Crystalline Transition Research Articles

Mössbauer Studies of LixFe1/3Mn1/3Ni1/3PO4 Cathode Materials

We report on the crystallographic and magnetic properties of LixFe1/3Mn1/3Ni1/3 PO4 (x = 0, 1) using x-ray diffraction (XRD), a vibrating sample magne- tometer (VSM), and Mossbauer spectroscopy. XRD analysis confirmed that the samples have an orthorhombic structure with space group Pnma. From the VSM measurements the samples exhibited an antiferromagnetic behavior with a Curie–Weiss temperature θ = − 162 K for x = 1, and θ = − 303 K for x = 0. The Neel temperature (TN) and spin reorientation temperature (TS) were determined to be 40 K and 10 K for x = 1, and 66 K and 25 K for x = 0. The hyperfine field (Hhf) of LiFe1/3Mn1/3Ni1/3PO4 had smaller values than that of Fe1/3Mn1/3Ni1/3PO4 due to the magnitude of the nearest-neighbor superexchange interaction. Isomer shift (δ) values indicate that the charge states of LiFe1/3Mn1/3Ni1/3PO4 are ferrous (Fe2+), and that of Fe1/3Mn1/3Ni1/3PO4 are ferric (Fe3+). The larger values of the electric quadrupole splitting (δEQ) for the Fe2+ phase compared to the Fe3+ phased originated from the different lattice and valence electron contributions due to the crystalline field and valence transition. Debye temperatures (θD) of 338 ± 5 K (x = 1), and 370 ± 5 K (x = 0) were obtained for the samples.

Spinning Cellulose Hollow Fibers Using 1-Ethyl-3-methylimidazolium Acetate⁻Dimethylsulfoxide Co-Solvent.

The mixture of the ionic liquid 1-ethyl-3-methylimidazolium acetate (EmimAc) and dimethylsulfoxide (DMSO) was employed to dissolve microcrystalline cellulose (MCC). A 10 wt % cellulose dope solution was prepared for spinning cellulose hollow fibers (CHFs) under a mild temperature of 50 °C by a dry–wet spinning method. The defect-free CHFs were obtained with an average diameter and thickness of 270 and 38 µm, respectively. Both the XRD and FTIR characterization confirmed that a crystalline structure transition from cellulose I (MCC) to cellulose II (regenerated CHFs) occurred during the cellulose dissolution in ionic liquids and spinning processes. The thermogravimetric analysis (TGA) indicated that regenerated CHFs presented a similar pyrolysis behavior with deacetylated cellulose acetate during pyrolysis process. This study provided a suitable way to directly fabricate hollow fiber carbon membranes using cellulose hollow fiber precursors spun from cellulose/(EmimAc + DMSO)/H2O ternary system.

Accelerated thermal ageing behaviour of bagasse fibers reinforced Poly (Lactic Acid) based biocomposites

Ageing behavior is one of the crucial factor for selection of material by designers and engineers, mainly for structural applications. Investigation of the ageing effect on biocomposites would supplement current knowledge and may help in encouraging their uses in real life applications. The current experimental investigation aims to determine the variation in various properties of Bagasse fibers reinforced Poly Lactic Acid (PLA) biocomposites during accelerated thermal ageing. Specimens of biocomposite were fabricated and exposed to temperature cycles of −20 °C and 65 °C (12 h each) for 12 weeks and characterized after every 4 weeks of exposure. Tensile and flexural properties exhibited steady improvement on exposure up to 8 weeks, followed by a reduction after ageing for 12 weeks. It can be concluded from X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) that significant change in crystalline and glass transition behavior happens during the exposure period.

