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Scanning electron microscopy (SEM) images of (a) fumed silica (FS), and (b–d) n-octadecane/FS composites with various n-octadecane mass fractions: (b) 60 wt%, (c) 70 wt%, and (d) 75 wt%.
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A novel n-octadecane/fumed silica phase change composite has been prepared as a building envelope with a high content of phase change material and improved energy efficiency. With a high porosity (88 vol%), the fumed silica provided sufficient space to impregnate a high quantity of n-octadecane (70 wt%). The composite exhibited high latent heat sto...
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One major limitation of phase-change materials (PCM) for thermal energy storage comes from their poor thermal conductivity hindering heat transfer process and power density. Nanocomposites PCMs, where highly conductive nanofillers are dispersed into PCM matrices, have been exploited in the past decades as novel latent heat storage materials with en...
In this paper, numerical and experimental investigations of thermal performance enhancement of horizontal longitudinal shell and tube latent heat thermal energy storage unit (LHTESU) via eccentricity (e), fin design optimization, and nanoparticles in the phase change material (PCM) of stearic acid are presented. An enthalpy-porosity-based two-dimen...
Citations
... Because fumed SiO 2 particles have an enormous specific surface area, they are prone to agglomerate because of van der Waals forces and hydrogen bonds among the silanol (Si-OH) groups located on their surfaces. 35 This agglomeration can create an interconnected porous network that makes the particles appear smaller and more irregular than their actual primary size as shown in Figure 4A. ZrO 2 and HA nanoparticles were found to have a spherical shape and are aggregated into clusters. ...
In clinical applications, resin‐based dental composites primarily face challenges with fractures and secondary caries. To overcome these issues, the physical characteristics of dental composites, especially mechanical properties, need to be improved. Hydroxyapatite (HA), present in the structure of the teeth, is preferred due to its biological properties, and zirconia (ZrO 2 ) nanoparticles are known to enhance the mechanical properties of this type of composites. The aim of this study is to develop resin‐based dental composites containing HA and ZrO 2 nanoparticles. The study also aims to explore the synergistic effect of these two nanoparticles on the physical properties of the developed composites. Composites with nine different compositions were prepared by mixing the components with the help of a mortar mill. The flexural and compressive strength, polymerization shrinkage, depth of cure and water sorption, and solubility properties of the prepared composites have been investigated. All composites have been found to meet the requirements of ISO 4049 standard. Among them, composite containing 5 wt. % HA and 1 wt. % ZrO 2 (H5Z1) has exhibited the highest flexural strength with an increase of 58% compared to the control sample, and composite containing 3 wt. % HA and 2 wt. % ZrO 2 (H3Z2) has exhibited the highest compressive strength with an increase of 22% compared to the control sample. Other physical properties of the composites have been found to be in an acceptable level.
Highlights
Dental composites with HA and ZrO 2 fillers were developed by a mortar mill.
Synergistic effect of HA and ZrO 2 nanoparticles was investigated.
Mechanical properties of dental composites were significantly improved.
Physical properties of dental composites were found to be at acceptable levels.
Depth of cure decreases with increasing HA and ZrO 2 loading.
... All types of modified FS exhibited a particle morphology similar to that of the 0-FS particles, consisting of three-dimensional networks of approximately 25 nm primary particles. Irregular FS pores formed by the interconnected primary particles were observed with sizes of 10-150 nm, with them belonging to the meso-or macropore range [40,41]. Thermogravimetric analysis (TGA) measurements were conducted at a heating rate of 10 °C/min from 25 to 800 °C under nitrogen (20 mL/min) with a TGA 4000 instrument (PerkinElmer, Waltham, MA, USA). ...
... All types of modified FS exhibited a particle morphology similar to that of the 0-FS particles, consisting of three-dimensional networks of approximately 25 nm primary particles. Irregular FS pores formed by the interconnected primary particles were observed with sizes of 10-150 nm, with them belonging to the meso-or macropore range [40,41]. TGA curves of the FS materials ( Figure 5) were obtained to investigate the grafting ratios of the modifiers listed in Table 1. ...
