scholarly journals Kinetics of Polyelectrolyte Gels

2020 ◽  
Vol 87 (6) ◽  
Author(s):  
Haohui Zhang ◽  
Mohammad Dehghany ◽  
Yuhang Hu
Keyword(s):  
Chemical Potential ◽  
Polymer Networks ◽  
Potential Gradient ◽  
Stimuli Responsive ◽  
Cross Diffusion ◽  
Crosslinked Polymer ◽  
Polyelectrolyte Gels ◽  
Kinetics Of ◽  
Ionizable Groups ◽  
And Diffusion

Abstract Polyelectrolyte (PE) gels consist of crosslinked polymer networks that are grafted with ionizable groups and ionic solution. Many stimuli-responsive gels, including pH-responsive, electric-responsive, and light-responsive ones, are PE gels. Most soft biological components are also PE gels. Due to the increasing scientific interests and applications of PE gels, a comprehensive model is needed. In PE gels, not only solvent, but also ions and other small molecules all diffuse inside, and the flows of the different components are coupled. This phenomenon is called cross-diffusion, meaning the flow of one species is not only driven by its own chemical potential gradient, but also influenced by the flow of other species. In this work, we develop a rigorous nonequilibrium thermodynamics framework to study the coupled deformation and diffusion of the PE gels where cross-diffusion is emphasized and quantified. Specific forms of free energy and kinetic laws are proposed. A finite element method is developed and implemented into abaqus through a user element subroutine. The model is used to simulate the deformation of biological axon and PE gels.The numerical results are compared with experimental data. It is shown that cross-diffusion generates anomalous effects not only on the flux but also on the deformation of PE gels.

scholarly journals Influence mechanism of excipients on drug crystallization: experimental investigation and model analysis and prediction

2022 ◽  
Author(s):  
Qiao Chen ◽  
Jingyun Weng ◽  
Gabriele Sadowski ◽  
Yuanhui Ji
Keyword(s):  
Crystal Growth ◽  
Growth Kinetics ◽  
Surface Reaction ◽  
Chemical Potential ◽  
Potential Gradient ◽  
Reaction Model ◽  
Reaction Rate Constant ◽  
Crystal Growth Kinetics ◽  
Kinetics Of ◽  
And Diffusion

The influence of temperature, stirring speed, and excipients on crystal growth kinetics of mesalazine and allopurinol was investigated through experiment and chemical potential gradient model. The results indicated that the Diffusion-Surface Reaction model (DSR (1,2)) showed good performance in modeling API crystal growth kinetics within the ARDs of 4%. Excipients played a crucial role in inhibiting crystal growth in all the systems. It can not only improve the API solubility, but also reduce the crystal growth rate. By comparing diffusion rate and surface-reaction rate constant within the DSR (1,2) model, it was found that the controlling step of mesalazine crystallization was surface-reaction. Allopurinol crystallization was dominated by both surface-reaction and diffusion. Meanwhile, the crystal growth kinetics of mesalazine and allopurinol were predicted successfully with the ARDs of 2.53% and 4.78%. This work provided a mechanistic understanding of polymer influence on the inhibition of API crystal growth.

Pulse Carburization of Steel – Model of the Process

2014 ◽  
Vol 354 ◽  
pp. 145-152 ◽  
Author(s):  
M. Zajusz ◽  
K. Tkacz-Śmiech ◽  
K. Dychtoń ◽  
Marek Danielewski
Keyword(s):  
Potential Gradient ◽  
Computer Experiments ◽  
Carbon Diffusion ◽  
Diffusion In Solids ◽  
Treatment Conditions ◽  
Carbon Transfer ◽  
Gas Carburizing ◽  
Kinetics Of ◽  
And Diffusion ◽  
Carburizing Process

Gas carburizing is a widely used heat treatment process in which carbon is transferred into steel. The hardening reliability involves an active control of mass transfer during the process and this is why understanding diffusion in solids is so essential to model the process. The currently used models are often based on the simplest, one-dimensional form of the diffusion equation in which diffusivity depends on composition. The objective of this work is to develop a model of carbon diffusion in multicomponent alloy subjected to pulse carburizing. The model is based on the Darken method (bi-velocity method) in which the diffusion velocity depends on the diffusion potential gradient and is independent of the choice of the reference frame while the drift velocity is common for the carbon and steel components. Our model allows predicting the kinetics of carbon transfer at various treatment conditions and is applied to the pulse carburizing process at constant temperature. The process is carried out by repeating consecutively a carburization stage, when the carburizing gas is supplied into a carburizing chamber, and a diffusion stage at vacuum conditions, when the carburizing gas is exhausted and only the diffusion of carbon takes place. The numerical calculations are made for varying carburization and diffusion periods and are confirmed by the experimental results. On the basis of the series of computer experiments some findings that are important in designing the carburizing technology are formulated.

