Refractive Index Tuning of Hybrid Materials for Highly Transmissive Luminescent Lanthanide Particle-Polymer Composites

A novel theoretical method to determine the effective optical properties of high refractive index nanocomposites

The continuous development of advanced optical devices towards high performance, miniaturization and integration has led to an increasing demand for high refractive index optical materials. Nanocomposites - made from high refractive index inorganic nanoparticles and good processability polymers - combine the advantages of both materials to create a synergistic effect. However, the diversity and complexity of the composites make laboratory preparation less efficient. Therefore, to prepare composites that meet the refractive index requirements, it is essential to predict the effective optical properties at different wavelengths. This study proposes a finite element parametric retrieval (FEPR) method to calculate the effective complex refractive index of nanocomposites (meff). The effects of the ratio of film thickness to particle diameter, particle arrangement, particle volume fraction (fv) and particle diameter (d) on meff are considered. The results demonstrate that changing the spatial arrangement, volume fraction and diameter of the particles can cause changes in the scattering effect of particles or the interaction between the electromagnetic waves and the particles, resulting in changes in the meff. Compared with effective medium theory (EMT), the FEPR method can be used to characterise the meff values in complex cases through finite element parametric modelling. The FEPR method is an efficient and accurate method for predicting the effective optical properties of nanocomposites, and can also be applied to the design and development of materials to discover the factors influencing the properties and variation patterns from large amounts of data, and to obtain predictive models that can guide the design of new materials.

Modification of polylactide by poly(ionic liquid)-b-polylactide copolymer and bio-based ionomers: Excellent toughness, transparency and antibacterial property

Polylactide (PLA) is one of the most attractive bioplastics as it can be produced from nontoxic renewable feedstock. However, its inherently poor toughness greatly limits its large-scale application. Cost-effectively toughening PLA without sacrificing its transparency remains a big challenge. We herein prepared an imidazolium-based poly(ionic liquid)-b-PLA copolymer (ILA) and ionomers as toughening agent for PLA through an integrative approach including continuous-monomer-feeding copolymerization, quaternization reaction, ion exchange and inter-ionomers blending. By blending PLA with the ILA and ionomers, we successfully obtained PLA materials with combined features including high toughness, good transparency and antibacterial properties. The effects of regulated ionomer composition and ILA compatibilizer on phase morphology, mechanical properties and transparency of the blends were systematically studied. The optimum formulation (PLA/E12/ILA 60/40/5) shows an impressive transmittance of 89-93 %, high impact strength of 45 kJ/m² and elongation at break at 170 %, which are about 17 and 24 times that of pure PLA, respectively. More interestingly, the presence of imidazolium cation and anion groups endows the blends with attractive antibacterial properties. Ion exchange between ILA copolymer and the imidazolium-containing ionomeric system leads to a synergistic effect of compatibilization and efficient toughening, providing a new strategy for develop high performance PLA materials.

Transparent Super-Repellent Surfaces with Low Haze and High Jet Impact Resistance

Transparent superhydrophobic surfaces are of vital significance for rising applications in optoelectronics, outdoor displays, building windows, and so on. However, facile fabrication of surfaces combining stable superhydrophobicity and high transparency with particularly low haze remains a challenge. Here, we demonstrate a nonfluorinated hierarchical surface, simply prepared by sequential spraying of a primer of poly(ethylene-co-acrylic acid) (EAA) and silica nanoparticles (SiO₂). The resultant surface shows remarkable liquid repellency (e.g., an apparent contact angle of >160° and a sliding angle of <2° for honey) and high transparency (a transmittance of ∼91% and a haze of ∼6%). Especially, flexible EAA adhesive enables the surface to resist water impinging (up to ∼15.0 m s^-1, higher than the terminal velocities of raindrops) and mechanical damaging. This super-repellent surface also presents excellent UV and chemical stability, sustaining a superhydrophobic state upon UVA exposure for 60 days and acidic corrosion or oil contamination for 7 days. With multirobustness and scalability, our coatings show great potential in related fields.

