Increase In Phase Transition Temperature Research Articles

Inserting intermolecular hydrogen bonds to achieve dimensional regulation and phase transition temperature enhancement

Organic-inorganic hybrid materials have become potential candidates in fields of light emitting diodes (LEDs), mechanical switches, energy conversion due to their excellent magneto-opto-electronic properties. Further improving the performance of materials is a prerequisite for achieving their commercial application. Currently, many effective strategies have been proposed and validated to enhance the properties of materials, but both simultaneously realizing the improvement phase transition temperature and dimensional regulation of materials remains a huge challenge. Here, we successfully synthesized two hybrid materials, (pyrrolidinium)PbI3 (Com-1) and (3-hydroxypyrrolium)6Pb5I16 (Com-2). In this work, the strategy of inserting intermolecular hydrogen bonds cleverly achieves a significant increase in phase transition temperature (ΔT = 81 K) and dimensional regulation (1D to 2D). Moreover, semiconductor properties of two compounds are investigated to be direct bandgap semiconductor. In short, inserting intermolecular hydrogen bonds between molecules is an effective strategy to improve physical performance.

Protection of bovine serum albumin through encapsulation in hybrid vesicles

This study focuses on hybrid vesicles (HVs) formed through co-assembly of soy phosphatidylcholine (SPC) and a triblock copolymer (F127). After elucidating the superior stability of HVs over the assemblies of neat SPC and F127, these were encapsulated with bovine serum albumin (BSA), as model a thermolabile protein. Characterizations were performed using dynamic light scattering (DLS), electron microscopy, circular dichroism and high-sensitivity differential scanning calorimetry. The size of HVs increased slightly at higher proportion of F127 and upon encapsulation of BSA. In spite of this, vesicles remained spherical and displayed a smooth surface. They showed superior dilution stability in comparison to neat copolymer micelles and phospholipid vesicles. Their stability can be ascribed to hydrophobic association between the phospholipid and copolymer, and manifested into increase in phase transition temperature of the former. We found that HVs could protect BSA from denaturation and unfolding when challenged by high solution temperature, pH changes and salt incorporation.

Programming molecular switches in water and ethanol via thermo-sensitive polymers for phase control in energetic crystals

The practical application of energetic materials, particularly 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), is frequently impeded by phase transition challenges. In this study, we propose a novel strategy to enhance the stability of CL-20 by employing a thermo-sensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), to modulate its phase transitions. Our approach involves the use of an in-situ polymerized polydopamine (PDA) shell as a platform for surface grafting through atom transfer radical polymerization, yielding a core-shell structured CL-20@PDA-PNIPAM. Through comprehensive characterization, the successful grafting of PNIPAM is confirmed, significantly enhanced the phase stability of CL-20. Notably, our core-shell structure exhibits a 13 °C increase in phase transition temperature compared to raw CL-20, thereby delaying the ε→α phase transition by over 80 min under combined thermal and solvent conditions. The enhanced stability is attributed to the hydrophobic nature of PNIPAM above its low critical solution temperature in water, which effectively shields the CL-20 crystal. These findings provide new insights into enhancing the stability and safety of energetic materials in complex environments, highlighting the potential of our molecular switch mechanism.

A Comparative Study on the Influence of Nanocellulose and Silicon Dioxide Nanoparticles on the Properties of a Metal–Organic Framework of Dimethylammonium Aluminum Sulfate Hexahydrate

In our research described here, for the first time, the influence of a soft inclusion of nanocellulose on the properties of dimethylammonium aluminum sulfate hexahydrate was investigated. For comparison, a harder inclusion of silicon dioxide nanoparticles was also used to combine with the dimethylammonium aluminum sulfate hexahydrate. The analyses of data for fresh samples of the composites revealed many similar anomalies created by the influences of the cellulose and silicon dioxide, including an increase in phase transition temperature, an anomalous relaxation and polarization switching. However, over time, the anomalous properties were not stable in the case of the samples containing nanocellulose, which, we suggest, was associated with the softness of the cellulose.

