Magnetic Resonance Studies of Liquid–Soft Solid Mixing by Extrusion

The mixing of immiscible liquids and soft solid materials is an important industrial activity. Various magnetic resonance (MR) techniques have been used to quantify the characteristics of a mixture of an immiscible liquid [poly-dimethylsiloxane (PDMS), 8.4 wt%] added to a commercial soap, both prior to and following ram extrusion, mimicking the incorporation of perfumes and other beneficial liquids into such products. In particular, MR was used to measure self-diffusion of the PDMS, the restricted nature of which was used to estimate the size of the PDMS liquid domains within the soft-solid matrix. In combination with MR imaging techniques these measurements were also used to probe the spatial distribution of such liquid domains. The mixtures were initially prepared using two methods: cold-mixing (at room temperature) or warm-mixing (at 55°C). Both mixing methods yielded similar self-diffusion characteristics prior to extrusion, corresponding to initial PDMS domain sizes of approximately 6.4 μm. Extruded cold-mixed samples showed elongation of the domains along the direction of extrusion whilst significant volume reduction (∼30%) was detected for the warm-mixed samples. Imaging revealed that the PDMS domain sizes did not vary in size or concentration with radius across the cylindrical extruded materials.