Upconversion nanoparticles as intracellular pH messengers

Upconversion nanoparticles (UCNPs) should be particularly well suited for measurement inside cells because they can be imaged down to submicrometer dimensions in near real time using fluorescence microscopy, and they overcome problems, such as photobleaching, autofluorescence, and deep tissue penetration, that are commonly encountered in cellular imaging applications. In this study, the performance of an UCNP modified with a pH-sensitive dye (pHAb) is studied. The dye (emission wavelength 580 nm) was attached in a polyethylene imine (PEI) coating on the UCNP and excited via the 540-nm UCNP emission under 980-nm excitation. The UC resonance energy transfer efficiencies at different pHs ranged from 25 to 30% and a Förster distance of 2.56 nm was predicted from these results. Human neuroblastoma SH-SY5Y cells, equilibrated with nigericin H+/K+ ionophore to equalize the intra- and extracellular pH' showed uptake of the UCNP-pHAb conjugate particles and, taking the ratio of the intensity collected from the pHAb emission channel (565-630 nm) to that from the UCNP red emission channel (640-680 nm), produced a sigmoidal pH response curve with an apparent pKa for the UCNP-pHAb of ~ 5.1. The UCNP-pHAb were shown to colocalize with LysoBrite dye, a lysosome marker. Drug inhibitors such as chlorpromazine (CPZ) and nystatin (NYS) that interfere with clathrin-mediated endocytosis and caveolae-mediated endocytosis, respectively, were investigated to elucidate the mechanism of nanoparticle uptake into the cell. This preliminary study suggests that pH indicator-modified UCNPs such as UCNP-pHAb can report pH in SH-SY5Y cells and that the incorporation of the nanoparticles into the cell occurs via clathrin-mediated endocytosis. Graphical abstract.

Supertough and Transparent Poly(lactic acid) Nanostructure Blends with Minimal Stiffness Loss

This contribution is an attempt to explore the effectiveness of a series of newly obtained thermoplastic elastomers (TPEs) as a toughening agent for modifying poly(lactic acid) (PLA). The TPEs, including ionically modified isotactic polypropylene-graft-PLA (iPP-g-PLA) copolymers with explicit graft length, graft density, and ionic group content, and an iPP-g-PLA copolymer with a very high molecular weight and explicit graft density, were elaborately designed and synthesized. The semicrystal or rubbery copolymer backbone originated from iPP was designed to improve the toughness and maintain a relatively high strength, while the grafted PLA side chain was to ensure a high level of compatibility with the PLA matrix. To obtain further enhancement in interfacial reinforcement, the imidazolium-based ionic group was also added during graft onto reaction. All of these graft copolymers were identified with randomly distributed PLA branches, bearing a very high molecular weight ((33-398) × 10⁴) and very high PLA content (57.3-89.3 wt %). Unprecedentedly, with a very small amount of newly designed TPE, the modified PLA blends exhibited a significantly increased elongation at break (up to about 190%) and simultaneously retained the very high stiffness and excellent transparency. The nanometer-scale phase-separated particles with good compatibility and refractive index matching to the PLA matrix were demonstrated to play a crucial role in the excellent performance. The findings suggested that the newly designed iPP-g-PLA copolymers are very economic, promising, and effective modifying agents for developing highly transparent and tough PLA-based sustainable materials.

Gradient Photonic Materials Based on One-Dimensional Polymer Photonic Crystals

In nature, animals such as chameleons are well-known for the complex color patterns of their skin and the ability to adapt and change the color by manipulating sophisticated photonic crystal systems. Artificial gradient photonic materials are inspired by these color patterns. A concept for the preparation of such materials and their function as tunable mechanochromic materials is presented in this work. The system consists of a 1D polymer photonic crystal on a centimeter scale on top of an elastic poly(dimethylsiloxane) substrate with a gradient in stiffness. In the unstrained state, this system reveals a uniform red reflectance over the entire sample. Upon deformation, a gradient in local strain of the substrate is formed and transferred to the photonic crystal. Depending on the magnitude of this local strain, the thickness of the photonic crystal decreases continuously, resulting in a position-dependent blue shift of the reflectance peak and hence the color in a rainbow-like fashion. Using more sophisticated hard-soft-hard-soft-hard gradient elastomers enables the realization of stripe-like reflectance patterns. Thus, this approach allows for the tunable formation of reflectance gradients and complex reflectance patterns. Envisioned applications are in the field of mechanochromic sensors, telemedicine, smart materials, and metamaterials.

Upconversion nanoparticles for sensing pH

Upconversion nanoparticles (UCNPs) can provide a vehicle for chemical imaging by coupling chemically sensitive dyes and quenchers. The mechanism for coupling of two anthraquinone dyes, Calcium Red and Alizarin Red S, was investigated as a function of pH. The green emission band of the UCNPs was quenched by a pH-dependent inner filter effect (IFE) while the red emission band remained unchanged and acted as the reference signal for ratiometric pH measurements. Contrary to previous expectation, there was little evidence for a resonance energy transfer (RET) mechanism even when the anthraquinones were attached onto the UCNPs through electrostatic attraction. Since the UCNPs are point emitters, only emitters close to the surface of the UCNP are within the expected Förster distance and UC-RET is <10%. The theoretical and experimental analysis of the interaction between UCNPs and pH-sensitive quenchers will allow the design of UCNP pH sensors for determination of pH via IFE.

Hybrid luminescent alginate hydrogels containing lanthanide with potential for acetone sensing

Alginate hydrogels containing YVO₄–Eu³⁺ have been prepared by using a facile method. These luminescent hydrogels can be used as sensors to detect acetone with quick response and good reversibility.