Development of high performance carbon nanotube/polymer composites

This project mainly concerned the development of novel engineering approaches to optimise the physical properties of the polymer composites with a low loading of carbon nanotubes (CNTs). It was additionally discovered that graphite oxide nanoplatelets (GONPs) can be a strong and affordable substitute for the CNTs in the polymer composites. Colloidal physics and coating methods were applied to fabricate semi-conductive CNT/polymer composites with low percolation threshold. Polyurethane (PU) latex and ultra high molecular weight polyethylene (UHWMPE) powder were used as hosting matrix in the colloidal physics method and coating method, respectively. In the colloidal physics method, the percolation threshold was found to be around O.5wt% MWCNTs and the electrical conductivity of the composites was improved by more than four orders of magnitude with the addition of I wt % multi-walled carbon nanotubes (MWCNTs). The study of rheological behaviour revealed that the addition of the MWCNTs led to the increase in the viscosity of the PU dispersion. In the coating method, the scanning electron microscopy (SEM) images confirmed the strong adhesion of the nanotubes on the surface of the powders. Sheet samples were prepared using compression moulding for electrical test. The percolation threshold for the powders with the size of 60)lm was around I wt% MWCNTs and the percolation threshold for the powders with the size of 100)lm was around 0.5wt% MWCNTs. A novel route was revealed to reduce the interfacial phonon scattering that is considered as the bottleneck for CNTs to highly improve the thermal conductivity of CNT/polymer composites. Semicrystalline PU dispersions were used as latex host to accommodate the MWCNTs following the colloidal physics method. The thermal conductivity increased from 0.15 Wm-'K-' to 0.47 Wm-'K", by -210%, as the addition of the MWCNTs increased to 3wt%. The morphology of the composites suggested that the continuous nanotube-rich phase existing in the interstitial space among the latex particles and the crystaIIites nucleated at the nanotube-polymer interface were the main factors for the effective reduction of interfacial phonon scattering. The optimisation of the crystalline layer around CNTs was studied based on the MWCNT/polycapro!actone (PCL) composites using differential scanning calorimetry (DSC). The study of the non-isothermal crystaIlisation showed that crystaIIisation temperature (Tc) increased with increasing incorporation of the nanotubes, and melting temperature (T m) and heat of fusion (ilHm) was almost unchanged. The incorporation of 2wt% nanotubes resulted in the biggest increase of the T c to be -11 QC. The study of the isothermal crystaIIisation showed the temperature, 14 DC higher than the Tc. was appropriate one to optimise the crystaIIine layer in the composite melts. It was revealed that the incorporation of 0.1 wt% nanotubes significantly affected the rate of crystal growth and crystalline morphology. For more incorporation of the nanotubes, the rate of crystal growth and crystaIIine morphology was less affected. The improvement in the Young's modulus of the composite with the thermal treatment confirmed the contribution of the crystalline layer to the load transfer across the non-covalent interface between the nanotube and polymer matrix. The preparation of the exfoliated GONPs in DMF was revealed. With this method in hand, two kinds of polymers including semi-crystaIline PCL and amorphous PU were selected to be incorporated with the GONPs using the solution method. It was found that the GONPs showed strong nucleating ability in the PCL matrix. The thermal treatment under the "14QC" rule could create an optimised crystalline layer on the surface of the GONPs from the composite melts. The bigger increase in the Young's modulus of the treated GONPIPCL composites confirmed that the crystaIIine layer nucleated on the surface of the GONPs could act as a non-covalent interface between the GONPs and PCL matrix. The significant reinforcement of the PU using GONPs was also disclosed. Morphologic studies showed thai, due to the formation of chemical bonding, strong interaction occurred between the GONPs and the hard segment ofthe PU, which allowed effective load transfer. The GONPs can prevent the formation of crystalline hard segments due to their two-dimensional structure. With the incorporation of 4.4wt% graphite oxide nanoplatelets, the Young's modulus and hardness of the PU were significantly increased by -900% and -327%, respectively. The resultant high anti-scratch property pointed to the promising application of these composite materials in surface coating.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Ultra-high enhancement in the toughness of polyethylene by exfoliated natural clay nanosheets

The full exfoliation of inorganic natural clay was engineered in a nonpolar polyethylene following a novel method without the involvement of any chemical modification to the surface of silicate layers. Tensile results showed that the toughening effect was dependent of strain rates, and the toughness of polyethylene was substantially improved by nearly five times with 0.5 wt % natural clay nanosheets at a strain rate of 0.15 s−1. Toughening mechanism was also discussed based on this new exfoliated syste

Stabilizing bijels using a mixture of fumed silica nanoparticles

Bijels are typically prepared by arresting the phase separation of two liquids using interfacial particles. The surface treatment of the particles is challenging but can be overcome at a cost (Cui et al., Science, 2013, 342, 460-463). Here, we use mixed commercial fumed-silica nanoparticles, giving a facile route to bijel production.</p

