A lauric acid-hybridized bentonite composite phase-changing material for thermal energy storage

In this study, a form-stable composite phase-changing material (PCM) was synthesised by a vacuum impregnation method. Natural Na-bentonite and lauric acid (LA) were used as the supporting material and PCM, respectively. In addition, flake graphite (FG) was used for enhancing the thermal conductivity of the form-stable composite PCM, besides for blocking the leakage of the PCM. Notably, with the addition of FG, the period of melting and freezing of the composite PCM decreased to a certain extend. Meanwhile, the heat-transfer characteristic of the composite increased. Moreover, the as-prepared form-stable composite PCM showed good thermal reliability after 200 cycles of thermal-cold treatment and has the potential to be used in thermal energy storage systems.

We have developed a shape-stabilized composite phase change material (PCM) for thermal-energy storage in this work. The as-prepared LA/Na-bentonite-1 seems to be a promising shape-stabilized composite PCM candidate for thermal-energy-storage systems.     

Experimental study of the thermal storage and mechanical properties of microencapsulated phase change composites during a supersonic cruise

Microencapsulated phase change composites, one of the high-efficiency thermal protection media, are widely used in the thermal protection of supersonic aircraft. The phase transition occurring during the cruise of supersonic aircraft leads to a change in the mechanical properties of microencapsulated phase change composites (MPCMs). In this study, we experimentally studied the variations of the mechanical properties of MPCMs during cruise. The effects of the volume fraction ratio of core to shell on the thermal storage and mechanical properties of the microencapsulated phase change composites are investigated. Results show that the latent heat capacity increases with an increase in the volume fraction ratio of core to shell. The deformation mode translates from a brittle fracture into a brittle deformation status during the phase transition. The mechanical properties of the MPCMs decrease at three conditions without phase transition, during phase transition and complete phase transition, respectively, with an increase in the ratio of core to shell as well as increased temperature. The above-mentioned findings can guide the design of a best thermal management system for supersonic aircraft.

Deformation mode will translate from a brittle fracture into a brittle deformation status during the microencapsulated phase change the composite phase transition.     

Molecular dynamics simulations of phase change materials for thermal energy storage: a review

Phase change materials (PCM) have had a significant role as thermal energy transfer fluids and nanofluids and as media for thermal energy storage. Molecular dynamics (MD) simulations, can play a significant role in addressing several thermo-physical problems of PCMs at the atomic scale by providing profound insights and new information. In this paper, the reviewed research is classified into five groups: pure PCM, mixed PCM, PCM containing nanofillers, nano encapsulated PCM, and PCM in nanoporous media. A summary of the equilibrium and non-equilibrium MD simulations of PCMs and their results is presented as well. The primary results of the simulated systems are demonstrated to be efficient in manufacturing phase change materials with better thermal energy storage features. The goals of these studies are to achieve higher thermal conductivity, higher thermal capacity, and lower density change, determine the melting point, and understand the molecular behaviors of PCM composites. A molecular dynamics-based grouping (PCM simulation table) was presented that is very useful for the future roadmap of PCM simulation. In the end, the PCFF force field is presented in detail and a case problem is studied for more clarity. The results show that simulating the PCMs with a similar strategy could be performed systematically. Results of investigations of thermal conductivity enhancement showed that this characteristic can be increased at the nano-scale by the orientation of PCM molecules.

Phase change materials (PCM) have had a significant role as thermal energy transfer fluids and nanofluids and as media for thermal energy storage.     

Moisture affinity of HDPE/phase-change material composites for thermal energy storage applications

Moisture adsoprtion can degrade the structural integrity of thermal energy storage devices and can negatively impact the capacity and charging/discharging behaviour. Steady-state and transient experiments are conducted at various operating temperatures to evaluate the moisture affinity of organic phase-change material (PCM) shape stabilized with high-density polyethylene (HDPE).

A composite HDPE/PCM filament for 3D printing thermal energy storage systems is naturally hydrophobic.     

