Search

Shiftsof the critical coagulation concentration (CCC) in particlesuspensions in salt solutions containing multivalent co-ions and monovalentcounterions are rationalized. One observes that the CCC is inverselyproportional to the valence, and this behavior is referred to as theinverse Schulze–Hardy rule. This dependence is establishedby means of measurements of the stability ratio for positively andnegatively charged latex particles with time-resolved light scattering.The same dependence is equally suggested by calculations of the CCCwith the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, wherebythe full Poisson–Boltzmann equation for the asymmetric electrolyteshas to be used. The latter aspect is essential, since in the caseof multivalent co-ions the surface charge is principally neutralizedby monovalent counterions. This rule complements the classical Schulze–Hardyrule, which applies in the case of multivalent counterions, and statesthat the CCC is inversely proportional to the sixth power of the valence. [ABSTRACT FROM AUTHOR]

Thin-film composite reverse osmosis membranes have remained the gold standard technology for desalination and water purification for nearly half a century. Polyamide films offer excellent water permeability and salt rejection but also suffer from poor chlorine resistance, high fouling propensity, and low boron rejection. We addressed these issues by molecularly designing a polyester thin-film composite reverse osmosis membrane using co-solvent-assisted interfacial polymerization to react 3,5-dihydroxy-4-methylbenzoic acid with trimesoyl chloride. This polyester membrane exhibits substantial water permeability, high rejection for sodium chloride and boron, and complete resistance toward chlorine. The ultrasmooth, low-energy surface of the membrane also prevents fouling and mineral scaling compared with polyamide membranes. These membranes could increasingly challenge polyamide membranes by further optimizing water-salt selectivity, offering a path to considerably reducing pretreatment steps in desalination.

Ion-selective optical microsensors based on surface-modified polystyrene (PS) beads with positively charged lipophilic solvatochromic dye (SD) on the surface were studied with K + as model ion. Water-soluble SDs are expelled into the aqueous phase by ion exchange with the cationic analyte of interest, resulting in a detectable color change. In contrast, lipophilic SDs are more attractive, as they appear to remain anchored to the surface after expulsion from the sensing phase. This transfers just the ionic chromophore functionality into the aqueous phase and allows the system to act as a reversible, truly self-contained sensor. In this work this mechanism was evaluated with ζ-potential measurements on microsensor suspensions. It indeed provides experimental evidence for the mechanism of SD transfer, as a reversal of the ζ-potential of the PS microsensors was observed for higher potassium concentrations with valinomycin-doped microspheres. For a discriminated ion such as sodium, the ζ-potential change occurs at much higher electrolyte concentrations, in agreement with sensor selectivity. Undoped microspheres showed no apparent dependence of ζ-potential on electrolyte concentration. The study also shows that the effective range of microsensor surface charge is tunable and depends on the concentration of the SD on the coating phase., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)