Reversible Binding of Multivalent Ions by Surfactant Self-Assembly

Abstract

High molecular weight nonionic surfactants have been chemically modified to bind multivalent ions reversibly by using a moderate temperature stimulus as an on/off mechanism. Only above the critical micellization temperature (CMT) does binding of multivalent ions take place, whereas below the CMT, no binding occurs to the free surfactant molecules. Different calorimetric techniques have been used to prove the reversible binding of multivalent ions. This tunable binding of multivalent metal ions allows for the improvement of many ion-exchange processes and offers attractive opportunities in the biomedical field.

Reversible Calcium(II)‐Ion Binding through an Apparent pKa Shift of Thermosensitive Block‐Copolymer Micelles

“…Apromising approach is the use of smart polymer systems in which at hermal trigger is used as as witch between the adsorption and desorption of multivalent ions,s uch as calcium(II). [7] Af ew examples have been reported in which the lower critical solution temperature (LCST) of poly(Nisopropyl acrylamide) (PNIPAAm) is used to switch between adsorption and desorption. [8] However,most of these systems deal with ion adsorption at elevated temperatures (40-50 8 8C) and ion desorption at ambient temperature levels (10-20 8 8C) and are thus not practical for many applications,s ince ions often need to be adsorbed from natural water sources, generally found at ambient temperature levels.Furthermore, for systems based on athermal switch, it would be ideal to use wastewater streams with slightly elevated temperatures for regeneration.…”

Multiresponsive Behavior of Functional Poly(p-phenylene vinylene)s in Water

“…Therefore, PDTriG was employed as it has a higher load of carboxylic acid groups. The polymer was solubilized in basic solution so that the carboxylic acid groups were present as carboxylate groups, which are known to bind with calcium(II) ions in a 2:1 fashion [60,61,62]. Upon addition of half an equivalent of calcium(II) ions compared to the carboxylate groups, all polymer precipitated out of solution, ascribed to interpolymer crosslinking by calcium(II)–carboxylate coordination as schematically depicted in Scheme 2.…”

Reversible Calcium(II)‐Ion Binding through an Apparent pKa Shift of Thermosensitive Block‐Copolymer Micelles

“…In a previous study, we found that divalent calcium(II) ions do not bind to isolated carboxylate groups 7. The sequestering of calcium(II) ions only occurs when polymeric surfactants aggregate into micelles, thus bringing the carboxylic acid end groups into close proximity.…”

“…A promising approach is the use of smart polymer systems in which a thermal trigger is used as a switch between the adsorption and desorption of multivalent ions, such as calcium(II) 7. A few examples have been reported in which the lower critical solution temperature (LCST) of poly( N ‐isopropyl acrylamide) (PNIPAAm) is used to switch between adsorption and desorption 8.…”