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Electrical Permittivity and Conductivity of a Graphene Nanoplatelet Contact in the Microwave Range
摘要： This paper investigates the electrical properties in the microwave range of a contact made by graphene nanoplatelets. The final goal is that of estimating the range of values for the equivalent electrical complex permittivity of a contact obtained by integrating low-cost graphene in the form of nanoplatelets (GNPs) into a high-frequency electrical circuit. To this end, a microstrip-like circuit is designed and realized, where the graphene nanoplatelets are self-assembled into a gap between two copper electrodes. An experimental characterization is carried out, both to study the structural properties of the nanomaterials and of the realized devices, and to measure the electromagnetic scattering parameters in the microwave range by means of a microstrip technique. A full-wave electromagnetic model is also derived and used to investigate the relationship between the measured quantities and the physical and geometrical parameters. The combined use of the experimental and simulation results allows for retrieving the values of the equivalent complex permittivity. The equivalent electrical conductivity values are found to be well below the values expected for isolated graphene nanoplatelets. The real part of the electrical relative permittivity attains values comparable to those obtained with GNP nanocomposites.
关键词： nanocomposite,permittivity,scattering parameters,graphene nanoplatelets
更新于2025-09-23 15:23:52
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Achieving high yield of graphene nanoplatelets in poloxamer-assisted ultrasonication of graphite in water
摘要： The role of surfactant (Pluronic? F 127) concentration on the yield and morphological characteristics of graphene nanoplatelets (GNPs) produced from the sonication of aqueous graphene suspensions is investigated in this work. By employing a wide surfactant concentration range (0.1–15 wt%) and sonication power densities up to 420 W L?1 we identify two graphene exfoliation regimes: the first occurs at low sonication power densities (<340 W L?1) and produces GNPs with sizes 200–300 nm, aspect ratios between 70 and 100, and concentrations up 1 mg mL?1. In that regime, the surfactant concentration has no effect on the exfoliation results. In the second exfoliation regime (>340 W L?1), surfactant concentrations greater than 10 wt% produce dramatic increases in GNP yields, namely up to 3.0 mg mL?1, and overall larger GNPs (350–500 nm) with smaller aspect ratios (5–60). We attribute these changes to the onset of a more energy intensive mechanism, termed cleavage. Cleavage involves the separation of graphite clusters in sub-bulk multi-layered graphene entities, as opposed to exfoliation, which involves the separation of individual or few-layer GNPs. Choosing an exfoliation regime by tuning simple process parameters enables control over the yield, size and morphology of the produced GNPs.
关键词： Poloxamer,Graphite exfoliation,Surfactant-assisted exfoliation,Ultrasonication,Graphene nanoplatelets
更新于2025-09-23 15:22:29
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Synthesis of electrospun nanofibrous structures with controlled optical and electrical properties
摘要： In this study, the optical and electrical influences of 2D graphene flakes in electrospun polycaprolactone (PCL) fibers were observed. Graphene nanoplatelets were added in different concentrations into the PCL solution, and then, using the electrospinning technique, fibers were built from that solution. Three samples were prepared with different graphene concentrations of 0% w/w, 0.5% w/w, and 2.0% w/w. From all three samples, fibers were prepared and tests were conducted for the identification of the properties of fibers. An optical spectroscopy test was performed to identify the optical behavior of the fibers. Scanning electron microscopy tests were conducted for the morphological characterization of the fibers. For the comparison of the electrical conductivity of the three samples, electrical tests were also conducted. In addition, Raman spectroscopy was conducted to characterize the graphene and PCL. This study shows that using graphene can change the properties of fibers, for example, as the graphene content increases, the fiber diameter also increases. Also, by varying the 2D graphene concentration, both electrical and optical properties can be tuned; this can be utilized in the synthesis of nanosensing surfaces and structures.
关键词： polycaprolactone,graphene nanoplatelets,optical properties,electrical properties,electrospun nanofibrous structures
更新于2025-09-23 15:19:57
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AIP Conference Proceedings [Author(s) 6TH INTERNATIONAL CONFERENCE ON PRODUCTION, ENERGY AND RELIABILITY 2018: World Engineering Science & Technology Congress (ESTCON) - Kuala Lumpur, Malaysia (13–14 August 2018)] - Development of nanocomposites on the basis of graphene nanoplatelets
摘要： The prospects for using a phenol-formaldehyde resin (PFR) as a reactive surfactant in the preparation of highly concentrated dispersions of carbon nanostructured materials (up to 1 %) are considered in the present paper. Modifying graphene nanoplatelets (GNPs) with this surfactant promotes the effect of targeted self-assembly of carbon nanoparticles in solution (with decreasing pH), which makes it possible to obtain nanocomposites with improved properties. It is important that the use of highly concentrated dispersions of PFR-modified GNPs in the production of nanocomposite materials does not require a preliminary removal of the surfactant. Based on the resulting dispersion, the mesoporous carbon/GNPs composite with a developed surface (3000 ? 4000 m2 g?1) was successfully synthesized. It can be used as an electrode material for supercapacitors and an adsorbent of organic and inorganic species for wastewater treatment purposes.
关键词： graphene nanoplatelets,reactive surfactant,self-assembly,nanocomposites,mesoporous carbon,phenol-formaldehyde resin
更新于2025-09-10 09:29:36
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Roll-to-Roll (R2R) Production of Ultrasensitive, Flexible, and Transparent Pressure Sensors Based on Vertically Aligned Lead Zirconate Titanate and Graphene Nanoplatelets
摘要： Despite extensive advances in the use of piezoelectric materials in flexible electronics, they have numerous shortcomings, including low efficiency, limited flexibility, and lack of transparency. Additionally, the production of these materials is often limited to small batch processes which are difficult to scale up for mass production. A novel method to produce ultrasensitive, high performance, flexible, and transparent piezoelectric materials where both lead zirconate titanate nanoparticles, and graphene nanoplatelets are aligned together in polydimethylsiloxane under an AC electric field in the thickness (“Z”) direction, is reported here for the first time. The electric field alignment improves the piezoelectric response along with transparency and also reduces the amount of filler required to achieve outstanding piezoelectric properties. The resulting ultrasensitive piezoelectric film is able to sense the pressure of a bird feather (1.4 mg) dropped from a certain distance, whereas at the touch of a fingertip, it can generate up to 8.2 V signal. Moreover, the mass production compatibility of the system is also demonstrated by producing a 3 m long and 15 cm wide large-area sample via a novel 44′ long roll-to-roll manufacturing line which is designed and developed by the group.
关键词： piezoelectric pressure sensor,flexible and transparent sensors,electric field–induced alignment,roll-to-roll manufacturing,PZT and graphene nanoplatelets
更新于2025-09-10 09:29:36
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Photo-oxidation of polypropylene/graphene nanoplatelets composites
摘要： The photo-oxidation behaviour of polymer nanocomposites depends not only on the photo-oxidation behaviour of the matrix, but also on the chemical composition, on the physical properties of the nanoparticles and on the possible interactions between the two phases. In the case of nanocomposites with carbonaceous particles, the main effect is a photo-stabilization due to the absorption of the UV energy and the radical scavenging action. In this work we investigated the effect of the presence of graphene nanoplatelets on the photo-oxidation behaviour of the polypropylene. The presence of the graphene nanoplatelets improves the photo-resistance of the polypropylene and this effect increases with the graphene content. This behaviour has been correlated with the exposed surface of the graphene and not to the dimensions of the graphene nanoplatelets.
关键词： Graphene nanoplatelets (GnP),Polypropylene,Photo-oxidation,Nanocomposites
更新于2025-09-04 15:30:14