Chain conformation in two-dimensional dense state.

In an effort to provide evidence concerning the conformation of many chains in strict two-dimensional (2D) dense state, we synthesized polymer chains of diameter of nanometers through an anionic polymerization process. The conformational characteristics of the long chain molecules in films of thickness h corresponding to the chain diameter a were directly obtained from atomic force microscopy observations. In 2D dispersed state, the conformations of the long chain molecules were typical Gaussian. However, in 2D dense state the long chain molecules were strongly interpenetrated. Their conformations were largely perturbed by the presence of neighbor chains and were not Gaussian. This result was in contradiction with the segregated globule model predicted by de Gennes. The central reason is that 2D space cannot be filled to normal density with 2D Gaussian globules; either the area must be greatly increased with consequently large voids, or the globule conformation must be expanded by allowing chains to interpenetrate each other.