Skin Constituents as Cosmetic Ingredients. Part II: A Study of Bio‐Mimetic Monoglycerides Behavior at the Squalene‐Water Interface by the “Pendant Drop” Method in a Dynamic Mode

This work aims at presenting the viscoelastic behavior of bio‐mimetic monoglycerides used as emulsifier in a mixture made of two non‐miscible liquids, squalene and water. The measurement of the interfacial tension, carried out by the “pendant drop” method in “dynamic” mode, made it possible to characterize these amphiphilic molecules according to the value of their elastic modulus, ?, as well as their relaxation time, τ_R.

The analysis of these parameters, as well as those developed in the previous publication [L. Blasco et al. (2006) Skin constituents as cosmetic ingredients. Part I: A Study of bio‐mimetic monoglyceride behavior at the squalene‐water interface by the “pendant drop” method in a static mode. J. Dispers. Sci. Technol., 27(6).] shows that the hydrocarbon chain structure, such as its length, the presence of one or more unsaturations, hydroxyl function, affects the behavior of surfactant molecules at the squalene/water interface.     

Elastic,dielectric and optical constants of the nematic mixture E49

The Merck nematic mixture E49 exhibits a large nematic interval (0–100 °C) and a large dielectric anisotropy. Both of these features make E49 interesting for applications and basic physics. Unfortunately, no systematic measurements of the material constants of this mixture and their temperature dependence have been reported in the literature. In this paper we report experimental measurements of the splay and bend elastic constants (K ₁₁ and K ₃₃) of the ordinary and the extraordinary refractive indices (n _ort and n _par) at the wavelength λ?=?632.8 nm and of the two elastic constants parallel and orthogonal to the director (ε_par and ε_ort) at the frequency ν?=?5?kHz. The temperature dependence of all of these parameters is found in the temperature range 25–99 °C. The measurements of the elastic constants are performed using both a dielectric and an optical method simultaneously on the same nematic sample. The results obtained using the two methods are in a satisfactory agreement between them within the estimated experimental uncertainty. The ordinary and the extraordinary indices are measured using the prism method.     

Highly elastic cobweb-like SiO/CNF composites with reconstructed heterostructure for high-efficient lithium storage

The silicon-based materials are promising candidates for lithium-ion batteries owing to their high energy density. However, achieving long lifespan under realistic conditions remains a challenge because of the volume expansion and low conductivity. In this work, the highly elastic cobweb-like composite materials consisted by SiO and nanofibers are designed and fabricated for high-efficient lithium storage by ball-milling & electrostatic spinning method. The reconstructed heterostructure and highly elastic nanofibers can simultaneously increase the conductivity and inhibit the “expansion effect” of silicon-based materials. The constructed electrode of n-SiO/CNF delivers an initial capacity of 1700 mAh/g, and maintains the capacities over 1000 mAh/g after 100 cycles at the current density of 500 mA/g. Meanwhile, this electrode can give an initial coulombic efficiency over 85% and maintains at 98% in the following charge/discharge processes. Furthermore, it exhibits efficient long-term electrochemical performance, maintaining the capacity at about 1000 mAh/g at a high current density of 1000 mA/g after 1000 cycles. This work could provide a promising strategy for enhancing the performance of silicon-based composite materials for practical application in lithium-ion batteries.     

氮化铂在高压下的相变及弹性性质的第一原理计算

用PBE形式下的广义梯度近似（GGA）赝势平面波方法研究了氮化铂的结构相变以及弹性性质,计算了氮化铂的氯化钠（B1）、氯化铯（B2）、闪锌矿（B3）、纤维矿（B4）等四种结构并应用高压下的焓与压强的关系,得出在常温常压下B4结构是最稳定的结构,这与Yu 等人得的结果一致,且 B4→B1及B1→B2的相变压强分别发生在36.7 GPa和 185.4 GPa,同时,研究了B4结构在高压的弹性性质,发现弹性常数、体模量、剪切模量、压缩波速、剪切波速以及德拜温度均随着压强的增大而单调增大     

