Renormalized Flory-Huggins lattice model of physicochemical kinetics and dynamic complexity in self-healing double-network hydrogel

Self-healing capability offers great designability on mechanical properties of double-network (DN) hydrogel. However, the thermodynamics understanding behind such physicochemical transitions and self-healing behaviors are yet to be explored properly. This study describes a renormalized Flory-Huggins lattice model for DN hydrogels, of which the physicochemical kinetics and dynamic complexity are resulted from stress-induced bond scission and macromolecule rearrangement. Based on the Flory-Huggins lattice model and Gaussian distribution theory, an extended free-energy model was formulated by the steric repulsive free-energy function. Afterwards, the function was used to identify the working mechanisms and thermodynamics in self-healing DN hydrogels with ultra-high mechanical strength. Finally, the effectiveness of model was demonstrated by applying it to predict the mechanical behaviors of DN hydrogels, where the analytical results showed good agreements with experiment data.     

Three-Dimensional Numerical Investigation of Steady State and Physiologically Realistic Pulsatile Flow through the Left Coronary Curved Artery with Stenosis

Theoretical Foundations of Chemical Engineering - Simulation of the behavior of stenosis arteries has received much attention as a research topic. Fluid mechanics of blood flow in the left coronary...     

Development of CO2-Philic Blended Membranes Using PIM–PI and PIM–PEG/PPG

Blending is a simple method through which one can effectively tailor new polymers exhibiting the properties of their parent ones. Because the original properties of polymers are maintained after blending, various studies have used these films as gas separation membranes. In this study, a new CO₂ separation membrane is developed by physically mixing a polymer of intrinsic microporosity (PIM) with high gas permeability, polyimide (PIM-PI), as the hard segment and CO₂-philic PIM-poly(ethylene glycol)/poly(propylene glycol), or PIM-PEG/PPG, as the soft segment. Prepared by adding 5 mol.% of PIM-PEG/PPG to PIM-PI, the blended membrane PPB-5, with a tensile strength of 54 MPa and 35.5% elongation at break, shows better mechanical properties than commercial high-performance polymer membranes developed for gas separation, PEG-based blended membranes, and corresponding copolymer membranes with similar compositions developed in a previous study. In addition, it shows high CO₂ permeability (1552.6 Barrer) and CO₂/N₂ selectivity (29.3) due to the well-developed microphase separation characteristics originating from the optimal two-component composition, and the gas separation performance is close to the Robeson (2008) upper bound.     

Apparent kinetics of nonisothermal high temperature oxidative degradation of ethylene homopolymers: effects of residual catalyst surface chemistry and structure

The effects of two supported residual catalysts—one Ziegler-Natta and another metallocene—on the nonisothermal thermooxidative degradation of the resulting ethylene homopolymers were investigated using TGA experiments and kinetic modeling. The rigorous constitutive kinetic model (developed in this study), unlike the analytical Horowitz and Metzger model, fitted very well to the entire TGA curve, without distribution of activation energy E _a , for n (overall degradation order)?=?1 for both polymers. Neither n nor E _a varied as a function of fractional weight loss of the polymer. Hence, the proposed unified molecular level concept of surface chemistry and structure of the residual catalysts held all through the degradation process. The above feature of n and E _a also indicates the suitability of the model formulation and the effectiveness of the parameter-estimation algorithm. Random polymer chain scission, with the cleavage of the ?C?C? and the ?O?O? (hydroperoxide) bonds, prevailed. The types of residual catalyst surface chemistry and structure varied the bond cleavage process. The metallocene Zr residual catalyst caused more thermooxidative degradation in MetCat?HomoPE than what the Ti one did in Z-N?HomoPE. The rigorous constitutive model-predicted apparent kinetic energy E _a , and frequency factor Z also support this finding. The proposed degradation mechanism suggests that the Zr residual catalyst more (i) decreased the activation energy required to decompose the ?C?C? and the ?O?O? bonds, and (ii) eliminated β-hydrogen (by the carbonyl functionalities) from the polymer chains. These findings were attributed to the differences in surface chemistry and structure of the residual catalysts. Therefore, the current study presents a rigorous constitutive kinetic model that duly illustrates the influence of the characteristic surface chemistry and structure of the residual catalysts on the high temperature oxidative degradation of polyethylenes.     