Thermal properties and reliabilities of myristic acid–paraffin wax binary eutectic mixture as a phase change material for solar energy storage

In this work, a myristic acid (MA)–paraffin wax (PW) binary eutectic phase change material (PCM) was prepared by a melt-solution blending method. The eutectic point of the MA–PW binary system was determined to be 62 wt% MA–38 wt% PW using a cooling curve. In addition, the phase transition properties and thermal stability of MA–PW binary eutectic PCM were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG) analysis. The melting temperature and latent heat as well as starting temperature of decomposition for MA–PW binary eutectic PCM were 41.99 °C, 171.43 J g⁻¹ and 137.86 °C, respectively. Besides, analysis of the chemical and crystal structures of MA, PW and MA–PW revealed no chemical reaction between MA and PW to produce a new molecular structure and no change in the crystal structure. Finally, MA–PW binary eutectic PCM still has good thermal properties and chemical stability after 500 cold–hot cycles.

A myristic acid (MA)–paraffin wax (PW) binary eutectic phase change material (PCM) was prepared by a melt-solution blending method, and its thermal performance and reliability were studied.     

Preparation,characterization, and thermal properties of novel fire-resistant microencapsulated phase change materials based on paraffin and a polystyrene shell

Paraffin and paraffin mixtures that are preferred as phase change materials in many thermal energy storage applications are highly flammable. Microencapsulation of paraffin in a polymeric shell can decrease flammability, however, breaking of the shell under fire conditions can still cause a high risk. In the current paper, microencapsulated paraffin with a polystyrene shell is prepared and halogen-free flame retardants (ortho-phosphoric acid and pentaerythritol) were applied with the novel approach of direct incorporation during the microencapsulation process. Thermal energy storage and fire retardancy properties were characterized before and after fire-retardant addition. The fire behavior of samples in concrete blocks was determined with standardized methods in order to assess their suitability in building applications. ortho-Phosphoric acid as a flame retardant in microencapsulated phase change material was tested for the first time in this study. The results support that the improved flame retardancy and thermal energy storage properties were achieved with the incorporation of a flame retardant on microcapsules for energy storing concrete samples.

Flame retardancy properties of paraffin-based microcapsules were enhanced using halogen-free fire retardants. The reducing on the heat of combustion, and improving on noncombustibility properties and microencapsulation ratio were achieved.     

Perylene bisbenzimidazole nonlinear dielectric material for energy storage

A novel perylene bisbenzimidazole comprising both donor and acceptor functional groups was designed, synthesized, and characterized. This structure exhibits potentially useful physical properties, including a nonlinear dielectric response to an increasing electric field. This material can be used in energy storage devices as the dielectric part of a capacitor. Energy storage devices based on film capacitors are targeting applications in a wide range of industrial, residential and transportation systems.

We synthesized and characterized an organic molecule which can serve as a unit for high-density energy storage.

