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

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Table 14.1: Main micro/nanoencapsulation techniques

Methods

Micro/nanoencapsulation techniques

Chemical

Interfacial polymerization, In situ polymerization, polycondensation,

polymer-polymer incompatibility, emulsion hardening, mini emulsion, liposome formation

Physico-chemical

Coacervation, polyelectrolyte multilayer,

supercritical fluids, sol-gel, solvent evaporation

Phisico-mechanical

Spray-cooling/chilling, extrusion, air-suspension coating,

fluidized-bed technology, microwave processing,

ultrasonic atomizer, electrospray

volved in the immobilization of bio-based repellents (e.g. immortelle oil) that, in a previous

study, showed good to excellent anti-mosquito repellent efficacy (Grancaric et al. 2020).

14.2

ENCAPSULATION TECHNIQUES AND SOL-GEL CHEMISTRY

Encapsulation techniques are generally divided into chemical and physical meth-

ods (which are also divided into physical-chemical and physical-mechanical processes)

(Ghayempour and Montazer 2016) and are summarized in Table 14.1 some are applied

with a gaseous and others with a liquid suspension medium.

Among the encapsulation methods listed in the table, the sol-gel process is considered

the most feasible method to prepare chemically homogeneous coatings that are able to open

promising applications in many areas such as optics, electronics, mechanics, energy, envi-

ronment, biology, solar and fuel cells, catalysts, sensors and functional intelligent coatings

such as antimicrobial coatings (Amiri and Rahimi 2016).

Sol-gel chemistry is based on hydrolysis and condensation of metal alkoxides or be-

tween hydrated metal species. Among many examples of alkoxide-based sol–gel chem-

istry, a large number of precursors involves early transition group metals (e.g. Ti, Zr) or

early p-block elements (e.g. Al, Si) (Danks et al. 2016). Metal alkoxides can be prepared

in different ways depending on the metal’s nature, such as the reaction of metal chlorides

with alcohols or the anodic dissolution of the metal into alcohol with an electroconductive

additive. The suitability of alkoxides for sol-gel chemistry and the outcome of the reactions

depend on several factors, such as the differences in electronegativity between oxygen and

metal, which affect the ionic character of the M-O bond, as well as the ability of dona-

tion/withdrawal of electrons of the alkyl/aryl chain on the stability of the alkoxyl groups.

These factors ultimately direct the gel structure by influencing the relative rates of hydrol-

ysis and condensation as well as the degree of oligomerization or polymerization.

Finally, viscosity and volatility, as physical factors, can influence the suitability of

alkoxides for sol-gel chemistry, along with process parameters such as the ratio of wa-

ter to alkoxide and the presence or concentration of catalysts, since silica sol-gel chemistry

is typically driven by acidic or basic catalysts that influence the structure of the resulting

gel. Hydrolysis leads to the replacement of an alkoxyl group by a hydroxyl group with a