Ordering Transition Temperature Research Articles

Effects of quantum dots on the nematic to smectic-A phase transition

ABSTRACT Experiments on the composites of liquid crystals and quantum dots showed the significant role of quantum dots on the properties of the nematic–smectic-A phase transition. The effects of quantum dots on the nematic-smectic-A phase transition have been discussed using Flory- Huggins theory of isotropic mixing and Landau-de Gennes theory. The impact of quantum dots on the smectic-A order parameters, nematic–smectic-A transition temperature, splay and bend elastic constants has been discussed. The smectic-A order parameters, transition temperature and elastic constants decrease with the increase of volume fraction of quantum dots.

Dilution of helical antiferromagnetic matrix of CaMn7O12 under nonmagnetic Ga[formula omitted] doping

The work reports dilution studies on antiferromagnetic CaMn7O12. Introduction of nonmagnetic ion in an antiferromagnetic matrix changes the magnetic properties in an interesting way. The study becomes significant due to the fact that remarkable increase in magnetization is observed as a result of substitution of a few of the magnetic Mn ions with the nonmagnetic Ga ion. For 5% doping of Ga, the magnetization value becomes nearly thrice of the un-doped CaMn7O12. A sequential decrease in antiferromagnetic ordering transition temperature is also observed with increasing Ga percentage in the parent compound. The solid solubility limit of Ga in the matrix is found to be nearly 5%, above which it start showing impurity peaks. Experimental results are well complemented with the Density functional theory (DFT) based calculations. Theoretical calculations are carried out on (CaMn7O12)3 unit cell with one Ga atom doped at different Mn sites resulting around 5% doping concentration. Besides identifying the most favourable doping site for Ga, results indicate a reduction of bulk band gap and significant increase in magnetization, both of which are in agreement with the experimental results.

Theoretical study of the nematic to isotropic phase transition in the mixtures of nematic liquid crystal and quantum dots nanoparticles

ABSTRACTThe nematic to isotropic phase transition in the mixtures of nematic liquid crystal and quantum dots nanoparticles has been studied. Flory Huggins theory of isotropic mixing and Landau-de Gennes theory have been used to study the nematic to isotropic phase transition. The effects of quantum dots nanoparticles on the nematic order parameter, transition temperature, and splay elastic constant have been discussed. The decrease of nematic order parameter, transition temperature, and splay elastic constant with the increase in volume fraction of quantum dots nanoparticles has been observed.

Predicting large comprehensive refrigeration performance of plastic crystals by compositing carbon architectures for room temperature application

Plastic crystals PE (pentaerythritol) possess colossal barocaloric effect (BCE) that is promising for solid-state refrigeration; however, the high phase transition temperature (> 400 K) and low thermal conductivity (<0.5 W·m−1·K−1) greatly hinder its practical application at room temperature. Here, we propose to complex plastic crystal (PC) with carbon nanotube/graphene architectures (CNT-Gra) to form [PC/CNT-Gra] composites and investigate the BCE based on molecular dynamics simulations. It is found that phase transition temperature of molecular order to disorder can be tuned by alloying PA (neopentane) or NPG (neopentyl glycol) into PE imbedded in CNT-Gra architectures. Importantly, we find that PE0.8PA0.2/CNT-Gra and PE0.75NPG0.25/CNT-Gra demonstrate both giant isothermal entropy changes ΔS (∼200 J·kg−1·K−1) and adiabatic temperature change ΔT (∼18 K) at room temperature. The large BCE mainly comes from the order–disorder transition of PC molecules imbedded in CNT-Gra architectures through analysis of the dynamic process of the composites. Importantly, the thermal conductivity of these campsites is as high as ∼10 W·m−1·K−1, enabling efficient thermal exchange that is vital for improving cooling performance of the cyclic refrigeration process. This work provides important insights for designing PC-based composites with optimized comprehensive cooling performance for potential room temperature refrigeration.

Effect of graphene nanoparticles on the isotropic to nematic phase transition

ABSTRACT A model combining with Flory-Huggins theory of isotropic mixing and Landau theory is developed to describe the effect of graphene nanoparticles on the isotropic to nematic phase transition. The temperature and concentration of graphene nanoparticles dependence on the orientational order parameter, transition temperature and thermodynamic quantities near the isotropic to nematic phase transition are discussed. The orientational order parameter, transition temperature and enthalpy near the isotropic to nematic phase transition increase with the increase of graphene nanoparticles.

