Advanced 3D-printed phase change materials

Abstract

3D printing strategies provide flexible solutions for complex and programmable thermal management and versatile material integration. 3D-printed composite phase change materials (PCMs) can overcome shape limitations and optimize structures to construct complex object designs for effective thermal management. Recently in Matter, Emily B. Pentzer et al. creatively proposed a facile strategy to print PCM-filled inks with excellent thermal regulation capacity via direct ink writing (DIW) technology without requiring prior encapsulation of PCMs. This 3D printing approach with a simplified manufacturing process and reduced costs facilitates the production of composite PCMs with complex geometries for retrofitting current buildings containing thermal energy storage materials. 3D printing strategies provide flexible solutions for complex and programmable thermal management and versatile material integration. 3D-printed composite phase change materials (PCMs) can overcome shape limitations and optimize structures to construct complex object designs for effective thermal management. Recently in Matter, Emily B. Pentzer et al. creatively proposed a facile strategy to print PCM-filled inks with excellent thermal regulation capacity via direct ink writing (DIW) technology without requiring prior encapsulation of PCMs. This 3D printing approach with a simplified manufacturing process and reduced costs facilitates the production of composite PCMs with complex geometries for retrofitting current buildings containing thermal energy storage materials. Main textHeating, ventilation, and air conditioning (HVAC) systems are the most commonly used method of temperature regulation in residential and commercial buildings. However, the continuing problems of HVAC systems have led to research on alternative materials and technologies. 3D printing as an additive manufacturing technology is capable of manufacturing multi-scale, multi-material, and multi-functional three-dimensional structures with ultra-high precision and ultra-high flexibility. This technology is expected to facilitate the integration of nanoencapsulated phase change materials (PCMs) for advanced multi-functional conceptual devices. The most popular nanoencapsulated composite PCMs are usually composed of nanoporous supporting materials and PCMs, thus guaranteeing their shape stability, leak-proof capability, and customizable thermal/electrical conductivity.1Chen X. Tang Z. Liu P. Gao H. Chang Y. Wang G. Smart utilization of multifunctional metal oxides in phase change materials.Matter. 2020; 3: 708-741Abstract Full Text Full Text PDF Scopus (48) Google Scholar,2Chen X. Gao H. Tang Z. Dong W. Li A. Wang G. Optimization strategies of composite phase change materials for thermal energy storage, transfer, conversion and utilization.Energy Environ. Sci. 2020; 13: 4498-4535Crossref Google Scholar Recently, nanoporous composite PCMs and related devices have been developing toward intelligence, multi-functionality, flexibility, and refinement. Specifically, composite PCMs with freely designed shapes and structures are definitely smarter in thermal energy management, wearable devices, and shape memory materials. However, the production of flexible lumped composite PCMs is still a big challenge because traditional manufacturing techniques are usually limited to post-impregnation strategies.3Aftab W. Huang X. Wu W. Liang Z. Mahmood A. Zou R. Nanoconfined phase change materials for thermal energy applications.Energy Environ. Sci. 2018; 11: 1392-1424Crossref Google Scholar,4Shchukina E.M. Graham M. Zheng Z. Shchukin D.G. Nanoencapsulation of phase change materials for advanced thermal energy storage systems.Chem. Soc. Rev. 2018; 47: 4156-4175Crossref PubMed Google Scholar Attractively, 3D printing strategies offer flexible solutions for complex and programmable composite PCMs. Different from traditional manufacturing methods, 3D printing can produce shape-changing composite PCMs without leakage, which is an important step toward the application of flexible devices.Direct ink writing (DIW) technology has widespread application prospects in 3D printing. Actually, designing viscoelastic inks with shear-thinning behavior is critical during the extrusion-based printing process.5Ma J. Ma T. Cheng J. Zhang J. 3D printable, recyclable and adjustable comb/bottlebrush phase change polysiloxane networks toward sustainable thermal energy storage.Energy Storage Mater. 2021; 39: 294-304Crossref Scopus (23) Google Scholar If the viscosity, surface tension, shear yield stress, shear elasticity, and loss modulus of the ink can be adjusted appropriately, direct printing of nanoencapsulated PCMs will be possible. Currently, numerous concentrated nanomaterial dispersions, such as graphene oxide and MXene, have been developed for DIW due to their extraordinary high viscoelasticity.6Zhang Y. Zhu G. Dong B. Wang F. Tang J. Stadler F.J. Yang G. Hong S. Xing F. Interfacial jamming reinforced Pickering emulgel for arbitrary architected nanocomposite with connected nanomaterial matrix.Nat. Commun. 