elib
DLR-Header
DLR-Logo -> http://www.dlr.de
DLR Portal Home | Imprint | Privacy Policy | Contact | Deutsch
Fontsize: [-] Text [+]

Surface Chemistry of Hydrophobic Silica Aerogels

Malfait, Wim J. and Zhao, Shanyu and Verel, Rene and Iswar, Subramaniam and Rentsch, Daniel and Fener, Resul and Zhang, Yucheng and Milow, Barbara and Koebel, Matthias M. (2015) Surface Chemistry of Hydrophobic Silica Aerogels. Chemistry of Materials, 27 (19), pp. 6737-6745. ACS Publications. DOI: 10.1021/acs.chemmater.5b02801 ISSN 0897-4756

Full text not available from this repository.

Official URL: http://dx.doi.org/10.1021/acs.chemmater.5b02801

Abstract

The properties of silica aerogels, and the ability to prepare them by ambient pressure drying, hinge on their chemical surface modification. Until now, quantitative analysis of the surface chemistry has not been possible by state-of-theart analytical methods. Here, we determine the surface chemistry of six archetypal, ambient pressure dried, hydrophobic silica aerogels and open-porous foams with quantitative 1H, 13C, and 29Si and 1H-29Si heteronuclear solid-state NMR spectroscopy. The quality of the external calibration, the validation by elemental analysis, and the consistency among the 1H, 13C, and 29Si MAS NMR data enable us to robustly quantify the surface chemistry of these classical silica materials. Four aerogels were derived from tetraethoxysilane (TEOS), polyethoxydisiloxane (PEDS), or waterglass precursors and hydrophobized with trimethylsilyl (TMS) groups through immersion in hexamethyldisilazane (HMDZ) in heptane, trimethylchlorosilane (TMCS) in heptane, or hexamethyldisiloxane (HMDSO) in ethanol. The resulting aerogels display remarkably similar chemistries despite their very different precursors (alkoxides, waterglass), hydrophobization agents (HMDZ, TMCS, HMDSO), and gelation and hydrophobization solvents (water, ethanol, heptane). The TMS content is nearly the same (22-27 wt %), the ethoxy content is low (<4 wt %), and the silica speciation displays a narrow range for all four aerogels. The 1H-29Si heteronuclear correlation spectra provide unambiguous evidence for the grafting of the TMS groups on the silica surfaces. Remarkably, the NMR data enable the prediction of the silica particle size to within 1 to 2 nm of that derived by TEM analysis. Two additional, inherently hydrophobic, ambient pressure dried, openporous silica foams were synthesized from methyltrimethoxysilane (MTMS) and from a MTMS-dimethyldimethoxysilane (DMDMS) mixture. The reduction in the number of bridging oxygens per Si atom, from 3.76 to 3.90 for TEOS, PEDS, or waterglass based aerogels, to 2.86 for the MTMS based open-porous foam, and to 2.48 for the MTMS-DMDMS derived openporous foam, results in a brittle-to-superflexible transition. Our results highlight the importance of the chemical treatment of the wet gels (hydrophobization and solvent exchange) on the final surface chemistry of silica aerogels.

Item URL in elib:https://elib.dlr.de/120369/
Document Type:Article
Title:Surface Chemistry of Hydrophobic Silica Aerogels
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Malfait, Wim J.UNSPECIFIEDUNSPECIFIED
Zhao, ShanyuUNSPECIFIEDUNSPECIFIED
Verel, ReneUNSPECIFIEDUNSPECIFIED
Iswar, SubramaniamUNSPECIFIEDUNSPECIFIED
Rentsch, DanielUNSPECIFIEDUNSPECIFIED
Fener, ResulUNSPECIFIEDUNSPECIFIED
Zhang, YuchengUNSPECIFIEDUNSPECIFIED
Milow, BarbaraUNSPECIFIEDhttps://orcid.org/0000-0002-6350-7728
Koebel, Matthias M.UNSPECIFIEDUNSPECIFIED
Date:4 September 2015
Journal or Publication Title:Chemistry of Materials
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:27
DOI :10.1021/acs.chemmater.5b02801
Page Range:pp. 6737-6745
Publisher:ACS Publications
ISSN:0897-4756
Status:Published
Keywords:Silica Aerogel solid-state NMR spectroscopy chemical surface modification Flexible Silica Aerogel
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Transport
HGF - Program Themes:Terrestrial Vehicles (old)
DLR - Research area:Transport
DLR - Program:V BF - Bodengebundene Fahrzeuge
DLR - Research theme (Project):V - NGC Fahrzeugstruktur (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Materials Research > Aerogele
Deposited By: Fener, Resul
Deposited On:20 Jun 2018 10:41
Last Modified:06 Sep 2019 15:19

Repository Staff Only: item control page

Browse
Search
Help & Contact
Information
electronic library is running on EPrints 3.3.12
Copyright © 2008-2017 German Aerospace Center (DLR). All rights reserved.