|
In this paper, tetraethyl orthosilicate ( TEOS ) as the precursor , a two-step sol - gel process alcohol gel , and then were in a solution of water / ethanol (H 2 O / EtOH) TEOS / EtOH solution in the two-step aging , in isopropanol / trimethylchlorosilane / n- hexane ( IPA / TMCS / n - hexane ) was carried out in a solution of a surface-modified hydrophobic block airgel , and the prepared aerogels performance . Solution in aging caused by the shrinkage of the airgel , the higher the temperature , the greater the shrinkage ; contraction is first increased and then reduced again to increase with time . The alcohol gel in the 30vol% H 2 O / EtOH solution of 60 ° C under 24 hours of aging , aging 16 hours 70 ° C under 70vol% TEOS / EtOH solution in the smallest contraction ; IPA at 60 ° C under / TMCS / n-Hexane solution surface modification total shrinkage of 48 hours will be reduced . Airgel block prepared by the above method has excellent hydrophobic properties , the contact angle close to 180 ° , soaked in water for a week after the mass change was only 7.69% , which decreased from 300 ° C heat-treated airgel hydrophobic properties , and immersed in water began when the mass change dramatically , an increase of nearly 2-fold after 3 days , thereafter quality is almost the same , the heat treatment changed the structure of the pores of the gel , so that it better connectivity , is also conducive to the absorption of water and a hydrophilic group The group has also increased. In addition, small-angle X -ray scattering experiments through the airgel , Porod scattering and fractal structure . Whether or not a member of the DCCA , airgel gas - solid two phases are present obvious interface to meet Porod's law , but after joining the DCCA will affect the size of the Porod constant ; DCCA airgel body fractal dimension has a greater impact , smaller surface fractal dimension ; also after joining the DCCA fractal characteristics range of materials .
|