Lipid layer thickness decrease due to meibomian gland dysfunction leads to tear film instability and reflex tear secretion

PurposeTo determine the clinical effects of ocular surface and Meibomian gland parameters on tear film stability among individuals with Meibomian gland dysfunction (MGD), those with aqueous deficient dry eye (ADDE), individuals with both conditions and normal controls.MethodsPatients were divided into four groups: normal controls, patients with ADDE, patients with MGD, and patients who fulfilled diagnostic criteria for ADDE and MGD (Mixed Group). Data for ocular symptom score, lid margin abnormality, ocular staining, tear break-up time, meiboscore, and lipid layer thickness (LLT) measured by a Lipiview interferometer, Schirmer test, and MGD severity score were collected.ResultsA total of 109 patients (109 eyes) were evaluated. In patients with MGD, LLT was significantly lower than the ADDE patients. However, the Schirmer test value was the highest in the MGD group. The LLT negatively correlated with meiboscore and MGD severity score in the MGD group. Significant correlation between Schirmer test value and meiboscore was definite in the MGD group.ConclusionsTear fluid secretion is more increased and lipid layer thickness is more decreased in MGD patients than in ADDE patients. Decreased lipid layer thickness caused by MGD-related tear film instability may stimulate reflex tear secretion. The obstructive MGD is more prevalent than hypersecretary MGD.

Key messages

• The tear film stability is affected by Mebomian gland dysfunction (MGD). The measurement of the tear film parameters including lipid layer thickness suggests that the obstructive MGD is more prevalent than hypersecretary MGD and the aqueous layer compensates the decreased lipid layer caused by MGD.

     

小切口抽脂联合连续埋线重睑成形术

目的 分析小切口抽脂联合连续埋线重睑成形术在不对称重睑整形中的作用.方法 选取自2018年1月至2019年12月于本院接收治疗的不对称重睑患者189例,按照随机数字法分为观察组(小切口抽脂联合连续埋线重睑成形术)和对照组(重睑成形术),对比分析两组患者分别治疗后对眼睑美观满意度、手术相关指标以及术后并发症发生率.结果 ...     

Dual-DMD hyperspectral spatial frequency domain imaging (SFDI) using dispersed broadband illumination with a demonstration of blood stain spectral monitoring

Spatial frequency domain imaging (SFDI) is a widefield diffuse optical measurement technique capable of generating 2D maps of sub-surface absorption and scattering in biological tissue. We developed a new hyperspectral SFDI instrument capable of collecting images at wavelengths from the visible to the near infrared. The system utilizes a custom-built monochromator with a digital micromirror device (DMD) that can dynamically select illumination wavelength bands from a broadband quartz tungsten halogen lamp, and a second DMD to provide spatially modulated sample illumination. The system is capable of imaging 10 wavelength bands in approximately 25 seconds. The spectral resolution can be varied from 12 to 30 nm by tuning the input slit width and the output DMD column width. We compared the optical property extraction accuracy between the new device and a commercial SFDI system and found an average error of 23% in absorption and 6% in scattering. The system was highly stable, with less than 5% variation in absorption and less than 0.2% variation in scattering across all wavelengths over two hours. The system was used to monitor hyperspectral changes in the optical absorption and reduced scattering spectra of blood exposed to air over 24 hours. This served as a general demonstration of the utility of this system, and points to a potential application for blood stain age estimation. We noted significant changes in both absorption and reduced scattering spectra over multiple discrete stages of aging. To our knowledge, these are the first measurement of changes in scattering of blood stains. This hyperspectral SFDI system holds promise for a multitude of applications in quantitative tissue and diffuse sample imaging.     

生理性重睑术的临床应用

目的 探讨符合重睑生理解剖结构的切开重睑成形术的临床应用.方法:自2018年10月到2019年4月我院收治的56例重睑术患者,随机分为观察组和对照组,观察组采用符合生理解剖结构的切开重睑成形术为研究对象,对照组运用传统切开重睑成形术为研究对象,观察患者术后伤口愈合情况,术后瘢痕以及患者满意度及并发症的情况.结果:所有患...     

