Liquid crystal (LC)-aqueous interfaces were shown to respond to the phospholipid interactions via optically observable ordering transitions; however, past attempts lack the quantification of the transport and fusion kinetics of the vesicles at the interfaces. Herein, we investigated the response of flowing LC-aqueous interfaces upon fusion of the vesicles formed by pure 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), or egg sphingomyelin or their mixtures with guest molecules. Using stabilized LC-aqueous interfaces in transparent microfluidic chips that allow spatiotemporal quantification using fluorescence, confocal, and polarized light microscopy, we demonstrated that flowing LC interfaces provide a rapid response to lipid adsorption, where their spatiotemporal interfacial distribution differs depending on the mechanical properties of their vesicles. We show that cholesterol-dissolved lipid complexes result in distinct LC-response kinetics, mainly associated to the changes in their rigidities. Considering the critical role of the mechanical properties of cell membranes in proper cellular function, this study is significant as it offers a continuous and rapid early diagnosis platform for detecting minor mechanical alterations in lipid bilayers, which may lead to cell dysfunction that contributes to critical diseases.

Detecting aqueous trace pollutants is a challenge in tracking environmental and public health. We report nanoparticle-decorated liquid crystal (LC) soft interfaced microfluidic platforms for detecting trace-level aqueous analytes. Silica nanoparticles functionalized with alkyl-terminated silanes were used to decorate the LC-aqueous interfaces and induce LC strain. The response of the LC flow sensor to various analytes, including industrial dyes, pharmaceuticals, and persistent chemicals, was investigated through the optically observable LC ordering transitions. The microfluidic results, supported by nanoparticle-integrated LC droplet-based sensors, showed a limit of detection (LOD) of 0.1 ppb with LC interfaces decorated with concentrated nanoparticles. Lowering the interfacial nanoparticle loading resulted in sensors achieving an impressive 4 orders of magnitude reduction in the LOD. While LC droplet-based sensors were unable to reach this sensitivity limit, such ultralow responses were strikingly observed in microfluidic sensor platforms by leveraging the interface geometry and localized straining at LC interfaces induced by nanoparticle positioning. We show that the sensors demonstrate selectivity for analytes characterized by aromatic structures. These features hold potential for various applications, including continuous tracking of micropollutants and medical diagnostics.

Non-Newtonian microfluidics play a crucial role in modern industrial and technological advancements, and in biological phenomena. We report how local variations in the alignment at the boundary of nematic liquid crystals (LCs) govern their flow characteristics under pressure-driven microfluidic conditions. Specifically, we micropatterned the LC anchoring conditions using a photocleavable self-assembled monolayers and investigated the resulting flow characteristics through measurement of flow resistances, and spatial variations in LC director fields as a function of the microfluidic flow. Combined experimental measurements and computational simulations showed that patterned anchoring induces pronounced coupling between flow and molecular alignment, leading to spatially heterogeneous flow regimes revealing backflow mechanisms, hysteresis, pattern-dependent, and rich topological structures. These findings establish a framework for controlling soft anisotropic fluids through interfacial patterning, offering new opportunities for adaptive and reconfigurable microfluidic systems. Nematic liquid crystals offer a way to explore anisotropic fluid dynamics, but are typically confined to uniform boundaries. Combining experiments and simulations, the authors show that patterning anchoring conditions with photocleavable monolayers induces strong flow-alignment coupling, revealing heterogeneous flow regimes.

