Thermal characteristics of expanded perlite/paraffin composite phase change material with enhanced thermal conductivity using carbon nanotubes

Shape-stabilized phase change materials based on porous supports for thermal energy storage applications

Thermal energy storage plays a crucial role in energy conservation and environmental protection Research on thermal energy storage of phase change materials (PCM) has been standing in the forefront of science Several evident defects exist in the phase change materials such as low thermal conductivity and leakage during the phase change process Meanwhile, the clay mineral materials have relatively high thermal conductivity and excellent adsorbability, which can successfully remedy the defects resided in PCM Thus, the researches on clay mineral-based form-stable phase change materials (FSPCM) were reviewed in this paper Nine kinds of clay mineral materials were summarized, that is kaolin, diatomite, sepiolite, montmorillonite, perlite, SiO2, attapulgite, vermiculite and fly ash The large specific surface area and prominent porous structure of clay mineral materials can successfully prevent the flow and leakage of PCM within the clay mineral-based FSPCM Hence, this paper can partly serve as a reference for thermal energy storage and conservation

Review on clay mineral-based form-stable phase change materials: Preparation, characterization and applications

Efforts to tune the performance of organic/inorganic composites are hindered owing to a lack of knowledge related to the interfacial interaction mechanisms. Here we investigated the interfacial structure, dynamics, energetics and mechanical properties between calcium silicate hydrates (C-S-H) and polymers by molecular dynamics (MD) simulation. In this work, polyethylene glycol (PEG), polyvinyl alcohol (PVA) and polyacrylic acid (PAA) are intercalated into nanometer channel of C-S-H sheets to construct the model of polymer/C-S-H composite. In the interfacial region, the calcium ions near the surface of C-S-H play mediating role in bridging the functional groups in the polymers and oxygen in the silicate chains by forming Os-Ca-Op bond. In addition to ionic bonding, the bridging oxygen (C-O-C) in the PEG, hydroxyl (C-OH) in the PVA and carboxyl groups (-COOH) in the PAA provide plenty oxygen sites to form H-bonds with silicate hydroxyl, interlayer water and calcium hydroxyl in C-S-H substrate. The interfacial binding energy is dependent on polarity of functional groups in the polymers, the stability of the H-bond and Ca-O bond, ranking in the following order: E(PAA)> E(PVA) > E(PEG). The PVA with small number of H-bonds formed between oxygen in PVA and water molecules, resulting in increasing the mobility of confined water in the interlayer region. On the other hand, PAA and PVA, with strong polarity, can provide more number of non-bridging oxygen sites that widely distributed along the polymer chains to associate with more calcium ions and H-bonds. Furthermore, uniaxial tensile test is utilized to study the mechanical behavior of the composites. The incorporation of polymers, strengthening the H-bonds in the interfacial region and healing the defective silicate chains, can inhibit the crack growth during the loading process, which both enhance the cohesive strength and ductility of the C-S-H gel. In particular, the intercalated PAA increases the Young's modulus, tensile strength and fracture strain of C-S-H gel to 22.27%, 19.2% and 66.7%, respectively. The toughening mechanism in this organic/inorganic system can provide useful guidelines for polymer selection, design, and fabrication of C-S-H/polymer nanocomposites, and help eliminate the brittleness of cement-based materials from the genetic level.

Molecular dynamics modeling of the structure, dynamics, energetics and mechanical properties of cement-polymer nanocomposite

A review on the mechanical properties of cement-based materials measured by nanoindentation

Calcium Silicate Hydrate from Dry to Saturated State: Structure, Dynamics and Mechanical Properties

Preparation and characterization of expanded perlite/paraffin composite as form-stable phase change material

Mechanical properties of calcium silicate hydrate (C–S–H) at nano-scale: A molecular dynamics study

Effects of foaming agent type on the workability, drying shrinkage, frost resistance and pore distribution of foamed concrete

Calcium silicate hydrate (C–S–H) gels, the main binding phase of cement paste, determine the mechanical properties of cementitious materials. In order to obtain the cohesive force in C–S–H gel, molecular dynamics was carried out to simulate the uniaxial tension test on C–S–H model along x, y and z direction. Due to the structure and dynamic differences of the layered structure, C–S–H model demonstrates heterogeneous mechanical behavior. The calcium silicate layer, constructed by Ca–O and Si–O ionic-covalent bonds, has stronger cohesive force than that of interlayer H-bond network. In addition, composition influence on mechanical performance has been investigated by variation of the Ca/Si ratio. High calcium content, de-polymerizing the silicate chain structure in C–S–H gel, weakens uniaxial tension strength and elastic modulus in three directions. More water molecules penetration into the defective silicate region further reduces the mechanical properties of C–S–H gel at high Ca/Si ratio. Composition analysis at nano-scale can provide molecular insights on the cementitious materials design with different Ca/Si ratios.

Yu Zhu

Papers

Calcium Silicate Hydrate from Dry to Saturated State: Structure, Dynamics and Mechanical Properties

Preparation and characterization of expanded perlite/paraffin composite as form-stable phase change material

Mechanical properties of calcium silicate hydrate (C–S–H) at nano-scale: A molecular dynamics study

Effects of foaming agent type on the workability, drying shrinkage, frost resistance and pore distribution of foamed concrete

Uniaxial tension study of calcium silicate hydrate (C–S–H): structure, dynamics and mechanical properties