We
have developed a polymer electrolyte membrane (PEM) material
using polymer-coated silica nanoparticles (NPs) by the reversible
addition-fragmentation chain-transfer polymerization with particles
(RAFT PwP) method. In this paper, we controlled the number density
of surface silanol groups on the silica NPs that not only maintain
the structure of the surface adsorbed polymers by RAFT PwP but also
form fast proton-conducting interface to study the silanol density
effect on proton conductivity. The number of surface silanol groups
was successfully increased by NaOH surface treatment and decreased
by heat treatment. Then, we clarified that silanol-rich silica NPs
with a polyacrylic acid and polystyrene block copolymer (PAA-b-PS) applied by RAFT PwP exhibit larger proton conductivity.
This result implies that hydrophilicity of the filler is one of the
important factors in the design of filler-functionalized PEM with
high proton conductivity.