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1. Influence of Surface Roughness on Interfacial Properties of Particle Networks

   https://doi.org/10.3390/colloids8020017  

   Correia, Elton L; Brown, Nick; Papavassiliou, Dimitrios V; Razavi, Sepideh (March 2024, Colloids and Interfaces)

   The behavior of colloidal particles near fluid interfaces has attracted significant scientific interest, as particles minimize the contact area between the two fluid phases, stabilizing interfacial systems. This study explores the influence of surface roughness on the properties of particle monolayers at the air–water interface, focusing on colloidal silica particles and fumed silica particles of similar hydrodynamic diameter. This research involves comparing low-surface-area (LSA) and medium-surface-area (MSA) fumed silica particles with spherical colloidal silica particles (250 nm in diameter). Utilizing a Langmuir trough, the interfacial particle networks are compressed and expanded. Analysis of surface pressure isotherms reveals that fumed silica particle monolayers form networks at a lower particle surface coverage compared to spherical particles. The spherical particle monolayer exhibits a higher apparent surface elasticity, indicating greater resistance to the applied compression compared to fumed silica networks. Additionally, monolayers formed by fumed silica particles display hysteresis even after successive compressions and expansions due to irreversible particle interlocking and the formation of multilayered aggregates. These findings provide insights into the impact of surface roughness on the behavior of particle monolayers at fluid interfaces, offering valuable information for designing and optimizing mechanisms involved in emulsion and foam stabilization. 

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2. Particle Size and Rheology of Silica Particle Networks at the Air–Water Interface

   https://doi.org/10.3390/nano13142114  

   Thakur, Siddharth; Razavi, Sepideh (July 2023, Nanomaterials)

   Silica nanoparticles find utility in different roles within the commercial domain. They are either employed in bulk within pharmaceutical formulations or at interfaces in anti-coalescing agents. Thus, studying the particle attributes contributing to the characteristics of silica particle-laden interfaces is of interest. The present work highlights the impact of particle size (i.e., 250 nm vs. 1000 nm) on the rheological properties of interfacial networks formed by hydrophobically modified silica nanoparticles at the air–water interface. The particle surface properties were examined using mobility measurements, Langmuir trough studies, and interfacial rheology techniques. Optical microscopy imaging along with Langmuir trough studies revealed the microstructure associated with various surface pressures and corresponding surface coverages (ϕ). The 1000 nm silica particle networks gave rise to a higher surface pressure at the same coverage compared to 250 nm particles on account of the stronger attractive capillary interactions. Interfacial rheological characterization revealed that networks with 1000 nm particles possess higher surface modulus and yield stress in comparison to the network obtained with 250 nm particles at the same surface pressure. These findings highlight the effect of particle size on the rheological characteristics of particle-laden interfaces, which is of importance in determining the stability and flow response of formulations comprising particle-stabilized emulsions and foams. 

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3. Janus Particles at Fluid Interfaces: Stability and Interfacial Rheology

   https://doi.org/10.3390/nano11020374  

   Correia, Elton L.; Brown, Nick; Razavi, Sepideh (February 2021, Nanomaterials)

   null (Ed.)

   The use of the Janus motif in colloidal particles, i.e., anisotropic surface properties on opposite faces, has gained significant attention in the bottom-up assembly of novel functional structures, design of active nanomotors, biological sensing and imaging, and polymer blend compatibilization. This review is focused on the behavior of Janus particles in interfacial systems, such as particle-stabilized (i.e., Pickering) emulsions and foams, where stabilization is achieved through the binding of particles to fluid interfaces. In many such applications, the interface could be subjected to deformations, producing compression and shear stresses. Besides the physicochemical properties of the particle, their behavior under flow will also impact the performance of the resulting system. This review article provides a synopsis of interfacial stability and rheology in particle-laden interfaces to highlight the role of the Janus motif, and how particle anisotropy affects interfacial mechanics. 

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4. Porous Polymer Structures with Tunable Mechanical Properties Using a Water Emulsion Ink

   https://doi.org/10.3390/ma17051074  

   Dantzler, Joshua_Z R; Gomez, Sofia Gabriela; Gonzalez, Stephanie; Gonzalez, Diego; Loera_Martinez, Alan O; Marquez, Cory; Hassan, Md Sahid; Zaman, Saqlain; Lopez, Alexis; Mahmud, Md Shahjahan; et al (March 2024, Materials)

   Recently, the manufacturing of porous polydimethylsiloxane (PDMS) with engineered porosity has gained considerable interest due to its tunable material properties and diverse applications. An innovative approach to control the porosity of PDMS is to use transient liquid phase water to improve its mechanical properties, which has been explored in this work. Adjusting the ratios of deionized water to the PDMS precursor during blending and subsequent curing processes allows for controlled porosity, yielding water emulsion foam with tailored properties. The PDMS-to-water weight ratios were engineered ranging from 100:0 to 10:90, with the 65:35 specimen exhibiting the best mechanical properties with a Young’s Modulus of 1.17 MPa, energy absorption of 0.33 MPa, and compressive strength of 3.50 MPa. This led to a porous sample exhibiting a 31.46% increase in the modulus of elasticity over a bulk PDMS sample. Dowsil SE 1700 was then added, improving the storage capabilities of the precursor. The optimal storage temperature was probed, with −60 °C resulting in great pore stability throughout a three-week duration. The possibility of using these water emulsion foams for paste extrusion additive manufacturing (AM) was also analyzed by implementing a rheological modifier, fumed silica. Fumed silica’s impact on viscosity was examined, revealing that 9 wt% of silica demonstrates optimal rheological behaviors for AM, bearing a viscosity of 10,290 Pa·s while demonstrating shear-thinning and thixotropic behavior. This study suggests that water can be used as pore-formers for PDMS in conjunction with AM to produce engineered materials and structures for aerospace, medical, and defense industries as sensors, microfluidic devices, and lightweight structures. 

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5. Structural analysis of bijels stabilized by magnetically responsive ellipsoidal particles

   https://doi.org/10.1063/5.0268127  

   Karthikeyan, Nikhil; Schiller, Ulf D (August 2025, Physics of Fluids)

   Bicontinuous interfacially jammed emulsion gels offer a versatile platform for emulsion templating of functional porous materials, including membranes, electrodes, and tissue-mimetic biomaterials. In many applications of such materials, the microstructure determines the properties and performance of devices. Characterization of the morphological structure of emulsion templates is, thus, an important step in developing fabrication methods for porous materials with tunable microstructure. We present a structural analysis of bijels stabilized by magnetic ellipsoidal particles. Using data from hybrid lattice Boltzmann-molecular dynamics simulations of binary liquids with suspended magnetic ellipsoidal particles, we analyze the bond orientational order within the interfacial particle layer, the mean and Gaussian curvature of the interfaces, and the topological properties of the emulsion morphology. The results suggests that the particle packing at the interface is influenced by the local topology as characterized by the Gaussian curvature, and the global topological properties can be linked to domain coarsening mechanisms, such as coalescence of domains and pinch-off of channels. By analyzing independent simulation runs with different initial conditions, we probe the statistical variations of different properties, including the channel size distribution and the average channel size. Our analysis provides a more detailed picture of the structural properties of bijels stabilized by magnetically responsive ellipsoids and can guide the optimization of interfacial particle packing and domain structure of particle-stabilized emulsion systems. 

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