Public defence in Engineering Physics, M.Sc. Zhen Lin

Title of the thesis: Synthesis of silica nanofibers for visible light scattering applications

Thesis defender: Zhen Lin
Opponent: Professor Marco Lattuada, University of Fribourg, Switzerland
Custos: Professor Olli Ikkala, Aalto University School of Science

Silica is one of the most abundant and safest materials on Earth. Silica nanoparticles come in many shapes and are useful in a wide range of optical applications. Among them, curly silica nanofibers are especially promising because they scatter visible light strongly, yet their formation process has remained unclear.

This doctoral research explores that these curly nanofibers can be synthesized through a simple water-in-oil emulsion method. The growth mechanism is investigated to explain their morphological features and to guide shape control. Then, these nanofibers can be assembled into highly porous white films that scatter light extremely well, which are brighter than commercial papers or films made from conventional nanoparticles. Moreover, embedding the fibers in polymers produces hazy films, whose haze can be tuned simply by stretching. Finally, for more advanced optical applications, a materials-based two-factor security system is created and demonstrated by integrating fluorescent silica nanofibers.

Overall, this work clarifies how curly silica nanofibers form, how to control their shapes, and how they can be used in advanced optical applications. Looking ahead, the insights and materials developed here may benefit fields such as nanoscience, optics, sensing, anti-counterfeiting, and information protection, offering new possibilities for next-generation optical materials and practical functional device design.

Keywords: silica nanofiber, morphological control, scattering, whiteness, haze

Thesis available for public display 7 days prior to the defence at Aaltodoc.