Crystallization Enthalpy Research Articles

Regression analysis for the determination of microplastics in sediments using differential scanning calorimetry

This research addresses the growing need for fast and cost-efficient methods for microplastic (MP) analysis. We present a thermo-analytical method that enables the identification and quantification of different polymer types in sediment and sand composite samples based on their phase transition behavior. Differential scanning calorimetry (DSC) was performed, and the results were evaluated by using different regression models. The melting and crystallization enthalpies or the change in heat capacity at the glass transition point were measured as regression analysis data. Ten milligrams of sea sand was spiked with 0.05 to 1.5 mg of microplastic particles (size: 100 to 200 µm) of the semi-crystalline polymers LD-PE, HD-PE, PP, PA6, and PET, and the amorphous polymers PS and PVC. The results showed that a two-factorial regression enabled the unambiguous identification and robust quantification of different polymer types. The limits of quantification were 0.13 to 0.33 mg and 0.40 to 1.84 mg per measurement for semi-crystalline and amorphous polymers, respectively. Moreover, DSC is robust with regard to natural organic matrices and allows the fast and non-destructive analysis of microplastic within the analytical limits. Hence, DSC could expand the range of analytical methods for microplastics and compete with perturbation-prone chemical analyses such as thermal extraction–desorption gas chromatography–mass spectrometry or spectroscopic methods. Further work should focus on potential changes in phase transition behavior in more complex matrices and the application of DSC for MP analysis in environmental samples.

The comparative study of crystallization transformation in Zr-Cu-Ag metallic glasses

The crystallization transformation in Zr-Cu-Ag metallic glasses have been comparatively studied. The crystallization enthalpy ΔHx lies in the range of −56.18 ∼ −46.90 J/g for Zr50Cu38Ag12 metallic glass and −55.69 ∼ −44.70 J/g for Zr50Cu36Ag14 metallic glass in their respective isothermal temperatures. The average crystallized volume fraction fmax corresponding to the maximum value of transformation rate [df/d(tIso − τ)]max is about equal to 0.52 and 0.55 for Zr50Cu38Ag12 and Zr50Cu36Ag14 metallic glasses. It is found that at the same isothermal temperature, [df/d(tIso − τ)]max becomes smaller, the time–temperature-transformation (TTT) diagram shifts to the right and time tmax required to reach [df/d(tIso − τ)]max becomes longer when Cu is replaced with Ag, which indicates that the thermal stability will be improved as Ag content rises in these metallic glasses. In addition, the type of growth is interface-controlled growth for Zr50Cu38Ag12 and Zr50Cu36Ag14 metallic glasses.

Temperature‐responsive palm oil‐based‐oleogels for encapsulation of D‐limonene: effect of fat crystallisation and melting point

SummaryD‐limonene is an important flavouring ingredient with a wide range of applications. However, its high volatility and low stability have severely impacted its application in the food industry. To address these limitations, temperature‐flavour release control system is expected to be established to reduce the loss of D‐limonene during processing and storage, as well as to control its release by temperature. The aim of the current study is to construct an oleogel system to encapsulate D‐limonene using carnauba wax as a gelling agent and palm oils (POs) as the base oil. POs with 24 °C, 38 °C, 42 °C, 48 °C, and 52 °C melting points were selected to systematically investigate the effects of the base oil melting point on the crystal morphology, interactions, physicochemical properties, microstructure, and D‐limonene release of the oleogels. The enthalpy of melting, enthalpy of crystallisation, hardness, stickiness, and gel strength increased in oleogels prepared using POs with a higher melting point. In addition, the oil‐binding capacity (OBC) (>95%) of the oleogels increased with the base oil melting point, while the fat crystal distribution became more homogeneous and denser. Based on the influence that extraction temperature has on the concentration of released D‐limonene (a lower concentration of aroma was released from high‐melting‐point POs oleogels at low temperatures (<1.9 mg mL−1), whereas the control group released >2.5 mg mL−1), suitable POs can be selected to achieve the release or retention of the aroma. These results demonstrate that a temperature‐responsive flavour delivery system can be prepared with different PO melting points. The molecular dynamics of flavour release revealed that storage temperature and fat crystalline state impact the cumulative release rate of D‐limonene.

