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A single-step self-organized pathway is harnessed to generate large-area and high-density liquid-crystal (LC) microdroplets via rapid spreading of an LC-laden volatile liquid film on an aqueous surfactant bath. The surfactant loading on the water bath and LC loading in the solvent fluid help in tuning the size, periodicity, and ordering of LC microdroplets. Remarkably, the experiments reveal a transition from a spinodal to heterogeneous nucleation pathway of dewetting when the surfactant loading is modulated from below to beyond the critical micellar concentration in the aqueous phase. In the process, a host of unprecedented drop formation modes, such as dewetting and contact-line instability, random ejection, and "fire cracker" toroid splitting, have been uncovered. Subsequently, the LC microdroplets on the air-water interface are employed as photomasks suitable for soft-photolithography applications. Such masks help in the decoration of a host of mesoscale three-dimensional features on the films of photoresists when photons are guided through the LC droplets. In such a scenario, phase transition of LC droplets under solvent vapor annealing is employed to control the movement of photons through drops and subsequently modulate the light exposure on the photoresist surface. Such a simple soft-photolithography setup leads to an array of flattened droplets on a positive resist, while donut features are observed on the negative tone. Remarkably, the orientation of nematogens within 4-cyano-4'-pentylbiphenyl droplets and at the three-phase contact-line provides additional handles in controlling the transmission of photons, which facilitates such a unique pattern formation. A number of low-cost and simple strategies are also discussed to order such soft-photolithography patterns. Importantly, with a minor modification to the same experimental setup, we could also measure the variation in the order parameter of the LC droplet during its phase transitions from the nematic to isotropic state.

Hypothesis Mixing of a chemical trigger of lower surface tension into a microdroplet with relatively higher surface tension can cause a rapid spreading of the droplet on a liquid-sublayer to form a host of metastable liquid morphologies such as sheets, toroids, threads, or droplets. Subsequently, such metastable fluidic objects break into a collection of droplets to form microemulsions. Experiments Introduction of surfactant loaded water or long-chain alcohols into an oleic acid microdroplet stimulate a rapid spreading of the same on a water sublayer, which helps in the formation of a metastable liquid sheet connected to a liquid toroid. Much like slipping films, the liquid sheet dewets the water underlayer through the formation of holes before they grow and coalesce to form liquid ribbons. While such liquid structures eventually break into an array of microdroplets, the liquid toroid expands before undergoing a Plateau-Rayleigh instability to form microdroplets. Findings A single step self-organization process in which a chemical trigger can convert a microdroplet into a liquid-toroid on a water surface, in absence of any rotational influence. A symmetric to asymmetric transition in toroid morphology is observed due to the changeover of laminar to turbulent flow regimes with the reduction in viscosity of fluid-sublayer or variation in chemical triggers. The toroid cross-section and droplet spacing after the toroid breakup follow a length scale evaluated from a linear stability analysis.

In this study, a membraneless photofuel cell, namely, μ-DropFC, was designed and developed to harvest chemical and solar energies simultaneously. The prototypes can also perform environmental remediation to demonstrate their multitasking potential as a sustainable hybrid device in a single embodiment. A hydrogen peroxide (H2O2) microdroplet at optimal pH and salt loading was utilized as a fuel integrated with Al as an anode and zinc phthalocyanine (ZnPC)-coated Cu as a cathode. The presence of n-type semiconductor ZnPC in between the electrolyte and metal enabled the formation of a photo-active Schottky junction suitable for power generation under light. Concurrently, the oxidation and reduction of H2O2 on the electrodes helped in the conversion of chemical energy into the electrical one in the same membraneless setup. The suspension of Au nanoparticles (Au NPs) in the droplet helped in enhancing the overall power density under photonic illumination through the effects of localized surface plasmon resonance (LSPR). Furthermore, the presence of photo-active n-type CdS NPs enabled the catalytic photo-degradation of dyes under light in the same embodiment. A 40 μL μ-DropFC could show a significantly high open circuit potential of ∼0.58 V along with a power density of 0.72 mW cm−2. Under the same condition, the integration of ten such μ-DropFCs could produce a power density of ∼7 mW cm−2 at an efficiency of 3.4%, showing the potential of the prototype for a very large scale integration (VLSI). The μ-DropFC could also degrade ∼85% of an industrial pollutant, rhodamine 6G, in 1 h while generating a power density of ∼0.6 mW cm−2. The performance parameters of μ-DropFCs were found to be either comparable or superior to the existing prototypes. In a way, the affordable, portable, membraneless, and high-performance μ-DropFC could harvest energy from multiple resources while engaging in environmental remediation.

Thin films of conducting polymers find applications in many emerging areas, such as packaging, sensing, coating, thin-film capacitors, organic integrated circuits, organic thin wires, and electrolu...