Cation disorder and the charge ordering transition temperature in La1/3(Sr1-xCax)2/3FeO3−δ investigated by mechanical spectroscopy

The lattice effect on the charge ordering in La1/3Sr2/3FeO3−δ is addressed by calcium ion substitution. Cation disorder effect due to size differences between A-site La3+, Sr2+, and Ca2+ has been found in La1/3(Sr1-xCax)2/3FeO3−δ perovskites. Below room temperature, a charge ordering transition has been detected by temperature dependent resistivity, differential scanning calorimeter, and mechanical spectroscopy. The charge ordering transition temperature TC shows a clear dependence on the variance of the A-site cation radius distribution. This result shows an important role of local lattice distortions on the charge ordering transition. As a comparison, octahedral titling transitions above room temperature were identified by mechanical spectroscopy, and the tilting transition temperatures are sensitive to the average cation radius. Finally, the implication of the cation disorder effect is discussed by a comparison of the case in manganates.

Comparative analysis of polyimide and aramid fabrics as arc protective materials

Arc explosion accidents in live working seriously threaten the safety of power workers. At present, the mainstream arc protective clothing material is aramid and blends of aramid. However, aramid will produce toxic gas under high temperature combustion, which is harmful to the health of operators. Therefore, it is a special challenge to study fabrics that are friendly to the human body and have a highly protective performance to protect electrical workers. Polyimide is nontoxic and has excellent high temperature resistance, flame retardation, and mechanical properties. In this paper, polyimide was proposed to be used as an arc protective clothing material. In order to explore the feasibility of polyimide in the field of arc protection, molecular dynamics simulation was used to compare the heat resistance of polyimide and aramid in terms of bond order and glass transition temperature. Referring to ASTM F1959 and IEC 61482-1-1, an arc test apparatus was built to test the protective properties of materials. The protection failure mechanism was analyzed by comparing the safety protective performance of polyimide and aramid fabric under the arc. It was found that polyimide has better arc thermal protective performance and break open threshold. The simulation and test results show that polyimide can be used as a material for arc protective clothing to improve protective performance.

A review of the oxygen vacancy ordering in surrogate structures simulating Pu-based nuclear ceramics

Advanced nuclear power systems and nuclear fuel cycles will require nuclear fuels capable of higher burnup and with higher transuranic concentrations than those previously developed for current nuclear power plants. Expensive qualification tests are required to validate the thermal and mechanical performance of fuels in normal and accident-scenario operations. Research of surrogate systems with specific properties and characteristics of advanced nuclear fuels can be an effective way to frame the problem, reduce costs, and support the technical development of future research. From this perspective, lanthanide counterparts like mixed oxides of Ce and Nd can provide replica systems for many technological properties of the actual fuels. These ceramic systems can lead to a better understanding of the fundamental irradiation processes responsible for the evolution of their microstructures, the interplay with charge and defect localisation, and the evolution of their mechanical properties. In non-stoichiometric MO2−x binary systems (M = Ce, Pr, and Tb), there is evidence of systematic ordering of vacancies resulting in a deviation from the ideal fluorite structure and the formation of several intermediate fluorite-related phases. Substitution of the 4+ cations with 3+ cations in these systems drives the formation of oxygen vacancies as a charge compensation mechanism. By analogy with MO2−x systems, a variety of similar intermediate phases would also be expected to form in the MO2:Ln2O3 (Ln = La, Nd, Gd … etc). However, in order to achieve chemical homogeneity and charge ordering, prolonged annealing just above the charge ordering transition temperature is required, covering a time-scale determined by the chemical diffusion coefficient. Achieving these conditions with powder metallurgy techniques, commonly employed in literature, is practically impossible. This paper reviews the transport properties and structural features found in these surrogate systems which may be helpful in addressing challenges facing advanced nuclear fuels. We present results of a recent diffraction experiment investigating the structure of neodymium doped ceria synthesised using soft chemical methods. The sample shows a deviation from previous literature as the diffraction data is best described by a monoclinic Ln6O11-type structure (SG P21/c), often referred to as “β phase” in PrO2−x.

