Scalable Manufacturing of Hierarchical Biphasic Bicontinuous Structures via Vaporization-Induced Phase Separation (VIPS)

Abstract

Studies of particle-stabilized biphasic structures have greatly expanded the possibilities of multiphasic systems by producing liquid composites with unique morphologies and properties. The solvent transfer-induced phase separation (STRIPS) method was previously introduced to prepare bicontinuous interfacially jammed emulsion gels (bijels), a unique class of particle-stabilized biphasic structures. Although STRIPS enables continuous processing, the requirement of an external aqueous phase may limit its application. In this work, a new method to produce a variety of three-dimensional multiphasic structures including bijels via vapor-induced phase separation (VIPS) is demonstrated. VIPS enables the fabrication of films and coatings by spreading or spraying a particle-laden suspension onto a surface without the need of an outer aqueous phase. Intriguingly, secondary nucleation of structures occurs within phase separated domains, leading to hierarchically bicontinuous biphasic structures. The dimensions of phase separated domains can be controlled by the rate of cosolvent removal. Moreover, a different path to bicontinuous morphology is identified, which does not occur via spinodal decomposition but rather relies on the formation of percolating structures of partially coalesced particle-covered droplets. The VIPS process provides a scalable path to produce bicontinuous biphasic composites with hierarchical structures for advanced coatings and membranes applications.

Bicontinuous interfacially jammed emulsion gels with nearly uniform sub-micrometer domains via regulated co-solvent removal

“…Within a few seconds, a thin layer of VIPS bijel is formed by the evaporation of ethanol, accelerated by an airstream (5 m s −1 ) parallel to the evaporating surface. 18 Subsequently, in the STRIPS stage of the process, the entire film is submerged into water to initiate further bijel maturation via STRIPS. During this stage, the ethanol content in the remaining homogeneous mixture must flux through the VIPS outer layer in order to partition to the outer aqueous phase.…”

“…15 STRIPS bijels with such aligned asymmetric structures have shown superior performance as filtration membranes. 4 We have also introduced the vaporization induced phase separation (VIPS) method 18 in which the gentle evaporation of a co-solvent minimized the influence of fluid flow on structure formation. However, the rate of co-solvent removal in VIPS is not high enough to form internal domains with sub-micrometer features, even with the help of airflow accelerating the evaporation.…”

Super‐Macroporous Lightweight Materials Templated from Bicontinuous Intra‐Phase Jammed Emulsion Gels Based on Nanochitin

“…The spinodal decomposition can be initiated by a) heating/cooling of a partially‐miscible solvent pair across the critical solubility temperature; [ 2 ] b) solvent transfer‐induced phase separation; [ 5,7 ] and c) vaporization‐induced phase separation. [ 8 ] Direct mixing has also been reported for bijel formation. [ 9 ] However, the fabrication of bijels requires interfacial‐active and neutral‐wetting particles, which must adsorb at interfaces rapidly while exhibiting no preferential interfacial curvature upon jamming.…”

“…The spinodal decomposition can be initiated by a) heating/cooling of a partially-miscible solvent pair across the critical solubility temperature; [2] b) solvent transfer-induced phase separation; [5,7] and c) vaporization-induced phase separation. [8] Direct mixing Non-equilibrium multiphase systems are formed by mixing two immiscible nanoparticle dispersions, leading to bicontinuous emulsions that template cryogels with interconnected, tortuous channels. Herein, a renewable, rod-like biocolloid (chitin nanocrystals, ChNC) is used to kinetically arrest bicontinuous morphologies.…”

Rapid production of bicontinuous macroporous materials using intrinsically polymerizable bijels

“…Inclusion of a monomer in the bijel's precursor formulation has been demonstrated in other systems, particularly in bijels formed by direct mixing, 22 solvent transfer, 23 and solvent evaporation. 24 However, our method offers important advantages over these existing protocols. First, bicontinuous structures formed through spinodal decomposition enjoy a number of morphological features unique to this mode of de-mixing, namely dynamic self similarity, uniform domain sizes, and negative Gaussian interfacial curvatures, as well as tunability of these parameters, which cannot be guaranteed through direct mixing routes.…”