Maria Sarno

Multiwalled carbon nanotube films as small-sized temperature sensors

We present the fabrication of thick and dense carbon nanotube networks in the form of freestanding films (CNTFs) and the study of their electric resistance as a function of the temperature, from 4 to 420 K. A nonmetallic behavior with a monotonic R(T) and a temperature coefficient of resistance around −7×10−4 K−1 is generally observed. A behavioral accordance of the CNTF conductance with the temperature measured by a solid-state thermistor (ZnNO, Si, or Pt) is demonstrated, suggesting the possibility of using CNTFs as temperature small-sized (freely scalable) sensors, besides being confirmed by a wide range of sensitivity, fast response, and good stability and durability. Concerning electric behavior, we also underline that a transition from nonmetal to metal slightly below 273 K has been rarely observed. A model involving regions of highly anisotropic metallic conduction separated by tunneling barrier regions can explain the nonmetallic to metallic crossover based on the competing mechanisms of the metal...

Controlled growth of CNT in mesoporous AAO through optimized conditions for membrane preparation and CVD operation.

Anodic aluminium oxide (RAAO) membranes with a mesoporous structure were prepared under strictly controlling experimental process conditions, and physically and chemically characterized by a wide range of experimental techniques. Commercial anodic aluminium oxide (CAAO) membranes were also investigated for comparison. We demonstrated that RAAO membranes have lower content of both water and phosphorus and showed better porosity shape than CAAO. The RAAO membranes were used for template growth of carbon nanotubes (CNT) inside its pores by ethylene chemical vapour deposition (CVD) in the absence of a catalyst. A composite material, containing one nanotube for each channel, having the same length as the membrane thickness and an external diameter close to the diameter of the membrane holes, was obtained. Yield, selectivity and quality of CNTs in terms of diameter, length and arrangement (i.e. number of tubes for each channel) were optimized by investigating the effect of changing the experimental conditions for the CVD process. We showed that upon thermal treatment RAAO membranes were made up of crystallized allotropic alumina phases, which govern the subsequent CNT growth, because of their catalytic activity, likely due to their Lewis acidity. The strict control of experimental conditions for membrane preparation and CNT growth allowed us to enhance the carbon structural order, which is a critical requisite for CNT application as a substitute for copper in novel nano-interconnects.

Carbon nanotube induced structural and physical property transitions of syndiotactic polypropylene

In this paper we have studied the effect of increasing carbon multi-walled nanotube (CNT) concentration in composites of syndiotactic polypropylene (sPP) having the same crystalline form but different morphologies. The attention was focused on the form I of sPP with different degrees of perfection (in terms of percentages of chains in helical conformation, crystal dimensions and crystallinity) obtained using two different quenching temperatures from the melt, i.e. 25 and 100 °C. We observed a decreasing effect of the crystallization temperature on increasing the nanotube content up to the samples with 10% of CNT, that show a very similar structural organization independent of the undercooling. Only the amorphous phase turns out more relaxed in the samples crystallized at the highest temperature. Either the thermal or the mechanical properties are improved on increasing the CNT content in both series of samples. The electrical conductivity increases in a similar manner in both series of samples and between 1 and 3 wt% it shows a sizable step of about eight orders of magnitude, a phenomenon that can be regarded as the onset of a percolating structure for which charge transport may take place.

Graphene Oxide Nanosheets as Effective Friction Modifier for Oil Lubricant: Materials, Methods, and Tribological Results

The tribological behaviour of graphene oxide nanosheets in mineral oil was investigated under a wide spectrum of conditions, from boundary and mixed lubrication to elastohydrodynamic regimes. A ball-on-disc setup tribometer has been used to verify the friction reduction due to nanosheets prepared by a modified Hummers method and dispersed in mineral oil. Their good friction and antiwear properties may possibly be attributed to their small structure and extremely thin laminated structure, which offer lower shear stress and prevent interaction between metal interfaces. Furthermore, the results clearly prove that graphene platelets in oil easily form protective film to prevent the direct contact between steel surfaces and, thereby, improve the frictional behaviour of the base oil. This evidence is also related to the frictional coefficient trend in boundary regime.

New 'chimie douce' approach to the synthesis of hybrid nanosheets of MoS2 on CNT and their anti-friction and anti-wear properties.

Hybrid organic-inorganic oleylamine@MoS2-CNT nanocomposites with different compositions were obtained by thermal decomposition of tetrathiomolybdate in the presence of oleylamine and high quality multiwalled carbon nanotubes (CNTs) previously prepared by the CCVD technique. The nanocomposite samples were characterized by the TEM, SEM TG-MS, Raman and XRD techniques and successfully tested as anti-friction and anti-wear additives for grease lubricants.