Synthesis and characterization of tetra-imidazolium hydroxides poly(fluorenylene ether sulfone) anion exchange membranes

Anion exchange membranes of poly(fluorenylene ether sulfone) containing imidazolium hydroxide-functionalized fluorenyl groups were synthesized by sequential polycondensation, chloromethylation, substitution with imidazolium and ion exchange. They showed elevated molecular weight, high solubility in polar aprotic solvents and strong chemically and thermally stability in comparison to alkyl quaternary ammonium-functionalized polymers. Different levels of substitution and ion exchange were tested; the resulting ionomer membranes showed high ion exchange capacities (IECs) of up to 1.96 mmol g^?1. The imidazolium-functionalized copolymer membranes showed lower water affinity and excellent chemical stability in alkaline conditions. They exhibited hydroxide conductivity above 10^?2 S cm^?1 at room temperature and outstanding chemical stability for up to 7 days without significant losses of ion conductivity.     

Minimization of surface friction effect on scratch‐induced deformation in polymers

Surface friction plays an important role in influencing the stress field development during scratch process, thus, scratch‐induced deformation mechanisms. In this study, three‐dimensional finite element method (FEM) parametric study was performed along with experimental validation to investigate the effect of surface friction on scratch‐induced deformation and its correlation with the constitutive behavior of polymers. As scratch depth and shoulder height are the key parameters for causing scratch visibility, the focus is to investigate the effect of surface friction on these two scratch‐induced deformation features and how the surface friction effect can be altered by varying the constitutive parameters. The FEM findings and experimental observations indicate that onset of groove formation during the scratch process is strongly influenced by yield stress and coefficient of surface friction. Also, the relative frictional effect on scratch‐induced deformation becomes minimal if the post‐yielding strain hardening slope of the polymer is high. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Crystallization kinetics of PE‐b‐isotactic PMMA diblock copolymer synthesized using SiMe2(Ind)2ZrMe2 and MAO cocatalyst

Polyethylene‐b‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer has important interfacial applications. Hence, a PE‐b‐isotactic PMMA diblock copolymer was synthesized using SiMe₂(Ind)₂ZrMe₂ and MAO cocatalyst. The polymerization mechanism and the origin of PMMA isotacticity were duly explained. An appropriate nonisothermal Avrami‐Erofeev crystallization model was developed to compare the crystallization kinetics of the above copolymer with that of a PE homopolymer. For both polymers, the model well matched the entire differential scanning calorimeter crystallinity profile, notably for a single Avrami‐Erofeev index, and predicted cylindrical crystal growth. This model particularly overcomes the limitations of the published nonisothermal crystallization models, and provides interesting insight into PE crystallization. The PMMA block significantly decreased the heats of crystallization and fusion, % crystallinity, and the relative crystallization function; increased the nonisothermal crystallization rate constant; and introduced minimal dilution effect whereas the PE block formed a continuous or percolated phase. This study correlates catalyst structure, copolymer block tacticity, and PE nonisothermal crystallization and melting behavior. © 2012 American Institute of Chemical Engineers AIChE J, 59: 200–214, 2013     

RADIATION EFFECT ON FREE CONVECTION LAMINAR FLOW FROM AN ISOTHERMAL SPHERE

Natural convection laminar flow from an isothermal sphere immersed in a viscous incompressible optically dense fluid in the presence of radiation effects has been investigated. The governing boundary layer equations are transformed into a non dimensional form and the resulting nonlinear systems of partial differential equations are reduced to local non-similarity boundary layer equations, which are solved numerically by two distinct, efficient methods, namely, (i) implicit finite difference method together with the Keller box scheme and (ii) local non-similarity method. Numerical results of the velocity and temperature profiles of the fluid are presented. The results of the shearing stress and the heat transfer rate in terms of skin-friction coefficient and Nusselt number respectively are also presented for a wide range of the radiation-conduction parameter or Planck number R _d (=0.0, 1.0, 2.0, 3.0), the surface heating parameter θ _w (=1.1, 1.2, 1.4), and Prandtl number Pr (=7.0, 10.0, 15.0, 20.0).     

Fertilizer use in Asian agriculture: implications for sustaining food security and the environment

This paper studies the role of chemical fertilizers in sustaining the growth in foodgrain production in the major rice growing countries in Asia. The trends in fertilizer consumption are reviewed, the yield response and change in policies in the fertilizer sector and their impact on fertilizer prices are assessed and factors affecting fertilizer demand are analyzed. The implications of sustaining food security and the environment on fertilizer use are critically examined, future projections on food and fertilizer demand are made and areas of research needed to achieve the targets are suggested.