Hydroxyapatite nanoparticles reinforced polyvinyl alcohol/chitosan blend for optical and energy storage applications

AbstractBiopolymer blend nanocomposite films composed of polyvinyl alcohol (PVA) and chitosan (CS) with varying quantities of hydroxyapatite (HA) nanoparticles were developed using a green solution casting method. The formation of blend nanocomposite was confirmed by Fourier‐transform infrared spectroscopy (FTIR), ultraviolet–visible (UV) spectrometer, field‐emission scanning electron microscopy (FE‐SEM), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Mechanical parameters such as tensile strength, percentage elongation at break, hardness, dielectric constant, and temperature‐dependent alternating current (AC) conductivity were analyzed. The bonding between the nanoparticles and PVA/CS blend was verified by the shift in distinctive peaks of blend in the nanocomposites to a higher wavenumber in the FTIR spectra. The UV spectra demonstrated the difference in absorbance and transmittance of the PVA/CS blend with the reinforcement of HA nanofillers. The bandgaps of the nanocomposites marginally decreased with an increase in nanoparticle loading. The SEM and XRD patterns revealed the ordered arrangement of the blend matrix due to the presence of nanoparticles. The assessment of thermal characteristics obtained from DSC and TGA demonstrated a clear increase in phase transition temperature and thermal stability of nanocomposites. The electrical conductivity measurement indicated a rise in dielectric constant and AC conductivity of blend nanocomposites with the addition of nanoparticles. The temperature‐dependent AC conductivity showed a reduction in activation energy as temperature and nanoparticle loading increased. The tensile strength and surface hardness of the PVA/CS blend nanocomposite increased with the dosage of HA content in the blend matrix.Highlights A series of polyvinyl alcohol (PVA)/chitosan (CS)/hydroxyapatite (HA) nanocomposites were prepared by the green method Enhanced optical property, thermal stability, and glass transition temperature Possess excellent dielectric constant and alternating current conductivity The inclusion of HA increased the mechanical strength of the PVA/CS blend A potential blend nanocomposite for flexible optoelectronic and charge storage devices.

Sugar-based Cryoprotectants Stabilize Liposomal Vesicles by Exhibiting a Cholesterol-like Effect.

Liposomal vesicles tend to fuse and aggregate during lyophilization. To avoid these events, cryoprotectants are added to the dispersion before lyophilization. Herein, we have compared the effect of three commonly used cryoprotectants (mannitol, MTL; trehalose, THL; and β-cyclodextrin, β-CD) upon structural characteristics of liposomes. The formulation was prepared using ethanol injection method, and cryoprotectants were tested at three dose levels (2, 6, and 10 mM). We have elucidated their effect on soy lecithin (SL) liposomes formulated with and without cholesterol (CHL). Characterizations were performed using scattering, thermal, and spectroscopic techniques. CHL molecules interacted hydrophobically with the SL bilayer. In spite of triggering a noticeable increase in the hydrodynamic diameter (about 30 nm), CHL promoted the stabilization of vesicles. Hydrogen bonding interactions were verified by the shift in -OH stretching over 3300-3500 cm-1. This manifested in an increased phase transition temperature (Tm) of SL liposomes. Tm increased further upon incorporation of cryoprotectants, particularly with β-CD. Enthalpic changes were indicative of an affinity interaction between phospholipids and cryoprotectants, regardless of the presence of CHL. β-CD showed concentration-dependent changes in the energetics of this interaction. The affinity of cryoprotectant-liposome interaction has been ranked as β-CD ≫ THL > MNT.

