The working principle of static mixers is based on repeated stretching, cutting, and stacking operations. Two‐way splitting (cutting) elements are most commonly used. Multiple splitting elements increase the compactness of the mixer, but an issue is the pressure consumption. Here we first investigate how to improve existing two way splitting and recombining flows. We use the serpentine channel geometry which relevance is that it is easy to fabricate on the interface between two halves of a mold or device. Next a parallel multiple splitting method is developed which is compact and efficient in terms of pressure consumption and uniformity of the resulting layer distribution. The final design represents a fully parallel multiple mixer, circularly shaped, that uses fan shaped channels (for a uniform flow length distribution) to guide the flow to its splitting channels, where it is turned and recollected in a second fan shaped channel. Because of its twelve‐way parallel splitting design, the device produces 24 layers in one mixing element and 288 layers in the second element and so on. Prototypes are fabricated, tested on performance, and compared with some existing static mixers using mixing speed, volume, length, and pressure drop as criteria. The new mixer outperforms the other designs, with an exception of the volume used. magnified image

The potential of structuring thermoplastic polymers by convection only, using a combination of static mixer elements, which easily produce stratified structures with thousands of layers, and the black box concept that serves to elegantly combine materials in standard co‐extrusion technology is investigated. The aim is to obtain an alternative for routes that try to structure organic matter such as polymers down to submicrometer levels, usually via self‐organization based on phase separation. Structure is characterized by its complexity, here defined by the level of hierarchy. Horizontal stratification, parallel to the surface, is level 0. Vertical stratification connected to horizontal surface layers, is level 1. A series of horizontal stratifications in distinct places vertically connected to the surface layers is level 2. Higher levels of hierarchy finally result in dendritic structures that are fractal. Applications of complex structures with a huge interface and guaranteed cocontinuity throughout the whole cross section of the products are found in, for example, membranes for fuel cells and gas separators, and in miniaturizing electronic and optical devices such as photovoltaic cells.

For a multitude of high‐end applications such as photovoltaics and membranes for fuel cells or gas separation, creating large internal surfaces via fractal structuring during polymer processing can result in unique possibilities for enhancing performance. Structuring is possible even in processing techniques like injection molding. Inspired by microfluidic practice, an optimized splitting and recombining static mixer is realized on the parting surface of a mold. Different geometries are used to multiply, rotate, and add stratified structures. After the obvious structuring of a number of parallel layers, attention is focused on layers perpendicular to the product surface. A combination of the two allows complex hierarchical fractal structures to be obtained. A first demonstration of its feasibility is reported.

Relatively recently, we advanced a route to create, in a controlled fashion, combined horizontal and vertical stratified structures by simple and energy‐efficient processing operations employing static mixing elements. While in state‐of‐the‐art static mixing the focus is on layer multiplication, here the aim is to create hierarchical fractal structures. Therefore, the main question addressed in this article is how structures, rather than layers, can be multiplied. The key aspect is the addition of layers on the sides or in the midplane of the flow during the process; every addition step increases the hierarchy by one level. This article derives the general formalism for forming fractal structures with controlled hierarchy, and we develop the language required to design and construct the dies. The main part of the article addresses this main topic and is based on the splitting serpentine static mixer geometry that can be easily made on the parting surfaces of a mold on both the micro‐ and the macroscale. The second part of the article addresses the strategy to minimize the number of mirroring steps, eventually avoiding mirroring completely, and is based on the rotation‐free multiflux static mixer geometry. With the design language derived, complex hierarchical fractal structures can be generated simply by changing the number and sequence of operators within extrusion dies or molds, providing a one‐step solution to produce material structures for potential use in diverse applications ranging from advanced mechanical systems to photovoltaic devices, where controlled assembly of dissimilar materials, and the realization of huge interfaces and genuine cocontinuity throughout the cross section, is critical.

Microfluidic devices as used, e.g., in lab‐on‐a‐chip and micro‐total‐analysis systems, are frequently fabricated using silicon or polydimethylsiloxane (PDMS)‐based technologies, both with their known disadvantages. Here, we design a fully polymeric, multifunctional microfluidic reactor device, using an alternative fabrication method, the two‐component co‐injection moulding technology, in which different polymer combinations—generally a flexible and a rigid thermoplastic polymer—can be applied. The prototype device is based on an ambi‐symmetrical design, combining two identical shells, that are each folded to occupy a 160 × 90 mm2 space and subsequently stacked into a 4 (double) layer system. One microfluidic reactor unit includes six different in‐ and output connections, six peristaltic pumps (built up from three membranes each), eighteen volume‐neutral, recoverable control valves, two fluid storages, and two efficient, flow splitting, rotating and recombining, serpentine mixers. The mixers realize an almost perfect baker's transformation and possess ten elements that create 2 × 410 layers with an individual striation thickness of 0.5 nm in 10 s. The total reactor volume amounts 7 mL. The capacity of the peristaltic pumps, with their stroke of 0.5 mm, equals about 35 µL · s−1 at an actuation frequency of 5 Hz. Actuation occurs by air pressure. One microfluidic device can be endlessly connected to its replicas.