Assembly of Hollow Yttrium Oxide Spheres from Nano-Sized Yttrium Oxide for Advanced Passive Radiative Cooling Materials.

This study presents significant advancements in passive radiative cooling (PRC), achieved using assembled hollow yttrium oxide spherical particles (AHYOSPs). We developed PRC films with enhanced optical properties by synthesizing micro-sized hollow Y2O3 particles and integrating them into a polydimethylsiloxane (PDMS) matrix. The findings revealed that AHYOSPs achieved a remarkable solar reflectance of 73.72% and an emissivity of 91.75%, significantly outperforming nano-sized yttrium oxide (NYO) and baseline PDMS. Field tests demonstrated that the AHYOSPs maintained their lowest temperature during daylight, confirming their superior cooling efficiency. Additionally, theoretical calculations using MATLAB indicated that the cooling capacity of AHYOSPs reached 103.77 W/m2, representing a substantial improvement over NYO and robustly validating the proposed nanoparticle assembly strategy. These results highlight the potential of structurally controlled particles to revolutionize PRC technologies, thereby offering a path toward more energy-efficient and environmentally friendly cooling solutions.

Fabrication of Yttrium Oxide Hollow Films for Efficient Passive Radiative Cooling.

In recent years, many parts of the world have researched the transition to renewable energy, reducing energy consumption and moving away from fossil fuels. Among the studies to reduce energy consumption, passive radiative cooling can reduce the energy used for building cooling, and to improve this, the optical properties of atmospheric window emissivity and solar reflectance must be increased. In this study, hollow yttrium oxide (H-Y2O3) was fabricated using melamine formaldehyde (MF) as a sacrificial template to improve the optical properties of passive radiative cooling. We then used finite-difference time-domain (FDTD) simulations to predict the optical properties of the fabricated particles. This study compares the properties of MF@Y(OH)CO3 and H-Y2O3 particles derived from the same process. H-Y2O3 was found to have a solar reflectance of 70.73% and an atmospheric window emissivity of 86.24%, and the field tests revealed that the temperature of MF@Y(OH)CO3 was relatively low during the daytime. At night, the temperature of the H-Y2O3 film was found to be 2.6 °C lower than the ambient temperature of 28.8 °C. The optical properties and actual cooling capabilities of the particles at each stage of manufacturing the hollow particles were confirmed and the cooling capabilities were quantified.

Passive Daytime Radiative Cooling by Thermoplastic Polyurethane Wrapping Films with Controlled Hierarchical Porous Structures.

Invited for this month's cover is a combined work of the Korea Research Institute of Chemical Technology together with the Chungnam National University, the University of California, Irvine, and Chung-Ang University. The cover shows the effective thermal management of a vehicle interior through the wrapping of stretchable passive radiative cooling film. Thermoplastic polyurethane (TPU) cooler film with a hierarchical porous structure shows a dramatic cooling effect compared to commercial paint in sunny, hot weather. The Research Article itself is available at 10.1002/cssc.202201842.

Passive Daytime Radiative Cooling by Thermoplastic Polyurethane Wrapping Films with Controlled Hierarchical Porous Structures.

Current research has focused on effective solutions to mitigate global warming and the accelerating greenhouse gas emissions. Compared to most cooling methods requiring energy and resources, passive daytime radiative cooling (PDRC) technology offers excellent energy savings as it requires no energy consumption. However, existing PDRC materials encounter unprecedented problems such as complex structures, low flexibility, and performance degradation after stretching. Thus, this study reports a porous structured thermoplastic polyurethane (TPU) film with bimodal pores to produce high-efficiency PDRC with efficient solar scattering using a simple process. The TPU film exhibited an adequately high solar reflectivity of 0.93 and an emissivity of 0.90 in the atmospheric window to achieve an ambient cooling of 5.6 °C at midday under a solar intensity of 800 W m-2 . Thus, the highly elastic and flexible TPU film was extremely suitable for application on objects with complex shapes. The radiative cooling performance of 3D-printed models covered with these TPU films demonstrated their superior indoor cooling efficiency compared to commercial white paint (8.76 °C). Thus, the proposed design of high-efficiency PDRC materials is applicable in various urban infrastructural objects such as buildings and vehicles.