Influence of iron deficiency anemia on glycated hemoglobin levels in non-diabetic Saudi women

ObjectiveStudies of patients with iron deficiency anemia (IDA) have shown a relationship between high glycated hemoglobin (HbA1c) and low hemoglobin (Hb) concentration. The present study was conducted to determine the influence of IDA on HbA1c in non-diabetic women.MethodsFifty-nine Saudi women (20 to 50 years old) were enrolled and categorized into groups according to their circulating hemoglobin concentration: Non-IDA (Hb ≥7.45 mmol/L; n = 38) and IDA (Hb ≤7.44 mmol/L; n = 21). The IDA group was further subdivided according to the severity of the IDA, as follows: mild (Hb 6.83 to 7.44 mmol/L; n = 9) and moderate–severe (Hb <6.83 mol/L; n = 12). HbA1c, Hb, ferritin, fasting blood glucose, and red blood cell (RBC) count were measured in each participant.ResultsHbA1c did not significantly differ between the groups, but the absolute HbA1c level was significantly lower in the mild and moderate–severe anemia groups than the non-anemic group, and was positively associated with Hb, ferritin, and RBC count. In addition, the HbA1c level was inversely associated with the Hb concentration.ConclusionsHbA1c is significantly associated with parameters related to IDA in non-diabetic Saudi women. Therefore, assessment of IDA-related parameters is recommended prior to making a diagnosis of diabetes.     

First principles study of electronic and nonlinear optical properties of A–D–π–A and D–A–D–π–A configured compounds containing novel quinoline–carbazole derivatives

Materials with nonlinear optical (NLO) properties have significant applications in different fields, including nuclear science, biophysics, medicine, chemical dynamics, solid physics, materials science and surface interface applications. Quinoline and carbazole, owing to their electron-deficient and electron-rich character respectively, play a role in charge transfer applications in optoelectronics. Therefore, an attempt has been made herein to explore quinoline–carbazole based novel materials with highly nonlinear optical properties. Structural tailoring has been made at the donor and acceptor units of two recently synthesized quinoline–carbazole molecules (Q1, Q2) and acceptor–donor–π–acceptor (A–D–π–A) and donor–acceptor–donor–π–acceptor (D–A–D–π–A) type novel molecules Q1D1–Q1D3 and Q2D2–Q2D3 have been quantum chemically designed, respectively. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations are performed to process the impact of acceptor and donor units on photophysical, electronic and NLO properties of selected molecules. The λ_max values (321 and 319 nm) for Q1 and Q2 in DSMO were in good agreement with the experimental values (326 and 323 nm). The largest shift in absorption maximum is displayed by Q1D2 (436 nm). The designed compounds (Q1D3–Q2D3) express absorption spectra with an increased border and with a reduced band gap compared to the parent compounds (Q1 and Q2). Natural bond orbital (NBO) investigations showed that the extended hyper conjugation and strong intramolecular interaction play significant roles in stabilising these systems. All molecules expressed significant NLO responses. A large value of β_tot was elevated in Q1D2 (23 885.90 a.u.). This theoretical framework reveals the NLO response properties of novel quinoline–carbazole derivatives that can be significant for their use in advanced applications.

Materials with nonlinear optical properties have significant applications in nuclear science, biophysics, medicine, chemical dynamics, solid physics & materials science. We show how π bridges, donors & acceptors can be reconfigured to improve optical properties.     

Synthesis of ZnO sol–gel thin-films CMOS-Compatible

Zinc oxide (ZnO) is a II–VI group semiconductor with a wide direct bandgap and is an important material for various fields of industry and high-technological applications. The effects of thickness, annealing process in N₂ and air, optical properties, and morphology of ZnO thin-films are studied. A low-cost sol–gel spin-coating technique is used in this study for the simple synthesis of eco-friendly ZnO multilayer films deposited on (100)-oriented silicon substrates ranging from 150 to 600 nm by adjusting the spin coating rate. The ZnO sol–gel thin-films using precursor solutions of molarity 0.75 M exhibit an average optical transparency above 98%, with an optical band gap energy of 3.42 eV. The c-axis (002) orientation of the ZnO thin-films annealed at 400 °C were mainly influenced by the thickness of the multilayer, which is of interest for piezoelectric applications. These results demonstrate that a low-temperature method can be used to produce an eco-friendly, cost-effective ZnO sol–gel that is compatible with a complementary metal-oxide-semiconductor (CMOS) and integrated-circuits (IC).

A low-cost sol–gel spin-coating technique is used in this study for the simple synthesis of eco-friendly ZnO multilayer films deposited on (100)-oriented silicon substrates ranging from 150 to 600 nm by adjusting the spin coating rate.     

Feasibility of spatial frequency domain imaging (SFDI) for optically characterizing a preclinical oncology model

Determination of chemotherapy efficacy early during treatment would provide more opportunities for physicians to alter and adapt treatment plans. Diffuse optical technologies may be ideally suited to track early biological events following chemotherapy administration due to low cost and high information content. We evaluated the use of spatial frequency domain imaging (SFDI) to characterize a small animal tumor model in order to move towards the goal of endogenous optical monitoring of cancer therapy in a controlled preclinical setting. The effects of key measurement parameters including the choice of imaging spatial frequency and the repeatability of measurements were evaluated. The precision of SFDI optical property extractions over repeat mouse measurements was determined to be within 3.52% for move and replace experiments. Baseline optical properties and chromophore values as well as intratumor heterogeneity were evaluated over 25 tumors. Additionally, tumor growth and chemotherapy response were monitored over a 45 day longitudinal study in a small number of mice to demonstrate the ability of SFDI to track treatment effects. Optical scattering and oxygen saturation increased as much as 70% and 25% respectively in treated tumors, suggesting SFDI may be useful for preclinical tracking of cancer therapies.OCIS codes: (170.3880) Medical and biological imaging, (170.5280) Photon migration, (290.1990) Diffusion, (170.0110) Imaging systems, (170.6510) Spectroscopy, tissue diagnostics, (290.5820) Scattering measurements     

提上睑肌缩短术+睑板部分切除术治疗中重度上睑下垂患者的疗效及安全性分析

目的分析提上睑肌缩短术+睑板部分切除术治疗中重度上睑下垂患者的疗效及安全性.方法选取我院2017年6月~2019年5月收治的中重度上睑下垂患者86例,依据随机数字表法分为2组,即对照组(43例)、研究组(43例),其中对照组行提上睑肌缩短术治疗,研究组行提上睑肌缩短术、睑板部分切除术联合治疗,对比两组疗效、并发症发生状况、上睑缘高度对称情况以及术前、术后1个月、6个月眼睑状况[上睑缘到瞳孔中点距离(MRD)、睑裂高度、上睑回退量].结果研究组总有效率为83.72%(36/43),高于对照组62.79%(27/43,P<0.05);研究组上睑缘高度对称优良率为97.67%(42/43),高于对照组72.09%(31/43,P<0.05);两组术后1个月、6个月MRD大于术前,睑裂高度小于术前(P<0.05);术后1个月、6个月,研究组上睑回退量小于对照组(P<0.05);研究组并发症发生率对比,研究组11.63%(5/43)小于对照组30.23%(13/43,P<0.05).结论中重度上睑下垂患者采用提上睑肌缩短术联合睑板部分切除术治疗效果显著,可明显改善上睑缘高度对称度以及眼睑状况,减少并发症发生,安全性高.     

Efficacy of topical azithromycin ophthalmic solution 1% in the treatment of posterior blepharitis

Introduction

Azithromycin, a broad-spectrum antibiotic with potent anti-inflammatory activities, has the potential to effectively treat blepharitis, an inflammatory disease of the eyelid with abnormal eyelid flora as an etiologic determinant. The present study compared the efficacy of topical azithromycin ophthalmic solution 1% (AzaSite®; Inspire Pharmaceuticals, Inc, NC, USA) combined with warm compresses (azithromycin group) to warm compresses alone (compress group) in patients with posterior blepharitis.

Methods

Twenty-one patients diagnosed with posterior blepharitis were randomized in an open-label study to receive either azithromycin plus warm compresses (10 patients), or compresses alone (11 patients). All patients were instructed to apply compresses to each eye for 5–10 minutes twice daily for 14 days. Each eye in the azithromycin group also received azithromycin solution (1 drop) twice daily for the first 2 days followed by once daily for the next 12 days. Patients were evaluated at study initiation (visit 1) and at end of treatment (visit 2) for the severity of five clinical signs: eyelid debris, eyelid redness, eyelid swelling, meibomian gland (MG) plugging, and the quality of MG secretion. At visit 2, patients also rated their degree of overall symptomatic relief.

Results

Twenty patients completed the study. At visit 2, patients in the azithromycin group demonstrated significant improvements in MG plugging, MG secretions, and eyelid redness as compared with the compress group. In the azithromycin group, MG plugging resolved completely in three patients and MG secretion returned to normal in two patients; no such results were seen in the compress group. Furthermore, a higher percentage of patients in the azithromycin group rated overall symptomatic relief as excellent or good. Visual acuity measurements and biomicroscopic evaluation revealed no ocular safety issues.