ABSTRACT Organic‐material‐based hybrid microstructures that integrate structural anisotropy with dual‐stimuli responsiveness offer emerging opportunities for externally driven functional systems. We present multi‐functional dual‐stimuli‐responsive microparticles that exhibit optical birefringence due to their lamellar crystalline architecture, enabling label‐free detection under a polarized light. The anisotropic internal structure generates polarization‐dependent optical contrast, enabling label‐free tracking through birefringence‐based microscopy, with birefringence values (Δn) ranging from 0.04 to 0.07. Simultaneously, these microparticles are composed of polymer‐lipid material (polycaprolactone and stearic acid), magnetic nanoparticles (MNPs), and polypyrrole nanoparticles (PPy NPs), enabling responsiveness to both magnetic and near‐infrared (NIR) stimuli. The magnetic and photothermal responses of microparticles are investigated in aqueous solutions and under biologically relevant conditions. As a proof‐of‐concept demonstration, we show directional actuation in response to magnetic fields and NIR light in these multifunctional anisotropic microstructures, highlighting their potential for microrobotic applications. Furthermore, we show their low hemolytic activity and cytotoxicity, thereby confirming their biocompatibility. The present study introduces a pioneering integration of birefringent optical tracking into a dual‐stimulus soft‐material platform that possesses shapes depending on the formation condition, ranging from flower‐like to ship‐like. This innovation establishes a structure‐enabled, multifunctional soft‐material platform in which optical, magnetic, and thermal responses are intrinsically coupled within a single microstructure.

The responsive interfaces formed by thermotropic liquid crystals (LC) and aqueous phases have been utilized in reactive and catalytic applications, yet their utilization in enzymatic studies has been dominated by natural enzymes. We introduced fullerene-based enzyme mimics and investigated the enzyme mimic-chemistry-dependent response characteristics of LC-aqueous interfaces. We employed hydrophilic and hydrophobic modifications to the fullerene-based enzyme mimics and performed structure and response characterizations of the LC-aqueous interfaces for tracking aqueous-phase catalytic hydrolysis of p-nitrophenyl acetate (pNPA) in solutions in contact with nematic 4-pentyl-4'-cyanobiphenyl (5CB) droplets. Polarized light microscopy revealed temporal 5CB droplet configuration changes upon substrate hydrolysis, while interfacial tension measurements and UV-vis spectrophotometry provided insight into adsorption characteristics, interfacial structuration, and reaction kinetics. Our findings demonstrated two distinct interfacial structuring: the enzyme-immobilized interfaces and the interfaces formed with the adsorption-desorption equilibrium of enzyme mimics. We showed that the tailored modifications of fullerene-based enzyme mimics significantly influenced the LC responsiveness toward enzymatic pNPA hydrolysis. The design flexibility of fullerene-based enzyme mimics allows for fine-tuned control of interfacial properties, significantly improves LC sensitivity, and promises to advance synthetic enzyme designs for use in biochemical sensing, environmental monitoring, and diagnostic technologies.

Research on aqueous-interfaced liquid crystals (LCs) offered valuable outcomes leading to successful applications in sensing and actuation systems. The forward leap of the promising findings in stagnant LC systems will be achieved by the integration of LCs into automated flow systems. In fundamental microfluidics studies, the structural transitions of LC were induced by external fields; yet they were constrained to hard-interfaced flow confinements. In this study, we investigate the structural transitions in flowing nematic LCs confined in microfluidic channels with accessible, stable LC-aqueous soft interfaces. We demonstrate in experiments and in simulations that the applied bulk and interfacial shear significantly transform the director configurations of the nematic LC, due to the anchoring properties at the soft interface. The director profiles, as well as the topology, are influenced substantially by the mechanical stresses induced at the vicinity of the aqueous interfaces depending on the interfacial anchoring conditions, bulk nematic directors, and the direction of the shear. The experimental observations presented herein will guide the ongoing research on the flow of LC in microenvironments and are likely to open new horizons in the development of autonomous platforms including more complex LC phases.

Liquid crystal (LC)-aqueous soft interface sensors have shown potential toward a wide range of analytes, which also include tracking of their reactions. While these sensors have shown promise in studying enzymatic activity, they have been limited to natural enzymes. A whole-synthetic approach is introduced for the detection of molecular species through their interactions with enzyme mimics. Highly stable and robust, fullerene-based synthetic enzyme mimics are employed, and the response of nematic LC droplets to their hydrolysis activity is investigated. This involves characterizing the structures of the LC droplets in the aqueous phase that facilitate enzymatic reactions, monitoring the responses of LC droplets to these interactions to sense enzymatic activity. Polarized light microscopy is employed to image the LC droplets, spectrophotometry to measure kinetics, and interfacial tension measurements for structural characterization of LC interfaces. These findings revealed an instantaneous response of the LC droplets that originate from the enzyme mimic-substrate interactions in the bulk phase, and the presence of the LC droplets does not noticeably influence the function and interactions of the enzyme mimics. These findings offer a new perspective on LC-based sensing systems that can be tailored to a wide range of substrates or enzyme-substrate interactions.

