Small angle neutron scattering experiments have observed the collapse of a star polymer above a critical concentration (c*) where stars begin to overlap.

The collapse results from desolvation of the interior of the star polymer with increasing concentration. This influence of solvent fluctuations on the structural variations may be a general property of soft matter systems.

Star polymers are synthetic macromolecules with linear polymer branches emanating from the molecular center. Independent distributions of star polymer and solvent were obtained by varying the contrast between the solvent and polymers with selective deuteration. Synthesis and isotopic substitution of star polymers was performed at the Center for Nanoscale Materials Science.

Work performed at Oak Ridge National Laboratory’s Spallation Neutron Source EQSANS instrument and the ORNL Center for Nanophase Materials Sciences is supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

X. Li, L. Porcar, L. Sanchez-Diaz, C. Do, Y. Liu, T.-H. Kim, W. Hamilton, G. Smith, K. Hong, W.-R. Chen, "Influence of Molecular Solvation on the Conformation of Star Polymers.” ACS Macro Letters 3 (2014): 458-461.