Modeling the effect of interfacial conductivity between polymer matrix and carbon nanotubes on the electrical conductivity of nanocomposites

This article presents the role of interfacial conductivity between the polymer matrix and nanoparticles in the electrical conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNT) by simple equations. In this methodology, CNT size, CNT conductivity, CNT waviness and interfacial conductivity express the effective length and effective concentration of CNT in PCNT. Additionally, the percolation threshold and the percentages of CNT in the conductive networks are defined by the above mentioned terms. Finally, a simple model is developed to suggest the electrical conductivity of PCNT by CNT dimensions, CNT conductivity, CNT waviness, interphase thickness, interfacial conductivity and tunneling distance. The developed model is applied to show the roles of all parameters in the conductivity. Also, the experimental levels of percolation threshold and conductivity for several samples are compared to the predictions to validate the developed equations. The interfacial conductivity directly controls the electrical conductivity of nanocomposites. In addition, thick interphase, low waviness and short tunneling distance increase the conductivity. Moreover, the predictions show good agreement with the experimental measurements, providing evidence in support of the developed equations.

This article presents the role of interfacial conductivity between the polymer matrix and nanoparticles in the electrical conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNT) by simple equations.     

Study on the interfacial properties of polymers around a nanoparticle

The interfacial properties of polymer chains on spherical nanoparticles are investigated using off-lattice Monte Carlo simulations. Results show that the number of adsorbed monomers increases whereas the number of adsorbed polymers decreases with increasing the polymer–nanoparticle interaction strength. The interfacial layer thickness is independent of the nanoparticle size and chain length. The interfacial monomers exhibit layering behaviors with three distinct layers. The mobility of monomers in the innermost layer is strongly dependent on the polymer–nanoparticle interaction strength. The interfacial monomers always keep moving, and no glassy layer is present around the nanoparticle. Finally, our results show that the motion of nanoparticle can weaken the adsorption of polymers but does not change the conformational property of adsorbed polymers.

The interfacial properties of polymer chains on spherical nanoparticles are investigated using off-lattice Monte Carlo simulations.     

Interaction between electrical stimulation,protein coating and matrix elasticity: a complex effect on muscle fibre maturation

In skeletal muscle tissue engineering, it remains a challenge to produce mature, functional muscle tissue. Mimicking the in vivo niche in in vitro culture might overcome this problem. Niche components include, for example, extracellular matrix proteins, neighbouring cells, growth factors and physical factors such as the elasticity of the matrix. Previously, we showed the effects of matrix stiffness and protein coating on proliferation and differentiation of muscle progenitor cells in a two‐dimensional (2D) situation. In the present study we have investigated the additional effect of electrical stimulation. More precisely, we investigated the effect of electrical stimulation on primary myoblast maturation when cultured on top of Matrigel^?‐ or laminin‐coated substrates with varying elasticities. The effect of electrical stimulation on differentiation and maturation was found to be dependent on coating and stiffness. Although electrical stimulation enhanced myoblast maturation, the effect was mild. We therefore conclude that, with the current regimen, electrical stimulation is not essential to create functional, mature muscle tissue. Copyright © 2010 John Wiley & Sons, Ltd.     

Water wettability of graphene: interplay between the interfacial water structure and the electronic structure

Wetting phenomena are ubiquitous and impact a wide range of applications. Simulations so far have largely relied on classical potentials. Here, we report the development of an approach that combines density-functional theory (DFT)-based calculations with classical wetting theory that allows practical but sufficiently accurate determination of the water contact angle (WCA). As a benchmark, we apply the approach to the graphene and graphite surfaces that recently received considerable attention. The results agree with and elucidate the experimental data. For metal-supported graphene where electronic interactions play a major role, we demonstrate that doping of graphene by the metal substrate significantly alters the wettability. In addition to theory, we report new experimental measurements of the WCA and the force of adhesion that corroborate the theoretical results. We demonstrate a correlation between the force of adhesion and WCA, and the use of the atomic force microscope (AFM) technique as an alternative measure for wettability at the nanoscale. The present work not only provides a detailed understanding of the wettability of graphene, including the role of electrons, but also sets the stage for studying the wettability alteration mechanism when sufficiently accurate force fields may not be available.

Wettability of graphene is characterized from first principles.