The high energy density materials driven by high storage permittivity are in huge demand due to their extensive applications in capacitors used in electric trains, hybrid electric vehicles, and aircraft. Nanocomposites, especially with conducting polymer exhibit characteristic properties such as well-organized framework, extensible, and rich dielectric strength, suitable for high-energy storage materials. The judicious choice of nanofillers for a given polymer matrix largely dictates the property enhancement in polymer nanocomposites. Herein, we explore GO, RGO and MnO2 as nanofillers to make binary (PANI-GO and PANI-RGO) and ternary nanocomposites (PANI-GO-MnO2 and PANI-RGO-MnO2) of PANI. The PANI-RGO-MnO2 ternary nanocomposite exhibits an excellent dielectric property owing to its hexagonal nanorods structure, as revealed by detailed morphological analysis. The in-situ polymerization of PANI ensures the formation of nanocomposites with uniform dispersion of MnO2 nanorods and RGO nanoflakes, which in turn yields high dielectric constant with excellent charge polarization. The frequency dependent study shows that the nanocomposites are quite stable over a long range of frequency, suitable for energy storage devices where high frequency is applied. The combination of high energy density with high breakdown strength indicates the potential applications of the nanocomposites in electrostatic capacitors and fabrication of high frequency dependent electronic components.

The hierarchical nanoscale structure plays a crucial role in achieving excellent property, which can successfully be used in preparing tailor-made materials for sensing applications. These hierarch...

Physical aging is a fundamental phenomenon for any polymeric material and is essential to understand correctly, especially to foretell the long-term behavior of the material. Change in properties with time has a great influence on its applicability and usability. Polyvinyl alcohol (PVA), one of the most widely used polymers especially in biomedical industries, due to its biocompatibility and biodegradability nature. Moreover, PVA hydrogel is widely used in tissue engineering applications because of its high porosity and water retention capacity. The influence of aging (viz., real-time aging) on the physical properties of PVA hydrogel is poorly understood. Herein, we present an aging (viz., real-time) study of PVA hydrogel over a long period, from 3-days to 300-days. The detailed morphological analysis based on FESEM reveals a significant change in microstructure, with coarsening of pores. The rheological study shows that the material becomes more elastic with aging. After 300 days of aging the PVA hydrogel becomes thermally more stable with a shift in the transition temperature based on DSC/TGA analysis. The change in macroscopic properties is linked with the change in microscopic structure, which is governed by the extensive hydrogen bonding (both intra- and inter-molecular) between hydroxyl groups, as is evident from FTIR studies. This extensive hydrogen bonding leads to the formation of a crosslinked three-dimensional network structure, which evolves with the aging time. The 300 days aged hydrogel microstructure resembles to the porcine liver structure, indicating that it may be useful as a scaffold for tissue engineering research purposes.

The amyloid-β peptide exists in the form of fibrils in the plaques found in the brains of patients with Alzheimer’s disease. One of the therapeutic strategies is the design of molecules which can destabilize these fibrils. We present a designed peptide KLVFFP5 with two segments: the self-recognition sequence KLVFF and a β-sheet breaker proline pentamer. Molecular dynamics simulations and docking results showed that this peptide could bind to the protofibrils and destabilize them by establishing hydrophobic contacts and hydrogen bonds with a higher affinity than the KLVFF peptide. In the presence of the KLVFFP5 peptide the β-sheet content of the protofibrils was reduced significantly, the hydrogen bonding network and the salt bridges were disrupted to a greater extent than the KLVFF peptide. Our results indicate that the KLVFFP5 peptide is an effective β-sheet disruptor which can be considered in the therapy of Alzheimer’s disease.

The senile plaques of neurotoxic aggregates of Aβ protein, deposited extraneuronally, mark the pathological hallmark of Alzheimer’s disease (AD). The natural compounds such as omega-3 (ω-3) polyunsaturated fatty acids (PUFAs), which can access blood–brain barrier, are believed to be potential disruptors of preformed Aβ fibrils to cure AD with unknown mechanism. Herein, we present the destabilization potential of three ω-3 PUFAs, viz. Eicosapentaenoic acid (EPA), Docosahexaenoic acid (HXA), and α-linolenic acid (LNL) by molecular dynamics simulation. After an initial testing of 300 ns, EPA and HXA have been considered further for extended production run time, 500 ns. The increased value of root mean square deviation (RMSD), radius of gyration, and solvent-accessible surface area (SASA), the reduced number of H-bonds and β-sheet content, and disruption of salt bridges and hydrophobic contacts establish the binding of these ligands to Aβ fibril leading to destabilization. The polar head was found to interact with positively charged lysine (K28) residue in the fibril. However, the hydrophobicity of the long aliphatic tail competes with the intrinsic hydrophobic interactions of Aβ fibril. This amphiphilic nature of EPA and HXA led to the breaking of inherent hydrophobic contacts and formation of new bonds between the tail of PUFA and hydrophobic residues of Aβ fibril, leading to the destabilization of fibril. The Molecular Mechanics Poisson–Boltzmann Surface Area (MM-PBSA) results explain the binding of EPA and HXA to Aβ fibril by interacting with different residues. The destabilization potential of EPA and HXA establishes them as promising drug leads to cure AD, and encourages prospecting of other fatty acids for therapeutic intervention in AD. Communicated by Ramaswamy H. Sarma

