title: Moisture-responsive films of cellulose stearoyl esters showing reversible shape transitions.
abstract: Moisture-responsive materials are gaining greater interest for their potentially wide applications and the readily access to moisture. In this study, we show the fabrication of moisture-responsive, self-standing films using sustainable cellulose as starting material. Cellulose was modified by stearoyl moieties at first, leading to cellulose stearoyl esters (CSEs) with diverse degrees of substitution (DSs). The films of CSE with a low DS of 0.3 (CSE0.3) exhibited moisture-responsive properties, while CSEs with higher DSs of 1.3 or 3 (CSE1.3 and CSE3) not. The CSE0.3 films could reversibly fold and unfold as rhythmical bending motions within a local moisture gradient due to the ab- and desorption of water molecules at the film surface. By spray-coating CSE3 nanoparticles (NPs) onto CSE0.3 films, moisture-responsive films with non-wetting surface were obtained, which can perform quick reversible bending movements and continuous shape transition on water. Furthermore, bilayer films containing one layer of CSE0.3 at one side and one layer of CSE3 at the other side exhibited combined responsiveness to moisture and temperature. By varying the thickness of CSE0.3 films, the minimal bending extent can be adjusted due to altered mechanical resistances, which allows a bending movement preferentially beginning with the thinner side.
authors.affiliation: Ernst-Berl-Institute for Chemical Engineering and Macromolecular Science, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287 Darmstadt, Germany.
authors.forename: Kai
authors.initials: K
authors.lastname: Zhang
authors.affiliation: Ernst-Berl-Institute for Chemical Engineering and Macromolecular Science, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287 Darmstadt, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Geissler
authors.affiliation: Clemens-Schöpf-Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 16, D-64287 Darmstadt, Germany.
authors.forename: Michaela
authors.initials: M
authors.lastname: Standhardt
authors.affiliation: Ernst-Berl-Institute for Chemical Engineering and Macromolecular Science, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287 Darmstadt, Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Mehlhase
authors.affiliation: Ernst-Berl-Institute for Chemical Engineering and Macromolecular Science, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287 Darmstadt, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Gallei
authors.affiliation: School of Mechanics and Engineering, Southwest Jiaotong University, 610031, Chengdu Chine.
authors.forename: Longquan
authors.initials: L
authors.lastname: Chen
authors.affiliation: Clemens-Schöpf-Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 16, D-64287 Darmstadt, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Marie Thiele