Unswollen layer of cross-linked polyisoprene at the solid interface

•A thin cross-linked rubber film on a solid substrate is heterogeneously swollen.•Un- and less-swollen layers were found at the substrate interface.•These interfacial layers are associated with bound rubber claimed in previous reports.

The density profile in a thin cross-linked polyisoprene (PI) film spin-coated on a quartz substrate in n-hexane was examined by specular neutron reflectivity. We found two layers with different PI densities at the substrate interface. The characteristics of the layers are discussed in terms of bound rubber typically associated with the field of rubber materials and adsorbed layers typically associated with the field of glassy materials.

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