Electric field-modulated evaporative thin film deposition of bio-particles for piezoelectric applications.

Bio-based functional materials can be used to replace or limit the use of synthetic materials sourced from unsustainable sources. However, the potential of such materials remains largely unexplored. In this study, we demonstrate the use of weak AC electric fields to deposit ultra-thin piezoelectric films from cellulose nanocrystals (CNC). This is the first time electric fields are used to realize <50 nm thick uniform bio-based piezoelectric films wherein the bioparticles exhibit unidirectional arrangement. Interestingly, we found that the use of weak AC electric fields of suitable frequencies completely mitigates the coffee ring effect (CRE), which results in defect-free uniform ultra-thin films. Additionally, the electric fields appear to help in realizing unidirectional alignment of particles in the films, which enhances their piezoelectric properties. The method was also tested for chitin nanocrystals (ChNC), which have a similar aspect ratio but bear opposite polarity surface charges, and the influence of the field on coffee ring formation and particle orientation in CNC thin film deposition was validated. The phenomena can be attributed to the constant spatio-temporal curvature of the evaporating liquid film, the transient state between the three-phase contact (TPC) line, the electric field-dependent contact angle, and the permanent and field-induced dipole moments. These factors lead to particle polarization and alignment. The films have an optimum electrical frequency of deposition at which they are continuous and uniformly thin, have unidirectional alignment of particles, and function as a single dipole.

Liquid-templated graphene aerogel electromagnetic traps.

For decades, the inherently reflective nature of metallic electromagnetic (EM) shields and their induced secondary EM pollution have posed significant challenges for sensitive electronics. While numerous efforts have been made to develop superior EM shielding systems, the issue of reflection dominancy in metallic substrates remains unresolved. Herein, we addressed this long-lasting obstacle by pairing metallic shields with ultra-lightweight (density of 3.12-3.40 mg cm-3) elastic anti-reflection aerogels, altering their shielding mechanism from dominant reflection (reflectance >0.8) to absorption (absorbance >0.7) by trapping EM waves inside the aerogel. The aerogel EM traps were generated using interfacial complexation, yielding engineerable filamentous liquid structures. These served as templates for aerogel creation through a follow-up process of freezing and lyophilization. The engineerable lossy medium of aerogels benefits from a multi-scale porous construct with the combined action of dielectric and conduction losses, highly dissipating the EM waves and minimizing the reflections. Notably, declining the diameter of aerogel filaments promoted its absorption dominancy, rendering it a potent dissipating medium for EM waves. Pairing a metallic substrate with filamentous aerogel EM traps has resulted in an exceptionally effective absorption-dominant shielding system, achieving absorbance levels between 0.70-0.81. This system offers a shielding effectiveness of 53-89 dB within the X-band frequency range. This innovation addresses a persistent issue in shielding science related to the reflective characteristics of metallic substrates, effectively inhibiting their induced EM reflections.

Structured Emulgels by Interfacial Assembly of Terpenes and Nanochitin.

Interfacial assemblies formed by colloidal complexation are effective in multiphase stabilization, as shown in structured liquids and Pickering emulgels. Herein, we demonstrate a type of biobased colloidal system that spontaneously stabilizes an organic phase in a continuous hydrogel phase. Specifically, a triterpene extracted from bark (betulin, BE) is added to an organic phase containing a coniferous resin (rosin acid, a diterpene). BE is shown to take part in strong noncovalent interactions with the nanochitin dispersed in the aqueous (hydrogel) phase, leading to a complex of high interfacial activity. The viscoelastic response of the system is rationalized by the presence of a superstable structured dual network. When used as a templating material, the emulgel develops into structured liquids and cryogels. The herein introduced all-biobased type of nanoparticle surfactant system forms a gel ("emulsion-filled" with "aggregated droplets") that features the functional benefits of both betulin and nanochitin.

Functional Janus structured liquids and aerogels.

