Organically modified silica aerogel with different functional silylating agents and effect on their physico-chemical properties Satish.A. Mahadik a, ⁎ ,1 , F. Pedraza a , V.G. Parale b,1 , Hyung-Ho Park b a Université de La Rochelle, Laboratoire des Sciences de L'Ingénieur pour l'Environnement (LaSIE, FRE-CNRS3474), Avenue Michel Crépeau, 17042 La Rochelle cedex 01, France b Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, South Korea abstract article info Article history: Received 8 June 2016 Received in revised form 14 August 2016 Accepted 22 August 2016 Available online xxxx In this paper, we have successfully focused on a hydrophobic silica aerogels synthesis by the ambient drying of silica gels and the silylation with mono-, di-, and tri-functional agents was studied to improve physico-chemical properties of the aerogels. Silylated silica aerogels with water contact angles 161 ± 2°, 152 ± 3°, 147 ± 3° were obtained using trimethylchlorosilane, dimethyldichlorosilane, and methyltrimethoxysilane as a mono-, di- and tri-functional silylation reagents, respectively. The prepared mono-functional silylated silica aerogels exhibited relatively high thermal stability, low thermal conductivity, transparency, high porosity, and enhanced superhydrophobicity with low surface free energy making them suitable as multifunctional for many domestic and industrial applications. Our mono-functional silylated silica aerogels showed superior physico-chemical properties compared with di- and tri-functional silylated silica aerogels. © 2016 Elsevier B.V. All rights reserved. Keywords: Sol-gel process Surface silylation Aerogel Superhydrophobic Ambient drying method 1. Introduction The silica aerogel has a porous network with 95–98% air and 5–2% solid material. It formed when trapped solvent within a gel is replaced by air, in such a way that solid particle networks within the gel do not allow to collapse during drying. Popular aerogel materials are organical- ly modified silica (OMROSIL). However, aerogels were mostly prepared from transition metals, metal alkoxide, polymers, CNT, carbide, polyim- ide (PI), resorcinol-formaldehyde (RF), poly vinyl alcohol (PVA), graphene and montmorillonite clay/polymer composites [1]. Aerogel was first find out in the early 1930s by Kistler while studying gels with a low content of solids [2]. The development of high performance, superhydrophobic, environmentally stable, porous, transparent, ther- mally stable OMROSIL aerogels can provide new applications in insula- tor, water filter, adsorbents for organic matters, and oil-spill problems [3–6]. Inorganic aerogels are naturally not suited to meet these require- ments when used alone; however, inorganic materials are often absor- bent to network collapse during water molecules trapping. Achieving highly porous 3D structured ORMOSIL aerogels in which surface components contribute to overall functionality is very important for enhancing aerogel performance by replacement of surface hydroxyl groups with functional groups in some significant way. For example, Gao et al. [7] demonstrated that sodium silicate based aerogels enhance thermal stability, porosity, and surface area by silylation process. More recently, Cheng et al. [8] have demonstrated that utilizing sodium alginate as the precursor and surface modification with a cold plasma treatment produce hydrophobic aerogels with low density, low volume shrinkage and enhanced mechanical strength of the network. However, the use of TEOS based aerogels have been restricted because of their hygroscopic nature, high shrinkage, low porosity, low thermal stability, and poor me- chanical properties. It has been demonstrated that by surface modifica- tion of silica aerogels through low energy alkyl groups on the surface with a different silylating agent improves the strength of native or un- modified aerogels [9,10]. In fact, some surface modification processes are able to be enhanced properties, but such methods often follow costly and complicated synthesis processes [11]. It is thus necessary to develop simple, cost effective, and more efficient surface silylation process for sig- nificant enhancement in physical and chemical properties of silica aerogels. To the best of our knowledge, studies of surface modification ef- fect on silica aerogels have exclusively focused on physical and chemical properties [12–16]; but functionality of silylating agents on their physical and chemical properties have not been clearly explored. In this work, we have developed a simple approach to improve physico-chemical properties of silica aerogels, and exploit the role of functional methyl groups to enhance wettability, surface nature, ther- mal degradation, optical transparency, and porosity. In this scheme, the fragility of silica aerogels has been successfully reduced by slow aging process. Furthermore, comparative study of silica aerogel silylated with mono-, di-, and tri-functional silylating agents on their physico- chemical properties, and most interesting effect of surface free energy (SFE) and their components on improved physico-chemical properties were reported. Journal of Non-Crystalline Solids 453 (2016) 164–171 ⁎ Corresponding author. E-mail address: superhydrophobicmaterial2100@gmail.com (S.A. Mahadik). 1 Department of Physics, Shivaji University, Kolhapur 416,004, India. http://dx.doi.org/10.1016/j.jnoncrysol.2016.08.035 0022-3093/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol