Evaluation of optimal dispersion conditions for CNT reinforced epoxy composites using cyclic voltammetry measurements

The optimum dispersion time of nanoparticles is important for obtaining uniform dispersion of fillers or other additives in a matrix. In this study, the optimal dispersion time of carbon nanotube (CNT) in a matrix was investigated using cyclic voltammetry (CV), measurement for different dispersion methods and times. In addition, the mechanical properties of CNT composites manufactured using different dispersion methods were evaluated by tensile and flexural tests. The CV and mechanical test results were correlated to the dispersion condition of CNT in the composites. It was found that tip-type sonication resulted in better dispersion than bath-type sonication. Improved CNT dispersion resulted in composites with both enhanced CV measurements and improved mechanical properties. In the study reported here, improvements in dispersion were generally accompanied by higher electrical currents. This suggests that the CV measurement method is an effective tool for determining optimal dispersion times, for different CNT dispersion processes.     

Dispersion properties of inhomogeneous nanostructures

We analyze the dispersive properties of inhomogeneous nanostructures (INSs) composed of alternating layers of different materials. Analysis of the interaction between the propagating pulse and the INS provides modified dispersion characteristics. An approximate theoretical model predicting the dispersion properties of the INS is developed and compared with more accurate numeric computation results. It is shown that the dispersion coefficient can be engineered by controlling the spatial distribution of the pulse carrier, the geometry of the INS, and the refractive indices of the materials combined to construct the INS. Specifically, the dispersion coefficient can be engineered to yield various types of dispersion, including normal dispersion, anomalous dispersion, and zero dispersion. As such, the discussed INS can be useful for applications that will benefit from engineered dispersion management and control.     

Dispersion of a solute in pulsatile non-Newtonian fluid flow through a tube

The unsteady dispersion of a solute by an imposed pulsatile pressure gradient in a tube is studied by modeling the flowing fluid as a Casson fluid. The generalized dispersion model is applied to study the dispersion process, and according to this process, the entire dispersion process is expressed in terms of two coefficients, the convection and the dispersion coefficients. This model mainly brings out the effects of yield stress and flow pulsatility on the dispersion process. It is observed that the dispersion phenomenon in the pulsatile flow inherently differs from the steady flow, which is due to a change in the plug flow radius during a cycle of oscillation. Also, it was found that the dispersion coefficient fluctuates due to the oscillatory nature of the velocity. It is seen that the dispersion coefficient changes cyclically, and the amplitude and magnitude of the dispersion coefficient increases initially with time and reaches a non-transient state after a certain critical time. It is also seen that this critical time varies with Womersley frequency parameter and Schmidt number and is independent of yield stress and fluctuating pressure component. It is observed that the yield stress and Womersley frequency parameter inhibit the dispersion of a solute. It is also observed that the dispersion coefficient decreased approximately 4 times as the Womersley frequency parameter increases from 0.5 to 1. The study can be used in the understanding of the dispersion process in the cardiovascular system and blood oxygenators.     

聚合物基复合材料制备中碳纳米管的分散方法

综述了碳纳米管／聚合物复合材料制备过程中碳纳米管预先分散所使用的方法。为实现碳纳米管在聚合物中的分散，首先要求加入的碳纳米管本身具备足够的分散度。碳纳米管的分散方法主要有：表面化学修饰、分散剂分散、超声分散、机械分散、溶剂分散。     

离散度参数对规则多边图形认知工效的影响

本研究用实验方法研究离散度参数对规则多边图形认知工效的影响。实验的自变量是图形的离散度参数，因变量是各离散度图形信号的反应时。实验的刺激材料是２５个离散度为０．３～０．７的规则多边图形。刺激材料的呈现与被试的反应记录都由计算机控制。结果表明：离散度适中（０．５左右）及偏小的图形信号认知工效较高，离散度从０．５增大到０．６，认知工效迅速下降，离散度继续增大，认知工效仍有下降，但趋势平缓。     

Measuring Lamb wave dispersion curves of a bi-layered plate and its application on material characterization of coating

This paper investigates the Lamb wave dispersion curves of a bi-layered plate and evaluates the feasibility of using the dispersion data to characterize the coating's material properties. The measurement of dispersion curves is based on a focusing PVDF transducer operating in a pulse/echo mode. An image displaying technique is used to determine the dispersion relation of Lamb waves from the measured data. Multiple dispersion curves of Lamb waves are accurately determined over a wide frequency range (4 to 20 MHz). Lamb wave dispersion curves for thin metal sheets electrodeposited with nickel coatings are measured. The elastic constants of the nickel coating are determined by comparing the experimental dispersion data with the theoretical ones calculated numerically. Potential applications of this measurement method are addressed     

