The protection of ultraviolet sensitive molecules through polymeric encapsulation and proximity

Exposure to ultraviolet (UV) radiation causes many materials to undergo chemical reactions leading to degradation. While the negative impact of UV radiation on human skin remains in the spotlight, many commercial products have also proven to be photosensitive, leading to the desire to protect molecules from photodegradation. The most common method of UV protection is to add protective materials such as UV absorbers or antioxidants to a formulation. Encapsulation of a photosensitive molecule is also a proven method of photoprotection. In this work, novel UV protective systems were created by encapsulating a photosensitive molecule, beta-carotene, in various polymer particle geometries with protectant molecules. The goal of this dissertation was to use such systems to examine the effect of proximity between photosensitive and UV protecting molecules.;Uniform particles were initially created in order to quantify the effect of encapsulation and to study the result of encapsulating beta-carotene with UV absorbers (oxybenzone, avobenzone, and octyl-4-methoxycinnamate (OMC)) and an antioxidant (vitamin E) in a polymer matrix. Particles were synthesized by the solvent evaporation method. UV protection was found to be dependent on the protectant added and the concentration of the protectant, except in the case of OMC. The most effective particle formulation contained both oxybenzone and vitamin E.;Experimental designs were created to discover the proper composition and procedure for synthesizing various core-shell particle geometries. These core-shell particles were used to study the effect of proximity on UV protection. The core-shell particles themselves offered more protection than the uniform particles, and in most cases the addition of a protectant increased UV protection. Splitting the protectant concentration between the core and shell did not have a significant effect in most cases. The optimal formulation consisted of a suspension of polymer particles containing vitamin E and beta-carotene in the particle core and a UV absorber in the particle shell. Other particle characteristics were studied, including particle size and shell thickness, and were found to have minimal effect. The core-shell particles provide a new protective system for photosensitive molecules as well as a method of studying the effect of proximity on UV protection.