Over the past century, rapid miniaturization of technologies has helped in the development of efficient, flexible, portable, robust, and compact applications with minimal wastage of materials. In this direction, of late, the usage of mesoscale liquid droplets has emerged as an alternative platform because of the following advantages: (i) a droplet is incompressible and at the same time deformable, (ii) interfacial area of a spherical droplet is minimum for a given amount of mass; and (iii) a droplet interface allows facile mass, momentum, and energy transfer. Subsequently, such attributes have aided towards the design of diverse droplet-based microfluidic technologies. For example, the microdroplets have been utilized as micro-reactors, colorimetric or electrochemical (EC) sensors, drug-delivery vehicles, and energy harvesters. Further, a number of recently reported lab-on-a-chip technologies exploit the motility, storage, and mixing capacities of the microdroplets. In view of this background, the review initiates discussion by highlighting the different attributes of the microdroplets such as size, shape, surface to volume ratio, wettability, and contact line. Thereafter, the effects of the surface or body forces on the properties of the droplets have been elaborated. Finally, the different aspects of such liquid droplet systems towards technological adaptations in health care, sensing, and energy harvesting have been presented. The review concludes with a tight summary on the potential avenues for further developments.

The clinical signature of Alzheimer's disease (AD) is the deposition of aggregated Aβ fibrils that are neurotoxic to the brain. It is the major form of dementia affecting older people worldwide, impeding their normal function. Finding and testing various natural compounds to target and disrupt stable Aβ fibrils seems to be a promising and attractive therapeutic approach. Four phenolic compounds from plant sources were taken into consideration for the present work, and were initially screened by docking. Ellagic acid (REF) came out to be the best binder of the Aβ oligomer from docking studies. To test the destabilization effect of REF on the Aβ oligomer, MD simulation was conducted. The simulation outcome obtained clearly indicates a drift of terminal chains from the Aβ oligomer, leading to the disorganization of the characteristically organized cross β structure of the Aβ fibrils. Increased values of RMSD, Rg, RMSF, and SASA are indicative of the destabilization of the Aβ fibril in the presence of REF. The disruption of salt bridges and a notable decline in the number of hydrogen bonds and β-sheet content explain the conformational changes in the Aβ fibril structure, ceasing their neurotoxicity. The MM-PBSA results revealed the binding of REF to chain A of the Aβ oligomer. The destabilization potential of ellagic acid, as explained by the MD simulation study, establishes it as a promising drug for curing AD. The molecular-level details about the destabilization mechanism of ellagic acid encourage the intensive mining of other natural compounds for therapeutic intervention for AD.

The aggregation and deposition of neurotoxic Aβ fibrils are key in the etiology of Alzheimer's disease (AD). It has been clinically recognized as a major form of dementia across the globe. Finding and testing various natural compounds to target Aβ fibrils to disrupt their stable structures seems to be a promising and attractive therapeutic strategy. The destabilization effects of caffeine on Aβ fibrils are investigated via in silico studies, where a series of molecular dynamics (MD) simulations, each of 100 ns, was conducted. The simulation outcomes obtained henceforth clearly indicated the drift of the terminal chains from the protofibrils, leading to disorganization of the characteristically organized cross-β structures of Aβ fibrils. The structural instability of Aβ17-42 protofibrils is explained through enhanced fluctuations in the RMSD, radius of gyration and RMSF values in the presence of caffeine. The key interactions providing stability, comprising D23-K28 salt bridges, intra- and inter-chain hydrogen bonding and hydrophobic interactions involving interchain A21-V36 and F19-G38 and intrachain L34-V36, were found to be disrupted due to increases in the distances between the participating components. The loss of β-sheet structure with the introduction of turns and α-helices in terminal chains may further inhibit the formation of higher order aggregates, which is necessary to stop the progression of the disease. The atomistic details obtained via MD studies relating to the mechanism behind the underlying destabilization of Aβ17-42 protofibrils by caffeine encourage further investigations exploring the potency of natural compounds to treat AD via disrupting preformed neurotoxic Aβ protofibrils.

Conducting polymers are usually good candidates for electrode materials of supercapacitors in spite of their lower cyclic stability, which can further be improved by combining with suitable nanofillers. In this work, we report the synthesis of nanocomposites of polyaniline (PANI), with equal weight% of graphene (G) and MoS2, prepared via in-situ oxidative polymerization of PANI, along with PANI-G binary nanocomposites. The morphological analysis confirms the formation of well-dispersed composite materials, and the ternary composite appears to be an interlayered structure of graphene and MoS2, encapsulating the PANI nanorods. As a result, the ternary composite exhibits an excellent supercapacitance behavior, suitable for energy storage applications as revealed by an enhanced cyclic stability. The ternary composite PANI-G-MoS2 symmetric electrode measurement exhibits a remarkably high specific capacitance (Cs, 142.30 F g−1) over binary composites under galvanostatic charge-discharge (GCD) cycles. The improved cyclic stability has contributed significantly in recovering the capacitance retention as high as 98.11% in comparison with pure PANI (∼40%) and binary composites (∼60–96%). Further, PANI-G-MoS2 symmetric electrode (viz., based on two electrode measurement) exhibits a high energy density (2.65 Wh kg−1) at a power density of 119.21 W kg−1, which is attributed to the high charge transport phenomenon occurs at the interfacial region between electrodes and electrolyte.

