Stretchable conductive networks of carbon nanotubes using plasticized colloidal templates

We present a study of the behavior of highly ordered, segregated single-wall carbon nanotube (CNT) networks under applied strain. Polymer latex templates induce self-assembly of CNTs into hexagonal (2D) and honeycomb (3D) networks within the matrix. Using mechanical and spectroscopic analysis, we have studied the strain transfer mechanisms between the CNT network and the polymer matrix. Axial deformation of the nanotube network under applied strain is indicated by downshifts in the 2D mode in the Raman spectra, as well as variation in the radial breathing modes.The slippage within nanotube bundles at high strain is indicated by a reduction in the 2D mode rate of change. The fractional resistance change of the composites with strain obeys power law dependence. We present a model for the behavior of CNT bundles under strain informed by these measurements, and potential applications for such composite materials in elastic electronic devices that can tolerate high strain

3D-printed PLA/PEO blend as biodegradable substrate coating with CoCl2 for colorimetric humidity detection

This study aimed to fabricate biodegradable substrate with colorimetric humidity indicator for detective moisture in food packaging. The poor properties of poly(lactic acid) (PLA) were enhanced by melt blending PLA with non-toxic poly(ethylene oxide) PEO at 180 °C. Specifically, three-dimensional (3D) substrates of PLA/PEO blends were fabricated by solvent-cast 3D printing. Furthermore, cobalt chloride (CoCl2) solution was printed onto the substrate with an inkjet printer to serve as a colorimetric humidity sensing indicator. It found that the flexibility and thermal stability of the PLA were improved and the hydrophilicity was increased with an increase in PEO content. Color changes and the sensitivity of this material were confirmed using image analysis and total color difference. The CoCl2 indicator displayed color changes that ranged from blue to pink under ambient conditions (above 60%RH), revealing suitable potential for frozen food packaging material with aim to detect amount of moisture in the packaging

Thermo-Mechanical Properties of Stretchable Nanocomposites Based on Honeycomb Networks of Carbon Nanotubes.

Waterborne polymer colloidal particles (i.e. latex) have been used as a template to fabricate carbon nanotube (CNT) composites. Plasticized colloidal crystals are able to assemble CNTs into ordered hexagonal, or honeycomb-like, networks with periodicity defined by the size and deformability of the polymer latex spheres used to form the nanocomposite. In this work, two-dimensional hexagonal networks have been formed by spin-coating the latex nanocomposite dispersion onto a substrate. The resulting monolayer composites have very interesting thermal expansion behaviour. Due to the significantly lower thermal expansion (CTE) of single-walled CNTs (SWNTs) compared to polymers, nanotube networks act as static belts surrounding latex particles in the thin film plane. The matrix with considerably higher CTE is, therefore, restricted to expand in the film plane. The polymer particles, consequently, expand in the out-of-plane direction, thus displaying a higher CTE in that direction. Ultimately the monolayer films may find application as nanoscale thermal actuators. By using latex matrices with low and high glass transition temperature values, random and ordered honeycomb-like CNT networks can be formed in bulk composite samples, respectively. The ability to control CNT network formation results in a variation of thermal conductivity (K) of the nanocomposites. Compared to the composite with random CNT networks, a K enhancement has been found when ordered segregated nanotube networks are created, especially in the case of SWNT composites that offer higher K than the case of composites consisting of multi-walled CNTs. In addition, the thermal percolation threshold has been found to be markedly low due to large excluded volume of the polymer matrix in ordered networks of SWNTs. After spin-coating particle monolayers of CNT-latex blends onto a polymer substrate, the mechanics of the unusual monolayer elasticity has been investigated. Polarized Raman spectroscopy reveals a uniform alignment of the nanotube networks in the strained monolayers. Systematic changes in the resulting Raman spectra of the monolayer under strain indicate that stress is transferred from the colloidal matrix to SWNT inclusions as observed from the Raman G’-band shift. These are explained by strain and slippage of individual SWNTs in the bundles. Additionally, elastic recovery of the monolayer has been found after being strained beyond failure, which may be related to the inter-tube van der Waals forces pulling individual tubes back to their bundles and, therefore, latex particles back to original morphology

Negotiation for Meaning in Synchronous EFL Chat

AbstractThis study examined the nature of the negotiations for meaning that took place in a series of up to twelve online chat sessions between eleven pairs of adult Thai learners of English and English speakers. The study implemented a triangulation approach for data analysis; data was drawn from chat scripts, interviews, and reflective notes written by the Thai speakers after each chat session. The chat scripts were analyzed for (a) triggers that caused comprehension difficulties, and (b) strategies used by the Thai speakers to solve communication problems. The findings suggested the potential benefit of reflective note writing for morphosyntactic improvement. Themorphosyntactic errors were often ignored in the original conversations because they had less effect than lexical triggers on comprehension. However, the Thai speakers reflected on their own interlanguage forms in the saved written conversations while writing their reflective notes and tried to correct them or requested help from other sources. In addition, the Thai speakers used strategies to solve communication problems that did not constitute negotiations of meaning in the classical sense, that is, dictionary consultation, word substitution and avoidance. Pedagogical implications are also included

Thermo-Mechanical Properties of Stretchable Nanocomposites Based on Honeycomb Networks of Carbon Nanotubes.

Waterborne polymer colloidal particles (i.e. latex) have been used as a template to fabricate carbon nanotube (CNT) composites. Plasticized colloidal crystals are able to assemble CNTs into ordered hexagonal, or honeycomb-like, networks with periodicity defined by the size and deformability of the polymer latex spheres used to form the nanocomposite. In this work, two-dimensional hexagonal networks have been formed by spin-coating the latex nanocomposite dispersion onto a substrate. The resulting monolayer composites have very interesting thermal expansion behaviour. Due to the significantly lower thermal expansion (CTE) of single-walled CNTs (SWNTs) compared to polymers, nanotube networks act as static belts surrounding latex particles in the thin film plane. The matrix with considerably higher CTE is, therefore, restricted to expand in the film plane. The polymer particles, consequently, expand in the out-of-plane direction, thus displaying a higher CTE in that direction. Ultimately the monolayer films may find application as nanoscale thermal actuators. By using latex matrices with low and high glass transition temperature values, random and ordered honeycomb-like CNT networks can be formed in bulk composite samples, respectively. The ability to control CNT network formation results in a variation of thermal conductivity (K) of the nanocomposites. Compared to the composite with random CNT networks, a K enhancement has been found when ordered segregated nanotube networks are created, especially in the case of SWNT composites that offer higher K than the case of composites consisting of multi-walled CNTs. In addition, the thermal percolation threshold has been found to be markedly low due to large excluded volume of the polymer matrix in ordered networks of SWNTs. After spin-coating particle monolayers of CNT-latex blends onto a polymer substrate, the mechanics of the unusual monolayer elasticity has been investigated. Polarized Raman spectroscopy reveals a uniform alignment of the nanotube networks in the strained monolayers. Systematic changes in the resulting Raman spectra of the monolayer under strain indicate that stress is transferred from the colloidal matrix to SWNT inclusions as observed from the Raman G’-band shift. These are explained by strain and slippage of individual SWNTs in the bundles. Additionally, elastic recovery of the monolayer has been found after being strained beyond failure, which may be related to the inter-tube van der Waals forces pulling individual tubes back to their bundles and, therefore, latex particles back to original morphology