Hong LI thesis defense on December 06th, 2022

15 November 2022
Hong LI completed his thesis at Cermav under the supervision of Redouane Borsali, CNRS Research Director. it is entitled "Self-assembly of carbohydrate-based brush-like block copolymers: colored biomaterials and photonic crystals". Click on the title for more information.

Abstract:

« Carbohydrates constitute a sustainable source of materials that have attracted a growing interest due to their “green” aspects, biocompatibility, biodegradability, and bio-recognition properties. Their industrial applications at the macroscopic scale are offering new solutions for biobased materials and they find applications in different sectors such as cosmetics, health, packaging, or microelectronics. Recently, a novel class of nanostructured systems obtained from the self-assembly of carbohydrate-based brush block copolymers (BRs) has been developed to achieve periodic organizations (a few hundred nm in domain spacings) resulting in materials exhibiting structural colors. They are the so-called one‐dimensional photonic crystals 1D-PCs, or Bragg stacks, that consist of alternating layers of high‐and low‐refractive index materials. At the specific wavelength for which the optical periodicity of the material matches the path length of a photon, a photonic band gap is formed, which prevents this frequency of light from propagating. At this wavelength, all reflected signals are in phase and add constructively, generating a reflected signal. Consequently, an iridescence can be observed in a similar way to the natural structurally-colored tissues, for instance, natural opals, the wings of some butterflies, the cuticles of beetles, and a variety of other animal and plant species. Based on the above consideration, my Ph.D. project was to explore the properties of colored materials made from the self-assemblies of a series of brush-like block copolymers made with polystyrene (PS) and maltoheptaose (MH) as side chains attached to a polynorbornene backbone. Those systems were synthesized by the “self-assembly glycopolymer group of CERMAV” with different molecular weights (MW) and targeting lamellar phases and therefore colored materials. The results that are presented in the thesis describe those results, namely, full-color display of the one-dimensional photonic crystals (1D-PCs) fabricated from the self-assembly of brush-like glycopolymers and their blends can be obtained exhibiting colorless, blue, green, orange to grey covering the entire UV-vis. spectrum range. Impressively, the optical appearance of the thin films can be quickly (in a controlled and reproducible manner) changed from colorless to blue, green, yellow, and orange within a few seconds by simply controlling the solvent atmosphere. «