Materials and Interfaces

Photochemical Bubble Generation from Polymer Films: Dependence on Molecular Structure and Application for Ultrasound Imaging

Pranaya P. Ghate — 2025-06-30

Photochemical generation of N₂ gas by aromatic azide derivatives dissolved in transparent polymers provides a way to generate bubbles without direct heating. In this work, it is shown that molecules
2-azidoanthracene (2N₃-AN), 2-(azidomethyl)anthracene (2N₃-CH₂-AN), 1-azidopyrene (N₃-PY), and
1-(azidomethyl)pyrene (N₃-CH₂-PY) are all capable of generating stable surface layers of N₂ bubble after exposure to 365 nm light. Bubble formation is modeled as a multistep kinetic process that involves molecular photolysis, gas transport through the polymer, and bubble nucleation in water. Direct conjugation of the azide substituent to the aromatic core leads to more rapid photolysis and facile bubble formation, but even azides with relatively slow reaction rates can generate dense bubble layers if high light intensities are used. Rapid transport of the photogenerated N₂ gas through the polymer appears to be general, with poly(methyl methacrylate), polystyrene and polycarbonate all supporting robust bubble growth. The photoinduced bubble layer was shown to significantly enhance the visibility of a coated glass pipette when imaged by an ultrasound instrument. The ability to prepare polymer coatings that undergo photochemical gas evolution provides a new functionality that may be useful in medical imaging applications.

Carbon Monoxide-Assisted Synthesis of Nickel Cobalt Phosphide Nanorods for the Hydrogen Evolution Reaction

Sarah York — 2025-06-20

The development of efficient and cost-effective catalysts for hydrogen evolution reaction (HER) is crucial for the advancement of electrochemical water splitting technology. Here, we report a novel synthetic method for the preparation of single-crystalline NiCoP nanorods with tunable aspect ratios using a CO-assisted, trioctylphosphine (TOP)-mediated approach. The introduction of CO gas at different temperatures allows for the control of the nanorod growth, resulting in various aspect ratios while maintaining a hexagonal crystal structure and a composition of 1:1 Ni/Co as NiCoP. Our results demonstrate that the NiCoP nanorods with higher aspect ratios exhibit improved HER activity and stability, with the highest aspect ratio nanorods showing the lowest overpotential and Tafel slope in both acidic and alkaline media. This study highlights the importance of controlling the size and morphology of bimetallic phosphide nanoparticles to optimize their catalytic activity for HER, providing new insights into the design and optimization of nanostructured catalysts for electrochemical water splitting applications.

Additive Manufacturing of Bioinspired Structural-Color Materials

Zhilong Cao — 2025-05-19

Structural color is ubiquitous in nature and biological systems, and synthetic structural-color materials have been considered as a more durable substitute for traditional pigments. Recent advancements in the additive manufacturing of exquisite photonic objects have enabled the preparation of structurally colored materials with customized properties. Herein, an up-to-date review about additive manufacturing of bioinspired structural-color materials is presented. This review begins with an overview of the direct ink writing of colloidal crystals, chiral liquid crystals, cellulose nanocrystals, and block copolymers. Then, significant advances in inkjet printing strategy are showcased, including inkjet printing of colloidal crystals and cellulose nanocrystals, inkjet printing inks on photonic polymer coatings, and inkjet printing based on total internal reflections. The third section focuses on the recent advances in other additive manufacturing methods, including digital light processing, two-photon lithography, and fused deposition modeling. This review summarizes a perspective on potential opportunities, challenges, and future prospects encountered by advanced printing technology and functional structural-color materials.

