| Autor: |
Abe K; Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-Cho, Koganei, Tokyo, 184-8588, Japan.; Micro/Bio/Nanofluidics Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tan-cha, Onna, Kunigami, Okinawa, 904-0497, Japan., Atkinson PS; School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK. lucas.goehring@ntu.ac.uk., Cheung CS; School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK. lucas.goehring@ntu.ac.uk., Liang H; School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK. lucas.goehring@ntu.ac.uk., Goehring L; School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK. lucas.goehring@ntu.ac.uk., Inasawa S; Graduate School of Bio-Application and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-Cho, Koganei, Tokyo, 184-8588, Japan.; Department of Applied Physics and Chemical Engineering, Tokyo University of Agriculture and Technology, Japan. inasawa@cc.tuat.ac.jp. |
| Abstrakt: |
Colloidal suspensions are the basis of a wide variety of coatings, prepared as liquids and then dried into solid films. The processes at play during film formation, however, are difficult to observe directly. Here, we demonstrate that optical coherence tomography (OCT) can provide fast, non-contact, precise profiling of the dynamics within a drying suspension. Using a scanning Michelson interferometer with a broadband laser source, OCT creates cross-sectional images of the optical stratigraphy of a sample. With this method, we observed the drying of colloidal silica in Hele-Shaw cells with 10 μm transverse and 1.8 μm depth resolution, over a 1 cm scan line and a 15 s sampling period. The resulting images were calibrated to show how the concentration of colloidal particles varied with position and drying time. This gives access to important transport properties, for example, of how collective diffusion depends on particle concentration. Looking at early-time behaviours, we also show how a drying front initially develops, and how the induction time before the appearance of a solid film depends on the balance of diffusion and evaporation-driven motion. Pairing these results with optical microscopy and particle tracking techniques, we find that film formation can be significantly delayed by any density-driven circulation occurring near the drying front. |