Conclusion

Azithromycin ophthalmic solution in combination with warm compresses provided a significantly greater clinical benefit than warm compresses alone in treating the signs and symptoms of posterior blepharitis.

     

Photophysical properties and fluorosolvatochromism of D–π–A thiophene based derivatives

Solvation-dependent photophysical properties of two push–pull thiophene-based compounds with donor–π–acceptor (D–π–A) structures were investigated using absorption, fluorescence emission and time resolved spectroscopy, and supported by different solvation models. Intramolecular charge transfer characteristics of the structurally similar 2-fluoro-4-(5-(4-methoxyphenyl)thiophen-2-yl)benzonitrile (MOT) and 4-(5-(4-(dimethylamino)phenyl)thiophen-2-yl)-2-fluorobenzonitrile (DMAT) were investigated. Significant enhancement of intramolecular charge transfer strength has been observed through molecular structure modification of the electron donating group from a methoxy to dimethylamine group. Ground state absorption spectra show a small red shift of about 10 nm and 18 nm while the fluorescence emission spectra show a large red shift of about 66 nm and 162 nm on changing from the nonpolar cyclohexane to the aprotic polar DMSO for MOT and DMAT, respectively. Dipole moment change from the ground state to the charge transfer excited state is calculated to be 6.6 D in MOT and 9.0 D in DMAT. The fluorescence quantum yield, fluorescence lifetime and the derived radiative and non-radiative rate constants were found to be better correlated to the emission energy rather than any of the solvent properties. Three multi-parametric relationships were used in the interpretation of the specific versus non-specific solute–solvent interactions, namely, Kamlet–Taft, Catalán and Laurence et al. models. The findings of these approaches are used to extract useful information about different aspects of solvent effects on the photophysical properties of the two studied compounds. Kamlet–Taft solvatochromic model indicates that non-specific interactions are dominant in controlling the photophysical properties. Catalán''s solvent dipolarity/polarizability parameter is found to play a significant role in solvatochromic behaviour which is also designated by the Laurence model.

Solvation-dependent photophysical properties of two push–pull thiophene-based compounds with donor–π–acceptor (D–π–A) structures were investigated using absorption, fluorescence emission and time resolved spectroscopy, and supported by different solvation models.     

儿童瞬目异常与睑板腺功能障碍的关系

目的探讨儿童瞬目异常与睑板腺功能障碍(MGD)的关系。方法选取我院2018年6月至2020年6月收治的45例瞬目异常患儿为研究对象,按儿童瞬目异常严重程度分为轻度组、中度组、重度组,每组15例。观察患儿双眼上睑MGD评分、泪膜破裂时间(BUT)、角膜荧光染色(FL)评分及蠕形螨数量。结果三组患儿的睑板腺排出能力、睑板腺分泌物性状、睑缘及睑板腺检查评分,FL评分及蠕形螨数量比较,差异具有统计学意义(P<0.05),其中重度组>中度组>轻度组(P<0.05)。三组患儿的BUT比较,差异具有统计学意义(P<0.05),其中重度组<中度组<轻度组(P<0.05)。结论儿童瞬目异常的严重程度与MGD的严重程度有关。     

Effect of the electron donating group on the excited-state electronic nature and epsilon-near-zero properties of curcuminoid-borondifluoride dyes

Epsilon-near-zero (ENZ) properties have been reported in organic molecular films. In particular, cyanine and squaraine films have been shown to exhibit ENZ properties in the visible spectral region with a strong 3^rd order nonlinear optical response near the ENZ spectral region. Noting both cyanine and squaraine belong to the polymethine family, a series of six curcuminoid borondifluoride (Curc) derivatives were developed to examine whether such a polymethine character is positively correlated with the ENZ property of the organic films. Those Curc derivatives possess a Donor–Acceptor–Donor (D–A–D) architecture with acceptor, AcacBF₂, located at the molecular center. The backbone of Curc is designed such that the donor strength can be tuned to transit between charge transfer (CT) and polymethine character. This balance between CT and polymethine character of the Curc series is examined based on the Lippert–Mataga plot. As donor strength in the D–A–D structure increases, CT character is less marked resulting in a more dominant polymethine character. The structural and optical properties of the Curc films with a thickness in the order of 30 nm were examined to correlate the polymethine character with the ENZ response. The results obtained in isotropic Curc thin films demonstrate that an increase of polymethine character associated with a stronger donor strength leads to an appearance/enhancement of the ENZ property in the visible spectrum range from 500 to 670 nm. Overall, this study provides useful guidelines to engineer new organic materials showing ENZ properties in a desired spectral range.