Inhibitory Effect of Lanthanides on Native Lipid Flip-Flop

The influence of ytterbium ions (Yb3+), a commonly used paramagnetic NMR chemical shift reagent, on the physical properties and flip-flop kinetics of dipalmitoylphosphatidylcholine (DPPC) planar supported lipid bilayers (PSLBs) was investigated. Langmuir isotherm studies revealed that Yb3+ interacts strongly with the phosphate headgroup of DPPC, evidenced by the increases in shear and compression moduli. Using sum-frequency vibrational spectroscopy, changes in the acyl chain ordering and phase transition temperature were also observed, consistent with Yb3+ interacting with the phosphate headgroup of DPPC. The changes in the physical properties of the membrane were also observed to be concentration dependent, with more pronounced modification observed at low (50 μM) Yb3+ concentrations compared to 6.5 mM Tb3+, suggesting a cross-linking mechanism between adjacent DPPC lipids. Additionally, the changes in membrane packing and phase transition temperatures in the presence of Tris buffer suggested that a putative Yb(Tris)3+ complex forms that coordinates to the PC headgroup. The kinetics of DPPC flip-flop in the gel and liquid crystalline (lc) phases were substantially inhibited in the presence of Yb3+, regardless of the Yb3+ concentration. Analysis of the flip-flop kinetics under the framework of transition state theory revealed that the free energy barrier to flip-flop in both the gel and lc phases was substantial increased over a pure DPPC membrane. In the gel phase, the trend in the free energy barrier appeared to follow the trend in the shear moduli, suggesting that the Yb3+-DPPC headgroup interaction was driving the increase in the activation free energy barrier. In the lc phase, activation free energies of DPPC flip-flop in the presence of 50 μM or 6.5 mM Yb3+ were found to mirror the free energies of TEMPO-DPPC flip-flop, leading to the conclusion that the strong interaction between Yb3+ and the PC headgroup was essentially manifested as a headgroup charge modification. These studies illustrate that the presence of the lanthanide Yb3+ results in significant modification to the lipid membrane physical properties and, more importantly, results in a pronounced inhibition of native lipid flip-flop.

Strain and crystallite size controlled ordering of Heusler nanoparticles having high heating rate for magneto-thermal application

Heusler compound nanoparticles with good structural ordering need to be investigated as a potential material class for magneto-thermal applications requiring heat generation in presence of an oscillating magnetic field. Here, we report an important finding of a structural parameter related to the product of the strain and the coherent crystallite size, that can be used to efficiently control the structural ordering and the magnetic property of the Heulser compound nanoparticles. The optimization of this product parameter is found to enhance both the structural ordering and magnetic transition temperature in Co2FeSn Heusler nanoparticles. Furthermore, using magnetic hyperthermia measurements we demonstrate the possibility of heat generation using Heusler compound nanoparticles comparable to that of conventional magnetic nanoparticles. This shall lead to the development of Heulser compounds for similar applications.

3d Metal Doping of Core@Shell Wüstite@ferrite Nanoparticles as a Promising Route toward Room Temperature Exchange Bias Magnets.

Nanometric core@shell wüstite@ferrite (Fe1-x O@Fe3 O4 ) has been extensively studied because of the emergence of exchange bias phenomena.Since their actual implementation in modern technologies is hampered by the low temperature at which bias is operating, the critical issue to be solved is to obtain exchange-coupled antiferromagnetic@ferrimagnetic nanoparticles (NPs) with ordering temperature close to 300 K by replacing the divalent iron with other transition-metal ions. Here, the effect of the combined substitution of Fe(II) with Co(II) and Ni(II) on the crystal structure and magnetic properties is studied. To this aim, a series of 20nm NPs with a wüstite-based core and a ferrite shell, with tailored composition, (Co0.3 Fe0.7 O@Co0.8 Fe2.2 O4 and Ni0.17 Co0.21 Fe0.62 O@Ni0.4 Co0.3 Fe2.3 O4 ) is synthetized through a thermal-decomposition method. An extensive morphological and crystallographic characterization of the obtained NPs shows how a higher stability against the oxidation process in ambient condition is attained when divalent cation doping of the iron oxide lattice with Co(II) and Ni(II) ions is performed. The dual-doping is revealed to be an efficient way for tuning the magnetic properties of the final system, obtaining Ni-Co doped iron oxide core@shell NPs with high coercivity (and therefore, high energy product), and increased antiferromagnetic ordering transition temperature, close to room temperature.

