Graphene electrode was fabricated by inkjet printing, as a new means of directly writing and micropatterning the electrode onto flexible polymeric materials. Graphene oxide sheets were dispersed in water and subsequently reduced using an infrared heat lamp at a temperature of ~200 °C in 10 min. Spacing between adjacent ink droplets and the number of printing layers were used to tailor the electrode's electrical sheet resistance as low as 0.3 MΩ/□ and optical transparency as high as 86%. The graphene electrode was found to be stable under mechanical flexing and behave as a negative temperature coefficient (NTC) material, exhibiting rapid electrical resistance decrease with temperature increase. Temperature sensitivity of the graphene electrode was similar to that of conventional NTC materials, but with faster response time by an order of magnitude. This finding suggests the potential use of the inkjet-printed graphene electrode as a writable, very thin, mechanically flexible, and transparent temperature sensor.
There is an ever-growing number of developments that aim to bring novel functionalities to polymer-coating systems with nanotechnology being one of them. This article will cover recent advances in the field of smart polymeric structures that are used in protective coatings in terms of stimulus and response, sensing mechanisms, and current or potential applications. Such structures are commonly based on polymers modified through organic or inorganic additives. Emphasis is placed on smart sensors used for detecting the onset of corrosion on polymer coated ferrous and nonferrous substrates. Examples of self-healing and repair through the action of microcapsules are also presented.
Irreversible and reversible chromatic transitions during heating and cooling cycles were investigated in polydiacetylene poly-PCDA (poly-10,12-pentacosadiynoic acid) composites with nanocrystalline zinc oxide (ZnO), titanium oxide (TiO 2 ), zirconium oxide (ZrO 2 ) and ZnO and ZrO 2 alloys. In contrast to pure poly-PCDA, poly-PCDA composites with nanocrystalline ZnO displayed rapid reversibility on thermal cycling, whereas the corresponding composites with nanocrystalline TiO 2 and ZrO 2 were irreversible, and poly-PCDA composites with thermally prepared ZnO and ZrO 2 alloys displayed slower reversibility. The mechanism of reversible and irreversible thermochromism in these materials was explored using Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and X-ray absorption fine structure (XAFS) spectroscopy. In pure poly-PCDA, heating leads to an irreversible strain on the polymer backbone to form a red phase, which is not released on cooling. In the presence of ZnO evidence is provided for chelation involving the side chain head groups which can release strain on cooling to rapidly form the blue phase. Chemical interaction coupled with reversible behavior was however observed only when the composites were prepared with ZnO having an average crystallite size of 300 nm and below with a fraction of an amorphous grain boundary phase. Poly-PCDA composites with ZnO/ZrO 2 alloys showing slower thermochromic reversibility can be used both as temperature and elapsed time-temperature sensors.
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