Effect of silicon carbide particles on the mechanical, thermal and structural properties of recycled high-density polyethylene

In this research work, recycled high-density polyethylene (rHDPE)/silicon carbide (SiC) composites were produced by melt compounding followed by injection moulding technique. It has been revealed from the mechanical properties that the addition of SiC increases the hardness, density, flexural strength of the composite and tensile strength of the composite. The impact strength at 15 wt-% SiC composite gives the best results. From the thermal analysis, it was observed that the addition of SiC in rHDPE increases the melting point and total enthalpy of crystallisation. The residual value of rHDPE composites increases with the rise in filler loading which enhances the thermal stability of the composites. Melt flow index (MFI) decreases with the increased in silicon carbide. The heat deflection temperature (HDT) increased with the loading of filler content. The contact angle analysis revealed the hydrophilic nature of the composite. MFI reduced with the incorporation of filler content. The SEM images concluded the agglomeration of the composite at higher filler fractions. These results confirm the possibility of using rHDPE/SiC composite to produce various parts for household commodities and structural applications.

Synthesis and characterization of microencapsulated paraffin with melamine-urea-formaldehyde shell modified with lignin

The study aims to fabricate MUF/paraffin microcapsules with lignin nanoparticles (LNPs)/ melamine-urea-formaldehyde (MUF) resin as hybrid shell material with different LNPs addition were synthesized in oil-in-water emulsion stabilized synergistically by styrene/maleic anhydride (SMA) and LNPs. The morphological characterization of LNPs was observed by transmission electron microscopy (TEM). The particle size of LNPs, the mean particle size and ξ potentials of SMA/LNPs mixture at pH =4.5 were investigated by zeta potential measurement. Field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analyzer (TGA), and differential scanning calorimetry (DSC) were characterized the morphologies, crystallography, chemical component, thermal stability and phase change properties of MUF/paraffin microcapsules with different LNPs addition. The results showed that MUF/paraffin microcapsules were spherical. The LNPs did not influence the chemical structure or crystal type of MUF/paraffin microcapsules. When the LNPs addition was 0.15 g, the melting enthalpy and crystallization enthalpy is respectively 130.03 and 121.92 J/g and the encapsulation efficiency of MicroC-15 is 61.04 %.

Investigation of thermo‐mechanical and viscoelastic properties of 3D‐printed Morinda citrifolia particle reinforced poly(lactic acid) composites

AbstractThe current study focuses on the development of innovative bio‐based filaments using new natural lignocellulosic particles obtained from the bark of the Morinda citrifolia L. plant as reinforcement. Polylactic acid (PLA 4043D) filaments with a diameter of 1.75 mm were produced by varying the volume fraction of M. citrifolia bark particles (MCBP) in three compositions (i.e., 0%, 3%, and 6%). These filaments were then used to print test specimens, which underwent quasi‐static mechanical tests (i.e., tensile and flexural; thermal characterization, thermo‐mechanical tests, and visco‐elastic analysis). The experimental findings demonstrated a remarkable improvement in the tensile strength (i.e., +15%) when the PLA was reinforced with 6% in volume of lignocellulosic particles. Additionally, 3% MCBP and 6% MCBP composites showed substantial increases in flexural strength and modulus (i.e., +25% and +34%), respectively; in comparison to the neat matrix. Moreover, the 3D‐printed composites exhibited significant enhancements in storage modulus, glass transition temperature, and structural stability at elevated temperatures. Hence, this work highlights the potential of the developed bio‐based filaments as feedstock filament material, enabling the production of various customized lightweight products in the automotive and sports industries like cycling helmets, protective guards, knee guards, etc.Highlights Innovative bio‐based filaments are developed for FDM 3D printing. Morinda citrifolia bark particles (MCBPs) reduce warping risk in PLA printing. The hot crystallization enthalpy of PLA increases with the addition of MCBP. 6% MCBP‐PLA exhibits the best mechanical performances. MCBP reinforcement reduces the thermal expansion of PLA.

Influence of cross-link density on the non-isothermal crystallization kinetics of polybutylene terephthalate

Kinetics of crystallization of the samples of cross-linked polybutylene terephthalate with different cross-link densities was studied experimentally using conventional differential scanning calorimetry (cooling rates 5 to 40 K·min–1) and fast scanning calorimetry (cooling rates 0.5 to 5000 K·s–1). The samples were obtained by copolycondensation of terephthaloyl chloride, 1,4-butanediol, and glycerol. The cross-linking degree was characterized using 1H NMR spectroscopy. An increase of the number of glycerol cross-links in polymer leads to a decrease in the crystallization and melting temperatures and suppression of crystallization process. The critical rate of crystallization decreases monotonically with increasing cross-linking degree from 2700 K·s–1 for linear polybutylene terephthalate to 110 K·s–1 for the sample with 270 mol·m–3 cross-link density. At the cross-link densities higher than 270 mol·m–3, the polymer does not crystallize even at 5 K·min–1 cooling rate. The observed dependence of the cold crystallization enthalpy on the previous cooling rate suggests that the homogeneous nuclei formation process also slows down with an increase in the cross-linking degree.