Janus structures have unique properties due to their distinct functionalities on opposing faces, but have yet to be realized with flowing liquids. We demonstrate such Janus liquids with a customizable distribution of nanoparticles (NPs) throughout their structures by joining two aqueous streams of NP dispersions in an apolar liquid. Using this anisotropic integration platform, different magnetic, conductive, or non-responsive NPs can be spatially confined to opposite sides of the original interface using magnetic graphene oxide (mGO)/GO, Ti3C2Tx/GO, or GO suspensions. The resultant Janus liquids can be used as templates for versatile, responsive, and mechanically robust aerogels suitable for piezoresistive sensing, human motion monitoring, and electromagnetic interference (EMI) shielding with a tuned absorption mechanism. The EMI shields outperform their current counterparts in terms of wave absorption, i.e., SET ≈ 51 dB, SER ≈ 0.4 dB, and A = 0.91, due to their high porosity ranging from micro- to macro-scales along with non-interfering magnetic and conductive networks imparted by the Janus architecture.

Composites based on electrospun fibers modified with cellulose nanocrystals and SiO2 for selective oil/water separation.

Membranes for water remediation require structural stability, efficient operation, and durability. In this work, we used cellulose nanocrystals (CNC) to reinforce hierarchical nanofibrous membranes based on polyacrylonitrile (PAN). Hydrolysis of the electrospun nanofibers (H-PAN) enabled hydrogen bonding with CNC and provided reactive sites for grafting cationic polyethyleneimine (PEI). In a further modification, anionic silica particles (SiO2) were adsorbed on the fiber surfaces, obtaining CNC/H-PAN/PEI/SiO2 hybrid membranes, which developed swelling resistance (swelling ratio of 6.7 compared to 25.4 measured for a CNC/PAN membrane). Hence, the introduced hydrophilic membranes contain highly interconnected channels, they are non-swellable and exhibit mechanical and structural integrity. By contrast with untreated PAN membranes, those obtained after modification displayed high structural integrity and allowed regeneration and cyclic operation. Finally, wettability and oil-in-water emulsion separation tests demonstrated remarkable oil rejection and separation efficiency in aqueous media.

All-Aqueous Bicontinuous Structured Liquid Crystal Emulsion through Intraphase Trapping of Cellulose Nanoparticles.

Here, we describe the all-aqueous bicontinuous emulsions with cholesteric liquid crystal domains through hierarchical colloidal self-assembly of nanoparticles. This is achieved by homogenization of a rod-like cellulose nanocrystal (CNC) with two immiscible, phase separating polyethylene glycol (PEG) and dextran polymer solutions. The dispersed CNCs exhibit unequal affinity for the binary polymer mixtures that depends on the balance of osmotic and chemical potential between the two phases. Once at the critical concentration, CNC particles are constrained within one component of the polymer phases and self-assemble into a cholesteric organization. The obtained liquid crystal emulsion demonstrates a confined three-dimensional percolating bicontinuous network with cholesteric self-assembly of CNC within the PEG phase; meanwhile, the nanoparticles in the dextran phase remain isotropic instead. Our results provide an alternative way to arrest bicontinuous structures through intraphase trapping and assembling of nanoparticles, which is a viable and flexible route to extend for a wide range of colloidal systems.

Interfacial Dilational Rheology of Molecular Films in DC Electric Fields.

We present a novel technique to measure the interfacial dilational rheology of a molecular film adsorbed at a water-oil interface in a direct-current (dc) electric field. A film of a highly polar subfraction of asphaltenes was allowed to adsorb at a water drop interface, surrounded by an organic phase and subjected to a dc electric field. The measurements involved calculations of the dynamic interfacial tension (IFT), while the drop was sinusoidally oscillated, using our in-house axisymmetric drop shape analysis (ADSA) algorithm adapted for electric fields. The amplitude of the IFT waveform over equilibrium IFT and the phase difference from the applied area oscillations were used in the estimation of surface moduli. The asphaltene films were found to become more elastic on increasing bulk concentrations and electric field strengths. However, the effect was not monotonous and observed to be governed by combinations of these parameters. The Lucassen-van den Tempel (LVDT) model was used to further elucidate the experimentally obtained interfacial dilational moduli.

