Microbial extracellular polymeric substances (EPS) produced from wastewater are generally heterodispersed, which is expected to influence their flocculation performances and mechanism, particularly in mixed particle systems. The different molecular weight (MW) fractions should contribute to the overall adsorption affinity and flocculation mechanism of EPS in single and dual clay systems. EPS harvested from bioreactors were size-fractionated into high, medium and low MW fractions (HMW, MMW, LMW, respectively). The harvested mixed EPS and its fractions were characterised by diverse analytical techniques coupled with optical reflectometry to investigate the role of each EPS fraction in the overall flocculation mechanism of EPS in kaolinite and montmorillonite clay systems. In single clay systems, both the harvested mixed EPS and the HMW-EPS fraction showed comparable flocculation performances. However, mixed EPS proved to be more efficient than the HMW-EPS fraction for dual clay flocculation. Site blocking effects were observed in mixed EPS: the LMW and MMW EPS first adsorbed to the surface due to higher diffusivities and faster mass transfer to the interface, while the HMW-EPS were slowly transported but were attached to the surface irreversibly and stronger than the LMW/MMW-EPS. We propose from this, a mixed EPS adsorption mechanism: extended anionic polymer tails in solution, thereby enhancing particle flocculation.

Using the numerical model of Scheutjens and Fleer we investigated, on a self-consistent field level, the equilibrium structure of the neurofilament brush formed by the projection domains of NF-H, NF-M, and NF-L proteins. Although the actual amino-acid sequences in the projection domains are coarse-grained, the different (realistic) solubilities of amino-acid residues and the specific distribution of its intrinsic charges inside the arms of the NF proteins are taken explicitly into account. We collect strong evidence that the electrostatic interactions are a dominant force that controls the NF brush structure. There exists a remarkable spatial separation of the H, M, and L tails. In a dephosphorylated NF we found confined and flowerlike conformations for the H and M projection domains, respectively. We demonstrate that the ionization of KSP repeats in NF proteins triggers a conformational transition in the H tail that leads to the expulsion of its terminal (KEP) domain to the periphery of the NF brush. We argue that the phosphorylation of the NF proteins in axons can both increase the interfilament distance and stabilize cross bridges between neurofilaments.

Anion exchange membranes (AEMS) are particularly prone to fouling when employed to desalinate polymer flooding produced water (PFPW), an abundant sub-product from the oil and gas industry. The formation of fouling on an AEM will be affected by the composition of the solution, which includes various dissolved salts, partially hydrolyzed polyacrylamide (HPAM), crude oil, and surfactants. Electrodialysis experiments were performed to desalinate feed solutions with different compositions, aiming to distinguish between their individual and combined effects. The solutions contained diverse mono- and divalent ions. The analysis included data collected during the desalination and characterization of the fouled AEMs by diverse analytical techniques. HPAM produced the most severe effects in terms of visible fouling and increase of resistance. This polyelectrolyte fouls the AEM by adsorbing on its surface and by forming a viscous gel layer that hampers the replenishment of ions from the bulk solution. Ca and Mg have a large influence on the formation of thick HPAM gel layers, while the oily compounds have only a minimal influence acting mainly as a destabilizing agent. The membranes also presented scaling consisting of calcium precipitates. The effects of the gel layer were minimized by applying current reversal and foulant-free solution.

Hydrophilic and hydrophobic weak polybasic brushes immersed in aqueous solutions of mixed salt counterions are considered using a mean-field numerical self-consistent field approach. On top of the solvent quality of the polymer, the counterion–solvent interactions are accounted for by implementing Flory–Huggins interaction parameters. We show that ion specificity within the brush can bring about large changes in conformation. It is found that the collapse transition of hydrophobic, weak polyelectrolyte brushes features an intermediate two-phase state wherein a subset of chains are collapsed in a dense layer at the substrate, while the remainder of chains are well-solvated and strongly stretched away from the it. Besides pH and ionic strength, solvent quality of counterions and the composition of ions in the solvent are important control parameters for the behavior of polyelectrolyte brushes. Increasingly hydrophobic counterions penetrate deeper within the brush and stabilize the collapsed region, while hydrophilic counterions do the opposite.