Bijels formed by direct mixing

By combining interfacial nanoparticles and molecular surfactants together with immiscible liquids of high viscosity, we develop an alternative strategy for creating bicontinuous interfacially jammed emulsion gels (bijels).</p

Calibrating ultrasonic sensor measurements of crop canopy heights: a case study of maize and wheat

Canopy height serves as an important dynamic indicator of crop growth in the decision-making process of field management. Compared with other commonly used canopy height measurement techniques, ultrasonic sensors are inexpensive and can be exposed in fields for long periods of time to obtain easy-to-process data. However, the acoustic wave characteristics and crop canopy structure affect the measurement accuracy. To improve the ultrasonic sensor measurement accuracy, a four-year (2018−2021) field experiment was conducted on maize and wheat, and a measurement platform was developed. A series of single-factor experiments were conducted to investigate the significant factors affecting measurements, including the observation angle (0−60°), observation height (0.5−2.5 m), observation period (8:00−18:00), platform moving speed with respect to the crop (0−2.0 m min−1), planting density (0.2−1 time of standard planting density), and growth stage (maize from three−leaf to harvest period and wheat from regreening to maturity period). The results indicated that both the observation angle and planting density significantly affected the results of ultrasonic measurements (p-value&lt; 0.05), whereas the effects of other factors on measurement accuracy were negligible (p-value &gt; 0.05). Moreover, a double-input factor calibration model was constructed to assess canopy height under different years by utilizing the normalized difference vegetation index and ultrasonic measurements. The model was developed by employing the least-squares method, and ultrasonic measurement accuracy was significantly improved when integrating the measured value of canopy heights and the normalized difference vegetation index (NDVI). The maize measurement accuracy had a root mean squared error (RMSE) ranging from 81.4 mm to 93.6 mm, while the wheat measurement accuracy had an RMSE from 37.1 mm to 47.2 mm. The research results effectively combine stable and low-cost commercial sensors with ground-based agricultural machinery platforms, enabling efficient and non-destructive acquisition of crop height information

Effects of shading on photosynthetic characteristics of wax apple leaves

The wax apple (Syzygium samarangense) is a highly valuable fruit species in Southeast Asia. To regulate the fruiting season, shading is commonly used to induce flowering in wax apple. However, the effects of shading on the growth of wax apple is not well understood. To address this, we conducted a study analyzing the photosynthetic characteristics of wax apple leaves under 40% and 90% shading rates. Our findings revealed that shading had a significant impact on the photosynthesis and branching tip development of wax apple. During shading treatments, the chlorophyll contents of the leaves increased to enhance light absorption efficiency. In the 40% shading treatment, the primary factor causing the decrease in net photosynthetic rate was stomatal limitation, while in the 90% shading treatment, both stomatal and non-stomatal limitations contributed to the decrease in net photosynthetic rate. These results are indications that sheading plays a key role in chlorophyll and photosynthesis in wax apple. These results will have led to a new research direction for genetic crop improvement

Bijels stabilized using rod-like particles

Bicontinuous interfacially jammed emulsion gels, in short 'bijels', rely on a trapped layer of colloidal particles for their stability. These structures have traditionally been created using spherical colloidal particles. Here we show for the first time the use of rod-shape particles to stabilize bijels. We show that domain size decreases more rapidly with particle concentration in the case of rods compared to spheres. Large-scale analysis and detailed examination of images show that the packing fraction of rods is much higher than expected, in part, due to the role of 'flippers'.</p

Optimizing Center Pivot Irrigation to Regulate Field Microclimate and Wheat Physiology under Dry-Hot Wind Conditions in the North China Plain

The dry-hot wind climate is one of the major agro-meteorological disasters associated with high temperature, low humidity, and specific wind forces, which seriously affects the yield of wheat in the North China Plain. A field experiment was conducted to investigate the field microclimate, net photosynthetic rate, chlorophyll content of flag leaves, grain filling rate, and wheat yield after sprinkler misting under the condition of a dry-hot wind climate in the 2018 and 2019 seasons. Two travel speeds, full and half speed, and the corresponding irrigation amounts of 2.5 and 5 mm were used by a center pivot irrigation system during dry-hot wind conditions. A treatment without irrigation was applied as a control. The results showed that the air temperature and relative air humidity were greatly improved within 60 min after irrigation, especially in the upper part of the canopy. The net photosynthetic rate of flag leaves under 5 mm irrigation was higher than that under 2.5 mm irrigation during the middle and late grain filling periods. The adverse effects of dry-hot wind on the chlorophyll content of the flag leaves were mainly concentrated in the late grain filling stage. In the two years of the experiment, the average 1000-grain weights of 5 and 2.5 mm of irrigation treatments were 4.3 and 2.8% higher, and the grain yields were 5.8 and 3.3% higher, respectively, than those of the non-irrigated yields. Overall, applying a small amount of water between 12:00&ndash;14:00 with a center pivot before the occurrence of dry-hot wind is an effective means to regulate the field microclimate and produce more yield in the North China Plain