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Oxygen Diffusivity (oxygen + diffusivity)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Oxygen Diffusion in Yttria-Stabilized Zirconia: A New Simulation Model

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004
R. Krishnamurthy
We present a multiscale modeling approach to study oxygen diffusion in cubic yttria-stabilized zirconia. In this approach, we employ density functional theory methods to calculate activation energies for oxygen migration in different cation environments. These are used in a kinetic Monte Carlo framework to calculate long-time oxygen diffusivities. Simulation results show that the oxygen diffusivity attains a maximum value at around 0.1 mole fraction yttria. This variation in the oxygen diffusivity with yttria mole fraction and the calculated values for the diffusivity agree well with experiment. The competing effects of increased oxygen vacancy concentration and increasing activation energy and correlation effects for oxygen diffusion with increasing yttria mole fraction are responsible for the observed dopant content dependence of the oxygen diffusivity. We provide a detailed analysis of cation-dopant-induced correlation effects in support of the above explanation. [source]

Influence of a novel castor-oil-derived additive on the mechanical properties and oxygen diffusivity of polystyrene

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010
Markus Klinger
Abstract Mechanical properties, densities, and oxygen diffusion coefficients have been measured in polystyrene samples (PS) as a function of additive loading. The additive employed is based on castor oil, and is a desirable alternative to phthalates. Tensile strength measurements indicate the additive renders PS stronger at low loadings, i.e. it antiplasticizes the material. In contrast, the additive plasticizes PS at high loadings. Specific volumes and oxygen diffusion coefficients do not show this dual behavior. Rather, one observes a monotonic decrease in density and oxygen diffusivity with an increase in additive loading. This suggests that the larger segmental motions responsible for the macroscopic properties of the polymer are influenced by the additive in a different manner than the local motions and confined changes in free volume that govern the mobility of oxygen. These data indicate that antiplasticization cannot be predicted solely from diffusivity and density measurements and, vice versa, trends in diffusivity cannot be deduced from mechanical measurements alone. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Diffusion and Monod kinetics to determine in vivo human corneal oxygen-consumption rate during soft contact-lens wear

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2009
Mahendra Chhabra
Abstract The rate of oxygen consumption is an important parameter to assess the physiology of the human cornea. Metabolism of oxygen in the cornea is influenced by contact-lens-induced hypoxia, diseases such as diabetes, surgery, and drug treatment. Therefore, estimation of in vivo corneal oxygen-consumption rate is essential for gauging adequate oxygen supply to the cornea. Phosphorescence quenching of a dye coated on the posterior of a soft contact lens provides a powerful technique to measure tear-film oxygen tension (Harvitt and Bonanno, Invest Ophthalmol Vis Sci 1996;37:1026,1036; Bonanno et al., Invest Ophthalmol Vis Sci 2002;43:371,376). Unfortunately, previous work in establishing oxygen-consumption kinetics from transient postlens tear-film oxygen tensions relies on the simplistic assumption of a constant corneal-consumption rate. A more realistic model of corneal metabolism is needed to obtain reliable oxygen-consumption kinetics. Here, physiologically relevant nonlinear Monod kinetics is adopted for describing the local oxygen-consumption rate, thus avoiding aphysical negative oxygen tensions in the cornea. We incorporate Monod kinetics in an unsteady-state reactive-diffusion model for the cornea contact-lens system to determine tear-film oxygen tension as a function of time when changing from closed-eye to open-eye condition. The model was fit to available experimental data of in vivo human postlens tear-film oxygen tension to determine the corneal oxygen-consumption rate. Reliance on corneal oxygen diffusivity and solubility data obtained from rabbits is no longer requisite. Excellent agreement is obtained between the proposed model and experiment. We calculate the spatial-averaged in vivo human maximum corneal oxygen-consumption rate as Q = 1.05 × 10,4 mL/(cm3 s). The calculated Monod constant is Km = 2.2 mmHg. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source]

Oxygen Diffusion in Yttria-Stabilized Zirconia: A New Simulation Model

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004
R. Krishnamurthy
We present a multiscale modeling approach to study oxygen diffusion in cubic yttria-stabilized zirconia. In this approach, we employ density functional theory methods to calculate activation energies for oxygen migration in different cation environments. These are used in a kinetic Monte Carlo framework to calculate long-time oxygen diffusivities. Simulation results show that the oxygen diffusivity attains a maximum value at around 0.1 mole fraction yttria. This variation in the oxygen diffusivity with yttria mole fraction and the calculated values for the diffusivity agree well with experiment. The competing effects of increased oxygen vacancy concentration and increasing activation energy and correlation effects for oxygen diffusion with increasing yttria mole fraction are responsible for the observed dopant content dependence of the oxygen diffusivity. We provide a detailed analysis of cation-dopant-induced correlation effects in support of the above explanation. [source]