سال:1386 | دوره: | شماره: |تعداد مقالات:7

In spite of the fact that cementitious and concrete materials are mainly used on a large scale and in huge quantities for roads, dams, bridges and building constructions, the mechanical behavior of these materials depends to a great extend on structural elements and phenomena which are effective on a micro and nanoscale. Although this is well known by researchers, material producers and engineers for many years, the aspect of nanoscience and nanotechnology has hardly found any special attention, so far. New efforts and possibilities of material engineering on nanoscale in other fields may well lead to a new leap forward to improve mechanical and physical properties as well as durability of this important group of composite construction materials. This paper intends to stimulate the application and development of nanoscientific and nanotechnological concepts of nanofiber materials and their applications in concrete. Due to the wide range of possibilities, however, it does not claim to present a complete overview of the whole field. This would clearly go beyond the scope of this paper. It rather gives a short outline on the related cementitious and concrete material problems and research topics where nanoscience and nanotechnology could produce a major contribution to improve the nanofibrous materials where research needs to be done. Capability to accurately predict failure in joints offers significant potential for developing higher performance structural designs that are safer at the same time since these nanotubes can be used to accurately assess the behavior of joints, members and structures. Nanofibrous cement based materials can monitor regions of partial damages, localized changes in strains, stresses and temperatures of any joints and members.

In this investigation the silicate nano structure of MCM-41 has been used for the production of nanofluid. The particles have negligible heat conductivity and therefore by their dispersion in a base fluid like water, it is possible to study the increase of heat conductivity due to the Brownian motion effects. In this work a suitable apparatus for the measurement of heat conductivity has been built and calibrated and then using the apparatus and preparing suitable nanofluids, the conductivity and the volumetric heat capacities have been measured. Experimental results show that the preparation time of the nanofluid using the ultrasonic method has pronounced effect on the increase of the conductivity. A twenty four hours preparation time for the nanofluid containing 2.5% (vol) of the particles results in a 7% increase in the conductivity of the base fluid while showing no significant increase in the volumetric heat capacity. Investigating the effect of increasing the temperature and volumetric percentage of the particles it can be deduced that Brownian nano particles movement is one of the main factors in increasing the thermal nanofluids conductivity.

Diamondoids are cage-like saturated hydrocarbons consisting of fused cyclohexane rings. The Diamondoids family of compounds is one of the best candidates for molecular building blocks (MBBs) in nanotechnology to construct organic nanostructures compared to other MBBs known so far. The challenge is to find a route for self-assembly of these cage hydrocarbons and their applications in the bottom-up synthesis. In this paper, a DNA-based self-assembly technique called “DNA Bridge-based Self-assembly” (DBS) is introduced to self-assemble the diamondoid molecules based upon a bottomup strategy. The results of our computations and simulations with different molecular mechanical force fields (MM+, AMBER, BIO+, and OPLS) and different optimization algorithms (Polak-Ribiere, Fletcher- Reeves, and block-diagonal Newton-Raphson) furthermore confirm the feasibility of the formation of such hybrid nanoarchitecture.

Due to unique applications of palladium nanoparticles, synthesis of these nanoparticles by a simple and low cost method is very important. In this work, Pd nanoparticles were synthesized with narrow size distribution by loading metal salt (Pd(OAc)2) into the polymeric matrix (PEG) as reducing agent and stabilizer. Also, the effect of metal salt concentration and PEG molecular weight on the conversion of Pd 2+ to nano Pd0 and synthesized palladium nanoparticles morphology were investigated by UV-vis spectroscopy, XRD and TEM. The UV results confirmed the significant effect of PEG molecular weight on the reduction reactivity of polymeric matrix. Also, TEM and XRD results revealed that metal salt concentration has significant effect on the synthesized Pd nanoparticles size.

Porous silicon layers have been prepared from n-type silicon wafers of (100) orientation. SEM, FTIR and PL have been used to characterize the morphological and optical properties of porous silicon. The influence of varying etching time in the anodizing solution, on structural and optical properties of porous silicon has been investigated. It is observed that pore size increases with etching time and attain maximum for 20 minutes and then decreases. The PL spectrum peak shifts towards the higher energy side, which supports the quantum confinement effect in porous silicon. The FTIR shows that the Si-Hn peaks are observed at the surface of the PS layer and these chemical species also give raise the PL in PS.

Cadmium sulfide nanoparticles were grown using wet chemical method by dissolving the reactants of cadmium acetate and sodium sulfide in the presence of thioglycerol (TG) as capping agent in ethanol solvent. Different nanoparticle sizes and size distribution were obtained through varying the molarities of thioglycerol. At higher TG concentration, synthesis provides a nearly monodisperse nanoparticles. Also this method reveals high stability of nanoparticles in ethanol solvent. Samples properties were investigated using UV-VIS absorption, photoluminescence spectroscopy and X-ray diffraction (XRD) methods.

In the present investigation efforts have been made to synthesis polyvinyl pyridine (PvPy) /C60 conjugates through 2, 2-azobisisobutyronitrile (AIBN) initiated insitu polymerization of PvPy in scCO2.The process of synthesis was monitored under different reaction conditions ranging 1200-1800psi, 60-90°C over 6 hours. The progress of polymerization was monitored rheoviscometrically. The concentration of PvPy and AIBN ranging 6.95-20.85*10-3 and 304.50-931.50*10-3 afforded PvPy/C60 conjugates in the yield (%) ranging 10.30-48.8. Selected PvPy/C60 conjugates were characterized through UV-VIS spectra, scanning electron microscopy, gel permeation chromatography and solution rheoviscometery.