Polyimide (PI) composite films with enhanced mechanical properties were prepared by incorporating modified fumed silica (FS) particles while preserving their optical and thermal characteristics. The PI matrix was synthesized using a fluorinated diamine, a fluorinated dianhydride, and a rigid biphenyl dianhydride via chemical imidization. Commercially available FS particles, including unmodified FS particles (0-FS) and particles modified with dimethyl (2-FS), trimethyl (3-FS), octyl (8-FS), octamethylcyclotetrasiloxane (D4-FS), and polydimethylsiloxane (PDMS-FS) were used. Scanning electron microscope images and nitrogen adsorption–desorption isotherms revealed well-defined porous structures in the FS particles. The water contact angles on the composite films increased compared to those of the pristine PI films, indicating improved water resistance. The PI/0-FS films exhibited a typical trade-off relationship between tensile modulus and elongation at break, as observed in conventional composites. Owing to the poor compatibility and agglomeration of the PDMS-FS particles, the PI/PDMS-FS composite films exhibited poor mechanical performance and diminished optical characteristics. Although the longer-chained FS particles (8- and D4-FS) improved the tensile modulus of the PI film by up to 12%, a reduction of more than 20% in toughness was observed. The PI composite films containing the methylated FS particles (2- and 3-FS) outperformed 8- and D4-FS in terms of mechanical properties, with PI/3-FS films showing an over 10% increased tensile modulus (from 4.07 to 4.42 GPa) and 15% improved toughness (from 6.97 to 8.04 MJ/m3) at 7 wt. % silica loading. Except for the PI/PDMS-FS composites, all composite film samples exhibited more than 86% transmittance at 550 nm. Regarding thermal properties, the glass transition temperature (Tg) and thermal stability remained stable for most composite films. In addition, PI/3-FS films demonstrated enhanced dimensional stability with lower coefficients of thermal expansion (from 47.3 to 34.5 ppm/°C). Overall, this study highlights the potential of incorporating specific modified FS particles to tailor the mechanical, optical, and thermal properties of PI composite films.
... Phase change composite (PCC) has been evaluated for application as building envelope in recent scientific study [26]. The PCC made from n-octadecane, and fumed silica demonstrated a high latent heat storage capacity of 155.8 J/g, which is superior to previously reported PCCs. ...
This paper reviews innovative building envelope technologies that can improve total building energy efficiency and reduce greenhouse gas emissions. The building envelope has a significant impact on energy and thermal performance, making various technologies like phase change materials, aerogel, and active and adaptive systems essential for enhancing the building envelope’s energy efficiency. Phase change materials reduce energy consumption by lowering peak heating and cooling loads, improving thermal comfort. Paraffin wax is considered the most dependable phase change material for building envelopes, as it can decrease energy consumption for heating and cooling. Study shows that active PCM thermal energy storage system can reduce room temperature by 6.8 °C in summer. Aerogel, in comparison, is recognized for its exceptional insulation capabilities and low density that minimize heat transfer and boost thermal insulation in buildings. Silica aerogel’s outstanding feature is its capacity to offer thermal performance that surpasses traditional insulation materials by 2–4 times, thereby delivering substantial energy savings of up to 35 %. Active and adaptive systems, such as smart windows and kinetic facades, enable real-time control of building envelope performance, improving energy efficiency and indoor comfort. Smart windows can lead to annual energy savings up to 35.9 kWh/m ² compared to traditional windows, and kinetic facades can reduce cooling loads for buildings up to 21 %. The review assesses various adaptive facade solutions for their suitability in diverse climate zones, versatility in application and energy efficiency. Despite the existence of some limitations and challenges, such as high costs and insufficient understanding of their long-term performance, the continuous development and deployment of these technologies can still yield a significant contribution to improving building energy efficiency and mitigating greenhouse gas emissions.
... In contrast, the three microcapsule samples kept their initial forms with no deformation during the whole heating process. Table 2 also lists the measured thermal conductivity at 25 ± 0.5 • C, and for the pure C 18 it was measured to be 0.193 ± 0.003 W/(m⋅K), which is between the value of 0.160 W/(m⋅K) (temperature was not specified) tested by Li et al. [21] and the value of 0.256 W/(m⋅K) tested by Nguyen et al [22] at room temperature. The organic SDB polymer shell has a low thermal conductivity, measured to be only 0.075 ± 0.002 W/(m⋅K). ...
We propose to enhance photothermal conversion via doping titanium carbide (Ti3C2) MXene nanosheets on the surfaces of phase-change microcapsules consisted of the n-Octadecane core and styrene divinylbenzene copol- ymer shell. Detected by scanning electron microscopy, the microcapsules showed a usually circular form with an appropriate dispersion. The thermal properties of the microcapsules were characterized using the differential scanning calorimetry and thermal conductivity instruments, realizing an excellent phase-change enthalpy of around 140 J/g, high encapsulation ratio of over 64 %, good heat transfer of 0.294 ± 0.003 W/(m⋅K), and great thermal reliability. More importantly, the microcapsules doped with Ti3C2 MXene nanosheets reach a solar-to- heat conversion efficiency of 85 ± 7 %, a substantial enhancement by 240 % in comparison with non-doping sample. The Ti3C2 MXene-doped microcapsules with excellent heat storage and solar-to-heat conversion capa- bilities offer great potential for high-efficiency solar energy utilization and can be applied to thermal energy storage systems and direct absorption solar collectors.
