Interfacial Jamming Research Articles

Chemistry, applications, and future prospects of structured liquids.

Structured liquids are emerging functional soft materials that combine liquid flowability with solid-like structural stability and spatial organization. Here, we delve into the chemistry and underlying principles of structured liquids, ranging from nanoparticle surfactants (NPSs) to supramolecular assemblies and interfacial jamming. We then highlight recent advancements related to the design of intricate all-liquid 3D structures and examine their reconfigurability. Additionally, we demonstrate the versatility of these soft functional materials through innovative applications, such as all-liquid microfluidic devices and liquid microreactors. We envision that in the future, the vast potential of the liquid-liquid interface combined with human creativity will pave the way for innovative platforms, exemplified by current developments like liquid batteries and circuits. Although still in its nascent stages, the field of structured liquids holds immense promise, with future applications across various sectors poised to harness their transformative capabilities.

AIE‐Switching and Enantioselective Reactivity at Jammed Liquid‐Liquid Interface

AbstractThe jammed liquid‐liquid interface offers an elegant approach to achieve non‐equilibrium shapes of liquids. The interfacial jamming subsequently brings about formation of 2D “solid‐like” assembly. In this work, biphasic reaction between a perylenediimide based luminogen benzoperylenediimide monoanhydride (Bp(Im)2MA) and diamines are demonstrated that rendered amide bond formation and in turn amide nanoconjugates across the oil‐water interface. Amide nanoconjugates formed with different diamines showed diamine alkyl chain length dependent varied interfacial properties and sizes. Jamming of the interface is judiciously utilized to induce aggregation of amide nanoconjugates which successfully established macroscopic Aggregation Induced Emission‐switching (AIE‐switching) behavior. Further, the versatility of this approach is extended to analyze the reactivity of chiral amino acids. The reaction between the Bp(Im)2MA luminogen and chiral amino acids exhibits macroscopic enantioselectivity at jammed interface via diverse surface coverage of the amino acids‐based amide nanoconjugates. The formation of discrete nanoscopic amide interfacial assembly for each of the L‐ and D‐ amino acids isomers is corroborated with Atomic Force Microscopy (AFM) images. This study extends a fascinating pathway to aid in understanding and fabrication of structurally diverse jammed interfaces and aggregation of organic molecules across an oil‐water interface.

Roll‐to‐Roll Fabrication of Bijels via Solvent Transfer Induced Phase Separation (R2R‐STrIPS)

AbstractBicontinuous interfacially jammed emulsion gels (bijels) are soft materials with applications in separation science, energy storage, catalysis, and tissue engineering. Bijels are formed by arresting the liquid–liquid phase separation of two immiscible liquids via interfacial jamming of colloidal particles. Current fabrication methods of bijels employ either batch processing or continuous‐flow microfluidic synthesis. Production methods with higher throughput are needed to facilitate large‐scale synthesis of bijels. Herein, it is shown that roll‐to‐roll processing (R2R) enables the fabrication of bijel films with controlled dimensions at rates of several cm3 per minute. Increasing the bijel production rate via R2R requires an understanding of the interaction of the bijel with the R2R substrate. The study demonstrates that controlling the wetting on the R2R substrate enables the synthesis of uniform bijel films with adjustable thickness. Moreover, this research shows that the bijel film microstructure depends on the mechanism of phase separation and particle surface functionalization. The resulting knowledge gains can help to leverage bijel synthesis from laboratory to industrial scales in the future, promoting the exciting application potentials of bijels.

Amphiphilic Heterografted Molecular Bottlebrushes with Tertiary Amine-Containing Side Chains as Efficient and Robust pH-Responsive Emulsifiers.

By combining the unique characteristics of molecular bottlebrushes (MBBs) and the properties of stimuli-responsive polymers, we show that MBBs with randomly grafted poly(n-butyl acrylate) and pH-responsive poly(2-(N,N-diethylamino)ethyl methacrylate) (PDEAEMA) side chains are efficient and robust pH-responsive emulsifiers. Water-in-toluene emulsions were formed at pH 4.0 and disrupted by increasing the pH to 10.0. The emulsion generation and disruption was reversible over the ten cycles investigated, and the bottlebrushes remained intact. The exceptional emulsion stability stemmed from the high interfacial binding energy of MBBs, imparted by their large molecular size and Janus architecture at the interface, as evidenced by the interfacial jamming and wrinkling of the assemblies upon reducing the interfacial area. At pH 10.0, PDEAEMA became water-insoluble, and the MBBs desorbed from the interface, causing de-emulsification. Consequently, we have shown that the judicious design of MBBs can generate properties of particle emulsifiers from their large size, while the responsiveness of the MBBs enables more potential applications.