Effect of the Synthesis Method on the Properties of Ultrafine YAG Powder

YAG materials has a number of unique properties, the application is very extensive. In this paper, the superfine YAG powder materials were prepared by co-precipitation method and hydrothermal precipitation method. The influence of synthesis process on the morphology of the powder was investigated. The results showed that the precursor powder prepared via the co-precipitation method is mainly from amorphous to crystalline transition with the increasing calcination temperature, the precursor agglomeration is more serious, In the process of increasing the calcination temperature, the dispersibility of the roasted powder is greatly improved, which is favorable for the growth of the crystal grains, so that the particle size of the powder is gradually increased, the YAG precursor prepared by the co-precipitation method is transformed into YAG crystals, the phase transition occurs mainly between 900 and 1100°C. When the molar ratio of salt to alkali is Y3+: OH-=1: 8 via the hydrothermal reaction, the YAG particles with homogeneous morphology can be obtained. When the molar ratio of salt and alkali is increased continuously, the morphology of YAG particles is not obviously changed. The co-precipitation method is easy to control the particle size, the hydrothermal method is easy to control the particle morphology.

Hydrogen production from vegetable oil via a chemical looping process with hematite oxygen carriers

Hydrogen production from vegetable oil via a chemical looping process with hematite oxygen carriers has been carried out in a fixed-bed reactor at 1023.15–1173.15 K. The lattice oxygen release process and crystalline transformation for the oxygen carrier in the reaction process are investigated. Results indicate that the maximum H2 composition achieved in the chemical looping hydrogen stage is over 91.72% when hematite oxygen carriers consisting of Fe2O3, Al2O3 and SiO2 are used. The active component Fe2O3 in oxygen carriers represents three reduced peaks corresponding to the crystalline form transition from Fe2O3 to Fe3O4. Up to 96.13% of the lattice oxygen in Fe2O3 can be consumed in the reduction process. The deep reduction of FeO to Fe represents a lower reaction rate with the exhaustion of the lattice. The maximum carbon conversion efficiency of vegetable oil of 79.10% when the ratio of water to oil is 1.2 and hydrogen-rich gas with a highest concentration of 91.72% are achieved in the chemical looping reforming stage and H2 production stage, respectively. The impurities in the gas are ascribed to the carbon deposition and steam reaction in the chemical looping process. The micrographs of fresh and used oxygen carriers present irregular and blocky structures, sintering is not observed after the multi-cycle reaction process. The crystalline form and reaction activity remain stable after 20-cycle experiments, suggesting that the hematite oxygen carrier is a promising candidate for hydrogen generation from vegetable oil via the chemical looping process.

Electrical and crystallization properties of indium doped Ge-Sb-Se films

Rapid advances in information technology rely on large capacity, high speed, and thermally stable phase-change nonvolatile materials. This work is investigating the capacitance-voltage characteristics of multinary chalcogenides (Ge15Sb80Se5 and Ge15Sb70Se10In5) to study their electrical properties and their reliant on frequency, bias voltage, and temperature. The results show different capacitance behavior for the two films, Ge15Sb80Se5 and Ge15Sb70Se10In5. Adding indium to Ge-Sb-Se alloy improved its thermal stability by increasing the crystallization temperature by almost 20 K, and shows a fast crystallization process. The results illustrate that the capacitance of Ge15Sb70Se10In5 film has a nonlinear-temperature behavior and becomes negative at high temperatures. The negative capacitance could be attributed to a significant increase in the conductivity of the film due to temperature and applied bias voltage. Moreover, during the phase change, the amorphous-crystalline interfaces might behave as a junction with a potential barrier where charge carriers accumulate. The nonlinearity in the capacitance and conductance is attributed to the nucleation-growth mechanism when the temperature becomes close to the amorphous–crystalline transition temperature (Tc).

(Invited) Investigation of Thickness, Symmetry and Defects in 2D Telluride Materials with Raman Spectroscopy