Wetting phenomena are ubiquitous in a variety of practical issues, including adhesion,¹ friction,² interfacial thermal conductance (Kapitza conductance),^3,4 to name just a few. Graphene has emerged as an important material for applications where water wettability plays a major role, e.g., as a lubricant,⁵ small-molecule gas sensor,^6,7 desalination membrane,^8,9 protective coating from electrochemical degradation,¹⁰ promotive coating for dropwise condensation,¹¹etc. Among these applications, to wet or not to wet is the key problem.^12,13 More recently, doping-induced tunable wettability was reported for graphene.^14,15Interactions between the wetting liquid and the solid it rests on are responsible for the wetting properties of a surface. The binding energy of individual molecules on the solid surface, obtained by quantum-mechanical calculations, has at times been used as an indicator of wettability.^14,16 A better indicator, however, is the water contact angle (WCA), an experimentally easily accessible parameter that characterizes macroscopically a surface''s wettability by water.^17,18 Large WCA, >90°, signifies hydrophobic behavior, whereas small WCA, <90°, signifies hydrophilic behavior. The past few years have witnessed increasing efforts to understand the wetting mechanism of graphitic carbon surfaces. Theoretical calculations of WCAs of graphitic carbon surfaces have so far been done primarily using classical potentials, by constructing an analytical interaction potential between water and the solid surface based on interatomic Lennard-Jones potentials^19–21 or classical molecular dynamics (CMD) simulations.^19,22–29 In those pioneering studies with the work-of-adhesion approach, one first computes the work of adhesion of a water slab on a surface and then employs the Young-Dupré equation that relates the work of adhesion to the WCA.^19,25–28 Alternatively, CMD can be sued to measures the shape of a water droplet on a surface and extract the WCA.^22–24Though these approaches have provided significant insights into wetting behavior,^19,22–28 they depend on the availability of reliable classical potentials. The construction of such potentials becomes a difficult task when many atomic species are present. For example, the interplay between ions such as Ca²⁺, Mg²⁺, SO₄²⁻, Na⁺ and Cl⁻ in saline water and calcite (CaCO₃) surfaces is responsible for the wettability alteration for oil recovery.^30,31 There are also cases, e.g., monolayers on metallic substrates, where explicit electron doping effects may play a major role, requiring electronic-structure calculations. While density functional theory (DFT) is the method of choice for predictive, atomic-scale calculations of interactions at the solid–water interface, the major difficulty lies in the limited time and length scales achievable by quantum MD (QMD) simulations.³² So far there exists only one report of QMD simulations of water nanodroplets, on graphene and hexagonal boron nitride monolayers.³³In this paper, we adopt the method based on the work of adhesion and the Young-Dupré equation, and employ an approximation that allows practical but sufficiently accurate DFT-based determination of the WCA. Benchmark calculations confirm that graphitic carbon surfaces are nonpolar and intrinsically hydrophilic, with their wettability determined by the dispersive interaction. The WCA gradually decreases with increasing number of graphene layers N, while a monolayer of adsorbed hydrocarbons is sufficient to render graphene hydrophobic, complementing similar results obtained using classical potentials.^20,21,25,34 In the presence of a metal substrate, electronic structure comes into play and electron doping of the graphene sheet by the metal substrate alters the wettability of graphene. We report new WCA and AFM (atomic force microscopy) measurements for Cu-supported monolayer and multilayer graphene that further corroborate the theoretical results. Finally, we demonstrate a correlation between the force of adhesion and WCA, and the use of the AFM technique as an alternative measure for wettability at the nanoscopic scale.     

Effect of surface wettability on the interfacial adhesion of a thermosetting elastomer on glass

Interfacial adhesion dictates properties and performance of both composites and adhesively bonded structures. Weak adhesion at the interfaces of polymer composites leads to void formation and debonding, which adversely affect composite structural integrity and mechanical performance. This work investigated the relationship between surface wettability and interfacial fracture energy with the goal of tailoring interfacial adhesion within polymer composites. A series of model functionalized surfaces was created using silane coupling agents with different organo-functionalities to alter surface wettability. Based on the analysis of interfacial fracture energy between a thermosetting elastomeric polymer network and model surfaces, interfacial adhesion was found to be positively correlated to resin wettability. The results provide a fast and simple approach to screen different material combinations for the development of novel polymeric composites and adhesively bonded structures with tailorable adhesion.

Interfacial adhesion is postively correlated with resin wettability.     

