An Aqueous Composition for Lubricant-Free, Robust, Slippery, Transparent Coatings on Diverse Substrates.

Transparent, durable coating materials that show excellent liquid repellency, both water and oil, have multiple applications in science and technology. In this perspective, herein, a simple aqueous chemical formulation is developed that provides a transparent slippery coating without any lubricating fluids, on various substrates extended over large areas. The coatings repel liquids having a range of polarity (solvents) as well as viscosity (oils and emulsions) and withstand mechanical strains. Exceptional optical transparency of 99% in the range of 350-900 nm along with high stability even after cyclic temperature, frost, exposure to sunlight, and corrosive liquids like aqua regia treatments, makes this material unique and widens its applicability in different fields. Besides, being a liquid, it can be coated on an array of substrates independent of their underlying topography, by various easily available techniques. Aside from these interesting properties, the coating is demonstrated as a potential solution contributing to the remediation of one of the biggest global issues of tomorrow: affordable drinking water. The coated surface can capture 5 L of water per day per m2 at 27 °C when exposed to an atmosphere of 63% relative humidity.

Organic Solvent-Free Fabrication of Durable and Multifunctional Superhydrophobic Paper from Waterborne Fluorinated Cellulose Nanofiber Building Blocks.

In view of a great demand for paper-based technologies, nonwettable fibrous substrates with excellent durability have drawn much attention in recent years. In this context, the use of cellulose nanofibers (CNFs), the smallest unit of cellulosic substrates (5-20 nm wide and 500 nm to several microns in length), to design waterproof paper can be an economical and smart approach. In this study, an eco-friendly and facile methodology to develop a multifunctional waterproof paper via the fabrication of fluoroalkyl functionalized CNFs in the aqueous medium is presented. This strategy avoids the need for organic solvents, thereby minimizing cost as well as reducing safety and environmental concerns. Besides, it widens the applicability of such materials as nanocellulose-based aqueous coatings on hard and soft substrates including paper, in large areas. Water droplets showed a contact angle of 160° (±2°) over these surfaces and rolled off easily. While native CNFs are extremely hydrophilic and can be dispersed in water easily, these waterborne fluorinated CNFs allow the fabrication of a superhydrophobic film that does not redisperse upon submersion in water. Incorporated chemical functionalities provide excellent durability toward mechanochemical damages of relevance to daily use such as knife scratch, sand abrasion, spillage of organic solvents, etc. Mechanical flexibility of the chemically modified CNF composed paper remains intact despite its enhanced mechanical strength, without additives. Superhydrophobicity induced excellent microbial resistance of the waterproof paper which expands its utility in various paper-based technologies. This includes waterproof electronics, currency, books, etc., where the integrity of the fibers, as demonstrated here, is a much-needed criterion.

Wettability of Complex Fluids and Surfactant Capped Nanoparticle-Induced Quasi-Universal Wetting Behavior.

Even though there are quite large studies on wettability of aqueous surfactants and a few studies on effects of nanoparticles on wettability of colloids, to the best of authors' knowledge, there is no study reported on the combined effect of surfactant and nanoparticles in altering the wettability. The present study, for the first time, reports an extensive experimental and theoretical study on the combined effect of surfactants and nanoparticles on the wettability of complex fluids such as nanocolloids on different substrates, ranging from hydrophilic with a predominantly polar surface energy component (silicon wafer and glass) to near hydrophobic range with a predominantly dispersive component of surface energy (aluminum and copper substrates). Systematically planned experiments are carried out to segregate the contributing effects of surfactants, particles, and combined particle and surfactants in modulating the wettability. The mechanisms and the governing parameters behind the interactions of nanocolloids alone and of surfactant capped nanocolloids with different surfaces are found to be grossly different. The article, for the first time, also analyzes the interplay of the nature of surfaces, surfactant and particle concentrations on contact angle, and contact angle hysteresis (CAH) of particle and surfactant impregnated colloidal suspensions. In the case of nanoparticle suspensions, the contact angle is observed to decrease for the hydrophobic system and increase for the hydrophilic systems considered. On the contrary, the combined particle and surfactant colloidal system shows a quasi-unique wetting behavior of decreasing contact angle with particle concentration on all substrates. Also interestingly, the combined particle surfactant system at all particle concentrations shows a wetting angle much lower than that of the only-surfactant case at the same surfactant concentration. Such counterintuitive observations have been explained based on the near-surface interactivity of the particle, fluid, and surfactant molecules based on effective slip length considerations. The CAH analyses of colloidal suspensions at varying surfactant and particle concentrations reveal in-depth physical insight into contact line pinning, and a unique novel relationship is established between the contact angle and differential energy for distorting the instantaneous contact angle for a pinned sessile droplet. A detailed theoretical analysis of the governing parameters influencing the wettability has been presented invoking the principles of DLVO (Derjaguin-Landau-Verwey-Overbeek), surface energy and interaction parameters influencing at the molecular scale, and the theoretical framework is found to support the experimental observations.