The rediscovery of graphene sparked the research zest on 2D materials. In general, 2D materials can be isolated from their 3D bulk crystals that host a layered crystal structure where the atoms in the same layer are bonded by covalent bonds and the adjacent layers are coupled by van der Waals (vdW) coupling. So far, more than 50 types of 2D materials have been achieved and studied. These materials belong to distinct crystal families and exhibit fabulous physical properties. Among them, 2D telluride materials are of great interests. Here, we present out recent work on Raman spectroscopy on two tullerides: WTe2 and ZrSiTe. Raman spectroscopy reveals the crystal structure information through the detection of lattice vibration modes. Due to its nondestructive nature and high test efficiency, Raman spectroscopy has been widely used in2D material research on crystal structure and optical characteristics. In this report, we first present the Raman spectra evolution with the thickness in 2D WTe2.1 WTe2 belongs to transition-metal dichalcogenide (TMD) family. It shows ultra-high non-saturating magnetoresistance up 45 Tesla, leading to great research interest all around the world in recent years. However, when layered TMDs are scaled down to a 2D geometry, structural and electronic transitions occur, leading to the emergence of properties not usually found in the bulk. Here, we report a systematic Raman study of the exfoliated semi-metallic WTe2 flakes with thickness ranging from few layers down to a single layer. A dramatic change in the Raman spectra occurs between the monolayer and few-layer WTe2 as a vibrational mode centered at ~86.9 cm−1 in the monolayer splits into two active modes at 82.9 and 89.6 cm−1 in the bilayer. Davydov splitting of these two modes is found in the bilayer, as further evidenced by polarized Raman measurements. Strong angular dependence of Raman modes on the WTe2 film thickness reflects that the directional interlayer interaction rather, than the isotropic van der Waals coupling is playing an essential role in the phonon modes, especially in anisotropic 2D WTe2 material. Therefore, the significant evolution of Raman modes with thickness and polarization can not only be a reliable fingerprint of the thickness and the crystallographic orientation, but also an ideal probe for the strong and directional interlayer interaction. Then, we extend our work to ZrSiTe, a topological nodal line semimetal. It has attracted lots of research interest recently because of the prediction that the single-layered ZrSiTe film is 2D topological insulator. So it is essentially important to investigate the crystalline structure transition occurring in single and few layers of ZrSiTe. Here, we demonstrate our recent Raman study on the lattice vibrational modes of 2D ZrSiTe. Unlike TMDs, ZrSiTe was not considered as a 2D material traditionally because the layers are not bonded by van der Waals coupling. However, due to the weak interaction between adjacent Te layers, ZrSiTe crystal is in the first time separated into the single layers by mechanical exfoliation. In a typical 2D ZrSiTe thin film, 3 Raman modes located at 95 cm-1, 228 cm-1, and 304 cm-1, can be clearly identified, which is in good agreement with theoretical calculations. However, in the single-layered ZrSiTe the intensity of Raman mode located at 131.7 cm-1 which can be attributed to the mode related to the lattice defects dominates the whole spectrum. This mode fades quickly with the increasing thickness and disappears at 3L. Our experimental and theoretical results manifest that such defect Raman mode can be enhanced by 4.8 times with higher defect concentration which provides a sensitive approach to detect the lattice defects when ZrSiTe reaches to its 2D limit. In conclusion, Raman spectroscopy is a powerful tool for the investigation of 2D materials. It not only provides an efficient way to determine the thickness of the materials but also shows clues of the interactions inside the crystal. Its sensitivity to the crystal defects makes it a valuable tool to reveal the crystal quality of 2D materials. The use of Raman spectroscopy in 2D material research will finally help us to interpret the physical properties when the materials are thinned down to their 2D geometry. 1 Yan Cao, Natalya Sheremetyeva, Liangbo Liang, Hui Yuan, Tingting Zhong, Vincent Meunier, and Minghu Pan, 2D Materials 3 (4), 035024 (2017).

Cathode Materials for Rechargeable Aluminum Metal Batteries: Molecular-Level Insights, Challenges, & Opportunities

Rechargeable aluminum batteries are an emerging energy storage technology with great potential due to the high capacity, global abundance, low cost, and inherent safety of aluminum metal. However, few cathode materials have been demonstrated that exhibit high energy density and cycle life, in part due to the challenges associated with the high charge density of trivalent aluminum cations and the highly reactive nature of the chloroaluminate-containing ionic liquids commonly used as electrolytes. Here, investigations of selected intercalation and conversion cathodes for rechargeable aluminum metal batteries will be presented, including crystalline transition metal compounds, graphite, and sulfur-containing materials. Molecular-scale understanding of their charge storage mechanisms will be discussed, revealed by a combination of electrochemical methods, solid-state magic-angle-spinning (MAS) NMR spectroscopy, in situ diffraction methods, and electron microscopy. Intrinsic challenges—and opportunities—associated with intercalation and conversion cathode materials will be discussed. Overall, the results yield insights into possible rational design strategies for developing next-generation cathode materials for rechargeable aluminum metal batteries with improved energy densities, rate capabilities, and cycle lifetimes.