Capacitors are among the simplest devices that store electrical energy and feature high charge–discharge rates, high power density, and a wide range of operating temperatures.¹ As a result, they have found use in many electronic devices and in numerous industrial applications. However, while capacitors feature high power density, they do not compete with the high gravimetric energy density of batteries, precluding their use as long-term energy storage devices. This disadvantage originates from the low polarizability of conventional dielectric materials found in modern industrial capacitors. We are developing new dielectric materials with high polarizability, high resistivity, and high breakdown voltage. These materials will widen the scope of capacitor applications to a variety of energy storage devices including transportation, industry, and residential applications.For traditional materials, dielectric polarizability is a constant value with stored energy sharing a linear relationship to the dielectric permittivity of the material. At high electric fields, however, many materials exhibit a nonlinear dielectric constant.² Commonly, these materials consist of highly polarizable molecules with electron-donating and/or electron-withdrawing groups on opposite sides of a large conjugated core. These groups can increase polarizability and further impart directionality to the delocalized electrons when an electric field is applied.Here we present the general structure for a non-linear dielectric chromophore, that we named dielectrophore, that would bring the combination of required properties into capacitors: high permittivity, resistivity, and breakdown strength, as well as good processability and mechanical flexibility.³ The main three components that build these properties are: the polyaromatic core, allowing π–π stacking within the material as well as high polarizability, donor and acceptor groups at each end of the conjugated core increasing the first hyperpolarizability, and insulating subunits that prevent current leakage within the capacitor (Fig. 1). In such structures, the cores are predominantly planar polycyclic molecular system which forms column-like supramolecular stacks by π–π interactions.Open in a separate windowFig. 1General representation of an ideal dielectrophore, such as 15.Perylene-3,4,9,10-tetracarboxylic acid diimides (PDIs) are among the most extensively used cores for studies of π–π stacking and columnar liquid crystalline structures. It is noteworthy that PDI-based molecules have been widely used as colorants and dyes, as well as chromophores for optoelectronic applications such as photovoltaics and organic field effect transistors. This is due to the combination of their optoelectronic properties, such as large extinction coefficients, high fluorescent quantum yields, strong electron-accepting ability (N-type semiconductors), and high thermal and chemical stability.⁴ Most of these properties originate from the delocalization of the π electrons of the PDI''s. In addition, the modular structure and straightforward synthesis of PDI-based molecules streamline the modification of their structures, which helps to bring all the required properties of our dielectrophores.Our theoretical studies demonstrated that linear polarizability of the PDIs can be strongly increased by transforming the diimide functions into the more conjugated benzimidazole derivatives and adding donor (NEt₂) and acceptor groups (NO₂) at the opposite sides of a molecule.⁵ Considering the predicted design, we propose molecule 15 as our target molecule (Fig. 1). Long alkyl chains are added via phenyl linkers at both sides of the molecule and bring significant impact into the resistivity of the potential capacitor and help with processability during the synthetic manipulations and film coating.One of the main advantages of 15 is the modularity of its synthesis, which can be performed as a step-wise addition of two substituted o-phenylenediamines to 13 (Scheme 1). 13 was synthesized according to a modified procedure reported by Xiao and co-workers (outlined in Scheme 1).⁶ In our synthesis, 3 is accessed through a 2-step derivatization of catechol (1) through an alkylation followed by a C–H activated borylation.⁷ The electron-acceptor diamine (7) was synthesized from 2,5-dinitroaniline (4) via bromination with NBS, followed by Suzuki coupling with 6, and further reduction of one of the nitro groups with ammonium sulfide. The electron donating diamine (12) was synthesized from 3-bromo-2,5-difluoronitrobenzene (8) via nucleophilic aromatic substitution at room temperature, followed by Suzuki coupling with 3 to isolate 10. A nucleophilic aromatic substitution with benzylamine at elevated temperature yields 11 and a deprotection/reduction using Pd(OH)₂/C and H₂ at 55 psi afforded 12. 14 was obtained in two steps by stirring diamine 7 with 13 in molten imidazole at 140 °C for 12 hours then further treating the product with an excess of para-toluenesulfonic acid in toluene at 100 °C to afford 14 in 37% overall yield (Scheme 1).Open in a separate windowScheme 1Synthesis of 15.15 was made through the condensation of mono-anhydride 14 with diamine 12 with the presence of zinc acetate in quinoline at 140 °C for 12 hours. Upon precipitation into methanol, 15 was isolated as a dark purple solid. It is important to mention that reactions of 13 with 7 and then 14 with 12 are likely not regioselective, even though steric factors favour the formation of the isomers 15a and 15b (Scheme 2) with donor/acceptor groups located farther from carboxamide group, especially in the case of the bulkier diethylamino group. Indeed, six additional isomers may be present, in addition to 15a and 15b (15c–h, see ESI^†). Column chromatography to separate these regioisomeric mixtures is shown to be quite challenging.⁸ Considering our theoretical studies, that demonstrated both syn- and anti-isomers to have similar predicted polarization values, separation of individual isomers is unnecessary.⁵Open in a separate windowScheme 2Main isomers of 15.15 was characterized with UV-vis and FTIR spectroscopic techniques and molecular weight was confirmed through mass spectrometry (see ESI^†). FTIR of 15 shows the absence of the anhydride carbonyl stretches of 14 at 1769 and 1732 cm⁻¹ respectively and the emergence of benzimidazole stretches at 1691, 1592, and 1573 cm⁻¹.⁹¹H NMR of 15 in 100% CDCl₃ initially exhibit very broad signals, but when 10% dTFA is added this aggregation is broken up (see ESI^†). The formation of the benzimidazole extends the length of conjugation considerably, this transformation can be clearly observed in the UV-vis spectra where the λ_max shifts from 523 nm for 13 to 555 nm for 14 (ESI^†). The λ_max shifts even further towards the near infrared region (752 nm) upon addition of the donor block (12) and making 15 (Fig. 2A). The drastic broadening of the band from 500 to 900 nm for 15 is caused by the extended conjugation, the formation of π–π-aggregates in the solution and the presence of a mixture of isomers,^8a as well as intramolecular charge transfer (ICT) in this push–pull system.¹⁰ The UV-vis spectrum in chloroform was predicted using a B3LYP/6-31H level of theory and compared with the experimental data (see ESI^†). The computed spectrum identifies three major bands at 409, 552, and 850 nm, respectively, in some agreement with the observed λ_max at 395, 525, and 752 nm (ESI^†). 15 was then cast into films on the Indium–Tin–Oxide (ITO)/glass substrate (see ESI^†) and charged through corona poling to test its nonlinear behaviour in the presence of an electric field.Open in a separate windowFig. 2(A) UV-vis absorption spectra of intermediates 13 (solid red), and 14 (dashed green), and final perylene-bisbenzimidazole 15 (dash-dot blue) (0.05 mg mL⁻¹ in CHCl₃). (B) Corona charging capacitor experiment of films cast from polypropylene (PP, dash black) and 15 (dash-dot blue).In corona poling, a sharp corona tip is charged up to several kilovolts until the electric breakdown of surrounding atmosphere occurs and the positive or negative ions are deposited on the film surface.¹¹ With this approach, a large electric field necessary to study the nonlinear response of the material is achieved. Once charge is deposited we used a Kelvin probe to measure the surface potential and its dependence on the amount of deposited charges, which can be determined by measuring the current from the bottom ITO electrode to the ground. This current is directly proportional to the voltage of the corona electrode, as expected, and is controlled by the corona current setting. It is then a simple calculation to convert the time under the corona charge deposition into the charge density on the top of the film. In our experiment, we use the current of 10⁻⁵ A and the area of the film is 11.5 × 6 cm².The results of the corona experiment are shown in Fig. 2B for the 2.165 μm thickness film of 15 and 6 μm polypropylene (PP) thin film for the comparison. PP is a common material used as a dielectric in many high voltage capacitors and shows a usual linear relationship between increasing charge density and a growing electric field (Fig. 2B). The dielectric constant of PP is estimated through this approach to be 2.9, close to the tabulated value.¹² When 15 is exposed to the same conditions, we observe a nonlinear voltage saturation at an electric field of 40 V μm⁻¹. We can conclude that in such nonlinear regime the deposition of additional charge leads to the increase of the polarization, not to the increase of the electric field. It should be emphasized that in PP films the electric breakdown occurs after about 10 seconds of the charge deposition, while 15 can sustain up to 5 hours at the same conditions. Correspondingly, the energy stored in the capacitor based on our molecule would be larger than that of the polypropylene-based capacitor by several orders of the magnitude.     

