Ion-Specific Hydration States of Zwitterionic Poly(sulfobetaine methacrylate) Brushes in Aqueous Solutions

Abstract

The ion-specific hydration states of zwitterionic poly­(3-(N-2-meth­acryl­oyl­oxy­ethyl-N,N-di­methyl)­ammonato­propane­sulfonate) (PMAPS) brushes in various aqueous solutions were investigated by neutron reflectivity (NR) and atomic force microscopy (AFM). The asymmetric hydration state of the PMAPS brushes was verified from the NR scattering-length density profiles, while the variation in their swollen thickness was complementary as determined from AFM topographic images. PMAPS brushes got thicker in any salt solutions, while the extent of swelling and the dimensions of swollen chain structure were dependent on the ion species and salt concentration in the solutions. Anion specificity was clearly observed, whereas cations exhibited weaker modulation in ion-specific hydration states. The anion specificity could be ascribed to ion-specific interactions between the quaternary ammonium cation in sulfobetaine and the anions. The weak cation specificity was attributed to the intrinsically weak cohesive interactions between the weakly hydrated sulfonate anion in sulfobetaine and the strongly hydrated cations. The ion-specific hydration of PMAPS brushes was largely consistent with the ion-specific aggregation state of the PMAPS chains in aqueous solutions.

2‐(N‐3‐Sulfopropyl‐N,N‐dimethyl ammonium)ethyl methacrylate modified graphene oxide embedded into cellulose acetate ultrafiltration membranes for improved performance

“…The surface area and pore volume of GO increased after oxidation to 61.6 m 2 ,g −1 and 0.45 cm 3 .g −1 respectively. Furthermore, GO exhibited a high‐average pore size of 31.2 nm compared to graphite with 29.2 nm demonstrating the expansion of the GO sheets during exfoliation 50,51 . After bromination of GO, a decrease in the surface area to 0.2648 m 2 .g −1 of GO‐Br was observed.…”

Lyotropic Morphology Transition of Double Zwitterionic Diblock Copolymer Aqueous Solutions

“…PSBs are insoluble to water at room temperature to produce opaque dispersion and show upper critical solution temperature in dilute solutions. [ 26–28 ] The sulfobetaine groups are well hydrated because of the strong charge–dipole interaction in the positively charged quaternary ammonium cations and negatively charged sulfonate anions, while the sulfobetaine groups produce a couple by the complementary association. The sulfobetaine binding restrains the conformational entropy gain through dissolution, leading to the limitation of solubility.…”

Specific Ion Effects on Adsorbed Zwitterionic Copolymers

“…However, for aqueous zwitterionic polymers, nonspecific ion effects are still the subject of ongoing study, 35 and specific ion effects have only been investigated in a few preliminary studies with conflicting findings. 37,38 Herein, we report direct measurements of interactions between net neutral aqueous copolymers adsorbed to colloidal particles and planar substrates versus [NaCl] and [MgSO 4 ] (Figure 1). A systematic investigation of different polymer types provides a basis to understand how nonspecific and specific ion effects determine the polymer interactions, dimensions, solution behavior, and their role in colloidal stability.…”

“…In contrast, zwitterionic polymers have moieties with closely spaced cationic and anionic groups that are net neutral but have strong dipoles; these polymers often display an opposite trend where increasing salt concentrations screen the intramolecular dipolar attraction to increase the chain dimensions ( “antipolyelectrolyte effect”). − Although ion effects are documented for many aqueous neutral polymers and polyelectrolytes, significant gaps remain in understanding ion-mediated polymer solvent quality and solution thermodynamics. However, for aqueous zwitterionic polymers, nonspecific ion effects are still the subject of ongoing study, and specific ion effects have only been investigated in a few preliminary studies with conflicting findings. , …”

“…Each end block is investigated based on its importance to biomedical applications and significant prior fundamental studies, ,− which provide important benchmarks and open questions. While prior studies have investigated on some specific ion-dependent responses for single polymers, ,− herein, we systematically compare and contrast the [MgSO 4 ] and [NaCl] dependence of interactions and dimensions of PMAPS and PMPC copolymers with a PEO copolymer (one of the most studied aqueous polymers).…”