... In our recent studies, fumed silica (FS) was used as a porous support to incorporate C18 PCMs with different functional groups, including n-octadecane and 1-octadecanol. 21,22 The FS consists of nanoparticles aggregated in a 3D-interconnected structure with an appropriate pore size and large pore volume (17 cm 3 /g) for an SSPCM support. A large amount of C18 PCMs (70−75 wt %) could be strongly adsorbed to the FS with good leakage resistance, thus enhancing the thermal efficiency as the TES capacity increased with increasing PCM content. ...
... The porous structure of the FS has been systematically reported in our recent study. 21 In brief, the FS consisted of nanosized particles aggregated in a highly interconnected porous framework (Figure 3a). The porous structure had a small number of micropores and numerous macropores with sizes in the range of 50−150 nm, allowing the adsorption of PCMs. ...
... Additionally, the FS had a large total pore volume and porosity of 17 cm 3 /g and 88%, respectively, as determined by mercury porosimetry. 21 In comparison with pure FS, the asobtained SSPCMs with increasing C 18 OOH content from 50 to 70 wt % showed a gradual increase in the amount of FS macropores, as observed from the SEM images (Figure 1b−d). The SSPCMs exhibited a decline in the N 2 adsorption− desorption isotherms (Figure 4a). ...
... As shown in that figure, the pure n-octadecane melts at 20.7 • C and freezes at 28.9 • C, while RTH18HC melts at 22.2 • C and freezes at 11.5 • C. Both the exothermic and endothermic peaks of two PCMs, were asymmetric, implying the existence of more than one crystalline phase. According to previous studies, the n-octadecane crystals consist of two crystalline phases αand β, which exhibit very close melting temperatures overlapping each other [67]. The similar asymmetric appearance of DSC peaks of RT18HC, could be explained based on its structure, which seems according to the Rubitherm data sheet [68], to be composed of more than one hydrocarbon (the main phase should be the hexadecane, C 16 H 34 ). ...
Carbon-red mud foam/paraffin hybrid materials were prepared and studied for their thermal energy storage and electromagnetic interference (EMI) shielding properties. The host matrices were prepared utilizing the polymeric foam replication method, with a polyurethane sponge as a template, resin as a carbon source, and red mud as a filler. The paraffins, n-octadecane (OD) and the commercial RT18HC, were used as organic encapsulant phase change materials (PCMs) into the open pore structure of the foams. The foams’ morphological and structural study revealed a highly porous structure (bulk density, apparent porosity P > 65%), which exhibits elliptical and spherical pores, sized from 50 up to 500 μm, and cell walls composed of partially graphitized carbon and various oxide phases. The hybrid foams showed a remarkable encapsulation efficiency as shape stabilizers for paraffins: 48.8% (OD), 37.8% (RT18HC), while their melting enthalpies (ΔHm) were found to be 126.9 J/g and 115.5 J/g, respectively. The investigated hybrids showed efficient electromagnetic shielding performance in frequency range of 3.5–9.0 GHz reaching the entry-level value of ~20 dB required for commercial applications, when filled with PCMs. Their excellent thermal and EMI shielding performance places the as-prepared samples as promising candidates for use in thermal management and EMI shielding of electronic devices as well.
... Over the past several decades, phase change materials (PCMs), particularly solid-liquid PCMs, have been extensively studied and have undergone a rapid development in both academic and industrial sectors because of their green nature and the high performance of their latent heat storage system. This type of material can store a significant amount of heat from solar energy or other industrial waste heat through the phase change process and then release the energy at different times or even different locations within a particular temperature range. 1 Given this flexibility, they have been effectively used for various innovative applications, such as smart textiles, 2 solar energy harvesting, 3 advanced building materials, 4,5 and medicine preservation. 6 However, a leakage problem during the solid-liquid transition prevents PCMs from being used in real thermal energy systems. ...
... This was attributed to the confinement effect of organics in the mesopores, which has been observed in nanocomposites, thereby enhancing the thermal stability of the SSPCMs. 5 Unlike the curve of C 18 H 3 /SBA-15-10.6, those of C 18 OH/SBA-15-10.6 ...
