Interfacial Jamming Research Articles

Adaptive Structured Pickering Emulsions and Porous Materials Based on Cellulose Nanocrystal Surfactants

AbstractTaking advantage of the formation and assembly of cellulose nanocrystal surfactants (CNCSs) at the water–oil interface, where polar cellulose nanocrystals (CNCs) and end‐functionalized polymer chains interact, the preparation and stability of emulsions prepared with CNCSs were investigated. The packing density of CNCSs at the interface can be adjusted by tuning parameters such as pH, ionic strength, and concentration/molecular weight of the end‐functionalized polymer ligands. Stable non‐spherical emulsions are obtained during homogenization, as a result of the interfacial jamming of CNCSs, with pH‐triggered reconfigurability. Porous materials are prepared by freeze‐drying creamed, CNCS‐stabilized emulsions. The cells of the porous materials have a controlled pore size and shape that are commensurate with the droplets in the emulsion and are responsive to pH. The behavior of the adaptive, reconfigurable supracolloidal system is coupled to its internal and surrounding environment.

Adaptive Structured Pickering Emulsions and Porous Materials Based on Cellulose Nanocrystal Surfactants

Taking advantage of the formation and assembly of cellulose nanocrystal surfactants (CNCSs) at the water-oil interface, where polar cellulose nanocrystals (CNCs) and end-functionalized polymer chains interact, the preparation and stability of emulsions prepared with CNCSs were investigated. The packing density of CNCSs at the interface can be adjusted by tuning parameters such as pH, ionic strength, and concentration/molecular weight of the end-functionalized polymer ligands. Stable non-spherical emulsions are obtained during homogenization, as a result of the interfacial jamming of CNCSs, with pH-triggered reconfigurability. Porous materials are prepared by freeze-drying creamed, CNCS-stabilized emulsions. The cells of the porous materials have a controlled pore size and shape that are commensurate with the droplets in the emulsion and are responsive to pH. The behavior of the adaptive, reconfigurable supracolloidal system is coupled to its internal and surrounding environment.

Onset Reduction and Stabilization of Cocontinuous Morphology in Immiscible Polymer Blends by Snowmanlike Janus Nanoparticles.

Interfacial jamming of monolayer nanoparticles is often required to kinetically arrest the cocontinuous morphology, which is not in favor of achieving high efficiency at low particle contents. In this paper, we find that the shape asymmetry of the snowmanlike Janus particles (JPs) has significant influence on the cocontinuous morphology of polymer blends under the melt-mixing process. The addition of 0.9 vol % snowmanlike JPs can almost have the onset concentration of cocontinuity in immiscible blends, which is much lower than the apparent interfacial jamming concentration. In addition, JPs show superior ability to stabilize the continuous morphology during annealing at high temperatures. The interfacial activity of asymmetric JPs is due to the decrease in the radius of the jamming curvature in the interfacial region as the shape asymmetry of the snowmanlike JPs increases. This result implies a general strategy to prepare Janus nanoparticles for a highly effective interfacial modification agent at low contents, which can induce the dispersed-phase continuity and suppress the coarsening of cocontinuous morphology simultaneously.

Electrostatic-Driven Dynamic Jamming of 2D Nanoparticles at Interfaces for Controlled Molecular Diffusion.

Dynamically engineering the interfacial interaction of nanoparticles has emerged as a new approach for bottom-up fabrication of smart systems to tailor molecular diffusion and controlled release. Janus zwitterionic nanoplates are reported that can be switched between a locked and unlocked state at interfaces upon changing surface charge, allowing manipulation of interfacial properties in a fast, flexible, and switchable manner. Combining experimental and modeling studies, an unambiguous correlation is established among the electrostatic energy, the interface geometry, and the interfacial jamming states. As a proof-of-concept, the well-controlled interfacial jamming of nanoplates enabled the switchable molecular diffusion through liquid-liquid interfaces, confirming the feasibility of using nanoparticle-based surfactants for advanced controlled release.

