title: Reversible Size Modulation of Aqueous Microgels via Orthogonal or Combined Application of Thermo- and Phototriggers.
abstract: Aqueous microgels that respond orthogonally to external temperature and light stimuli and to a combination of both stimuli were developed. N-Vinylcaprolactam (VCL) was copolymerized with small feed amounts (<5 mol %) of 4-[(4-methacryloyloxy)phenylazo] benzenesulfonic acid (ABSA) and cross-linked with N,N'-methylenebis(acrylamide) (BIS) to synthesize monodisperse and colloidally stable P(VCL-BIS-ABSA) microgels. The volume phase transition information on the microgels under both orthogonal and combined application of temperature and light stimuli was investigated in situ by dynamic light scattering (DLS) instrument. Modeling of this information by the Flory-Rehner theory describes and aids the preliminary understanding of the main features in the volume phase transition of these photoresponsive microgels. Interestingly, the microgels rapidly deswell upon UV irradiation (λ = 365 nm), even as the trans-ABSA pendant groups are converted to the more polar cis state. The variation in the content of the pendant azobenzene groups in the microgels allows for reversible modulation of the phototriggered volume change. We propose that the approach of the sulfonic acid groups of cis-ABSA toward the polymer backbone causes the disruption of hydrogen bonding interactions between water molecules and the carbonyl groups of VCL.
authors.affiliation: DWI - Leibniz Institute for Interactive Materials e.V. , Forckenbeckstr. 50, 52056 Aachen, Germany.|Institute of Technical and Macromolecular Chemistry, RWTH Aachen University , Worringerweg 1, 52074 Aachen, Germany.
authors.forename: Dazril I
authors.initials: DI
authors.lastname: Phua
authors.affiliation: DWI - Leibniz Institute for Interactive Materials e.V. , Forckenbeckstr. 50, 52056 Aachen, Germany.|Institute of Technical and Macromolecular Chemistry, RWTH Aachen University , Worringerweg 1, 52074 Aachen, Germany.
authors.forename: Krisztian
authors.initials: K
authors.lastname: Herman
authors.affiliation: Institute for Research in Biomedicine Barcelona , Carrer de Baldiri Reixac, 08028, Barcelona, Spain.
authors.forename: Andreea
authors.initials: A
authors.lastname: Balaceanu
authors.affiliation: Institute of Physics, Cologne University of Applied Sciences , Steinmülleralle 1, 51643 Gummersbach, Germany.
authors.forename: Juri
authors.initials: J
authors.lastname: Zakrevski
authors.affiliation: DWI - Leibniz Institute for Interactive Materials e.V. , Forckenbeckstr. 50, 52056 Aachen, Germany.|Institute of Technical and Macromolecular Chemistry, RWTH Aachen University , Worringerweg 1, 52074 Aachen, Germany.
authors.forename: Andrij
authors.initials: A
authors.lastname: Pich