7 research outputs found

    Natural Rubber–Filler Interactions: What Are the Parameters?

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    Reinforcement of a polymer matrix through the incorporation of nanoparticles (fillers) is a common industrial practice that greatly enhances the mechanical properties of the composite material. The origin of such mechanical reinforcement has been linked to the interaction between the polymer and filler as well as the homogeneous dispersion of the filler within the polymer matrix. In natural rubber (NR) technology, knowledge of the conditions necessary to achieve more efficient NR–filler interactions is improving continuously. This study explores the important physicochemical parameters required to achieve NR–filler interactions under dilute aqueous conditions by varying both the properties of the filler (size, composition, surface activity, concentration) and the aqueous solution (ionic strength, ion valency). By combining fluorescence and electron microscopy methods, we show that NR and silica interact only in the presence of ions and that heteroaggregation is favored more than homoaggregation of silica–silica or NR–NR. The interaction kinetics increases with the ion valence, whereas the morphology of the heteroaggregates depends on the size of silica and the volume percent ratio (dry silica/dry NR). We observe dendritic structures using silica with a diameter (<i>d</i>) of 100 nm at a ∼20–50 vol % ratio, whereas we obtain raspberry-like structures using silica with <i>d</i> = 30 nm particles. We observe that in liquid the interaction is controlled by the hydrophilic bioshell, in contrast to dried conditions, where hydrophobic polymer dominates the interaction of NR with the fillers. A good correlation between the nanoscopic aggregation behavior and the macroscopic aggregation dynamics of the particles was observed. These results provide insight into improving the reinforcement of a polymer matrix using NR–filler films

    Experimental configuration of single-molecule force spectroscopy assays.

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    <p>Scheme illustrating the measurement configuration that was used during the experiments with no force applied (A) and under force (B) when the stage was moving. C is a close-up of B.). The pilus attached to the trapped bead is disproportionally long for reasons of depiction. The 10.5-μm mounting bead (MB) was immobilized on the coverslip while the 1-μm probe bead (PB) was trapped by optical tweezers (OT). A piliated bacterium was non-specifically attached to the MB and a pilus to the PB. When the coverslip was moved, and the trap kept in a fixed position, a force was directly exerted on the pilus. (C) Assuming adhesion to be non-specific, the most likely situation is that a portion of the pilus was attached (white subunits) and not solely the adhesion pilin (red subunit). Only a part of the pilus (black subunits) was thus subjected to the applied force.</p

    Histograms of persistence length <i>L</i><sub><i>p</i></sub> (nm).

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    <p>The positions are provided by fitting WLC model to force spectroscopy data on the Pil strain and its pili-displaying derivatives with 1.5 μM BSA or 15 μM BSA for the Pil p<i>srtA</i> strain. Data were fitted using the Gaussian function (solid line) and Gaussian multi-peak analysis (solid line and black star (*)).</p

    Transmission electron micrograph of Pil strain.

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    <p>(A) Pil strain bacterium (scale bar is 500 nm). A close-up of a pilus (black square) is shown in (B) with higher contrast and (C) image analysis of the contour.</p