2021; 12: 111Crossref Scopus (16) Google Scholar If PCMs are incorporated into the printable matrix (such as graphene oxide and MXene), the corresponding 3D-printed composite PCMs will shine in photothermal energy conversion and storage. More interestingly, the thermal performance of composite PCMs can be improved by optimizing the combination of nanomaterials and optimizing the printing geometry. For example, octadecane/graphene phase change microlattices with a bean pod structure can facilitate light propagation throughout the phase change microlattices, thus realizing the rapid collection and transfer of solar thermal energy.7Yang Z. Jia S. Niu Y. Lv X. Fu H. Zhang Y. Liu D. Wang B. Li Q. Bean-pod-inspired 3D-printed phase change microlattices for solar-thermal energy harvesting and storage.Small. 2021; 17: e2101093Crossref Scopus (18) Google ScholarAdvanced building materials and infrastructure are benefiting from 3D printing technology. This technology provides a platform for facilitating the integration of nanoencapsulated PCMs in advanced phase change building materials. Advanced thermal management based on PCMs for passive control of building heating and cooling can reduce energy losses, which is of great strategic importance.8Song M. Niu F. Mao N. Hu Y. Deng S. Review on building energy performance improvement using phase change materials.Energy Build. 2018; 158: 776-793Crossref Scopus (231) Google Scholar Recently in Matter, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar creatively proposed a facile DIW technique to produce and print PCM-filled inks with excellent thermal regulation capacity that utilized spherical PCM particles as a viscosity modifier in a photocurable, leak-proof resin matrix. PCM beads were prepared by being emulsified at high temperature, dispersed in commercially available acrylate resins, printed, and cured with UV light. As shown in Figure 1A, the purposes of PCM beads were modifying ink rheology and imparting thermal management function. Photopolymerization realized the elastic sealing of PCMs without the use of shell materials. Based on this design concept, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar successfully printed inks (up to 63% PCMs) with excellent thermal regulation capacity and virtually no leakage during multiple melting and solidifying cycles. In addition, versatile PCMs with different phase transition temperatures (eicosane, paraffin, and hexatriacontane) can be simultaneously integrated into the resin and printed without compromising integrity. The rheological properties of the ink are critical in 3D printing. Specifically, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar conducted a preliminary evaluation of viscosity and yield stress of inks with different PCM loading levels for printability. Incorporating PCM beads into the resin imparted shear-thinning behavior, i.e., viscosity decreases with increasing shear rate. Generally, the increase filler concentration enhanced the viscosity, but had little influence on the magnitude of the shear-thinning behavior, indicating that inks can be formulated to attain optimal thixotropic behavior for DIW printing because the materials were sheared during the extrusion process. Increasing the loading level of PCM beads can strengthen the yield stress, which improves the ink’s ability to maintain its shape after extrusion. However, indiscriminately increasing the loading level of PCMs will cause the granular ink to fail to form a uniform paste. Therefore, an upper limit of the loading level of PCMs exists for printable compositions.As is well known, solid-liquid PCMs suffer from loss of integrity and volume change limitations during melting. The traditional solution is the microencapsulation of PCMs. Such rigid PCM microcapsules can be integrated into building materials to produce monolithic structures.10Zhu N. Li S. Hu P. Wei S. Deng R. Lei F. A review on applications of shape-stabilized phase change materials embedded in building enclosure in recent ten years.Sustain. Cities Soc. 2018; 43: 251-264Crossref Scopus (70) Google Scholar However, the shell materials have a negative impact on the thermal energy storage density. In this work, 3D printing technology harnesses the advantages of DIW and eliminates the inherent issues of current microencapsulation techniques (fluid leakage upon volume change) for facilitating the incorporation of PCMs into building materials, thus simplifying the manufacturing process. A limited temperature regulation range is another challenge of single PCMs. Since the ink formulation is not dependent on the chemical properties of PCMs, multiple PCMs can be simultaneously integrated into a single ink, allowing for a wider operating temperature window and promoting its thermal management capability. Ultimately, the authors 3D printed hollow house models with PCM-filled ink serving as effective thermal buffers in the melting temperature range of PCMs. Compared with houses without PCMs, 3D-printed PCM-based houses mitigated temperature fluctuations