Amphiphilic Heterografted Molecular Bottlebrushes with Tertiary Amine‐Containing Side Chains as Efficient and Robust pH‐Responsive Emulsifiers

AbstractBy combining the unique characteristics of molecular bottlebrushes (MBBs) and the properties of stimuli‐responsive polymers, we show that MBBs with randomly grafted poly(n‐butyl acrylate) and pH‐responsive poly(2‐(N,N‐diethylamino)ethyl methacrylate) (PDEAEMA) side chains are efficient and robust pH‐responsive emulsifiers. Water‐in‐toluene emulsions were formed at pH 4.0 and disrupted by increasing the pH to 10.0. The emulsion generation and disruption was reversible over the ten cycles investigated, and the bottlebrushes remained intact. The exceptional emulsion stability stemmed from the high interfacial binding energy of MBBs, imparted by their large molecular size and Janus architecture at the interface, as evidenced by the interfacial jamming and wrinkling of the assemblies upon reducing the interfacial area. At pH 10.0, PDEAEMA became water‐insoluble, and the MBBs desorbed from the interface, causing de‐emulsification. Consequently, we have shown that the judicious design of MBBs can generate properties of particle emulsifiers from their large size, while the responsiveness of the MBBs enables more potential applications.

Solvent Quality and Aggregation State of Asphaltenes on Interfacial Mechanics and Jamming Behavior at the Oil/Water Interface.

The formation of highly stable water-in-oil emulsions results in complications in both upstream and downstream processing. Emulsion stability in these systems has been connected to the adsorption of surface-active asphaltenes that are assumed to form a rigidified film at the oil/water (o/w) interface. Full characterization of this behavior is needed to allow for engineered solutions for enhanced oil recovery. Interfacial properties, such as surface pressure and interfacial elasticity, are implicated in the stabilizing mechanism for these observed films. Asphaltenes are known to be interfacially active in both good solvents (aromatics) and poor solvents (high ratio of aliphatic to aromatic). However, due to inherent complexities present in asphaltene studies, the details of the mechanical properties of the interface remain poorly understood. Despite the widely accepted perception that asphaltenes form persistent rigid films at fluid-fluid interfaces, the connection between bulk solution properties and interfacial mechanics has not been resolved. Here, the effects of solvent quality on the interfacial properties of asphaltene dispersions are determined by using a well-defined asphaltene/solvent system. Interfacial rigidity is observed only under poor solvent conditions, while the good solvent system remains fluid-like. The interfacial rheology under good and poor solvent conditions is measured simultaneously with surface pressure measurements to track interfacial development. It is shown that surface pressure and dilatational modulus measurements are not indicators of whether an interface demonstrates rigid behavior under large compressions. Finally, conditions required for asphaltene-coated interfaces to exhibit the mechanical behavior associated with a rigidified interface are defined. This work provides a framework for quantifying the impact of the aggregation state of asphaltenes on the stability and mechanics at the o/w interface.

Reconfigurable Magnetic Liquid Building Blocks for Constructing Artificial Spinal Column Tissues.

All-liquid molding can be used to transform a liquid into free-form solid constructs, while maintaining internal fluidity. Traditional biological scaffolds, such as cured pre-gels, are normally processed in solid state, sacrificing flowability and permeability. However, it is essential to maintain the fluidity of the scaffold to truly mimic the complexity and heterogeneity of natural human tissues. Here, this work molds an aqueous biomaterial ink into liquid building blocks with rigid shapes while preserving internal fluidity. The molded ink blocks for bone-like vertebrae and cartilaginous-intervertebral-disc shapes, are magnetically manipulated to assemble into hierarchical structures as a scaffold for subsequent spinal column tissue growth. It is also possible to join separate ink blocks by interfacial coalescence, different from bridging solid blocks by interfacial fixation. Generally, aqueous biomaterial inks are molded into shapes with high fidelity by the interfacial jamming of alginate surfactants. The molded liquid blocks can be reconfigured using induced magnetic dipoles, that dictated the magnetic assembly behavior of liquid blocks. The implanted spinal column tissue exhibits a biocompatibility based on in vitro seeding and in vivo cultivating results, showing potential physiological function such as bending of the spinal column.

