Using Micromachined Molds, Partial-curing PDMS Bonding Technique, and Multiple Casting to Create Hybrid Microfluidic Chip for Microlens Array

In a previous study, we presented a novel manufacturing process for the creation of 6 × 6 and 8 × 8 microlens arrays (MLAs) comprising lenses with diameters of 1000 μm, 500 μm, and 200 μm within an area that covers 10 mm × 10 mm. In the current study, we revised the manufacturing process to allow for the fabrication of MLAs of far higher density (15 × 15 and 29 × 29 within the same area). In this paper, we detail the revised manufacturing scheme, including the micromachining of molds, the partial-curing polydimethylsiloxane (PDMS) bonding used to fuse the glass substrate and PDMS, and the multi-step casting process. The primary challenges that are involved in creating MLAs of this density were ensuring uniform membrane thickness and preventing leakage between the PDMS and glass substrate. The experiment results demonstrated that the revised fabrication process is capable of producing high density arrays: Design I produced 15 × 15 MLAs with lens diameter of 0.5 mm and fill factor of 47.94%, while Design II produced 29 × 29 MLAs with lens diameter of 0.25 mm and fill factor of 40.87%. The partial-curing PDMS bonding system also proved to be effective in fusing PDMS with glass (maximum bonding strength of approximately six bars). Finally, the redesigned mold was used to create PDMS membranes of high thickness uniformity (coefficient of variance <0.07) and microlenses of high lens height uniformity (coefficient of variance <0.15).

Investigation of the Effect of Non-Uniform Membrane Properties on Performance of Mini/Microchannel Energy Recovery Ventilator Devices

Membrane based energy recovery ventilators (ERV) can be used to recover sensible and latent energy from exhaust-to-supply air in building applications. These typically consist of parallel layers of membrane separating the air streams, across which heat and moisture are exchanged. Reducing equipment cost and size remain a key challenge for continued commercialization and adoption of these devices. As membrane effectiveness improves, the air-side heat resistance can begin to dominate transport. To mitigate this, minichannel flow passages (DH < 2 mm) can be used to reduce convective heat and mass transfer. Channels can be formed through direct manipulation of membrane (e.g., pleating, corrugating, etc.), or through the use of spacer or other insert. The use of multiple parallel channels can result in large spatial variations in driving temperature and humidity ratio differences in a single layer membrane, impacting overall transport. Furthermore, the local membrane mass transfer resistance is typically a function of the surface temperature and relative humidity and not a constant value throughout the device. Accurate design models are required to appropriately size ERV equipment and maximize performance for a given equipment volume. Thus, the goal of this study is to use simulation tools to understand how the use of parallel mini- and microchannels and non-uniform membrane properties effect the performance of a membrane ERV in a building application. A two dimensional coupled heat and mass transfer resistance network model is developed. The model is compared against existing data from more detailed CFD analysis, and used to parametrically investigate effects different inlet conditions on device performance.

Preparation Uniform of TiO2 Microporous Ceramic Membrane Supported by Al2O3

In this study, a TiO2 ceramic membrane was coated on the porous Al2O3 ceramic support by a dip-coating method using a self-designed apparatus. A flat, low-porous and uniform membrane was obtained based on the optimized ingredient and fluidity of TiO2 suspension. The effects of thickening agent content on the stability of the membrane casting solution and the microstructure of the membrane were investigated.

Structure of cellular ESCRT-III spirals and their relationship to HIV budding

The ESCRT machinery along with the AAA+ ATPase Vps4 drive membrane scission for trafficking into multivesicular bodies in the endocytic pathway and for the topologically related processes of viral budding and cytokinesis, but how they accomplish this remains unclear. Using deep-etch electron microscopy, we find that endogenous ESCRT-III filaments stabilized by depleting cells of Vps4 create uniform membrane-deforming conical spirals which are assemblies of specific ESCRT-III heteropolymers. To explore functional roles for ESCRT-III filaments, we examine HIV-1 Gag-mediated budding of virus-like particles and find that depleting Vps4 traps ESCRT-III filaments around nascent Gag assemblies. Interpolating between the observed structures suggests a new role for Vps4 in separating ESCRT-III from Gag or other cargo to allow centripetal growth of a neck constricting ESCRT-III spiral.

Free Vibration of a Thin-Film Inflated Torus

In this paper an overview of the mathematical model for an inflated thin-film toroidal structure is provided. In particular, attention has been confined to determine the free vibrations of inflated circular toroidal members. The provided solution is based on an improved set of equations of motion for uniform membrane. From which the dependence of natural frequencies on material properties, dimension, mode of vibration, and the inner pressure can be investigated. The validity of the developed models was verified by comparing some of the computed results with those available for special cases. Numerical results for natural frequencies and mode shapes are provided for a specific thin-film inflated torus.