No abstract

The study of colloidal liquid crystals (LCs) reveals fundamental insights into the nature of ordered materials, giving rise to emergent properties with fascinating applications in soft matter nanotechnology. Here we investigate the shape instabilities, layer undulations, dynamic assembly, and collective behaviors in evaporating a cellulose nanocrystal-based cholesteric LC drop. During the drying process, the drop edges are pinned to the substrate with spontaneous convective flow occurring along the drop, which leads to nonequilibrium sliding of the individual cholesteric fragment with active ordering as well as hydrodynamic fluctuations and flow transitions in the bulk cholesteric phase.

A strong shear flow was imposed on the melt of polycarbonate (PC) microfibrils with β-nucleation agent reinforced isotactic polypropylene (iPP) during the melt second flow process, i.e. gas-assisted injection molding (GAIM). A special shell-core structure was formed in the iPP/PC microfibrils with β-nucleation agent (PP/PC/β-NA) composites. A lot of β-transcrystalline and α-transcrystalline superstructures were observed in the skin and sub-skin regions, whereas β-spherulite structures were formed in the gas channel region. There is no doubt that the distinct hierarchical structure has great potential to significantly improve the mechanical performance of the composites, and the experimental results verify this. The results of the mechanical performance testing show that the yield strength of the PP/PC/β-NA composites reached 61.9 MPa, which is 19.7 MPa higher than that of the iPP parts molded by GAIM (G-iPP) (42.2 MPa). The tensile modulus of the PP/PC/β-NA composites (3.3 GPa) increased by 135%, compared to that of G-iPP (1.4 GPa). The high content of β-crystals improved the elongation at break of the composites compared to the iPP/PC microfibril (PP/PC) composites; the elongation at break of the PP/PC/β-NA composites (13%) is over 3 times greater than that of the PP/PC composites (4%).

The macromolecular organization in system composed of anionic poly(acrylic acid) (PAA) and cationic chitosan (Cs), with different degrees of deacetylation (DD), under extensive elongational flow, is described. Cs/PAA nanofibers were obtained, and polyelectrolyte complexation only occurred when fibers were immersed in fluid media of a certain pH. Assembled polyelectrolytes complexes formed a pH-triggered system, as demonstrated by reversible change of the swelling degree, by 3 orders of magnitude, and a change on the elastic modulus, by 2 orders of magnitude. Both the swelling degree and the elastic modulus proved sensitive to the DD of Cs. Rheological measurements showed that increased DD of Cs resulted in a decrease in viscosity of both pure Cs and precursor Cs/PAA solutions, attributed to repulsive interactions between ionized amino groups in Cs. At the same time, a DD-dependent change in balance between hydrogen bonding and ion-dipole interactions between the components in Cs/PAA, was responsible for the more pronounced viscosity decrease in these solutions.

Manipulation of optical paths by three-dimensional (3D) integrated optics with customized stacked building blocks has gained considerable attention. Herein, we present functional thin films with assembly ability for 3D integrated optics based on nanocomposites made of cellulose nanocrystals (CNCs) embedded in hydrogen-bonded (H-bonded) interpolymer complexes (IPCs). We selected H-bonded IPC poly(ethylene oxide) and neutralized poly(acrylic acid) to render films assembly ability without undesired interplay with charge distribution in CNCs. The CNCs can form a stable chiral nematic liquid crystalline phase with long-range orientational order and helical organization. The resulting nanocomposites are characterized with a high elastic modulus of 8.8 GPa and an adhesion strength of 1.35 MPa through reversible intermolecular interactions at the contact interface upon exposure to acidic vapor. Instead, simply stacked into 3D optics, these functional thin films serve as a facile material for providing a conceptually simple approach to assemble 3D integrated optics with different liquid crystalline orderings to manipulate the light polarization state.