Structure-Property Relationships of Electrospun CdS Quantum Dot Fibers with Mechanically Modulated Reversible Chirality

Over the last three decades, electrospinning has gained increasing interest as a synthesis technique for micro and nano fibers due to its tunability and versatility. For the first time, electrospinning induced self-assembly of Cadmium Sulfide (CdS) magic sized clusters (MSCs) and their resulting chiroptical properties are discussed. The MSCs assemble into hexagonal mesophase during synthesis and the higher-level structures arise during the evaporation process. Through electrospinning, multiple hexagonal mesophase bundles are postulated to form twisted nanofibrils. These nanofibrils collectively constitute the microfiber as the result of self-assembly. Using Field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) the morphology of the microfibers and the arrangement of the observed fibrillar structures are studied. The chiroptical properties of the fiber mats are extensively studied using Circular dichroism (CD) spectroscopy.<br/><br/>We improve the uniaxial fiber orientation, thereby synthesizing chiral microfibers with high dissymmetric factors ((~0.02) and linear dichroism (LD), comparable to thin films of the same material. Reversible changes in CD signals and reduced electron dipole alignment (i.e., LD) occur on stretching of the fibers embedded in elastomeric films. To study the alignment of the mesophase filaments and inter-filament distance upon stretching, Synchrotron based small angle X-ray scattering (SAXS) was used. We confirm a 4-scan method for removing Linear Dichroism-Linear Birefringence (LD-LB) and photo elastic modulator contributions and isolating true CD is applicable for such fibrous webs. This work provides the groundwork for further study of electrospun chiral fibers by bringing forth new research questions regarding the assembly of MSCs into fibrous structures.