The use of conductive polymer composites (CPCs) as strain sensors has been widely investigated and various resistivity-strain sensitivities are desirable for different applications. In this study, the use of mixed carbon fillers and functionalized carbon nanotubes was demonstrated to be vital for preparing thermoplastic polyurethane (TPU)-based strain sensors with tunable sensitivity. To understand the strain sensing behavior, we carried out scanning electron microscopy (SEM), Raman spectroscopy, wide-angle X-ray diffraction (WAXD), mechanical test, and rheology-electrical measurement. Hybrid fillers of multi-walled carbon nanotubes (MWNTs) and carbon black (CB) could reduce the entanglement in conductive network structure, thus increase the resistivity-strain sensitivity. Furthermore, incorporation of additional functionalized MWNTs in the CPCs could enhance the interfacial interaction between nanofillers and TPU, leading to further increase in sensitivity. Through such a simple method, strain sensors could be efficiently fabricated with large strain-sensing capability (strain as large as 200%) and a wide range of strain sensitivity (gauge factor ranging from 5 to 140238). Finally, the exponential revolution of resistive response to strain was fitted with a model based on tunneling theory by Simmons. It was observed that the change in tunneling distance and the number of conductive pathways could be accelerated significantly by adjusting conductive network structure and interfacial interaction. This study provides a guideline for the preparation of high-performance CPC strain sensors with a large range of resistivity-strain sensitivity.

The development of facile methods for screening organic functional molecules through C-H bond activation is a revolutionary trend in materials research. The prediction of mechanochromism as well as mechanochromic trends of luminogens is an appealing yet challenging puzzle. Here, we present a strategy for the design of mechanochromic luminogens based on the dipole moment of donor-acceptor molecules. For this purpose, a highly efficient route to 2,7-diaryl-[1,2,4]triazolo[1,5-a]pyrimidines (2,7-diaryl-TAPs) has been established through programmed C-H arylation, which unlocks a great opportunity to rapidly assemble a library of fluorophores for the discovery of mechanochromic regularity. Molecular dipole moment can be employed to explain and further predict the mechanochromic trends. The 2,7-diaryl-TAPs with electron-donating groups on the 2-aryl and electron-withdrawing groups on the 7-aryl possess a relatively small dipole moment and exhibit a red-shifted mechanochromism. When the two aryls are interchanged, the resulting luminogens have a relatively large dipole moment and display a blue-shifted mechanochromism. Seven pairs of isomers with opposite mechanochromic trends are presented as illustrative examples. The aryl-interchanged congeners with a bidirectional emission shift are structurally similar, which provides an avenue for understanding in-depth the mechanochromic mechanism.

SUMMARYThere was a tremendous advantage of using the generalized co-ordinate system to express various types of laminate theories. With two layer-dependent terms of both the zeroth-and the first-order of thickness co-ordinate, a generalized zigzag theory was presented in a previous study. Due to its success in laminate analysis, the feasibility of assigning the two high-order terms, i.e. the second-and the third-order terms, of the generalized zigzag theory as layer-dependent variables was of primary interest. It was found that a so-called global-local superposition technique could be used for expressing the laminate theories in an explicit manner, namely recursive equations, to retain the advantage of numerical efficiency. Based on the superposition technique, the fundamental roles of the individual terms are identified. It is concluded that not only the completeness of the terms, but also the inclusion of as many terms as possible, is important to a laminate theory. It then is the goal of this study to look into a laminate theory which can satisfy the requirement of completeness and include all the first-, second-and third-order terms in an assumed displacement field. A special technique, namely hypothesis for double superposition, is presented to achieve the goal. The feasibility of the hypothesis is demonstrated in this study. Although not verified mathematically, the hypothesis seems to be capable of giving accurate and efficient laminate theories. 1997 by John Wiley & Sons, Ltd.

No abstract

No abstract

No abstract

With the use of a recursive technique, this paper presents an overall comparison of laminate theories based on displacement hypothesis. A generalized polynominal form is used to unify the displacement hypothesis. Both theories available in the literature and inferable from the existing theories are addressed. Firstly, Shear Deformation Theories are recognized to give good results for in-plane stresses but poor results for interlaminar stresses. However, Layerwise Theories give excellent results for both global and local distributions of displacement and stress (both in-plane and out-of-plane). A compromising theory, the Generalized Zigzag Theory, is presented. Due to its success in laminate analysis, a series of Quasi-layerwise Theories are presented. Unfortunately, a physical impossibility-coordinate dependency-takes place. It then requires a Global-Local Superposition Technique to formulate the laminate theories. By examining the results of Superposition Theories, it is concluded that the completeness of the terms is very important. Based on a Hypothesis for Double Superposition, this study presents three Double-Superposition Theories. They are verified to give excellent numerical accuracy, along with computational efficiency, when compared with elasticity solutions.

Chitosan-alginate microcapsules were evaluated as a method of oral delivery of IgY antibodies. Physical characteristics, encapsulation efficiency (EE%), the loading capacity for IgY (IgY loading percentage, %, w/w of microcapsules), gastro-resistance, and release characteristics of these microcapsules in vitro under varying pH were investigated. Optimum physical factors were established for preparation of homogeneous, spherical, and smooth microcapsules. IgY loading% was not significantly altered by pH of the encapsulation medium. Encapsulation efficiency was highest (73.93%) at a pH of 3.5, above which EE% decreased significantly (p < 0.05). IgY was released from microcapsules upon exposure to simulated intestinal fluid (SIF, pH 6.8), and decreasing pH increased significantly IgY release (p < 0.05). The stability of IgY in simulated gastric fluid (SGF, pH 1.2) was greatly improved by encapsulation in chitosan-alginate microcapsules, and the residual activity was not affected by pH of the encapsulation medium. Moreover, microencapsulated IgY was significantly resistant to pepsin hydrolysis. This approach may enable intact IgY to reach target microorganisms within the lower digestive tract.