Papers by Keyword: PDMS (Polydimethylsiloxane)

Abstract: Pressure sensitive paint (PSP) has become a useful tool to measure the surface pressure distribution of aerodynamic components replacing conventional pressure taps. For the PSP technique based on the luminescence quenching by oxygen, improvement of its sensitivity is important. In this study, we synthesized palladium octaethylporphyrin (PdOEP) as luminophor and embeded PdOEP in polydimethylsiloxane (PDMS) as polymeric binder to make up of pressure sensitive paints. We used UV/Vis spectrometer and spectrofluorimeter to study the absorption and phosphorescence spectra of PdOEP. In addition, by our self-made experimental setup, the sensitivity of PSPs were examined especially in the range of pressure below 150 Pa. As a result, it is clarified that the PSP using PdOEP as a luminophore and using PDMS as a binder has very high sensitivity to oxygen pressure in low pressure conditions below 150 Pa.

Abstract: Electrostatically actuated microvalves are appealing candidates to build fully integrated microfluidic circuits because of the direct transduction of electrical signals into mechanical responses at low power consumption levels. Practical solutions, however, are still lacking due to their multi-layered architecture and difficulties in incorporating heterogeneous materials. In this paper, we report the design and fabrication process of an electrostatically actuated gas microvalve amenable to large scale integration for gas flow control. The device we designed consists of an upper die, containing a flexible electrode sealed by a thin elastic membrane, and a lower die, containing gas channels of trapezoidal cross-section and fixed electrodes. Each microvalve is defined by one fixed electrode spanning the floor and sidewalls of the trapezoidal gas channel and one corresponding flexible electrode suspended above the channel. In contrast to the conventional parallel-plate arrangement of electrodes, the two electrodes are approximated starting from the edges of the trapezoidal gas channel during the actuation step, which is advantageous for lowering the required actuation voltage. The upper die was fabricated by replica molding in polymeric material, the lower die was fabricated in a glass substrate by conventional microfabrication techniques, and the two dies were subsequently aligned and bonded using an adhesive layer. This reported low cost fabrication process could be implemented in any basic microfabrication facility. When a net pressure up to 1 bar was applied to the gas channel, reasonable flow rate was achieved. We also observed displacement of the flexible membrane when a DC voltage of 200 V was applied to a pair of electrodes. These preliminary results show that this microvalve is a promising candidate for integrated on-chip valving and will allow for building large scale microfluidic circuits with reduced power consumption.

Abstract: This paper proposes a new way to detect the gas-leakage through PDMS. We use PDMS instead of Pyrex #7740 glass to seal the backside V-grooves of silicon pressure sensors. We put the packaged sensor into a pressurized chamber with CO2 at 300 psi. By observing the output voltage of the pressure sensor, the time history for CO2 permeating into the sensor cavity was easily found. In experiments, we use several PDMS membranes with different thickness, from 45 to 2000 μm, to package the pressure sensors and investigate the gas-leakage of PDMS. The gas leaking through PDMS is shown to be governed by diffusion mechanism, and the diffusion coefficients derived from CO2 leaking history is 2.2×10-9 m2/sec, matched with the previous work.

Abstract: A liquid tunable diffractive/refractive hybrid lens which combines the use of high precision diamond turning and soft lithography is developed in this work. This diffractive/refractive hybrid lens comprises a Fresnel lens and a tunable refractive lens automatically aligned during the fabrication process. Multiple PDMS hybrid lens devices can be fabricated from the diamond-turned master mould and AFM results show that the surface quality of the PDMS lenses meets the requirements for optical purposes. The hybrid lens is tested with a green laser (λ = 532nm) and experimental results demonstrate a tunability of more than 20mm.

Abstract: Microlenses are important components in optical data interconnects and MEMS-based microscopy imaging. Several microfabrication processes have been developed for the production of microlens arrays. However, assembly of microlens arrays is usually required. In this paper, we demonstrate the application of PDMS membrane patterning based on parylene C lift-off to the construction of PDMS microlens arrays on a glass substrate without an assembly step.

