Zeng Fan

Post-Treatments for Multifunctional Property Enhancement of Carbon Nanotube Fibers from the Floating Catalyst Method.

We investigated the effects of the synthesis conditions and condensation processes on the chemical compositions and multifunctional performance of the directly spun carbon nanotube (CNT) fibers. On the basis of the optimized synthesis conditions, a two-step post-treatment technique which involved acidification and epoxy infiltration was also developed to further enhance their mechanical and electrical properties. As a result, their tensile strength and Youngs modulus increased remarkably by 177% and 325%, respectively, while their electrical conductivity also reached 8235 S/cm. This work may provide a general strategy for the postprocessing optimization of the directly spun CNT fibers. The treated CNT fibers with superior properties are promising for a wide range of applications, such as structural reinforcements and lightweight electric cables.

Significant Enhancement in the Thermoelectric Properties of PEDOT:PSS Films through a Treatment with Organic Solutions of Inorganic Salts

UNLABELLED Conducting polymers have promising thermoelectric application because they have many advantages including abundant elements, mechanical flexibility, and nontoxicity. The thermoelectric properties of conducting polymers strongly depend on their chemical structure and microstructure. Here, we report a novel and facile method to significantly enhance the thermoelectric properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) films through a treatment with organic solutions of inorganic salts. N,N-Dimethylformamide (DMF) and a common inorganic salt like zinc chloride (ZnCl2) are used as the solvent and solute of the solutions, respectively. The treatments can significantly increase both the Seebeck coefficient and electrical conductivity of the PEDOT PSS films. The thermoelectric properties of the PEDOT PSS films are sensitive to the experimental conditions, such as the salt concentration, treatment temperature, and the cation of the salts. After treatment at the optimal experimental conditions, the PEDOT PSS films can exhibit a Seebeck coefficient of 26.1 μV/K and an electrical conductivity of over 1400 S/cm at room temperature. The corresponding power factor is 98.2 μW/(m·K(2)). The mechanism for the enhancement in the thermoelectric properties is attributed to the segregation of some PSSH chains from PEDOT PSS and the conformation change of PEDOT chains as a result of the synergetic effects of inorganic salts and DMF.

Higher PEDOT Molecular Weight Giving Rise to Higher Thermoelectric Property of PEDOT:PSS: A Comparative Study of Clevios P and Clevios PH1000

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising candidate as the next-generation thermoelectric (TE) material. Its TE properties are strongly dependent on its chemical and electronic structures. In this paper, we investigated the effect of PEDOT molecular weight on the TE properties of PEDOT:PSS films by a comparative study on two commercial grades of PEDOT:PSS, Clevios P, and Clevios PH1000. Dynamic light scattering (DLS) and Raman spectra imply that the PEDOT of Clevios PH1000 possesses longer conjugated chains than that of Clevios P. The TE properties of both the Clevios P and Clevios PH1000 films can be significantly enhanced through various post treatments, including solvent treatment, germinal diol treatment, organic solution treatment, and acid treatment. After these treatments, the treated Clevios PH1000 films constantly show both superior Seebeck coefficients and electrical conductivities over the treated Clevios P films. It is attributed to the higher molecular weight of PEDOT for the former than the latter. For the treated Clevios PH1000, longer PEDOT chains result in large PEDOT domains, facilitating the charge conduction a semimetallic behavior. Tuning the oxidation level of PEDOT:PSS is a facile way to enhance their TE property. A base treatment with sodium hydroxide was subsequently performed on both the treated Clevios P and Clevios PH1000 films. The power factors of both grades of PEDOT:PSS films were remarkably increased by a factor of 1.2-3.6. Still, both the conductivity and the Seebeck coefficient of a based-treated Clevios PH1000 film are superior over those of a control Clevios P film. The highest power factor the former is 334 μW/(m K2) for the former while only 11.4 μW/(m K2) for the latter. They are different by a factor of about 30 times.