Rheology of graphene oxide stabilized Pickering emulsions.

Pickering emulgels stabilized by graphene oxide (GO) with didodecyldimethylammonium bromide (DDAB) as an auxiliary surfactant and liquid paraffin as the oil phase have proved to be an excellent 3D printable ink. This paper elucidates the structure of such emulgels by a combination of microscopy before and after intensive shear as well as broadband dielectric spectroscopy and rheology in the linear and nonlinear regime. An increase of the DDAB surfactant and GO-contents leads to a systematic increase of modulus and viscosity, a reduction of the limits of the nonlinear regime and a more complicated variation of the normal forces, with negative normal forces at high shear rate  for low GO-contents and positive normal forces at high GO-contents. The interfacial jamming behavior studied by morphology, rheology and dielectric spectroscopy is explained based on droplet deformation, jamming and recovery phenomena.

Interfacial Assembly and Jamming of Soft Nanoparticle Surfactants into Colloidosomes and Structured Liquids.

Nanoparticle surfactant (NPS) offers a powerful strategy to generate all-liquid constructs that integrate the inherent properties of the NPs into 3D architectures. Here, using the co-assembly of fluorescent polymeric nanoparticles and amine-functionalized polyhedral oligomeric silsesquioxane, the assembly and jamming behavior of a new type of NPS at the oil-water interface is uncovered. Unlike "solid" inorganic nanoparticles, "soft" polymeric nanoparticles can reorganize when jammed, leading to a relaxation and deformation of the interfacial assemblies, for example, the 3D printed sugar-coated haw stick-like liquid tubules. With NPS serving as emulsifiers, stable Pickering emulsions are prepared that can be converted into robust colloidosomes with pH responsiveness, showing numerous potential applications for encapsulation and controlled release.

Stabilizing and structuring oil–oil interfaces by molecular brush surfactants

AbstractOil‐in‐oil emulsions provide a unique platform for numerous applications not compatible with water or aqueous systems. However, the limited types and complicated synthesis process of surfactants are problematic. Here, we put forward a simple, yet powerful strategy to stabilize the oil–oil interface, then prepare oil‐in‐oil emulsions, by using the co‐assembly of polar molecular brushes and nonpolar oligomeric ligands at the DMF–octane interface. Molecular brush surfactants (MBSs) form and assemble in situ at the interface, minimizing the interfacial energy and producing a robust film. We find that the binding energy of MBS to the interface is sufficiently high, leading to the construction of structured liquids by the interfacial jamming of MBSs. Using MBSs as emulsifiers, different types of emulsions including DMF‐in‐octane, octane‐in‐DMF, and high internal phase emulsions can be easily prepared, showing promising applications in microreactor systems and advanced composite materials.

Reconfigurable Liquids Constructed by Pillar[6]arene‐Based Nanoparticle Surfactants

AbstractThe interfacial jamming of nanoparticle surfactants offers the possibility of structuring liquids and fabricating all‐liquid constructs with advanced functionality. However, less attention has been given to structured liquids with multiple responsiveness. Here, we show a novel, yet highly simplified nanoparticle surfactant model, pillar[6]arene (PA[6]) surfactant, by taking advantage of the host–guest interactions between a water‐soluble PA[6] and an oil‐soluble ligand, ferrocenium terminated polystyrene. PA[6] surfactants form rapidly at the oil–water interface, assemble into an elastic film with excellent mechanical strength, and when jammed, offer a “solid‐like” assembly to lock‐in highly nonequilibrium shapes of the liquids. The interfacial assembly/jamming and disassembly/unjamming of PA[6] surfactants can be controlled by chemical redox or competitive guest reagents, endowing the structured liquids with redox or guest‐competitive responsiveness.

Reconfigurable Liquids Constructed by Pillar[6]arene-Based Nanoparticle Surfactants.

