Gas permeation in PDMS monitored by on-site pressure sensors

[[abstract]]This paper proposes a new methodology to detect the gas-leakage and the corresponding diffusion coefficient of PDMS. The authors use PDMS instead of Pyrex #7740 glass to seal the backside V-grooves of pressure sensor chips. The packaged sensor is put into a pressure testing machine and pressurized with CO2 at 300 psi. By observing the output voltage, the time history for CO2 permeating into cavity of the sensor was easily to be found. In this paper, the authors use several PDMS membranes with different thickness, from 45 to 2000 弮m, to package the sensors and investigate the gas-leakage of PDMS. The gas leaking through PDMS is shown to be governed by the diffusion mechanism, and the diffusion coefficients derived from CO2 leaking history of PDMS chip frames is 2.2?10-9 m /s, matched with the previous work. The thickness effect of PDMS on the diffusion mechanism is also addressed.[[incitationindex]]EI[[conferencetype]]國際[[conferencedate]]20100120~20100123[[iscallforpapers]]Y[[conferencelocation]]Xiamen, Chin

Predictive simulation of non-steady-state transport of gases through rubbery polymer membranes

A multiscale, physically-based, reaction-diffusion kinetics model is developed for non-steady-state transport of simple gases through a rubbery polymer. Experimental data from the literature, new measurements of non-steady-state permeation and a molecular dynamics simulation of a gas-polymer sticking probability for a typical system are used to construct and validate the model framework. Using no adjustable parameters, the model successfully reproduces time-dependent experimental data for two distinct systems: (1) O_2 quenching of a phosphorescent dye embedded in poly(n-butyl(amino) thionylphosphazene), and (2) O_2, N_2, CH_4 and CO_2 transport through poly(dimethyl siloxane). The calculations show that in the pre-steady-state regime, permeation is only correctly described if the sorbed gas concentration in the polymer is dynamically determined by the rise in pressure. The framework is used to predict selectivity targets for two applications involving rubbery membranes: CO_2 capture from air and blocking of methane cross-over in an aged solar fuels device

Development of gas sensors for binary mixtures and solvent-free sample preparation techniques based on polymeric membranes

Tese de doutoramento. Engenharia Química. 2005. Faculdade de Engenharia. Universidade do Port

Gas Pressure Measurement Device and Medical Vacuum Design

Two methods are used in a digital pressure meter available in the market, namely positive pressure, and negative pressure. The positive one is used to measure the air pressure on a sphygmomanometer and medical gas pressure at an outlet in the treatment room so that operators can easily check medical gas pressure for the safety of the patient, or they can routinely check to find out how much pressure of the medical gas. Based on the background, the research aimed to design a digital pressure meter equipped with a medical gas measurement mode so that the device can be used to calibrate the sphygmomanometer, suction pump, and measure the medical gas pressure available at the medical gas outlet in each treatment room

Oxygen Measurement During Cell Culture: From Multiwell Plates to Microfluidic Devices