Structured Ultra-Flyweight Aerogels by Interfacial Complexation: Self-Assembly Enabling Multiscale Designs.

The rapid co-assembly of graphene oxide (GO) nanosheets and a surfactant at the oil/water (O/W) interface is harnessed to develop a new class of soft materials comprising continuous, multilayer, interpenetrated, and tubular structures. The process uses a microfluidic approach that enables interfacial complexation of two-phase systems, herein, termed as "liquid streaming" (LS). LS is demonstrated as a general method to design multifunctional soft materials of specific hierarchical order and morphology, conveniently controlled by the nature of the oil phase and extrusion's injection pressure, print-head speed, and nozzle diameter. The as-obtained LS systems can be readily converted into ultra-flyweight aerogels displaying worm-like morphologies with multiscale porosities (micro- and macro-scaled). The presence of reduced GO nanosheets in such large surface area systems renders materials with outstanding mechanical compressibility and tailorable electrical activity. This platform for engineering soft materials and solid constructs opens up new horizons toward advanced functionality and tunability, as demonstrated here for ultralight printed conductive circuits and electromagnetic interference shields.

Emulsions in external electric fields.

Water is co-produced with crude oils, generally in the form of water-in-crude oil emulsions. The oil and water phases need to be separated before export. Separation is performed in gravity separators with the addition of chemical demulsifiers and, sometimes, with the application of an electric field by using an electrocoalescer. The present article reviews several aspects of electrocoalescence by considering the effect of the electric field from the molecular to a macroscopic scale: the oil-water interface, single drop effects, two drop interactions, and finally emulsions at laboratory scales. Experimental results together with Dissipative Particle Dynamics (DPD) simulation results are presented. The review begins with water-oil interface under an electric field and followed by single drop electrohydrodynamics. The electric field is shown to influence the adsorption of crude oil indigenous surface-active components (asphaltenes) due to the electrohydrodynamic (EHD) flows. The interactions between two droplets in the presence of electric field and the factors governing the drop-drop coalescence are discussed in detail. DPD simulations help to elucidate thin film breakup during (electro)-coalescence of two water droplets, where the oil film has drained out to nanometer thickness. The film is comprised of surfactant and demulsifier molecules, and the simulations capture the pores formation in the film when a DC field is applied. The results demonstrate influence of the molecular structure of the surfactant and demulsifier, and their interactions. The subsequent section describes experimental techniques to assess the resolution of crude oil emulsions at the laboratory scale. The focus is on low-field Nuclear Magnetic Resonance (LF-NMR) which allows a determination of various emulsion features such as the droplet size distribution (DSD) and the brine profile (variation of the concentration of water with the height of the emulsion sample) and their evolution with time. Application of the technique in emulsion treatment involving chemical demulsifiers and electric field is presented. The review concludes with description of commercial industrial electrocoalecers such as the Vessel Internal Electrostatic Coalescer (VIEC) and the Compact Electrostatic Coalescer (CEC).

Experimental Evidence of Enhanced Adsorption Dynamics at Liquid-Liquid Interfaces under an Electric Field.