Structural Modifications of DPPC Bilayers upon Inclusion of an Antibacterial Cationic Bolaamphiphile.

The emergence of antibiotic-resistant bacterial strains has fostered fundamental research to develop alternative antimicrobial strategies. Among the several systems proposed so far, the association complexes (nanoplexes) formed by transcription factor decoys (TFDs), i.e., short oligonucleotides targeting a crucial bacterial transcription factor, and a bolaform cationic amphiphile, 10,10'-(dodecane-1,12-diyl)-bis-(9-amino-1,2,3,4-tetrahydroacridinium) chloride (12-bis-THA), have demonstrated their potential in vitro and in vivo. The application of these nanoplexes is hampered by a scarce colloidal stability, which can be addressed by including the bolaamphiphile in a liposomal carrier, which is then associated to the TFD. The present study reports an investigation on the effects of 12-bis-THA on the structure of synthetic lipid bilayers to assess the morphology of the mixed assemblies, gain insight into the location of the host within the bilayer, and determine the loading capacity of the carrier. Our results demonstrate that 12-bis-THA promptly inserts within 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) bilayers, bending its C-12 spacer chain to adopt a conelike shape and shifting the gel-liquid crystalline transition of the chains to lower temperatures. The host liposomal structure is retained for a bolaamphiphile concentration of up to 3.2% mol to DPPC, whereas higher concentrations lead to the destabilization by means of a detergency-like mechanism, with the simultaneous existence of different lamellar-based structures, such as liposomes, bicelles, and rafts, in which DPPC and 12-bis-THA could be present in different molar ratios. Overall, these results shed light on the interaction of the bolaamphiphile with a lipid bilayer and provide valuable insight to better formulate the antimicrobial amphiphile in liposomal carriers to circumvent the colloidal instability of nanoplexes.

Structural and photoluminescence properties of thermally stable Eu3+activated CaWO4 nanophosphor via Li+ incorporation

In the present paper, we have reported the variation of CaWO4:Eu3+ nano phosphors with different compositions of Li+, (LEC) (Li+ = 2, 5, 7 and 10 at%). The as-prepared (ASP) samples are annealed at 900 °C to eliminate unwanted organic moieties present in the sample and to improve crystallinity. These nanoparticles are characterized by X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), X-ray photoelectron spectroscopy (XPS), Fourier transform IR spectroscopy (FTIR), Raman spectroscopy, photoluminescence studies. FTIR gives the absorption band at ~832 cm−1, which corresponds to antisymmetric vibrations due to O-W-O band in the WO42- tetrahedron. This is also confirmed by the Raman Spectroscopy. CaWO4 has a crystal of the Scheelite type having C4 h point group symmetry and I41/a space group symmetry. The surface/ particle morphology of 900 °C annealed samples studied using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) and show the formation of nanosheet like structure. Annealed samples of lithium co-doped CaWO4:Eu3+nanoparticles have shown the red luminescence which is attributed due to the strong host contribution and different energy transfers from Li+ ions to host matrix under 392 nm excitations. Li+ ion improves the crystallinity and radiative transition rate and these materials may be potential candidates for white light emitting diodes and may be widely used as optoelectronic materials.

