Reversible and dynamical control of aggregation and soft adhesion of T-responsive polymer-coated colloids

Abstract

International audienceColloids 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 at substrate. In order to endow the colloids with reversible and temperature-controlled interactions , silica or polystyrene microbeads (d =200 nm and 1 µm) 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 > T c = 32 ± 1 • C, reversible aggre-gation 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 Tramp of 10 • C/min from below to above T c. The particle-substrate interaction was found to hinder the near-wall diusion and provoke the soft adhesion, as revealed by observation of characteristic conned Brownian motion. Resulting connement potential stiness prole 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

Cationic PLGA Nanoparticle Formulations as Biocompatible Immunoadjuvant for Serum Production and Immune Response against Bothrops jararaca Venom

“…The importance of charge was also observed in nanoparticle stability. Instability phenomena are related with the interaction of electrostatic, steric and solvation forces; unstable systems might present flocculation, sedimentation and coalescence [38][39][40]. The nanoparticle-PEI behavior was maintained even after association with BJ venom (Figure 1B).…”

Two-Stage Collapse of PNIPAM Brushes: Viscoelastic Changes Revealed by an Interferometric Laser Technique

“…Thereby, these measurements average over many particles, possibly obscuring details about the collapse . Alternative methods that measure the Brownian motion of single particles are video microscopy or interference-based laser techniques. − The sampling rate of video microscopy is limited to about a kilohertz, , and thus it can be used to investigate effects that occur at shorter time-scales. Laser-based techniques can measure up to megahertz .…”