Performance enhancement of a thermal energy storage system using shape-stabilized LDPE/hexadecane/SEBS composite PCMs by copper oxide addition

Thermal Energy Storage (TES) technologies based on Phase Change Materials (PCMs) with small temperature differences have effectively promoted the development of clean and renewable energy. The organic phase change materials are most commonly used in latent heat TES (LHTES). Nevertheless, the trend of this type of material limits their applications because of their low thermal conductivities and liquid leakage over the phase transition process. Copper oxide (CuO) microparticles served as an additive to enhance thermal performance and a series of shape-stabilized composite PCMs (SSPCMs) were prepared by physical impregnation. The composites were characterized for their micro-morphology, chemical structure, thermal degradation stability and thermal energy storage performance with the aid of SEM, FT-IR, ATG, infrared thermography (IRT) and DSC, respectively. To obtain the maximally efficient energy storage capacity, the mass fraction of Hex (PCM) was found to be 75%, with a good form stability, which surmounts almost all mass fraction values reported in the literature. The ATG curves of all PCM composites revealed that addition of CuO has increased the onset degradation temperature and the maximum weight loss temperature. During the heating and cooling processes, leakage and impairment of the composite PCM were not detected. Significant enhancement in melting time and larger heat storage capacity were observed when 15% CuO was added to the SSPCM as revealed by IRT. The DSC results of the SSPCM composite indicated that the presence of CuO microparticles in PCM composites reduces the supercooling effect during the phase change process and increases the energy storage/release capacity with suitable phase change temperatures for building TES applications.

