The Concept of Nano Insulation Materials - Challenges, Opportunities, and Experimental Investigations

Abstract

The world of today is experiencing an ever-increasing interest and focus on material scarcity and abundancy, energy efficiency and renewable and non-polluting energy harvesting. The main driving force of this increasing focus is global warming and climate changes due to emission of greenhouse gases to the atmosphere through various man-made processes. In this regard, the building sector represents one of the major sectors with a large potential for improvements, both for renovation of existing buildings and construction of new ones. Buildings which are thermally well insulated will have less energy demand for heating and cooling, i.e. energy-efficient buildings. Thus, there is a quest to invent and make thermal insulation materials with a low thermal conductivity and other suitable properties, to avoid undesirable thick building envelopes as would have been the case when applying traditional thermal insulation materials in situations where a large thermal resistance is required. This has led to an increased interest for today's state-of-the-art thermal insulation materials with low thermal conductivities, where especially commercial vacuum insulation panel (VIP) and aerogel products have experienced increased use during the last decades. However, VIPs and aerogels have several disadvantages, among them high costs for both VIPs and aerogels, and the loss of vacuum, either by perforations or long-term diffusion One of the promising candidates for becoming the high-performance or super insulation material (SIM) of tomorrow is nano insulation materials (NIM). The utilization of the Knudsen effect in order to reach very low thermal conductivities represents the governing principle of NIMs. Wanting the SIM and NIM to be functioning with air at atmospheric pressure in their pores, the size of the pores should be made very small in the nano range well below 100 nm according to calculations exploiting the Knudsen effect. NIMs may be manufactured in several ways, and herein a few possible pathways will be discussed. A special focus will be given on the experimental synthesis and investigations of hollow silica nanospheres (HSNS) by applying a sacrificial template method, where the inner nanosphere diameter and the shell thickness can be controlled through the parameters of the syntheses. Thus, the HSNS may be tailor-made with the desired low thermal conductivity.