with a 10% lower temperature during heating and a 40% higher temperature during cooling (Figure 1B). This method does not require microencapsulation of PCMs before they are integrated into the composite materials, thereby using off-the-shelf structural materials to achieve effective passive thermal management and reducing the manufacturing costs.Generally, this study shows how to use 3D printing technology to encapsulate PCMs for thermal management of building materials. The excellent adaptability of DIW makes this strategy compatible with a wide range of photopolymer matrices and PCMs without prior microencapsulation of PCMs. 3D printing technology is capable of adjusting the loading levels of different PCMs particles to achieve the desired thermal management capability. However, the energy storage density of composite PCMs used for residential thermal regulation in this study needs to be further improved to boost the thermal regulation capability. Selecting appropriate PCMs is the key to the development of high-performance phase change building materials. Priority should be given to PCMs with suitable phase change temperature to reach the appropriate ambient temperature for human comfort, and to PCMs with larger latent heat to store or release more heat during the phase change process. Enhanced thermal conductivity, excellent reversibility, and small amounts of expansion and contraction should also be considered. In addition, the preparation process of phase change building materials should also be simplified. Future efforts should aim to balance the mechanical properties, thermal energy storage density, and practical engineering applications of phase change building materials, thus enabling design of advanced thermal management systems that satisfy commercial technical requirements. In conclusion, 3D printing technology offers the ability to produce objects with complex geometries, and it allows the integration of thermal energy storage materials into existing buildings. It is noteworthy that there are fewer reported applications of 3D printing for reliable and efficient thermal energy storage. Therefore, it is highly desirable to explore and implement a suitable combination of PCM encapsulation technology and 3D printing technology to simultaneously satisfy requirements for efficient thermal energy storage, scalable manufacturing, and leak-proof capability. Main textHeating, ventilation, and air conditioning (HVAC) systems are the most commonly used method of temperature regulation in residential and commercial buildings. However, the continuing problems of HVAC systems have led to research on alternative materials and technologies. 3D printing as an additive manufacturing technology is capable of manufacturing multi-scale, multi-material, and multi-functional three-dimensional structures with ultra-high precision and ultra-high flexibility. This technology is expected to facilitate the integration of nanoencapsulated phase change materials (PCMs) for advanced multi-functional conceptual devices. The most popular nanoencapsulated composite PCMs are usually composed of nanoporous supporting materials and PCMs, thus guaranteeing their shape stability, leak-proof capability, and customizable thermal/electrical conductivity.1Chen X. Tang Z. Liu P. Gao H. Chang Y. Wang G. Smart utilization of multifunctional metal oxides in phase change materials.Matter. 2020; 3: 708-741Abstract Full Text Full Text PDF Scopus (48) Google Scholar,2Chen X. Gao H. Tang Z. Dong W. Li A. Wang G. Optimization strategies of composite phase change materials for thermal energy storage, transfer, conversion and utilization.Energy Environ. Sci. 2020; 13: 4498-4535Crossref Google Scholar Recently, nanoporous composite PCMs and related devices have been developing toward intelligence, multi-functionality, flexibility, and refinement. Specifically, composite PCMs with freely designed shapes and structures are definitely smarter in thermal energy management, wearable devices, and shape memory materials. However, the production of flexible lumped composite PCMs is still a big challenge because traditional manufacturing techniques are usually limited to post-impregnation strategies.3Aftab W. Huang X. Wu W. Liang Z. Mahmood A. Zou R. Nanoconfined phase change materials for thermal energy applications.Energy Environ. Sci. 2018; 11: 1392-1424Crossref Google Scholar,4Shchukina E.M. Graham M. Zheng Z. Shchukin D.G. Nanoencapsulation of phase change materials for advanced thermal energy storage systems.Chem. Soc. Rev. 2018; 47: 4156-4175Crossref PubMed Google Scholar Attractively, 3D printing strategies offer flexible solutions for complex and programmable composite PCMs. Different from traditional manufacturing methods, 3D printing can produce shape-changing composite PCMs without leakage, which is an important step toward the application of flexible devices.Direct ink writing (DIW) technology has widespread application prospects in 3D printing. Actually, designing viscoelastic inks with shear-thinning behavior is critical during the extrusion-based printing process.5Ma J. Ma T. Cheng J. Zhang J. 3D printable, recyclable and adjustable comb/bottlebrush phase change polysiloxane networks toward sustainable thermal energy storage.Energy Storage Mater. 