Epsilon-near-zero (ENZ) properties have been reported in organic molecular films.     

不同强度运动对大鼠自由基代谢影响的研究

目的：研究不同强度运动对大鼠血清、骨骼肌、心肌、肝脏中自由基代谢的变化。方法：18只雄性Wistar大鼠随机分为安静对照组（CG）、适度运动组（MG）和运动性低血色素组（SG）,每组6只。5周递增负荷跑台运动后测定血清、腓肠肌、心肌、肝脏丙二醛（MDA）、总抗氧化能力（T-AOC）。结果：经5周递增负荷跑台运动后,MG组T-AOC活性在血清、腓肠肌、肝脏中显著高于CG组（P<0.01）;SG大鼠各组织中MDA含量明显高于CG和MG（P<0.01）,T-AOC活性（除心肌外）明显低于MG（P<0.01）。结论：①适度运动可提高大鼠各组织总抗氧化能力,增强机体清除自由基的能力。②长时间大强度递增负荷跑台运动导致的总抗氧化能力下降,脂质过氧化反应增强是引起运动性低血色素的重要原因之一。     

Magnetic and spectroscopic properties of Ni–Zn–Al ferrite spinel: from the nanoscale to microscale

This article presents the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni_0.6Zn_0.4Fe_1.5Al_0.5O₄ (NZFAO) nanoparticles (NPs). The samples were successfully synthesized by the sol–gel method followed by annealing of the as-synthesized at 600, 800, 900, 1050, and 1200 °C. This approach yielded the formation of a highly crystalline structure with crystallite size ranging from 17 nm to 40 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques, as well as energy disperse spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman spectroscopy, were used in order to determine the structural and morphological properties of the prepared samples. Rietveld XRD refinement reveals that Ni–Zn–Al ferrite nanoparticles crystallize in inverse cubic (Fd$\bar{3}$m) spinel structure. Using FTIR spectra, the elastic and thermodynamic properties were estimated. It was observed that the particle size had a pronounced effect on elastic and thermodynamic properties. Magnetic measurements were performed up to 700 K. The prepared ferrite samples present the highest Curie temperature, which decreases with increasing particle size and which is consistent with finite-size scaling. The thickness of the surface shell of about 1 nm was estimated from size-dependent magnetization measurements using the core–shell model. Besides, spin resonance, magnetostriction, temperature coefficient of resistance (TCR), and electrical resistivity properties have been scientifically studied and appear to be different according to their size. The optical properties of synthesized NZFAO nanoparticles were investigated, and the differences caused by the particle sizes are discussed on the basis of the phonon confinement effect. This effect was also inspected by the Raman analysis. Tuning of the physical properties suggests that the Ni–Zn–Al ferrite samples may be promising for multifunctional diverse applications.

This article presents the annealing effect on the structural, elastic, thermodynamic, optical, magnetic, and electric properties of Ni_0.6Zn_0.4Fe_1.5Al_0.5O₄ (NZFAO) nanoparticles (NPs).     

Ultra-small aqueous glutathione-capped Ag–In–Se quantum dots: luminescence and vibrational properties

We introduce a direct aqueous synthesis of luminescent 2–3 nm Ag–In–Se (AISe) quantum dots (QDs) capped by glutathione (GSH) complexes, where sodium selenosulfate Na₂SeSO₃ is used as a stable Se²⁻ precursor. A series of size-selected AISe QDs with distinctly different positions of absorption and PL bands can be separated from the original QD ensembles by using anti-solvent-induced size-selective precipitation. The AISe–GSH QDs emit broadband PL with the band maximum varying from 1.65 eV (750 nm) to 1.90 eV (650 nm) depending on the average QD size and composition. The PL quantum yield varies strongly with basic synthesis parameters (ratios of constituents, Zn addition, duration of thermal treatment, etc.) reaching 4% for “core” AISe and 12% for “core/shell” AISe/ZnS QDs. The shape and position of PL bands is interpreted in terms of the model of radiative recombination of a self-trapped exciton. The AISe–GSH QDs reveal phonon Raman spectra characteristic for small and Ag-deficient tetragonal Ag–In–Se QDs. The ability of ultra-small AISe QDs to support such “bulk-like” vibrations can be used for future deeper insights into structural and optical properties of this relatively new sort of QDs.