Studying the effects of asphaltene oxidation on wax crystallization and rheological properties in waxy crude oils

Oxidation in crude oil production is unavoidable. Oxidized asphaltenes, interacting with waxes during crystallization, profoundly alter wax precipitation and gel behavior in crude oils. This research evaluated the impact of asphaltene oxidation on the wax precipitation characteristics and rheological properties of waxy crude oils during the processes of crude oils extraction and transportation. A comprehensive structural characterization of the asphaltenes was conducted, revealing an increase in aromaticity and a reduction in the length and abundance of aliphatic chains following oxidation, accompanied by the formation of larger asphaltene aggregates. Subsequently, an investigation into the wax precipitation behaviors of waxy model oils showed that asphaltenes were involved in the crystallization processes of wax molecules, which had a minor impact on wax precipitation characteristics (crystallization and crystallization enthalpy). However, it had a significant influence on the rheological properties (pour point, flow curve and gel strength) of the systems. And it was also observed that the degree of influence was dependent on the structure and composition of the given asphaltenes and waxes. Asphaltenes with abundant aliphatic chains (before oxidation) tended to assume favorable positions during the crystallization process, which interfered to some extent with the normal growth of wax crystals and resulting in a transition from a “strong gel” to a “weak gel” network structure of wax crystals. Conversely, the oxidized asphaltenes with a high aromaticity exhibited a greater interference with wax crystal growth. This interference not only more effectively hindered the establishment of the wax crystal network but also prompted the formation of an “extremely fragile gel structure”.

Cellulose nanocrystal stabilized copper nanoparticles for grafting phase change materials with high thermal conductivity

Phase change materials (PCMs) have recently garnered significant attention for thermal energy storage applications. However, widely used PCMs, such as polyethylene glycol (PEG), suffer from low heat conductivity, poor thermal stability, and a tendency to leak, limiting their practical use. Therefore, the objective of this study is to develop a highly thermally conductive composite PCM using PEG and a thermally conductive nanomaterial, specifically cellulose nanocrystals supported by copper nanoparticles (CNC@Cu-NPs). The CNC@Cu-NPs nanocomposite material was used as a matrix to support polyethylene glycol (PEG), resulting in a shape-stable phase change material termed PEG/CNC@Cu-NPs. The obtained PEG/CNC@Cu-NPs were characterized using various analytical techniques. Fourier transform infrared spectroscopy (FTIR) analysis revealed the chemical linkages between PEG and cellulose nanocrystals through a radical polymerization reaction. Polarizing optical microscopy (POM) images of PEG/CNC@Cu-NPs exhibited spherocrystal morphology with smaller sizes compared to pure PEG, suggesting that CNC inhibited PEG side-chain mobility. According to differential scanning calorimetry, the suggested PEG/CNC@Cu-NPs demonstrated a temperature transition between 0.51 °C to 24.5 °C with enthalpies of fusion and crystallization measured at 92.19 and 98.54 J/g, respectively, while also exhibiting excellent cycling stability after 60 heating/cooling cycles. The addition of a modest amount of copper nanoparticles resulted in a remarkable improvement (>50 %) in the thermal conductivity of the PCM. Thermal imaging using an infrared camera showed that PEG/CNC@Cu-NPs exhibited a delay of 10 min in heating compared to pure CNC, confirming the good heat retention capacity of the developed composite material. Based on the aforementioned findings, the proposed PEG/CNC@Cu-NPs PCM offers promising application possibilities in the field of thermal energy storage.

Morphologies of Comb-like Polyacrylic Acid/Polyacrylate Copolymers as Functions of the Degree of Derivatization with n-C22H45 Side Chains.

