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This study concerns the determination of effective transport coefficients for multiscale composite materials used in various electrochemical systems. The effective transport coefficients are indispensable in macroscale modeling of such systems. We propose an integrated approach which for a given two-phase or three-phase microstructure allows us to systematically determine the exact values of different effective transport coefficients such as diffusivity of a species or electric conductivity. In addition to electron microscopy, this approach combines state-of-the-art techniques of mathematical homogenization, image processing and numerical computation. When only partial information about the microstructure is available, rigorous upper and lower bounds are available on the effective transport coefficients and we demonstrate that the commonly used Bruggeman’s formula may in fact violate the lower bound in some regimes. These upper bounds also allow one to quantify how much the transport properties of the material with a given composition could be improved. The proposed approach is illustrated by analyzing a three-phase electrode material of an actual Li-ion battery. We also quantify the uncertainty of the effective transport coefficients resulting from possibly imprecise information about the material properties of the individual phases and address the question concerning the importance of resolving all three phases.

Experimental investigations on thermodiffusion have been conducted for five different ternary mixtures of methane, n-butane, and n-dodecane at a high temperature and pressure. While the mole fraction of methane was fixed at 0.2 the mole fraction of n-dodecane was varied from 0.7 to 0.2. The experiments were performed in a microgravity environment on board the satellite FOTON-M3. It was found that in all mixtures, n-dodecane separated to the cold side whereas methane segregated to the hot side. n-butane, the species with an intermediate density, showed a change in sign as its mole fraction was increased. At low concentrations it collected on the cold side but moved in the opposite direction with an increase in its mole fraction. The role of the relative density coupled with the species concentrations has been used to explain the thermodiffusion factor in each mixture. Computational investigations showed a similar behavior. However, the theoretical model was not able to capture the sign change of n-butane accurately. The inadequate representation of the significance of the relative densities and the mole fraction of the species has been found as the reason for this.

In an unprecedented experimental investigation, a ternary and a four component hydrocarbon mixture at high pressure have been studied in a nearly convection free environment to understand the thermodiffusion process. A binary mixture has also been investigated in this environment. Experimental investigations of the three mixtures have been conducted in space onboard the spacecraft FOTON-M3 thereby isolating the gravity-induced convection that otherwise interferes with thermodiffusion experiments on Earth. The experimental results have also been used to test a thermodiffusion model that has been calibrated based on the results of previous experimental investigations. It was found that with an increase in the number of components in the mixtures, the performance of the thermodiffusion model deteriorated. Computational analysis was also made to estimate the possible sources of errors. Simulations showed that the vibrations of the spacecraft could influence the estimates of thermodiffusion factors. It was also found that they are sensitive to slight variations in the temperature of the mixture.

No abstract

Heteroatom-doped carbon dot (CD)-reinforced flexible, antioxidant, and UV-resistant polymeric thin films have been fabricated by a facile physical compounding strategy associated with the ‘cast and peel’ technique. The prepared CDs were found to be stable in aqueous media because of their zeta potential value (−5.85 mV). There was no significant change in the zeta potential values during 7 days of storage, indicating the long-term stability of CPCDs. CD-reinforced thermoplastic starch (TPS)/κ-carrageenan hybrid films have been developed as antioxidants to improve the shelf-life of agro-products. Besides this, they also qualified for mechanical strength (>40 MPa), transparency (∼77%), nondeteriorative dimensional integrity at a high relative humidity (∼97%), and UV-resistant properties. For assessing the food preservation behavior, the leaching of CDs also has been studied by time-dependent sustained release in different food simulant media, where it showed a gradual alteration of entrapment efficacy in high-polarity gradient environments. The mechanism of CD release has been obtained from the non-Fickian fittings of the initial preplateaued kinetic data. Surprisingly, when these nanodots were arrested inside the polymer matrix, the film also showed excellent water vapor impermeability, low moisture retention, sufficient toughness, and superficial compliance to external flexing and stretching. Also, CD-based TPS/κ-carrageenan films exhibited strong antioxidant activity, as determined by 1,1-diphenyl-2-picrylhydrazyl (>85%) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid assays (>90%). Thus, these hybrid films could be promoted as ideal alternatives for food packaging with their thin, flexible, tough, antioxidant, and moisture-impermeable properties.

No abstract

Fluorescent nanocarbons are well-proficient nanomaterials because of their optical properties and surface engineering. Herein, Apium graveolens-derived carbon dots (ACDs) have been synthesized by a one-step hydrothermal process without using any surplus vigorous chemicals or ligands. ACDs were captured via an in situ gelation reaction to form a semiinterpenetrating polymer network system showing mechanical robustness, fluorescent behavior, and natural adhesivity. ACDs-reinforced hydrogels were tested against robust uniaxial stress, repeated mechanical stretching, thixotropy, low creep, and fast strain recovery, confirming their elastomeric sustainability. Moreover, the room-temperature self-healing behavior was observed for the ACDs-reinforced hydrogels, with a healing efficacy of more than 45%. Water imbibition through hydrogel surfaces was digitally monitored via "breathing" and "accelerated breathing" behaviors. The phytomedicine release from the hydrogels was tuned by the ACDs' microstructure regulatory activity, resulting in better control of the diffusion rate compared to conventional chemical hydrogels. Finally, the phytomedicine-loaded hydrogels were found to be excellent bactericidal materials eradicating more than 85% of Gram-positive and -negative bacteria. The delayed network rupturing, superstretchability, fluorescent self-healing, controlled release, and antibacterial behavior could make this material an excellent alternative to soft biomaterials and soft robotics.