Enhanced surface free energy of polyimide fibers by alkali treatment and its interfacial adhesion behavior to epoxy resins

In this article, polyimide (PI) fibers were modified by alkali treatment, and PI fiber-reinforced epoxy composites were fabricated. The effects of different alkali treatment times on the surface properties of the PI fibers and the adhesion behaviors of PI fiber/epoxy composites were studied. The surface morphologies, chemical compositions, mechanical properties, and surface free energy of the PI fibers were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, single-fiber tensile strength analysis, and dynamic contact angle analysis, respectively. The results show that alkali treatment plays an important role in the improvement of the surface free energy and the wettability of PI fibers. We also found that, after the 3 min, 30 °C, 20 wt% NaOH solution treatment, the fibers possessed good mechanical properties and surface activities, and the interlaminar shear strength of the composites increased to 64.52 MPa, indicating good interfacial adhesion properties.     

几种微构件材料的表面能及纳观黏附行为研究

对微机电系统（MEMS）中几种常用构件材料的表面能及其主要影响因素进行了探讨,并与材料表面的纳观黏附性能进行了分析比较.用Owens二液法计算出硅基材料的表面能在60—75 mJ/m²之间,它们之间总表面能的差异主要归结为表面能极性分量的差异,表面粗糙度的存在使表观表面能有所偏高.施加自组装分子膜后的表面能大为降低,粗糙度的存在可以使其表面能进一步减小.纳观黏附力和表面能之间有一定的对应关系.另外,在研究中发现表面粗糙度对纳观黏附行为的影响较小. 关键词： MEMS 表面能 纳观黏附 粗糙度     

Effect of surface treatment on sand erosion behavior of glass beads-filled epoxy resin

Effects of the adhesion between filler particle and matrix on the erosion rate were studied in cured epoxy resin filled with glass beads having mean diameter 17 um. In order to observe the effect of adhesion on erosion rate. the filler particles were treated with silane coupling agent, silicone oil and washed by acetone as well. The filler content of the specimen was varied and also the specimens were attacked by different size angular particles. The comparison of each type of specimen shows that by using acetone and silicone oil for surface treatment, the erosion rate is relatively high. Whereas the specimen in which the filler was treated by silane have low erosion rate. The difference of erosion behavior is influenced by impacting particle size and filler content. Using small impacting particles and also low filler content, the erosion behavior between silane and acetone treated was quite different. On the other hand, using large impacting particles and high filler content, the erosion behavior between them was similar.     

Pt(110)表面自吸附原子能量和力的改进分析型嵌入原子法分析

采用改进分析型嵌入原子法计算了Pt(110)表面自吸附原子的能量和法向力.当Pt吸附原子位于Pt(110)表面第一层原子的二重对称洞位上0.11nm时最稳定.Pt吸附原子的最佳迁移路径是由一个二重对称洞位沿密排方向迁移到最近邻的另一个二重对称洞位.在吸附原子远离表面的过程中，将依次经过排斥、过渡和吸引等三个区域.在排斥区和过渡区，由于吸附原子与表面原子间强的相互作用势，吸附原子的能量和法向力的形貌图均为(110)面原子排列的复形，与对势理论和嵌入原子法得到的结果一致.在吸引区，由于多体相互作用及晶体中原子 关键词： 金属表面 自吸附 能量 力     

环氧树脂的等离子体表面梯度刻蚀及沿面闪络性能研究

结合等离子体表面刻蚀方法与梯度改性方法,实现了氧化铝/环氧树脂表面的等离子体梯度刻蚀。利用扫描电子显微镜(SEM)、表面轮廓仪、X射线光电子能谱分析(XPS)、高阻计、闪络电压和表面电位测试系统,对比了未处理、等离子体均匀刻蚀、等离子体梯度刻蚀三种情况的样片表面形貌、化学元素和电气参数,研究了等离子体梯度刻蚀对沿面闪络性能的提升机理。结果表明,等离子体表面刻蚀可提升环氧树脂表面粗糙度、提高样片表面电导率、浅化陷阱能级以及提升沿面闪络电压。等离子体梯度刻蚀对闪络电压的提升效果要优于等离子体均匀刻蚀,相比于未处理样片最大可提升26.5%。分析认为针-针电极的电场分布可划分为三结合点处附近的高场强区和电极之间的低场强区,加快高场强区的表面电荷消散速率并适当控制低场强区表面电荷迁移速率,可以最大程度地提升样片整体的沿面闪络性能。     