Spatialization and Prediction of Seasonal NO2 Pollution Due to Climate Change in the Korean Capital Area through Land Use Regression Modeling.

Urbanization is causing an increase in air pollution leading to serious health issues. However, even though the necessity of its regulation is acknowledged, there are relatively few monitoring sites in the capital metropolitan city of the Republic of Korea. Furthermore, a significant relationship between air pollution and climate variables is expected, thus the prediction of air pollution under climate change should be carefully attended. This study aims to predict and spatialize present and future NO2 distribution by using existing monitoring sites to overcome deficiency in monitoring. Prediction was conducted through seasonal Land use regression modeling using variables correlated with NO2 concentration. Variables were selected through two correlation analyses and future pollution was predicted under HadGEM-AO RCP scenarios 4.5 and 8.5. Our results showed a relatively high NO2 concentration in winter in both present and future predictions, resulting from elevated use of fossil fuels in boilers, and also showed increments of NO2 pollution due to climate change. The results of this study could strengthen existing air pollution management strategies and mitigation measures for planning concerning future climate change, supporting proper management and control of air pollution.

Cool White Polymer Coatings based on Glass Bubbles for Buildings.

While most selective emitter materials are inadequate or inappropriate for building applications, here we present a techno-economically viable optical coating by integrating glass bubbles within a polymer film. A controlled glass bubble volume concentration from 0 to 70% leads to a selective solar reflectivity increase from 0.06 to 0.92 while the mid-infrared emissivity remains above 0.85. Outdoor measurements show the polymer coating on a concrete surface can provide a temperature reduction up to 25 °C during the day when conduction and convection are limited and a net cooling power greater than 78 W/m2 at a cost less than $0.005/W. The impact of polymer coating on common buildings is estimated as potential annual energy savings of 2-12 MJ/m2 and CO2 emission savings of 0.3-1.5 kg/m2. More savings are expected for higher surface-area-to-volume-ratio buildings, and the polymer coating is also expected to resolve cooling issues for old buildings with no air conditioning.

Spatiotemporally Controlled Plasticity and Elasticity in 3D Multi-Shape Memory Structures Enabled by Elemental Sulfur-Derived Polysulfide Networks with Intrinsic NIR Responsiveness.

Thermadapt shape memory polymers (SMPs), utilizing a variety of dynamic covalent bond exchange mechanisms, have been extensively studied in recent years but it is still challenging to address several constraints in terms of limited accuracy and complexity for constructing 3D shape memory structures. Here, an effective and facile preparation of thermadapt SMPs based on elemental sulfur-derived poly(phenylene polysulfide) networks (PSNs) is presented. These SMPs possess intrinsic near-infrared (NIR)-induced photothermal conversion properties for spatiotemporal control of their plasticity and elasticity. The NIR-controllable plasticity and elasticity of the PSNs enable versatile shape manipulation of 3D multi-shape memory structures, including building block assembly, reconfiguration, shape fixing/recovery, and repair.

Synergistic Effects of Various Ceramic Fillers on Thermally Conductive Polyimide Composite Films and Their Model Predictions.

In this study, thermally conductive composite films were fabricated using an anisotropic boron nitride (BN) and hybrid filler system mixed with spherical aluminum nitride (AlN) or aluminum oxide (Al2O3) particles in a polyimide matrix. The hybrid system yielded a decrease in the through-plane thermal conductivity, however an increase in the in-plane thermal conductivity of the BN composite, resulting from the horizontal alignment and anisotropy of BN. The behavior of the in-plane thermal conductivity was theoretically treated using the Lewis⁻Nielsen and modified Lewis⁻Nielsen theoretical prediction models. A single-filler system using BN exhibited a relatively good fit with the theoretical model. Moreover, a hybrid system was developed based on two-population approaches, the additive and multiplicative. This development represented the first ever implementation of two different ceramic conducting fillers. The multiplicative-approach model yielded overestimated thermal conductivity values, whereas the additive approach exhibited better agreement for the prediction of the thermal conductivity of a binary-filler system.

