Abstract
Aging in water of a TiO 2-based nanocomposite used in sunscreen cosmetics has been studied as a function of light and time. It consisted initially in a TiO 2 core, coated with Al(OH) 3 and polydimethylsiloxane (PDMS) layers. Size measurement, coating alteration, and surface charge were followed by laser diffraction, TEM/EDS, ICP-AES and electrophoretic mobility measurement. The nanocomposite rapidly underwent progressive dispersion in the aqueous phase, enabled by the dissolution of the PDMS layer. A stable suspension of colloidal byproducts from 50 to 700 nm in size was formed. Their positively charged Al(OH) 3 surface was evidenced with an isoelectric point around 7–8, controlling the dispersion stability. The critical coagulation concentrations measured with NaCl and CaCl 2 was 2 × 10 −2 and 8 × 10 −3 M respectively. The presence of natural organic matter affected the colloidal stability according to the NOM/byproduct ratio. A 2 wt% ratio favored bridging flocculation, whereas a 20 wt% ratio induced sterical stabilization.
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