2020 Fiscal Year Annual Research Report
Dynamics of polyelectrolyte adsorption and colloidal flocculation studied using model colloids
| Project/Area Number |
20F20388
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| Research Institution | University of Tsukuba |
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Principal Investigator |
小林 幹佳 筑波大学, 生命環境系, 准教授 (20400179)
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| Co-Investigator(Kenkyū-buntansha) |
GEONZON LESTER 筑波大学, 生命環境科学研究科(系), 外国人特別研究員
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| Project Period (FY) |
2020-11-13 – 2023-03-31
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| Keywords | water-soluble polymer / optical tweezers / microfluidics / hydrodynamic flow / colloids / adsorption |
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| Outline of Annual Research Achievements |
Methodologies to investigate the adsorption/desorption kinetics of water-soluble polymer to colloidal particles using optical tweezers and microfluidics were developed. The approach allows the time-course observation on the adsorption kinetics of water-soluble polymer onto the colloidal particles with varying conditions from the viewpoint of the single-particle level. Experiments on the adsorption of the polymer were still ongoing.
Nevertheless, in order to understand the effect of hydrodynamic drag on the spherical particle, studies on the hydrodynamic shear force on a particle at different locations near-wall were performed using optical tweezers and microfluidics. For a particle translating near walls, drag friction coefficient factors were studied. Optical tweezers were used to trap silica particles and probe the fluid shear stress on the particle. Combining optical tweezers and microfluidic, the friction coefficients with and without shear flow were obtained. Results show that the drag coefficient increases dramatically at a distance close to the wall because of the hydrodynamic friction, and at the same time, it is constant at approximately large distances. The observations are in good agreement and consistent with the expectations from the hydrodynamic theory.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The project aimed to understand the adsorption kinetics of the water-soluble polymer onto colloidal particles from the viewpoint of the single-particle level. To approach the problem, methodologies were developed using optical tweezers and microfluidics. This technology will provide an understanding of the kinetics of adsorption of a water-soluble polymer onto the colloidal particle in the presence of hydrodynamic flow at the single-particle level.
However, to better understand the effect of hydrodynamic flow on the particle in a microfluidic channel, the drag friction coefficient near-wall was initially studied in detail with and without shear flow. This study is fundamentally important, most especially in experiments involving microfluidics. Our findings show a drastic increase of drag friction coefficient as the particle is brought closer to the wall due to the hydrodynamic effect, consistent with the expectations from the hydrodynamic theory. These provide practical information to position the colloidal particle at any location within the flow field for the future experiments.
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| Strategy for Future Research Activity |
Based on the obtained results and following the developed methodology, the kinetics of adsorption/desorption of water-soluble polymers onto the colloidal particles will be investigated in detail at different experimental conditions using optical tweezers and microfluidics. In addition, the effect of external flow on the change of hydrodynamic layer thickness will be evaluated. This will be verified using electrophoretic mobility.
The dynamics of aggregation of mono and bidisperse particles will then be studied. Force interaction of colloidal particles will be investigated using optical tweezers and a micropipette. This study will provide an understanding of the dynamics of aggregation of colloidal particles, which is crucial for the fate of wastewater particulates.
The utilization of biopolymers with different functional properties as novel natural-based polymeric flocculants will also be investigated. Different types of biopolymers, i.e., carrageenans, pectin, etc., will be used. Following the developed methodologies, the adsorption/desorption of biopolymers on the surface of the colloidal particles will be analyzed using particle tracking, optical tweezers, microfluidics, and electrophoretic mobility analysis. The effect of the molecular weight will also be studied by controlling the molecular weight of biopolymers using physical and chemical depolymerization procedures.
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