人为扰动的模型势函数及其动力学特征

目前,结合高精度从头算方法和全维量子动力学计算,对四原子气相反应,理论计算可以获得与实验结果完全一致的结果。一般情况下,一个精确的量子动力学模拟需要一个精确的势能面,但是在实际的计算当中,势能面的拟合误差是不可避免的。在本文中,我们考察了在模型势能面外加各种扰动时的动力学反应行为,在2维的势能面上进行了量子动力学计算。反应速率常数对近反应能垒区域或最小能量反应路径上的干预是较为敏感的,但是在势能面上的其它地方加入的外加干扰对反应速率影响不大。本文给出一个比较重要的和比较简单的结论,在量子动力学模拟中,在精确的势能面上增加相关的扰动,会帮助我们更深入地理解给定类型的反应,对于一个特定体系,其精确势能面上可以作为一个模型体系研究。     

The mechanics and thermodynamics of edge fracture: the critical energy release rate,the compatibility constraint,and the bond potential

Following Gurtin and many others, the critical energy release rate is commonly identified as an ill-defined surface energy. The primary objectives of this paper are to clarify the definition of this surface energy and the role of the entropy inequality in the discussion of critical conditions. In view of an increasing emphasis on ab initio computations, a secondary objective is to show how the critical energy release rate and the compatibility constraint 1 Si, X, Oh, ES and Slattery, JC. 2010. Phil. Mag., 90: 655[Taylor & Francis Online] , [Google Scholar] can be used to solve a problem for which we have experimental data, using only ab initio estimates of surface tension and bond potential, both of which are increasingly available.     

形状和原子数对纳米晶表面能的影响

确定了德拜温度与原子相互作用势的相互关系以及直角形纳米晶原子的平均配位数与形状和 原子数的关系.应用统计物理理论得到直角形纳米晶的表面能随温度、原子数和形状的变化 规律.以Ar纳米晶为例，讨论了形状和原子数对纳米晶表面能的影响. 关键词： 纳米晶 表面能 形状和线度     

Effect of ending surface on energy and Young's modulus of single-walled carbon nanotubes studied using linear scaling quantum mechanical method

By using a linear scaling self-consistent charge, density functional tight-binding (SCC-DFTB) method and an ab intio Dmol3 calculation, the energy and Young's modulus as a function of tube length for (10, 0) single-walled carbon nanotubes (SWCNTs) are investigated. It was found that with increasing the length of SWCNTs the Young's modulus increases rapidly, then, there is a slow increase, which ultimately approaches a constant value after the length is increased to ~20 nm, whereas a reversed variation tendency was found for the average energy of atoms in SWCNTs with a change of the tube length. We found that the characters of the length-dependent energy and Young's modulus stem from the changed P_y-DOS of atoms in the ending region of the tube. Here one simple formula is proposed for quantitatively explaining the length-dependent energy and modulus.     

Study of surface cell Madelung constant and surface free energy of nanosized crystal grain

Surface cell Madelung constant is firstly defined for calculating the surface free energy of nanosized crystal grains, which explains the physical performance of small crystals and may be greatly beneficial to the analysis of surface states and the study of the dynamics of crystal nucleation and growth. A new approximative expression of the surface energy and relevant thermodynamic data are used in this calculation. New formula and computing method for calculating the Madelung constant α of any complex crystals are proposed, and the surface free energies and surface electrostatic energies of nanosized crystal grains and the Madelung constant of some complex crystals are theoretically calculated in this paper. The surface free energy of nanosized-crystal-grain TiO₂ and the surface electrostatic energy(absolute value) of nanosized-crystal-grain α -Al₂O₃ are found to be the biggest among all the crystal grains including those of other species.     