In this work, we investigate the adsorption of surface-active compounds at the water-oil interface subjected to an electric field. A fluid system comprising a pendent water drop surrounded by an asphaltene-rich organic phase is exposed to a DC uniform electric field. Two subfractions of asphaltenes having contrasting affinities to the water-oil interface are used as surface-active compounds. The microscopic changes in the drop shape, as a result of asphaltene adsorption, are captured and the drop profiles are analyzed using our in-house code for axisymmetric drop shape analysis (ADSA) under an electric field. The estimates of dynamic interfacial tension under different strengths of the field (E0) and concentrations of the asphaltene subfractions (C) are used to calculate adsorption dynamics and surface excess. The experimental observations and careful analyses of the data suggest that the externally applied electric field significantly stimulates the mass-transfer rate at the liquid-liquid interface. The enhancement in mass transport at the water-oil interface can be attributed to the axisymmetric electrohydrodynamic fluid flows generated on either side of the interface. The boost in mass transport is evident from the growing decay in equilibrium interfacial tension (γeq) and increased surface excess (Γeq) upon increasing strength of the applied electric field. The mass-transfer intensification does not increase monotonously with the electric field strength above an optimum E0, which is in agreement with the previous theoretical studies in the literature. However, these first explicit experimental measurements of adsorption at an interface under an electric field suggest that the optimum E0 is determined by characteristics of the surface-active molecules.

Antibiotic Therapy for Children with Diarrhea in a Low-Resource Setting: A Syndromic Approach.

OBJECTIVE: To compare age and protein-energy malnutrition (PEM) - the predispositions - and fever and abnormal leukocyte count (ALC) - the SIRS criteria - in hospitalized children with and without diarrhea. DESIGN: A prospective case-control study. SETTING: A pediatric ward of a general hospital in a low-resource setting. PARTICIPANTS: Totally, 445 consecutive admissions to the pediatric ward of a general hospital over a period of 1 year were included in this prospective case-control study; hemodynamically unstable subjects (11) were excluded. INTERVENTIONS: Age, PEM, fever, and ALC were assessed in 59 patients with diarrhea and compared with 375 control patients without diarrhea. Odds ratios with confidence intervals were determined; the chi-square test and binary logistic regression analysis were also performed. MAIN OUTCOME MEASURES: Associations of diarrhea with age, PEM, fever and ALC singly and various combinations of predispositions and SIRS parameters. RESULTS: Infancy and ALC were significantly associated with diarrhea. PEM or fever alone was not significantly associated with diarrhea; however, the probability of developing diarrhea was significantly higher when a combination of ALC and PEM was observed. The combination of infancy, PEM, and ALC carried a sensitivity of 81·36%; for other combinations, sensitivity varied between 70% and 80%. The combination of infancy and ALC had the lowest sensitivity (59·32%) but the best specificity (61·07%). CONCLUSION: The association/presence of a combination of SIRS parameters (fever and ALC) and predispositions (infancy and PEM) in children with diarrhea may help in deciding whether antibiotic therapy should be initiated.

Double burden of malnutrition among Indian schoolchildren and its measurement: a cross-sectional study in a single school.

OBJECTIVE: This cross-sectional study set in a single school on the outskirts of a large city aimed to document the extent of double burden of malnutrition (coexistence of overnutrition and undernutrition) among Indian schoolchildren from lower socioeconomic groups, and to determine if mid-upper arm circumference (MUAC) can be used as a proxy for body mass index (BMI). SUBJECTS: The total number of participants was 1444, comprising 424 girls and 1020 boys belonging to playgroups and grades 1 to 7. MEASUREMENTS: Anthropometric measurements, such as participants' MUAC, height and weight were measured using standard techniques. Descriptive statistics for BMI and MUAC were obtained based on gender; z-scores were computed using age-specific and sex-specific WHO reference data. The distribution of variables was calculated for three groups: girls, boys and all participants. Homogeneous subsets for BMI and MUAC were identified in the three groups. Age-wise comparisons of BMI and MUAC were conducted for each gender. MAIN OUTCOME MEASURES: (1) To know if MUAC and BMI are correlated among boys and girls. (2) To study BMI and MUAC z-score distribution among the participants. RESULTS: MUAC was positively correlated with BMI in both boys and girls. The following BMI z-score distribution was observed: severe acute malnutrition (SAM), 5 (0.3%); moderate acute malnutrition (MAM), 146 (10.1%) and undernourished, at risk of MAM/SAM, 141 (9.8%); obese, 21 (1.5%); overweight, 36 (2.5%) and pre-obese, 136 (9.4%). The distribution of categories of children based on MUAC z-scores was: SAM, 7 (0.5%); MAM, 181 (12.5%) and undernourished, at risk of MAM/SAM, 181 (12.5%); obese, 19 (1.3%); overweight, 178 (12.3%) and pre-obese, 135 (9.3%). CONCLUSIONS: SAM/MAM/undernourished states and obesity/overweight/pre-obese states, indicating undernutrition more than overweight, coexist among Indian schoolchildren from lower middle/lower socioeconomic categories. BMI and MUAC were significantly correlated. MUAC identifies both undernutrition and overnutrition by early detection of aberrant growth.