Thermal Energy Storage (TES) technologies based on Phase Change Materials (PCMs) with small temperature differences have effectively promoted the development of clean and renewable energy.     

Vanillin decorated chitosan as electrode material for sustainable energy storage

Energy storage materials made from bioresources are crucial to fulfil the need for truly sustainable energy storage. In this work, vanillin, being a lignin-derived molecule, is coupled to chitosan, a biobased polymer backbone, and used as a redox active electrode material. The structure of those electrodes is highly defined, leading to better product security than in lignin based electrodes, which have been presented as sustainable electrodes in the past. With over 60% of saccharide units in chitosan functionalised by vanillin, the concentration of redox functionalities in the copolymer is significantly higher than in lignin materials. Composites with carbon black require no further binders or additives to be used as electrode material and show reversible charge storage up to 80 mA h g⁻¹ (respective to the total electrode material) and good stability. Consequently, these electrodes are amongst the best performing electrodes made from regrown organic matter.

To replace dangerous and rare components in battery electrodes, more sustainable energy storage materials made from biowaste and wood-based vanillin are presented.     

Preparation and characterization of lauric acid–stearic acid/expanded perlite as a composite phase change material

Rapid energy consumption stimulates the development of energy-saving materials. In this work, the L–S eutectic mixture used as a PCM was compounded with EP via vacuum adsorption to synthesize LS/EP CPCM. The maximum mass adsorption rate of EP on L–S is determined to be 70% via leakage experiments. The microscopic morphology, chemical, and crystal structure were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD), respectively. The phase change properties were measured by differential scanning calorimetry (DSC). The melting temperature of LS/EP is 37.79 °C, with a latent heat of 126.05 J g⁻¹, and it has a crystallinity of over 90%. The thermal decomposition was evaluated by TGA. The initial decomposition temperature is 132.20 °C for LS/EP. In addition, the results of accelerated phase change cycling experiments showed that LS/EP CPCM has good reliability.

(1) The maximum mass adsorption rate of EP on L–S is 70%. (2) The melting temperature of LS/EP is 37.79 °C, with latent heat of 126.05 J g⁻¹, and it has a crystallinity of over 90%. (3) LS/EP CPCM has good thermal stability and reliability.     

Significantly enhanced dielectric constant and energy storage properties in polyimide/reduced BaTiO3 composite films with excellent thermal stability

In this work, reduced BaTiO₃ (rBT) particles with a large number of defects sintered in a reducing atmosphere (95N₂/5H₂) were introduced into polyimide (PI) matrix without using any modifier or surfactant components. The rBT/PI composite films fabricated by an in situ polymerization method showed significantly enhanced dielectric constant and energy storage density. The dielectric constant of the rBT/PI composite with 30 wt% rBT reached up to 31.6, while maintaining lower loss (tg δ = 0.031@1000 kHz) compared to pure PI (ε_r = 4.1). Its energy storage density (9.7 J cm⁻³ at 2628 kV cm⁻¹) was enhanced by more than 400% over that of pure PI (1.9 J cm⁻³ at 3251 kV cm⁻¹), and was greater than the energy density of the best commercial biaxially-oriented-polypropylenes (BOPP) (1.2 J cm⁻³ at 6400 kV cm⁻¹). The energy storage efficiency was around 90% due to the linear dielectric performance of rBT/PI composite films. The improved dielectric constant and energy storage density could be attributed to the combined effect of the interface interaction between two phases and the surface defects of rBT induced by the reducing atmosphere. Therefore, rBT/PI composite films with high dielectric constant, energy storage density and storage efficiency may have potential applications in the preparation of embedded capacitors.

The semiconductor properties of reduced barium titanate, with a high energy density of 9.7 J cm⁻³.     

Liposil, a promising composite material for drug storage and release.