Light-Driven Crawling of Molecular Crystals by Phase-Dependent Transient Elastic Lattice Deformation

The light-driven crawling of a molecular crystal that can form three phases, (α, β, and γ) is presented. Laser irradiation of the molecular crystal can generate phase-dependent transient elastic lattice deformation. The resulting elastic lattice deformation that follows scanning irradiation of a laser can actuate the different phases of molecular crystal to move with different velocity and direction. Because the γ phase has a large Young's modulus (ca. 26 GPa), a force of 0.1 μN can be generated under one laser spot. The generated force is sufficient to actuate the γ-formed molecular crystals in a wide dimensional range to move longitudinally at a velocity of about 60 μm min⁻¹, which is two orders of magnitude faster than the α and β phases.     

Anisotropic Poisson Effect and Deformation-Induced Fluorescence Change of Elastic 9,10-Dibromoanthracene Single Crystals

Elastic organic crystals have attracted considerable attention as next-generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10-dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior. We clearly observed a Poisson effect for the crystal, where the short axes (b and c-axes) of the crystal are contracted upon elongation along the long axis (a-axis). Moreover, we found that the Poisson's ratios along the b-axis and c-axis are largely different. Theoretical molecular simulation suggests that the tilting motion of the anthracene may be responsible for the large deformation along the c-axis. Spatially resolved photoluminescence (PL) measurement of the bent elastic crystals reveals that the PL spectra at the outer (elongated), central (neutral), and inner (contracted) sides are different from each other.     

Anisotropic Poisson Effect and Deformation‐Induced Fluorescence Change of Elastic 9,10‐Dibromoanthracene Single Crystals

Elastic organic crystals have attracted considerable attention as next‐generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10‐dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior. We clearly observed a Poisson effect for the crystal, where the short axes (b and c‐axes) of the crystal are contracted upon elongation along the long axis (a‐axis). Moreover, we found that the Poisson's ratios along the b‐axis and c‐axis are largely different. Theoretical molecular simulation suggests that the tilting motion of the anthracene may be responsible for the large deformation along the c‐axis. Spatially resolved photoluminescence (PL) measurement of the bent elastic crystals reveals that the PL spectra at the outer (elongated), central (neutral), and inner (contracted) sides are different from each other.     

Study on wave dispersion characteristics of piezoelectric sandwich nanoplates considering surface effects

In this study, the wave propagation properties of piezoelectric sandwich nanoplates deposited on an orthotropic viscoelastic foundation are analyzed by considering the surface effects (SEs). The nanoplates are composed of a composite layer reinforced by graphene and two piezoelectric surface layers. Utilizing the modified Halpin-Tsai model, the material parameters of composite layers are obtained. The displacement field is determined by the sinusoidal shear deformation theory (SSDT). The Euler-Lagrange equation is derived by employing Hamilton’s principle and the constitutive equations of piezoelectric layers considering the SEs. Subsequently, the nonlocal strain gradient theory (NSGT) is used to obtain the equations of motion. Next, the effects of scale parameters, graphene distribution, orthotropic viscoelastic foundation, and SEs on the propagation behavior are numerically examined. The results reveal that the wave frequency is a periodic function of the orthotropic angle. Furthermore, the wave frequency increases with the increase in the SEs.

     

时滞效应对弹性地基上梁主共振响应影响分析

本文研究了弹性地基上梁主共振响应的时滞效应．基于Hamilton原理,建立了时滞影响下弹性地基上梁的非线性运动微分方程,采用多尺度法,求得了时滞效应下主共振响应调制方程以及稳定性条件．通过数值算例,分析了时滞和调谐参数影响下主共振响应的峰值及幅频响应特性．结果表明,地基反力中的时滞效应对主共振响应影响较大,会导致共振域偏移,在一定区间内,响应幅值随时滞变化先减小再增大,呈现出周期性,并导致幅频曲线弯曲程度增大．