Hindawi Publishing Corporation Advances in Materials Science and Engineering Volume 2013, Article ID 483651, 6 pages http://dx.doi.org/10.1155/2013/483651 Research Article Synthesis of Hollow Silica Nanospheres by Sacrificial Polystyrene Templates for Thermal Insulation Applications Linn Ingunn C. Sandberg, 1 Tao Gao, 2 Bjørn Petter Jelle, 1,3 and Arild Gustavsen 2 1 Department of Civil and Transport Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway 2 Department of Architectural Design, History and Technology, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway 3 Department of Materials and Structures, SINTEF Building and Infrastructure, 7465 Trondheim, Norway Correspondence should be addressed to Linn Ingunn C. Sandberg; linn.sandberg@ntnu.no Received 10 January 2013; Accepted 21 February 2013 Academic Editor: Marcel Ausloos Copyright © 2013 Linn Ingunn C. Sandberg et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Monodisperse polystyrene (PS) spheres with controllable size have been synthesized by a straight forward and simple procedure. Te as-synthesized PS spheres have a typical diameter ranging from ∼180 nm to ∼900 nm, where a reduced sphere size is obtained by increasing the polyvinylpyrrolidone (PVP)/styrene weight ratio. Te PS spheres function as sacrifcial templates for the fabrication of hollow silica nanospheres (HSNSs) for thermal insulation applications. By modifying the silica coating process, HSNSs with diferent surface roughness are obtained. All resulting HSNSs show typically a thermal conductivity of about 20mW/(mK), indicating that the surface phonon scattering is probably not signifcant in these HSNS samples. 1. Introduction A substantial amount of the total heat loss of residential buildings passes through the opaque building envelopes, as these components normally account for the largest contact area towards the outside environment. As the demand for energy efciency in building codes becomes increasingly stringent, it is necessary to reduce the unwanted thermal loss of existing and future building envelopes. Tis can either be done by increasing the wall thickness when conven- tional thermal insulation materials such as mineral wool or expanded polystyrene (EPS) is used, or install state-of-the- art superinsulating materials such as aerogel blankets/mats or vacuum insulation panels (VIPs). Increased wall thickness is unwanted as foor space is lost and/or modifcation of the adjoining building elements becomes necessary. Major downsides with state-of-the-art insulation materials of today are their high cost (VIP and aerogel), their fragility, risk of puncturing, no building site adaptation, and ageing issues (VIP). An alternative to meet the demands of the future regard- ing thermal resistance of building envelopes is to develop a new generation of thermal insulation materials. One path which can be followed, is to create nano insulation materials (NIMs), which aim to utilize physical principles such as the Knudsen efect to reduce the thermal conductivity of the material to a minimum [1]. A NIM is a homogeneous, nanostructured material with closed or open nanosized pores where the gas molecules in the pores are more likely to collide with the pore walls rather than with each other, see Figure 1 [2]. Te overall property of NIM can be controlled by tuning, for example, the pore sizes (i.e.,  or  in Figure 1), the chemical composition of the matrix materials, and the packing manner/density. For example, Luo and Ye have reported recently a nanofoam consisting of polymer nanocapsules [3], of which the thermal conductivity is about 0.016–0.023 W/(mK), depending on the sizes of the nanocap- sules. Similar results have also been reported for inor- ganic materials such as hollow silica nanospheres (HSNSs) [2, 4, 5].