Figure 3

Proton-resisting effect of OH-rich poly(OEGMA₅₂₆) brushes.

(a) Different responses to acid stimulation of poly(OEGMA₅₂₆)- and poly(OEGMA₄₇₅)-coated chips, as monitored by QCM in real time. When the HCl (pH 5.0) was introduced, the frequency decreased due to the switch from the gaseous to liquid phases, reaching a baseline for both chips. When the pH changed to 1.0, the frequency of the poly(OEGMA₄₇₅)-grafted chip (10.6 nm thick polymer layer, red line) increased significantly, whereas the poly(OEGMA₅₂₆)-grafted (9.2 nm) chip showed no response (< 20 Hz for over 1 hour, black line). The blue line indicates the frequency level corresponding to the complete loss of the surface mass. (b) When a poly(OEGMA₄₇₅) layer (α) was covered with a proton shelter copolymer layer (β) (the gray bars), the acid-responsiveness (measured as the desorption ratio: ratio of the detached mass to the whole mass) was significantly inhibited compared with those without the proton shelter layer (the white bars). The bottom axis label shows the dry thickness of each layer.