The interfacial jamming of nanoparticle surfactants offers the possibility of structuring liquids and fabricating all-liquid constructs with advanced functionality. However, less attention has been given to structured liquids with multiple responsiveness. Here, we show a novel, yet highly simplified nanoparticle surfactant model, pillar[6]arene (PA[6]) surfactant, by taking advantage of the host-guest interactions between a water-soluble PA[6] and an oil-soluble ligand, ferrocenium terminated polystyrene. PA[6] surfactants form rapidly at the oil-water interface, assemble into an elastic film with excellent mechanical strength, and when jammed, offer a "solid-like" assembly to lock-in highly nonequilibrium shapes of the liquids. The interfacial assembly/jamming and disassembly/unjamming of PA[6] surfactants can be controlled by chemical redox or competitive guest reagents, endowing the structured liquids with redox or guest-competitive responsiveness.

A nanosheet-based combination emulsifier system for bulk-scale production of emulsions with elongated droplets and long-term stability

In this study, we investigate the emulsion type, droplet morphology and emulsion stability that can be achieved using a novel combination emulsifier system which consists of water-soluble α-zirconium phosphate tetrabutyl ammonium (α-ZrP-TBA) nanosheets as the particulate emulsifier and Span 80 as the oil-soluble emulsifier, with the two emulsifiers present in distinct phases. We find that water-in-oil emulsions were formed for water volume fractions < 0.3, and oil-in-water (O/W) emulsions were formed for water volume fractions > 0.3. This phase inversion point was found to be the same irrespective of whether the emulsifier was only Span 80 or only nanosheet or their combination. Varying the concentrations of either surfactant or the nanosheet did not alter the phase inversion point. The emulsions with the greatest stability against creaming were formed using the combination emulsifier and were found to be the O/W type, that were stable for 3 months. Interestingly, we find that droplets in these stable emulsions were nonspherical, with the aspect ratio of droplets increasing with nanosheet and Span 80 concentration, suggesting a synergistic interaction between the two emulsifiers to create elongated droplets. We perform capillary neck thinning experiments to show that the combination emulsifier system offers unique interfacial properties that are different from either emulsifier alone, suggesting that interfacial jamming could occur to produce elongated droplets. Taken together, our results suggest a novel route to bulk-scale production of O/W emulsions that have long-term emulsion stability with unique droplet morphology.

Bijel rheology reveals a 2D colloidal glass wrapped in 3D.

We present rheological evidence demonstrating the glass-like nature of bicontinuous interfacially jammed emulsion gels (bijels). Under small amplitude oscillatory shear, bijels exhibited rheological signatures akin to α and β relaxation that are also invariable to interfacial tension changes, behaviors which are reminiscent of caged particle dynamics found in colloidal glasses, and well described by a previously reported adaptation of mode-coupling theory for colloidal glass rheology. Guided by their rheological signatures and supported by particle detachment and attraction energy approximations, we rationalize that bijels can be represented as 2-dimensional (2D) colloidal glasses that percolate in 3-dimensional (3D) space, and attractive interactions are not required for their stability. To provide further support for this conjecture, we qualitatively compare the rheology of bijels and a capillary suspension that is stabilized by strong, rigid capillary bridges between the particles, beyond their limit of linear viscoelasticity. Our results demonstrate that the strong adsorption of particles to the continuous interface and the lack of strong attractive interparticle forces enable recovery by interfacial tension into new jammed configurations after shear deformation. These behaviors are qualitatively different from those in the capillary suspension, where the breaking of attractive interparticle bonds results in dramatic changes to the microstructure and rheology over a narrow range of shear amplitudes. Our findings unveil bijels as 2D colloidal glasses weaving in 3D space and establish that interparticle attractions are not required for stability in bijels, and interfacial jamming alone is sufficient to impart viscoelasticity and gel-like rheology to these materials.

Advanced 3D-printed phase change materials

Advanced 3D-printed phase change materials

Oscillating sessile liquid marble - A tool to assess effective surface tension

A long-standing problem of liquid-marble based technology is the inconsistency of the effective surface tension values. This inconsistency could be due to particle size, particle type, volume of the liquid marble or the preparation method. The prevailing liquid marble preparation method is to roll a droplet on a powder bed. The lack of control of rolling duration or revolution speed could contribute to the inconsistent effective surface tension values. We hypothesize that a systematic preparation approach could improve the consistency of the effective surface tension values. In this work, we (i) determine the effective surface tension using the natural oscillation of a sessile liquid marble and (ii) investigate the effects of liquid marble preparation methods on the effective surface tension for the first time. We find that the effective surface tension values of a liquid marble prepared manually are inconsistent. In comparison, a systematic preparation method improves the consistency of the measured effective surface tension values. Interestingly, the systematic preparation at higher revolution speed causes interfacial jamming at the liquid marble shell which decreases the consistency. The results from this work can provide a deeper understanding of the fundamental characteristics of liquid marbles.