An Anisotropic Hydrogel with Simple Preparation and Well-Defined Structure as a New Platform for Flexible Sensors with Directional Strain and Force Sensing

Yitong Xie — 2025-06-25

As a platform to construct the next-generation flexible strain and force sensors, anisotropic hydrogels have recently attracted considerable attention, with an expectation that they would visualize the anisotropic motion of biological systems in a direction-specific manner. To date, a number of anisotropic hydrogels have been developed with an intensive pursuit to improve their practical performance, so that their composition, preparation, and structure have become increasingly complex over the years. In fact, most of these anisotropic hydrogels are prepared from many components including naturally occurring materials, using multiple steps that often require skillful control of kinetic events. Therefore, although some of them show good performances, their complicated and unclear structures make it difficult to elucidate the relationship between structure and properties. As an approach complementary to such trend, here we report a very simple anisotropic hydrogel that would provide a versatile platform for flexible sensors with directional sensing capability. This hydrogel was simply prepared by one-pot reaction from two components, i.e., by magnetic orientation of titanate nanosheet (TiNS) in water and subsequent in-situ formation of a polyacrylamide network. In the resulting hydrogel (TiNS-gel), TiNS platelets were arranged in a lamellar structure with highly oriented, periodic, and homogeneous state. Due to such structure, TiNS-gel exhibited remarkable anisotropy in tensile modulus, nanostructural transformability, and ionic conductivity. Furthermore, TiNS-gel changed its electrical resistance upon tensile deformation, demonstrating its potential utility as a flexible strain and force sensor. TiNS-gel, characterized by easy synthesis, simple composition, well-defined structure, and various anisotropic properties will serve as a useful platform for developing flexible devices with direction-selective strain and force sensing capabilities.

Development of a Temperature-Responsive Polymer Network with Enhanced Transparency and Volume Shrinkage via Star-Shaped PEG-b-PNIPA Block Copolymer

Kai Kawabata — 2025-07-10

In this study, a temperature-responsive polymer network was successfully synthesized by using a 4-arm star-shaped polyethylene glycol (PEG) derivative as an initiator and polymerizing N-isopropylacrylamide (NIPA) as a secondary acrylamide. The resulting star-shaped block copolymer was used as a building block to prepare a polymer network. Detailed analysis of the polymerization process (including SEC and ¹H NMR) confirmed the successful synthesis and high control over the star-shaped block copolymer structure. The obtained star-shaped block copolymer was crosslinked under semi-dilute conditions via a click reaction, incorporating the hydrophilic PEG into the poly(N-isopropylacrylamide) (PNIPA) network. This network exhibits a lower critical solution temperature (LCST) behavior at 32.5°C in water. The introduction of PEG led to unique properties, such as volume shrinkage upon heating while maintaining optical transparency, due to the effective suppression of phase separation within the network. This advancement overcomes the limitations of conventional PNIPA-based gels and expands their potential applications in optical sensors, actuators, and biomedical devices. The results highlight the promising applications of this polymer network in the development of advanced smart materials.

Stimuli-Responsive Naphthalene Diimide-Based Charge-Transfer Liquid Materials Showing Thermal Response to Tune Photoluminescent Properties

Takumi Omura — 2025-06-04

Stimuli-responsive luminescent liquid materials have recently attracted considerable attention due to their potential to address the limitations of solid-state materials, such as the necessity of organic solvents and the difficulty in fabricating composite systems. Liquid-state materials offer superior processability and enable facile modulation of photophysical properties by simply selecting appropriate solutes. In particular, molecular designs incorporating electron-donating or electron-accepting properties into liquid materials allow to form charge-transfer (CT) complexes upon dissolving solutes with their opposite electronic properties, altering both solution color and photoluminescence (PL) behavior. In this study, we developed a room-temperature supercooled liquid material based on an electron-accepting naphthalene diimide (NADI) derivative, BR-Val-NADI. Upon dissolving electron-rich naphthalene-based derivatives (NA-##s) into BR-Val-NADI, NA-##/BR-Val-NADI with CT character were readily obtained as solutions, exhibiting various colors and PL properties. NA-##/BR-Val-NADI also functioned as printable PL inks that could be applied onto various substrates such as glass and paper. Notably, the PL properties of NA-##/BR-Val-NADI were responsive to thermal stimuli, with temperature-induced changes in PL color and PL off/on switching. These results highlight the potential of NA-##/BR-Val-NADI as a new class of stimuli-responsive soft materials for applications in printable photonic devices and smart sensing platforms.