2021; 39: 294-304Crossref Scopus (23) Google Scholar If the viscosity, surface tension, shear yield stress, shear elasticity, and loss modulus of the ink can be adjusted appropriately, direct printing of nanoencapsulated PCMs will be possible. Currently, numerous concentrated nanomaterial dispersions, such as graphene oxide and MXene, have been developed for DIW due to their extraordinary high viscoelasticity.6Zhang Y. Zhu G. Dong B. Wang F. Tang J. Stadler F.J. Yang G. Hong S. Xing F. Interfacial jamming reinforced Pickering emulgel for arbitrary architected nanocomposite with connected nanomaterial matrix.Nat. Commun. 2021; 12: 111Crossref Scopus (16) Google Scholar If PCMs are incorporated into the printable matrix (such as graphene oxide and MXene), the corresponding 3D-printed composite PCMs will shine in photothermal energy conversion and storage. More interestingly, the thermal performance of composite PCMs can be improved by optimizing the combination of nanomaterials and optimizing the printing geometry. For example, octadecane/graphene phase change microlattices with a bean pod structure can facilitate light propagation throughout the phase change microlattices, thus realizing the rapid collection and transfer of solar thermal energy.7Yang Z. Jia S. Niu Y. Lv X. Fu H. Zhang Y. Liu D. Wang B. Li Q. Bean-pod-inspired 3D-printed phase change microlattices for solar-thermal energy harvesting and storage.Small. 2021; 17: e2101093Crossref Scopus (18) Google ScholarAdvanced building materials and infrastructure are benefiting from 3D printing technology. This technology provides a platform for facilitating the integration of nanoencapsulated PCMs in advanced phase change building materials. Advanced thermal management based on PCMs for passive control of building heating and cooling can reduce energy losses, which is of great strategic importance.8Song M. Niu F. Mao N. Hu Y. Deng S. Review on building energy performance improvement using phase change materials.Energy Build. 2018; 158: 776-793Crossref Scopus (231) Google Scholar Recently in Matter, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar creatively proposed a facile DIW technique to produce and print PCM-filled inks with excellent thermal regulation capacity that utilized spherical PCM particles as a viscosity modifier in a photocurable, leak-proof resin matrix. PCM beads were prepared by being emulsified at high temperature, dispersed in commercially available acrylate resins, printed, and cured with UV light. As shown in Figure 1A, the purposes of PCM beads were modifying ink rheology and imparting thermal management function. Photopolymerization realized the elastic sealing of PCMs without the use of shell materials. Based on this design concept, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar successfully printed inks (up to 63% PCMs) with excellent thermal regulation capacity and virtually no leakage during multiple melting and solidifying cycles. In addition, versatile PCMs with different phase transition temperatures (eicosane, paraffin, and hexatriacontane) can be simultaneously integrated into the resin and printed without compromising integrity. The rheological properties of the ink are critical in 3D printing. Specifically, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar conducted a preliminary evaluation of viscosity and yield stress of inks with different PCM loading levels for printability. Incorporating PCM beads into the resin imparted shear-thinning behavior, i.e., viscosity decreases with increasing shear rate. Generally, the increase filler concentration enhanced the viscosity, but had little influence on the magnitude of the shear-thinning behavior, indicating that inks can be formulated to attain optimal thixotropic behavior for DIW printing because the materials were sheared during the extrusion process. Increasing the loading level of PCM beads can strengthen the yield stress, which improves the ink’s ability to maintain its shape after extrusion. However, indiscriminately increasing the loading level of PCMs will cause the granular ink to fail to form a uniform paste. Therefore, an upper limit of the loading level of PCMs exists for printable compositions.As is well known, solid-liquid PCMs suffer from loss of integrity and volume change limitations during melting. The traditional solution is the microencapsulation of PCMs. Such rigid PCM microcapsules can be integrated into building materials to produce monolithic structures.10Zhu N. Li S. Hu P. Wei S. Deng R. Lei F. A review on applications of shape-stabilized phase change materials embedded in building enclosure in recent ten years.Sustain. Cities Soc. 2018; 43: 251-264Crossref Scopus (70) Google Scholar However, the shell materials have a negative impact on the thermal energy storage density. In this work, 3D printing technology harnesses the advantages of