Orientation and Grain Size in MAPbI3 Thin Films: Influence on Phase Transition, Disorder, and Defects

In recent years, record efficiencies of halide perovskite-based devices have been achieved by processing high-quality thin films, where small morphology differences seem to be relevant for optimized optoelectronic functionality. However, a detailed understanding on how small morphological changes in perovskite films affect their structural and optoelectronic properties is still missing. Here, we investigate the influence of small morphology differences (i.e., increased grain size and crystallographic orientation), which are induced by hot-pressing methylammonium lead iodide (MAPbI3) thin films, on the structural properties, phase transition behavior, energetic disorder, and defects. To this end, detailed temperature-dependent photoluminescence (PL) and absorption analyses from 300 K down to 5 K are performed. The morphology differences, confirmed by scanning electron microscopy and X-ray diffractometry analyses, result in an increased phase transition temperature for hot-pressed (HP) films, which we attribute to less strain. Moreover, fluence-dependent and transient PL measurements reveal a lower defect density in HP films. Here, besides grain size, also the degree of orientation appears to enhance the charge carrier lifetimes. The identified interdependence of strain and defect properties with film morphology suggests small differences in the perovskite’s energetic disorder. Our work thus emphasizes the importance that even small structural differences in halide perovskites have on their optoelectronic functionality, spurring their further optimization.

Fatigue and Aging in a Ferroelectric Composite Based on Triglycine Sulfate Combined with Nanocellulose

For the first time, the influence of fatigue and aging effects on phase transition and ferroelectric switching is studied for the composite based on ferroelectric polycrystals of triglycine sulfate and nanocellulose with different concentrations. The fatigue in samples was created by the exposure to a sinusoidal electric field, while the aging was investigated for samples after 240 h under dry conditions without the pre-exposure. It was figured out that the exposure led to the increase in phase transition temperature and the inhibition of polarization switching. On the contrary, the aging resulted in improving polarization switching and reducing the phase transition temperature.

Design of Multilevel Storage Medium through Sb2Te3/Ga2Sb3 Phase-Change Heterostructure

The phase-change heterojunction Sb2Te3/Ga2Sb3 thin films with different thickness ratios and periods were designed and prepared by the magnetron sputtering technique. The multi-level resistance states of phase-change heterojunction Sb2Te3/Ga2Sb3 film were investigated from the perspective of material and device. As for the constant thickness ratio, both the phase transition temperature and electrical resistance increase with the decrease of periods. Especially, the heterojunction [Sb2Te3(7 nm)/Ga2Sb3(3 nm)]3 film experiences the twice resistance jumps at 208 and 290 °C, respectively, exhibiting the obvious triple-resistance states. The phase structure and vibrational modes of [Sb2Te3(7 nm)/Ga2Sb3(3 nm)]3 film during the different crystallization stages were observed by the structural characterization. X-ray diffraction and Raman spectroscopy verified the changes in the phase structure and vibrational modes of the film, respectively. The [Sb2Te3(7 nm)/Ga2Sb3(3 nm)]3 film has a lower surface roughness than the pure Sb2Te3, which was proved by atomic force microscopy. Phase change memory devices based on the [Sb2Te3(7 nm)/Ga2Sb3(3 nm)]3 films were fabricated to evaluate the electrical properties and verify the three-state process of the heterostructure. All the results show that the phase-change heterostructure Sb2Te3/Ga2Sb3 films have the potential to achieve triple-state storage by tuning the thickness ratios and periods, which is conducive to improving the information storage density.

Microstructure and properties of Cu-Al-Ni-Mn-Y alloy with precipitation and effective strengthening by aging treatment

The Cu-11Al-3Ni-2.5Mn-1Y alloy prepared by hot-press sintering was subjected to aging treatment at different temperatures of 350 °C, 400 °C, 450 °C, 500 °C and 550 °C, respectively. The phase composition, microstructure, mechanical and damping properties were characterized. The results show that the alloys after the ageing treatment are mainly composed of 18 R martensite and 2 H martensite. The precipitation phase begins to appear and the best comprehensive properties are obtained at the aging temperature of 450 °C. The hardness and strength values reached 347.6 HV and 642.6 MPa, respectively. The strengthening mechanisms are mainly involved in lattice distortion and dislocation increment effect caused by solution strengthening, shearing and hindering effect of precipitated phases and dislocations, fine grain strengthening effect caused by grain size reduction, and the increase of large angle grain boundary. Simultaneously, the room temperature damping reached 0.0723, which is 93 % higher than the original sample of 0.38. The improvement of damping properties is closely related to the changes in the number and size of martensite, the interfacial damping effect caused by precipitated phases, and the pinning and unpinning reaction between dislocations and precipitated phases. Therefore, alloys with both high mechanical and high damping properties can be obtained by proper aging treatment. In addition, the increase in phase transition temperature of high temperature damping properties also provides some guidance for the exploration and development of this alloy in the high temperature field.