Modelling the Growth and Aggregation of Gold Nanoparticles Using Liquid-Phase Transmission Electron Microscopy

THao Ngo — 2025-06-18

The ability to synthesize nanoparticles of desired shape, size and composition relies heavily on our understanding on how to finely control various factors influencing the formation, such as the kinetics of growth. Fundamental study on the nucleation and growth of nanoparticles found itself at the forefront with the application of liquid-phase transmission electron microscopy (LTEM) in the investigation of dynamic growth and assembly processes. Since early study using LTEM to observe and quantify the nucleation and growth of single colloidal platinum nanoparticles, several theoretical models have been developed. More complex mode of formation was also revealed based on a hybrid growth process of gold on platinum icosahedral nanoparticles to form core-shell structures. These studies have been carried out by focusing on single or a small number of nanoparticles. Herewith, we present a study on the establishment of an analytical method to quantify the particle formation using in situ LTEM technique. This approach is based on the analysis of median particle size and focused on main events accounted for the formation of nanoparticles at a given time. We found that unlike the cases for single particle analysis, the observed formation rate could not be explained by any single formation mode, such as diffusion- and/or reaction-controlled growth described by the Liftshitz-Slyosov-Wagner theory or formation through coalescence as described by the Smoluchowski aggregative kinetics. A global fit was used to describe the entire formation of nanoparticles in an ensemble.

Steady-State Synthesis of Colloidal Metal Nanocrystals

Jianlong He — 2025-06-20

Despite remarkable progress, colloidal synthesis of metal nanocrystal is still far away from reaching the goal for robust, reproducible, and scalable production. Even with the adoption of seed-mediated growth, the synthesis can still be complicated by issues such as self-nucleation, galvanic replacement, stochastic symmetry reduction, and unwanted compositional variation. All these issues can be addressed by switching to steady-state synthesis characterized by a slow, constant, and tightly controlled reduction rate. Steady-state synthesis can be achieved by adding one reactant dropwise while using the other reactant in large excess, but this method is not suitable for scale-up production in a continuous flow reactor. There is a pressing need to develop alternative methods capable of establishing the steady-state kinetics characteristic of dropwise addition while introducing both reactants by one-shot injection. In this Perspective, we discuss a number of methods that allow for both one-shot injection and steady-state synthesis.

Colorimetric Plasmonic Nanosensors for Environmental Pollution Monitoring

Xueyong Zhang — 2025-07-09

Environmental pollution, particularly water contamination by heavy metals and organic pollutants, presents a critical global challenge requiring effective monitoring solutions. Colorimetric plasmonic nanosensors, primarily utilizing gold nanoparticles (AuNPs) due to their exceptional stability and tunable optical properties, offer a promising approach for rapid, cost-effective, and label-free pollutant detection. This review highlights recent advancements in AuNP-based colorimetric plasmonic nanosensors for environmental monitoring. We explore their fundamental sensing mechanisms and critically examine their applications in detecting a broad spectrum of waterborne contaminants, including heavy metals, inorganic species, and diverse organic pollutants. By showcasing the versatility and potential of these emerging technologies, this review emphasizes their significant contribution towards developing more efficient and accessible tools for mitigating environmental pollution and protecting public health.

Self-Assembly of Hydrogen-Bonded Fibrous FeII Triazole Complexes and Their Spin Crossover Characteristics in Organic Media