水性塑料凹印油墨分散工艺的研究

改变不同颜料分散技术参数制备水性塑料凹印油墨,考察油墨分散技术对分散效果的影响。结果表明:砂磨机中使用锆珠作为研磨介质,对颜料的研磨分散效果比用玻璃珠效果要好;使用砂磨机研磨分散颜料时,应该使用适当直径大小的研磨介质;研磨时间对颜料分散影响较大,要保证足够的研磨时间;均质机对颜料分散的效果比砂磨机的研磨效果好。     

衍射透镜的色散分析

基于标量衍射理论，本文分析了衍射透镜的色差，首次得出了计算其色散的数学表达式。结果表明，衍射透镜的色散包两个部分：材料色散和波长色散，二者所占的比例随孔径值的不同而变化。     

激波驱动下硝酸异丙酯的分散变化规律研究

研究液滴的分散过程对于阻止火灾蔓延、提高内燃机效率、改进云雾爆轰武器和提高云雾爆轰控制技术有着重要的作用。通过高速摄影技术以及压力测量系统,着重研究液态燃料硝酸异丙酯（IPN）的分散过程,分析液膜厚度和激波强度对IPN液膜分散的影响。IPN液膜初始阶段以水平方向的分散为主;随后,以竖直方向的分散为主。水平方向,液膜抛洒先进入减速阶段,随着液膜厚度H的增加,液膜分散效果变差,分散需要的时间更长,其分散表征与石油醚相似。IPN液膜分散所需能量要高于石油醚。激波强度超过某个值之后,超压比ε随液膜厚度H呈线性变化,可以为液膜分散提供足够的能量。当H＜12 mm时,IPN液膜的分散变化过程主要受激波强度影响;当H＞12 mm时,IPN液膜的分散变化过程主要受液膜厚度影响。     

超声波及分散剂对纳米SiO2/CaCO3/Al2O3颗粒分散特性的影响

在材料科学领域,颗粒的均匀分散是获得具有较好的显微结构和性能材料制品的基础。采用分光光度计法表征分散效果,研究了超声波及不同分散稳定剂复合作用下纳米SiO_2、纳米CaCO_3、纳米Al_2O_3颗粒的分散性能,并结合DLVO理论探讨了分散机理,给出了分散剂优选方案。结果表明,超声波处理纳米颗粒悬浮液可以有效打破纳米颗粒团聚;不同分散剂对不同纳米颗粒的分散效果差异较大,NS颗粒相比NC、NA更难被分散剂分散,分散剂SHMP、SDBS作用效果随用量的增大先增强后减弱,分散剂PCS作用效果随用量的增加而增强;分散剂种类、用量会影响纳米悬浮颗粒的双电层厚度和颗粒周围空间微环境,从而影响分散体系的稳定性。     

硅氧烷改性环氧树脂复合水分散液的分散稳定性和流变性能

通过苯丙类单体与环氧树脂进行接枝聚合反应,制备了大分子链中含有羧基的水性自乳化环氧-苯丙共聚物的复合树脂,然后加入三乙醇胺中和,再进行硅氧烷改性制成硅氧烷改性的环氧树脂复合水分散液。对复合水分散液的分散稳定性和流变性能进行研究,结果表明,随着亲水单体(MAA)含量的增加,水分散稳定性提高,表观黏度增大;中和度降低,表观黏度减小,中和度在90%~110%时,水分散稳定性最好,表观黏度基本不变;在分散液稳定的前提下,硅氧烷含量增大,表观黏度逐渐减小。     

Is bone a Cosserat solid?

In a viscoelastic composite material including bone, acoustic waves undergo both geometric and viscoelastic dispersions as they propagate through the medium. The viscoelastic dispersion is characterized by an increase in phase velocity with increase in frequency, while the geometric dispersion is well-known. By comparing the dispersion data on these and other types of materials, it has been noted that the increases in the ultrasonic velocities for bones are much larger than those for simple viscoelastic solids and composites, suggesting an additional dispersion mechanism. This additional dispersion can be explained by Mindlin's theory on the Cosserat continuum with microstructure.     

Group delay and chromatic dispersion of thin-film-based,narrow bandpass filters used in dense wavelength-division-multiplexed systems

Theoretical analysis is made for thin-film-based, 200- and 100-GHz narrow bandpass filters with respect to the intensity response as well as to the chromatic dispersion. The results indicate that the narrower the passband, the higher the chromatic dispersion. The maximum chromatic dispersion appears at the edges of the 0.5-dB passband, owing to the fast change of the group delay in the region. The deviation of chromatic dispersion induced by manufacturing error is simulated. Effective-medium approximation layers are added to simulate the contribution of surface roughness and the mixture interfaces to the passband ripple as well as the chromatic dispersion. The simulations are compared with the experimental results. The measured chromatic dispersion matches the general trend of the theoretical calculation. The imperfect surface and layer mismatch induce additional ripples across the 0.5-dB passband. The maximum chromatic dispersion within a 0.5-dB passband is 20.7 and 54.9 ps/nm for 200- and 100-GHZ narrow bandpass filters, respectively.     