Graphene-based structural adhesive to enhance adhesion performance

This paper proposes the design of a new graphene nano-modified formulation to enhance the mechanical performance of structural adhesives. Well-characterized graphene platelets, produced through an effective approach for bulk production and morphology control, were embedded at different contents inside an epoxy adhesive based on tetraglycidylmethylene dianiline (TGMDA). The adhesive formulations were used to manufacture bonded joints, according to ASTM 2095, to analyze the effect of graphene platelets on the tensile strength of the joints. The effect of incorporating graphene in the adherents was also considered. Epoxy adhesives filled with graphene at a concentration of 1 wt% significantly enhanced the mechanical behavior of the bonded joints. Only in the case of unfilled adherents, the inclusion of 4 wt% graphene did not have a significant effect on the mechanical performance. This is likely due to the agglomeration of nanofillers causing heterogeneity in large domains at the interface between adherents and adhesives. The effect of graphene incorporation in the adherents, acting on the chemical compatibility between adhesives and adherent surfaces, led to a considerable increase in tensile strength in comparison with the corresponding joints with unfilled adherents. This beneficial effect is most probably due to the cumulative effects of intermolecular interactions between the graphene platelets and resin networks.

Preparation and Physical Properties of Carbon Nanotubes–PVA Nanocomposites

Nanocomposite materials were prepared by incorporating multiwall carbon nanotubes (MWNTs), obtained by acetylene catalytic chemical vapor deposition (CCVD) on Co/Fe‐modified MgO, within poly(vinyl alcohol) (PVA). Before incorporation, nanotubes were oxidized to obtain better compatibilization with the polymer. It has been found that the addition of COOH‐functionalized and purified MWNTs improves the mechanical response, increases the glass transition temperature, and delays the thermal oxidation of PVA. Furthermore, the PVA crystallinity seems to be enhanced by the presence of nanotubes.

CNTs tuning and vertical alignment in anodic aluminium oxide membrane

Abstract Anodic aluminium oxide (AAOM) membranes were used for template growth of carbon nanotubes (CNT) inside their pores by chemical vapour deposition (CVD) of different hydrocarbons, in the absence of transition metal catalyst. A composite material, containing one nanotube for each channel, having the same length as the membrane thickness and the external diameter close to the diameter of the membrane holes, was obtained. Yield, selectivity, and quality of CNTs in terms of diameter (up to very thin CNT), carbon order, length, arrangement (i.e. number of tubes for each channel), purity, that are critical requisites for several applications were optimized by investigating the effect of changing the hydrocarbon feedstock gas, also in the presence of hydrogen. The samples produced using methane as a feedstock have a well ordered structure. The role of the alumina channels surface during the CNT growth has been investigated and its catalytic activity has been proved for the first time.

Influence of the catalyst-nanotube spacing on the synthesis of polymer-functionalized multiwalled carbon nanotubes by “grafting from” approach

Polynorbornene-functionalized multiwalled carbon nanotubes (MWCNTs) were prepared by a “grafting from” approach, on varying the catalyst-MWCNT spacing to evaluate the influence of the starting catalyst-MWCNT distance on the polymerization efficiency. In particular, 2nd generation Grubbs catalysts and Hoveyda-Grubbs catalysts, both active in the ring opening metathesis polymerization of olefins, were grafted on MWCNTs at 8 to 12 atom spacing from the nanotube surface, and the activity of initiators was tested in the 2-norbornene polymerization. According to our results, initiator performances depend (i) on the length of the arm connecting the catalyst to the MWCNTs, being initiators with longer arms more efficient, and (ii) on the class of Ru catalysts, being Hoveyda-Grubbs catalysts surprisingly more active at room temperatures than 2nd generation Grubbs catalysts. High fractions (80–95 wt%) of polymer covalently bound to the nanotubes in the MWCNT-grafted polynobornene obtained composites were achieved.

Real time radiation dosimeters based on vertically aligned multiwall carbon nanotubes and graphene

Measurements of the absorbed dose and quality assurance programs play an important role in radiotherapy. Ionization chambers (CIs) are considered the most important dosimeters for their high accuracy, practicality and reliability, allowing absolute dose measurements. However, they have a relative large physical size, which limits their spatial resolution, and require a high bias voltage to achieve an acceptable collection of charges, excluding their use for in vivo dosimetry. In this paper, we propose new real time radiation detectors with electrodes based on graphene or vertically aligned multiwall carbon nanotubes (MWCNTs). We have investigated their charge collection efficiency and compared their performance with electrodes made of a conventional material. Moreover, in order to highlight the effect of nanocarbons, reference radiation detectors were also tested. The proposed dosimeters display an excellent linear response to dose and collect more charge than reference ones at a standard bias voltage, permitting the construction of miniaturized CIs. Moreover, an MWCNT based CI gives the best charge collection efficiency and it enables working also to lower bias voltages and zero volts, allowing in vivo applications. Graphene based CIs show better performance with respect to reference dosimeters at a standard bias voltage. However, at decreasing bias voltage the charge collection efficiency becomes worse if compared to a reference detector, likely due to graphenes semiconducting behavior.