Polymers with crystallizable side chains have numerous applications, and their properties depend on their crystal morphologies and phase separation. Structural analysis on a wide spatial scale plays an important role in controlling the thermal properties and higher-order structures of these polymers. In this study, we elucidated the melting and crystallization processes of copolymers with varying crystallizable side-chain fractions over a wide spatial range. Differential scanning calorimetry revealed that the enthalpies of melting and crystallization increased linearly with increasing crystallizable side-chain fraction. The results of wide-angle X-ray scattering indicated that the crystal lattice was hexagonal. Conversely, spherulite-like higher-order architectures with linear structures and radial spreading were observed in the highly crystallizable components, but no micrometer-scale structures were observed in the less crystallizable components. In situ small-angle X-ray scattering was used to elucidate the phase separation and mixing processes. Lamellar crystallites were observed at crystallizable side-chain fractions of >55 wt.%, whereas small crystallites were observed at fractions of <45 wt.%. At temperatures above the order-disorder transition temperature, density fluctuations caused by correlation holes were observed. These properties have a strong effect on the crystallizable side-chain fraction.

Phase change composite fiber membranes based on polyurethane/polyethylene glycol/silica with super-wetting and photothermal properties

Phase change materials (PCMs) temperature regulation by absorbing or releasing heat. Meanwhile, silicon dioxide nanoparticles (SiO2 NPs) can effectively increase the reflectance of visible and near-infrared light, lowering the surface temperature of fibers. In this study, electrospinning technology was employed to fabricate polyurethane/polyethylene glycol (PU/PEG) fiber membranes, which were made with PEG serving as thermal energy storage material and PU acting as a mechanically strong supporting material. Then, a layer of SiO2 NPs was electrosprayed onto the surface of phase change fibers, finally creating a composite fiber membrane with superwettability and a photothermal regulating function. The results showed that, although the static WCA of PU/PEG/SiO2 fiber membrane reached around 115.4°, liquid water droplets (100 μL) slowly penetrated into the fiber membrane and the penetrating velocity was faster than that of a hydrophilic PU/PEG membrane. The melting enthalpy (ΔHm) of the fiber membrane could be kept at 86.30 J/g when the loading amount of PEG was 1.25 times that of the PU. The phase change fiber membrane's variations in the ΔHm and crystallization enthalpy (ΔHc) after 100 heating-cooling cycles were less than 5 %, indicating its great thermal stability. Through the introduction of hydrophilic SiO2 NPs, the average reflectance of PU/PEG/SiO2 fiber membranes in visible and near-infrared light at 500–1250 nm was increased to 85.17 %. After 40 min of xenon lamp irradiation, the surface temperature of PU/PEG/SiO2 fiber membranes was 4.19 °C lower than that of fibers without SiO2 NPs, demonstrating its effective cooling ability. This work proposes an effective strategy for preparing intelligent textiles with features, such as quick drying, infrared stealth and refrigeration capabilities.

Enhancing thermal energy storage in buildings with novel functionalised MWCNTs-enhanced phase change materials: Towards efficient and stable solutions

Phase change materials (PCMs) are a promising panacea to tackle the intermittency of renewable energy sources, but their thermal performance is limited by low thermal conductivity (TC). This pioneering work investigates the potential of organic PCM-enriched surface-modified and un-modified multi-walled carbon nanotubes (MWCNTs) for low-temperature thermal energy storage (TES) applications. The functionalised and un-functionalised MWCNTs enhanced PCM have demonstrated a TC enhancement of 158 % and 147 %, respectively, at 25 °C. However, the TC value of the unmodified MWCNTs-based PCM dropped by 52.5 % after 48 h at 25 °C, while that of the functionalised MWCNTs-based PCM remained stable. A DSC analysis of up to 200 thermal cycles confirmed that the surface-modified and un-modified MWCNTs had no major effect on the peak melting and cooling temperatures of the nano-enhanced PCMs although a minor decrease of 7.5 % and 7.7 % in the melting and crystallisation enthalpies, respectively, was noticed with the inclusion of functionalised MWCNTs. Moreover, functionalised MWCNTs incorporated PCMs have led to increases in specific heat capacity by 23 % with an optimal melting enthalpy value of 229.7 J/g. In addition, no super-cooling, no phase segregation, and a small phase change temperature were noticed with these nano-enhanced PCMs. Finally, no chemical interaction from nano-PCMs was seen in the FT-IR spectra with the incorporation of both functionalised and un-treated MWCNTs. It is evident that the functionalised MWCNT-based PCM has better thermal stability and it offers a promising alternative for improving thermal storage and management capabilities in buildings, contributing to a sustainable and energy-efficient building design.

