On the interfacial width in triblock versus diblock copolymers: A neutron reflectivity investigation

The relationship between the interfacial width in a lamellar triblock copolymer and that in the respective lamellar diblock has been investigated by neutron reflectivity, taking advantage of the surface-induced orientation of the domains parallel to the free surface in thin copolymer films. The effective interfacial width in a poly(vinyl-2-pyridine)-polystyrene-poly(vinyl-2-pyridine) triblock is found to be similar to 38% narrower than that for the respective diblock. This difference is discussed in relation to theoretical predictions and is tentatively attributed to a reduced contribution of the thermal fluctuations of the concentration profiles to the effective interfacial width because of the presence of the mid-block bridges connecting the end-block domains in the triblock lamellae.