This work presents a triboelectric nanogenerator (TENG) fabrication using polytetrafluoroethylene, aluminum foil, and cellulose paper. Mechanical interactions lead to atomic defects that stimuli the delocalized electrostatic charge carriers and kinetic energy. The addition of ionic salt’s microdroplets improved the TENG’s performance. Eventually, surface charge activities have escalated the electrical signals. Further, studied spontaneously increased charge transport performance at the steady-state condition in the presence of NaCl ionic droplets. We considered that these ionic activities actively participated in detecting salt ions.

We observe variations in the electrical resistance across a conducting water microdroplet when it was placed on a glass substrate before being mechanically vibrated at natural frequency with the help of an acoustic source. The reduction in the resistance across the droplet was magnified owing to the formation of vortices in the matrix when the periodic oscillation of the surface was increased. The variation in the resistance could be tuned with the frequency of the sound source, which was found to be maximum when a 10 μL droplet was vibrated at ∼320 Hz. Interestingly, the variation in resistance across the oscillating droplet could follow and distinguish the musical notes in the octaves (“sur”) or rhythmic cycles (“taal”) originating from musical instruments such as flute, harmonium, whistle, and tabla. Further, when a suspension of urease-stabilized gold–cadmium–sulfide nanocomposite was suspended inside the droplet and mixed with an analyte containing urea solution, the change in the resistance during t...

The development of energy storage materials with high specific energy for futuristic applications is high in demand. Hybrid electric vehicles, solar energy harvesting, and commercial energy management systems are a few of the prospective applications of supercapacitors. We report the fabrication of symmetric tandem supercapacitors (STSC) using PANI-RGO-ZnO nanocomposite. The in-situ polymerization of PANI ensures the formation of a well-mixed nanocomposite. The detailed morphological analysis reveals that the PANI-RGO-ZnO 2:1 (PANI:ZnO) possesses a higher surface area, which contributes significantly towards excellent ionic diffusion resulting in a high specific capacitance (~40 F g−1) at a current density of 0.05 A g−1. The fabricated symmetric supercapacitor device (SSC) exhibits excellent electrochemical performance and high capacitance retention of ~86% over 5000 cycles at a scan rate of 100 mV s−1. The SSC device reveals notable specific energy and specific power of ~5.61 Wh kg−1 and ~403 W kg−1, respectively. The STSC system exhibited a steady voltage ~6.0 V, and demonstrated the performance of the fabricated device by glowing LEDs and operating a DC motor. The exquisite properties of the SSC electrode can be attributed to the synergistic effects of ZnO, PANI, and RGO in PANI-RGO-ZnO 2:1 nanocomposite.

Alzheimer’s is a fatal neurodegenerative disease for which there is no cure at present. The disease is characterized by the presence of plaques in the brains of a patient, which are composed mainly of aggregates of the amyloid-β peptide in the form of β-sheet fibrils. Here, we investigated the possibility of exploiting the superior binding ability of aromatic amino acids to a particular model of the amyloid-β fibrils. which is a difficult target for drug design. The β-sheet breaker peptide LPFFD was modified with aromatic amino acids and its binding to these fibrils was studied. We found that the orientation and the electrostatic complementarity of the modified peptide with respect to the fibrils played a crucial role in determining whether its binding was improved by the aromatic amino acids. The modified LPFFD peptides were able to bind to those fibril residues. which are important in the aggregation of amyloid-β peptides and thus can potentially inhibit the further aggregation of the amyloid-beta peptides by blocking their interactions. We found that the tryptophan modified LPFFD peptides had the best binding affinities. In most cases, the aromatic amino acids in the N-terminus of the modified peptides made more contacts with the fibrils than those in the C-terminus. We also found that increasing the aromatic content did not significantly improve the binding of the LPFFD peptide to the fibrils. Our study can serve as a basis for the design of novel peptide-based drugs for Alzheimer’s disease in which aromatic interactions play an important role.

Alzheimer’s disease is a leading cause of dementia in the elderly population for which there is no cure at present. Deposits of neurotoxic plaques are found in the brains of patients which are composed of fibrils of the amyloid-β peptide. Molecules which can disrupt these fibrils have gained attention as potential therapeutic agents. Δ-tetrahydrocannabidiol (THC) is a cannabinoid, which can bind to the receptors in the brain, and has shown promise in reducing the fibril content in many experimental studies. In our present study, by employing all atom molecular dynamics simulations, we have investigated the mechanism of the interaction of the THC molecules with the amyloid-β protofibrils. Our results show that the THC molecules disrupt the protofibril structure by binding strongly to them. The driving force for the binding was the hydrophobic interactions with the hydrophobic residues in the fibrils. As a result of these interactions, the tight packing of the hydrophobic core of the protofibrils was made loose, and salt bridges, which were important for stability were disrupted. Hydrogen bonds between the chains of the protofibrils which are important for stability were disrupted, as a result of which the β-sheet content was reduced. The destabilization of the protofibrils by the THC molecules leads to the conclusion that THC molecules may be considered for the therapy in treating Alzheimer’s disease.