Insight into the synthesis and thermomechanical properties of “short‐long” type biobased aliphatic polyesters

AbstractA series of biobased “short‐long” chain aliphatic polyesters having high molecular weight were successfully synthesized using dimethyl sebacate and diols with different carbon chain lengths via a two‐step melt‐polycondensation method by using titanium butoxide as a catalyst. The diols chain length and its odd‐even effect on the structure–property relationship, crystallinity, and thermomechanical properties of the polyesters were systemically investigated. The synthesized polyesters displayed weight‐average molecular weight between 23,600 to 72,900 g/mol and a maximum intrinsic viscosity of 0.933 dL/g. With increasing the diol chain length, the molecular weight of the polyesters increased linearly, except for poly(butylene sebacate) (PBS). Altogether, the “odd‐even” effect of the diol chain on the crystalline (Tc)/melting temperature (Tm), and melting/ crystallization enthalpies of the polyester's were observed. Poly(pentylene sebacate) (PPeS) has the highest weight‐average molecular weight of 72,900 Da, Tm of ∼55.4°C, degradation temperature (Td,max) of about 404°C, and highest storage modulus (E′ at 25°C) of 661 MPa compared to other short‐chain polyesters. PBS and PPeS showed the appearance of sharp intensity peaks from XRD diffraction patterns, indicating higher crystallinity in the material, in accordance with crystallization enthalpies (ΔHc) values from the differential scanning calorimetry (DSC) thermograms. These fabricated biobased polymers with 100% bio‐content, low melting temperature range, rapid crystallization, and high thermal stability suggest good processability and can offer an alternative option to nonrenewable thermoplastic polyesters for potential applications.

Performance analysis of hybrid expanded graphite-NiFe2O4 nanoparticles-enhanced eutectic PCM for thermal energy storage

This current experimental study aims to resolve the demerits of pure PCM by introducing the hybrid nanomaterial-induced composite PCM (HNIPCM) with practical feasibility on solar water heater performance using an indigenously developed setup. To settle out these performance characteristics, expanded graphite (EG) and nickel ferrite nanoparticles (NiFe2O4) with different weight concentrations (ɸ = 1–5 %) were used for the first time as a thermophysical property-enhancing filler material inside a eutectic organic-organic PCM (polyethylene glycol 6000/paraffin wax) by two-step method. A detailed study on the physical and chemical stability, surface morphology, and thermal feasibility of the HNIPCM was conducted to provide the optimized characteristics for the target applications. The energy storage capacity, melting and crystallization temperature, thermal stability, thermal reliability, thermal behaviour, and thermal conductivity were also examined by DSC, TGA, thermal cycling, and charging-discharging, respectively. The HNIPCM with 3 wt% filler concentration revealed comparatively well-balanced thermophysical properties among the prepared samples. The results also showed that the melting point, crystallization point, melting enthalpy, and crystallization enthalpy were changed to 54.55 °C, 48.83 °C, 128.52 J/g, and 129.02 J/g, respectively, for HNIPCM with 3 wt% of filler material in comparison with eutectic PCM of 59.14 °C, 41.23 °C, 154.37 J/g, and 155.21 J/g. An increase in thermal conductivity up to 253.72 %, enhancement in the charging and discharging rate, and good stability up to 500 working cycles with a 12.19 °C decrease in the supercooling were also observed with no physical and chemical alteration. The real-time performance of the prepared HNIPCM was also investigated using a novel indigenously developed solar water heater at different inclination angles (40°, 45°, and 50°), flow rates (1.2 LPM, 2.2 LPM, and 5.2 LPM), and charging periods (90mins, 120mins, and 180mins). Comparatively higher performance at a 45° inclination angle, 2.2LPM water low rate with 68.99 % efficiency (day) and 50.45 % (night) was observed. The enhanced thermophysical properties of the HNIPCM made it suitable for a viable candidate for solar thermal energy, air conditioners, TES, and electronic cooling units.

Time-Temperature-Transformation (TTT) Diagram of Battery-Grade Li-Garnet Electrolytes for Low-Temperature Sustainable Synthesis.

