Quantum-Efficiency Enhancement and Mechanical Responsiveness of Solid-State Photoluminescence Materials Based on Uniaxial Cellulose Nanocrystal Arrays in Flexible Polymer via Assembly-Induced Emission

Assembling cellulose nanocrystals (CNCs) can induce solid-state photoluminescence based on Stokes scattering. Such photoluminescence is free of photo-quenching and should have great potential in optical materials, whereas poor flexibility of assembled CNC arrays limits its applications. Here, a co-assembly of binary components including 1D nanoparticles and long-chain polymers had been explored to introduce the uniaxial CNC arrays into a transparent poly (vinyl alcohol) (PVA) membrane, which enhanced the mechanical properties, especially the stretchable property. Besides, the CNC assembly was controlled by adjusting the volume ratio between CNC and PVA. The result indicated that co-assembly with PVA could improve the uniaxial orientation of assembled CNC arrays, which played a crucial role in enhancing the emission quantum-efficiency (EQE) of CNC. Stretching the PVA/CNC membrane could furthermore induce an enhancement in EQE together with a gradual shift in emission wavelength. The mechanism study on that stimulation-response suggested that the enhancement and shift came from the change in the uniaxial orientation degree and periodicity of the CNC assembly, respectively. Since the stimulation-responsive enhancement in EQE (from ca. 40% to ca. 60%) can even be observed by naked eyes, we believe such cellulose-based materials can be widely used in optical sensors.

Convective meniscus splitting of polysaccharide microparticles on various surfaces

In contrast to convective self-assembly methods for colloidal crystals etc., “convective meniscus splitting method” was developed to fabricate three-dimensionally ordered polymeric structures. By controlling the geometry of evaporative interface of polymer solution, a deposited membrane with uniaxial orientation and layered structures can be prepared. Here it is demonstrated that xanthan gum polysaccharide microparticles with diameter ~ 1 µm can bridge a millimeter-scale gap to form such a membrane because the capillary force among the particles is more dominant than the gravitational force on the evaporative interface. This method is applicable for various substrates with a wide range of wettability (water contact angle, 11°–111°), such as glass, metals, and plastics. The specific deposition can be also confirmed between frosted glasses, functional-molecules-modified glasses, and gold-sputtered substrates. By using such a universal method, the membrane formed on a polydimethylsiloxane surface using this method will provide a new strategy to design a functional polysaccharide wall in microfluidic devices, such as mass-separators.

Inducing Enantiosensitive Permanent Multipoles in Isotropic Samples with Two-Color Fields

We find that two-color fields can induce field-free permanent dipoles in initially isotropic samples of chiral molecules via resonant electronic excitation in a one-$$3\omega $$ 3 ω -photon versus three-$$\omega $$ ω -photons scheme. These permanent dipoles are enantiosensitive and can be controlled via the relative phase between the two colors. When the two colors are linearly polarized perpendicular to each other, the interference between the two pathways induces excitation sensitive to the molecular handedness and orientation, leading to uniaxial orientation of the excited molecules and to an enantio-sensitive permanent dipole perpendicular to the polarization plane. We also find that although a corresponding one-$$2\omega $$ 2 ω -photon versus two-$$\omega $$ ω -photons scheme cannot produce enantiosensitive permanent dipoles, it can produce enantiosensitive permanent quadrupoles that are also controllable through the two-color relative phase.

REGULARITIES OF FORMATION OF SYNTHETIC OPTICAL ANISOTROPY OF POLYMETHYL METHACRYLATE FOR POLARIMETRIC APPLICATION

General principles of wav plate manufacturing are considered. The possibility of the formation of synthetic optical anisotropy of polymethyl methacrylate (PMMA) by the method of its uniaxial stretching is investigated. The most promising is a method for manufacturing waveplates, which includes the stage of controlled stretching of the polymer material to the required phase shift value, which would generally exclude the stage of machining the plates. The general orderliness of the molecules in the polymer resulting from stretching (orientation) leads to the oriented state of the polymer, and, consequently, to the general anisotropy of the physical and optical properties. In this state, a clearly pronounced uniaxial orientation of polymer chains is observed. As a result, chain macromolecules, randomly (statistically) oriented in the initial PMMA, acquire orientation under the influence of an external directed tensile force. The anisotropy of the optical properties of uniaxially stretched PMMA is manifested in the fact that it has different refractive indices for light polarized parallel to the direction of stretching (orientation) and in the perpendicular direction (birefringence). The regularities of the formation of the synthetic optical anisotropy of PMMA have been studied. The dependences of the birefringence values of uniaxially stretched PMMA on the initial sheet thickness, stretching temperature, and degree of stretching have been measured. It has been shown that the value of birefringence is directly proportional to the thickness of the initial sheet and the degree of stretching and inversely proportional to the stretching temperature. The spectral dependence of the birefringence value is measured. Achromatic and superachromatic waveplates were made from uniaxially stretched PMMA. The spectral characteristics of the phase shift of the manufactured waveplates are given. The availability of the starting material, the technological simplicity of the formation of the initial components for waveplates, as well as the possibility of manufacturing waveplates of large dimensions and high quality, make polymethyl methacrylate with artificially induced anisotropy a promising material for the manufacture of achromatic and superachromatic waveplates.

High strength in combination with high toughness in robust and sustainable polymeric materials

In materials science, there is an intrinsic conflict between high strength and high toughness, which can be resolved for different materials only through the use of innovative design principles. Advanced materials must be highly resistant to both deformation and fracture. We overcome this conflict in man-made polymer fibers and show multifibrillar polyacrylonitrile yarn with a toughness of 137 ± 21 joules per gram in combination with a tensile strength of 1236 ± 40 megapascals. The nearly perfect uniaxial orientation of the fibrils, annealing under tension in the presence of linking molecules, is essential for the yarn’s notable mechanical properties. This underlying principle can be used to create similar strong and tough fibers from other commodity polymers in the future and can be used in a variety of applications in areas such as biomedicine, satellite technology, textiles, aircrafts, and automobiles.