Article Cite This: Macromolecules XXXX, XXX, XXX−XXX
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Hydrophobic Clay Aerogel Composites through the Implantation of Environmentally Friendly Water-Repellent Agents Omar Abo Madyan and Mizi Fan*
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Civil Engineering, College of Engineering, Design and Physical Sciences, Brunel University, London UB8 3PH, United Kingdom ABSTRACT: Clay aerogel composites have high potential to be used in the construction industry as an insulation material; however, their hydrophilic nature may result in an amount of moisture absorption that could significantly hinder both physical and mechanical properties. This study develops hydrophobic clay aerogel composites using an environmentally friendly freeze-drying process. This was achieved by using three water dispersible repellent components: WDisRep1, WDisRep3, and WDisRep4. Microstructure, wettability, moisture resistance, mechanical properties, and thermal conductivity of the developed clay aerogel composites were fully characterized to understand working mechanisms and performance. The composites exhibited superior mechanical and physical properties in which the composites’ moisture absorbance was reduced by up to 40%, while maintaining excellent dimensional stability. The aerogel composites achieved a contact angle of 140° with a 93% reduction in water absorption. The composites achieved a compressive modulus as high as 3.2 MPa while maintaining low thermal conductivity at 0.038 W/(m K).
1. INTRODUCTION Aerogels are classified as low density and highly porous materials compromised of an interconnected three-dimensional solid network structure, with >90% being occupied with air. The most common synthesis of aerogels, first introduced by Kistler in 1931,1,2 involves replacing the pore liquid of a gel with a gas/air through supercritical drying techniques.3 Silica aerogels are the most commonly investigated and are attractive for many industrial sectors due to their unique properties, such as high specific surface area (500−1200 m2/g), high porosity (80−99.8%), low density (0.3−0.05 g/cm3), and low thermal conductivity values (0.01−0.02 W/(m K)).4,5 The mandate for cost reduction and the utilization of abundant, natural, and nontoxic materials to prepare functional materials have driven research to formulate new categories of aerogels for effective and efficient implementation in many different applications.6,7 Clay aerogel is one of these developments, a relatively new type of aerogel introduced in 1987.8 Clay aerogel is prepared through an environmentally friendly freeze-drying process, in which a clay and/or polymer suspension is frozen and then the ice is sublimed, leaving behind a dry solid network with properties similar to those of foamed polymers.8,9 Clay aerogels are characterized with a unique lamellar “house of cards” structure which is responsible for their unique properties, such as low density (