DIW and eliminates the inherent issues of current microencapsulation techniques (fluid leakage upon volume change) for facilitating the incorporation of PCMs into building materials, thus simplifying the manufacturing process. A limited temperature regulation range is another challenge of single PCMs. Since the ink formulation is not dependent on the chemical properties of PCMs, multiple PCMs can be simultaneously integrated into a single ink, allowing for a wider operating temperature window and promoting its thermal management capability. Ultimately, the authors 3D printed hollow house models with PCM-filled ink serving as effective thermal buffers in the melting temperature range of PCMs. Compared with houses without PCMs, 3D-printed PCM-based houses mitigated temperature fluctuations with a 10% lower temperature during heating and a 40% higher temperature during cooling (Figure 1B). This method does not require microencapsulation of PCMs before they are integrated into the composite materials, thereby using off-the-shelf structural materials to achieve effective passive thermal management and reducing the manufacturing costs.Generally, this study shows how to use 3D printing technology to encapsulate PCMs for thermal management of building materials. The excellent adaptability of DIW makes this strategy compatible with a wide range of photopolymer matrices and PCMs without prior microencapsulation of PCMs. 3D printing technology is capable of adjusting the loading levels of different PCMs particles to achieve the desired thermal management capability. However, the energy storage density of composite PCMs used for residential thermal regulation in this study needs to be further improved to boost the thermal regulation capability. Selecting appropriate PCMs is the key to the development of high-performance phase change building materials. Priority should be given to PCMs with suitable phase change temperature to reach the appropriate ambient temperature for human comfort, and to PCMs with larger latent heat to store or release more heat during the phase change process. Enhanced thermal conductivity, excellent reversibility, and small amounts of expansion and contraction should also be considered. In addition, the preparation process of phase change building materials should also be simplified. Future efforts should aim to balance the mechanical properties, thermal energy storage density, and practical engineering applications of phase change building materials, thus enabling design of advanced thermal management systems that satisfy commercial technical requirements. In conclusion, 3D printing technology offers the ability to produce objects with complex geometries, and it allows the integration of thermal energy storage materials into existing buildings. It is noteworthy that there are fewer reported applications of 3D printing for reliable and efficient thermal energy storage. Therefore, it is highly desirable to explore and implement a suitable combination of PCM encapsulation technology and 3D printing technology to simultaneously satisfy requirements for efficient thermal energy storage, scalable manufacturing, and leak-proof capability. Heating, ventilation, and air conditioning (HVAC) systems are the most commonly used method of temperature regulation in residential and commercial buildings. However, the continuing problems of HVAC systems have led to research on alternative materials and technologies. 3D printing as an additive manufacturing technology is capable of manufacturing multi-scale, multi-material, and multi-functional three-dimensional structures with ultra-high precision and ultra-high flexibility. This technology is expected to facilitate the integration of nanoencapsulated phase change materials (PCMs) for advanced multi-functional conceptual devices. The most popular nanoencapsulated composite PCMs are usually composed of nanoporous supporting materials and PCMs, thus guaranteeing their shape stability, leak-proof capability, and customizable thermal/electrical conductivity.1Chen X. Tang Z. Liu P. Gao H. Chang Y. Wang G. Smart utilization of multifunctional metal oxides in phase change materials.Matter. 2020; 3: 708-741Abstract Full Text Full Text PDF Scopus (48) Google Scholar,2Chen X. Gao H. Tang Z. Dong W. Li A. Wang G. Optimization strategies of composite phase change materials for thermal energy storage, transfer, conversion and utilization.Energy Environ. Sci. 2020; 13: 4498-4535Crossref Google Scholar Recently, nanoporous composite PCMs and related devices have been developing toward intelligence, multi-functionality, flexibility, and refinement. Specifically, composite PCMs with freely designed shapes and structures are definitely smarter in thermal energy management, wearable devices, and shape memory materials. However, the production of flexible lumped composite PCMs is still a big challenge because traditional manufacturing techniques are usually limited to post-impregnation strategies.3Aftab W. Huang X. Wu W. Liang Z. Mahmood A. Zou R. Nanoconfined phase change materials for