S2O分子高激发振动光谱及势能面的代数研究

本文利用代数方法研究了非对称弯曲三原子分子S2O分子处于C～1A′电子态的能谱及其稳定构型下的势能面,通过对30条光谱数据的拟和得到的RMS误差为2.40 cm-1.结果表明,利用此代数Hamiltonian很好的实现了能级再现,它预测了振动总量子数达到20的全部振动能级(在本文中我们只列举到v= 9),同时我们计算了分子的解离能与力常数.通过与实验值比较证明了这种方法在计算这类分子的有效性.     

Kinetic energy release of diatomic and linear triatomic molecules in intense femtosecond laser fields

The kinetic energy release of fragment ions produced by the interaction of femtosecond laser pulse radiation with diatomic and linear triatomic molecules N_2, CO, CO_2 and CS_2 is investigated. In the case of linear polarization, angles at which the kinetic energy release of ions has the maximum value are different from the alignment of molecules though the kinetic energy release of fragment atomic ions depends on the angle between the laser polarization vector and the detection axis of the time-of-flight. For the diatomic molecules, the critical internuclear distance in multielectron dissociative ionization with a circularly polarized light is larger than that with a linearly polarized light. For linear triatomic molecules, our data indicate that a concerted Coulomb explosion process is a universal phenomenon in the interaction of molecules with intense laser fields, even in the circularly polarized regime. During two C－O (or C－S) bonds breaking simultaneously, the C ion obtained larger energy in circular polarization than that in the linear polarization. Different variations of kinetic energy release between the diatomic and the linear triatomic molecules are discussed.     

表面活性剂对气-液界面纳米颗粒吸附规律的影响

通过测定及分析纳米颗粒和表面活性剂-纳米颗粒复配体系在自由吸附过程与动态收缩过程中表面张力的变化,总结了纳米颗粒在气-液界面的吸附排布规律以及表面活性剂对其吸附规律的影响.实验结果表明,自由吸附过程中,随矿化度增加、阳离子活性剂浓度增加,平衡表面张力降低,这与颗粒吸附密度增加及颗粒润湿性改变有关.浓度低于临界胶束浓度(CMC)时,阳离子活性剂体系与混合体系的表面张力差异证明了阳离子活性剂可以通过静电作用吸附于纳米颗粒表面,进而部分溶解于水相;而阴离子活性剂与纳米颗粒相互作用力较弱,对表面张力影响较小.纳米颗粒体系在液滴收缩过程中,表面张力从自由吸附平衡态进一步降低大约9 m N/m,说明自由吸附过程中纳米颗粒不能达到紧密排布;同时表面张力呈现为缓慢降低、快速降低和达到平衡三部分,表面压缩模量可达70 m N/m,满足了液膜Gibbs稳定准则,这将有助于提高泡沫或者乳液稳定性.纳米颗粒-表面活性剂体系在液滴收缩过程中表面张力降低值随活性剂浓度增加而减小;表面压缩模量由高到低依次为:纳米颗粒>阳离子活性剂-纳米颗粒>阴离子-纳米颗粒>表面活性剂.     

Investigation of magnetic field effect on surface and finite-site free energy in one-dimensional Ising model of nanosystems

We investigate a one-dimensional (1-D) Ising model for finite-site systems. The finite-site free energy and the surface free energy are calculated via the transfer matrix method. We show that, at high magnetic fields, the surface free energy has an asymptotic limit. The absolute surface energy increases when the value of f (the ratio of magnetic field to nearest-neighbor interactions) increases, and for f?≥?10 approaches a constant value. For the values of f?≥?0.2, the finite-site free energy also increases, but slowly. The thermodynamic limit in which physical properties approach the bulk value is also explored.     

B2-和B19'-NiTi表面原子弛豫、表面能、电子结构及性能的理论研究

采用基于密度泛函理论的第一性原理系统研究了B2-和B19'-NiTi合金所有低指数表面的表面能、表面结构稳定性、表面电子结构等性质.计算结果表明两种NiTi合金所有低指数表面的原子弛豫主要集中在表面2-3个原子层,且以Ti原子为终止原子表面构型的原子振荡最为剧烈,Ni和Ti原子共同终止表面构型的原子振荡最小;价电荷密度沿着表面构型向真空层方向快速衰减;表面能计算结果显示其与配位数成反相关.B2-和B19'-NiTi合金的非密排且非化学计量比表面的表面能取决于Ti的化学势,表面能数值较高;而密排面的表面构型符合化学计量比,其表面能较低,表现出卓越的化学稳定性;其中以B2-NiTi(101)密排面的表面稳定性最优.     