Flow of two immiscible fluids gives rise to variety of flow patterns, which influence transportation process. In this work, we present detailed analysis on the prediction of flow pattern maps and radial distribution of volume fraction, pressure and velocity of a pair of immiscible liquids through a horizontal pipeline by computational fluid dynamics (CFD) simulation using ANSYS FLUENT 6.3. Moderately viscous oil and water have been taken as the fluid pair for study. Volume of fluid (VOF) method has been employed to predict various flow patterns by assuming unsteady flow, immiscible liquid pair, constant liquid properties, and co-axial flow. From the grid independent study, we have selected 47 037 number of quadrilateral mesh elements for the entire geometry. Simulation successfully predicts almost all the flow patterns (viz., plug, slug, stratified wavy, stratified mixed and annular), except dispersion of oil in water and dispersion of water in oil. The simulated results are validated with experimental results of oil volume fraction and flow pattern map. Radial distribution of volume fraction, pressure and velocity profiles describe the nature of the stratified wavy, stratified mixed and annular flow pattern. These profiles help to developing the phenomenological correlations of interfacial characteristics in two-phase flow.

The AB5 type toxin produced by the Vibrio cholerae bacterium is the causative agent of the cholera disease. The cholera toxin (CT) has been shown to bind specifically to GM1 glycolipids on the membrane surface. This binding of CT to the membrane is the initial step in its endocytosis and has been postulated to cause significant disruption to the membrane structure. In this work, we have carried out a combination of coarse-grain and atomistic simulations to study the binding of CT to a membrane modelled as an asymmetrical GM1-DPPC bilayer. Simulation results indicate that the toxin binds to the membrane through only three of its five B subunits, in effect resulting in a tilted bound configuration. Additionally, the binding of the CT can increase the area per lipid of GM1 leaflet, which in turn can cause the membrane regions interacting with the bound subunits to experience significant bilayer thinning and lipid tail disorder across both the leaflets.

Materials with high specific energy and specific power, along with chemical and structural stability, are in huge demand due to their numerous applications, including solid-state electronic devices and wearable electronics. Nanocomposites comprising of both conducting and non-conducting polymers exhibit excellent charge transfer mechanism along with high dielectric strength and structural stability, which enhances their appropriateness as efficient energy storage materials. Herein, we explore the application of Nylon-6 (PA6), polyaniline (PANI) and reduced graphene oxide (rGO) in preparing ternary nanocomposite (PA6/rGO/PANI) by varying the ratio of PA6 and PANI, for a fixed amount of rGO along with binary (PA6/PANI and rGO/PANI) nanocomposites. Among them, PA6/rGO/PANI 1:2 exhibits an excellent supercapacitance performance owing to its high surface area, low charge transfer resistance, high cyclic stability, and exceptional ionic rate capability. We have observed reasonable dielectric properties (viz., dielectric permittivity and dielectric loss), which is attributed to the stacking property of rGO with PA6 and PANI chains. The in-situ polymerization of PANI ensures the formation of well-dispersed nanocomposites with the hierarchical nanostructures, as revealed by the detailed morphological study. The galvanostatic charge-discharge measurement exhibits remarkable reversibility with capacitance retention of ~ 98%. The fabricated symmetric supercapacitor device based on PA6/rGO/PANI 1:2 exhibits noteworthy specific capacitance (38 F g−1), specific energy (~ 3.66 Wh kg‒1) and specific power (~ 234.84 W kg‒1), suggesting significant charge accumulation over the electrode surfaces, which is attributed to the synergistic effect of PA6 and PANI in the presence of rGO. The excellent electrochemical properties indicate its potential applications in self-powered electronic appliances effectively.

Self-organization of large-area micro- or nanoscale patterns, using an inexpensive one-step process, is proposed for the fabrication of low-cost, high-performance organic solar cells. The authors employ spin dewetting of a conductive polymer to fabricate an array of micro- to nanoscale ordered heterojunctions, and demonstrate improvements in the key performance indicators of the resulting organic photovoltaic devices. A theoretical study with appropriate boundary conditions is carried out to understand the pattern formation, and simulations are performed to probe the effects of varying active-layer geometry on device characteristics.

A layered structure of triboelectric nanogenerator (TENG) has been fabricated in the contact separation mode with plain paper, highly dielectric (PTFE) polytetrafluoroethylene and conductive aluminium layers, respectively. The output responses were recorded in form of electrical voltage by the triggering of mechanical interactions over the TENGs surface. A size dependent analysis has been studied, followed by the function of current density and generated power. Thermal behaviour on the TENG surface revealed an inverse output voltage response.

