Copolymer Lubricant

This research aims to provide insights into the adsorption behaviors of two monomers of triblock copolymers (1,2-dimethoxyethane (1,2-DME) and 1,2-dimethoxypropane (1,2-DMP)) on a TiO₂ surface in aqueous solution. A multiscale theoretical framework by means of the density functional theory (DFT), ab initio molecular dynamics (AIMD), and classical molecular dynamics (MD) simulations is established. The DFT calculation confirms that these molecules adsorb more energetically on a hydroxylated surface than pure oxide. There is a difference in adsorption behaviors between 1,2-DMP and 1,2-DME molecules due to the covalent bonding between carbons and oxygen of the hydroxylated TiO₂ surface. The AIMD simulation reveals that the adsorption of both copolymers to the TiO₂ surface is hindered by the presence of water with 1,2-DME exhibiting a weaker adsorption than 1,2-DMP. The presence of 1,2-DME on the TiO₂ surface with water produced a smaller number of hydroxyl groups on the surface than 1,2-DMP. Moreover, the dissociative adsorption of water onto the rutile surface is the main cause for a chemical formation of terminating hydroxyl groups. The number of associated bonds is insignificant compared to the dissociated one since the dissociative adsorption is more favored than the associative one. MD simulation indicates that triblock copolymers adsorb stronger on the hydroxylated surface with a thinner adsorbed film thickness than that on the pure rutile. The presence of terminal hydroxyl groups on the rutile surface helps reducing the friction for aqueous 17R2 triblock copolymers, while it results in an increase of friction for normal copolymer L62.

Probing the frictional properties of soft materials at the nanoscale

The understanding of friction in soft materials is of increasing importance due to the demands of industries such as healthcare, biomedical, food and personal care, the incorporation of soft materials into technology, and in the study of interacting biological interfaces. Many of these processes occur at the nanoscale, but even at micrometer length scales there are fundamental aspects of tribology that remain poorly understood. With the advent of Friction Force Microscopy (FFM), there have been many fundamental insights into tribological phenomena at the atomic scale, such as 'stick-slip' and 'super-lubricity'. This review examines the growing field of soft tribology, the experimental aspects of FFM and its underlying theory. Moving to the nanoscale changes the contact mechanics which govern adhesive forces, which in turn play a pivotal role in friction, along with the deformation of the soft interface and dissipative phenomena. We examine recent progress and future prospects in soft nanotribology.

Friction-Active Surfaces Based on Free-Standing Anchored Cellulose Nanofibrils

A specific feature of fibrous surfaces is the dependence of their mechanical properties on the alignment of the fibers. Vertically aligned fibers enhance friction and adhesion, whereas horizontal fibers are known to act as a lubricant reducing the friction. Many plants form a specific fibrous mucilage cover around their seeds upon hydration. This mucilage consists of cellulose, hemicelluloses, and strongly hydrophilic pectins. We show that the controlled critical-point drying of hydrated seed mucilage of three exemplary seed mucilage-rich plant species results in the exposure of free-standing cellulose nanofibers with a very high aspect ratio and anchored to the seed surface. The structural dimensions of the cellulose nanofibers are similar to the vertically aligned carbon nanotubes and the contact elements in the adhesion system of the gecko that show an outstanding high dry friction and adhesion. Tribological experiments demonstrate very high average friction coefficients when sliding a smooth and stiff probe over the surface of such arrays of dry free-standing cellulose nanofibrils in the range from 1.4 to 1.8. The high friction values most likely arise from bending of the single cellulose fibers and their alignment with the counterpart surface in close contact. We suggest the potential of free-standing cellulose nanofibrils of plant seed mucilage as a natural and ecologically friendly material where high contact forces to surfaces in dry environments are desired.

Micelles, mixed micelles, and applications of polyoxypropylene (PPO)-polyoxyethylene (PEO)-polyoxypropylene (PPO) triblock polymers

This review gives a brief outline of various micellar properties of triblock polymers such as critical micellization concentration, critical micellization temperature, and microviscosity. Detailed discussion of the effect of temperature on micellar properties of various triblock polymer mixtures is given. Applications of triblock polymers in solubilization as drug delivery agents, as nano drug, for the synthesis of gold nanoparticles, for cobalt determination, etc. are discussed.