Organic semiconducting oligomers for use in thin film transistors.

We provide an overview of the basic concepts of scaling and dimensional analysis, followed by a review of some of the recent work on applying these concepts to modeling instrumented indentation measurements. Specifically, we examine conical and pyramidal indentation in elastic-plastic solids with power-law work-hardening, in power-law creep solids, and in linear viscoelastic materials. We show that the scaling approach to indentation modeling provides new insights into several basic questions in instrumented indentation, including, what information is contained in the indentation load-displacement curves? How does hardness depend on the mechanical properties and indenter geometry? What are the factors determining piling-up and sinking-in of surface profiles around indents? Can stress-strain relationships be obtained from indentation load-displacement curves? How to measure time dependent mechanical properties from indentation? How to detect or confirm indentation size effects? The scaling approach also helps organize knowledge and provides a framework for bridging micro- and macroscales. We hope that this review will accomplish two purposes: (1) introducing the basic concepts of scaling and dimensional analysis to materials scientists and engineers, and (2) providing a better understanding of instrumented indentation measurements.

Scaling, dimensional analysis, and indentation measurements

The objective of this article was to review the use of carbon black (CB) as a conductive filler in polymers and polymer blends. Important properties of CB related to its use in conducting polymers are discussed. The effects of polymer structure, molecular weight, surface tension, and processing conditions on electrical resistivity and physical properties of composites are discussed. Several percolation models applicable to CB/polymer blends are reviewed. Emphasis is placed on recent trends using polymer blends as the matrix to obtain conducting composites at a lower CB loading. A criterion for the distribution of CB in polymer blends is discussed. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 299–313, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10025

Carbon black filled conducting polymers and polymer blends

The growth in the application of electronic devices across a broad spectrum of military, industrial, commercial and consumer sectors has created a new form of pollution known as noise or radio frequency interference (RFI) or electromagnetic radiation or electromagnetic interference (EMI) that can cause interference or malfunctioning of equipment. Therefore, there is a greater need for the effective shielding of components from its adverse effects. This review surveys the shielding materials like metals, conducting plastics and conducting polymers for the control of electromagnetic radiations. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

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EMI shielding: Methods and materials—A review

Thermal processing of starch-based polymers

The absolute intensity of the small-angle X-ray scattering (SAXS) of poly(ethy1ene terephthalate) (PET) samples crystallized at different temperatures for different times was measured by means of a Kratky camera. The correlation function and the interface distribution function were calculated, and the values obtained from different methods for the long period L, the crystal thickness, l,, the thickness of the amorphous regions la, and the linear degree of crystallinity XCL were compared with each other. After a critical examination of the different methods, including model calculations of the interface distribution function and the correlation function, it is shown that, in the case of a broad distribution of thicknesses, the interface distribution function gives the more reliable results for l , , la , and L. By comparing the linear degree of crystallinity x c ~ determined from SAXS with the degree of crystallinity x c as determined from wide-angle X-ray scattering or from density, it is concluded that the material is not homogeneously filled with lamellar stacks. The coherently scattering lamellar stack consists of only 3-6 lamellae.

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Novel aspects in the structure of poly(ethylene terephthalate) as revealed by means of small angle x-ray scattering

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed.

Microhardness relating to crystalline polymers

The microindentation hardness technique has been employed to examine the II → I polymorphic transformation of i-PBu1 taking place upon aging at room temperature. The hardness values of form I are shown to be remarkably higher than those of form II due to the denser packing of chains in the hexagonal crystal modification. The kinetics of the II → I transformation has been followed by means of microindentation hardness measurements in real time. The influence of molar mass and crystallization temperature on the kinetics of the polymorphic transformation is examined. Results suggest that the rate of polymorphic transformation is independent of molecular weight. In addition, it is seen that increasing the crystallization temperature (up to 105 °C) notably reduces the time required for a full transformation of form II into form I. The influence of the fraction of amorphous material on the rate of polymorphic transformation is discussed.

https://digital.csic.es/bitstream/10261/237857/1/Polymorphism%20of%20Isotactic%20Poly%281-butene%29.pdf

Polymorphism of isotactic poly(1-butene) as revealed by microindentation hardness. 1: Kinetics of the transformation

The study of electrical conductivity of high-density polyethylene-carbon-fibre composites mixed with different concentrations of carbon black is reported. The influence of the mixing procedure of the additives and material preparation is examined with regard to the conductivity values. The use of these two filler types in polyethylene composites combines the conducting features of both. Thus, while fibres provide charge transport over large distances (several millimetres), carbon black particles improve the interfibre contacts. Results are discussed with reference to simple electrical models. It is shown that for composites in which the segregated carbon black-polyethylene component lies above the percolation threshold the electrical interfibre contacts are activated through carbon black particle bridges, leading to a conductivity rise. This effect is more relevant in the case of shorter fibres. Processing of the material involving fibre orientation, such as in injection-moulding, decreases drastically the conductivity level reached.

Electrical conductivity of polyethylene-carbon-fibre composites mixed with carbon black

http://digital.csic.es/bitstream/10261/242945/1/Temperature-dependence%20of%20polymorphism.pdf

F. J. Baltá Calleja

Papers

Novel aspects in the structure of poly(ethylene terephthalate) as revealed by means of small angle x-ray scattering

Microhardness relating to crystalline polymers

Polymorphism of isotactic poly(1-butene) as revealed by microindentation hardness. 1: Kinetics of the transformation

Electrical conductivity of polyethylene-carbon-fibre composites mixed with carbon black

Temperature dependence of polymorphism in electrospun nanofibres of PA6 and PA6/clay nanocomposite