Specific Ion Effects on Adsorbed Zwitterionic Copolymers

Abstract

We report direct measurements of interactions, dimensions, and solution behavior of adsorbed nonionic and zwitterionic triblock copolymers as a function of aqueous [NaCl] and [MgSO 4 ] in the range 0−1 M. Total internal reflection microscopy is used to measure kT-and nanometer-scale interactions between hydrophobic colloids and surfaces with adsorbed triblock copolymers with central poly(propylene oxide) (PPO) blocks and end blocks of the following: poly(ethylene oxide) (PEO), poly(3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate) (PMAPS), and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC). The findings indicate the following qualitatively different and unique behavior for each polymer: PEO layers are [NaCl]-independent but collapse and become less repulsive and eventually attractive with increasing [MgSO 4 ]; PMAPS layers are increasingly repulsive and extended with increasing [NaCl] but become less repulsive/extended with increasing [MgSO 4 ]; and PMPC layers are completely insensitive to both [NaCl] and [MgSO 4 ]. A competition between solvated molecular interactions and structures appears to explain the unique response of each polymer to nonspecific and specific ion effects as a function of aqueous salt solution composition.

Blood Protein Exclusion from Polymer Brushes

“…Protein was dissolved in 150 mM NaCl and sonicated for 30 min. Glass microscope slides (Fisher) were cleaned in acetone, 100 mM KOH, and Milli-Q deionized water and spin coated with polystyrene (3% w/w polystyrene in toluene at 3000 rpm for 30 s). Silica colloids (2.34 μm, Bangs) were rendered hydrophobic by coating with 1-octadecanol (Sigma-Aldrich) via a well-established literature method for creating highly stable dispersions …”

“…Ensemble TIRM was used to measure interactions between polymer coated colloids and slide as in previous work. ,− Our setup and analysis is similar to single particle studies, , except we use a CCD camera for 3D particle tracking) . In brief, total internal reflection of a 633 nm HeNe laser (Melles Griot) onto a prism at 68 degrees (Figure A) generated an evanescent wave with a decay length of β –1 = 113 nm.…”

“…We spatially resolve interactions between adsorbed PEG copolymer brushes in the presence of protein on kT -scale energies and with nanometer spatial resolution from super-resolution 3D particle tracking using ensemble Total Internal Reflection Microscopy (TIRM) . TIRM , has been used to measure nonspecific , and specific interactions , between adsorbed proteins and macromolecules, as well as, interactions between adsorbed and unadsorbed synthetic macromolecules vs solvent quality. − Such measurements have unique characteristics for investigating protein adsorption, including that they (1) are direct, sensitive, and nonintrusive, (2) provide information about different particles and surface locations (to address nonuniformity), and (3) are performed for dynamic equilibrium conditions (capable of detecting soft coronas) . Experiments are designed to unambiguously identify protein adsorption, or lack of adsorption, based on mutually exclusive outcomes for net colloid–wall interactions (Figure B,eq ): either positive protein adsorption altering macromolecular repulsion or negative protein adsorption manifested as depletion attraction (i.e., attractive contribution due to protein exclusion from surfaces) …”

Superlubricity Achieved with Zwitterionic Brushes in Diverse Conditions Induced by Shear Actions

“…Polymers can obtain optimal properties to solve different tasks by combining desirable supramolecular structures with local monomers through the polymerization reaction . Polymer brushes are such a kind of supramolecular assemblies, which consist of polymer chains densely anchored by one end on the substrate in a good solvent, and are commonly used in surface modifications. − Moreover, this kind of surface modification by anchoring polymer brushes on the substrates is attractive for controlling interfacial properties, such as friction, wettability, adhesion, and biocompatibility. − Nowadays, polymer brushes are found to be great boundary lubricants in liquid environments, which offer a simple and promising way to control surface friction. − Spencer et al grafted polyethylene glycol (PEG) onto polylysine, which was adsorbed on the surface of charged silica by electrostatic interaction. − Thus, the long chain of PEG could be extended into the aqueous solution to form the polymer brushes, thereby greatly enhancing the lubrication performance on the rolling test condition.…”

Macroporous Polyzwitterionic Gels As Versatile Intermediates for the Fixation and Release of Anions

“…However, the incorporation of low-molecular-weight electrolytes in this solution facilitates the shielding of attractive electrostatic forces of the formed dipole . Hence polymer chain expansion can occur and solubilize the polyzwitterion in aqueous solution in the presence of electrolytes. − …”