Laponite/lauric arginate stabilized AKD Pickering emulsions with shell-tunable hydrolytic resistance for use in sizing paper

Utilizing the assembly and formation of laponite/lauric arginate (LAE) complexes near the water-oil interface, where laponite and LAE interact, the stability and preparation of alkyl ketene dimer (AKD) Pickering emulsions with tunable shells were investigated. Stable spherical emulsions were generated with homogenization due to the interfacial jamming of laponite/LAE complexes. The packing density of laponite at the oil/water interface was adjustable via LAE concentration tuning. The Pickering system with a tunable shell, droplet size, resistance to oil agglomeration and hydrolysis over a long period of time was achieved based on LAE loading. Hydrophobic paper with a 126.6° of water contact angle was prepared under a surface sizing process with the laponite/LAE-stabilized AKD emulsion loading of 0.12 wt% LAE, which exhibited 90 days' long-term storage stability. The confocal laser scanning microscopy (CLSM) shows that laponite/LAE forms a dense layer at the oil/water interface and 3D-network in a continuous phase. The properties provided by laponite/LAE, a highly efficient complex with resistance to phase permeability and hydrolysis, open new opportunities in biodegradable and food-grade emulsifiers for paper sizing agents, where LAE achieves synergistic effects with laponite.

Visualizing Interfacial Jamming Using an Aggregation‐Induced‐Emission Molecular Reporter

AbstractWith the interfacial jamming of nanoparticles (NPs), a load‐bearing network of NPs forms as the areal density of NPs increases, converting the assembly from a liquid‐like into a solid‐like assembly. Unlike vitrification, the lineal packing of the NPs in the network is denser, while the remaining NPs can remain in a liquid‐like state. It is a challenge to determine the point at which the assemblies jam, since both jamming and vitrification lead to a solid‐like behavior of the assemblies. Herein, we show a real‐time fluorescence imaging method to probe the evolution of the interfacial dynamics of NP surfactants at the water/oil interface using aggregation‐induced emission (AIE) as a reporter for the transition of the assemblies into the jammed state. The AIEgens show typical fluorescence behavior at densities at which they can move and rotate. However, when aggregation of these fluorophores occurs, the smaller intermolecular separation distance arrests rotation, and a significant enhancement in the fluorescence intensity occurs.

Visualizing Interfacial Jamming Using an Aggregation-Induced-Emission Molecular Reporter.

With the interfacial jamming of nanoparticles (NPs), a load-bearing network of NPs forms as the areal density of NPs increases, converting the assembly from a liquid-like into a solid-like assembly. Unlike vitrification, the lineal packing of the NPs in the network is denser, while the remaining NPs can remain in a liquid-like state. It is a challenge to determine the point at which the assemblies jam, since both jamming and vitrification lead to a solid-like behavior of the assemblies. Herein, we show a real-time fluorescence imaging method to probe the evolution of the interfacial dynamics of NP surfactants at the water/oil interface using aggregation-induced emission (AIE) as a reporter for the transition of the assemblies into the jammed state. The AIEgens show typical fluorescence behavior at densities at which they can move and rotate. However, when aggregation of these fluorophores occurs, the smaller intermolecular separation distance arrests rotation, and a significant enhancement in the fluorescence intensity occurs.

Surface Tension: Effect of Core Liquid Surface Tension on the Liquid Marble Shell (Adv. Mater. Interfaces 5/2021)

Reduction of the core liquid surface tension of a liquid marble enhances the penetration of the encapsulating particles into it and decreases the shell thickness, keeping the shell mass almost constant. A further reduction of the surface tension causes interfacial jamming of the encapsulating particles which increases both the shell thickness and mass. More details can be found in article number 2001591 by Nam-Trung Nguyen, Chin Hong Ooi, and co-workers.