Preliminary tests in the field of drug storage and release of composite materials known as liposils were described. These silica-based particles were obtained via liposome templating. The non-porous amorphous silica cladding of liposils protected the liposomes which retained the fundamental properties of their phospholipid bilayer. In an improved synthesis, two formulations were used, one with and the other without cholesterol in the phospholipid bilayer. Stability tests were done using carboxyfluorescein as a model hydrophilic drug loaded in the liposomes aqueous phase before the templating process. The stability of the loaded liposils was analyzed at two different pH (1.2 and 7.4) in a flow cell, according to the USP 28 norm. At pH 1.2, the silica shell was stable and prevented their rapid degradation. Interestingly, at pH 7.4 the analysis of the release kinetics revealed that the hydrolysis of the silica shell initially released intact liposomes. Characterizations of liposils were done at various steps of these processes. The stability observed for liposils make them good starting material for drug storage and release schemes. For instance, functionalization of their external surface should improve their capture by cells whereby drug release could then be induced by external stimuli, such as ultrasounds or microwaves.     

Shape-stabilized composite phase change film with good reversible thermochromic properties fabricated via phase inversion-assisted impregnation

In this study, the regenerated porous cellulose film (LD) was properly prepared by dissolving cellulose in a LiCl/DMAc solvent though a simple phase inversion method. LD has a porous structure, good mechanical properties and great thermal stability. In order to form a shape-stabilized reversible thermochromic phase change film (DTLD), a reversible thermochromic compound (DTBC) was added into the LD by simple vacuum impregnation. The effect of the weight ratio of 1-dodecanol/tetradecanol complex solvent (3 : 7, 2 : 8, 1.5 : 8.5 and 1 : 9) on the phase change properties was investigated. DTLD (1.5 : 8.5) showed the highest latent heat storage of 174.00 J g⁻¹ with the suitable phase change temperature at 37.5 °C. The low thermal conductivity of DTLD (1.5 : 8.5) at 10 °C (50 °C) was 0.396 ± 0.004 W m⁻¹ K⁻¹ (0.408 ± 0.002 W m⁻¹ K⁻¹). The color of DTLD (1.5 : 8.5) can change reversibly between colorless and blue as temperature changes. Melting–cooling tests after 100 cycles indicated that DTLD (1.5 : 8.5) has a high latent heat storage capacity of 169.65 J g⁻¹. A shape-stable reversible thermochromic phase change composite assembled from a regenerated porous cellulose membrane as a support matrix is expected to be applied to the field of thermal energy storage.

In this study, the composite phase-change cellulose-based film was prepared by phase inversion-assisted impregnation.     

Enabling chloride salts for thermal energy storage: implications of salt purity

Molten salts for use as heat transfer fluids in concentrated solar or nuclear power plants have experienced a resurgence over the past decade with a special focus on chloride-based salt mixtures, particularly for use in concentrating solar power and fast-spectrum nuclear reactors. Salt purification, specifically oxide removal, is required even for high purity commercial salts and can be achieved using many different methods. Carbochlorination, however, proves most effective according to thermodynamics and produces a gaseous byproduct easily removed from the salt. A variety of carbochlorinating reagents and reagent combinations were evaluated for thermodynamic favorability in the removal of common impurities in MgCl₂-based feedstock or coverage gases used in industrial systems. Carbon tetrachloride exhibited superior purification thermodynamics above the melting point of common MgCl₂-based salt compositions. Salt with composition of 68 : 32 mol% KCl : MgCl₂ was purified on the kilogram scale by sparging with carbon tetrachloride, reducing dissolved oxide to trace levels (42 μmol MgO/kg salt). Interestingly, the lower purity salts exhibited magnesium and oxygen presence along grain boundaries in the corrosion layers while the purified salts did not, highlighting the need for decreased oxide content. The lessened corrosivity of the highly purified salt suggests a proper salt treatment may reduce dependence on specialized materials for use with molten salts.

The purification of molten salts by carbochlorination produces low oxide content salt minimizing corrosion in 316L stainless steel and alloy-N.     

Enhanced energy storage density of all-organic fluoropolymer composite dielectric via introducing crosslinked structure

