Likai Yang, Jun Wei Chua, Xinwei Li, Yijing Zhao, Ba Quoc Thai, Xiang Yu, Yong Yang*, Wei Zhai*, “Superior broadband sound absorption in hierarchical ultralight graphene oxide aerogels achieved through emulsion freeze-casting” Chemical Engineering Journal, 2023, link

In this work, we fabricated a hierarchically porous ultralight graphene oxide (GO) aerogel through a novel emulsion freeze-casting process of an air-in-water emulsion. Microstructural analysis of the aerogels reveals a hierarchical pore morphology consisting of highly inter-connected pores produced from the emulsion bubbles and the micro-pores produced by freeze-casting. Sound absorption measurements revealed that an aerogel with a surfactant-to-GO weight ratio of 1:1 displays an average absorption coefficient of up to 0.86 at a broadband frequency range between 250 Hz and 6300 Hz, a vast improvement by up to 58% as compared to conventional GO aerogels. Numerical microstructural models were developed to model the acoustic absorption phenomenon and understand the mechanisms behind enhanced sound absorption. These models identified the enhanced acoustic absorption as attributed to the increased air-wetting area as derived from the high reticulation rate in this hierarchical microstructure. Overall, we demonstrate the potential of leveraging the highly interdependent material-process-structure relationships of GO aerogel production to achieve hierarchical GO aerogels as advanced ultralight sound-absorbing materials.

Xinyu Dong, Quyang Liu, Yijing Zhao, Wei Zhai *, Highly robust and hydrophobic aerogel beads with dandelion-like structure for water treatment, Chemical Engineering Journal, 2023, link

Taking inspiration from dandelion blowballs, we propose a fabrication strategy to prepare hierarchically structured chitosan aerogel beads by combining droplet freeze casting and silylation grafting. The chitosan aerogel beads consist of a hierarchical structure, with a spherical macro-shape, a centrosymmetric radially aligned microstructure, and a nano-scale siloxane coating. As a result, the dandelionlike hierarchical structure endows the aerogel beads with a fine combination of high mechanical efficiency and functional properties. With an average density of only 0.08 g/cm3, the aerogel beads can sustain more than 2.2 MPa of stress at 80% deformation. Their chitosan skeleton, despite being inherently water dissolvable, is modified to be highly hydrophobic (contact angle = 147◦, rolling angle = 4.2◦), even under prolonged water blasts. Further, the aerogel beads not only showcase the capability to quickly absorb various pollutants with good reusability, but also can be assembled into customizable configurations, demonstrating their filtration capability and excellent thermal insulation with a thermal conductivity of 32.5 mW⋅m-1⋅K-1. Benefiting from these excellent properties, our aerogel beads represent a promising engineering material for water treatment and thermal insulation.

X Dong, BW Chua, T Li, W Zhai*, Multi-directional freeze casting of porous ceramics with bone-inspired microstructure, Materials & Design. 2022

Herein, inspired by the cancellous bone, we propose a novel multi-directional freeze casting technique to prepare highly mechanically efficient porous ceramics. A multi-directional temperature field is ingeniously designed to mimic the stress-responsive growth pattern of the cancellous bone. To further the lateral structural control, ceramic fibers are incorporated to form mineral bridging. In this process, alumina-mullite composite ceramics are prepared with hierarchical structures, including micro-level multi-oriented struts, sub-micro-level interlamellar bridges and nano-level eutectic phases. They endow the ceramics with high porosity (~75%) and high strength in all 3D spatial directions (8.4 – 20.1 MPa), while effectively preventing the catastrophic brittle failure. Therefore, the mechanically enhanced porous ceramics demonstrate the remarkable controllability of multi-directional freeze casting in hierarchical structures.

X Dong†, X Guo†, Q Liu, Y Zhao, H Qi, and W Zhai*, Strong and tough conductive organo-hydrogels via freeze-casting assisted solution substitution, Advanced Functional Materials. 2022:2203610, link

We developed an integrated strategy of freeze-casting assisted solution substitution (FASS) for hierarchically structured strong and tough conductive organo-hydrogels. The FASS strategy simultaneously endowed the organo-hydrogels with excellent mechanical properties and multi-functionality in one step. As an exemplary material, the prepared polyvinyl alcohol (PVA) organo-hydrogel with solvent content up to 87 wt% exhibits a combination of high strength (6.5 MPa), high stretchability (1710% in strain), ultra-high toughness (58.9 MJ m⁻³), as well as high ionic conductivity up to 6.5 S m⁻¹ with excellent strain sensitivity.

X Lan, Y Hou, X Dong, Z Yang, BQ Thai, Y Yang*, W Zhai*, All-ceramic SiC aerogel for wide temperature range electromagnetic wave attenuation, ACS Applied Materials & Interfaces. 2022 Mar 22, link

We developed a freeze casting and carbothermal reduction reaction process for all-ceramic SiC aerogels. The all-ceramic SiC aerogel is ultralight with a density of 0.2 g/cm³ and possesses a low thermal conductivity of about 0.05 W/mK. The material composition remains stable at temperatures up to 800 °C. The optimum all-ceramic SiC aerogel exhibits effective whole X-band attenuation (>90%) at a fixed thickness of 3.3 mm from room temperature to 400 °C.

Y Liu, W Zhai*, K Zeng, Study of the freeze casting process by artificial neural networks, ACS Applied Materials & Interfaces. 2020 Aug 12; 12(36):40465-74, link

Freeze casting technology has experienced vast development since the early 2000s due to its versatility and simplicity for producing porous materials. We proposed an artificial neural network (ANN) to analyze the influence of critical parameters on freeze-cast porous materials.