Advances in Science and Technology Vol. 60

Abstract: Shape memory polymers are a promising class of stimuli-responsive materials that have dual-shape capability. This kind of materials can recover their shape in a predefined way from temporary shape to desired permanent shape when exposed to an appropriate stimulus. In the development and extensive application of synthetic shape memory polymers on textile industrials, the thermal and hygrothermal effects of wool materials have attracted considerable attention. In this article the fundamental concept of the shape memory polymers and the fundamental aspects of the shape-memory effect were reviewed. The thermal and hygrothermal effects of wool materials were also summarized to discuss the shape memory behavior of wool materials. Besides the effects of synthetic shape memory polymers on the thermal and hygrothermal of the woven wool fabrics were introduced to show the shape memory behavior of treated wool further.

Abstract: Carbon nanotubes (CNTs) are of great technical interest because of their high strength (~37 GPa), good electrical conductivity, excellent thermal conductivity (3 000 W m-1K-1), and good thermal stability at both low and high temperatures. A difficulty has been absence of reliable methods of controlling assembly of the large numbers of CNTs required for practical applications. We have developed, in collaboration with our partners at the NanoTech Institute, University of Texas at Dallas, a solid-state process for spinning CNTs into yarns without the use of binders that usually degrade the electrical and thermal conductivities. The singles yarns were twisted together to give coarser (multi-stranded) stronger yarns that were knitted using a miniature 5-needle machine. Mechanical and electrical properties of the yarns and knitted tubes were assessed simultaneously using specially developed test equipment. Some specific applications under investigation include using the CNT yarns as incandescent and x-ray filaments, as electrodes for biomedical applications, and as composites with high toughness. Tests show the biocompatibility of the CNT yarns for selected cell lines is high.

Abstract: In our previous work, we have produced a photochromic wool fabric by applying a thin layer of hybrid silica-photochromic dye onto the wool surface. The coating showed a very fast optical response, but had little influence on the fabric handle, however durability was low. In this context, we reported that durability of the hybrid layer can be improved by introducing epoxy groups into the silica matrix via co-hydrolysis and co-condensation of an alkyl trialkoxysilane (ATAS) and 3-glycidoxypropyltrimethoxysilane (GPTMS). The presence of epoxy groups in the silica enhanced both washing and abrasion durabilities. Also, the optical response speed was slightly increased as well. Effects of the type of alkyl silane and the GPTMS:alkyl silane ratio on the coating durability, fabric handle and optical response were examined.

Abstract: This paper presents an illustrated discussion of the potential for creative design applications of thermochromic textiles brought into contact with specifically designed heat-profiling circuitry. The results are derived from a current research programme at the design/technology interface on the application of colour change technology in interior textile design. Examples are given of textile samples combining printed thermochromics with circuitry to demonstrate the aesthetic qualities that can be achieved from integration of the technologies in a flexible fabric system. Dynamic colour change effects controlled by prototype circuitry and power electronics are demonstrated. The paper concludes with an analysis of the potential for product/artefact development in the area of “smart” design and how, as a consequence, a responsive interior might be envisaged.

Abstract: This paper reports a novel method of developing SMART nanocomposite membranes and coatings by in situ synthesis of iron oxide particles in a Poly(vinyl alcohol) (PVA)matrix, using co-precipitation of different amounts of Fe(II) and Fe(III) taken in an alkaline medium. Poly(vinyl alcohol) was used to encapsulate iron oxide nanoparticles, as scaffold for particle nucleation and its influence on particle size and on magnetic properties were studied. The ferrogels were prepared by a freeze/thawing process of the solutions containing magnetite nanoparticles. Magnetite particles with an average diameter of 20-40 nm were obtained homogeneously within the matrix because of the tridimensional structure and chelating capacities of PVA. Calcium-alginate PVA gel was used to encapsulate the iron oxide/PVA nanocomposite. The mechanical properties and the saturation magnetization of the system were measured. The combination of magnetic properties of iron nanoparticles with the biocompatibility of calcium-alginate suggests that these materials have great potential for use as controlled delivery systems activated externally by magnetic stimuli.

Abstract: The majority of organismic surfaces, like the plant cuticle, is not smooth but micro-structured. Moreover, they are often covered with hydrophobic wax crystals, some hundred nm in size. The combination of micro- and nanostructures, together with a hydrophobic chemistry, generates the phenomenon of super-hydrophobicity: Water-droplets on such surfaces exhibit contact angles above 140°. Furthermore, dirt particles can barely adhere and are removed by running water only, hence they are called ‘self-cleaning’. The underlying physico-chemical principles were successfully applied to technical prototypes. This technical conversion was patented and the trade mark Lotus-Effect® was introduced in the mid 1990s. Since then several Lotus-Effect® products like a façade paint, a glass coating or a spray were introduced. Another area of application for which prototypes exist, are textiles for awnings, tents or other outdoor purposes. Recently a different aspect of such surfaces is investigated: structures retaining air under water. Several floating plants and semiaquatic animals show this ability. The aim of this project is to develop technical surfaces for long time application in ships and pipelines, as an air film between surface and liquid leads to drag reduction and thus savings of energy.

Abstract: Textiles are increasingly studied to use them as sensing and measuring devices of body parameters. For this purpose they need to be modified to provide on the one hand reliable and stable electroconductive properties and on the other they should be biocompatible. This can be achieved by depositing electroconductive materials such as metals on the textile surface. Gold is an ideal material to use as it offers the aforementioned criteria and can be applied as a thin coating on the surface of a fibre, yarn or fabric. We developed gold coated yarns that are highly electrically conductive, skin-friendly and stable. In this presentation, we describe the gold coating method and show first results of the characterisation of the coated yarns. A commercially available polyester yarn was coated with a thin layer of gold by using an electroless plating method. The plating solution was optimised towards the concentration of each component, the working temperature and pH. The quantitative analysis of the surface coverage of gold with EDAX and cyclic voltammetry showed in both cases a surface coverage of more than 95%. For the future, research will be continued to characterise the longterm behaviour of the yarns.

Abstract: Polyvinylidene fluoride (PVDF) based electrospun nanoweb fibers with outstanding piezo-, pyro- and ferroelectric behavior are being intensely studied by many researchers, especially for touch-sensor applications. In order to further improve the advantageous characteristics of PVDF nanoweb fibers, we focused our attention on studying the effect of filling PVDF solution with calculated amount of calcium chloride (CaCl2) or multi-walled carbon nanotube (MWCNT), and their electrospun nanoweb fibers were analyzed for the changes in β-crystalline phase, and its associated piezoelectric characteristics using a custom-made sensor set-up developed in our lab. FT-IR spectroscopy was used to confirm the changes in the β-crystalline content with varying content of CaCl2 and MWCNT. SEM data revealed the reducing fiber diameter with increasing CaCl2 content. PVDF nanoweb subjected to pressure showed changes in touch sensing property as analyzed using an oscilloscope integrated with Labview program. Overall, the PVDF nanoweb containing the additives used in our study exhibited greater sensitivity-in-touch for use in smart apparel applications compared to unmodified PVDF nanoweb, and the results are reported in detail here.