Structural Similarity-Induced Inter-Component Interaction in Silicone Polymer-Based Composite Sunscreen Film for Enhanced UV Protection

Film-forming agents are key ingredients in achieving long-lasting and effective sun protection by sunscreens. However, studies on the synergistic effects of film-forming agents with different properties as well as the interaction between film-forming agents and powders are scarce, restricting the development of sunscreens with strong ultraviolet (UV)-shielding effects. Herein, we innovatively adopt polysiloxane-15 as the soft film, trimethylsiloxysilicate as the hard film, and vinyl dimethicone/methicone silsesquioxane crosspolymer as the functional powder to construct a co-assembled sunscreen film, and we investigate the property-enhancing effects of the sunscreen film as well as the interaction between the silicone polymer-based film-forming agents and functional powder therein. The results show that structural similarity is essential to generating film-forming agent-powder interactions, which primarily enhance the Si-O bond binding energy, thereby enhancing the lasting protection effect of sunscreens. In addition, the inter-component interaction of the co-assembled sunscreen film inhibits the agglomeration of sunscreen paste to facilitate the formation of a homogeneous film, endowing the sunscreen with excellent UV protection abilities, with the sun protection factor (SPF) and protection factor of UVA (PFA) values increased by 61.58 and 43.84%, respectively. This work offers novel insights into the optimization of film-forming agent properties and the development of durable and efficient sunscreens.