A novel kinetic approach to crystallization mechanisms in polymers

Kinetics of polymer crystallization is capable of modeling the polymer crystallization processes by revealing their mechanisms. Although complexities of polymer crystallization processes are familiar, a generalized approach for their kinetic modeling has not yet been suggested. This paper presents a concise review of the pre-existing kinetic approaches to polymer crystallization, including their pros and cons, putting a special emphasis on the necessity of approaches to polymer crystallization. A systematic and advanced approach comprising an innovative kinetic framework to model polymer crystallization processes is put forward using Hoffman-Lauritzen theory. Kinetic functions are developed for predicting the crystallization mechanisms of simple as well as complicated polymer crystallization processes. The suggested kinetic approach is experimentally justified by its effective applications to non-isothermal glass and melt crystallization of poly(ethylene 2,5-furandicarboxylate). An account of the soundness of the proposed kinetic approach and its prospective applications are also discussed.     

Development of optimized triaxially electrospun titania nanofiber-in-nanotube core-shell structure

One dimensional (1D) nanostructures and its derivatives can be manipulated to serve special functions like hollow structure, and higher surface area. 1D TiO₂ nanotube-in-nanofibers (NF@NT) are developed through triaxial electrospinning followed by a calcination process. A blended solution of polyvinyl pyrrolidone and tetra-butyl titanate is used in outer and inner layers of nanofibers, respectively, while paraffin oil is used in the middle layer. The optimized triaxial nanofibers of 669.4 ± 52.43 nm are developed at 7.5 w/w% concentration, 28 kV applied voltage, and 24 cm spinning distance. TiO₂ NF@NT structure is obtained through calcination of optimized triaxial nanofibers at 550°C. Subsequently, the morphology of TiO₂ NF@NT and its uniform diameter distribution is confirmed through scanning electron microscopy. Fourier-transform infrared spectroscopy results indicates the formation of TiO₂ NF@NT. X-Rays diffraction pattern peaks also reveals the presence of both anatase and rutile crystalline phases. The presence of only titanium (Ti) and oxygen (O) elements in the TiO₂ NF@NT is confirmed through energy dispersive X-ray spectroscopy. Brunauer–Emmett–Teller analysis indicates that TiO₂ NF@NT has a higher specific surface area of ~141.68 m²/g compared with the solid TiO₂ nanofiber (~75.31 m²/g). This study can be adopted to develop TiO₂ NF@NT for wide range of application.     

Performance optimization of microfluidic paper fuel-cell with varying cellulose fiber papers as absorbent pad

Miniaturization of devices, combined with other features such as portability, proneness to automation, rapid performance, amenability to integration, multiplexing, and cost-effectiveness, is rapidly increasing for various sensing and energy harvesting applications. One such emerging area is the development of microfluidic fuel cell on cellulose papers, which has enormous scope to optimize its performance. This is primarily because such devices eliminate the need for membranes as well as external pumps since they have built-in colaminar flow embedded capillaries. Such peripherals are usually used in conventional microfluidic fuel cells, which are fabricated using methods like photolithography, PDMS lithography, and 3D printing. This paper presents investigations on microfluidic paper–based fuel cells (MPFCs) with different cellulose absorbent pads for their performance optimization. Herein, the MPFC utilizes formic acid as fuel, oxygen from quiescent air as oxidant, and sulfuric acid as electrolyte for conducting ionic exchange under colaminar flow. The electrodes are realized through simple pencil strokes depositing a thin layer of graphite. The porous graphite electrodes act as diffusion agents breathing oxygen directly from the atmospheric air. Such an MPFC configuration, costing less than US $1, was optimized to achieve maximum energy density by examining various combinations of absorbent pads with different grades of cellulose papers. It is seen that the maximum open circuit potential is 0.46 V, while the maximum current and power densities are 1505.66 μAcm⁻² and 173.97 μWcm⁻², respectively, with a grade 6 absorbent pad. Such performance can be further enhanced by investigating MPFCs with various graphite pencils with a diverse number of strokes at different concentration levels.     

Thermo-oxidative decomposition of multi-walled carbon nanotubes: Kinetics and thermodynamics

Abstract

Multi-walled carbon nanotubes (MWCNTs) are familiar well owing to their capability of finding wide-reaching applications based on their fascinating properties. Kinetics of thermally activated processes in MWCNTs can help in understanding and controlling those processes which might eventually lead to develop materials with optimized efficiencies. Even though, inadequate information on the kinetics of thermal decomposition of WMCNTs has been reported in the literature, and its thermodynamics is yet to be addressed. In this regard, the present study deals with a detailed kinetic investigation on the thermo-oxidative decomposition of MWCNTs by employing advanced kinetic approaches. Kinetic analysis of MWCNTs decomposition reveals that although the kinetic triplets remain comparable, reaction model under isothermal condition is not the same as under non-isothermal conditions. It alters from contracting cylinder (non-isothermal) to random nucleation followed by isotropic growth of particles (isothermal). Thermodynamics of MWCNTs thermal decomposition points out that the process is non-spontaneous with enhanced endothermicity. In addition, the structure of activated complex is found to be relatively more organized in comparison with the reactant. An account of the interpretations of the obtained kinetic and thermodynamic parameters is also given and discussed in this study.     

