New Resistive Switching and Self-Regulating Heating in Foliated Graphite/Nickel Polyvinyl Chloride Nanocomposites

Polyvinyl chloride- (PVC-) based nanocomposites containing nanosized graphite and nickel nanoparticles (GN) as conductive fillers to achieve positive temperature coefficient of resistance (PTCR) thermistors and self-regulating heater function have been successfully fabricated. The microstructure of the foliated graphite and nanocomposites was examined by scanning electron microscopy (SEM). The effect of GN content on the static electrical conductivity, carrier's mobility, and number of charge carriers of the nanocomposites was studied. The applicability of nanocomposites as PTCR thermistors was examined by monitoring the conductivity as a function of temperature. It is found that the conduction mechanism in PVC/GN nanocomposites is governed by tunneling mechanism. Also, the applied voltage versus current and temperature were studied to check the applicability of composites as self-regulating heater. The results show that the PVC/GN nanocomposites might have potential applications in PTCR devices, self-regulating heater, and temperature sensors

Data Fitting to Study Ablated Hard Dental Tissues by Nanosecond Laser Irradiation.

Laser ablation of dental hard tissues is one of the most important laser applications in dentistry. Many works have reported the interaction of laser radiations with tooth material to optimize laser parameters such as wavelength, energy density, etc. This work has focused on determining the relationship between energy density and ablation thresholds using pulsed, 5 nanosecond, neodymium-doped yttrium aluminum garnet; Nd:Y3Al5O12 (Nd:YAG) laser at 1064 nanometer. For enamel and dentin tissues, the ablations have been performed using laser-induced breakdown spectroscopy (LIBS) technique. The ablation thresholds and relationship between energy densities and peak areas of calcium lines, which appeared in LIBS, were determined using data fitting. Furthermore, the morphological changes were studied using Scanning Electron Microscope (SEM). Moreover, the chemical stability of the tooth material after ablation has been studied using Energy-Dispersive X-Ray Spectroscopy (EDX). The differences between carbon atomic % of non-irradiated and irradiated samples were tested using statistical t-test. Results revealed that the best fitting between energy densities and peak areas of calcium lines were exponential and linear for enamel and dentin, respectively. In addition, the ablation threshold of Nd:YAG lasers in enamel was higher than that of dentin. The morphology of the surrounded ablated region of enamel showed thermal damages. For enamel, the EDX quantitative analysis showed that the atomic % of carbon increased significantly when laser energy density increased

The relation between the peak areas of calcium lines and energy densities.

<p>(a) calcium line peak area versus energy density for enamel (b) calcium line peak area versus energy density for dentin.</p

EDX spectra.

<p>(A) EDX spectrum of non-irradiated enamel tissue. (B) EDX spectrum of irradiated enamel tissue at energy density of 11.2 J/m².</p

SEM images.

<p>Enamel surface after ablation with Nd:YAG laser at energy density of 17.2 J/cm² and 100 shots.</p

Elements atomic % for non-irradiated and irradiated dentin tissue at energy densities of 5.6, 11.2, and 17.2 J/cm².

<p>Elements atomic % for non-irradiated and irradiated dentin tissue at energy densities of 5.6, 11.2, and 17.2 J/cm².</p

SEM images.

<p>dentin surface after ablation with Nd:YAG laser at energy density of 11.2 J/cm² and 100 shots.</p

Ca/P ratio for non-irradiated and irradiated enamel and dentin tissues at energy densities of 5.6, 11.2, and 17.2 J/cm².

<p>Ca/P ratio for non-irradiated and irradiated enamel and dentin tissues at energy densities of 5.6, 11.2, and 17.2 J/cm².</p

LIBS spectra of enamel and dentin laser ablation.

<p> The intensity in arbitrary units (a.u.) of calcium lines in the LIBS spectra of enamel and dentin Nd:YAG laser ablation.</p