data_availability_Grandi_Soft_Matter.zip

The number of free surfaces in a polymer ultra-thin film has a strong influence on its physical and

mechanical properties. In this study, Young’s modulus as well as the glass transition temperature

of multinanolayer coextruded polymer films, hence with no free surfaces, have been measured. We

observe that contrary to the case of free-standing or supported ultra-thin films, there is no depression

of the glass transition temperature or the Young modulus, but an increase for the latter as the layer

thickness decreases, whatever the polymer pair (with various compatibilities). It is proposed that

this increase is associated with the rise of interphase volume fraction in the films. An interphase

modulus of about 25 GPa can be extracted from the empirical model, about 10 times higher than

the typical modulus value of a glassy polymer. This value does not appear to depend on the nature

of the polymers, meaning that the presence of entanglements at the interfaces is not a key factor to

explain the increase in Young’s modulus of multinanolayer films.