Reversible and dynamical control of aggregation and soft adhesion of T-responsive polymer-coated colloids
[Display omitted] •Particle–particle and particle–substrate adhesion are controlled by temperature.•Thermo-responsive polymer coating ensures reversible aggregation and adsorption.•Adhesion stiffness is finely tuned by the fraction of thermo-responsive polymer.•Two adhesion regimes suggest different...
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Veröffentlicht in: | Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 2017-11, Vol.532, p.510-515 |
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Sprache: | eng |
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•Particle–particle and particle–substrate adhesion are controlled by temperature.•Thermo-responsive polymer coating ensures reversible aggregation and adsorption.•Adhesion stiffness is finely tuned by the fraction of thermo-responsive polymer.•Two adhesion regimes suggest different polymer blocks arrangements.
Colloids with aggregation and adhesion properties reversibly tunable by shift of pH, T, light etc. can be designed by deposition of stimuli-responsive polymer chains on the particle surface. The aim of this work was to investigate how to control the strength of temperature-triggered attraction by analysing self-aggregation kinetics and soft adhesion of colloids to a flat substrate. In order to endow the colloids with reversible and temperature-controlled interactions, silica or polystyrene microbeads (d=200nm and 1μm) were coated by mixed solutions of poly(lysine)-grafted-polyethylenoxide (PLL-g-PEG, for steric repulsion) and PLL-g-PNIPAM (i.e. PLL with poly-N-isopropylacrylamide T-responsive side chains). PEG-coated particles were stable in suspension, while the presence of PNIPAM provoked, at T>Tc=32±1°C, reversible aggregation and/or adsorption on glass plates. Dynamic light scattering following a T-jump from 25°C to 40°C was used to measure the aggregation rate and corresponding stability ratio W. For a molar fraction of PLL-g-PNIPAM, f, ranging from 100% down to about 20%, particles aggregate rapidly with slowly increasing W. Below f≈20%, W increases by 3 orders of magnitude. The real-time 2D tracking method was used to monitor (x, y) positions of particles in suspension above microscope glass slides during a T-triggered adsorption. In order to capture transitory dynamics near PNIPAM collapse transition, particles tracks were recorded within a T-ramp of 10°C/min from below to above Tc. The particle-substrate interaction was found to hinder the near-wall diffusion and provoke the soft adhesion, as revealed by observation of characteristic confined Brownian motion. Resulting confinement potential stiffness profile α(f) presents a crossover from constant to linearly increasing at f≈20%. Altogether, the characteristic coverage f*≈20% is interpreted as a crossover from discrete to continuous coverage pattern within the soft contact domain. |
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ISSN: | 0927-7757 1873-4359 |
DOI: | 10.1016/j.colsurfa.2017.04.011 |