title: Bimodality and re-entrant behaviour in the hierarchical self-assembly of polymeric nanoparticles.
abstract: We show that a film of a suspension of polymer grafted nanoparticles on a liquid substrate can be employed to create two-dimensional nanostructures with a remarkable variation in the pattern length scales. The presented experiments also reveal the emergence of concentration-dependent bimodal patterns as well as re-entrant behaviour that involves length scales due to dewetting and compositional instabilities. The experimental observations are explained through a gradient dynamics model consisting of coupled evolution equations for the height of the suspension film and the concentration of polymer. Using a Flory-Huggins free energy functional for the polymer solution, we show in a linear stability analysis that the thin film undergoes dewetting and/or compositional instabilities depending on the concentration of the polymer in the solution. We argue that the formation via 'hierarchical self-assembly' of various functional nanostructures observed in different systems can be explained as resulting from such an interplay of instabilities.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore, India.
authors.forename: Sarika
authors.initials: S
authors.lastname: C K
authors.affiliation: Department of Mechanical Engineering, Indian Institute of Science, Bangalore, India. gtom@mecheng.iisc.ernet.in.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Tomar
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore, India. basu@physics.iisc.ernet.in.
authors.forename: J K
authors.initials: JK
authors.lastname: Basu
authors.affiliation: Institut für Theoretische Physik, Westfälische Wilhelms-Universität Münster, Wilhelm Klemm Str. 9, D-48149 Münster, Germany and Center of Nonlinear Science (CeNoS), Westfälische Wilhelms Universität Münster, Corrensstr. 2, 48149 Münster, Germany. u.thiele@uni-muenster.de.
authors.forename: Uwe
authors.initials: U
authors.lastname: Thiele