Jingjie Yeo

Determination of the Young's modulus of silica aerogels – an analytical–numerical approach

The superior thermal, optical, acoustical, and mechanical properties of a nano-porous and ultra-light material called silica aerogel have been known to science since the 1930s. In this study, we propose a new analytical–numerical model of a silica aerogel to predict its Youngs modulus. The molecular dynamics (MD) simulation method was adopted to model and simulate the backbone of silica aerogels with different densities in an improved negative pressure rupturing method, and their mechanical properties were investigated. To generate the model using MD, the traditional method was improved by changing the sequence of its procedures, and it was proven to be a more stable and physically representative method. In the prediction, we proposed a two-level nano-porous structure model according to our simulations and the widely accepted fractal structure of silica aerogels. The Youngs modulus of a silica aerogel, which is shown in a power–law relationship with the density of samples, was derived by the two-level hierarchical model and uniaxial tension tests. We envisage that this new model can be applied in more analytical–numerical studies to reveal other interesting mechanical properties of silica aerogels.

Nanoscale Fluid Mechanics Working Principles of Transverse Flow Carbon Nanotube Membrane for Enhanced Desalination

This work introduces the transverse flow carbon nanotube (CNT) membrane, a novel membrane configuration designed to separate salt from water efficiently. The transverse flow CNT membrane uses transverse flow across horizontally stacked CNT, with neighboring CNT separated by a critical slit size. Through molecular dynamics (MD) simulation, the nano-fluidics interactions involved in the separation of salt from water using the transverse flow CNT membrane is studied. The simulation shows that this new membrane offers superior desalination performance, with permeability more than two times that of atom-thick graphene slit membrane, and orders of magnitude higher than conventional membranes. The effects of the nano-channels formed by the transverse flow CNT membrane on the behavior of water molecules and salt ions in a desalination system are studied in further detail with thermodynamic free energy computations, oxygen density mapping and hydrogen bond network studies. This simple but effective design offers an alternative solution for the practical use of CNT for efficient desalination.

Effects of Nanoporosity on the Mechanical Properties and Applications of Aerogels in Composite Structures

Aerogels are ultralight solids with nanoporous structure and are one of the world’s lightest materials available in the market. It is a dry gel, principally made up of 99.8 % of air and weighing just around three times that of air. The first aerogels were realized in 1931, when Kistler (J Phys Chem 36:52–64, 1932) attempted to remove liquid from a wet gel. It started out with the testing of the hypothesis that the liquid in a jelly can be replaced by a gas so as to avoid the collapse of the wet gel. He postulated that it was possible to slowly expand the supercritical fluid within a gel and obtain an air-filled non-collapsed gel structure. He subsequently succeeded in producing silica aerogels with densities in the range 20–100 kg/m3, as well as aerogels of alumina, tungsten, ferric, and stannic oxides. Today, silica aerogel is frequently used in nanocomposites for their light weight and excellent thermal insulating properties. In this chapter, we document some of the silica aerogel-filled carbon composite sandwich structures we have recently developed and also numerically examine the underlying mechanisms which enable silica aerogels to possess extreme insulation properties and especially how pore size plays a major role.