thermal energy applications.Energy Environ. Sci. 2018; 11: 1392-1424Crossref Google Scholar,4Shchukina E.M. Graham M. Zheng Z. Shchukin D.G. Nanoencapsulation of phase change materials for advanced thermal energy storage systems.Chem. Soc. Rev. 2018; 47: 4156-4175Crossref PubMed Google Scholar Attractively, 3D printing strategies offer flexible solutions for complex and programmable composite PCMs. Different from traditional manufacturing methods, 3D printing can produce shape-changing composite PCMs without leakage, which is an important step toward the application of flexible devices. Direct ink writing (DIW) technology has widespread application prospects in 3D printing. Actually, designing viscoelastic inks with shear-thinning behavior is critical during the extrusion-based printing process.5Ma J. Ma T. Cheng J. Zhang J. 3D printable, recyclable and adjustable comb/bottlebrush phase change polysiloxane networks toward sustainable thermal energy storage.Energy Storage Mater. 2021; 39: 294-304Crossref Scopus (23) Google Scholar If the viscosity, surface tension, shear yield stress, shear elasticity, and loss modulus of the ink can be adjusted appropriately, direct printing of nanoencapsulated PCMs will be possible. Currently, numerous concentrated nanomaterial dispersions, such as graphene oxide and MXene, have been developed for DIW due to their extraordinary high viscoelasticity.6Zhang Y. Zhu G. Dong B. Wang F. Tang J. Stadler F.J. Yang G. Hong S. Xing F. Interfacial jamming reinforced Pickering emulgel for arbitrary architected nanocomposite with connected nanomaterial matrix.Nat. Commun. 2021; 12: 111Crossref Scopus (16) Google Scholar If PCMs are incorporated into the printable matrix (such as graphene oxide and MXene), the corresponding 3D-printed composite PCMs will shine in photothermal energy conversion and storage. More interestingly, the thermal performance of composite PCMs can be improved by optimizing the combination of nanomaterials and optimizing the printing geometry. For example, octadecane/graphene phase change microlattices with a bean pod structure can facilitate light propagation throughout the phase change microlattices, thus realizing the rapid collection and transfer of solar thermal energy.7Yang Z. Jia S. Niu Y. Lv X. Fu H. Zhang Y. Liu D. Wang B. Li Q. Bean-pod-inspired 3D-printed phase change microlattices for solar-thermal energy harvesting and storage.Small. 2021; 17: e2101093Crossref Scopus (18) Google Scholar Advanced building materials and infrastructure are benefiting from 3D printing technology. This technology provides a platform for facilitating the integration of nanoencapsulated PCMs in advanced phase change building materials. Advanced thermal management based on PCMs for passive control of building heating and cooling can reduce energy losses, which is of great strategic importance.8Song M. Niu F. Mao N. Hu Y. Deng S. Review on building energy performance improvement using phase change materials.Energy Build. 2018; 158: 776-793Crossref Scopus (231) Google Scholar Recently in Matter, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar creatively proposed a facile DIW technique to produce and print PCM-filled inks with excellent thermal regulation capacity that utilized spherical PCM particles as a viscosity modifier in a photocurable, leak-proof resin matrix. PCM beads were prepared by being emulsified at high temperature, dispersed in commercially available acrylate resins, printed, and cured with UV light. As shown in Figure 1A, the purposes of PCM beads were modifying ink rheology and imparting thermal management function. Photopolymerization realized the elastic sealing of PCMs without the use of shell materials. Based on this design concept, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar successfully printed inks (up to 63% PCMs) with excellent thermal regulation capacity and virtually no leakage during multiple melting and solidifying cycles. In addition, versatile PCMs with different phase transition temperatures (eicosane, paraffin, and hexatriacontane) can be simultaneously integrated into the resin and printed without compromising integrity. The rheological properties of the ink are critical in 3D printing. Specifically, Emily B. Pentzer et al.9Wei P. Cipriani C.E. Pentzer E.B. Thermal energy regulation with 3D printed polymer-phase change material composites.Matter. 