Observation of chain stretching in Langmuir diblock copolymer monolayers.

We report observations of chain stretching in diblock copolymer monolayers on the surface of a selective solvent. Using neutron reflectivity, we have studied the concentration profile of the submerged block over a large range of surface density \ensuremath{\sigma} (chains per area) for two different molecular weights. The observed increase in the layer thickness is weaker than the ${\mathrm{\ensuremath{\sigma}}}^{1/3}$ prediction of mean-field and scaling theories for the limiting behavior, but is in agreement with recent numerical self-consistent-field calculations by Whitmore and Noolandi [Macromolecules 23, 3321 (1990)].