Tailoring biomimetic polymer networks towards an unprecedented combination of versatile mechanical characteristics.

Biomimetic polymeric materials, adopting the basic molecular design principles of biological materials, have been extensively studied in recent years but it is still challenging to combine assorted mechanical characteristics in a single material. Here, we present a simple and effective strategy to prepare mechanically robust yet resilient biomimetic polymer networks by utilizing dual noncovalent and covalent cross-linkings. Tailoring the dual cross-links consisting of thiourea noncovalent interactions and epoxy-amine covalent linkages in the biomimetic polymer networks enables a rare combination of excellent elastic modulus (1.1 GPa), yield stress (39 MPa), extensibility (320%), as well as complete strain and performance recovery after deformation at room temperature. The biomimetic polymer networks also exhibit highly adaptive mechanical properties in response to multiple-stimuli including strain rate, temperature, light, and solvent.

Synthesis of Poly(phenylene polysulfide) Networks from Elemental Sulfur and p-Diiodobenzene for Stretchable, Healable, and Reprocessable Infrared Optical Applications.

The synthesis and characterization of poly(phenylene polysulfide) networks (PSNs) with controlled average sulfur ranks, from elemental sulfur (ES) and p-diiodobenzene (DIB), are investigated. The PSN films, prepared via simple hot pressing, are found to possess large extensibility up to around 300% and complete recovery of shape and mechanical properties after deformation, which are attributed to the loosely cross-linked network structures mainly consisting of linear poly(phenylene polysulfide) chains. The covalent polysulfide linkages in the PSNs also exhibit dynamic behaviors under ultraviolet (UV) or thermal treatment, thus, enabling self-healing and reprocessing of the films when scratched and broken, respectively. Combined with the unique mechanical properties of the PSNs, their high refractive index and excellent infrared (IR) transparency contribute to the preparation of stretchable, healable, and reprocessable IR transmitting materials for potential deformable and stretchable optical applications.

Anisotropy-Driven High Thermal Conductivity in Stretchable Poly(vinyl alcohol)/Hexagonal Boron Nitride Nanohybrid Films.

Controlling the anisotropy of two-dimensional materials with orientation-dependent heat transfer characteristics is a possible solution to resolve severe thermal issues in future electronic devices. We demonstrate a dramatic enhancement in the in-plane thermal conductivity of stretchable poly(vinyl alcohol) (PVA) nanohybrid films containing small amounts (below 10 wt %) of hexagonal boron nitride ( h-BN) nanoplatelets. The h-BN nanoplatelets were homogeneously dispersed in the PVA polymer solution by ultrasonication without additional surface modification. The mixture was used to prepare thermally conductive nanocomposite films. The in-plane thermal conductivity of the resulting PVA/ h-BN nanocomposite films increased to 6.4 W/mK when the strain was increased from 0 to 100% in the horizontal direction. More specifically, the thermal conductivity of a PVA/ h-BN composite film with 10 wt % filler loading can be improved by up to 32 times as compared to pristine PVA. This outstanding thermal conductivity value is significantly larger than that of materials currently used in in-plane thermal management systems. This result is attributed to the anisotropic alignment of h-BN particles in the PVA chain matrix during stretching, enhancing phonon conductive paths and hence improving the thermal conductivity and thermal properties of PVA/ h-BN nanocomposite films. These polymer nanocomposites have low cost as the amount of expensive conductive fillers is reduced and can be potentially used as high-performance materials for thermal management systems such as heat sink and thermal interface materials, for future electronic and electrical devices.

Highly anisotropic thermal conductivity of discotic nematic liquid crystalline films with homeotropic alignment.

Discotic nematic liquid crystal (DNLC) films are prepared by thermal treatment and a photo-crosslinking reaction inside sandwiched glass plates. The DNLC films exhibit outstanding in-plane thermal conductivity which is much larger than cross-plane thermal conductivity. The homeotropic alignment and higher crosslinking density of DNLCs in the films further increase the thermal conductivity anisotropy.

Large-Area CVD-Grown Sub-2 V ReS2 Transistors and Logic Gates.

