Why does it necessary to use sol gel step after gelatin step when preparing emulsion ?

2.2.2. Preparation of sol-gel matrix
Tetraethoxysilane (TEOS) were used as precursors for the sol-gel glass. TEOS (7 ml), 3.0
ml of distilled water and 0.1 ml of 0.04 M HC1 were mixed together and sonicated for 20
min. The resulting product was diluted with an equal volume of distilled water. The resulting
mixture (0.5 ml) was mixed with 0.25 ml sodium borate buffer solution (pH 9) and (0.1 ml,
0.2 ml) bR solution to create a film-forming solution. Triethanolamine (TEA) was chosen as
sensitizing additives. The concentration of chemical additives was in the range of 0.01–0.4
M. For the preparation of chemically modified films, bR solution was mixed with TEA,
before mixing with the sol mixture, and afterwards 0.02 ml of the bR-chemical additives
mixture was added to 0.12 ml of the sol mixture [7,8].