Efficient and affordable synthesis of Li+ functional ceramics is crucial for the scalable production of solid electrolytes for batteries. Li-garnet Li7 La3 Zr2 O12-d (LLZO), especially its cubic phase (cLLZO), attracts attention due to its high Li+ conductivity and wide electrochemical stability window. However, high sintering temperatures raise concerns about the cathode interface stability, production costs, and energy consumption for scalable manufacture. We show an alternative "sinter-free" route to stabilize cLLZO as films at half of its sinter temperature. Specifically, we establish a time-temperature-transformation (TTT) diagram which captures the amorphous-to-crystalline LLZO transformation based on crystallization enthalpy analysis and confirm stabilization of thin-film cLLZO at record low temperatures of 500 °C. Our findings pave the way for low-temperature processing via TTT diagrams, which can be used for battery cell design targeting reduced carbon footprints in manufacturing.

Time‐Temperature‐Transformation (TTT) Diagram of Battery‐Grade Li‐Garnet Electrolytes for Low‐Temperature Sustainable Synthesis

AbstractEfficient and affordable synthesis of Li+ functional ceramics is crucial for the scalable production of solid electrolytes for batteries. Li‐garnet Li7La3Zr2O12−d (LLZO), especially its cubic phase (cLLZO), attracts attention due to its high Li+ conductivity and wide electrochemical stability window. However, high sintering temperatures raise concerns about the cathode interface stability, production costs, and energy consumption for scalable manufacture. We show an alternative “sinter‐free” route to stabilize cLLZO as films at half of its sinter temperature. Specifically, we establish a time‐temperature‐transformation (TTT) diagram which captures the amorphous‐to‐crystalline LLZO transformation based on crystallization enthalpy analysis and confirm stabilization of thin‐film cLLZO at record low temperatures of 500 °C. Our findings pave the way for low‐temperature processing via TTT diagrams, which can be used for battery cell design targeting reduced carbon footprints in manufacturing.

Preparation and properties of vermiculite modified by triphenylbutylphosphonium bromide and PBAT composite film

AbstractIn this study, quaternary phosphonium salt (P4) was prepared, vermiculite (VMT) was modified by P4, and P4@VMT/poly (butylene adipate‐co‐terephthalate) (PBAT) composite film was prepared by the solution method. The structure of the synthesized P4 was determined by nuclear magnetic resonance and infrared. The structure and performance of P4 modified vermiculite were explored and analyzed by particle size, XRD, infrared and micro‐morphology. The structure, thermal properties, crystallization properties, rheological properties, cross‐section morphology, tensile properties and antibacterial properties of pure PBAT film and P4@VMT/PBAT composite film were tested and compared. The results show that the crystallization temperature and melting temperature of P4@VMT/PBAT composite film are higher than those of pure PBAT film. With the increase in P4@VMT content, the thermal stability of the composite film becomes worse, and the crystallization enthalpy, melting enthalpy and crystallinity also decrease, while the storage modulus, loss modulus and complex viscosity of P4@VMT/PBAT composite film increase significantly. In addition, compared with pure PBAT film, the tensile strength of P4@VMT/PBAT‐20% composites decreased by 12.0% and the elongation at break decreased by 95.7%.Highlights Successful synthesis of phosphonium quaternary P4 and modification of vermiculite. The properties of P4@VMT/PBAT composite films with different contents were studied.

Designing Poly(3,4-ethylenedioxythiophene) Polystyrene Sulfonate/Graphene Oxide/Graphene Nanosheet/Polyethylene Glycol Phase-Change Composites with Superior Thermal Management for Photo-thermoelectric Generators.

Recently, growing interest in self-powered devices has led to the invention of new energy conversion devices. Photo-thermoelectric generators (PTEGs) have rapidly developed for their ability to harvest both light and thermal energy, but these devices are overly dependent on the continuity of energy input and cannot sustain output in an emergency situation. In the current study, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/graphene oxide (GO)/graphene nanosheets (GNPs)/polyethylene glycol (PEG) phase-change composites (PCCs) were prepared with freeze-drying and vacuum-filling processes to acquire materials suitable for imparting energy storage characteristics to PTEGs. The melting and crystallization enthalpies of the PCCs fabricated based on the PEDOT:PSS/GO/GNP aerogels can reach 211.5 and 207.6 J g-1, respectively, which increase by nearly 5% compared with pure PEG, and the growth rate of thermal conductivity of the composites is as high as 262.7% (1.12 W m-1 K-1). Meanwhile, the excellent photothermal properties and high-temperature shape stability that pure PEG does not possess can also be imparted to PCCs by the aerogels. The PTEG assembled with PCCs and thermoelectric components can achieve a continuous output of over 1500 s after 300 s of light irradiation. After integrating the output of the device during the lamp on/off period, it is found that the total output of the device during the light-off period (8.4 V and 9.6 mW) can far exceed its total output during the light-on period (2.7 V and 4.4 mW). This work provides guidance for modulating the performance of PCCs and giving PTEGs the ability to operate under emergency or extremely harsh conditions and the prepared PTEGs are highly promising for practical use.