Halogen tuning toward dielectric switch and band gap engineering in one-dimensional hybrid materials

Organic-inorganic hybrids with multiple tunable functions are very attractive for potential applications in sensors, smart switches, etc. To investigate the effect of halogen tuning on the properties of hybrid materials, two new multifunctional organic-inorganic hybrid compounds [3-hydroxy-azetidinecation]2SbX5 (1: X = Cl; 2: X = Br) are successfully synthesized here by replacing halogen anions. Reversible structural phase transitions accompanied by anomalous changes in dielectric constants are found when heating (T1 = 362 K; T2 = 373 K). Both two compounds have the same space group change from P212121 (Low Temperature Phase) to Pnma (High Temperature Phase). When replacing Cl with Br, the phase transition temperature increases by ca. 10 K and the band gap changes from 3.21 eV to 2.75 eV. Based on the above properties, this work could provide an effective molecular design strategy for the exploration and construction of temperature-tunable, lower bandgap semiconductor hybrid materials.

Study based on “Heat Flux - Energy Saving Pointer”: Exploring why phase change materials is not energy efficient enough on internal wall in cold region

The combination of phase change materials (PCMs) with internal envelopes is an effective way to enhance the thermal performance of buildings. However, it may be non-energy efficient in some applications. Due to the lack of in-depth exploration, Heat Flux-Energy Saving Pointer (HF-ESP) is proposed to investigate the direction conversion and numerical change of PCM heat flux. In addition, Relative Depth of Activation (RDA) and HF-ESP are combined to evaluate the thermal behavior of PCM. In the whole winter, the energy change caused by PCM in different cases is about 132–233 MJ. However, this change does not necessarily bring benefits, and the energy-saving effect should be evaluated based on the offset of positive and negative returns. RDA of case 2 and case 4 are 98.56% and 33.77% respectively, but they can save almost the same energy. It indicates that the higher latent heat utilization does not necessarily mean the better energy-saving effect. When the phase transition temperature is 17 °C (lower than indoor temperature), PCM will lead to non-energy saving reversals of heat flux. With the increase of phase transition temperature, it will gradually transform into energy-saving reversals. This work can provide some references for balancing initial investment and operating costs.

Analyzing Frequency Spectra of Dielectric Loss to Clarify Influence of L,α-alanine Doping on Phase Transition in Triglycine Sulfate

As reported in the literature, the doping of L,α-alanine (LA) led to increasing the phase transition temperature in triglycine sulfate (TGS) – a bio-ferroelectric material that has been widely applied in industry. The nature of this anomaly is commonly investigated by considerably complicated theoretical and experimental techniques. Unlike previous studies, the present work proposes a simple physical method of analyzing frequency spectra for dielectric loss to clarify the relationship between the movement of phase transition positions and the shift of relaxation frequencies observed in the spectra. The experimental results obtained for LA-doped TGS samples synthesized at different LA contents (0, 5, 10, 20, and 30 wt.%) were used for the analysis. It was indicated that the increase in phase transition temperature was accompanied by the decrease in relaxation frequencies due to the enhanced viscosity created by strong hydrogen bonds formed between amino acids of alanine and TGS structure.

Ferroelectric Switching and Phase Transition in Composites from Ferroelectric Metal–Organic Framework of [ND4][Zn(DCOO)3] and Silicon Dioxides

A composite from a ferroelectric metal–organic framework of [ND4][Zn(DCOO)3] and nano-dispersed silicon dioxides nanoparticles (nSiO2) has been synthesized. The study investigates the influence of nSiO2 on ferroelectric switching and phase transition properties in [ND4][Zn(DCOO)3]. It was indicated that the addition of nSiO2 led to the increase in phase transition temperatures and the inhibition of repolarization in ferroelectric parts. When the nSiO2 amount increased, the saturated dielectric hysteresis loops were more difficult to obtain and transformed into unsaturated ones with the rise of coercive field. The residual water molecules kept on nSiO2 were found to be responsible for the above anomalies.

