The formation and destabilization of viscoelastic filaments are of importance in many industrial and biological processes. Filament instabilities have been observed for viscoelastic fluids but recently also for soft elastic solids. In this work, we address the central question of how to connect the dynamical behavior of viscoelastic liquids to that of soft elastic solids. We take advantage of a biopolymer material whose viscoelastic properties can be tuned over a very large range by its pH, and study the destabilization and ensuing instabilities in uniaxial extensional deformation. In agreement with very recent theory, we find that the interface shapes dictated by the instabilities converge to an identical similarity solution for low-viscosity viscoelastic fluids and highly elastic gels. We thereby bridge the gap between very fluid and strongly elastic materials. In addition, we provide direct evidence that at late times an additional filament instability occurs due to a dynamical phase separation.

Optically active nanoparticles (NPs) are potential building blocks for bottom‐up functional technology in applications such as displays, sensors, and sunscreens. For sunscreens in particular, NPs can be used as delivery systems for organic UV filters in order to minimise skin exposure to these molecules. Here, we investigate the synthesis of size‐tunable ethyl cellulose NPs (ECNPs) and their application as carriers for multiple organic UV filters. We prepared ECNPs with sizes of 50 to 165 nm via an antisolvent precipitation technique and investigate the incorporation of three commonplace organic UV filters – oxybenzone, avobenzone, and octinoxate – into the ECNPs. We found the particle loading varied greatly with each UV filter. Photodegradation of the UV filters remained unchanged upon incorporation into ECNPs and was not affected by co‐encapsulating the antioxidant α‐tocopherol. These results can significantly advance the development of environmentally friendly functionalized nanoparticles and UV‐protective coatings.

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UV-absorbing nanoparticles are prepared with an entirely biobased composition, as a novel environmentally-friendly photoprotection technology.