Ten phase change materials (PCMs) with various functional groups and alkyl chain lengths, including three alkanes (C14C18), four carboxylic acids (C12C18), and four alcohols (C12C18), were impregnated into mesoporous silica materials (SBA‐15) with three distinct pore sizes. The non‐freezable layer thickness (TNL) of the shape‐stable phase change materials (SSPCMs) was calculated, and the effects of the functional groups and alkyl chain lengths of the PCMs on the TNL were investigated. Because of the hydrogen bond (H‐bond) with the silanol groups, the TNL values of SSPCMs containing alcohols and carboxylic acids were greater than those containing alkanes. Furthermore, the H‐bond nature of alcohols is stronger than that of carboxylic acids, resulting in higher values of TNL for the alcohols. As the alkyl chain length increased, the TNL increased for alcohols but decreased for carboxylic acids. By modifying the silica surface with methyl groups to weaken the interfacial H‐bonds, the TNL of PCMs was remarkably reduced; consequently, the crystallization fraction of the PCMs increased. Specifically, the crystallization fractions of PCMs in the methylated SBA‐15 silica increased by 4%‐5% (depending on the pore size of SBA‐15) for alkanes, 6%‐11% for carboxylic acids, and 17%‐20% for alcohols compared with those for unmodified SBA‐15 silica. The promoted crystallization fractions greatly enhanced the heat storage capacity of the SSPCMs. Ten PCMs were impregnated into cylindrical SBA‐15 silica and their non‐freezable layer thicknesses (TNL) were calculated using a geometric technique. The TNL values were investigated with the chain lengths and functional groups of the PCMs. Alcohol PCMs exhibited larger TNL because of the stronger H‐bonding nature but their TNL values were reduced in methylated silica.
... 2 During the daytime, PCMs absorb heat and melt due to temperature rise; at night, as the temperature decreases, they release the stored heat and solidify. Several organic PCMs (paraffins, 6,7 biobased PCMs, 8 fatty alcohols 9 ) and inorganic PCMs (CaCl 2 ·6H 2 O, 10 Na 2 SO 4 ·10H 2 O 11 ) have been investigated for building applications. Inorganic PCMs usually show advantages of low cost, flame retardance, and relatively high latent heat storage capacity. ...
A series of n-octadecane/mesoporous silica (C18/MS) shape-stabilized phase change materials (SSPCMs) with varying C18 content were prepared, and the effects of adsorbed C18 distributed within porous MS on the thermal properties were analyzed. As characterized, C18 was first infiltrated into the mesoporous space, resulting in a SSPCM with a maximum of ∼52 wt % C18. Additional adsorption of C18 occurred on the external surface of MS. Consequently, the optimum 70 wt % C18 SSPCM had no C18 leakage and exhibited a heat storage capacity of 135.6 J/g and crystallinity of 83.5%, which were much larger than those of 52 wt % C18 SSPCM (60.2 J/g and 68.2%, respectively). The prepared C18/MS SSPCMs showed excellent thermal stability and thermal reliability up to 1000 accelerated thermal cycle tests. Moreover, the C18/MS SSPCM incorporated in gypsum effectively reduced the temperature changes compared with the original gypsum, suggesting the promising application of the prepared C18/MS SSPCM for energy-saving building applications.
... 43,44 After the impregnation of paraffin, high-intensity C-H bonds (2,852 cm À1 , 2,920 cm À1 , 2,958 cm À1 , 1,465 cm À1 , and 1,380 cm À1 ) show in PCM films both with and without the silane coating. Compared with the X-ray diffraction (XRD) patterns of pure MXene and pure paraffin at 0 C (see Figures S4 and S5), all of the peaks that represent MXene (2q = 23 and 18 , which correspond to peaks at 28 and 19 in Figure S4 because of the larger discrete layer spacing separated by BC lamellar) and that represent paraffin (2q = 11 and 15 in Figure S5, probably induced by the n-octadecane component in the commercial paraffin used) 45 are found in the XRD patterns of PCM films as shown from the XRD patterns in Figure 3B. The normal peaks of pure paraffin at $21 and $23 did not appear, which were covered up by the broadened peaks of MXene sheets. ...
To survive extreme weather, antifreeze beetles have a smart thermal management system, which relies on light absorption by the black surface and energy storage by antifreeze proteins. Inspired by the energy storage behavior of antifreeze proteins, we design a composite film, which is fabricated via impregnation of organic phase change material (PCM) in a surface-modified MXene/bacterial-cellulose aerogel. The resulting composite aerogel-based PCM film shows an increased loading capacity of organic PCM, increased phase change latent heat, and enhanced mechanical properties. Combining these thermal insulation and thermal energy storage properties, a submillimeter-thick film with an aerogel layer can maintain a comfortable temperature range for more than 800 s. This is more than double compared to the system without the films, and is a proof of concept for bioinspired photothermal-conversion/thermal-storage integration.