Electrostatic‐Driven Dynamic Jamming of 2D Nanoparticles at Interfaces for Controlled Molecular Diffusion

AbstractDynamically engineering the interfacial interaction of nanoparticles has emerged as a new approach for bottom‐up fabrication of smart systems to tailor molecular diffusion and controlled release. Janus zwitterionic nanoplates are reported that can be switched between a locked and unlocked state at interfaces upon changing surface charge, allowing manipulation of interfacial properties in a fast, flexible, and switchable manner. Combining experimental and modeling studies, an unambiguous correlation is established among the electrostatic energy, the interface geometry, and the interfacial jamming states. As a proof‐of‐concept, the well‐controlled interfacial jamming of nanoplates enabled the switchable molecular diffusion through liquid–liquid interfaces, confirming the feasibility of using nanoparticle‐based surfactants for advanced controlled release.

Enthalpy-Enhanced Janus Nanosheets for Trapping Nonequilibrium Morphology of Immiscible Polymer Blends

Janus particles are promising for self-assembly at the liquid/liquid interface due to coexistence of the Pickering effect and the different wettability of both sides. In this study, we synthesize a Janus nanosheet and evaluate its ability to trap nonequilibrium morphology by interfacial self-assembly. The Janus nanosheet was synthesized by selectively grafting polymer chains, polystyrene (PS) or polyisoprene (PI), on each side of a silica nanosheet. The selective grafting method endow the nanosheet with two different wettabilities, which make it ideal for self-assembly and further jamming at the PS/PI interface. The interfacial jamming of the nanosheet trapped the intermediate, nonequilibrium morphology during phase separation of the polymer blends. Compared to other Janus materials, the Janus nanosheet has higher interfacial activity and reduces the free energy of the system more effectively due to its 2D structure. Only 2 wt % of Janus nanosheet is required to break the threshold and reach the jammed st...

Liquid Letters.

Using the interfacial jamming of cellulose nanocrystal (CNC) surfactants, a new concept, termed all-liquid molding, is introduced to produce all-liquid objects that retain the shape and details of the mold with high fidelity, yet remain all liquid and are responsive to external stimuli. This simple process, where the viscosity of the CNC dispersion can range from that of water to a crosslinked gel, opens tremendous opportunities for encapsulation, delivery systems, and unique microfluidic devices. The process described is generally applicable to any functionalized nanoparticles dispersed in one liquid and polymer ligands having complementary functionality dissolved in a second immiscible liquid. Such sculpted liquids retain all the characteristics of the liquids but retain shape indefinitely, very much like a solid, and provide a new platform for next-generation soft materials.

Systems of mechanized and reactive droplets powered by multi-responsive surfactants.

Although 'active' surfactants, which are responsive to individual external stimuli such as temperature, electric or magnetic fields, light, redox processes or chemical agents, are well known, it would be interesting to combine several of these properties within one surfactant species. Such multi-responsive surfactants could provide ways of manipulating individual droplets and possibly assembling them into larger systems of dynamic reactors. Here we describe surfactants based on functionalized nanoparticle dimers that combine all of these and several other characteristics. These surfactants and therefore the droplets that they cover are simultaneously addressable by magnetic, optical and electric fields. As a result, the surfactant-covered droplets can be assembled into various hierarchical structures, including dynamic ones, in which light powers the rapid rotation of the droplets. Such rotating droplets can transfer mechanical torques to their non-nearest neighbours, thus acting like systems of mechanical gears. Furthermore, droplets of different types can be merged by applying electric fields and, owing to interfacial jamming, can form complex, non-spherical, 'patchy' structures with different surface regions covered with different surfactants. In systems of droplets that carry different chemicals, combinations of multiple stimuli can be used to control the orientations of the droplets, inter-droplet transport, mixing of contents and, ultimately, sequences of chemical reactions. Overall, the multi-responsive active surfactants that we describe provide an unprecedented level of flexibility with which liquid droplets can be manipulated, assembled and reacted.

