Development of mullite-SiC nanocomposites by pyrolysis of filled polymethylsiloxane gels

Comparative characterization of polymethylsiloxane hydrogel and silylated fumed silica and silica gel

“…Polymethylsiloxane (PMS) materials have drawn considerable fundamental and technological interest because of their applications as components of nanocomposites [1][2][3], copolymers for synthesis of ion-conducting polymeric materials [4][5][6][7][8][9][10][11]. PMS is used in chromatography [12][13][14], e.g., for coating of a silica surface [15], and in medicine as a component of medicinal preparations (e.g., Cleocin, Universal Washaid, USA), implants, adjuvant Capsil (Aquatrols, USA; Scotts, USA), a vaccine adjuvant [16], etc.…”

“…The properties of PMS materials in different forms (hydrogels, xerogels, dry powders, etc.) depend on the cross-linking degree, which is maximal in dry xerogel (hydrophobic), in which all the Si atoms are bonded by three siloxane bonds (≡Si-O) 3 SiCH 3 , and on the hydration degree. Heating/drying of PMS hydrogels can lead to loss of the hydrophilic properties because of enhancement of crosslinking by the Si-O-Si bonds on condensation of hydrophilic silanols [28].…”

“…The hydrophilic-hydrophobic properties of the PMS hydrogel and xerogel surfaces can be close to those of partially and completely silylated fumed silica, respectively [31][32][33][34][35][36] because these materials have close specific surface area (200-300 m 2 /g) and the same surface functionalities (≡SiCH 3 , ≡SiOH, and ≡Si-O-Si≡) and are characterized by textural porosity (i.e., voids between particles nondensely packed in secondary structures). The hydrophobic functionalities (trimethylsilyl, TMS, or dimethylsilyl, DMS) on a silylated silica surface inhibit formation of a continuous layer of adsorbed water [33].…”

“…A similar effect can be expected for PMS hydrogel and suspension. However, the differences in the structure of primary particles of PMS [17,18,28] and silylated fumed silica [31,37], as well as in the composition of surface sites ((≡Si-O) 3 SiCH 3 and (≡Si-O) 2 Si(OH)CH 3 for PMS and ≡Si-OSi(CH 3 ) 3 and (≡Si-O) 2 Si(CH 3 ) 2 for TMSand DMS-nanosilica, respectively), can lead to certain differences in the behavior of bound water, as well as in the physicochemical characteristics of concentrated and diluted aqueous suspensions, hydrogels, and dry powders with these materials. Wetting/drying of nanosilica, which is composed of rigid primary particles forming nonrigid aggregates and agglomerates of aggregates, changes both structural and morphological characteristics of the powder [37,38].…”

Low dielectric constant porous BN/SiCO made by pyrolysis of filled gels

“…All the investigated samples showed a uniform distribution of the filler particles in the hybrid gel matrix in agreement with the earlier results from our laboratory with other fillers. 10,11 To further rule out the possibility of sedimentation of the filler before gelation, the densities of the discs obtained from the bottom and from the top of the original gel rods were measured and compared. The same value was found showing that the distribution of the filler particles along the height of the samples was homogeneous.…”