An investigation of the high-avidity antibody response to glycoprotein 120 of human immunodeficiency virus type 1

The avidity of antibodies for antigens can be measured by determining what remains bound after exposing the antibody-antigen complex to a chaotropic agent such as urea. This method has been gaining popularity for assessing the immune response to the human immunodeficiency virus type 1 (HIV-1) surface glycoprotein gp120 (or its counterpart from simian immunodeficiency virus), during natural infection or after subunit vaccination. High-avidity antibodies have been considered to be a possible correlate of protection. We have examined the avidity assay to determine what it, in fact, measures. First, we studied the development of the anti-gp120 response in seroconverting individuals. Urea elution reduced the polyclonal anti-gp120 titers by 3- to 10-fold. After allowing for the consequent reduction in assay sensitivity, there was no obvious change in the rate of development of the high-avidity and unfractionated antibody responses. Furthermore, in the one individual who developed a strong autologous, virus-neutralizing response, the appearance of neutralizing antibodies and high-avidity antibodies did not coincide. Antibodies to the V3 loop, when present, comprised a major fraction of the polyclonal response that survives urea elution. We next examined the effect of urea elution on the binding to gp120 of a panel of monoclonal antibodies (MAbs). Urea treatment preferentially eluted MAbs to discontinuous rather than continuous epitopes, independent of their affinities. Furthermore, these patterns of epitope stability were unaltered by the presence of polyclonal anti-gp120 antibodies. As most broadly neutralizing anti-gp120 antibodies recognize discontinuous epitopes, this skewing effect must be taken into account when interpreting studies using polyclonal sera.     

Influence of Amphiphilic Plasticizer on Properties of Thermoplastic Starch Films

Thermoplastic starch powders and films were produced by using different combinations of hydrophilic (malic acid and water) and amphiphilic (isoleucine and butyric acid) plasticizers. Spray drying was used to produce thermoplastic starch powder followed by compression molding for the development of films. In all plasticized formulations, the rate of retrogradation was inhibited until the seventh day. The crystallinity and moisture sensitivity of the freshly prepared films were dependent on amphiphilic plasticizer quantity in formulation. Fourier transform infrared spectroscopy and thermogravimetric analysis showed an effective interaction of starch with isoleucine. Isoleucine formulated films showed the highest tensile strength, whereas malic acid-rich films showed better strain values.     

Analysis of multiscale mortar mixed approximation of nonlinear elliptic equations

A multiscale mortar mixed finite element method is established to approximate non-linear second order elliptic equations. The method is based on non-overlapping domain decomposition and mortar finite element methods. The existence and uniqueness of the approximation are demonstrated, and a priori $L^2$-error estimates for the velocity and pressure are derived. An error bound for mortar pressure is proved. Convergence estimates of the mortar pressure are based on a linear interface formulation having the discrete-pressure dependent coefficient. Optimal order convergence is achieved on the fine scale by a proper choice of mortar space and polynomial degree of approximation. The quadratic convergence of the Newton–Raphson method is proved for the nonlinear algebraic system arising from the mortar mixed formulation of the problem. Numerical experiments are performed to support theoretic results.     

An enhanced anonymous identity‐based key agreement protocol for smart grid advanced metering infrastructure

Sprouting populace mass within the urban areas furnishes critical challenges of providing uninterruptible community services to fulfill the primitive needs of inhabitants in smart cities. Smart cities facilitate and uplift the living standards of inhabitants through various smart systems or infrastructures, and smart grid is one of them. Secure transmission is a key requirement in the advanced metering infrastructure (AMI) of most smart grids, and key establishment cryptographic protocols can be used to achieve such a requirement. Designing efficient and secure key establishment protocols for AMI remains challenging. For example, in this paper, we reveal several weaknesses in the identity‐based key establishment protocol of Mohammadali et al (published in IEEE Trans Smart Grid, 2017), which is based on elliptic curves. We then improve their protocol and prove its security in the random oracle model. We also demonstrate that the improved protocol achieves both anonymity and untraceability, before presenting a comparative summary of the security and computational overheads of the proposed protocol and several other existing protocols.     

A lightweight authentication and key agreement protocol preserving user anonymity

Nowadays with widespread employment of the Internet, servers provide various services for legal users. The vital issue in client/server connections is authentication protocols that make the communication channel safe and secure against famous attacks. Recently, Kumari et al. and Chaudhry et al. proposed two authentication and key agreement protocols and illustrated that their proposed protocols are secure against various security attacks. However, in this paper we demonstrate that both protocols are vulnerable to off-line password guessing attacks. Moreover, we show that Kumari et al.’s protocol does not provide the property of user anonymity. In order to overcome these weaknesses, we propose a lightweight authentication and key agreement protocol. The correctness of the proposed protocol is proved using BAN logic. Security analysis demonstrates that the proposed protocol resists various security attacks and provides user anonymity. Furthermore, performance analysis confirms that the computation cost of the proposed protocol is acceptable.