Elucidating the effect of additives on the alkyl chain packing of a double tail cationic surfactant

HypothesisSome low molecular weight additives can strongly influence the phase behavior of aqueous surfactant systems, and this offers an important handle to control the properties of surfactant solutions and thus to optimize the stability and performance of various formulations. ExperimentsThe surfactant dioctadecyldimethylammonium chloride (DODAC) self-assembles into two lamellar phases in water, the gel phase (Lβ) and the liquid crystalline phase (Lα). Here, we present approaches to tune the gel-to-liquid crystalline transition temperature (Tm) with the use of additives. The effects of urea, sodium butyrate and butyric acid on the packing behavior of DODAC were determined. The surfactant phases were characterized using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and small/wide angle X-ray scattering (SWAXS). FindingsAll three additives - urea, sodium butyrate and butyric acid yield a single and stable lamellar phase. Urea and sodium butyrate have only minor effects on Tm, butyric acid gives a large decrease as it stabilizes the Lα phase with respect to the Lβ phase. From the bilayer thickness of the gel phase an interdigitated or tilted packing of the surfactant molecules is suggested. The addition of sodium butyrate gives a highly interdigitated gel structure and resulted in the transition from lamellar liquid crystal to an isotropic L3 phase.

THERMOKINETIC EMF IN SHAPE MEMORY ALLOYS UNDER THERMOELASTIC PHASE TRANSFORMATIONS

It is known that thermokinetic EMF occurs in homogeneous materials when the heating zone moves along a conductor. The obligatory occurrence of this kind of EMF is associated with phase transformations that proceed in a local heat-affected zone, for example, iron undergoes an allotropic transformation at 700–800 °C. It is natural to assume that this phenomenon can be observed in shape memory alloys under thermoelastic phase transformation that takes place at much lower temperatures. The studies presented here showed that the thermokinetic EMF appearance in titanium nickelide alloys is possible during the movement both of the heating zone (reverse phase transformation) and of the cooling zone (direct phase transformation). The physical justification for the EMF appearance is provided, according to which thermokinetic EMF is initiated as a result of a potential difference between the areas of direct and reverse phase transformations that occur due to the temperature influence along the TiNi wire sample. The paper also considers the thermokinetic EMF appearance in an amorphous–crystalline thin ribbon of Ti50Ni25Cu25 when a high-temperature local heating zone moves along it. This phenomenon is associated with the process of crystallization of material, i. e., amorphous to a crystalline state transition. Thermokinetic EMF also occurs when the interface between the amorphous and crystalline phases is heated locally. In this case, the thermokinetic EMF appearance is associated with a potential difference between the regions and similar to thermokinetic EMF occurring in the thermocouple. Studies on the thermokinetic EMF appearance due to the temperature effect on shape memory alloys during thermoelastic phase transformations allows one to more fully understand the thermokinetic EMF phenomenon. The results can find practical application in non-destructive testing of physical-mechanical properties of these alloys and as energy sources.

RE2O3-alkaline earth-aluminosilicate fiber glasses: Melt properties, crystallization, and the network structures

Glasses and/or glass fibers of a new glass system, RE2O3 (RE = Sc,Y, La)-MgO-CaO-Al2O3-SiO2, were studied in detail, covering rare earth (RE) effects on high temperature viscosity, liquidus temperature and crystalline phases, softening and glass transition temperature, and speciation reactions of aluminum (AlOx, x = 4, 5) and silicate network (Qn, n = 4, 3, 2) using 27Al and 29Si MAS NMR and Raman spectroscopic methods. Rare earth oxides (RE2O3) were shown to have a dual functionality, i.e., decreasing melt viscosity like a network modifier depolymerizing glass network, but increasing viscosity at low temperature, i.e., glass softening temperature (Tsoft) and transition temperature (Tg), strengthening the glass network functioning like Al2O3. Liquidus temperature (TLiq) was found to be sensitive to the type of RE2O3 modifications in terms of their ionic field strength (IFS); Sc3+ of the highest IFS increased, but La3+ of the lowest IFS decreased TLiq. Effect of Y3+ (intermediate IFS) on TLiq resembles Sc3+ only at higher concentration. The overall results suggest that RE ions of different IFS have different “true” solubility limits in the host glass matrix, above which RE2Si2O7 crystallizes. All of the glasses with and without RE2O3 contained predominately four-fold coordinated aluminum, AlO4; yet replacement of CaO by RE2O3 increased AlO5 according to 27Al MQMAS NMR spectroscopic measurements. Raman spectroscopic results suggested that depolymerization of the silicate network.

