kT-Scale Interactions and Stability of Colloids with Adsorbed Zwitterionic and Ethylene Oxide Copolymers

We report synthesis of novel zwitterionic triblock copolymers and direct measurements of their interactions when adsorbed to colloids and surfaces. We investigate triblock copolymers with poly(2-methacryloyloxyethylphosphorylcholine) (PMPC) end blocks separated by a poly(propylene oxide) (PPO) center block, with comparison to poly(ethylene oxide) PEO-PPO-PEO analogues. Interaction potentials are measured for a molecular weight series of PMPC and PEO copolymers adsorbed to hydrophobic colloids of varying diameter and planar surfaces. Findings indicate that, for the same number of repeat units, PMPC brushes generate repulsion at several times the distance of PEO brushes. PEO brush dimensions and interactions show good agreement with polymer brush models, whereas PMPC interactions suggest layer architectures with chain extensions approaching the PMPC block contour length. While PEO blocks must have 2-3 times as many repeat units to generate the same thickness as PMPC blocks, PMPC and PEO layers of the same thickness generate equivalent interactions and colloidal stability.