Dispersion Analysis of Short Carbon Fibers in Two‐Phase Fluids

ABSTRACT Dispersion of short fibers in two‐polymer mixtures is complex. Selective adsorption of polymer chains causes fibers either to aggregate into bundles or to preferentially distribute in one of the polymer phases, depending on the size and orientation of the polymer domain. To observe the process, we systematically investigated the morphology evolution of short carbon fibers in non‐polar paraffin oil upon the addition of a polar solvent, a mixture considered to be similar to carbon fiber dispersion in HDPE/PA6. Adding a small amount of formamide, the uniformly dispersed short fibers in paraffin oil gradually aggregate into a fibril network, as evidenced by a gradual increase in mixture viscosity. This is rationalized by the fact that many formamide drops preferentially segregate at the junction of two fibers due to capillarity. With increasing formamide loading, the capillary force between formamide and carbon fibers drives the fibers aggregation into bundles, and ultimately coagulation into big clusters. This process was confirmed by a gradual decrease in viscosity. Enhancing the shear rate and paraffin oil viscosity effectively suppresses bundle formation. Furthermore, adjusting the capillary force by matching the surface tension of the polar solvent facilitates morphology control from the fibril network to the bundle formation.