The influence of repellent coatings on surface free energy of glass plate and cotton fabric

The aim of this research was to determine the influence of chemical finishes on the surface properties of glass plate, considered as a model homogeneous smooth surface and cotton fabric as a non-ideal heterogeneous rough surface. Microscopic slides and 100% cotton fabric in plain weave were coated with fluorocarbon polymers (FCP), paraffin waxes with zirconium salts (PWZ), methylolmelamine derivatives (MMD), polysiloxanes with side alkyldimethylammonium groups (PSAAC) and aminofunctional polysiloxanes (AFPS). From the goniometer contact angle measurements of different liquids, the surface free energy of the coated glass plates was calculated according to approaches by Owens-Wendt-Kaelble, Wu, van Oss-Chaudhury-Good, and Li-Neumann-Kwok. The results showed that all the coatings decreased the surface free energy of the substrate, which was also influenced by the liquid combination and the theoretical approach used. In spite of the fact that the liquid contact angles were much higher on the coated fabric samples than on glass plates and resulted in the lower values of work of adhesion, a very good correlation between the coatings deposited on both substrates was obtained. The presence of repellent coatings FCP, PWZ and MMD converted the solid surface from polar to highly apolar by masking the functional groups of glass and cellulose. PSAAC and AFPS coatings did not decrease the solid surface free energy to such an extent as the former three coatings due to their monopolar character.     

Effect of the surface free energy on the behaviour of surface and guided waves

The aim of this paper is to evaluate the influence of the surface free energy upon the propagation of the eigenmodes of structures, by studying successively (a) the Rayleigh wave for an elastic half-space, (b) the Lamb waves for an elastic layer, and (c) the guided modes for a tri-layer structure (e.g., metal/adhesive/metal). The surface free energy is a parameter which appears in the jump conditions of stresses and displacements at each interface, and which consequently modifies the eigenmodes, solutions of the boundary conditions system. As expected, the Rayleigh wave is dispersive and its velocity increases when the surface free energy increases. In the same way, the velocity of Lamb waves also increases except at normal angle of propagation where the surface free energy does not arise. Moreover, near the Rayleigh angle, the behaviour of the A₀ and S₀ Lamb modes varies strongly according to the surface free energy. Similar results are observed for the tri-layer structure.     

Kr-CS体系势能面及束缚态能级的理论研究

本文利用从头算方法首次计算得到Kr原子与CS分子在“冻结核”近似下的相互作用离散势能点, 并拟合得到二维势能面. 该体系在R=7.76 a0, =111.4o处存在一个近T型的全域极小值, 势能值为-178.54 cm-1, 整个势能面表现较强的各向异性. 在该势能面基础上数值求解体系的薛定谔方程, 计算得到体系J ≤ 15的束缚态能级及微波谱跃迁频率.     

表面钝化效应对GaAs纳米线电子结构性质影响的第一性原理研究

纳米线表面存在大量的表面态,它们能够引起电子分布在纳米线表面,使得纳米线的电学性质对表面条件变得更加敏感,严重地制约器件的性能.表面钝化能够有效地移除纳米线的表面态,进而能够有效地优化器件的性能.采用基于密度泛函理论的第一性原理计算方法研究了表面钝化效应对GaAs纳米线电子结构性质的影响.考虑了不同的钝化材料,包括氢元素、氟元素、氯元素和溴元素.研究结果表明:具有小尺寸的GaAs裸纳米线的能带结构呈间接带隙特征,表面经过完全钝化后,转变为直接带隙特征;GaAs纳米线表面经过氢元素不同位置和不同比例钝化后,展示出不同的电学性质;表面钝化的物理机理是钝化原子与纳米线表面原子通过电荷补偿移除纳米线表面的电子态;与氢元素钝化相比,GaAs纳米线表面经过氟元素、氯元素和溴元素钝化后,带隙宽度较小,原因是氟元素、氯元素和溴元素在钝化过程中具有较小的电荷补偿能力,不能完全移除表面态.