Liquid droplets loaded with paramagnetic or diamagnetic salts, namely liquibots, showed controlled migration inside a fluid medium and on slippery solid surfaces under remote magnetic guidance. The water or oilbots of size ranging from a millimetre to a few microns showed facile attraction, repulsion, division, and coalescence when guided by a magnetic field. The speed of the liquibots could be tuned by varying the size, salt-loading, and magnetic field strength. While the paramagnetic liquibot migrated towards a magnet with a velocity as high as ∼8 body length per s, the diamagnetic one migrated away from the field with a maximum velocity of ∼1 body length per s. The liquibots transported and delivered commercially available drugs to targeted locations showing their potential as drug-delivery vehicles. Remarkably, the experiments showed the utility of the liquibots in digital microfluidics because they moved easily on slippery solid surfaces. For example, a waterbot was split into many droplets on an oil coated solid surface before forming the patterns resembling polygons under magnetic guidance. Further, the liquibot based Packman™ game could also be played with the help of magnetic guidance. The extent of control demonstrated on the motions of the remotely guided liquibots could be useful in diverse futuristic applications including drug-transport, digital-microfluidics, and droplet-electronics.

Experimental results on flow patterns and pressure drop characteristics of viscous oil–water flow through undulated pipeline in peak configuration have been studied in this work. Undulated pipeline consists of two inclined sections (uphill and downhill) connected between two horizontal pipes (upstream and downstream) at peak configuration. Experiments have been conducted over a wide range of superficial velocities of oil ( U SO = 0.015–1.3 m/s) and water ( U SW = 0.1–1.2 m/s). Seven different flow patterns (viz., plug, slug, wavy stratified, stratified mixed, wispy annular, dispersion of oil in water and dispersion of water in oil) are identified by visual, imaging and electrical conductance probe techniques at all the four sections. Our results shows that present undulation (5°) has a marginal effect on the flow behavior of viscous oil–water mixture and the range of fluid velocity differs for a particular flow pattern. The pressure gradient characteristics across the peak experiences relatively more pressure gradient as compared to upstream and downstream at U SW ⩾ 0.6 m/s, which is attributed to the combined effect of undulation (viz., peak configuration) along the pipeline, flow pattern, and effective viscosity and density of the fluid mixture.

Summary We report dynamic Monte Carlo simulation results on the crystallization of double crystalline A-B diblock copolymer, wherein the melting temperature of A-block is higher than B-block. Crystallization of A-block precedes the crystallization of B-block upon cooling from a homogeneous melt. The interaction between A-type and B-type units is modelled as the repulsive interaction to represent their mutual immiscibility. The morphological development is controlled by the interplay between crystallization and microphase separation. With increasing segregation strength, we observe a gradual decrease in crystallinity accompanying with smaller and thinner crystals. During crystallization, A-block crystallizes first and creates confinement for the crystallization of the B-block. Thus, crystallization of B-block slows down, influencing the overall crystal morphology. With changing block composition, we observe a non-monotonic trend in the crystallization behaviour (viz., crystallinity, lamellar thickness) of A-block when B-block composition is significantly higher than A-block. This non-monotonic trend is attributed to the dilution effect of the B-block.

Summary Self-assembly in polymeric material is facilitated by the presence of active hetero-atoms either along the backbone or as pendant groups. Self-assembly leads to a rich variety of morphological pattern influencing various properties of polymeric materials. Presence of branching along the backbone chain also imparts remarkable change in polymeric properties. We report dynamic Monte Carlo (DMC) simulation study on solution behavior of branched polymers. We take multi-arm telechelic star polymers (TSP, one branch point with terminal active groups) and H-shaped branched polymers (homopolymers with two branch points), elucidating the driving mechanisms of collapse transition and morphological development. The presence of terminal active groups in TSP drives the collapse transition producing segregated and compact globule structure, on deteriorating solvent quality. On the other hand, presence of two branch points in H-shaped polymers incorporates conformational heterogeneity (viz., entropically originated) and produces segregated globule structures. The terminal functional groups in TSP form aggregate, resembles to “watermelons” (WM) and double watermelon (DWM) depending on the number of arms and mode of cooling. In H-polymers, conformational heterogeneity leads to the formation of segregated backbone and branch units (resembles to “Sandwich” or “Janus” morphology) rather an evenly distributed structure consisting of all the units, accompanying with a larger size of branches compared to the backbone.

A versatile graphene coated glass microswimmer displayed directed motions under the influence of applied electric field, chemical potential gradient and external magnetic field. The directed chemical locomotion took place from the region of lower to higher pH with speed ∼13 body lengths per second due to asymmetric catalytic decomposition of dilute hydrogen peroxide across the motor surface. The negative surface potential of graphene coated motor developed an electrical double layer in an alkaline medium which in turn engendered electrophoretic mobility towards anode when the external electrostatic field was applied. Inclusion of sparsely populated ferromagnetic iron nanoparticles on the surface of the motor offered the magnetic remote control on the motion. The coupled in situ and external controls enabled the motor to develop complex motions in diverse open and confined environments. For example, the motor could approach, pick-up, tow, and release a heavy cargo inside microchannel. Remarkably, the motor (∼67 μg) could successfully drive out a ∼1000 times heavier payload (∼0.67 mg) displaying the ability to overcome the drag force of ∼2619 pN with the help of coupled in situ and remote guidance.

