  To investigate the structural changes upon thermal treatment of resorcinol
formaldehyde latex (RFL) interfacial layer in rubber-cord flexible composite, a
multiscale approach has been employed. High-resolution AFM mapping showed a
significant increase of the modulus of the RF phase from 1.2 GPa to 2.3 GPa and
latex phase (L) from 0.3 GPa to 0.8 GPa after a thermal exposure at 100{\deg}C
for 10 days. The increase of the RF and L phases elastic modulus was correlated
with the increase of the oxygen content in RFL layer based on the measurements
by SEM-EDX. Besides by combining finite element simulations and AFM modulus
profiling, the presence of an interphase region (over 280 nm) between the RFL
and the rubber regions was identified and was not deteriorated by the thermal
treatment. Peel adhesion testing revealed that the increase of RF and L phases
rigidity after thermal treatment was detrimental for the interfacial adhesion
of the rubber composite.
