Current Nanoscience - Volume 7, Issue 5, 2011

Ag nanofluids with different concentration (0.03˜ 0.12vol%) were prepared by dispersing chain-like Ag clusters into ethylene glycol. The thermal conductivity and rheological behaviors of the Ag nanofluids were investigated at temperatures ranging from room temperature (15.8 °C) to 65 °C. The results show that the Ag nanofluids is Newtonian flow. The relative viscosity of the Ag nanofluids increases with the raise of particle volume fraction and is independent of temperature. The effective thermal conductivity of the Ag nanofluids increases with the particle volume fraction and temperature. It implies that the Ag nanofluids are better than the base fluid as heat transfer fluids especially in high temperature conditions. The viscosity and effective thermal conductivities of the Ag nanofluids can not be predicted by present models, and more work is needed to be done in the future.

In this work, the Fe3O4 magnetic nanoparticles with different shapes and average sizes of 15 to 180 nm were synthesized by an electrooxidation method, the size and shape of the particles were experimentally controlled by tuning the parameters of potential and electrolyte temperature, and its structure was conducted by XRD, forming the Fe3O4 phase. FT-IR confirmed that the stabilizer molecules can cover the particle surfaces. The resultant TEM and SEM showed that the particles have polycrystalline structure, and their size, shapes and surface morphology change dramatically under different potentials and temperatures. Also the particle size dependency was obtained by using UV-Vis spectroscopy, indicating that their maximum absorption wavelength and peak width decrease with increasing temperature and potential.

The Physic Nut seed oil extracted by screw pressing was assayed for free radical scavenging activity by DPPH and tyrosinase inhibition activity by the dopachrome methods. The oils gave both activities similar to vitamin C. The maximum loading of the oil in niosomes composed of Tween 61/cholesterol at 3:7 molar ratio prepared by chloroform film method with sonication was 1%w/v. The niosomes were stable at 28°C for 8 weeks with an average size determined by dynamic light scattering (DLS) of about 120 nm. The oil entrapped in niosomes gave higher scavenging and tyrosinase inhibition activity than the unentrapped oil of about 3-5 and 1-2 times (p < 0.1), respectively. This study has indicated the potential enhancement of free radical scavenging activity and tyrosinase inhibition activity of Physic Nut oil by entrapping in niosomes.

The two important controllable parameters in the dip-pen nanolithography (DPN) process, such as writing temperature and velocity, are used to investigate the related effects on mechanisms of transference of alkanethiol self-assembled monolayer (SAM), transfer number, gasification number, and nanowire formation using molecular dynamics simulations. The simulated results show that the molecular transport ability during the direct-write process from the tip to the substrate is dependent on writing temperature and velocity, because the molecules have high kinetic energy and undergo fast diffusion when the temperature is increased; high transfer ability occurs at a slow writing velocity. The nanowire thickness and length increase significantly with increasing writing temperature, and its length increases much faster than its thickness (height). When the writing temperature is increased, transfer number and gasification number of the molecules become dramatically larger. The transfer number of ink molecules increases with decreasing writing velocity.