title: Tuning Morphologies of Langmuir Polymer Films Through Controlled Relaxations of Non-Equilibrium States.
abstract: Langmuir polymers films (LPFs) frequently form nonequilibrium states which are manifested in a decay of the surface pressure with time when the system is allowed to relax. Monitoring and manipulating the temporal evolution of these relaxations experimentally helps to shed light on the associated molecular reorganization processes. We present a systematic study based on different compression protocols and show how these reorganization processes impact the morphology of LPFs of poly(γ-benzyl-L-glutamate)(PBLG), visualized by means of atomic force microscopy. Upon continuous compression, a fibrillar morphology was formed with a surface decorated by squeezed-out islands. By contrast, stepwise compression promoted the formation of a fibrillar network with a bimodal distribution of fibril diameters, caused by merging of fibrils. Finally, isobaric compression induced in-plane compaction of the monolayer. We correlate these morphological observations with the kinetics of the corresponding relaxations, described best by a sum of two exponential functions with different time scales representing two molecular processes. We discuss the observed kinetics and the resulting morphologies in the context of nucleation and growth, characteristic for first-order phase transitions. Our results demonstrate that the preparation conditions of LPFs have tremendous impact on ordering of the molecules and hence various macroscopic properties of such films.
authors.affiliation: †Institute of Physics, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany.
authors.forename: Sivasurender
authors.initials: S
authors.lastname: Chandran
authors.affiliation: †Institute of Physics, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Dold
authors.affiliation: ‡Ecole Nationale Superieure de Chimie de Rennes, 35708 Rennes Cedex 7, France.
authors.forename: Amaury
authors.initials: A
authors.lastname: Buvignier
authors.affiliation: §Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Potsdam D-14424, Germany.
authors.forename: Kai-Steffen
authors.initials: KS
authors.lastname: Krannig
authors.affiliation: §Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Potsdam D-14424, Germany.|∥Institute of Chemistry, Universität Potsdam, Potsdam D-14476, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Schlaad
authors.affiliation: †Institute of Physics, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany.|#Freiburg Centre for Interactive Materials and Bio-inspired Technologies, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany.|¶Freiburg Materials Research Center, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany.
authors.forename: Günter
authors.initials: G
authors.lastname: Reiter
authors.affiliation: †Institute of Physics, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany.|¶Freiburg Materials Research Center, Albert Ludwigs Universität Freiburg, Freiburg 79085, Germany.
authors.forename: Renate
authors.initials: R
authors.lastname: Reiter