Amorphous nickel oxide and crystalline manganese oxide nanocomposite electrode for transparent and flexible supercapacitor

Among numerous active electrode materials, transition metal oxides are promising electrode materials in supercapacitors. Here, we fabricated amorphous nickel oxide and crystalline manganese oxide nanocomposite positive electrode for transparent and flexible supercapacitor. The nanocomposite was prepared via a two-step method. First, the amorphous nickel oxide film was prepared using a room-temperature chemical solution deposition and photochemical method. UV light irradiation causes condensation and densification of nickel oxide film by photochemical activation at room temperature. Second, the crystalline manganese oxide was prepared by chemical bath deposition method. The synergistic effect of the two components provides high electrochemical activity. A high-performance, transparent and flexible asymmetric supercapacitor was made of the nanocomposite positive electrode and worked in a wide voltage window of 1.2 V. An area capacitance of 48.1 mF/cm2 and an energy density of 9.62 µWh/cm2 at a power density of 28.9 µW/cm2 were achieved. After a 10,000 cycles, the capacitance of the device retains about 90% of its initial value. The high integrated electrochemical performances of the device were attributed to higher storage and transport capacity of the nanocomposite for both ions and electrons. These findings make amorphous and crystalline transition metal oxide nanocomposites as advanced electrode materials for transparent and flexible supercapacitors.

Evolution of optical properties and band structure from amorphous to crystalline Ga2O3 films

The optical properties and band structure evolution from amorphous to crystalline Ga2O3 films was investigated in this work. Amorphous and crystalline Ga2O3 films were obtained by changing the growth substrate temperatures of pulsed laser deposition and the crystallinity increase with the rising of substrate temperature. The bandgap value and ultraviolet emission intensity of the films increase with the rising of crystallinity as observed by means of spectrophotometer and cathodoluminescence spectroscopy. Abrupt bandgap value and CL emission variations were observed when amorphous to crystalline transition took place. X-ray photoelectron spectroscopy core level spectra reveal that more oxygen vacancies and disorders exist in amorphous Ga2O3 film grown at lower substrate temperature. The valence band spectra of hard X-ray photoelectron spectroscopy present the main contribution from Ga 4sp for crystalline film deposited at substrate temperature of 500 oC, while extra subgap states has been observed in amorphous film deposited at 300 oC. The oxygen vacancy and the extra subgap density of states are suggested to be the parts of origin of bandgap and CL spectra variations. The experimental data above yields a realistic picture of optical properties and band structure variation for the amorphous to crystalline transition of Ga2O3 films.

Liquid-crystal Assembly of Semiflexible-coil/Homopolymer Blends: a Dissipative Particle Dynamics Study

The liquid-crystal assembly of semiflexible-coil diblock copolymers with coil or semiflexible homopolymers is studied by dissipative particle dynamics simulation. Phase diagrams of the blends and orientation ordering parameters among semiflexible blocks are constructed as a function of chain stiffness and homopolymer volume fraction. For semiflexible-coil/coil blends with varying stiffness of semiflexible blocks, we display the rich phase behaviors of the system transited from coil-coil/coil to rod-coil/coil blends. The disorder-lamellae or lamellae-liquid crystalline transition and “dry brush” phenomenon induced by coil homopolymers are observed. For semiflexible-coil/semiflexible blends, adding semiflexible homopolymers also leads to a disorder-order transition and even a transition between monolayer and bilayer smectic-A phase. The results demonstrate that blending homopolymers into semiflexible copolymers can induce liquid-crystal assembly and even improve the orientation ordering of semiflexible blocks effectively.

