Synthesis of Silica-Based Nano Insulation Materials for Potential Application in Low-Energy or Zero Emission Buildings

Sacrificial polystyrene (PS) templates have been used for synthesis of silica -based nano insulation materials (NIM). The PS was synthesized by a simple procedure where parameters as polyvinylpyrrolidone /styrene ratio and potassium persulfate amount were adjusted. Thereafter the PS template s were coated with silica by using tetraethyl orthosilicate (TEOS). The time used for adding TEOS was varied to investigate the effect on how the silica particles attached to the PS surface and the resulting silica spheres. By modifying the process, different PS templates were obtained. The thermal conductivity was measu red for hollow silica spheres originating from the coating process of 198 nm PS templates, and the results showed thermal conductivities around 38 mW/(mK) for long -time measurements (160 -640 s). Controlled synthesis of this silica -based NIM might be a step ping -stone on the path to a new generation of high -performance thermal insulation materials with low thermal conductivity, which can be used in the building envelope of low -energy or zero emission buildings in the futurepublishedVersio

Air-Filled Nanopore Based High-Performance Thermal Insulation Materials

State-of-the-art thermal insulation solutions like vacuum insulation panels (VIP) and aerogels have low thermal conductivity, but their drawbacks may make them unable to be the thermal insulation solutions that will revolutionize the building industry regarding energy-efficient building envelopes. Nevertheless, learning from these materials may be crucial to make new and novel high-performance thermal insulation products. This study presents a review on the state-of-the-art air-filled thermal insulation materials for building purposes, with respect to both commercial and novel laboratory developments. VIP, even if today’s solutions require a core with vacuum in the pores, are also treated briefly, as they bear the promise of developing high-performance thermal insulation materials without the need of vacuum. In addition, possible pathways for taking the step from today´s solutions to new ones for the future using existing knowledge and research are discussed. A special focus is made on the possible utilization of the Knudsen effect in air-filled nanopore thermal insulation materials.Acknowledgements. This work has been supported by the Research Council of Norway within the Nano2021 program through the SINTEF and NTNU research project “High-Performance Nano Insulation Materials” (Hi-Per NIM).publishedVersio

Utilizing the Knudsen Effect in the Quest for Super Insulation Materials

Initiatives to incorporate energy efficiency measures and strategies in the building sector have gained attention for several decades, and with increased focus on zero energy and zero emission buildings, such initiatives will probably still continue to emerge for several more decades to come. Development of new high-performance thermal insulation materials and super insulation materials (SIM) for the advanced building envelopes of tomorrow may play an essential role in this regard. Very thick building envelopes are not desirable due to several reasons, e.g. considering space issues with respect to both economy, floor area, transport volumes, architectural restrictions and other limitations, material usage and existing building techniques. Hence, the stage is set for the development of new thermal insulation materials with a very low thermal conductivity, thus allowing the usage of relatively thin building envelopes with a very high thermal resistance and thereby substantially reduced heat loss. In porous materials, when the mean free path of the gas molecules becomes larger than the pore diameter, there will be a decrease in the gas thermal conductivity including the gas and pore wall interaction, which is referred to as the Knudsen effect. This study will present our on-going efforts utilizing the Knudsen effect attempting to make SIMs with a nanoporous air-filled structure at atmospheric pressure, i.e. nano insulation materials (NIM). Some possible pathways to NIMs and SIMs like e.g. the template foaming method and the internal gas release method are promising with respect to their high potential, however, so far large experimental challenges have made us abandon these methods for the moment. That is, currently we are pursuing to make NIMs by the sacrificial template method, more specifically by the synthesis of hollow silica nanospheres (HSNS), where both the inner sphere diameter and shell thickness may be tailor-made and thereby determining the thermal conductivity

