Environmentally responsive photonic polymers

\u3cp\u3eStimulus-responsive photonic polymer materials that change their reflection colour as function of environmental stimuli such as temperature, humidity and light, are attractive for various applications (e.g. sensors, smart windows and communication). Polymers provide low density, tunable and patternable materials. This feature article focusses on various autonomously responding photonic polymer materials such as hydrogels, block copolymers and liquid crystals and discusses their potential industrial implementation.\u3c/p\u3

Characterization of conductive multiwall carbon nanotube/polystyrene composites prepared by latex technology, Carbon 45

Abstract Conductive multiwall carbon nanotube/polystyrene (MWCNT/PS) composites are prepared based on latex technology. MWCNTs are first dispersed in aqueous solution of sodium dodecyl sulfate (SDS) driven by sonication and then mixed with different amounts of PS latex. From these mixtures MWCNT/PS composites were prepared by freeze-drying and compression molding. The dispersion of MWCNTs in aqueous SDS solution and in the PS matrix is monitored by UV-vis, transmission electron microscopy, electron tomography and scanning electron microscopy. When applying adequate preparation conditions, MWCNTs are well dispersed and homogeneously incorporated in the PS matrix. The percolation threshold for conduction is about 1.5 wt% of MWCNTs in the composites, and a maximum conductivity of about 1 S m À1 can be achieved. The approach presented can be adapted to other MWCNT/polymer latex systems

Carbon nanotube/isotactic polypropylene composites prepared by latex technology: Morphology analysis of CNT-induced nucleation

The crystallization behavior of isotactic polypropylene (iPP) in the vicinity of single-wall and multiwall carbon nanotubes (SWCNTs and MWCNTs) has been studied. Combined DSC and transmission electron microscopy (TEM) investigations of bulk composite materials reveal that CNTs nucleate iPP when crystallizing from the quiescent melt and that iPP crystals form a transcrystalline layer of aligned iPP lamellar crystals around the nucleating CNT. The pronounced nucleation effect and the formation of a transcrystalline layer is observed also for ultrathin film CNT/iPP samples. Corresponding diffraction studies show that in bulk as well as in the case of the ultrathin film samples only the ?-phase of iPP exists. The transcrystalline layer is highly oriented around the nucleating CNTs, and the crystallographic c-axes of the lamellae are oriented perpendicular to the long axis of the nucleating CNT, which is in contradiction to assumptions done in other studies. This crystallization behavior is discussed and a possible explanation is provided based on iPP macromolecules wrapped around rather than aligned along the CNTs prior to formation of the nucleus. © 2008 American Chemical Societ

Well-adhering, easily producible photonic reflective coatings for plastic substrates

\u3cp\u3eThe development of well-adhering, easily producible photonic reflective coatings is still a challenge. Here, an easy-to-produce, industrial viable process is reported that uses a primer layer of the so-called type II photoinitiator to obtain an excellent adhesion between a plastic substrate and one-dimensional (1D) photonic liquid crystalline coatings. Furthermore, a good alignment of the reactive cholesteric liquid crystal mixture is obtained using a bar-coating process, without alignment layers or surfactants. After photopolymerization, cross-hatch tape tests show a good adhesion of the photonic coating having a reflection band of 50% transmission with almost no scattering. Additionally, we demonstrate the ability to create well-adhering ∼100% reflective coatings by coating double layers and the ability to create single-layered cholesteric broadband reflectors using solely a reactivity gradient created by the primer layer. Our new interfacial method gives new opportunities to use reflecting 1D photonic coatings in industrial processes and applications and allows the bonding of almost any polymer to a plastic substrate.\u3c/p\u3