An industrially relevant continuous flow blending process has been developed that controllably forms in the melt various structured distributions of carbon black particles to impart uniform or directional conductivities to extrusions such as film, sheet, or tubing. A range of electrical properties was selectable on line via process parameter specification. Process control also made possible production of extrusions with graduated or periodic properties such that functional materials and devices can be extracted from extrusions. The process was enabled by chaotic advection, a recent sub-field of fluid mechanics, and was previously demonstrated in part for particulate additives with batch devices. Unlike conventional mixing where the focus is on attaining uniform particle dispersions, chaotic advection inherently promoted structure formation in melts at increasingly smaller length scales such that percolation thresholds can be reduced. Because conducting conditions are attained at low solid additive loadings, a reverse percolation effect was also induced via controlled structure breakdown. Progressive structure formation is related to electrical properties and processing conditions. Methods are applicable to other melt-processable materials and additives. (c) 2004 Elsevier Ltd. All rights reserved.