Liquid Marbles: Liquid Shaping Based on Liquid Pancakes (Adv. Mater. Interfaces 2/2018)

Water in milliliter order forms a pancake shape on a superhydrophobic surface. Subjecting such a pancake to interfacial jamming of nanoparticles allows a segmenting manipulation on the pancake. Based on this mechanism, liquid can be shaped into various shapes such as rings, characters and channels, which are characterized with accurate profile, large size, and high transparency. This is reported by Xiaoguang Li and co-workers in article number 1701139.

Monolayer nanoparticle-covered liquid marbles derived from a sol-gel coating

A sol-gel coating consisting of hydrophobic SiO2 nanoparticles (NPs) was used to produce monolayer NP-covered (mNPc) liquid marbles. The simplest approach was rolling a droplet on this coating, and an identifiable signet allowed determination of the coverage ratio of the resulting liquid marble. Alternatively, the particles were squeezed onto a droplet surface with two such coatings, generating surface buckling from interfacial NP jamming, and then a liquid marble was produced via a jamming-relief process in which water was added into the buckled droplet. This process revealed an ∼7% reduction in particle distance after interfacial jamming. The mNPc liquid marbles obtained by the two methods were transparent with smooth profiles, as naked droplets, and could be advantageously used in fundamental and applied researches for their unique functions.

Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA.

Protein adsorption and assembly at interfaces provide a potentially versatile route to create useful constructs for fluid compartmentalization. In this context, we consider the interfacial assembly of a bacterial biofilm protein, BslA, at air-water and oil-water interfaces. Densely packed, high modulus monolayers form at air-water interfaces, leading to the formation of flattened sessile water drops. BslA forms elastic sheets at oil-water interfaces, leading to the production of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil microcapsules are unstable but display arrested rather than full coalescence on contact. The disparity in stability likely originates from a low areal density of BslA hydrophobic caps on the exterior surface of water-in-oil microcapsules, relative to the inverse case. In direct analogy with small molecule surfactants, the lack of stability of individual water-in-oil microcapsules is consistent with the large value of the hydrophilic-lipophilic balance (HLB number) calculated based on the BslA crystal structure. The occurrence of arrested coalescence indicates that the surface activity of BslA is similar to that of colloidal particles that produce Pickering emulsions, with the stability of partially coalesced structures ensured by interfacial jamming. Micropipette aspiration and flow in tapered capillaries experiments reveal intriguing reversible and nonreversible modes of mechanical deformation, respectively. The mechanical robustness of the microcapsules and the ability to engineer their shape and to design highly specific binding responses through protein engineering suggest that these microcapsules may be useful for biomedical applications.

Interfacial Assembly and Jamming Behavior of Polymeric Janus Particles at Liquid Interfaces.

The self-assembly and interfacial jamming of spherical Janus nanoparticles (JNPs) at the water/oil interface were investigated. Polymeric JNPs, made by cross-linking polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (PS-PB-PMMA), with a high interfacial activity assemble at the water/oil interface. During the self-assembly at the interface, the interfacial energy was reduced and a dynamic interlayer was observed that is responsive to the pH of the aqueous phase. Unlike hard particles, the JNPs are composed of polymer chains that can spread at the liquid-liquid interface to maximize coverage at relatively low areal densities. In a pendant drop geometry, the interfacial area of a water droplet in oil was significantly decreased and the JNPs were forced to pack more closely. Entangling of the polymer chains causes the JNPs to form a solid-like interfacial assembly, resulting in the formation of wrinkles when the interfacial area is decreased. The wrinkling behavior, the retention of the wrinkles, or the slow relaxation of the liquid drop back to its original equilibrium shape was found to depend upon the pH.

