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Hollow silica nanospheres (HSNS) have been the subject of intense studies as a possible building block that may successfully bring about nano insulation materials (NIM) with substantially reduced thermal conductivity. The reported thermal conductivity values of the HSNS are currently ranged between 20 and 90 mW/(mK). In this work, we have investigated the thermal properties of HSNS as a function of the corresponding structural parameters such as inner pore diameter, porosity, shell thickness, and size of the silica nanoparticles constituting the shell of HSNS. HSNS with sizes less than 100 nm was specifically synthesized in an attempt to lower the expressed thermal conductivity values to be below 20 mW/(mK), which may be used as a potential target towards superinsulation materials used in building applications. Furthermore, synthetic approaches to gain insights into the mechanism and formation of HSNS, i.e., the influence of reaction parameters on the structural characteristics of HSNS, have been thoroughly discussed in this work.

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. Copyright © 2018, Printed by the University of Victoria, British Columbia, Canada This conference proceeding is released under a Creative Commons Attribution-Non-commercial- Share Alike 4.0 license (CC-BY-NC-SA).

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).

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 templates 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 measured 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 stepping-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 future. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC-BY-NC-ND 4.0 license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Vacuum insulation panels (VIPs) are regarded as one of the most promising high performance thermal insulation solutions on the market today. Thermal performances three to six times better than still-air are achieved by applying a vacuum to an encapsulated micro-porous material, resulting in a great potential for combining the reduction of energy consumption in buildings with slim constructions. However, thermal bridging due to the panel envelope and degradation of thermal performance through time occurs with current technology. Furthermore, VIPs cannot be cut on site and the panels are fragile towards damaging. These effects have to be taken into account for building applications as they may diminish the overall usability and thermal performance. This paper is as far as the authors know the first comprehensive review on VIPs. Properties, requirements and possibilities of foil encapsulated VIPs for building applications are studied based on available literature, emphasizing thermal bridging and degradation through time. An extension is made towards gas-filled panels and aerogels, showing that other high performance thermal insulation solutions do exist. Combining the technology of these solutions and others may lead to a new leap forward. Feasible paths beyond VIPs are investigated and possibilities such as vacuum insulation materials (VIMs) and nano insulation materials (NIMs) are proposed. This work has been supported by the Research Council of Norway, AF Gruppen, Glava, Hunton Fiber as, Icopal, Isola, Jackon, maxit, Moelven ByggModul, Rambøll, Skanska, Statsbygg and Takprodusentenes forskningsgruppe through the SINTEF/NTNU research project ”Robust Envelope Construction Details for Buildings of the 21st Century” (ROBUST).

In today’s society there is an increased focus on various energy aspects. Buildings constitute a large part of the total energy consumption in the world. In this respect it is important to have the optimum heat balance in buildings. That is, in a cold climate one wants to have as well thermally insulated building envelopes as possible. However, even in cold climates there might often be relatively long periods of overheating in the buildings, for example, due to solar heat gains and excessive heat loads from miscellaneous indoor activities. In warm climates overheating is most often the case, for example, in office work spaces with large window glass facades and extensive use of electrical equipment. Insulation retrofit is among the most cost-effective measures, even more cost-effective than, for example, solar photovoltaics. The traditional thermal insulation materials of today have typically thermal conductivities between 33 and 40 mW/(mK). State-of-the-art thermal insulation includes vacuum insulation panels (VIPs) with conductivities between 3 and 4 mW/(mK) in fresh condition to typically 8 mW/(mK) after 25 years aging due to water vapor and air diffusion into the VIP core material, which has an open pore structure. Puncturing the VIP envelope causes an increase in the thermal conductivity to about 20 mW/(mK). The main emphasis of this work centers around the possibilities of inventing and developing innovative and robust highly thermal insulating materials. That is, within this work the objective is to go beyond VIPs and other current state-of-the-art technologies. New concepts are introduced, that is, advanced insulation materials (AIMs) as vacuum insulation materials (VIMs), gas insulation materials (GIMs), nano insulation materials (NIMs), and dynamic insulation materials (DIMs). These materials may have closed pore structures (VIMs and GIMs) or either open or closed pore structures (NIMs). The DIMs aim at controlling the material insulation properties, that is, solid state thermal conductivity, emissivity, and pore gas content. Fundamental theoretical studies aimed at developing an understanding of the basics of thermal conductance in solid state matter at an elementary and atomic level have been addressed. The ultimate goal of these studies is to develop tailor-made novel high performance thermal insulation materials and dynamic insulation materials, the latter one enabling to control and regulate the thermal conductivity in the materials themselves, that is from highly insulating to highly conducting. Furthermore, requirements of the future high performance thermal insulation materials and solutions have been proposed. At the moment, the NIM solution seems to represent the best high performance low conductivity thermal solution for the foreseeable future. If robust and practical DIMs can be manufactured, they have great potential due to their thermal insulation regulating abilities. © The Author(s) 2010. Reprints and permissions: sagepub.co.uk/journalsPermissions.nav. This is the authors' accepted and refereed manuscript to the article.

Buildings constitute a very large part of the total energy consumption in the world. In order to avoid heat losses according to stricter regulations, building envelope thicknesses are increasing continually when applying traditional thermal insulation materials. Vacuum insulation panels (VIPs) allow the combination of high thermal insulation and thin building envelopes, but unfortunately VIPs are suffering from ageing effects and lack of flexibility and robustness. This work investigates the possibilities of inventing and developing innovative and robust highly thermal insulating materials. That is, within this work the objective is to go beyond VIPs and other current state-of-the-art technologies. New concepts are introduced, e.g. vacuum insulation materials (VIMs), nano insulation materials (NIMs), gas insulation materials (GIMs) and dynamic insulation materials (DIMs). These materials may have closed pore structures (VIMs and GIMs) or either open or closed pore structures (NIMs). The DIMs aim at controlling the thermal conductivity. Fundamental theoretical studies aimed at developing an understanding of the basics of thermal conductance in solid state matter at an elementary and atomic level have been addressed. The ultimate goal is to develop tailor-made novel high performance thermal insulation materials and dynamic insulation materials, the latter one enabling to control and regulate the thermal conductivity in the materials themselves, i.e. from highly insulating to highly conducting. Furthermore, requirements of the future high performance thermal insulation materials and solutions have been proposed. Currently, the NIMs seem to represent the best high performance low conductivity thermal solution for the foreseeable future, while DIMs, if they can be made robust and practical, have great potential due to their thermal insulation regulating abilities. ispartof: pages:1-10 ispartof: IVIS 2009 Proceedings pages:1-10 ispartof: International Vacuum Insulation Symposium location:London date:18 Sep - 19 Sep 2009 status: published