牛脱细胞骨基质的生物力学特性及其黏附性

背景:脱细胞骨基质作为一种天然骨生物衍生材料,应用于骨组织工程支架有着其独特的优越性。目的:观察牛松质骨脱细胞后骨基质的生物力学特性、孔隙率及其黏附特性,探讨其作为组织工程骨天然支架材料的可行性。设计、时间及地点:力学实验采用随机对照观察,于2008-02/06在天津医科大学总医院骨科实验室完成。材料:新鲜牛股骨来自16月龄雄性蒙古牛,体质量350kg;新生24h内SD大鼠3只。方法:利用100g/LNaCl联合1%TritonX-100的方法制备脱细胞骨基质。脱细胞骨基质脱钙切片。利用ElectroForce3200力学试验仪对标本进行压力加载测试。利用新生SD大鼠颅骨传代培养第3代成骨细胞与脱细胞骨基质复合培养12h。空白对照组置于9g/LNaCl溶液。主要观察指标:①苏木精-伊红染色观察骨基质平均空隙直径及空隙率。②观察骨基质弹性强度、破坏载荷、弹性模量。③采用细胞计数法计算两者的黏附率。结果:①利用100g/LNaCl与1%TritonX-100联合可达到良好脱细胞效果,与对照组比较,脱细胞后实验组骨小梁无明显破坏。②所测得牛脱细胞骨细胞外基质空隙直径为(376.33±80.91)μm,空隙率为(70.15±2.98)%。③力学测试此脱细胞方法对骨基质力学特性无显著影响。④脱细胞骨基质与体外培养成骨细胞具有良好的黏附性能,黏附率为62.38%。结论:牛松质骨脱细胞骨基质较完整的去除了细胞的免疫原性,具有良好的骨组织工程支架材料力学性质,接近生理结构的空隙直径及孔隙率,黏附性能满足支架材料的要求。     

The effect of variations in fibre length on the impact strength of poly(methyl methacrylate) resin reinforced with ultra-high-modulus polyethylene fibre

A previous study demonstrated that the impact strength of poly(methyl methacrylate) resin can be improved by including randomly distributed 6-mm lengths of ultra-high-modulus polyethylene (UHMPE) fibre. In this study the effect of varying the fibre length on impact strength, fibre distribution and manipulative properties of the resin were investigated. A scanning electron microscopic examination of fibres at the fracture surface was also carried out. It was found that a 1% by weight loading of 3-mm, 6-mm and 12-mm fibre significantly improved impact strength when compared to control resin, the 3-mm and 6-mm groups performing significantly better than the 12-mm group. The 3-mm and 6-mm fibres afforded the optimum manipulative properties in the mixing and processing of the resin. Scanning electron microscopy revealed evidence of fibre pull-out.     

脱钙骨基质材料的生物学表现：降解性能、孔隙率及其黏附性能特征

目的：体外观察脱钙骨基质的降解性能及孔隙率,同时采用兔骨髓间充质干细胞与脱钙骨基质在体外复合培养,了解兔骨髓间充质干细胞对这种天然材料的黏附能力. 方法：实验于2005-01-08/03-15在兰州大学骨科研究所进行.取6月龄的青紫蓝兔1只,麻醉后处死,取四肢骨干骺端及椎体松质骨,采用Urist提供的方法制作脱钙骨基质,将脱钙骨基质置于磷酸盐缓冲溶液中12周测定其降解率;用液体置换法测其孔隙率;用细胞计量法测定生长良好的浓度为1×10^8L^-1的第3代骨髓间充质干细胞与脱钙骨基质复合培养6 h后的黏附率. 结果：脱钙骨基质的降解随时间的延长逐渐加速,8周前,其降解速率较慢,8周后,其降解速度明显加快,完全降解需要10～12周,与骨髓间充质干细胞的增殖规律近似;所测脱钙骨基质孔隙率为（77.15±3.44）%;1×10^8L^-1的第3代骨髓间充质干细胞与脱钙骨基质的平均黏附率为71.25%. 结论：脱钙骨基质的降解曲线与骨髓间充质干细胞的增殖曲线相一致,具备良好的孔隙率和黏附率,提示脱钙骨基质可能为软骨组织工程比较理想的生物支架材料.     

宫腔粘连与刮宫操作相关性研究

目的探讨刮宫操作与宫腔粘连及严重程度的相关性。方法回顾性分析重庆市第五人民医院近5年收治的96例宫腔镜下诊断为宫腔粘连的患者。结果月经量减少28例(29.1%)、闭经26例(27.1%)和不孕31例(32.3%),此3项是宫腔粘连就诊的主要原因,余下11例因习惯性流产、腹痛等原因就诊。患者均有宫腔操作史,在这些引起宫腔粘连的操作中,稽留流产清宫占47.9%(46/96),人工流产清宫占34.3%(33/96),顺产后清宫占12.5%(12/96),其余5例有宫内节育器置入或取出史。发生中、重度粘连与产后清宫有关,其差异有统计学意义(P0.05),与清宫次数无关,差异无统计学意义(P0.05)。结论各种刮宫操作可引起宫腔粘连,产后清宫易导致中、重度宫腔粘连,刮宫次数与粘连程度无明显相关性。     

Characterizing the bifurcating configuration of hydrogen bonding network in interfacial liquid water and its adhesion on solid surfaces