Ruddlesden\u2013Popper 2D perovskites of type (C6H9C2H4NH3)2(CH3NH3)n\u22121PbnI3n+1 (n\u2009=\u20091\u20134) for optoelectronic applications

Ruddlesden–Popper (RP) phase metal halide organo perovskites are being extensively studied due to their quasi-two dimensional (2D) nature which makes them an excellent material for several optoelectronic device applications such as solar cells, photo-detectors, light emitting diodes (LEDs), lasers etc. While most of reports show use of linear carbon chain based organic moiety, such as n-Butylamine, as organic spacer in RP perovskite crystal structure, here we report a new series of quasi 2D perovskites with a ring type cyclic carbon group as organic spacer forming RP perovskite of type (CH)2(MA)n−1PbnI3n+1; CH = 2-(1-Cyclohexenyl)ethylamine; MA = Methylamine). This work highlights the synthesis, structural, thermal, optical and optoelectronic characterizations for the new RP perovskite series n = 1–4. The demonstrated RP perovskite of type for n = 1–4 have shown formation of highly crystalline thin films with alternate stacking of organic and inorganic layers, where the order of PbI6 octahedron layering are controlled by n-value, and shown uniform direct bandgap tunable from 2.51 eV (n = 1) to 1.92 eV (n = 4). The PL lifetime measurements supported the fact that lifetime of charge carriers increase with n-value of RP perovskites [154 ps (n = 1) to 336 ps (n = 4)]. Thermogravimetric analysis (TGA) showed highly stable nature of reported RP perovskites with linear increase in phase transition temperatures from 257 °C (n = 1) to 270 °C (n = 4). Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) are used to investigate the surface morphology and elemental compositions of thin films. In addition, the photodetectors fabricated for the series using (CH)2(MA)n−1PbnI3n+1 RP perovskite as active absorbing layer and without any charge transport layers, shown sharp photocurrent response from 17 nA/cm2 for n = 1 to 70 nA/cm2 for n = 4, under zero bias and low power illumination conditions (470 nm LED, 1.5 mW/cm2). Furthermore, for lowest bandgap RP perovskite n = 4, (CH)2MA3Pb4I13 the photodetector showed maximum photocurrent density of ~ 508 nA/cm2 at 3 V under similar illumination condition, thus giving fairly large responsivity (46.65 mA/W). Our investigations show that 2-(1-Cyclohexenyl)ethylamine based RP perovskites can be potential solution processed semiconducting materials for optoelectronic applications such as photo-detectors, solar cells, LEDs, photobatteries etc.

Preparation, composition, phase transition and electrical conductivity of two novel ferroelectric composites from Rochelle salt filled with pristine and oxidized MWCNT

A comparative study on dielectric properties was conducted for two series of ferroelectric composites prepared from Rochelle salt (RS) filled with a conductive filler of multiwalled carbon nanotubes in pristine (MWCNT) or oxidized (OMWCNT) forms. FTIR technique was utilized to evaluate characterization of functional groups in the composites. The obtained results indicated that the oxidization of MWCNT resulted in the significant increase in phase transition temperature of RS, while reduced dielectric loss and conductivity of composite samples in comparison with the use of pristine MWCNT. Besides, the influence of OMWCNT and MWCNT content on properties of RS was also considered.

