Changes in surface energy and electrical conductivity of polyimide (PI)-based nanocomposite films filled with carbon nanotubes (CNTs) induced by UV exposure are gaining considerable interest in ...microelectronic, aeronautical, and aerospace applications. However, the underlying mechanism of PI photochemistry and oxidation reactions induced by UV irradiation upon the surface in the presence of CNTs is still not clear. Here, we probed the interplay between CNTs and PIs under UV exposure in the surface properties of CNT/PI nanocomposite films. Changes in contact angles and surface electrical conductivity at the surface of CNT/PI nanocomposite films after UV exposure were measured. The unpaired electron intensity of free radicals generated by UV exposure was monitored by electron paramagnetic resonance. Our study indicates that the covalent interactions between CNTs and radicals generated by UV irradiation on the PI surfaces tailor the surface energy and surface conductivity through anchoring radicals on CNTs. Surprisingly, adding CNTs into PI films exposed to UV leads to antagonistic contributions of dispersion and polar components to the surface energy. The surface electrical conductivity of the CNT/PI nanocomposite films has been improved due to an enhanced hopping behavior with dense π-conjugated CNT sites. To explain the observed changes in surface energy and surface conductivity of CNT/PI nanocomposite films induced by UV exposure, a qualitative model was put forward describing the covalent interactions between UV-induced PI free radicals and CNTs, which govern the chemical nature of surface components. This study is helpful for characterizing and optimizing nanocomposite surface properties by tuning the covalent interactions between components at the nanoscale.
Nonlinear absorption of suspensions of graphene nanosheets with the number of layers from one to three was studied using the Z-scan method with femtosecond excitation at 1030 nm wavelength. A large ...modulation depth and lower saturation intensity of the suspensions as compared with nonlinear absorption of single-layer graphene were shown. Dynamics of photoexcited carriers for different duration of excitation pulse was considered. The values of the absorption cross section and the density of photoexcited carriers in single-layer graphene were estimated. The presence of two-photon absorption (TPA) in suspensions of graphene nanosheets and the absence of noticeable TPA in single-layer graphene were shown.
A mixture of water suspensions of graphene oxide (GO) and polytetrafluoroethylene (PTFE) was used to make the films GO–PTFE (50:50). They became conductive (2.0–2.8 S/cm) while maintaining ...flexibility after reduction with hydrazine and subsequent annealing at 370 °C. The structure and morphology of the reduced films (rGO–PTFE) are examined in detail by means of a number of techniques such as scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Raman, and contact angle wetting. The results of the films tested as current collectors in a metal-free supercapacitor with electrodes from microwave exfoliated GO and an acid (1 M H2SO4) electrolyte are presented.
The nonlinear optical absorption of aqueous suspension with a few-layer (4–5 layers) molybdenum disulfide (MoS
2
) was investigated by Z- and P-scan methods using second harmonic generation from ...Yb-doped femtosecond pulsed laser. Two regions with different nature of the nonlinear absorption were registered when the intensity of the incident radiation increased from low to high values. The 3-level model for one-photon transitions in the few-layer MoS
2
was proposed for describing the experimental data. Absorption cross sections and relaxation times for interband and intraband transitions under femtosecond excitation on 514 nm have been estimated.
When nanocarriers are used for drug delivery they can often achieve superior therapeutic outcomes over standard drug formulations. However, concerns about their adverse effects are growing due to the ...association between exposure to certain nanosized particles and cardiovascular events. Here we examine the impact of intravenously injected drug-free nanocarriers on the cardiovasculature at both the systemic and organ levels. We combine in vivo and in vitro methods to enable monitoring of hemodynamic parameters in conscious rats, assessments of the function of the vessels after sub-chronic systemic exposure to nanocarriers and evaluation of the direct effect of nanocarriers on vascular tone. We demonstrate that nanocarriers can decrease blood pressure and increase heart rate in vivo via various mechanisms. Depending on the type, nanocarriers induce the dilation of the resistance arteries and/or change the responses induced by vasoconstrictor or vasodilator drugs. No direct correlation between physicochemical properties and cardiovascular effects of nanoparticles was observed. The proposed combination of methods empowers the studies of cardiovascular adverse effects of the nanocarriers.
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The thin MAPbI3 and MA0.15FA0.75Cs0.1PbI3 perovskite films have strong nonlinear absorption with coefficients of 443 ± 20 and 830 ± 50 cm GW–1, respectively, due to two-photon ...absorption at 1064 nm. The photochemical degradation of perovskite films was observed upon irradiation with femtosecond pulses at 532 nm, and the depth of photodegradation decreased in perovskite films protected with a PMMA polymer layer.
Ultrafast pulse generation in all-normal dispersion Yb-doped fiber laser on 1.04 μm have been reported. Stable self-starting pulse generation in output of the ring fiber laser have been investigated ...where nonlinear polarization rotation interacted with contribution from the single walled carbon nanotube saturable absorber. Laser pulses with 0.7 nJ pulse energy and 1.7 ps pulse width at 35.6 MHz repetition rate were achieved. The output pulse could be externally compressed to width of 180 fs by pair of gratings.
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