Journal of Microscopy, Vol. 00, Issue 0 2017, pp. 1–11 doi: 10.1111/jmi.12603 Received 2 November 2015; accepted 22 June 2017 Study of the surfactant role in latex–aerogel systems by scanning transmission electron microscopy on aqueous suspensions A. PERRET ∗ , G. FORAY ∗ , K. MASENELLI-VARLOT ∗ , E. MAIRE ∗ & B. YRIEIX † ∗ Univ Lyon, INSA-Lyon, UCBL, MATEIS, CNRS UMR5510, F-69621, Villeurbanne, France †EDF R&D, MMC, Avenue des Renardi` eres – Ecuelles -77818 MORET SUR LOING, Cedex, France Key words. ESEM, image analysis, in situ, liquid, STEM. Summary For insulation applications, boards thinner than 2 cm are un- der design with specific thermal conductivities lower than 15 mW m -1 K -1 . This requires binding slightly hydropho- bic aerogels which are highly nanoporous granular materials. To reach this step and ensure insulation board durability at the building scale, it is compulsory to design, characterise and analyse the microstructure at the nanoscale. It is indeed nec- essary to understand how the solid material is formed from a liquid suspension. This issue is addressed in this paper through wet-STEM experiments carried out in an Environmental Scan- ning Electron Microscope (ESEM). Latex–surfactant binary blends and latex–surfactant–aerogel ternary systems are stud- ied, with two different surfactants of very different chemical structures. Image analysis is used to distinguish the different components and get quantitative morphological parameters which describe the sample architecture. The evolution of such morphological parameters during water evaporation permits a good understanding of the role of the surfactant. Introduction The Kyoto protocol commits State Parties to reduce green- house gases emissions, as they play a major role on global warming. This implies to develop renewable energies but also to reduce the energy demand. The building sector accounts for nearly 40% of the global energy use, and was up to recent years one of the least optimised sectors in terms of energy sav- ings. Super insulation materials defined by conductivities in any case lower than 15 mW m -1 K -1 are about to offer the op- portunity of a tremendous energy saving. Physically, the two steps to reach such a low conductivity are first to keep the gas in molecular containment (state said of Knudsen) (Friecke & Tillotson, 1997), so in mesoporosities in the 20–50 nm range, and second to deal with very low densities. Correspondence to: Karine Masenelli-Varlot, Universit´ e de Lyon, INSA-Lyon, UCBL, MATEIS, CNRS UMR5510, F-69621, France. Tel: +33472437103; fax: +33472438830; e-mail: karine.masenelli-varlot@insa-lyon.fr Silica aerogels exhibit such interesting features and can now be synthesised by nonsupercritical drying thanks to inten- sive research and development (Mielke & Von Dungen, 1997; Field & Scheidemantel, 2004; Koebel et al., 2012; Yrieix et al., 2012). The silica aerogels dried at atmospheric pressure come out in the form of a granular material such as sand or cal- cium carbonate commonly used in the concrete industry. Each grain (10 μm to 5 mm) is composed of a silica network, in turn composed of a hydrophobised silica skeleton (3–7 nm). Such aerogels with a 90 vol% mesoporosity are characterised by conductivities around 15 mW m -1 K -1 (Yrieix et al., 2012), much less than static dry air. In order to design insulation products with aerogels inside, one has to ensure simultane- ously some thermal properties and other functional properties (mechanical, handling, transportation etc.). Several possible products include (i) filling some of the cavities with aerogels (i.e. glass shielding), (ii) trapping the aerogels in a loosely connected fibre network or (iii) connecting aerogel particles with a binder. In this last case, whatever the organic or mineral binder used, its own conductivity is tremendous (>1000 mW m -1 K -1 ) compared to the one of the aerogel. Thus the scientific issues are the architecture design and then the control of the 3D network formed by each phase, namely (i) the aerogel, (ii) the binder and (iii) the porosities. The industrial elaboration processes of most aerogel prod- ucts for superinsulation applications imply aqueous steps (Mielke & Von Dungen, 1997; Field et al., 2004; Yrieix et al., 2012). Indeed, binders are either hydraulic (plaster or ce- ment) or organic such as latex particles in suspension in water. Thus, surfactants have to be used to ensure a proper packing and binding of the hydrophobic aerogel particles. The surfac- tant/binder and surfactant/aerogel particle interactions are expected to play a major role on composite material final ar- chitecture due to the hydrophobic/hydrophilic nature of com- pounds and to the antagonism in insulation material proper- ties compacity and low skeleton connectivity. Measuring the early surfactant distribution in the wet state and how it evolves from the very beginning (wet state or dense suspension) up to the end (dry solid material) is of great concern in composite C  2017 The Authors Journal of Microscopy C  2017 Royal Microscopical Society