Vibrational and electrical investigations of a uniaxially stretched polystyrene/carbon nanotube composite

Multiwall carbon nanotube (MWCNT)/polystyrene (PS) composite materials were prepared in the absence and in the presence of a surfactant. TEM analysis reveals the formation of chains made of several nanotubes tied up together upon application of the surfactant while an almost random distribution is observed without any treatment. These nanotubes are seen to be highly oriented in the uniaxially stretched composite. It is shown that the presence of the surfactant and the alignment reduce electrical conductivity while polymer chain orientation remains insensitive to these parameters.     

单圈绝对式光电轴角编码器的研究

在对传统绝对式光电轴角编码器编码方法原理研究的基础上,设计了一种单圈绝对式光电轴角编码器.详细地介绍了该编码器的位置定位算法,具体给出了信号拾取装置和信号采集系统的硬件设计方法,并分析了影响编码器准确度的主要因素.检测结果表明该编码器的原理和设计是正确的,为实现光电轴角编码器的小型化、智能化提供了理论依据和试验基础.     

A convenient way of interpreting steady shear rheo-optical data of semi-dilute polymer solutions

Rheo-mechanical and rheo-optical investigations were carried out with the aim of determining the influence of deformation and orientation or disentangling of polymer coils on the flow behavior in the non-Newtonian region of the flow curve, for a moderately concentrated network solution. To avoid the influence of polydispersity this was done on a series of narrowly distributed polystyrene standards (dissolved in toluene). By using steady state shear flow measurements it was possible to detect qualitatively a reduction in the entanglement density within the non-Newtonian flow region. Birefringence experiments were able to show that deformation of the polymer coils also occurs in the Newtonian flow region, which has no effect on the flow behavior in this range, whereas in the non-Newtonian flow region the increase in deformation is lower than in the Newtonian range. The flow birefringence and its orientation can be described over the whole range of the flow curve with a newly developed equation system (Eq. 8 and 14) derived from the stress states of a sheared solution using the stress-optical rule. Starting from these equations, it could be shown, that in the Newtonian flow region a mastercurve in form of a reduced birefringence Δn′/η₀=f(γ˙) and a reduced orientation φ= f(γ˙/γ˙ _crit) can be plotted, independent from concentration and molar mass. A comparison of the experimentally determined orientation angle and birefringence curve form with theoretical deformations and orientations of polymer coils in a solution state, without intermolecular interactions, was able to demonstrate that the flow behavior of a moderately concentrated network solution is determined decisively (approximately to 85%) by the disentanglement. Received: 8 May 2000 Accepted: 12 September 2000     

Nonlinear electromechanical analysis: a constitutive theory for perovskite type ferroelectrics

A constitutive theory is established in this paper to describe the nonlinear electromechanical behavior of perovskite type ferroelectrics subjected to external stress and external electric field. In the proposed theory, each domain is considered as an inclusion. The Helmholtz free energy and Gibbs free energy of a constituent element, that are derived by using micromechanics approaches, are functionals of the orientation distribution function (ODF) that depicts the domain distribution patterns. By applying the internal variable theory and expanding ODF in Fourier series, the yielding condition, the evolution of ODF, and the constitutive relation are obtained. In terms of the simplification of the constitutive relation, theoretical predictions are compared with experimental results. There is an agreement between the theoretical and the experimental results, indicating that the theory is reasonable and applicable. It should be pointed out that the constitutive model proposed in this paper is restricted to ferroelectric materials exhibiting transformation from cubic to tetragonal only.     

红外光谱在聚对苯二甲酸乙二醇酯纤维结构研究中的应用

回顾了近年来红外光谱在聚对苯二甲酸乙二醇酯(PET)纤维结构研究中的应用,介绍了纤维制样技术,归纳了构象含量、取向、折叠链含量等结构参数的表征方法及其应用,以及这些结构参数与纤维性能间的联系。     

Compatibility of PVC-chlorinated PVC mixtures

This study deals with the compatibility of a poly(vinyl chloride) mixed separately with two industrial chlorinated poly(vinyl chlorides), denoted PVC/C1 and PVC/C2 (chlorine contents of 65.2 and 67.5%, respectively). The technique of mixing, examined for different compositions, is the main parameter for the compatibility of the resins. The mixtures were prepared either with a Brabender plastograph, with a milling cylinder at 190°C (the mixture being fluid), or by sintering at a temperature between 180 and 200°C under pressure. We determined the complex components of the elasticity modulus as a function of temperature (from 50 to 170°C at a frequency of 110 Hz) for each mixture, using a Rheovibron viscoelastometer. The study of the structure of the mixtures, based on the variation of the tangent of the loss modulus, allows us to say that the compatibility of polymers depends on the chlorine contents in chlorinated PVC; thus, at 65.2% the chlorinated polymer seems to be compatible with PVC, but at 67.5% the mixture shows the characteristics of a two-phase system. The compatibility is also dependent on processing methods.     

