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1. Designing bijels formed by solvent transfer induced phase separation with functional nanoparticles

   https://doi.org/10.1039/C9SM00289H  

   Boakye-Ansah, Stephen; Schwenger, Matthew S.; Haase, Martin F. (April 2019, Soft Matter)

   Bicontinuous interfacially jammed emulsion gels (bijels) formed via solvent transfer induced phase separation (STrIPS) are new soft materials with potential applications in separations, healthcare, or catalysis. To facilitate their applications, means to fabricate STrIPS bijels with nanoparticles of various surface chemistries are needed. Here, we investigate the formation of STrIPS bijels with nanoparticles of different wettabilities, ranging from partially hydrophobic to extremely hydrophilic. To this end, the surface wettability of silica nanoparticles is tailored by functionalization with ligands bearing either hydrophobic or hydrophilic terminal groups. We show that partially hydrophobic particles with acrylate groups can impart short-term stability to STrIPS bijels on their own. However, to enable long-term stability, the use of cationic surfactants is needed. Partially hydrophobic particles require short chain surfactants for morphological stability while glycerol-functionalized hydrophilic particles require double chain cationic surfactants. Variation of the surfactant concentration results in various STrIPS bijel morphologies with controllable domain sizes. Last, we show that functional groups on the nanoparticles facilitate interfacial cross-linking for the purposes of reinforcing STrIPS bijels. Our research lays the foundation for the use of a wide variety of solid particles, irrespective of their surface wettabilities, to fabricate bijels with potential applications in Pickering interfacial catalysis and as cross-flow microreactors. 

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

   https://doi.org/10.1039/d2mh01479c  

   Wang, Tiancheng; Riggleman, Robert A.; Lee, Daeyeon; Stebe, Kathleen J. (April 2023, Materials Horizons)

   Porous materials possess numerous useful functions because of their high surface area and ability to modulate the transport of heat, mass, fluids, and electromagnetic waves. Unlike highly ordered structures, disordered porous structures offer the advantages of ease of fabrication and high fault tolerance. Bicontinuous interfacially jammed emulsion gels (bijels) are kinetically trapped disordered biphasic materials that can be converted to porous materials with tunable features. Current methods of bijel fabrication result in domains that are micrometers or larger, and non-uniform in size, limiting their surface area, mechanical strength, and interaction with electromagnetic waves. In this work, scalable synthesis of bijels with uniform and sub-micrometer domains is achieved via a two-step solvent removal process. The resulting bijels are characterized quantitatively to verify the uniformity and sub-micrometer scale of the domains. Moreover, these bijels have structures that resemble the microstructure of the scale of the white beetle Cyphochilus. We find that such bijel films with relatively small thicknesses (<150 μm) exhibit strong solar reflectance as well as high brightness and whiteness in the visible range. Considering their scalability in manufacturing, we believe that VIPS-STRIPS bijels have great potential in large-scale applications including passive cooling, solar cells, and light emitting diodes (LEDs). 

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3. Effect of (3-aminopropyl)triethoxysilane on dissolution of silica nanoparticles synthesized via reverse micro emulsion

   https://doi.org/10.1039/D2NR01190E  

   Kang, Hyunho; Lee, Jihyeon; O'Keefe, Tana; Tuga, Beza; Hogan Jr., Christopher J.; Haynes, Christy L. (June 2022, Nanoscale)

   Silica nanomaterials have been studied based on their potential applications in a variety of fields, including biomedicine and agriculture. A number of different molecules have been condensed onto silica nanoparticles’ surfaces to present the surface chemistry needed for a given application. Among those molecules, (3-aminopropyl)triethoxysilane (APS) is one of the most commonly applied silanes used for nanoparticle surface functionalization to achieve charge reversal as well as to enable cargo loading. However, the colloidal stability of APS-functionalized silica nanoparticles has not been thoroughly studied, which can be problematic when the high reactivity of amine groups is considered. In this study, four different types of silica nanoparticles with varied location of added APS have been prepared via a reverse micro emulsion process, and their colloidal stability and dissolution behavior have been investigated. Systematic characterization has been accomplished using transmission electron microscopy (TEM), silicomolybdic acid (SMA) spectrophotometric assay, nitrogen adsorption–desorption surface area measurement, and aerosol ion mobility-mass spectrometry to track the nanoparticles’ physical and chemical changes during dissolution. We find that when APS is on the interior of the silica nanoparticle, it facilitates dissolution, but when APS is condensed both on the interior and exterior, only the exterior siloxane bonds experience catalytic hydrolysis, and the interior dissolution is dramatically suppressed. The observation and analyses that silica nanoparticles show different hydrolysis behaviors dependent on the location of the functional group will be important in future design of silica nanoparticles for specific biomedical and agricultural applications. 

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4. Bicontinuous Interfacially Jammed Emulsion Gels (bijels) as Media for Enabling Enzymatic Reactive Separation of a Highly Water Insoluble Substrate

   https://doi.org/https://doi.org/10.1038/s41598-019-42769-8  

   Cha, Sanghak; Lim, Hyun Gyu; Haase, Martin F.; Stebe, Kathleen J.; Jung, Gyoo Yeol; Lee, Daeyeon (April 2019, Scientific reports)

   Although enzymes are efficient catalysts capable of converting various substrates into desired products with high specificity under mild conditions, their effectiveness as catalysts is substantially reduced when substrates are poorly water-soluble. In this study, to expedite the enzymatic conversion of a hydrophobic substrate, we use a bicontinuous interfacially jammed emulsion gel (bijel) which provides large interfacial area between two immiscible liquids: oil and water. Using lipase-catalyzed hydrolysis of tributyrin as a model reaction in a batch mode, we show that bijels can be used as media to enable enzymatic reaction. The bijel system gives a four-fold increase in the initial reaction rate in comparison to a stirred biphasic medium. Our results demonstrate that bijels are powerful biphasic reaction media to accelerate enzymatic reactions with various hydrophobic reagents. This work also demonstrates that bijels can potentially be used as reaction media to enable continuous reactive separations. 

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5. A basic model for the nonlinear rheology of bijels

   https://doi.org/10.1122/8.0000914  

   Ching, Herman; Mohraz, Ali (January 2025, Journal of Rheology)

   We examine the rheology of bicontinuous interfacially jammed emulsion gels (bijels) beyond the limit of linear viscoelasticity and propose a simple model that connects bijel rheology to anticipated microstructural changes in the continuous particle-laden interface. The basic elements of our model are constructed from a linear stress relaxation experiment, which suggests glasslike rheology mediated by α (out-of-cage) and β (in-cage) particle dynamics along the interface in this limit. Extending to medium amplitude oscillatory shear experiments then reveals signatures of nonlinearity, which we rationalize as the combined effect of shear-induced dilation of the interface and its simultaneous recompaction by interfacial tension, as well as potential buckling along portions of the interface under compression. Informed by these observations, we present a double Maxwell model with sigmoidal nonlinearities introduced to account for how interfacial dilation and recompaction affect the intercage particle dynamics (α relaxation) along the interface and buckling. This simple model successfully captures the general features of nonlinear rheology in bijels, indicating that their linear-to-nonlinear transition is associated with loss of compaction along the dilated and buckling along the compacted regions of the interface. Our results shed initial light on the microstructural origins of nonlinear rheology in bijels and the reconfigurability afforded in these systems by the balance of glassy particle dynamics and interfacial recompaction under shear deformation. 

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