Growth Kinetics of Quantum Size ZnO Particles

1998 ◽  
Vol 536 ◽  
Author(s):  
E. M. Wong ◽  
J. E. Bonevich ◽  
P. C. Searson
Keyword(s):  
Growth Kinetics ◽  
Ostwald Ripening ◽  
Chemical Potential ◽  
Colloidal Suspensions ◽  
Green Emission ◽  
Blue Shift ◽  
Constant Current ◽  
Mass Model ◽  
Zno Particles ◽  
Kinetics Of

AbstractColloidal chemistry techniques were used to synthesize ZnO particles in the nanometer size regime. The particle aging kinetics were determined by monitoring the optical band edge absorption and using the effective mass model to approximate the particle size as a function of time. We show that the growth kinetics of the ZnO particles follow the Lifshitz, Slyozov, Wagner theory for Ostwald ripening. In this model, the higher curvature and hence chemical potential of smaller particles provides a driving force for dissolution. The larger particles continue to grow by diffusion limited transport of species dissolved in solution. Thin films were fabricated by constant current electrophoretic deposition (EPD) of the ZnO quantum particles from these colloidal suspensions. All the films exhibited a blue shift relative to the characteristic green emission associated with bulk ZnO. The optical characteristics of the particles in the colloidal suspensions were found to translate to the films.

scholarly journals Polyelectrolyte Gels: A Unique Class of Soft Materials

Gels ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 102
Author(s):  
Ferenc Horkay
Keyword(s):  
Exchange Process ◽  
Interaction Strength ◽  
Soft Materials ◽  
Industrial Applications ◽  
Future Research ◽  
Swelling Kinetics ◽  
Polyelectrolyte Gels ◽  
Ion Exchange Process ◽  
Counter Ions ◽  
Kinetics Of

The objective of this article is to introduce the readers to the field of polyelectrolyte gels. These materials are common in living systems and have great importance in many biomedical and industrial applications. In the first part of this paper, we briefly review some characteristic properties of polymer gels with an emphasis on the unique features of this type of soft material. Unsolved problems and possible future research directions are highlighted. In the second part, we focus on the typical behavior of polyelectrolyte gels. Many biological materials (e.g., tissues) are charged (mainly anionic) polyelectrolyte gels. Examples are shown to illustrate the effect of counter-ions on the osmotic swelling behavior and the kinetics of the swelling of model polyelectrolyte gels. These systems exhibit a volume transition as the concentration of higher valence counter-ions is gradually increased in the equilibrium bath. A hierarchy is established in the interaction strength between the cations and charged polymer molecules according to the chemical group to which the ions belong. The swelling kinetics of sodium polyacrylate hydrogels is investigated in NaCl solutions and in solutions containing both NaCl and CaCl2. In the presence of higher valence counter-ions, the swelling/shrinking behavior of these gels is governed by the diffusion of free ions in the swollen network, the ion exchange process and the coexistence of swollen and collapsed states.

scholarly journals Biosorption and Diffusion Modeling of Pb(II) by Malt Bagasse

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Klaiani B. Fontana ◽  
Giane Gonçalves Lenzi ◽  
Erica R. L. R. Watanabe ◽  
Ervin Kaminski Lenzi ◽  
Juliana A. M. T. Pietrobelli ◽  
...  
Keyword(s):  
Sorption Process ◽  
Isotherm Models ◽  
Diffusion Modeling ◽  
Biosorption Capacity ◽  
Kinetic And Thermodynamic Parameters ◽  
Pseudo Second Order ◽  
Ph Optimization ◽  
Kinetics Of ◽  
And Diffusion

The removal of Pb(II) from water by biosorption processes onto malt bagasse was investigated and the kinetic and thermodynamic parameters were obtained; additionally a diffusion modeling was proposed. The characterization of malt bagasse was performed by FTIR and SEM/EDS. The experiments were conducted in batch system and an experimental design based response surface methodology was applied for agitation speed and pH optimization. The kinetics of biosorption followed pseudo-second-order model and the temperature of the process affected the biosorption capacity. Isotherm models of Langmuir, Freundlich, and Elovich were applied and the Langmuir model showed better fit and the estimated biosorption capacity was 29.1 mg g−1. The negative values obtained for ΔG° and positive values of ΔH° confirm, respectively, the spontaneous and endothermic nature of the process. The diffusion modeling was performed based on experiments in the absence of agitation to investigate the influence of the biosorbent on the sorption process of Pb(II) ions.

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