2021; 4: 1975-1989Abstract Full Text Full Text PDF Scopus (19) Google Scholar conducted a preliminary evaluation of viscosity and yield stress of inks with different PCM loading levels for printability. Incorporating PCM beads into the resin imparted shear-thinning behavior, i.e., viscosity decreases with increasing shear rate. Generally, the increase filler concentration enhanced the viscosity, but had little influence on the magnitude of the shear-thinning behavior, indicating that inks can be formulated to attain optimal thixotropic behavior for DIW printing because the materials were sheared during the extrusion process. Increasing the loading level of PCM beads can strengthen the yield stress, which improves the ink’s ability to maintain its shape after extrusion. However, indiscriminately increasing the loading level of PCMs will cause the granular ink to fail to form a uniform paste. Therefore, an upper limit of the loading level of PCMs exists for printable compositions. As is well known, solid-liquid PCMs suffer from loss of integrity and volume change limitations during melting. The traditional solution is the microencapsulation of PCMs. Such rigid PCM microcapsules can be integrated into building materials to produce monolithic structures.10Zhu N. Li S. Hu P. Wei S. Deng R. Lei F. A review on applications of shape-stabilized phase change materials embedded in building enclosure in recent ten years.Sustain. Cities Soc. 2018; 43: 251-264Crossref Scopus (70) Google Scholar However, the shell materials have a negative impact on the thermal energy storage density. In this work, 3D printing technology harnesses the advantages of DIW and eliminates the inherent issues of current microencapsulation techniques (fluid leakage upon volume change) for facilitating the incorporation of PCMs into building materials, thus simplifying the manufacturing process. A limited temperature regulation range is another challenge of single PCMs. Since the ink formulation is not dependent on the chemical properties of PCMs, multiple PCMs can be simultaneously integrated into a single ink, allowing for a wider operating temperature window and promoting its thermal management capability. Ultimately, the authors 3D printed hollow house models with PCM-filled ink serving as effective thermal buffers in the melting temperature range of PCMs. Compared with houses without PCMs, 3D-printed PCM-based houses mitigated temperature fluctuations with a 10% lower temperature during heating and a 40% higher temperature during cooling (Figure 1B). This method does not require microencapsulation of PCMs before they are integrated into the composite materials, thereby using off-the-shelf structural materials to achieve effective passive thermal management and reducing the manufacturing costs. Generally, this study shows how to use 3D printing technology to encapsulate PCMs for thermal management of building materials. The excellent adaptability of DIW makes this strategy compatible with a wide range of photopolymer matrices and PCMs without prior microencapsulation of PCMs. 3D printing technology is capable of adjusting the loading levels of different PCMs particles to achieve the desired thermal management capability. However, the energy storage density of composite PCMs used for residential thermal regulation in this study needs to be further improved to boost the thermal regulation capability. Selecting appropriate PCMs is the key to the development of high-performance phase change building materials. Priority should be given to PCMs with suitable phase change temperature to reach the appropriate ambient temperature for human comfort, and to PCMs with larger latent heat to store or release more heat during the phase change process. Enhanced thermal conductivity, excellent reversibility, and small amounts of expansion and contraction should also be considered. In addition, the preparation process of phase change building materials should also be simplified. Future efforts should aim to balance the mechanical properties, thermal energy storage density, and practical engineering applications of phase change building materials, thus enabling design of advanced thermal management systems that satisfy commercial technical requirements. In conclusion, 3D printing technology offers the ability to produce objects with complex geometries, and it allows the integration of thermal energy storage materials into existing buildings. It is noteworthy that there are fewer reported applications of 3D printing for reliable and efficient thermal energy storage. Therefore, it is highly desirable to explore and implement a suitable combination of PCM encapsulation technology and 3D printing technology to simultaneously satisfy requirements for efficient thermal energy storage, scalable manufacturing, and leak-proof capability. The authors acknowledge funding from the National Natural Science Foundation of China (No. 51902025 ), Fundamental Research Funds for the Central Universities (No. 2019NTST29 ), and the China Postdoctoral Science Foundation (No. 2020T130060 and 2019M660520 ). Thermal energy regulation with 3D printed polymer-phase change material compositesWei et al.MatterApril 12, 2021In BriefIn the US, 20% of energy is consumed in the active thermal management of buildings. This work offers a solution by incorporating phase change materials (PCMs), which absorb and release heat at key temperatures, into 3D printable materials. 3D printing can reproduce complex architectural features, and the PCM-containing structures produced can minimize the energy used for thermal management of buildings. This work provides the potential to easily retrofit existing buildings and reduce the energy consumed in their thermal management. Full-Text PDF Open Archive