Dry liquid crystal marbles are structures that consist of cholesteric liquid crystal (CLC) droplets prepared by the mixture of chiral-doped thermotropic LCs encapsulated by cellulose nanocrystals (CNCs) that have been dried under ambient conditions. The characterizations revealed that CLC droplets were successfully encapsulated by self-standing CNC shells and responsive to the external gaseous stimulus. The dry LC marbles offer several advantages over previously reported LC-based gas sensors, such as fast response against minor external stimuli, and ease of handling, which make them particularly attractive for practical applications in sensing. We demonstrate the use of these marbles for detecting toluene vapor, a common industrial solvent and pollutant, which we also use to understand the response characteristics. The dry CLC marbles exhibit a significant response to toluene vapor with a detection limit below 500 ppm, attributed to the change of pitch size of the helical structure of CLC droplets induced by the toluene vapor. The CNC-capsulated CLC droplets were stable in emulsion for up to two weeks, and their dried form exhibited a sensitive response upon toluene exposure. The real-time experiments revealed that the LC marbles can be used multiple times without a significant loss of sensitivity, where 90 % of the maximum response was observed at 13.3 ± 4.7 s. These dry LC marbles can also be utilized in other areas, including drug delivery, optical devices, and biosensors.

We introduce nanoparticle-assisted liquid crystal (LC) droplet-based sensors that allow determination of low-level concentrations of aqueous soluble species. The silica nanoparticles functionalized with mixed monolayers composed of two distinct groups, hydrophobic alkane tail- and charged group-terminated silanes, facilitated ternary physical interactions between the model analytes (methylene blue (MB) or methyl orange (MO)) and the nematic mesogens 5CB (4-cyano-4'-pentylbiphenyl), and the interfacial species of the nanoparticle. The response of the LC droplets was measured upon nanoparticle adsorption as a function of analyte concentration, which was characterized by the optical determination of the configuration distributions of the LC droplets. We highlight the importance of the charging and the composition of the nanoparticle interfaces for analytical purposes that allow accurate determination of the concentration of the analytes on the order of 0.01 ppb. Such a low concentration corresponds to a low interfacial coverage of nanoparticles, indicating the promisingly high sensitivity of the sensor platform to target analytes. Distinct from the past examples of the LC-based sensors, the nanoparticle-assisted LC sensors allow detection of the species that do not directly cause an ordering transition at the LC-water interfaces, which allow a broader range of analytical targets. The sensor platform that we report herein can be easily tunable for a range of target molecules and will find use in the determination of a wide range of micropollutants in aqueous environments.

Forming membranes by tangential flow deposition of cellulose nanocrystal (CNC) suspensions is an attractive new approach to bottom-up membrane fabrication, providing control of separation performance using shear rate and ionic strength. Previously, the stabilization of these membranes was achieved by irreversibly coagulating the deposited layer upon the permeation of a high-ionic-strength salt solution. Here, we demonstrate for the first time the chemical cross-linking of carboxyl-containing TEMPO-oxidized CNCs by Ag(I)-catalyzed oxidative decarboxylation and the stabilization of CNC membranes using this post-treatment. Cross-linking of TEMPO-CNCs was first demonstrated in suspension via turbidity, dynamic light scattering, and storage (G ') and loss (G '') moduli measurements. Membranes were formed by filtering a 0.15 wt % TEMPO-CNC suspension onto a porous support, followed by permeation of the cross-linking solution containing AgNO3 and KPS through the deposited layer. Rejection for Blue Dextran with a 5 kDa molecular weight was 95.3 +/- 1.9%, 90.6 +/- 3.7%, and 95.9 +/- 1.0% for membranes made from suspensions of TEMPO-CNC, desulfated TEMPO-CNC. and TEMPO-CNC with 100 mM NaCl, respectively. Suspensions with added NaCl led to membranes with improved stability and cholesteric self-assembly in the membrane layer. Membranes subjected to cross-linking post-treatment remained intact upon drying, while those stabilized physically using 200 mM AlCl3 solution were cracked, demonstrating the advantage of the cross-linking approach for scale-up, which requires drying of the membranes for module preparation and storage.