Oxygen is an important regulator of normal cell behavior. Proper supply of oxygen is required to maintain ATP production, while perturbation of oxygen supply alters cell behavior and leads to tissue damage and cell death. In vivo, cells are exposed to a mean partial pressure of oxygen between 0.03 to 0.09 atm that is tissue specific. In contrast, conventional cell cultures are routinely performed at an atmospheric oxygen level of 0.21 atm. The disparity between in vivo and in vitro oxygen levels have been shown to affect cell viability, growth and differentiation. Continuous measurements and control of oxygen levels are thus critical to maintaining proper cell behavior. Current methods of oxygen measurement are invasive, difficult to integrate with microscopy and lack imaging capabilities. To improve the current state of measurements, we have developed a new non-invasive oxygen sensor for in vitro cell culture. The sensor was prepared by incorporating a porphyrin dye, Pt(II) meso-Tetra(pentafluoro-phenyl)porphine (PtTFPP), into gas permeable poly(dimethylsiloxane) (PDMS) thin films. The response of the sensor to oxygen followed the linear Stern-Volmer equation and demonstrated an order of magnitude higher sensitivity compared to other sensors (KSV = 548 ± 71 atm-1). A multilayer design created by sandwiching the PtTFPP-PDMS with a thin film of Teflon AF followed by a second layer of PDMS effectively mitigated against cytotoxicity effects and provided a suitable substrate for cell attachment. To demonstrate the utility of the sensor, oxygen measurements were made continuously with NIH 3T3 mouse fibroblast cells. The oxygen levels were found to decrease as a result of oxygen consumption by the cells. Using Fick's law, the data was analyzed and a per-cell oxygen consumption rate for the 3T3 fibroblasts was calculated. In addition, cells were clearly visualized on the sensor demonstrating the ability to integrate with phase-contrast and fluorescence microscopy. Next, human hepatocellular carcinoma HepG2 were cultured on the oxygen sensor and continuous oxygen measurements showed a drastic decrease in oxygen level such that the cells were exposed to hypoxic conditions within 24 h. The per-cell oxygen consumption rate for HepG2 was determined to be 30 times higher than the 3T3 fibroblasts, confirming the high metabolic nature of these cells. At high densities, oxygen flux measurements showed an asymptotic behavior reaching the theoretical maximum of the culture condition. When the oxygen diffusion barrier was reduced, the oxygen flux increased, demonstrating insufficient oxygenation for HepG2 at these densities. In routine culture, HepG2 adhere to their neighboring cells which results in formation of cell clusters. Oxygen measurement confirmed the presence of oxygen gradient across the cell clusters with the lowest oxygen levels observed in the middle. Finally, we successfully integrated the oxygen sensor into microfluidic systems. The sensor provided real-time non-invasive measurements of oxygen levels on-chip. To regulate the oxygen levels in the device, water with different dissolved oxygen concentrations was used instead of gas. This method successfully mitigated the problems of pervaporation associated with previous devices. Physiologically relevant oxygen levels and oxygen gradients were easily generated on the device and the results showed excellent agreement with numerical simulations

Investigation of mass transport processes in a microstructured membrane reactor for the direct synthesis of hydrogen peroxide

Microstructured membrane reactors present a promising approach to master the productivity and safety challenges during the direct synthesis of hydrogen peroxide. However, various mass transport processes occur in this complex system. In order to gain a deeper understanding of these processes, the saturation and desaturation behaviour of the liquid reaction medium with the gaseous reactants is investigated experimentally to examine possible cross-contamination. Moreover, the employed PDMS membrane’s permeances to hydrogen and oxygen are researched at different pressures, by using a variable-pressure/constant-volume setup for the behaviour at ambient pressure and a constant-pressure/variable-volume setup for the behaviour at elevated pressures. A mathematical model in MATLAB is applied to simulate the results. It is shown that a certain desaturation of the gasses through the membrane occurs, and the results are underlined by the modelled ones using a solution-diffusion model in MATLAB. Thus a constant flushing of the gas channels of the reactor is required for safety reasons. Moreover, the measured permeance values indicate that the species transport is mainly limited by the diffusion in the liquid phase and not the membrane resistance

Predictive simulation of non-steady-state transport of gases through rubbery polymer membranes

A multiscale, physically-based, reaction-diffusion kinetics model is developed for non-steady-state transport of simple gases through a rubbery polymer. Experimental data from the literature, new measurements of non-steady-state permeation and a molecular dynamics simulation of a gas-polymer sticking probability for a typical system are used to construct and validate the model framework. Using no adjustable parameters, the model successfully reproduces time-dependent experimental data for two distinct systems: (1) O_2 quenching of a phosphorescent dye embedded in poly(n-butyl(amino) thionylphosphazene), and (2) O_2, N_2, CH_4 and CO_2 transport through poly(dimethyl siloxane). The calculations show that in the pre-steady-state regime, permeation is only correctly described if the sorbed gas concentration in the polymer is dynamically determined by the rise in pressure. The framework is used to predict selectivity targets for two applications involving rubbery membranes: CO_2 capture from air and blocking of methane cross-over in an aged solar fuels device