We demonstrated the fabrication of large-area ReS2 transistors and logic gates composed of a chemical vapor deposition (CVD)-grown multilayer ReS2 semiconductor channel and graphene electrodes. Single-layer graphene was used as the source/drain and coplanar gate electrodes. An ion gel with an ultrahigh capacitance effectively gated the ReS2 channel at a low voltage, below 2 V, through a coplanar gate. The contact resistance of the ion gel-gated ReS2 transistors with graphene electrodes decreased dramatically compared with the SiO2-devices prepared with Cr electrodes. The resulting transistors exhibited good device performances, including a maximum electron mobility of 0.9 cm2/(V s) and an on/off current ratio exceeding 104. NMOS logic devices, such as NOT, NAND, and NOR gates, were assembled using the resulting transistors as a proof of concept demonstration of the applicability of the devices to complex logic circuits. The large-area synthesis of ReS2 semiconductors and graphene electrodes and their applications in logic devices open up new opportunities for realizing future flexible electronics based on 2D nanomaterials.

Electrically conductive graphene/polyacrylamide hydrogels produced by mild chemical reduction for enhanced myoblast growth and differentiation.

Graphene and graphene derivatives, such as graphene oxide (GO) and reduced GO (rGO), have been extensively employed as novel components of biomaterials because of their unique electrical and mechanical properties. These materials have also been used to fabricate electrically conductive biomaterials that can effectively deliver electrical signals to biological systems. Recently, increasing attention has been paid to electrically conductive hydrogels that have both electrical activity and a tissue-like softness. In this study, we synthesized conductive graphene hydrogels by mild chemical reduction of graphene oxide/polyacrylamide (GO/PAAm) composite hydrogels to obtain conductive hydrogels. The reduced hydrogel, r(GO/PAAm), exhibited muscle tissue-like stiffness with a Young's modulus of approximately 50kPa. The electrochemical impedance of r(GO/PAAm) could be decreased by more than ten times compared to that of PAAm and unreduced GO/PAAm. In vitro studies with C2C12 myoblasts revealed that r(GO/PAAm) significantly enhanced proliferation and myogenic differentiation compared with unreduced GO/PAAm and PAAm. Moreover, electrical stimulation of myoblasts growing on r(GO/PAAm) graphene hydrogels for 7days significantly enhanced the myogenic gene expression compared to unstimulated controls. As results, our graphene-based conductive and soft hydrogels will be useful as skeletal muscle tissue scaffolds and can serve as a multifunctional platform that can simultaneously deliver electrical and mechanical cues to biological systems. STATEMENT OF SIGNIFICANCE: Graphene-based conductive hydrogels presenting electrical conductance and a soft tissue-like modulus were successfully fabricated via mild reduction of graphene oxide/polyacrylamide composite hydrogels to study their potential to skeletal tissue scaffold applications. Significantly promoted myoblast proliferation and differentiation were obtained on our hydrogels. Additionally, electrical stimulation of myoblasts via the graphene hydrogels could further upregulate myogenic gene expressions. Our graphene-incorporated conductive hydrogels will impact on the development of new materials for skeletal muscle tissue engineering scaffolds and bioelectronics devices, and also serve as novel platforms to study cellular interactions with electrical and mechanical signals.

A Carbonaceous Membrane based on a Polymer of Intrinsic Microporosity (PIM-1) for Water Treatment.

As insufficient access to clean water is expected to become worse in the near future, water purification is becoming increasingly important. Membrane filtration is the most promising technologies to produce clean water from contaminated water. Although there have been many studies to prepare highly water-permeable carbon-based membranes by utilizing frictionless water flow inside the carbonaceous pores, the carbon-based membranes still suffer from several issues, such as high cost and complicated fabrication as well as relatively low salt rejection. Here, we report for the first time the use of microporous carbonaceous membranes via controlled carbonization of polymer membranes with uniform microporosity for high-flux nanofiltration. Further enhancement of membrane performance is observed by O2 plasma treatment. The optimized membrane exhibits high water flux (13.30 LMH Bar-1) and good MgSO4 rejection (77.38%) as well as antifouling properties. This study provides insight into the design of microporous carbonaceous membranes for water purification.