Continuous Carbon Nanotube-Based Fibers and Films for Applications Requiring Enhanced Heat Dissipation

The production of continuous carbon nanotube (CNT) fibers and films has paved the way to leverage the superior properties of individual carbon nanotubes for novel macroscale applications such as electronic cables and multifunctional composites. In this manuscript, we synthesize fibers and films from CNT aerogels that are continuously grown by floating catalyst chemical vapor deposition (FCCVD) and measure thermal conductivity and natural convective heat transfer coefficient from the fiber and film. To probe the mechanisms of heat transfer, we develop a new, robust, steady-state thermal characterization technique that enables measurement of the intrinsic fiber thermal conductivity and the convective heat transfer coefficient from the fiber to the surrounding air. The thermal conductivity of the as-prepared fiber ranges from 4.7 ± 0.3 to 28.0 ± 2.4 W m(-1) K(-1) and depends on fiber volume fraction and diameter. A simple nitric acid treatment increases the thermal conductivity by as much as a factor of ∼3 for the fibers and ∼6.7 for the thin films. These acid-treated CNT materials demonstrate specific thermal conductivities significantly higher than common metals with the same absolute thermal conductivity, which means they are comparatively lightweight, thermally conductive fibers and films. Beyond thermal conductivity, the acid treatment enhances electrical conductivity by a factor of ∼2.3. Further, the measured convective heat transfer coefficients range from 25 to 200 W m(-2) K(-1) for all fibers, which is higher than expected for macroscale materials and demonstrates the impact of the nanoscale CNT features on convective heat losses from the fibers. The measured thermal and electrical performance demonstrates the promise for using these fibers and films in macroscale applications requiring effective heat dissipation.

Recent Development of Thermoelectric Polymers and Composites

Thermoelectric materials can be used as the active materials in thermoelectric generators and as Peltier coolers for direct energy conversion between heat and electricity. Apart from inorganic thermoelectric materials, thermoelectric polymers have been receiving great attention due to their unique advantages including low cost, high mechanical flexibility, light weight, low or no toxicity, and intrinsically low thermal conductivity. The power factor of thermoelectric polymers has been continuously rising, and the highest ZT value is more than 0.25 at room temperature. The power factor can be further improved by forming composites with nanomaterials. This article provides a review of recent developments on thermoelectric polymers and polymer composites. It focuses on the relationship between thermoelectric properties and the materials structure, including chemical structure, microstructure, dopants, and doping levels. Their thermoelectric properties can be further improved to be comparable to inorganic counterparts in the near future.

Stretchable heaters with composites of an intrinsically conductive polymer, reduced graphene oxide and an elastomer for wearable thermotherapy

Thermal therapy is an effective physical treatment method for arthritis, stiff muscles, joint injuries, and injuries to the deep tissue of skin. Stretchable or even wearable electric heaters with uniform heating behavior are regarded as the next-generation electronic devices, which have been extensively studied for the personal thermal management and healthcare purpose. In this work, highly stretchable electrothermal heaters were developed by using composites of intrinsically conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS), elastomeric waterborne polyurethane (WPU) and reduced graphene oxide (rGO). rGO was mixed into the PEDOT:PSS/WPU blends to improve the temperature uniformity because rGO has high thermal conductivity while the polymers have very low thermal conductivity. The PEDOT:PSS/WPU/1 wt% rGO composite film exhibits an electrical conductivity of 18.2 S cm−1 and an elongation at break of 530%. The electrothermal performances of the polymer heaters were investigated with respect to the applied voltage, tensile strain, and the voltage on/off cycling process. The heater shows stable heating behavior under repetitive voltage on/off cycles, and the temperature remains almost unchanged under a tensile strain of up to 30%. The devices can be comfortably attached to the skin of humans, for example on the wrist, and they exhibit a uniform and stable heating profile even under mechanical disturbance. Due to their outstanding stretchability, biocompatibility, desirable electrical and thermal conductivities, the WPU/PEDOT:PSS/rGO composites can be used in wearable and long-term thermotherapy applications.

Advanced properties of multiwalled carbon nanotube elastomer composites

Multiwalled nanotube (MWNT)/fluoroelastomer (FKM) composites were synthesised through a simple and cost efficient method. MWNTs were dispersed in the FKM by an open two-roll mill followed by vulcanisation inside a compression moulding machine. The morphologies and rheological and mechanical properties of the MWNT/FKM composites with different MWNT mass fractions were systematically investigated. Compared with the carbon black (CB)/FKM composites fabricated via the same method, the MWNT/FKM composites demonstrated higher degree of crosslinking and better mechanical properties. By adding 5 wt-% MWNTs in the FKM matrix, the hardness, tensile strength and abrasion resistance of the FKM were significantly improved by 12, 120 and 13% respectively. Compared to CB, MWNTs show higher reinforcing efficiency due to their higher aspect ratio and surface area that result in higher crosslink density and stronger filler–polymer interaction.