title: Dimensional and Structural Control of Silica Aerogel Membranes for Miniaturized Motionless Gas Pumps.
abstract: With growing public interest in portable electronics such as micro fuel cells, micro gas total analysis systems, and portable medical devices, the need for miniaturized air pumps with minimal electrical power consumption is on the rise. Thus, the development and downsizing of next-generation thermal transpiration gas pumps has been investigated intensively during the last decades. Such a system relies on a mesoporous membrane that generates a thermomolecular pressure gradient under the action of an applied temperature bias. However, the development of highly miniaturized active membrane materials with tailored porosity and optimized pumping performance remains a major challenge. Here we report a systematic study on the manufacturing of aerogel membranes using an optimized, minimal-shrinkage sol-gel process, leading to low thermal conductivity and high air conductance. This combination of properties results in superior performance for miniaturized thermomolecular air pump applications. The engineering of such aerogel membranes, which implies pore structure control and chemical surface modification, requires both chemical processing know-how and a detailed understanding of the influence of the material properties on the spatial flow rate density. Optimal pumping performance was found for devices with integrated membranes with a density of 0.062 g cm(-3) and an average pore size of 142.0 nm. Benchmarking of such low-density hydrophobic active aerogel membranes gave an air flow rate density of 3.85 sccm·cm(-2) at an operating temperature of 400 °C. Such a silica aerogel membrane based system has shown more than 50% higher pumping performance when compared to conventional transpiration pump membrane materials as well as the ability to withstand higher operating temperatures (up to 440 °C). This study highlights new perspectives for the development of miniaturized thermal transpiration air pumps while offering insights into the fundamentals of molecular pumping in three-dimensional open-mesoporous materials.
authors.affiliation: EMPA, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Shanyu
authors.initials: S
authors.lastname: Zhao
authors.affiliation: EPFL, Swiss Federal Institute of Technology Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.affiliation: EPFL, Swiss Federal Institute of Technology Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Maeder
authors.affiliation: EPFL, Swiss Federal Institute of Technology Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Paul
authors.initials: P
authors.lastname: Muralt
authors.affiliation: EMPA, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Nayoung
authors.initials: N
authors.lastname: Kim
authors.affiliation: EMPA, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Santhosh Kumar
authors.initials: SK
authors.lastname: Matam
authors.affiliation: EMPA, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Eunho
authors.initials: E
authors.lastname: Jeong
authors.affiliation: Seattle University , Seattle, Washington 98122, United States.
authors.forename: Yen-Lin
authors.initials: YL
authors.lastname: Han
authors.affiliation: EMPA, Swiss Federal Laboratories for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Matthias M
authors.initials: MM
authors.lastname: Koebel
mesh_terms: D005740:Gases / Q000737:chemistry*; D005782:Gels / Q000737:chemistry*; D055617:Micro-Electrical-Mechanical Systems / Q000295:instrumentation / Q000379:methods*; D008904:Miniaturization; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013814:Thermal Conductivity
chemical_list: D005740:Gases; D005782:Gels; D012822:Silicon Dioxide
keywords: Knudsen flow; aerogel membrane; low-temperature cofired ceramics; miniaturized gas pump; sodium silicate