Utilizing the Knudsen Effect in the Quest for Super Insulation Materials

Initiatives to incorporate energy efficiency measures and strategies in the building sector have gained attention for several decades, and with increased focus on zero energy and zero emission buildings, such initiatives will probably still continue to emerge for several more decades to come. Development of new high-performance thermal insulation materials and super insulation materials (SIM) for the advanced building envelopes of tomorrow may play an essential role in this regard. Very thick building envelopes are not desirable due to several reasons, e.g. considering space issues with respect to both economy, floor area, transport volumes, architectural restrictions and other limitations, material usage and existing building techniques. Hence, the stage is set for the development of new thermal insulation materials with a very low thermal conductivity, thus allowing the usage of relatively thin building envelopes with a very high thermal resistance and thereby substantially reduced heat loss. In porous materials, when the mean free path of the gas molecules becomes larger than the pore diameter, there will be a decrease in the gas thermal conductivity including the gas and pore wall interaction, which is referred to as the Knudsen effect. This study will present our on-going efforts utilizing the Knudsen effect attempting to make SIMs with a nanoporous air-filled structure at atmospheric pressure, i.e. nano insulation materials (NIM). Some possible pathways to NIMs and SIMs like e.g. the template foaming method and the internal gas release method are promising with respect to their high potential, however, so far large experimental challenges have made us abandon these methods for the moment. That is, currently we are pursuing to make NIMs by the sacrificial template method, more specifically by the synthesis of hollow silica nanospheres (HSNS), where both the inner sphere diameter and shell thickness may be tailor-made and thereby determining the thermal conductivity

A Review of Materials Science Research Pathways and Opportunities for Building Integrated Photovoltaics

Building integrated photovoltaics (BIPV) represent a powerful and versatile tool for achieving the ever-increasing demand for energy-efficient and energy-harvesting buildings of the near future. The BIPV systems offer an aesthetical, economical and technical solution to integrate solar cells harvesting solar radiation to produce electricity being an integral part of the climate envelopes of buildings. Building integration of photovoltaic (PV) cells are carried out on sloped roofs, flat roofs, facades and solar shading systems, where the BIPV systems replace the outer building envelope skin, thus serving simultaneously as both a climate screen and a power source generating electricity. Hence, BIPV may provide savings in materials and labour, in addition to reducing the electricity costs. Nevertheless, in addition to specific requirements put on the solar cell technology, as the BIPV systems act as the climate protection screen it is of major importance to have satisfactory requirements on rain tightness and durability, where various building physical issues such as heat and moisture transport in the building envelope also must be considered and accounted for. Research within materials science in general and within PV technology may enable and accelerate the development of highly innovative and efficient BIPV materials and systems. Sandwich, wavelength-tuned, dye-sensitized, material-embedded concentrator, flexible (e.g. copper indium gallium selenide CIGS and cadmium telluride CdTe), thin amorphous silicon, quantum dot, nanowire, brush-paint and spray-paint solar cells, different surface technologies and various combinations of these are examples of possible research pathways for PV and BIPV. From a materials science perspective, this work presents a review bridging the path from the current state-of-the-art BIPV to possible research pathways and opportunities for the future BIPV.ACKNOWLEDGEMENTS. This work has been supported by the Research Council of Norway and several partners through the research projects ”Building Integrated Photovoltaics for Norway” (BIPV Norway) and ”The Research Centre on Zero Emission Buildings” (ZEB).publishedVersio

Hollow Silica Nanospheres as Thermal Insulation Materials for Construction: Impact of their Morphologies as a Function of Synthesis Pathways and Starting Materials

Hollow silica nanospheres (HSNS) show a promising potential to become good thermal insulators with low thermal conductivity values for construction purposes. The thermal conductivity of HSNSs is dependent on their structural features such as sizes (inner diameter and shell thickness) and shell structures (porous or dense), which are affected by the synthetic methods and procedures including reaction medium, polystyrene template, and silica precursor. Formation of thermally insulating HSNS was favoured by alkaline reaction, whereby highly porous silica shells were formed, promoting less silica per volume of material, thus a lower solid state thermal conductivity. The Knudsen effect is in general reducing the gas thermal conductivity including the gas and pore wall interaction for materials with pore diameters in the nanometer range, which is also valid for our HSNS reported here. Further decreasing the pore sizes would invoke a higher impact from the Knudsen effect. The additional insulating effect of the inter-silica voids (median diameter D50 ≈ 15 nm) within the shell coating contributed also to the insulating properties of HSNS. The synthesis route with tetraethyl orthosilicate (TEOS) was more robust and produced more porous silica shells than the one with water glass (Na2SiO3, WG), although the latter might represent a greener synthetic methodThis work has been supported by the Research Council of Norway and several partners through ‘‘The Research Centre on Zero Emission Buildings” (ZEB, project no. 193830) and by the Research Council of Norway through the research project ‘‘High- Performance Nano Insulation Materials” (Hi-Per NIM, project no. 250159) within the Nano2021 program. Furthermore, the Research Council of Norway is acknowledged for the support to the ‘‘Norwegian Micro- and Nano-Fabrication Facility” (NorFab, project no. 245963/F50).acceptedVersio