Polymer-based dielectrics have been attracted much attention to flexible energy storage devices due to their rapid charge–discharge rate, flexibility, lightness and compactness. Nevertheless, the energy storage performance of these dielectric polymers was limited by the weak dielectric breakdown properties. Crosslinked structure has been proven efficient to enhance breakdown strength (E_b) and charge–discharge efficiency (η) of polymer film capacitors. However, crosslinked networks usually lead to low electric displacement of dielectric capacitors, which greatly restrict their energy storage density (U_d). In this work, we present a tri-layered composite via layer-by-layer casting technology, where crosslinked polyvinylidene fluoride (c-PVDF) was used as the inter-layer to offer high breakdown strength, and the outer ternary fluoropolymer layers with high dielectric constant could provide high electric displacement. The optimal tri-layered composites exhibit an ultrahigh discharge energy density of 18.3 J cm⁻³ and a discharge efficiency of 60.6% at 550 kV mm⁻¹. This energy density is much higher than that of the PVDF terpolymer and commercially biaxially oriented polypropylene (BOPP, 1–2 J cm⁻³). The simulation results prove that the enhanced energy density originates from the effectively depressed charge transport in crosslinked structure at high applied electric field. Moreover, this work provides a feasible method for developing flexible all-organic high-energy-density composites for polymer capacitors.

High energy density is achieved for all-organic composites by introducing crosslinked structure.     

A composite material model for improved bone formation

The combination of synthetic polymers and calcium phosphates represent an improvement in the development of scaffolds for bone‐tissue regeneration. Ideally, these composites provide both mechanically and architecturally enhanced performances; however, they often lack properties such as osteoconductivity and cell bioactivation. In this study we attempted to generate a composite bone substitute maximizing the available osteoconductive surface for cell adhesion and activity. Highly porous scaffolds were prepared through a particulate leaching method, combining poly‐ε‐caprolactone (PCL) and hydroxyapatite (HA) particles, previously coated with a sucrose layer, to minimize their embedding by the polymer solution. Composite performances were evaluated both in vitro and in vivo. In PCL–sucrose‐coated HA samples, the HA particles were almost completely exposed and physically distinct from the polymer mesh, while uncoated control samples showed ceramic granules massively covered by the polymer. In vivo results revealed a significant extent of bone deposition around all sucrose‐coated HA granules, while only parts of the control uncoated HA granules were surrounded by bone matrix. These findings highlight the possibility of generating enhanced osteoconductive materials, basing the scaffold design on physiological and cellular concepts. Copyright © 2010 John Wiley & Sons, Ltd.     

Form-stable phase change composites based on nanofibrillated cellulose/polydopamine hybrid aerogels with extremely high energy storage density and improved photothermal conversion efficiency

The development of form-stable phase change materials (PCMs) with superior photothermal conversion efficiency and high phase change enthalpy is critical for the utilization of solar energy. In this work, nanofibrillated cellulose (NFC)/polydopamine (PDA) hybrid aerogels (NPAs) were synthesized by cation-induced gelation of NFC/PDA suspension. Then, novel form-stable PCMs with superior energy storage density and improved photothermal conversion efficiency were successfully synthesized by impregnating n-octacosane into NPAs. Differential scanning calorimetry (DSC) analysis showed that the composite PCMs exhibited extremely high phase transition enthalpy (>248 J g⁻¹) and excellent thermal reliability. Thermogravimetric analysis (TG) showed that the composite PCMs exhibited excellent thermal stability. In photothermal experiments, PDA acted as a photon trap and effectively improved the photothermal conversion efficiency (up to 86.7%) of the composite PCMs. In conclusion, the synthesized composite PCMs displayed high phase change enthalpy and superior photothermal conversion efficiency, suggesting their promising characteristics for solar energy utilization applications.

Novel form-stable composite phase change materials were fabricated by impregnating n-octacosane into nanofibrillated cellulose/polydopamine hybrid aerogels.     

Molecular solar thermal systems – control of light harvesting and energy storage by protonation/deprotonation

Molecular solar thermal (MOST) systems that undergo photoisomerizations to long-lived, high-energy forms present one approach of addressing the challenge of solar energy storage. For this approach to mature, photochromic molecules which can absorb at the right wavelengths and which can store a sufficient amount of energy in a controlled time period have to be developed. Here we show in a combined experimental and theoretical study that incorporation of a pyridyl substituent onto the dihydroazulene/vinylheptafulvene photo-/thermoswitch results in molecules whose optical properties, energy-releasing back-reactions and energy densities can be controlled by protonation/deprotonation. The work thus presents a proof-of-concept for using acid/base to control the properties of MOST systems.

The optical properties of pyridyl-substituted dihydroazulene (DHA) photoswitches can be tuned by protonation/deprotonation as well as the thermal back-reaction rate and amount of heat release from the vinylheptafulvene (VHF) photoisomers.