碳纳米管增强铝基复合材料分散方法研究进展

碳纳米管与铝基体的结合,可以获得导电和导热性良好及综合力学性能优异的复合材料,有望成为新一代轻质高强、结构功能一体化的复合材料.在制备碳纳米管增强铝基复合材料过程中,碳纳米管的团聚将降低界面结合,诱发缺陷产生,导致性能大幅下降,因此,调控优化碳纳米管的分散状态、含量成为获取良好界面结合,获得高性能碳纳米管增强铝基复合材...     

Differential forms of the Kramers-Krönig dispersion relations

Differential forms of the Kramers-Kronig dispersion relations provide an alternative to the integral Kramers-Kronig dispersion relations for comparison with finite-bandwidth experimental data. The differential forms of the Kramers-Kronig relations are developed in the context of tempered distributions. Results are illustrated for media with attenuation obeying an arbitrary frequency power law (/spl alpha/(/spl omega/) = /spl alpha//sub 0/ + /spl alpha//sub 1/ |/spl omega/|/sup y/). Dispersion predictions using the differential dispersion relations are compared to the measured dispersion for a series of specimens (two polymers, an egg yolk, and two liquids) exhibiting attenuation obeying a frequency power law (1.00 /spl les/ y /spl les/ 1.99), with very good agreement found. For this form of ultrasonic attenuation, the differential Kramers-Kronig dispersion prediction is found to be identical to the (integral) Kramers-Kronig dispersion prediction.     

Dispersion of linearly polarized light propagating in a thin birefringent plate

We analyze theoretically the dispersion of linearly polarized light propagating in a uniaxial anisotropic medium where multibeam interference is present. Explicit expressions of the group-delay dispersion for transmitting waves are derived for the simplest situation, and the effect of dispersion on pulse broadening is analyzed for a few selected cases. Our results reveal that at normal incidence and in the situation where the optic axis is parallel to the surface of birefringent plate (in the x-y plane), the dispersion of the refracted wave decreases with the extent of birefringence. In particular, the dispersion for the electric field parallel to the polarization direction of the incident light changes with the rotation angle between the optic axis and the polarization direction of the incident field, whereas the dispersion for the refracted field whose direction is vertical to the polarization of incident light is independent of this angle. For oblique incidence, dispersion varies substantially for different incident angles. In the situation where the optic axis is in the x-z plane at either normal or oblique incidence, the dispersion increases in a periodically oscillating manner as a function of the relative thickness of the birefringent plate.     

超声波在碳纤维水泥基材料制备中的应用研究

为提高碳纤维在水泥基复合材料中的分散性,提出了两种改进的超声波辅助制备工艺——超声波分散纤维和超声波分散纤维加少量硅灰.应用电阻测试法评价了这两种工艺对碳纤维水泥浆的匀化效果,同时研究了超声波处理时间对复合材料匀化效果的影响.研究结果表明:由于超声波空化作用和机械作用可使纤维得到预分散,两种改进的超声波辅助制备工艺都可以提高碳纤维水泥基复合材料的均匀性;而且超声波处理时间越长,匀化效果越好,但达到一定时间后,匀化效果趋于饱和.     

具有奇异色散特性的光子晶体光纤

光子晶体光纤作为一种结构特殊的一类新型光纤,引起了全世界的广泛关注,尤其是它所拥有的奇异色散特性,已使它在许多领域得到了实际应用.阐述了光子晶体光纤奇异的色散特性:短波零色散、近零超平坦色散和高负色散.     

Group velocity and dispersion model of coupled-cavity waveguides in photonic crystals

A theoretical model of the group velocity, dispersion parameter, and dispersion slope of coupled-cavity waveguides in photonic crystals is reported. Results arising from closed-form expressions show a good agreement with simulation results obtained by employing a plane-wave expansion method. Coupled-cavity waveguides present interesting dispersion properties that may be employed in applications such as optical signal processing, dispersion compensation, and optical delay lines.     

PET/纳米SiO2复合材料的制备I. 纳米SiO2在PET单体EG中的分散性研究

以EG为分散介质，研究了分散方法，分散剂的种类，分散剂的浓度及分 散时间为纳米SiO2在EG中分散性的影响，用TEM对其分散情况进行表征，并对其分散机理进行探讨与研究。其结果表明，不同的分散方法，不同种类的分散剂及不同的分散剂浓度，不同的分散时间对SiO2在EG中的分散性有不同的影响。