Phase-transition kinetics of silicon-doped titanium dioxide based on high-temperature X-ray-diffraction measurements

Titanium dioxide (TiO2) is widely used as a pigment, additive in food, and personal care. The properties and applications of titanium dioxide vary with crystal structure. In this study, in situ high-temperature X-ray diffraction was used to examine the effect of silicon doping on the phase-transition kinetics of titanium dioxide. Transformation from anatase to rutile titanium dioxide was observed in real time; the Rietveld method was used to calculate the rutile content. The first-order kinetic and Johnson-Mehl-Avrami-Kohnogorov models were compared; the latter was in better agreement with the data. The experimental results showed that the crystal growth process was controlled by the growth of the interface. The phase-transition temperatures for samples with 0%, 5%, and 7.5% silicon were 600, 620, and 630 ​°C, respectively; the activation energies were 212.3, 228.0, and 293.9 ​kJ/mol, respectively. This increase in phase transition temperature and activation energy indicates that doping with silicon inhibits the transformation of anatase to rutile titanium dioxide.

Room temperature ferromagnetism in multiferroic BaCoF[formula omitted] thin films due to surface, substrate and ion doping effects

Using a microscopic model and the Green’s function technique we have studied the influence of different surface, size and substrate effects on the magnetic properties of BaCoF4 thin films. The magnetization and the magnetic phase transition temperature increase for a compressible substrate Al2O3, whereas they decrease for a tensile substrate such as MgO. The film thickness influences also the magnetic properties. We have discussed a competition, a concurrence between the surface and substrate effects. Doping of bulk BaCoF4 with Al ions leads to weak room temperature ferromagnetism. Due to the magnetoelectric coupling is obtained that the polarization increases with increasing external magnetic field.

PEMBUATAN RESISTANT STARCH PATI BERAS DENGAN METODE ENZIMATIS DAN FISIK

Rice is the leading food and a carbohydrate source for most of the world's and Indonesia population, but most rice tends to have a high glycemic index (IG). A product with a low IG is better, not only for people with diabetes but also for healthy people. Resistant starch (RS) functions as a new food ingredient that has a low glycemic index. RS is a part of starch or starch products resistant to digestion when through a gastrointestinal tract. RS has the same physiological effects as dietary fiber, can affect body weight and energy balance, increase lipid excretion to reduce calorie intake and reduce serum lipid levels, zero caloric content so that it can be used as a low-calorie food additive that can control body weight effectively. RS can be made through starch modification by physical treatment (heat treatment), chemical treatment, enzymatic treatment, and a combination of heat and enzymatic. Factors that influence RS's formation include starch properties, starch interactions with other components, processing conditions, heat processes, other treatments, and storage conditions. Therefore, the rice starch modification that contains a lot of RS needs to be known. Rice starch Hydrolysis with the dual enzyme α-amylase and pullulanase (DMT) can increase the highest RS level (51.0%) due to the increased degree of starch crystallinity. High RS results in an increase in gelatinization temperature, ΔH and phase transition temperatures, and a decrease in the speed of starch hydrolysis and weight loss.

High concentration of the ester-linked ω-hydroxy ceramide increases the permeability in skin lipid model membranes

The ester-linked ω-hydroxy acyl chain linked to a sphingosine base referred to as CER EOS is essential for the skin barrier lipid organization. While the majority of the skin lipids form a dense, crystalline structure, associated with low permeability, the unsaturated moiety of CER EOS, (either the linoleate or the oleate chain) exists in a liquid phase at the skin's physiological temperature. Thus, the relationship between CER EOS and barrier function is not entirely comprehended. We studied the permeability and lipid organization in skin lipid models, gradually increasing in CER EOS concentration, mixed with non-hydroxy sphingosine-based ceramide (CER NS) in an equimolar ratio of CERs, cholesterol, and free fatty acids (FFAs) mimicking the ratio in the native skin. A significant increase in the orthorhombic-hexagonal phase transition temperature was recorded when CER EOS concentration was raised to 70 mol% of the total CER content and higher, rendering a higher fraction of lipids in the orthorhombic phase at the expense of the hexagonal phase at physiological temperature. The model's permeability did not differ when CER EOS concentration ranged between 10 and 30% but increased significantly at 70% and higher. Using CER EOS with a perdeuterated oleate chain, it was shown that the fraction of lipids in a liquid phase increased with CER EOS concentration, while the neighboring CERs and FFAs remained in a crystalline state. The increased fraction of the liquid phase therefore, had a stronger effect on permeability than the increased fraction of lipids forming an orthorhombic phase.