Abstract: This paper focuses on the preparation of siloxane-polyurethane hybrid materials using a sol-gel method. The global aim of the project is to tailor mechanical properties, degradability rate, bioactivity and biocompatibility to design scaffolds for musculoskeletal applications. A series of seven hybrid materials were synthesized with varying the proportion of polydimethylsiloxane (PDMS), and Polyurethane (PU). The organic part ratios (by weight) employed were (% PDMS:% PU) 30:0, 35:5, 20:10, 15:15, 10:20, 5:25, and 0:30. The organic part was reacted with constant 70 % TEOS to obtain the hybrid materials. A sol-gel process was selected for the synthesis of the hybrids. The characterization of materials was carried out by the fourier-infrared spectroscopy (FT-IR), x-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electronic microscopy (SEM) and proton nuclear magnetic resonance (1H-NMR) techniques in order to analyze the structure, microstructure and chemical composition of the hybrid materials. Gelification time depends on the proportion of PU used. When no PU is employed, the gel time is 8 hours but it rises up to 18 days for 30 % of polyurethane. Materials range from opaque to translucent but with a greater fragility for greater amounts of polyurethane. No differences in the bonding of materials could be appreciated.

Abstract: One of the key factors to obtain large displacements and high efficiency with dielectric electroactive polymer (DEAPs) actuators is to have compliant electrodes. Attempts to scale DEAPs down to the mm or micrometer range have encountered major difficulties, mostly due to the challenge of micropatterning sufficiently compliant electrodes. Simply evaporating or sputtering thin metallic films on elastomer membranes produces DEAPs whose stiffness is dominated by the metallic film. Low energy metal ion implantation for fabricating compliant electrodes in DEAPs presents several advantages: a) it is clean to work with, b) it does not add thick passive layers, and c) it can be easily patterned. We use this technology to fabricate DEAPs micro-actuators whose relative displacement is the same as for macro-scale DEAPs. With transmission electron microscope (TEM) we observed the formation of metallic clusters within the elastomer (PDMS) matrix, forming a nano-composite. We focus our studies on relating the properties of this nano-composite to the implantation parameters. We identified the optimal implantation parameters for which an implanted electrode presents an exceptional combination of high electrical conductivity and low compliance.

Abstract: This study describes the results on the fabrication, testing and analysis of curved micro nozzle/diffuser. First, we use different polymers, SU-8 and polydimethylsiloxane (PDMS) for the fabrication of curved micro nozzle/diffuser. By using the low-temperature bonding technique, we can combine the structure with the glass and accomplish the component. In order to understand the investigation and analysis of fluid dynamics characteristics, we measure the pressure and flow of curved micro nozzle/diffuser and the commercially available software CFD was adopted for analyzing the performance of straight and curved micro nozzle/ diffuser. If we have a given Reynolds number, the experimental data shows the pressure loss of the diffuser is lower than that of the nozzle due to the change of momentum. Furthermore, the results also indicate that the pressure loss coefficient of both curved nozzle and diffuser decrease with the Reynolds number. All the experimental and numerical data Eventually are compared with each other. The numerical data was found good agreement with previous analytic solution and experimental results. In sum, the theoretical analysis and design basis from this study can be formulated as the reference in the fabrication of micro nozzle/diffuser.

Abstract: In this study, a high performance peristaltic micropump has been developed and investigated. The micropump has three cylinder chambers which are connected through microchannels and two normally closing active membrane valves at inlet/outlet for high pumping pressure performance. A circular shaped miniature LIPCA has been developed and manufactured for actuating diaphragms. In this LIPCA, a 0.1mm thickness PZT ceramic is used as an active layer. As a result, the actuator has shown to produce large out-of-plane deflection and consumed low power. During the design process, a coupled field analysis was conducted to predict the actuating behavior of a diaphragm. The actuator behavior was investigated both theoretically and experimentally. In addition, MEMS technique was used to fabricate the peristaltic micropump. Judging from experimental flow rate and pumping pressure results, the present peristaltic micropump has higher performance than the same kind of micropump developed elsewhere.