Keita Kuroiwa — 2025-06-06

The lipophilic linear Fe^II triazole complexes [Fe^II(L)₃]Cl₂ (L = 1–5) were synthesized using ligands 1–5 containing amide bonds between alkyl chains and 1,2,4-triazole ligands with various spacer methylene length. When the amido and ether linkages are introduced in the alkyl chain moiety, the iron complexes are dissolved in chloroform, [Fe^II(1)₃]Cl₂ forms a pale purple jelly-like phase. The purple color is accompanied by a structured absorption around 540 nm, characteristic of iron (II) in the low spin (LS) state. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) of the jelly-like phase confirm the formation of networks of fibrous nano assemblies with widths of 10–30 nm. The observed widths are larger than the molecular lengths of the triazole ligands. The pale purple jelly-like phase turned into a pale-yellow solution by heating above ca 310 K, indicating the formation of high spin (HS) state complexes. The complexes show irreversible spin crossover in the solid state, characterized by SQUID. Interestingly, an abrupt spin crossover is observed in solution reversibly with some thermal hysteresis. UV-vis spectra also showed reversible spin crossover phenomena dependent on the spacer length between the amide group and the Fe(II) triazole complexes. IR spectra of these complexes in chloroform show the formation of hydrogen bonding from amide groups, which enhanced alkyl-chain packing in the coordination polymers. The freeze-dried iron triazole complexes form lamellar structures, which indicates the alkyl chains extending radially from the octahedral triazole complex moiety are oriented in a lamellar packing due to the presence of flexible ether linkages in alkyl chains, which allowed decoupling the alignment of the dodecyloxy alkyl chains from the spacer methylenes connected to the Fe(II) triazole complexes. Introducing amide bondages to the lipophilic one-dimensional coordination systems stabilizes the low-spin state by hydrogen bond networks. It provides hysteresis in the spin crossover in solution, ascribed to the recombination of hydrogen bonds during the temperature change between the heating and cooling sides. Combining hydrogen bonds and lipophilic one-dimensional complexes provides a valuable means to enhance their stability and control physical properties in solution.

Photonic properties of colloidal crystal elastic sheets formed by electrostatic repulsion and shear stress and their fundamental deformation modes

Hiroshi Fudouzi — 2025-05-15

We have developed a non-close-packed type elastic colloidal crystal sheet through a simple shear-induced process. The colloidal crystal state, in which the (111) plane exhibited significant orientation due to shear stress, was successfully stabilized in the 4-hydroxybutyl acrylate (4-HBA) monomer precursor dispersed with desalted silica colloidal particles through the implementation of UV irradiation radical polymerization. Consequently, a solid colloidal crystal sheet was produced, capable of reversibly modulating its structural color in response to elastic deformation. In this article report will address the stress response functions of this sheet due to elastic deformation of stretching, compressing and bending. In addition, a rapid structural color change at 4.17 ms unit by impacting, and durability repeating elongating rubber sheet for 100,000 times are investigated for practical use. Since the fabrication of this elastic colloidal crystal material is easy to scale up, a low-cost manufacturing process is expected.

Sn-TiO₂/PTA Nanocomposite Films for High-Contrast Rewritable Media with Visible-Light-Driven Black Coloration

Yao Dou — 2025-05-15

Photochromic materials are pivotal for rewritable smart media, yet conventional systems suffer from sluggish kinetics, UV dependency, and low optical contrast. Herein, we present a visible-light-responsive Sn-TiO₂/phosphotungstic acid (PTA) nanocomposite film mediated by polyvinylpyrrolidone (PVP) that addresses these challenges through interfacial engineering and bandgap modulation. Sn-doped TiO₂ nanoparticles, synthesized hydrothermally, are covalently linked to phosphotungstic acid (PTA) clusters via PVP-assisted dispersion, enabling efficient charge separation under 450 nm illumination. The Sn-TiO₂/PTA/PVP nanocomposite film achieves ultrafast coloration within 10 s, attributed to the reduction of W⁶⁺ to W⁵⁺ in PTA. The colored state exhibits remarkable air stability (48 h) and rapid recovery (<30 min) via H₂O₂ vapor, sustaining >80 reversible cycles without degradation. With a narrowed bandgap (2.23 eV) and broadband intervalence charge transfer (IVCT) absorption (600–800 nm), the film demonstrates high-contrast black-state coloration and 2-day legibility as a rewritable medium. This work overcomes the limitations of organic dyes and UV-dependent systems, offering an inorganic, eco-friendly platform for smart displays, anti-counterfeiting labels, and energy-efficient photochromic technologies.