Reduction of graphene oxide/alginate composite hydrogels for enhanced adsorption of hydrophobic compounds.

Carbon-based materials, consisting of graphene oxide (GO) or reduced GO (rGO), possess unique abilities to interact with various molecules. In particular, rGO materials hold great promise for adsorption and delivery applications of hydrophobic molecules. However, conventional production and/or usage of rGO in aqueous solution often causes severe aggregation due to its low water solubility and thus difficulties in handling and applications. In our study, to prevent the severe aggregation of GO during reduction and to achieve a high adsorption capacity with hydrophobic compounds, GO/alginate composite hydrogels were first prepared and then reduced in an aqueous ascorbic acid solution at 37 °C. Adsorption studies with a model hydrophobic substance, rhodamine B, revealed that the reduced composite hydrogels are more highly absorbent than the unreduced hydrogels. In addition, the adsorption properties of the composite hydrogels, which are consequences of hydrophobic and ionic interactions, could be modulated by controlling the degree of reduction for the adsorption of different molecules. The composite hydrogels embedding rGO can be very useful in applications related to drug delivery, waste treatment, and biosensing.

Enhanced thermoelectric performance of bar-coated SWCNT/P3HT thin films.

The influence of processing conditions, such as ink concentration and coating method, on the thermoelectric properties of SWCNT/P3HT nanocomposite films was investigated systematically. Using simple wire-bar-coating, SWCNT/P3HT nanocomposite films with high thermoelectric performance could be obtained without additional P3HT doping. The wire-bar-coated SWCNT/P3HT nanocomposite films exhibited power factors of up to 105 µW m(-1) K(-2) at room temperature. The SWCNT bundles with diameters in the range of 6-23 nm formed an interconnected network in the wire-bar-coated nanocomposite films. Network formation in these nanocomposite films was expected to be strongly related to the development of electrical pathways due to inter-SWCNT bundle connections. This study suggests that the thermoelectric performance of SWCNT/P3HT nanocomposite films could be optimized by controlling their processing conditions and morphology.

Thermally conductive polyamide 6/carbon filler composites based on a hybrid filler system.

We explored the use of a hybrid filler consisting of graphite nanoplatelets (GNPs) and single walled carbon nanotubes (SWCNTs) in a polyamide 6 (PA 6) matrix. The composites containing PA 6, powdered GNP, and SWCNT were melt-processed and the effect of filler content in the single filler and hybrid filler systems on the thermal conductivity of the composites was examined. The thermal diffusivities of the composites were measured by the standard laser flash method. Composites containing the hybrid filler system showed enhanced thermal conductivity with values as high as 8.8 W (m · K)-1, which is a 35-fold increase compared to the thermal conductivity of pure PA 6. Thermographic images of heat conduction and heat release behaviors were consistent with the thermal conductivity results, and showed rapid temperature jumps and drops, respectively, for the composites. A composite model based on the Lewis-Nielsen theory was developed to treat GNP and SWCNT as two separate types of fillers. Two approaches, the additive and multiplicative approaches, give rather good quantitative agreement between the predicted values of thermal conductivity and those measured experimentally.

Thermal conductivity improvement of surface-enhanced polyetherimide (PEI) composites using polyimide-coated h-BN particles.

In this study, we investigated the thermal conductivities and mechanical properties of polyetherimide (PEI) composites using polyimide (PI)-coated h-BN (PI-BN) particles. We found that PI-coated h-BN effectively increased adhesion with the PEI matrix, imparting enhanced mechanical and thermal stability and thermal conductivity with increasing BN content. The thermal conductivity of the PEI composite containing 60 wt% PI-BN was 3.3 W m(-1) K(-1), while the thermal conductivity of the PEI/BN composite without modification was 2.6 W m(-1) K(-1). The PEI/PI-BN composites show higher impact strengths than the PEI/BN composites because of less BN particle agglomeration and good wettability between PEI and h-BN. The results indicate that the PI-coated BN incorporated into the PEI matrix effectively enhances the thermal conductivity and mechanical properties of the PEI composites.