Sunscreen, transparent

Sunscreens are transparent organic substances that penetrate into the skin and absorb ultraviolet radiation. Common classes of sunscreens include benzophe-nones, PABA derivatives, cinnamates, salicylates, and dibenzoylmethanesJ3 Ben-zophenones have a primary protective range in the UVA region and include oxy-benzone (Fig. 12.9.1), 270-350 nm dioxybenzone (Fig. 12.9.2), 206-380 nm ... 

Manufacturers have already begun to take advantage of some of these nanoparticle properties. Sunscreens, which protect users from burns by absorbing or deflecting harmful rays, are often made from chemicals such as titanium dioxide or zinc oxide that are particularly effective. These sunscreens often leave a whitish residue—which used to be common on the nose of a pool or beach lifeguard—but when companies embedded nanoparticles of titanium dioxide or zinc oxide instead of bulkier particles, the creams become transparent yet maintained or even increased their effectiveness. With no embarrassing residue, these sunscreens have become popular. 

Particles are known to scatter light as well as absorb it and this produces the white or pale appearance of fine powders. The even smaller nano-sized particles, however, are transparent because the scattering efficiency is reduced. This effect has led to the use of nanoparticles in sunscreens and cosmetics. These will still absorb ultraviolet light but will scatter less visible light. 

One of the most famous nanoparticles is the buckyball, a molecule made up of 60 carbon atoms arranged in a soccer-ball shape. Some skin creams now include buckyball molecules. Another widely used nanoparticle is zinc oxide. For years, swimmers applied zinc oxide as a thick sunscreen paste, but the new nano-sized version of the compound is so small that it looks transparent when slathered on as sunblock. The makers of these products say the nanoparticles can reflect light and fight off damage to skin cells better than normal-sized particles. A few cosmetics manufacturers are experimenting with nanoparticles in eye shadow and lipsticks to see if the tiny molecules can produce different colors or new visual effects like iridescence, where colors seem to constantly change. 

Nanostructured Ti02 particles (particle size 5-50 nm) are used as sunscreens in the cosmetic industry. Nanosized Ti02 is an effective absorber of UV-B (280-320 nm) and UV-A radiation (320-400 nm). Because ofits small particle size, itappears transparent [2.70]. Intensive research work is in progress worldwide aimed at utilizing the photoactivity of Ti02. Titanium dioxide catalyzes the decomposition of organic compounds in wastewater [2.71]. 

The most significant property of transparent zinc oxide is again the absorption of UV radiation. The main application of zinc oxide is in sunscreens. The usual industrial manufacturing process is either direct combustion of high-purity zinc metal in a plasma with oxygen [5.196] according to the reaction ... 

Polymer supported 2-hydroxybenzophenones and 2-(2-hydroxyphenyl)-2ff-benzotriazoles have useful properties in articles used under high exposure of LTV U t, examples are transparent durable acrylic films, outdoor paints, transparent coatings for optical lenses, transparent protective layers of silver mirrors in solar concentrators or films used in encapsulation systems for photovoltaic modides in solar conversion devices [26, 54, 82, 92, 293]. Polymeric LS can also be used in cosmetics as sunscreening components of emulsions and ointments for protection of sensitive human skin against sunburn [324] or in medical aids, as nonleachable U V absorbing components of silicone rubber for vision aids (contact lenses) [99]. 

Very rarely has a problem of efficacy or safety been observed when a manufacturer developed a product containing certain sunscreens packaged in a clear transparent pack because such products are normally stopped in the development phase, before they reach the marketplace. In those instances where it has occurred, a discoloration was noted adjacent to the walls of the package. This poses an esthetic problem, generally, analytically not detectable or affecting either product efficacy or safety (7). 

Tm). The high thermal neutron absorption cross-sections and high melting points of various lanthanides (Sm, Eu, Dy, Gd) are two properties that make them ideal for use in nuclear reactor control rod applications. Cerium dioxide has been developed into a sunscreen that has higher transparency and higher ultraviolet blocking proper-... 

Sunscreens and Cosmetics Sunscreens help to protect human skin in a formulation to spread smoothly. It is capable of absorbing and reflecting UV rays and transparent to visible light. The use of nanoparticles in cosmetics has raised a number of concerns about their safety and toxicity. 

Figure 18-7 Absorption spectrum of typical sunscreen lotion shows absorbance versus wavelength in the ultraviolet region. Sunscreen was thinly coated onto a transparent window to make this measurement. [From D. W. DanielJ. Chem. Ed, 1994,...

Common white pigment in paints, toothpaste, sunscreens and foodstuffs. Filters both UV-A and UV>B and used as nanoparticles in sunscreen formulations to increase transparency on the skin. It is the most widely studied semiconductor for DSC applications. Nano-particulate titania has a very high surfk e area which allovi significant e soqdion to ate orb visible li t and to inject electixHis... 

Due to their transparency, microemulsions represent a very attractive type of cosmetic formulation, e.g. hair styling gels, perfume gels, bath preparations, sunscreen gels, etc. Their main problem is the relatively high surfactant concentration required for their formulation compared with nano- and macroemulsions. Proper choice of the surfactant system used for their formulation is required to avoid any side-effects, e.g. skin irritation. To arrive at the optimum composition of microemulsion systems, one needs to the phase diagram for these multicomponent formulations. 

Ceria also exhibits optical properties suitable for potential applications. Ceria has characteristics ideal for use as a broad-spectrum inorganic sunscreen in personal care products it is quite transparent to visible light, but has excellent ultraviolet absorption ability. Thin ftims of ceria have a high refractive index n = 2.05), and dc... 

A., Villaluenga, 1., Berriozabal, G., de Miguel, Y.R., and Bergstrom, L. (2013) Dispersion and surface functionalization of oxide nanoparticles for transparent photocatalytic and UV-protecting coatings and sunscreens. Sci Technol, Adv. Mater., 14, 2. 

Uses Emollient, solubilizer aux. emulsifier in micro-emulsion systems used in the prep, of clear, aq. emollient systems for cl. sunscreen preps, transparent skin care lotions and creams, and trasparent hair care prods. 

The transparent visual aspect of nano-emulsions with droplet sizes below 200 nm makes them especially attractive for application in cosmetics. Apart from the appearance, similar to that of microemulsions, other advantages of nano-emulsions for cosmetic applications are their kinetic stability, a droplet size that can be controlled, and the possibility to achieve improved active delivery. For all these reasons, nano-emulsions have attracted increasing interest in the cosmetic field, as reflected by the papers [8,10,106] and numerous patents [19-21,23,24,27,107-111] that have appeared in the last few years. Oil-in-water nano-emulsions with a droplet size lower than 100 nm have been described in patents as hair- and skin-care [19,21,23,24,107-109], makeup [110], and sunscreen [20,111] formulations. 

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