Evidence of room temperature magnetodielectric and cluster glass behavior of Sr substituted Y-type Ba2Mg2Fe11.48Mn0.52O22 hexaferrite

We have presented a systematic study on structural, magnetic, and magnetodielectric (MD) properties of Y-type Ba2-xSrxMg2Fe11.48Mn0.52O22 (0 < x ≤ 1) hexaferrite. The temperature-dependent DC magnetization results exhibit Sr substitution enhances spin ordering transition temperature TI (TII) from 52 K (210 K) to 73 K (315 K). AC magnetic characterization suggests the presence of single cluster-glass transition (Tf1) at 45 K for x = 0.25. Interestingly, for higher Sr substitution x > 0.25, double cluster class transition is observed. The freezing temperature Tf1 decreases with an increase in x, while Tf2 increases substantially with x. The saturation magnetization (Ms) value is found to be decreased from 28.88 emu/g for x = 0.25 to 26.28 emu/g for x = 0.75 at 300 K. However, for x > 0.75 this value increases. Raman modes at 78, 135, 335, and 694 cm−1 show a gradual increase in Raman shift up to x = 0.75, but a drastic decrease is seen for x > 0.75. Along with enhanced magnetic properties, Sr doped sample shows better MD properties. The MD% value at RT increases with doping concentration up to x = 0.75 (MD% ∼1.2); beyond that, its value decreases. The maximum value of frequency-independent MD% and magnetoloss ML% of the BSMFM25 is found to be ∼3.5 and ∼0.2, respectively in the presence of a 1.3 T field at 100 Hz. The H-dependent MD exhibits symmetric anomalies close to the H-induced transition indicating an exchange-striction phenomenon in the samples.

Physical properties of microwave and solid state synthesized La0.7Na0.3MnO3

We report the structural, magnetic, electrical and broadband microwave absorption in La0.7Na0.3MnO3 sample synthesized by microwave (MW) irradiation (Na0.3LMO_MW) and compare them to the sample synthesized by solid-state (SS) reaction method (Na0.3LMO_SS). Single phase Na0.3LMO_MW was synthesized at 800 °C in 30 min, whereas, Na0.3LMO_SS sample was obtained by sintering at 1200 °C for 48 h. Although both these samples show ferromagnetic transition at TC ∼324.8 K, the MW-synthesized sample shows distinct physical properties: broad ferromagnetic transition, smaller saturation magnetization, a large difference between the magnetic ordering and metal-insulator transition temperatures, a large high-field magnetoresistance, a table top-like magnetocaloric effect, and a large low-field microwave absorption compared to the solid state synthesized sample. These differences are suggested to arise from magnetic heterogeneity induced by smaller grain size and surface spin disorder in the MW synthesized La0.7Na0.3MnO3.

Reactive spark plasma-assisted synthesis of metastable rare-earth ferrites with widely tunable charge ordering transfer properties.

Although the d-band correlations within metastable rare-earth ferrites (ReFe2O4) enable charge ordering transition functionalities beyond conventional semiconductors, their material synthesis yet requires a reducing atmosphere that is toxic and explosive. Herein, we demonstrate a reactive spark plasma sintering (RSPS) strategy to effectively synthesize metastable ReFe2O4 (Re = Er, Tm, Yb, Lu) simply in coarse vacuum within a greatly shortened reaction period. High flexibility is gained in adjusting their rare-earth composition and thereby the charge ordering transition temperature within 218-330 K. Assisted by the temperature-dependent near edge X-ray absorption fine structure (NEXAFS) analysis, an elevation in the Fe3+/Fe2+ orbital configuration within ReFe2O4 was observed compared to previous reports, and it is consistent with their higher Mott temperature and activation energy observed in their electrical transportations. This work elucidates stabilization of the metastable phase (e.g., ReFe2O4) via the non-equilibrium processes of RSPS beyond the thermodynamic restrictions.

Experimental clathrate superhydrides EuH6 and EuH9 at extreme pressure conditions

