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nanoparticle friction in the viscous polymer melt. This phenomenon was accompanied by a translational motion of the nanoparticles caused by their magnetisation, eventually leading to the formation of dipolar chains, evidenced by a pronounced anisotropy in the 2D SAXS patterns and further confirmed by electronic microscopy (end of the yellow zone in Figure 32b). Of particular interest was the non-monotonic dynamics experienced by the nanoparticles during the magnetic irradiation (see XPCS measurements in Figure 32c). While the
characteristic time of the autocorrelation function was presumably infinite at low temperature, indicating the absence of particle motion in the presence of crystallites (black curve), it was found to be 10 times faster under induction heating (orange curve) than convective heating (blue curve) for a similar temperature of about 180°C (molten state). Even more interesting, measuring the dynamics after reaching the maximum in temperature (Tmax in Figure 32b) revealed a progressive slowing down of the nanoparticles owing to their agglomeration into dipolar chains, explaining their lower frictional activity.
These results highlight the intricate interactions between the incident magnetic stimulus, the nano-heater particles and their motion within a complex, non-Newtonian fluid. Beyond possible applications at the industrial lengthscale (see patent [2]), these experiments are an invitation to further investigate the fundamental nature of the friction between stimulated nanoparticles and their environment. They represent the first steps in the design of a quantitative model to predict the T(t) curves from the characteristics of the materials, notably in terms of polymer viscosity and nanoparticle-oriented parameters such as deflection angle in the field, roughness, etc.
PRINCIPAL PUBLICATION AND AUTHORS
Fate of Magnetic Nanoparticles during Stimulated Healing of Thermoplastic Elastomers, A. Pommella (a), P. Griffiths (a,b), G. Coativy (b), F. Dalmas (a), S. Ranoo (c), A.M. Schmidt (c), F. Méchin (d), J. Bernard (d), T. Zinn (e), T. Narayanan (e), S. Meille (a), G.P. Baeza (a), ACS Nano 17, 17394-17404 (2023); https:/doi.org/10.1021/acsnano.3c05440 (a) Univ. Lyon, INSA Lyon, Université Claude Bernard Lyon 1, CNRS, MATEIS, UMR 5510, Villeurbanne (France) (b) Univ. Lyon, INSA Lyon, Université Claude Bernard Lyon 1, LGEF, EA682, Villeurbanne (France) (c) Chemistry department, Institute for Physical Chemistry, University of Cologne, Cologne (Germany) (d) Univ. de Lyon, INSA Lyon, Université Claude Bernard Lyon 1, Université Jean Monnet, CNRS, UMR 5223, Ingénierie des Matériaux Polymères, Villeurbanne (France) (e) ESRF
REFERENCES
[1] P. Griffiths et al., Macromolecules 55, 831-843 (2022). [2] G.P. Baeza et al., https:/data. inpi.fr/brevets/FR3119792
Fig. 32: a) Original setup for SAXS and XPCS measurements in presence of a high-frequency oscillator magnetic field. Left: Principle. Right: Actual configuration on beamline ID02. b) Temperature vs. time during induction heating. The red solid line represents the usual temperature trajectory ( pizza-in-oven case). c) XPCS autocorrelation function at various time during heating in presence or not of an oscillatory magnetic field.
