جستجوی مقالات مرتبط با کلیدواژه « ضریب نفوذ » در نشریات گروه « شیمی »

In this paper, the molecular diffusion coefficient is calculated by obtaining experimental data of gas diffusion in stagnant solvent and using mathematical models based on Fick's second law. The purpose of this paper is to calculate the ethylene diffusion coefficients in n-methyl pyrrolidone (NMP) solvent at initial pressures of 600, 800 and 1100 kPa and temperatures of 278.1, 298.1 and 328.1 K using two available models. Although similar to previous researches, the experimental results from both models showed that the diffusion coefficients increase with increasing temperature, the type of dependence on temperature as DAB = A.Tn has been different from the researchers' point of view. To examine, the experimental results were compared with the predictions of Wilke-Chang model, in which n = 5.65, and Diaz model, in which n =8.5. The dependence of the molecular diffusion coefficient on temperature in the two experimental models is different, and the prediction of the Diaz model had better agreement to the experimental data of this study.

In recent years, the development of nanoparticles in the field of drug release has received much attention. This research aims to develop new methods for the physical modification of Fe3O4 superparamagnetic nanoparticles with polymers through physical retention. In this study, after synthesizing the biodegradable polycaprolactone-polyethylene glycol magnetic copolymer, the anticancer drugs doxorubicin and Chrysin in these polymers were encapsulated by dual emulsion (w / o / w). The effect of temperature and pH on drug release was investigated. After performing kinetic studies, the diffusion coefficient of drug release was also studied. The drug distribution was considered uniform and the system was assumed to be in Cartesian coordinates. The results showed that the diffusion coefficient of drug release followed Fick's law. At first, due to the high concentration difference of drugs in the early times, the diffusion coefficient was higher, but then with time and with decreasing the concentration difference, the diffusion coefficient decreased and remained constant.

Because of the importance of diffusion coefficient and its high application in mass transfer calculations, many correlations have been proposed in order to predict it in various systems. In this paper, one of the most simple, general and applicable correlation to estimate diffusivity in liquid systems, Siddiqi-Lucas correlation, selected and its accuracy and capability in calculation of diffusivity of various liquid systems have been investigated. Results indicate that average absolute errors of this correlation in diffusivity prediction are 25.1% and 20.8% in hydrocarbon mixtures and aqueous solutions, respectively. Also, the calculations show that average absolute error for alcoholic solutions is 44.8% and more than 30% of calculated diffusion coefficients in these systems have an error of more than 60% while the in non-alcohols solutions average error is 18.9% and less than 2% of results have an error of more than 60%. Because of the weakness of this correlation in the prediction of diffusion coefficients in systems including alcoholic solvents, and the results of previous studies, literatures which depict higher prediction errors using most relations for alcoholic solutions with respect to non-alcoholic solutions, and since, there is not a particular relation for these systems, a new correlation in the form of Siddiqi-Lucas relation proposed to calculate diffusivity in alcoholic systems. Using this relation, the average error decreased from 44.8% to 28.5% and the results percentage with error more than 70% decreased from 24 to zero. For more verification, the results of proposed relation compared with Wilk-Chang results, Tyn-Calus and Hayduk-Minhas correlations, and the results indicated a good improvement in calculated coefficients and the higher accuracy of the proposed relation which makes its usage reasonable and necessary.