We report dynamic Monte Carlo simulation results on the crystallization of double crystalline symmetric A-B diblock copolymer, wherein the melting temperature of A-block is higher than B-block. Crystallization of A-block precedes the crystallization of B-block upon cooling from a homogeneous melt. The morphological development is controlled by the interplay between crystallization and microphase separation. With increasing segregation strength, we observe a gradual decrease in crystallinity accompanying with smaller and thinner crystals. During crystallization, A-block crystallizes first and creates confinement for the crystallization of B-block. Thus, crystallization of B-block slows down influencing the overall crystal morphology. At higher segregation strength, due to the repulsive interaction between blocks, block junction is stretched out, which is reflected in the increased value of mean square radius of gyration. As a result, a large number of smaller size crystals form with less crystallinity. The onset of microphase separation shifts towards higher temperature with increasing segregation strength. Isothermal crystallization reveals that the transition pathways strongly depend on segregation strength. The value of Avrami index shows the formation of two dimensional lamellar crystals of both the blocks. Two-step (sequential), compared to one-step (coincident) isothermal crystallization, produces higher crystallinity in A-block, however, the crystallinity of B-block is almost identical in both the cases.

We report detailed analysis on the flow patterns of moderately viscous oil–water two-phase flow through a circular horizontal pipe with an internal diameter of 0.025 m. Lubricating oil and water wi...

We report dynamic Monte Carlo (DMC) simulation study of solution behavior of multi-arm telechelic star polymers, wherein the number of branching (f) increases with decreasing arm length (n); thus keeping the total number of monomer (N) in the molecule around a constant value. On deteriorating solvent quality, the conformational change occurs from an open to a compact globule structure. The terminal functional groups form aggregate as the solution is cooled progressively and the aggregation phenomenon drives the collapse transition. The transition temperature follows a non-monotonic trend with the functionality, in comparison with an equivalent series of star homopolymers. The non-monotonic behavior of telechelic star polymer is attributed to the interplay between enthalpic gain due to end-monomer aggregation and entropic loss due to loop formation. Structural analysis reveals that, aggregation of end group yields a structure resembles to “watermelons” (WM). Simulation results for the systems with varying N (keeping f or n constant and varying n or f) shows the similar mechanism to the constant N system. Further, we discuss results on highly branched telechelic star polymer with shorter arm length, where, we observe the formation of collapsed structures with single and double aggregates in isothermal and non-isothermal cooling respectively.

Blending of two or more pure polymers is an effective way to produce composites with tunable properties. In this paper, we report dynamic Monte Carlo simulation results on the crystallization of crystalline/crystalline (A/B) symmetric binary polymer blend, wherein the melting temperature of A-polymer is higher than B-polymer. We study the effect of segregation strength (arises from the immiscibility between A- and B-polymers) on crystallization and morphological development. Crystallization of A-polymer precedes the crystallization of B-polymer upon cooling from a homogeneous melt. Simulation results reveal that the morphological development is controlled by the interplay between crystallization driving force (viz., attractive interaction) and de-mixing energy (viz., repulsive interaction between two polymers). With increasing segregation strength, the interface becomes more rigid and restricts the development of crystalline structures. Mean square radius of gyration shows a decreasing trend with increasing segregation strength, reflecting the increased repulsive interaction between A- and B-polymers. As a consequence, a large number of smaller size crystals form with lesser crystallinity. Isothermal crystallization reveals that the transition pathways strongly depend on segregation strength. We also observe a path-dependent crystallization behavior in isothermal crystallization: two-step (sequential) isothermal crystallization yields superior crystalline structure in both A- and B-polymers than one-step (coincident) crystallization.

The study of the ability of drug molecules to enter cells through the membrane is of vital importance in the field of drug delivery. In cases where the transport of the drug molecules through the membrane is not easily accomplishable, other carrier molecules are used. Spherical fullerene molecules have been postulated as potential carriers of highly hydrophilic drugs across the plasma membrane. Here we report the coarse-grain molecular dynamics study of the translocation of C60 fullerene and its derivatives across a cell membrane modeled as a 1, 2-distearoyl-sn-glycero-3-phosphocholine (DSPC) bilayer. Simulation results indicate that pristine fullerene molecules enter the bilayer quickly and reside within it. The addition of polar functionalized groups makes the fullerenes less likely to reside within the bilayer but increases their residence time in bulk water. Addition of polar functional groups to one half of the fullerene surface, in effect creating a Janus particle, offers the most promise in developing fullerene models that can achieve complete translocation through the membrane bilayer., 25 pages, 9 Figures, 1 Table