Coalescence Behavior of Stable Pendent Drop Pairs Held at Different Electric Potentials.

In this work, we studied the electrocoalescence behavior of stable pendent drop pairs and compared the results with clean drops, where the interface is void of surface-active compounds. The drop phase was brine and the drop-oil interface was stabilized by aging into asphaltene and demulsifier solutions. The experiments involving asphaltene-laden drops required the bulk phase to be clear for visualization of the drops, which is realized by a procedure to replace the asphaltene-containing dark bulk phase by a pure solvent mixture. The narrowly spaced pendent drops, maintained at different electric potentials, acquired net surface charge of opposite polarity, which led to the Coulombic attraction in the drop pair. After the application of voltage, a drop pair was observed to remain at a standstill, attracted, or coalesced depending on the interdrop separation, drop size, and potential difference. We systematically investigated the influence of different surface-active compounds on interfacial stabilization and electrostatic drop-drop attraction and coalescence behavior. Interestingly, the experimental data showed that a drop pair coalesces at a lower potential (ΔVcrit) when the drop-oil interface is populated with the surface-active molecules. Similarly, the minimum voltage (ΔVm) needed to induce attraction between two stable drops and the degree of the attraction are different than those of the clean drops. Furthermore, the demulsifier-laden drops exhibited dissimilar attraction, coalescence, and noncoalescence characteristics to the drops stabilized in asphaltene solutions. Our analysis suggested that the asphaltenes and the commercial demulsifiers differently influenced the drops' response to the applied electric potential. The contrasting coalescence nature of the stable drops could be attributed to a complex interplay between hydrodynamics, electrostatics, and interfacial reorganization of the molecules and charges.

Methodology to calculate interfacial tension under electric field using pendent drop profile analysis.

In this paper, we present a methodology to calculate interfacial tension of a water-oil interface under an electric field. The Young-Laplace equation, conventionally used to estimate surface/interfacial tension in axisymmetric drop shape analysis (ADSA), is modified to include electrostatic effects. The solution needs normal component of the Maxwell stress at the interface which is calculated separately by solving the Laplace equation for electric potential. The optimized fitting between the resulting theoretical profile and the experimentally obtained profile results into Bond number which is used to calculate the apparent value of interfacial tension. The algorithm can process a large number of drop profiles in one go. The methodology can be applied in the ADSA studies for adsorption dynamics where a drop is held for a long time while surface active molecules are allowed to adsorb. The method discussed in this paper will help the future studies in adsorption dynamics at fluid interfaces under electric field and the resulting interfacial property evolution.

An Innovative Air-Oxygen Blender for Continuous Positive Airway Pressure Support in Resource-Poor Locations: A Feasibility Study.

Objectives: The objectives of this study are (i) to evaluate the feasibility of using an inexpensive air pump to maintain reliable oxygen concentration in a continuous positive airway pressure (CPAP) system and (ii) to evaluate whether an inexpensive air pump can maintain infant 02 sats >90%. Methods: This prospective study, which included 19 babies in pilot phase and 90 during extension phase, was conducted at a neonatal intensive care unit in a resource-poor academic medical center in India. The intervention involved introduction of an air pump in the CPAP delivery system. Outcome measures were oxygen concentration in the air-oxygen blend and oxygen saturation of the study babies. Results: Oxygen concentration at the outlets ranged between 56 and 70% and in the blend between 42 and 51%. Oxygen saturation ranged between 90 and 97%. Conclusion: A simple and inexpensive air pump can work as a safe and effective oxygen blender.

Influence of a Propagating Megahertz Surface Acoustic Wave on the Pattern Deposition of Solute Mass off an Evaporating Solution.

We study the influence of a megahertz Rayleigh surface acoustic wave (SAW), propagating in a solid substrate, on the pattern deposition of a solute mass off an evaporating solution. An experimental procedure, where a film of a solution undergoes a controlled evaporation in a chamber, shows that the SAW alters the state of the pattern deposition. Increasing the power of the SAW supports an increase in the density of the deposited patterns. Beyond threshold conditions, the deposited patterns merge and we observe the deposition of a solid film. A simplified theory suggests that the SAW deforms the geometry of the film, which is predominantly governed by the capillary stress. The deformation of the film taking place alongside with the evaporation of the solution increases the concentration near the pinned three phase contact line at the front of the film, which is closer to the source of the SAW, on the expense of the concentration at the rear. The increased concentration translates to the deposition of solute mass over an increased area near the front of the film, which explains the experimental observation.

Out-of-pocket nonmedical expenses associated with out-patient treatment of common childhood illnesses.

BACKGROUND: Out-of-pocket expenses, medical and non-medical, have an impoverishing effect on the family. OBJECTIVE: Determine non-medical out-of-pocket expenses incurred during out-patient attendance for primary care services. METHODS: A descriptive survey was undertaken at a rural medical college using interviewer-administered questionnaire to parents of children <6 years over a period of 6 weeks. Seventy-six participants were interviewed for collecting demographic data and actual cost on travel and meals. RESULTS: Median expenditure for travel was Indian rupees (INR) 20 with inter-quartile range (IQR) 14-48 and on food it was INR 110 with IQR 40-155. Median total expenditure on the visit was INR 122 with IQR 61-220. Among those who travelled >5 km, 36% attendance was for respiratory complaints, 27% with fever and as many as 86% for vaccination. CONCLUSION: Families in rural India have substantial costs incurred in OPD attendance, most of which is for preventive health care such as immunization.

Home-made continuous positive airways pressure device may reduce mortality in neonates with respiratory distress in low-resource setting.

OBJECTIVE: To study the effectiveness of locally assembled low-cost version for continuous positive airway pressure (CPAP) delivery. PATIENTS: Babies with respiratory distress from two contiguous periods, one with CPAP therapy and the other without, were compared for following parameters: birth weight, gestational age, severity of respiratory distress, as assessed by Silverman-Anderson retraction score (SARS), maximum SARS, days taken for score to become 0, duration of oxygen therapy, hospital stay and the outcome. RESULTS: The profile of subjects was comparable in two groups. Severity of respiratory distress (SARS) was significantly higher in post-CPAP group. Time taken for SARS to become 0 and number of deaths were significantly lower, and the duration of oxygen administration and hospital stay were significantly higher in post-CPAP group. The cost of an individual disposable CPAP unit was ∼Rs 160 (USD 3). CONCLUSION: A low-cost and locally assembled CPAP delivery system may reduce neonatal mortality among babies with respiratory distress.

Teaching primary care in pediatric outpatient department in developing countries: a feasibility study.

We studied the feasibility of teaching primary care to undergraduate medical students in an outpatient department (OPD) using a specially developed teaching package. Teaching was conducted in four 30 min sessions during a 4 week rotation term, and a test was offered at the end. We concluded, on the basis of grades achieved in the test, that it is feasible to impart primary care knowledge through OPD teaching using structured teaching goals for teachers.