Three-dimensional hierarchical porous carbon surface-decorated graphitic carbon foam/stearic acid composite as high-performance shape-stabilized phase change material with desirable photothermal conversion efficiency

To simultaneously improve the photothermal conversion and encapsulation capacity of phase change material (PCM), a three-dimensional hierarchical porous carbon surface-decorated graphitic carbon foam (SGF) was developed. Employing this SGF as an encapsulated skeleton for stearic acid (SA), a unique shape-stabilized SA/SGF composite PCM was successfully prepared after vacuum impregnation. The porous carbon surface exhibits a uniform and fluffy three-dimensional continuous network structure well adhered onto the pore walls of the SGF; it can act as a desirable interfacial layer between SA and the SGF, which gives the composite effective encapsulation performance and good interfacial compatibility. The as-prepared composite has a loading capacity of 78.16% for melted SA without any leakage, and possesses a thermal conductivity of 3.25 W/mK with 1377% higher than that of SA and a compressive strength of 4.41 MPa (increasing 283.5% than the SGF). Further, the melting and crystallization enthalpy of the composite reaches 167.6 J/g and 167.5 J/g, respectively, with a thermal storage efficiency of up to 95.13%; meanwhile, it displays excellent thermal cycle stability revealed by keeping an enthalpy of 92.80% after 200 thermal cycles. More importantly, it presents a high photothermal conversion of 90.14% at 200 mW/cm2 with the ability to serve as a stable heat source during solar-thermal-electric conversion. Consequently, the composite has great potential in solar storage and waste heat recycle.

Chalcogenopheno[3,2-b]pyrrole-Containing Donor-Acceptor-Donor Organic Semiconducting Small Molecules for Organic Field-Effect Transistors.

A group of chalcogenopheno[3,2-b]pyrroles, including thieno[3,2-b]pyrrole (TP), furo[3,2-b]pyrrole (FP), and selenopheno[3,2-b]pyrrole (SeP), and thieno[3,2-b]thiophene (TT) electron-donating units were coupled with a thiophene-flanked diketopyrrolo[3,4-c]pyrrole (ThDPP) acceptor to generate four donor-acceptor-donor (D-A-D) semiconducting small molecules (ThDPP-TT, ThDPP-FP, ThDPP-TP, and ThDPP-SeP). This study systematically investigated the differences between chalcogenopheno[3,2-b]pyrroles and TT. From the characterizations, chalcogenopheno[3,2-b]pyrrole-containing molecules showed lower band gaps and binding-energy cold crystallization behavior. The enthalpies of cold crystallization were correlated with the weight of the chalcogen in ThDPP-FP, ThDPP-TP, and ThDPP-SeP, which were evaluated as intermolecular chalcogen-bond interactions between chalcogen and pyrrole nitrogen in chalcogenopheno[3,2-b]pyrroles. A stronger chalcogen bond interaction resulted in stronger self-aggregation in thin films with thermal treatment, which resulted in a polycrystalline structure in chalcogenopheno[3,2-b]pyrrole-containing molecules. For the application in an organic field-effect transistor, all four molecules showed good performance with the highest hole mobilities as 6.33 × 10-3 cm2 V-1 s-1 for ThDPP-TT, 2.08 × 10-2 cm2 V-1 s-1 for ThDPP-FP, 1.87 × 10-2 cm2 V-1 s-1 for ThDPP-TP, and 6.32 × 10-3 cm2 V-1 s-1 for ThDPP-SeP, and the change of mobility is well correlated to the root-mean-square roughness of the thin films. Overall, all the chalcogenopheno[3,2-b]pyrrole-containing molecules showed lower band gaps, polymorphism, and better charge transport properties compared to TT-containing molecules, which motivates replacing TT with chalcogenopheno[3,2-b]pyrroles in conjugated polymers, non-fullerene small molecular acceptors, and narrow-band-gap donors.