Nano Insulation Materials Exploiting the Knudsen Effect

As the world's focus is turned even stronger toward miscellaneous energy efficiency and saving aspects, the development of new high-performance thermal insulation materials for building applications will play an important role in this regard. The aim of the presented study is to develop an understanding for the governing thermal transport mechanisms and utilize the Knudsen effect in nanoporous insulation materials through theoretical concepts and experimental laboratory explorations, thus being able to synthesize nano insulation materials (NIM) with very low thermal conductivity values as a major goal. NIMs based on hollow silica nanospheres (HSNS) have been synthesized by a sacrificial template method, where the idea is that the heat transport by gas conductance and gas/solid state interactions decreases with decreasing pore diameters in the nano range as predicted by the Knudsen effect. HSNS with reduced thermal conductivity compared to their solid counterparts have been prepared where the hollow sphere cavities and voids between the spheres are filled with air at atmospheric pressure, i.e. eliminating the need for various measures like e.g. protective metallized foils to maintain a vacuum or expensive low-conducting gases in the cavities and voids. Hence, HSNS represent a promising stepping-stone toward the future high-performance thermal insulation materials.publishedVersio

Nano Insulation Materials Exploiting the Knudsen Effect

As the world's focus is turned even stronger toward miscellaneous energy efficiency and saving aspects, the development of new high-performance thermal insulation materials for building applications will play an important role in this regard. The aim of the presented study is to develop an understanding for the governing thermal transport mechanisms and utilize the Knudsen effect in nanoporous insulation materials through theoretical concepts and experimental laboratory explorations, thus being able to synthesize nano insulation materials (NIM) with very low thermal conductivity values as a major goal. NIMs based on hollow silica nanospheres (HSNS) have been synthesized by a sacrificial template method, where the idea is that the heat transport by gas conductance and gas/solid state interactions decreases with decreasing pore diameters in the nano range as predicted by the Knudsen effect. HSNS with reduced thermal conductivity compared to their solid counterparts have been prepared where the hollow sphere cavities and voids between the spheres are filled with air at atmospheric pressure, i.e. eliminating the need for various measures like e.g. protective metallized foils to maintain a vacuum or expensive low-conducting gases in the cavities and voids. Hence, HSNS represent a promising stepping-stone toward the future high-performance thermal insulation materialspublishedVersio

A Review of Research Pathways and Opportunities for Building Integrated Photovoltaics from a Materials Science Perspective

Research within materials science photovoltaics (PV) technologies may enable and accelerate the development of highly innovative and efficient building integrated photovoltaics (BIPV) materials and systems. Sandwich, wavelength-tuned, dye sensitized, material-embedded concentrator, flexible (e.g. copper indium gallium selenide CIGS and cadmium telluride CdTe), crystalline silicon on glass (CSG), thin amorphous silicon, quantum dot, nanowire, brush-paint and spray-paint solar cells and various combinations of these are examples of possible research pathways for PV and BIPV. Furthermore, other surface technologies may also be very interesting and promising for utilization on solar cells, e.g. light-trapping geometries, anti-reflection, self-cleaning, superhydrophobic and icephobic surfaces. From a materials science perspective, this work presents a review and bridges the path from the current state-of-the-art BIPV to possible research pathways and opportunities for the future BIPV.publishedVersio