Liquid Tubule Formation and Stabilization Using Cellulose Nanocrystal Surfactants

AbstractStructured liquids, generated by the interfacial formation, assembly, and jamming of nanoparticle (NP)‐surfactants at liquid/liquid interfaces, maintain all the desirable characteristics of each liquid, while providing a spatially structured framework. Herein, we show that rod‐like cellulose nanocrystal (CNC)‐based NP‐surfactants, termed CNC‐surfactants, are formed rapidly at the liquid/liquid interface, assemble into a monolayer, and, when jammed, offer a robust assembly with exceptional mechanical properties. Plateau–Rayleigh (PR) instabilities of a free‐falling jet of an aqueous medium containing the CNCs into a toluene solution of amine end‐functionalized polystyrene are completely suppressed, allowing the jetting of aqueous tubules that are stabilized when the CNC‐surfactants are jammed at the interface. These results open a new platform for the additive manufacturing techniques, for example, three‐dimensional (3D) printing, of all‐liquid constructs.

Liquid Tubule Formation and Stabilization Using Cellulose Nanocrystal Surfactants.

Structured liquids, generated by the interfacial formation, assembly, and jamming of nanoparticle (NP)-surfactants at liquid/liquid interfaces, maintain all the desirable characteristics of each liquid, while providing a spatially structured framework. Herein, we show that rod-like cellulose nanocrystal (CNC)-based NP-surfactants, termed CNC-surfactants, are formed rapidly at the liquid/liquid interface, assemble into a monolayer, and, when jammed, offer a robust assembly with exceptional mechanical properties. Plateau-Rayleigh (PR) instabilities of a free-falling jet of an aqueous medium containing the CNCs into a toluene solution of amine end-functionalized polystyrene are completely suppressed, allowing the jetting of aqueous tubules that are stabilized when the CNC-surfactants are jammed at the interface. These results open a new platform for the additive manufacturing techniques, for example, three-dimensional (3D) printing, of all-liquid constructs.

Liquid plasticine: controlled deformation and recovery of droplets with interfacial nanoparticle jamming.

Air-exposed droplet systems are widely applied in material preparation and experimental design. Recently, a droplet system with unusual properties featured by a liquid-like appearance and solid-like deformability was produced. However, it was then just an interesting and perplexing phenomenon in the absence of basic understandings and clear perspectives for applications. Here we reveal that stable droplet deformation is attributed to monolayer nanoparticle jamming at the water/vapor interface, and that the normal shape can be recovered by jamming relieving. The degree of jamming affects the droplet shape and transparency and can be tuned by the squeezing force and droplet volume. Using these properties and control methods, we develop the deformed droplet into "liquid plasticine" with predesigned shapes, super-high transparency, and arbitrarily large volume. We demonstrate that liquid plasticine could be used as liquid lenses, channel-like containers, and miniature reactors.

Foams stabilised by mixtures of nanoparticles and oppositely charged surfactants: relationship between bubble shrinkage and foam coarsening.

We have studied foams stabilised by surfactant-decorated nanoparticles adsorbed at the bubble surfaces. We show that the controlled compression of a single bubble allows one to understand the coarsening behavior of these foams. When bubbles are compressed, the particles become tightly packed in the surface layer. They lose their mobility, and the interface becomes solid-like when the jammed state is reached. Further compression leads to interfacial buckling characterised by crumpled surfaces. We find that the surface concentration of particles at which the jamming and the buckling transitions occur are independent of the surfactant concentration. This is a surprising feature. It suggests that the surfactants are mandatory to help the particles adsorb at the interface and that they change the equilibrium surface concentration of the decorated particles. But they do not affect the surface properties once the particles are adsorbed. We measured the compression elastic modulus of the surface in the jammed state and found it to be compatible with the Gibbs condition for which the spontaneous dissolution of bubbles is arrested. Due to this effect, the coarsening process of a foam composed of many close-packed bubbles occurs in two steps. In the first step, coarsening is slow and coalescence of the bigger bubbles is observed. In the second step, a number of very small bubbles remains, which exhibit crumpled surfaces and are stable over long times. This suggests that foam coarsening is arrested once the smallest bubbles become fully covered after the initial shrinking step.