The hull and geodetic numbers of orientations of graphs

For an oriented graph D, let I_D[u,v] denote the set of all vertices lying on a u-v geodesic or a v-u geodesic. For S⊆V(D), let I_D[S] denote the union of all I_D[u,v] for all u,v∈S. Let [S]_D denote the smallest convex set containing S. The geodetic number g(D) of an oriented graph D is the minimum cardinality of a set S with I_D[S]=V(D) and the hull number h(D) of an oriented graph D is the minimum cardinality of a set S with [S]_D=V(D). For a connected graph G, let O(G) be the set of all orientations of G, define g⁻(G)=min{g(D):D∈O(G)}, g⁺(G)=max{g(D):D∈O(G)}, h⁻(G)=min{h(D):D∈O(G)}, and h⁺(G)=max{h(D):D∈O(G)}. By the above definitions, h⁻(G)≤g⁻(G) and h⁺(G)≤g⁺(G). In the paper, we prove that g⁻(G)<h⁺(G) for a connected graph G of order at least 3, and for any nonnegative integers a and b, there exists a connected graph G such that g⁻(G)−h⁻(G)=a and g⁺(G)−h⁺(G)=b. These results answer a problem of Farrugia in [A. Farrugia, Orientable convexity, geodetic and hull numbers in graphs, Discrete Appl. Math. 148 (2005) 256-262].     

Effect of melt temperature on the phase morphology, thermal behavior and mechanical properties of injection-molded PP/LLDPE blends

<正>The phase morphology and thermal behavior of various isotactic polypropylene(PP)/linear low density polyethylene(LLDPE) blends were investigated with aid of scanning electron microscopy(SEM) and differential scanning calorimetry(DSC),respectively.The effect of barrel(melt) temperature on the morphology,thermal behavior and the resultant mechanical properties of the injection molded bars was the research focus,and the influence of LLDPE composition was also taken into account.It was found that the mechanical properties,especially the tensile ductility and the impact strength,were greatly affected by the processing temperature.The samples obtained at low temperatures had the highest elongation at break and impact strength,while those molded at high temperatures had the poorest toughness.Two reasons were responsible for that:first,the phase size in the samples increased with the processing temperature;second, possible orientation existed in the samples obtained at low processing temperatures.     

3D refractive index profile for the characterization of necking phenomenon along stretched polypropylene fibres

The phenomenon of neck formation in polymers has attracted considerable attention. During the cold-drawing process an initial undrawn material is transformed into anisotropic one across a narrow transition region called ‘neck’. The Video Opto-Mechanical (VOM) device attached with multiple-beam Fizeau fringes techniques are used to stretch polypropylene (PP) fibres. A iPP sample is stretched to have a neck at room temperature. The optical properties of the deformed material over the necking region are examined. Another PP sample is stretched (without necking deformation) at room temperature and the optical properties are also examined. The task of this study is to characterize and assess the necking phenomenon along cold-drawn polypropylene (iPP) fibre axis. The effect of necking on the optical properties of the fibre is confirmed by the determination of the 3D refractive index profile at different regions along the deformed PP fibre. Also the orientation function is calculated for the necked sample. The contour lines of microinterferograms are given for illustrations.     

Phase compositions and ferroelectric properties of Pb(Zr0.52,Ti0.48)O3 thin films with different highly orientations prepared by a sol-gel route

It is shown that different highly oriented Pb(Zr_0.52,Ti_0.48)O₃ films can be obtained on Pt/Ti/SiO₂/Si substrate using a sol-gel technique. The effects of pyrolysis temperature on the orientation, phase composition and ferroelectric properties of the films are investigated. It is found the ferroelectric hysteresis loops of (1 1 1)-oriented film, (1 1 1) and (1 0 0) mix-oriented film can both be saturated when the external electric field is large enough, whereas the hysteresis loop of (1 0 0)-oriented film is difficult to saturate. The analysis of X-ray diffraction indicated the possibility of different phase composition in different oriented films under large film residual stress. Higher remnant polarization (53 μC/cm²) for (1 0 0)-oriented film can be attributed to its more tetragonal phase composition, which results in that the in-plane domain switching can continuously occur with external electric field increasing.