The interfacial structures of liquid water molecules adjacent to a solid surface contribute significantly to the interfacial properties of aqueous solutions, and are of prime importance in a wide spectrum of applications. In this work, we use molecular dynamics (MD) simulations to explore the interfacial structures, mainly in term of hydrogen bonding network, of a liquid water film interacting intimately with solid surfaces, which are composed of [100] face centered cubic (FCC) lattices. We disclose the formation of a bifurcating configuration of hydrogen bonds in interfacial liquid water and ascribe its occurrence to the collective effects of water density depletion, hydrogen bonds and local polarization. Such bifurcating configuration of interfacial water molecules consists of repetitive layer by layer water sheets with intra-layer hydrogen bonding network being formed in each layer, and inter-layer defects, i.e., hydrogen bonds formed between two neighboring layers of interfacial water. A lower bound of 2.475 for the average number of hydrogen bonds per interfacial water molecule is expected. Our MD study on the interfacial configuration of water on solid surfaces reveals a quadratic dependence of adhesion on the solid–liquid affinity, bridging the gap between the macroscopic interfacial property W_adh and the microscopic parameter ε_SL of the depth of the Lennard-Jones solid–liquid potential.

Bifurcating configuration of hydrogen bonding network in interfacial liquid water influences its adhesion on solid surfaces.     

Investigation on the role of interfacial water on the tribology between graphite and metals

We investigated the role of interfacial water on the atomic-scale tribology of graphite by contact atomic force microscopy. Upon the approach of Au and Pt tips toward graphite in water, the hydration layers on the respective surfaces interact with each other. This results in a discontinuous motion of the metallic tips towards the graphite surface. Snap-in forces measured with Au and Pt tips scale with their respective water adsorption energies. Moreover, we observed significant differences for the atomic-scale friction between the Au and Pt tips and graphite in water. The atomic-scale sliding friction between an Au tip and graphite is characterized by low friction forces (F_f < 1 nN in the range of normal force values F_n = 1–10 nN) and by a periodic stick-slip that corresponds to the honeycomb structure of graphite. With a Pt tip, the sliding friction on graphite in water is characterized by high friction forces (F_f ≈ 5 nN in the range of normal force values F_n = 1–10 nN) and by an atomic-scale stick-slip whose characteristic lengths may correspond to an ordered water adsorption layer between platinum and graphite.

We investigated the role of interfacial water on the atomic-scale tribology of graphite by contact atomic force microscopy.     

A look between the cardiomyocytes: the extracellular matrix in heart failure

The extracellular matrix (ECM) of the heart dynamically interacts with various cellular components of the myocardium, including the myocytes and connective tissue cells. With the development and progression of heart failure, left ventricular (LV) myocardial remodeling occurs. The progression of LV remodeling is accompanied by alterations in the structure and function of the ECM that occur after injury resulting from neurohormonal activation, changes in LV loading conditions, and alterations in myocardial perfusion and metabolism and is secondary to a host of nonmyocyte signaling pathways that affect repair and remodeling of the myocardium as a whole. This article attempts to review some of these processes and their interactions and to provide a focus to the often overlooked contribution of the ECM to the development and progression of heart failure and thereby its potential role as a target for therapy for heart failure.     

Circulating adhesion molecules in the critically ill: A comparison between trauma and sepsis patients

Objective  

The time course of circulating adhesion molecules was monitored in traumatized and sepsis patients.     

Effects of critical interfacial shear strength between a polymer matrix and carbon nanotubes on the interphase strength and Pukanszky's “B” interphase parameter

In this paper, the “B” interphase parameter in the Pukanszky model and interphase strength for polymer carbon nanotube (CNT) nanocomposites are expressed by the critical interfacial shear strength (τ_c) and interfacial shear strength (τ) between a polymer matrix and CNTs. A suggested model and a developed Pukanszky model for tensile strength of nanocomposites are combined to develop the equations for “B” and interphase strength. Many experimental data for various samples confirm the models. The impacts of all parameters on the “B” and interphase strength are explained to approve the developed equations. The contour plots display the same trends for the roles of all parameters in the “B” and interphase strength. Low “τ_c”, high “τ”, thin and large CNTs as well as a dense interphase are ideal to obtain the high levels for “B” and interphase strength. Among the studied parameters, CNT size largely controls the “B” and interphase strength, while the waviness and strength of CNTs play insignificant roles.

In this paper, the “B” interphase parameter in the Pukanszky model and interphase strength for polymer carbon nanotube (CNT) nanocomposites are expressed by the critical interfacial shear strength (τ_c) and interfacial shear strength (τ) between a polymer matrix and CNTs.