Stabilizing Liquid Drops in Nonequilibrium Shapes by the Interfacial Jamming of Nanoparticles

Nanoparticles assemble at the interface between two fluids into disordered, liquid-like arrays where the nanoparticles can diffuse laterally at the interface. Using nanoparticles dispersed in water and amine end-capped polymers in oil, nanoparticle surfactants are generated in situ at the interface overcoming the inherent weak forces governing the interfacial adsorption of nanoparticles. When the shape of the liquid domain is deformed by an external field, the surface area increases and more nanoparticles adsorb to the interface. Upon releasing the field, the interfacial area decreases, jamming the nanoparticle surfactants and arresting further shape change. The jammed nanoparticles remain disordered and liquid-like, enabling multiple, consecutive deformation and jamming events. Further stabilization is realized by replacing monofunctional ligands with difunctional versions that cross-link the assemblies. The ability to generate and stabilize liquids with a prescribed shape poses opportunities for reactive liquid systems, packaging, delivery, and storage.

Kinetically Trapped Co-continuous Polymer Morphologies through Intraphase Gelation of Nanoparticles

We describe an approach to prepare co-continuous microstructured blends of polymers and nanoparticles by formation of a percolating network of particles within one phase of a polymer mixture undergoing spinodal decomposition. Nanorods or nanospheres of CdSe were added to near-critical blends of polystyrene and poly(vinyl methyl ether) quenched to above their lower critical solution temperature. Beyond a critical loading of nanoparticles, phase separation is arrested due to the aggregation of particles into a network (or colloidal gel) within the poly(vinyl methyl ether) phase, yielding a co-continuous spinodal-like structure with a characteristic length scale of several micrometers. The critical concentration of nanorods to achieve kinetic arrest is found to be smaller than for nanospheres, which is in qualitative agreement with the expected dependence of the nanoparticle percolation threshold on aspect ratio. Compared to structural arrest by interfacial jamming, our approach avoids the necessity for neutral wetting of particles by the two phases, providing a general pathway to co-continuous micro- and nanoscopic structures.

Non-equilibrium particle-field simulations of polymer-nanocomposite dynamics

We present a theoretical framework for simulating dynamic processes in polymeric fluids with embedded nanoparticles. The method couples an Eulerian, field-theoretic description of polymer hydrodynamics with a Lagrangian technique for tracking particles of arbitrary shape and size. Results are presented which reproduce nanoparticle localization in diblock nanosphere composites and interfacial jamming in homopolymer blend nanocomposites. Some of the method's unique capabilities are demonstrated by simulating systems containing non-spherical particles, particles of multiple sizes, and surface driven self-assembly.

Controlled Jamming of Particle-Laden Interfaces Using a Spinning Drop Tensiometer

When particles adsorb at a fluid/fluid interface at a sufficiently high concentration, the interface loses mobility and displays solidlike characteristics, a phenomenon called "interfacial jamming". Jamming can arrest interfacial tension-driven morphological coarsening in liquid/liquid or gas/liquid systems and therefore stabilize two phase morphologies with unusual interfacial shapes, for example, nonspherical drops and bubbles, and bijels. Here, we conduct a systematic study of interfacial tension-driven jamming of a particle monolayer using a spinning drop tensiometer (SDT). A drop of mineral oil surrounded by ethylene glycol was spun into a cylindrical shape in a SDT. With decreasing rotational rate, the cylindrical drop retracted due to interfacial tension, thus reducing the interfacial area. In the case of particle-covered drops, drop retraction caused an increase in interfacial particle concentration. Accordingly, when the specific interfacial area became comparable to that of a close packing of particles, interfacial jamming occurred and drop retraction was arrested. Fast interfacial contraction or low particle loadings led to less compact jammed monolayers, that is, with a larger specific interfacial area. There was also significant hysteresis between compressing versus expanding the jammed monolayer, suggesting that a certain minimum stress is required for unjamming. Limited experiments with the same particles at a mineral oil/silicone oil interface showed altogether different behavior. In this case, particles did not spread at the interface and a particle-free portion of the interface coexisted with a particle-covered portion. This suggests that the monolayer behavior at this nonpolar/nonpolar interface is dominated by interparticle attraction.