We report a detailed investigation on the measurement and prediction of pressure gradient characteristics of moderately viscous lubricating oil-water flow through a horizontal pipe of 0.025 m internal diameter. Experiments are carried out over a wide range of phase velocities of both oil (USO = 0.015–1.25 m/s) and water (USW = 0.1–1.1 m/s). Experimental pressure gradients yield significant errors when fitted to the existing correlations, which are largely used for gas-liquid flow. To predict pressure gradient characteristics for liquid-liquid flow, the existing correlations need to be modified. We propose two correlations, based on the Lockhart–Martinelli's approach (by modifying the correlation between the Lockhart–Martinelli parameter and a two-phase multiplier suitable for the present system) and dimensionless analysis, following the Buckingham's Pi-theorem. We observe significant improvement in the prediction of pressure gradient. The correlation based on the dimensionless analysis predicts better with an average absolute error of 17.9%, in comparison with the modified Lockhart–Martinelli correlation, which yields an average error of 22%, covering all the flow patterns. The present analysis shows better prediction as compared to two-fluid model Zhang et al. (2012, “Modeling High-Viscosity Oil/Water Concurrent Flow in Horizontal and Vertical Pipes,” SPE J., 17(1), pp. 243–250) and Al-Wahaibi (2012, “Pressure Gradient Correlation for Oil-Water Separated Flow in Horizontal Pipes,” Exp. Therm. Fluid Sci., 42, pp. 196–203) work.

We report dynamic Monte Carlo simulation on conformational transition of H-shaped branched polymers by varying main chain (backbone) and side chain (branch) length. H-shaped polymers in comparison with equivalent linear polymers exhibit a depression of theta temperature accompanying with smaller chain dimensions. We observed that the effect of branches on backbone dimension is more pronounced than the reverse, and is attributed to the conformational heterogeneity prevails within the molecule. With increase in branch length, backbone is slightly stretched out in coil and globule state. However, in the pre-collapsed (cf. crumpled globule) state, backbone size decreases with the increase of branch length. We attribute this non-monotonic behavior as the interplay between excluded volume interaction and intra-chain bead-bead attractive interaction during collapse transition. Structural analysis reveals that the inherent conformational heterogeneity promotes the formation of a collapsed structure with segregated backbone and branch units (resembles to 'sandwich' or 'Janus' morphology) rather an evenly distributed structure comprising of all the units. The shape of the collapsed globule becomes more spherical with increasing either backbone or branch length., 36 pages, 15 figures

Monte Carlo simulations show that copolymers with uniformly (or periodically) distributed sticky comonomers collapse "cooperatively," abruptly forming a compact intermediate comprising a monomer shell surrounding a core of the aggregated comonomers. In comparison, random copolymers collapse through a relatively less-compact intermediate comprising a comonomer core surrounded by a fluffy monomer shell that densifies over a wide temperature range. This difference between the collapse pathways for random and uniform copolymers persists to higher chain lengths, where uniform copolymers tend to form multiple comonomer cores. In this paper, we describe the formation of such an intermediate state, and the subsequent collapse, by recognizing that these arise from the expected balance between comonomer aggregation enthalpy and loop formation entropy dictated by the chain microstructure. (c) 2007

We present dynamic Monte Carlo lattice simulations of the coil to globule collapse of single chains of a copolymer comprising monomer units, m and c, wherein there is a net attractive interaction between c-units. As the copolymer is cooled, the solvent quality becomes poorer, and the size of the chain decreases, driven by the net m-m and c-c attractions. The strong c-c attraction increases the overall solvophobicity of the chain relative to a homopolymer and, therefore, copolymers collapse more abruptly and at a higher effective temperature relative to homopolymers. We compare copolymers with homopolymers by rescaling collapse data to the same theta values to account for the effect of overall solvophobicity. This comparison shows that the behavior of copolymers and the corresponding homopolymers is identical as the chain size reduces from high temperatures to the theta value. Beyond theta, copolymers with c-content < similar to 50% collapse more abruptly than either homopolymer, after accounting for the difference in overall solvophobicity. Collapse of copolymers containing higher c-content is dominated entirely by the c-c attractions, and these chains behave qualitatively like homopolymers with a higher effective solvophobicity. Analysis of the chain structure during collapse provides a structural reason for the qualitative change in copolymer collapse at low c-content. When such copolymers are cooled below theta, the c-units rapidly aggregate to form an isotropic, compact core surrounded by an anisotropic solvated shell of m-units. The shell densifies as the copolymer is further cooled, but remains anisotropic for the finite chain sizes investigated.

The effect of "sticky" additives (viz., those that have attractive interactions with the polymer) on polymer crystallization, has been investigated by dynamic Monte Carlo (DMC) simulations. Additive-polymer attractive interactions result in a slowing down of the polymer chain diffusivity in the melt state. Our results show that with increasing additive stickiness, polymer crystallinity decreases monotonically, and thinner crystallites form, viz., crystallization is inhibited by the presence of sticky additives. Unusually, the observed "specific heat" peak at the phase transition shows nonmonotonic behavior with additive stickiness, and exhibits a maximum for intermediate values of additive stickiness. While the origins of this unexpected behavior are not clear, we show that it correlates with a large interchange between crystalline and amorphous states of the monomers, in the vicinity of the additives. At this intermediate additive stickiness, we also find that crystallization follows a qualitatively different route--crystallinity shows a non-Avrami-like evolution, unlike the case at low or high additive stickiness.