Characteristics of TiO2 thin films surfaces treated by O2 plasma in dielectric barrier discharge with the assistance of external heating

TiO2 thin films were treated with plasma with the assistance of external heating. This plasma was produced with an O2 dielectric barrier discharge (DBD) at atmospheric and near-atmospheric gas pressures. For comparison, the samples were annealed in O2 gas and also treated with O2 DBD plasma alone. The effects of these treatments on photocatalytic activity were compared by evaluating the photodecomposition of methylene blue dye in aqueous solution. The photocatalytic activity of the heat-assisted plasma-treated sample was the most enhanced among the treatment processes. The net photodecomposition of the heat-assisted plasma-treated sample was slightly higher than or comparable to that of TiO2 anatase-phase nanoparticle powder. The photocatalytic activity enhancement can be attributed to an increase in the effective concentration of photogenerated carriers on the surface. This increase is driven by the synergistic effect between an increase in the depletion layer width and an increase in the optical absorption due to the crystalline transition from the bronze to the anatase phases. This crystalline transition occurred at a lower temperature than the annealing transformation temperature.

A Soft Shape Memory Reversible Dry Adhesive

Transfer printing is a critical procedure for manufacturing stretchable electronics. During such a procedure, stamps are utilized to transfer micro devices from silicon wafers to stretchable polymeric substrates. In addition to conventional silicone rubber stamps, epoxy resin based shape memory stamps have been developed and the transfer yield is thus significantly promoted. However, elastic modulus of the epoxy stamps is too high at both glassy and rubbery states, which may break the brittle micro devices during the adhesion process under mechanical pressure. In this work, we synthesized a copolymer of butyl acrylate (BA) and polycaprolactone diacrylate (PCLDA) as a soft reversible dry adhesive enabling a shape memory capability based on crystalline transition of polycaprolactone (PCL) segments. For the sample containing 40 wt% BA and 60 wt% PCLDA, Young’s modulus was 8.3 and 0.9 MPa respectively below and above the thermal transition temperature, which was much lower than that of the epoxy adhesive. On the other hand, the soft material still provided nearly ideal shape memory fixity and recovery ratios. Subsequently, shape memory surface with cone-shaped microstructure was prepared, which enabled a heating induced strong-to-weak adhesion transition when the microstructure recovered from a pressed temporary morphology to the permanent cone-shaped morphology. Such a soft reversible dry adhesive may contribute to large-scale and automated transfer printing processing.

Confinement-induced liquid crystalline transitions in amyloid fibril cholesteric tactoids.

Chirality is ubiquitous in nature and plays crucial roles in biology, medicine, physics and materials science. Understanding and controlling chirality is therefore an important research challenge with broad implications. Unlike other chiral colloids, such as nanocellulose or filamentous viruses, amyloid fibrils form nematic phases but appear to miss their twisted form, the cholesteric or chiral nematic phases, despite a well-defined chirality at the single fibril level. Here we report the discovery of cholesteric phases in amyloids, using β-lactoglobulin fibrils shortened by shear stresses. The physical behaviour of these new cholesteric materials exhibits unprecedented structural complexity, with confinement-driven ordering transitions between at least three types of nematic and cholesteric tactoids. We use energy functional theory to rationalize these results and observe a chirality inversion from the left-handed amyloids to right-handed cholesteric droplets. These findings deepen our understanding of cholesteric phases, advancing their use in soft nanotechnology, nanomaterial templating and self-assembly.

The Effect of SiC Polytypes on the Heat Distribution Efficiency of a Phase Change Memory.

The amorphous to crystalline transition of germanium-antimony-tellurium (GST) using three types of silicon carbide’s structure as a heating element was investigated. Simulation was done using COMSOL Multiphysic 5.0 software with separate heater structure. Silicon carbide (SiC) has three types of structure; 3C-SiC, 4H-SiC and 6H-SiC. These structures have a different thermal conductivity. The temperature of GST and phase transition of GST can be obtained from the simulation. The temperature of GST when using 3C-SiC, 4H-SiC and 6H-SiC are 467K, 466K and 460K, respectively. The phase transition of GST from amorphous to crystalline state for three type of SiC’s structure can be determined in this simulation. Based on the result, the thermal conductivity of SiC can affecting the temperature of GST and changed of phase change memory (PCM).