AbstractThe multifunctional responsive interfaces of liquid crystal (LC) and water are employed in fundamental research (colloidal assembly) and promising applications (sensing, release, and material synthesis). The stagnant LC systems, however, limit their use in continuous, automated applications. A microfluidic platform is reported where stable LC flow is maintained between aqueous interfaces. The LC‐water soft interface is defined by the preferential wetting of the two phases at the chemically heterogeneous microchannel interfaces. It is shown that the LC‐water interfaces are stable up to significant pressure differences across the interfaces and maintain responsive characteristics. The stability is in a range to cover the perpendicular and flow‐aligned regimes at low and high flow velocities, respectively, in co‐current or counter‐current flow configurations. The LC configuration at the vicinity of the aqueous interfaces is influenced by the shear induced by the bulk LC flow and by the contacting aqueous phases allowing modulation of the LC strain at the responsive interfaces. The simplicity of the construction and operation of the soft‐interface LC flow platform shows promise and meets the fundamental requirements for their integration into next‐generation autonomous platforms.

Past studies demonstrated that the microcargo carrying aqueous droplets trapped in LCs through elastic stresses can be triggered to release by applying shear to LC-bulk interfaces. Herein, we report our investigations on the release mechanisms of such microcargo entrapped in aqueous droplets of W-in-LC emulsions via interfacial shear caused by the synthetic micro-stirrer microparticle assemblies of iron oxide particles rotated with a magnetic field. We show that a three fold control over the release rate of the tracer molecules is possible that have initial release rates of 14.3 ± 2.5 μg cm-2 h-1, 26.5 ± 3.4 μg cm-2 h-1, and 46.9 ± 4.6 μg cm-2 h-1 when the rotation of magnetic flux was 250, 500 and 1000 rpm, respectively. We measure the release rates to reduce to 5.4 ± 1.2 μg cm-2 h-1, 6.3 ± 0.7 μg cm-2 h-1, and 20.0 ± 3.2 μg cm-2 h-1 after 60 min of shearing at 250, 500 and 1000 rpm, respectively. We present evidence for the release mechanism resulting in such temporal release profiles that correlate with the magnitude of the shear applied to the interface, interfacial coverage of the microstirrers, and the creaming effect of the aqueous droplets doped with tracers. We also report that the influence of the interfacial density of the microparticles that showed an intermediate areal density is required to achieve a maximized release rate. Additionally, we found evidence of the influence of the droplet charge that critically determines the release. This study highlights the importance of the colloidal and interfacial phenomena in the release profiles of the dispersed droplets present in a LC medium.

Colloidal self-assembly has gained significant interest in scientific and technological advances. We investigated the self-assembly of the colloids at fluidic interfaces that mediate elastic interactions. Whereas past studies have reported the assembly of micrometer- or molecular-sized species at aqueous interfaces of liquid crystals (LCs), herein we study the assembly of intermediate-sized nanoparticles. Specifically, surface-modified silica nanoparticles (50 to 500 nm) were adsorbed at the liquid crystal-water interfaces and their positioning was investigated using electron microscopy after polymerization. The study revealed that the electric double layer forces and the elastic forces caused by LC strain are dominant in the assembly of nanoparticles and their contributions can be tuned to direct the self-assembly guided by the sub-interface symmetry of confined cholesteric LCs. At high ionic strengths, we observed a strong localization of nanoparticles at the defects, whereas intermediate strengths resulted in their partial enrichment into cholesteric fingerprint patterns with an interaction energy of ≈3 kBT. This result is comparable with the calculations based on the strength of the binary interactions of the nanoparticles. The findings also support the role of ion partitioning at the LC-aqueous interfaces on the formation of the assemblies. The results can be utilized for applications in sensors, microelectronics, and photonics.

Precise control over membrane performance by tuning fabrication parameters is highly desirable. We developed ultrafiltration membranes by depositing cellulose nanocrystals (CNCs) on a porous support via tangential flow filtration, followed by irreversibly coagulating the deposited layer by permeating highly concentrated AlCl3 solution. By varying electrostatic interactions between nanocrystals during deposition, via varying ionic strength and pH of CNC suspensions, membrane performance was tuned. Increasing NaCl concentration of CNC sus-pensions from 0 to 50 mM increased Blue Dextran (5 kDa) rejection from 93% to 98.5% at high tangential flowrate and from 82% to 98% at low tangential flowrate. For membranes fabricated at high tangential flowrate, beta-lactoglobulin (18 kDa) rejections increased from 94% to 98% when NaCl concentration increased from 0 to 25 mM. Increasing pH of CNC suspensions also increased probe molecule rejections, implying smaller interparticle distance between CNCs in the deposit layer. Pure water permeance of membranes were comparable to com-mercial membranes of similar separation properties. Polarized optical microscopy analyses showed that align-ment of CNCs and their aggregates, or tactoids, affect the morphology of CNC deposits. In all cases, decreasing electrostatic repulsion between nanocyrstals increased rejection regardless of CNC alignment, which provides a simple parameter for tuning CNC membrane performance.

Targeted, on‐demand delivery has been of interest using materials responsive to environmental stimuli. A delivery technique based on precise release of aqueous microdroplets from a liquid crystal (LC) medium with contactless stimulation is presented. A nematic LC is doped with a photothermal dye that produces heat under near IR light exposure. The heat is used to overcome the elastic strains in the LC phase, promoting the release of initially entrapped water droplets to the neighboring aqueous solution. Designing the geometry of LC‐based emulsions and tuning the light intensity and position allows for manipulation of the release in two distinct modes defined as pulsated and continuous. In the pulsated mode, water droplets are released transiently from the casted water‐in‐LC emulsion layer based on sweeping by the moving isotropic‐nematic phase boundary controlled by light. In the continuous mode, water droplets are ejected continuously from a droplet‐shaped water‐in‐LC emulsion, due to a heating‐induced internal flow controlled by light. The droplet release by contactless stimulation is used for the on‐demand dosing of dopamine and its oxidizing reagent from isolated reservoirs to obtain an in situ reaction signal for a hydrogen peroxide assay. A new dual‐mode release system developed with photothermal LCs holds potential in drug release, controlled mixing, and photothermal therapy.

Cellulose nanocrystals (CNCs) of 180 nm length and 8 nm diameter were deposited on porous supports by tangential flow filtration followed by salt permeation to form ultrafiltration membranes. At a high enough shear rate on the support surface, CNCs aligned in the direction of flow, showing a nematic order. The shear rates for transition to the nematic phase determined from rheology analysis, polarized optical microscopy, and membrane performance were consistent with one another, at ca. 10 s-1. Permeating an AlCl3 solution through the shear-aligned CNC deposit stabilized the CNC layer by screening repulsive electrostatic interactions, and the stable CNC layer was obtained. On changing the surface shear rate from 10 to 50 s-1, the order parameter of CNCs increased from 0.17 to 0.7 and the rejection for Blue Dextran (5 kDa) increased from 80.4 to 92.7% and that for β-lactoglobulin (18 kDa) increased from 89.6 to 95.4%. Hence, a simple and scalable method for controlling rejection properties of ultrafiltration membranes is developed, which uses aqueous CNC suspensions to form the selective layer.

Stimuli-responsive properties of liquid crystals (LCs), when combined with their optical properties, offer sensitive and rapid sensing applications. Here, we propose and demonstrate a microcapillary-based method to be applied for the online detection of amphiphilic species, which can be further used for tracking biological and chemical species in aqueous media. Specifically, we used compartments (300-1400 μm) of nematic 4-cyano-4'-pentylbiphenyl (5CB) that were positioned into cylindrical glass microcapillaries that promote homeotropic anchoring. The flat surfaces of the cylindrical LC compartments were in contact with an aqueous media. We characterized the equilibrium and nonequilibrium response of LCs upon a change in their anchoring at the aqueous interfaces. Upon anchoring transition, we observed the formation of a positively charged defect at the proximity of the interface that moved to the center of the LC compartment and reached equilibrium, a four-petal configuration. This transition was observed to take an average of 41 ± 19 min., which we related to the motion of the defect due to the imbalance of the elastic forces. During the transition, we observed metastable states which could be removed via thermal treatment. We showed the capillary sensors to be useful considering their ease of additional quantification. We also show that the sensors are reversible that facilitate temporal and cumulative quantification. The findings reported in this study can further be used to develop sensors for specific purposes that require continuous tracking of the chemical and biological species that is critical for the health and safety of the individuals and society.

Cholesteric liquid crystals (CLCs) are widely used as optical sensors against volatile organic compounds (VOCs), whose sensitivity can be increased with the help of strain. However, the specificity and reusability of these structures should be increased to achieve their successful integration into useful applications. For this purpose, we developed an interpenetrating polymeric network (IPN) based on poly(RM257) structure of CLC-templated polymeric films and polydimethylsiloxane (PDMS). Contrary to the generic CLC-hosted IPN sensors that use CLC structures to optically report the changes in the polymeric matrix, we employed the collaborative responsiveness of the constituents of the IPN (both CLC-templated and penetrated polymeric structures) to improve the sensor performance. The elastic swelling of PDMS structure increased the durability and reusability of the poly(RM257) polymeric sensor upon exposure to even high VOC vapor concentrations up to their saturation. The sensor tests of both poly(RM257) and IPN films were carried out against four different VOC vapors namely toluene, hexane, acetone, ethanol and also water vapor. The results showed that the synergistic swelling of PDMS and poly(RM257) polymeric structures against vapors directly affected the sensor performance in terms of earned specificity and enhanced sensitivity. Moreover, the real-time experiments showed that the measurement accuracy, response, and recovery time of the polymeric sensors were also improved significantly by the development of IPN as compared to their non-IPN counterparts. This study shows a promise towards further engineering of sensors against various applications through detailed design of the constituent polymers against targeted species.

Nematic liquid crystal (LC) droplets have been widely used for the detection of molecular species. We investigate the response of micrometer sized nematic LC droplets against the adsorption of nanoparticles from aqueous media. We synthesized ti 100 nm-in-diameter silica nanoparticles and modified their sur-faces to mediate either planar or homeotropic LC anchoring and a pH-dependent charge. We show sur -face functionality-and concentration-dependent configurations of the droplets consistent with the change in the surface anchoring and the formation of local heterogeneities upon adsorption of the nanoparticles to LC-aqueous interfaces. The adsorption of nanoparticles modified with dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP, homeotropic) exhibit a transition from bipolar to radial, whereas the adsorption of -COOH-terminated counterparts (planar) did not cause a configura-tion transition. By manipulating the electrostatic interactions, we controlled the adsorption of the nanoparticles to the LC-aqueous interfaces, providing access to the physicochemical properties of the nanoparticles. We demonstrate a temporal change in the droplet configurations caused by the adsorption of the nanoparticles functionalized with -COOH/DMOAP mixed monolayers. These results provide a basis for studies in applications for the detection of nano-sized species, for sensing applications that combine nanoparticles with LCs, and for the synthesis of anisotropic composite particles with complex structures. (c) 2021 Elsevier Inc. All rights reserved.