Generation of Local Diffusioosmotic Flow by Light Responsive Microgels

Langmuir, vol. 38, pp. 6343–6351

Abstract

Here we show that microgels trapped at a solid wall can issue liquid flow and transport over distances several times larger than the particle size. The microgel consists of cross-linked poly( N -isopropylacrylamide- co -acrylic acid) (PNIPAM-AA) polymer chains loaded with cationic azobenzene-containing surfactant, which can assume either a trans- or a cis- state depending on the wavelength of the applied irradiation. The microgel, being a selective absorber of trans -isomers, responds by changing its volume under irradiation with light of appropriate wavelength at which the cis -isomers of the surfactant molecules diffuse out of the particle interior. Together with the change in particle size, the expelled cis -isomers form an excess of the concentration and subsequent gradient in osmotic pressure generating a halo of local light-driven diffusioosmotic ( l -LDDO) flow. The direction and the strength of the l -LDDO depends on the intensity and irradiation wavelength, as well as on the amount of surfactant absorbed by the microgel. The flow pattern around a microgel is directed radially outward and can be maintained quasi-indefinitely under exposure to blue light when the trans-/cis -ratio is 2/1, establishing a photostationary state. Irradiation with UV light, on the other hand, generates a radially transient flow pattern, which inverts from inward to outward over time at low intensities. By measuring the displacement of tracer particles around neutral microgels during a temperature-induced collapse, we can exclude that a change in particle shape itself causes the flow, i.e., just by expulsion or uptake of water. Ultimately, it is its ability to selectively absorb two isomers of photosensitive surfactant under different irradiation conditions that leads to an effective pumping caused by a self-induced diffusioosmotic flow.

Authors 6

1. Anjali Sharma

   University of Potsdam

   Affiliation as printed

   Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany

2. Marek Bekir

   University of Potsdam

   Affiliation as printed

   Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany

3. Nino Lomadze

   University of Potsdam

   Affiliation as printed

   Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany

4. Se‐Hyeong Jung Aachen DWI-Leibniz-Institute for Interactive Materials e.V Functional and Interactive Polymers Institute of Technical and Macromolecular Chemistry

   DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   DWI-Leibniz Institute for Interactive Materials e.V., 52074 Aachen, Germany

   Functional and Interactive Polymers, Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, 52074 Aachen, Germany

5. Andrij Pich Aachen DWI-Leibniz-Institute for Interactive Materials e.V Functional and Interactive Polymers Institute of Technical and Macromolecular Chemistry

   Maastricht University · DWI – Leibniz Institute for Interactive Materials · RWTH Aachen University

   Affiliation as printed

   Aachen Maastricht Institute for Biobased Materials (AMIBM), Maastricht University, 6167 RD Geleen, The Netherlands

   DWI-Leibniz Institute for Interactive Materials e.V., 52074 Aachen, Germany

   Functional and Interactive Polymers, Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, 52074 Aachen, Germany

6. Svetlana A. Santer corresponding

   University of Potsdam

   Affiliation as printed

   Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany