Silica-Based Organic/Inorganic Hybrid Treatments as Anti-Mosquito Textile Finishing

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Figure 14.3: Influence of pH on the structure and growth of gel.

Hydrolysis and condensation rates, and therefore the structure of silica gels, can also

be influenced by solvents due to their interaction with the silicon center. Indeed, many

silicon alkoxides are insoluble in water and the alkoxide ratio/ water is often adjusted to

limit hydrolysis. In addition, the molecular chemistry of silicon is much more diverse than

simple tetra-alkoxides, and many compounds exist with the general structure SiR(OR)3,

SiR2(OR)2 or SiR3OR. Finally, the presence of chelating agents can reduce hydrolysis and

condensation rates.

Sol-gel coatings have high mechanical, chemical and thermal stability, controllable

porosity and they do not show absorbance in the visible range. Thanks to these features,

it is possible to develop innovative properties in the sol-gel matrices, mixing additives up

to a level of about 30% of precursors (Böttcher et al. 1999). The so obtained solutions,

after deposition, gelification and drying, form stable film onto coated materials. The re-

lease of encapsulated liquids from the silica film can be controlled by adjusting the sil-

ica/agent mass ratio, chemically modifying the silica matrix, adding soluble or swelling

pore-forming substances and managing the preparation conditions. Generally, the use of

encapsulated products offers greater convenience, better storage stability and controlled

release of encapsulated organic substances. In the last years, investigations have been con-

ducted on the immobilization and controlled release of different bioactive liquids through

a modified silica coating to evaluate possible applications for functionalized fabrics (Haufe

et al. 2008). The study was mainly focused on antimicrobial and anti-allergic effects due

to natural oils and treatment of diseased respiratory tract by immobilized high volatility

biological agents. A single-phase hybrid network combining organic and inorganic compo-

nents, with molecular-scale interactions, then provides a new path to customize the desired

thin-film coating properties for different applications (Amiri and Rahimi 2016).

14.3

ANTI-MOSQUITO FINISHING BY SOL-GEL TECHNIQUE

The development of innovative technologies can introduce new functionalities to tex-

tiles without modifying their appearance, thus introducing barrier properties for many

application fields such as antibacterial and mosquito-repellent textiles. In particular,