Effect of pH on the nanostructure of an amphiphilic carbosilane/methacrylic acid block copolymer at air/water interface

The nanostructure of a monolayer of the ionic amphiphilic diblock copolymer, poly(1,1-diethylsilacyclobutane)-block-poly(methacrylic acid) (poly(Et₂SB-b-MAA)) with different MAA chain lengths on water, was investigated at various pH by in-situ X-ray reflectometry. The monolayer nanostructure was similar in acidic and neutral conditions, but significantly different on the subphase of pH10. With the long MAA polymer a dense carpet layer was detectable, but the carpet/brush structure in the monolayer was not observed. The short MAA chain sample on the subphase of pH10 had an Et₂SB layer in monolayer explicitly thicker than that in an acidic or neutral condition at the same surface pressure. The differences in monolayer nanostructure can be attributed to the difference in ionization condition of carboxylic groups in the MAA chain.