A direct aqueous synthesis, composition- and size-dependent absorption, photoluminescence, and vibrational properties of ultra-small glutathione-capped Ag-deficient Ag–In–Se quantum dots are reported.     

Synthesis and characterization of novel donor–acceptor type electrochromic polymers containing diketopyrrolopyrrole as an acceptor and propylenedioxythiophene or indacenodithiophene as a donor

A range of low band gap donor–acceptor conjugated polymers (P1–P3) with backbones composed of diketopyrrolopyrrole (DPP), propylenedioxythiophene (ProDOT) and indacenodithiophene (IDT) units were designed and synthesized using the Stille coupling reaction. The optical, electrochemical and electrochromic properties of the resultant polymers were thoroughly characterized. These polymers showed exceptional solubility in common organic solvents and displayed thermal stability at a high temperature. The optical and electrochemical measurements revealed slight variations in the maximum absorptions and oxidation peaks depending on the intrinsic D–A ratio in each polymer, and narrow band gaps lower than 1.60 eV were found for these polymers. Upon oxidation, the polymer films exhibit distinct color changes (pale violet-red to dark gray for P1, rosy brown to silver for P2, atrovirens to light grey for P3) in the VIS and NIR regions. Moreover, the electrochromic switching studies indicated that these polymers have favorable switching properties, such as rapid response speed and high optical contrast and coloration efficiency, and are outstanding candidates for electrochromic applications.

Three novel D–A type conjugated copolymers were prepared, illustrating excellent electrochromic properties, such as desirable color switches, high optical contrasts, fast response time, and high color efficiency.     

Magnetic–plasmonic Ni@Au core–shell nanoparticle arrays and their SERS properties

In this paper, large-area magnetic–plasmonic Ni@Au core–shell nanoparticle arrays (NPAs) with tunable compositions were successfully fabricated by a direct laser interference ablation (DLIA) incorporated with thermal dewetting method. The magnetic properties of the Ni@Au core–shell NPAs were analyzed and the saturation magnetization (M_s) of the Ni₈₀@Au₂₀ nanoparticles was found to be higher than that of nickel-only nanoparticles with the same diameter. Using Rhodamine 6G (R6G) as a Raman reporter molecule, the surface enhanced Raman scattering (SERS) property of the Ni@Au core–shell NPAs with a grain size distribution of 48 ± 42 nm and a short-distance order of about 200 nm was examined. A SERS enhancement factor of 2.5 × 10⁶ was realized on the Ni₅₀@Au₅₀ NPA substrate, which was 9 times higher than that for Au nanoparticles with the same size distribution. This was due to the enhanced local surface plasmon resonance (LSPR) between the ferromagnetic Ni cores and the surface polariton of the Au shells of each nanoparticle. The fabrication of the Ni@Au core–shell NPAs with different compositions offers a new avenue to tailor the optical and magnetic properties of the nanostructured films for chemical and diagnostic applications.

In this paper, large-area magnetic–plasmonic Ni@Au core–shell nanoparticle arrays (NPAs) with tunable compositions were successfully fabricated by a direct laser interference ablation (DLIA) incorporated with thermal dewetting method.     

Generalized nano-thermodynamic model for capturing size-dependent surface segregation in multi-metal alloy nanoparticles

Multi-metal alloy nanoparticles (NPs) offer new avenues for exploration and design of nanoscale-properties, e.g., catalytic, electronic and optical properties, by virtue of their tunable composition. A method that can aid such exploration by accurately predicting the size-, shape- and composition-dependent elemental distribution associated with nanomaterials is crucially missing. A nano-thermodynamic model based on distribution coefficients Δ is introduced to fill this gap. Δ is employed to predict surface segregation in NPs as a function of the NP size and composition. Interestingly, we find Δ to be independent of size for NPs beyond 2 nm. This key finding motivates the construction of thermodynamic tables for distribution coefficients using segregation observed with one or more NP sizes. The tables can enable accurate prediction of phase diagrams for nanomaterials across a wide-range of sizes. Key concepts of this new theory are demonstrated with Au–Pt–Pd, Ag–Au–Pd and Ni–Pt–Pd, which are found to exhibit complex size-dependent segregation behavior for 2–6 nm NPs and relatively weaker size-dependence beyond 6 nm. Numerically well-converged values of Δ are calculated for small NPs using Monte Carlo simulations in the canonical ensemble. Simulations are based on an embedded atom method (EAM) potential for metal alloys.

Nano-thermodynamic model captures thermodynamic preference of metal species for different regions of a nanoparticle while accounting for size effects.