The recent discovery of a class of sodalitelike clathrate superhydrides (e.g., ${\mathrm{YH}}_{6}$, ${\mathrm{YH}}_{9}$, ${\mathrm{ThH}}_{9}$, ${\mathrm{ThH}}_{10}$, and ${\mathrm{LaH}}_{10}$) at extreme pressures, which commonly exhibit high-temperature superconductivity with the highest ${T}_{c}$ approaching 260 K for ${\mathrm{LaH}}_{10}$, opened up a new era in the search for high-temperature superconductors in metal superhydrides. There is high interest in finding alternative clathrate superhydrides that might witness the long-dreamed room-temperature superconductivity. Here, we target the experimental synthesis of europium (Eu) superhydrides where theory can fail for the prediction of superconductivity. We pressurized and laser heated a mixture of metal Eu and ammonia borane $({\mathrm{NH}}_{3}{\mathrm{BH}}_{3})$ in a diamond-anvil cell and successfully synthesized the clathrate structured ${\mathrm{EuH}}_{6}$ and ${\mathrm{EuH}}_{9}$ at conditions of 152 GPa and 1700 K, and 170 GPa and 2800 K, respectively. Two nonclathrate structured phases of ${\mathrm{EuH}}_{5}$ and ${\mathrm{EuH}}_{6}$ were also synthesized that are not reported in lanthanide superhydrides. Theoretical simulations predicted that all the synthesized europium hydrides are magnetic, where the electrical resistance measurements suggest a possible magnetic order transition temperature at around 225 and 258 K, respectively, for ${\mathrm{EuH}}_{5}$ and clathrate ${\mathrm{EuH}}_{6}$. Our work has created a model superhydride platform for subsequent investigations on how a strongly correlated effect and magnetism can affect the superconductivity of superhydrides.

A Sub-Micron-Thick stretchable adhesive layer for the lamination of arbitrary elastomeric substrates with enhanced adhesion stability

Binding two separate elastomeric substrates is of great importance for the fabrication of next generation stretchable devices including epidermal electronics and soft robotics. However, it is still extremely challenging to find an adhesive to bind arbitrary elastomers with excellent adhesion strength and reliability without compromising the stretchability of the laminated elastomeric substrates. In this study, a sub-micron-thick (∼500 nm) stretchable adhesive was synthesized by using a vapor-phase deposition method. The stretchable adhesive consists of a copolymer film containing curable epoxy and hydroxyl functionalities with sufficiently low glass transition temperature (Tg) in order to render the adhesive elastomeric. Moreover, depositing the adhesive layer in vapor phase induced an interpenetrating polymer network (IPN) at the interface between the elastomeric substrate and stretchable adhesive layer, which enabled strong binding between arbitrary elastomeric substrates such as polydimethylsiloxane (PDMS), Silbione™, 3 M VHB™, and Ecoflex™, with substantially enhanced adhesion stability and high transparency. The adhesion strength was fully retained even after more than 105 times of repeated stretch-release cycles of 50% strain. The IPN-induced stretchable but ultrathin adhesive layer developed in this study will serve as a platform bonding technology for the wide range of soft matter engineering applications.

Review of the influence of copper and chromium substitution on crystal structure, magnetic properties and magnetocaloric effect of GdFe2−x(Cu, Cr)x (x = 0, 0.1, 0.15 and 0.2) intermetallic compounds

The iron-based compounds GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) were synthesized successfully by means of arc-melting and annealing at 800 °C for one week. The structural, magnetic and magnetocaloric properties of these intermetallic compounds were investigated systematically in detail using X-ray powder diffraction (XRD) analysis, Scanning electron microscopy (SEM) equipped with Energy dispersive X-ray spectroscopy (EDS), and magnetic measurements. The Rietveld analysis of X-ray diffraction patterns proves that GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds crystallize in the cubic laves phase MgCu2-type structure with the Fd3̄m space group. Gadolinium and iron atoms statistically occupy the 8a and 16d sites respectively. Moreover, copper and chromium atoms substitute the iron atoms at site 8a in the MgCu2-type structure. The temperature dependence of magnetization studied in a broad temperature range reveals that all compounds exhibit a ferromagnetic-paramagnetic transition at Curie temperature (TC). We find that the substitution of iron by copper and chromium leads to a decrease in the magnetic ordering transition temperature. The Arrott plots of all our samples show the occurrence of a second-order phase transition. Besides, the performance of magnetocaloric effect (MCE) for GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds was evaluated by the magnetic entropy change (ΔSM) and the related Relative Cooling Power (RCP). In the vicinity of TC, the ΔSM reached a maximum value of 0.79 J/kg.K, 1.2 J/kg.K, 1.4 J/kg.K and 2.5 J/kg.K, while the RCP was found to be 13.2 J/kg, 21.6 J/kg, 31.7 J/kg and 44.3 J/kg, respectively for GdFe2−xCux (x = 0, 0.1, 0.15 and 0.2) compounds. Furthermore, the GdFe2−xCrx (x = 0.1, 0.15 and 2) compounds show ΔSM values of about 0.9 J/kg.K, 1.3 J/kg.K and 1.8 J/kg.K, and RCP values of 14.8 J/kg, 25.4 J/kg and 36.8 J/kg respectively, under a field change of 1.56 T. Through these results, the GdFe2−x(Cu,Cr)x (x = 0, 0.1, 0.15 and 0.2) compounds can be an attractive materials for use in magnetic refrigeration and heat pumping technology above room temperature.

