Method for producing aerogels

Abstract

The invention relates to a method for producing aerogels, in particular silica aerogels, by way of a sol-gel process.

1 . A hydrophobic silica aerogel,
 characterized in that the aerogel has absolute sizes of 0.01 to 10 mm for a particle, has a bulk density of 0.05 to 0.30 g/cm 3  and has a contact angle with water of 130 to 165°.   
     
     
         2 . The hydrophobic silica aerogel according to  claim 1 , characterized in that the aerogel has absolute sizes of 0.1 to 8 mm for a particle. 
     
     
         3 . The hydrophobic silica aerogel according to  claim 1 , characterized in that the aerogel has a bulk density of 0.08 to 0.25 g/cm 3 . 
     
     
         4 . The hydrophobic silica aerogel according to  claim 1 , characterized in that the aerogel has an average pore diameter of less than 300 nm. 
     
     
         5 . The hydrophobic silica aerogel according to  claim 1 , characterized in that the aerogel has a contact angle with water of 140 to 165°. 
     
     
         6 . The hydrophobic silica aerogel according to  claim 1 , characterized in that the aerogel is produced via a sol-gel process. 
     
     
         7 . The hydrophobic silica aerogel according to  claim 6 , characterized in that the sol-gel process involves an in situ hydrophobicization of the gel carried out as it is formed. 
     
     
         8 . The method as claimed in  claim 6 , characterized in that the gel is formed in the presence of at least one hydrophobicizing agent. 
     
     
         9 . The method as claimed in  claim 8 , characterized in that the hydrophocizing agent is selected from the group consisting of phosphonates, sulfonates, substituted amines, silanes, polysiloxanes, siliconates, carboxylic acid derivatives, ethoxylates, polyethers, and mixtures thereof. 
     
     
         10 . The method as claimed in  claim 9 , characterized in that the method utilizes a polysiloxane having reactive functional groups. 
     
     
         11 . The method as claimed in  claim 10 , characterized in that the method utilizes a polysiloxane having reactive functional entities selected from the group consisting of hydroxyl groups, amine groups and carboxyl groups. 
     
     
         12 . The method as claimed in  claim 10 , characterized in that the method utilizes a polysiloxane having a weight-average molar mass M w  in the range from 250 to 50 000 g/mol. 
     
     
         13 . The method as claimed in  claim 9 , characterized in that the method utilizes a silane of general formula I
   R 1   n SiR 2   4-n    (I)
   
       where
 n=1 to 3; 
 R 1 =a substituent selected from the group consisting of C 1 - to C 30 -alkyl and C 6 - to C + -aryl; and 
 R 2 =a substituent selected from the group consisting of a halide, and OX where X=hydrogen, alkyl, aryl, polyether and a carboxylic acid derivative. 
 
     
     
         14 . The method as claimed in  claim 6 , characterized in that it utilizes a siliconate of general formula II
   HO—[Si(R)(OM)—O—] n H   (II)
   
       where
 n=1 to 6; 
 R=a substituent selected from the group consisting of C 1 - to C 10 -alkyl and C 6 - to C 15 -aryl; and 
 M=monovalent metal. 
 
     
     
         15 . The method as claimed  claim 6 , carried out in a medium selected from the group consisting of only one dissolving medium and only one dispersing medium. 
     
     
         16 . The method as claimed in  claim 13 , characterized in that the medium selected is a polar medium. 
     
     
         17 . The method as claimed in  claim 13 , characterized in that the medium selected is a polar protic medium. 
     
     
         18 . The method as claimed in  claim 13 , characterized in that the medium is selected from the group consisting of alcohols, amines and water. 
     
     
         19 . The method as claimed in  claim 13 , characterized in that the medium is selected from the group consisting of a C 1 - to C 8 -alcohols. 
     
     
         20 . The method as claimed in  claim 12 , characterized in that the medium is selected from the group consisting of methanol, ethanol, propanol and water.