Anomalous subsurface thermal behavior in tissue mimics upon near infrared irradiation mediated photothermal therapy.

Photothermal therapy using (Near Infrared) NIR region of EM spectrum is a fast emerging technology for cancer therapy. Different types of nanoparticles may be used for enhancing the treatment. Though the treatment protocols are developed based on experience driven estimated temperature increase in the tissue, it is not really known what spatiotemporal thermal behavior in the tissue is. In this work, this thermal behavior of tissue models is investigated with and without using nanoparticles. An increased temperature inside tissue compared to surface is observed which is counter intuitive from the present state of knowledge. It is shown from fiber level microstructure that this increased temperature leads to enhanced damage at the deeper parts of biomaterials. Nanoparticles can be utilized to control this temperature increase spatially. A multiple scattering based physical model is proposed to explain this counterintuitive temperature rise inside tissue. The results show promising future for better understanding and standardizing the protocols for photothermal therapy.

Graphene from sugar and its application in water purification.

This paper describes a green method for the synthesis of graphenic material from cane sugar, a common disaccharide. A suitable methodology was introduced to immobilize this material on sand without the need of any binder, resulting in a composite, referred to as graphene sand composite (GSC). Raman spectroscopy confirmed that the material is indeed graphenic in nature, having G and D bands at 1597 and 1338 cm(-1), respectively. It effectively removes contaminants from water. Here, we use rhodamine 6G (R6G) as a model dye and chloropyrifos (CP) as a model pesticide to demonstrate this application. The spectroscopic and microscopic analyses coupled with adsorption experiments revealed that physical adsorption plays a dominant role in the adsorption process. Isotherm data in batch experiments show an adsorption capacity of 55 mg/g for R6G and 48 mg/g for CP, which are superior to that of activated carbon. The adsorbent can be easily regenerated using a suitable eluent. This quick and cost-effective technique for the into a commercial water filter with appropriate engineering.

Numerical simulation of a fully baffled biological reactor: the differential circumferential averaging mixing plane approach.

A modified mixing plane approach for steady state simulation of flow field in fully baffled biological reactor is presented and discussed. Without requiring any experimental input, this approach of dividing the vessel into suitable number of connected and disconnected zones; solving steady state equation separately in each zone and then transferring information between them, provides a computationally less intensive alternative for simulating the flow in the whole vessel. Impeller used is the standard Rushton Turbine positioned at mid-height of the reactor and simulations are carried out using standard k-epsilon turbulence model implemented in CFD code FLUENT. Meshing is done using tetrahedral elements such that mesh size gradually increases from the center to the periphery. Most of the previous simulation works present only a few aspects of the flow field with scant importance to the energy balance in the tank and near tip turbulence. In this work, complete model prediction for velocity field and turbulence parameters (near tip and in the bulk region) are validated by comparison with experimental data. As compared to previous simulation works, the results predicted by this "Differential circumferential averaging mixing plane approach" show a better qualitative and quantitative agreement with the published experimental data. A distribution of energy dissipation in various zones of vessel is presented. Also a qualitative picture of flow field and stagnant zones inside the reactor is presented and discussed. Comparison of flow characteristics for different number of baffles shows that for the present dimension of the vessel, five baffles gives maximum enhanced mixing.