Effective model for rare-earth Kitaev materials and its classical Monte Carlo simulation* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0302904 and 2016YFA0300504), the National Natural Science Foundation of China (Grant Nos. U1932215, 11774419, 11574392, and 11974421), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB33010100), the Fundamental Research

Recently, the family of rare-earth chalcohalides were proposed as candidate compounds to realize the Kitaev spin liquid (KSL) [Chin. Phys. Lett. 38 047502 (2021)]. In the present work, we firstly propose an effective spin Hamiltonian consistent with the symmetry group of the crystal structure. Then we apply classical Monte Carlo simulations to preliminarily study the model and establish a phase diagram. When approaching to the low temperature limit, several magnetic long range orders are observed, including the stripe, the zigzag, the antiferromagnetic (AFM), the ferromagnetic (FM), the incommensurate spiral (IS), the multi- Q , and the 120° ones. We further calculate the thermodynamic properties of the system, such as the temperature dependence of the magnetic susceptibility and the heat capacity. The ordering transition temperatures reflected in the two quantities agree with each other. For most interaction regions, the system is magnetically more susceptible in the ab-plane than in the c-direction. The stripe phase is special, where the susceptibility is fairly isotropic in the whole temperature region. These features provide useful information to understand the magnetic properties of related materials.

RENiO3 Single Crystals (RE = Nd, Sm, Gd, Dy, Y, Ho, Er, Lu) Grown from Molten Salts under 2000 bar of Oxygen Gas Pressure

The electronic properties of transition-metal oxides with highly correlated electrons are of central importance in modern condensed matter physics and chemistry, both for their fundamental scientific interest, and for their potential for advanced electronic applications. The design of materials with tailored properties has been, however, restricted by the limited understanding of their structure-property relationships, which are particularly complex in the proximity of the regime where localized electrons become gradually mobile. RENiO3 perovskites, characterized by the presence of spontaneous metal to insulator transitions, are one of the most widely used model materials for the investigation of this region in theoretical studies. However, crucial experimental information needed to validate theoretical predictions is still lacking due to their challenging high-pressure synthesis, which has prevented to date the growth of sizable bulk single crystals with RE different than La, Pr and Nd. Here we report the first successful growth of single crystals with RE = Nd, Sm, Gd, Dy, Y, Ho, Er and Lu and sizes up to ~75 {\mu}m, grown from molten salts in temperature gradient under 2000 bar oxygen gas pressure. The crystals display regular prismatic shapes with flat facets, and their crystal structures, metal-insulator and antiferromagnetic order transition temperatures are in excellent agreement with previously reported values obtained from polycrystalline samples. The availability of such crystals opens access to measurements that have hitherto been impossible to conduct. This should contribute to a better understanding of the fascinating properties of materials with highly correlated electrons, and guide future efforts to engineer transition metal oxides with tailored functional properties.

A spectroscopic study of the composition and conformation of cholesteryl and wax esters purified from meibum

Elucidating wax ester (WE) and cholesteryl ester (CE) compositional, structural and functional relationships is key to our understanding of how these lipids are involved in natural and pathological processes. Little is known about how CE and WE interact with one another. The focus of the present study is to bridge this gap of knowledge. CE and WE were collected from human meibum as a source of esters with complex hydrocarbon chains. MgO column chromatography was used to separate WE and CE. The esters were characterized using 1H-NMR and Fourier transform infrared spectroscopy. The complexity of the hydrocarbon chains of native WE and CE influenced how changes in the ratio of WE and CE ester influenced some lipid phase transitional parameters but not others. Changes in CE content of WE/CE mixtures undoubtedly modifies the hydrocarbon chain conformation and packing of the mixture. The nature of the change depends on the conformation of the WE and CE. Differences in the complexity of the hydrocarbon chains are likely not to be a major influence on alterations in the order or phase transition temperature when more ordered WE is added to less ordered CE.