Properties of Nanoparticles PDF

PROPERTIES OF NANOPARTICLES Materials when reduced to nanosize display very different properties. Opaque substances become transparent Eg. Cu Inert materials become catalyst. Eg. Pt, Au Insulators become conductors Eg. Si Insulators and conductors totally depend on the bandgap between their valence...

PROPERTIES OF NANOPARTICLES Materials when reduced to nanosize display very different properties. Opaque substances become transparent Eg. Cu Inert materials become catalyst. Eg. Pt, Au Insulators become conductors Eg. Si Insulators and conductors totally depend on the bandgap between their valence band and conduction band Grain size becomes 1 to 100nm These materials are exceptionally strong, hard, ductile at high temperature. Materials are wear-resistant, erosion-resistant, corrosion-resistant and chemically very reactive. 5 properties are involved Optical Magnetic Mechanical Electrical Chemical  For small (~30 nm) monodisperse gold nanoparticles, the surface plasmon resonance phenomenon causes an absorption of light in the blue-green portion of the spectrum (~450 nm) while red light (~700 nm) is reflected, yielding a rich red color Nano gold can look red, orange, or even blue! The color depends on the size and shape of the nanoparticles, as well as the distance between them. Here, the red nano gold particles are about 20 nanometers across, while the orange nano gold particles are about 80 nanometers across. Silver nanoparticles absorb and scatter light with extraordinary efficiency. Their strong interaction with light occurs because the conduction electrons on the metal surface undergo a collective oscillation when they are excited by light at specific wavelengths. This oscillation is known as a surface plasmon resonance (SPR), and it causes the absorption and scattering intensities of silver nanoparticles to be much higher than identically sized non-plasmonic nanoparticles. Silver nanoparticle absorption and scattering properties can be tuned by controlling the particle size, shape, and the local refractive index near the particle surface. The Effect of Size on Optical Properties The optical properties of spherical silver nanoparticles are highly dependent on the nanoparticle diameter. The extinction spectra of 10 sizes of NanoXact Silver nanoparticles at identical mass concentrations (0.02 mg/mL) are displayed in the figure below. Smaller nanospheres primarily absorb light and have peaks near 400 nm, while larger spheres exhibit increased scattering and have peaks that broaden and shift towards longer wavelengths (known as red-shifting). Paramelle et al. (2014) have published a paper using nanoComposix silver nanoparticles that corroborates our data (extensive supplementary information available here). Extinction (the sum of scattering and absorption) spectra of NanoXact silver nanoparticles with diameters ranging from 10 - 100 nm at mass concentrations of 0.02 mg/mL. BioPure nanoparticles have optical densities that are 50-times larger.)  ELECTRICAL PROPERTIES Electrical properties: Depend on number of free electrons, collision of electrons and dimensions of material. At the nanoscale, the dimensions are altered. There is a sharp decrease in dimensions in the nanoscale that leads to a decrease in capacitance of the material. A single electron can alter the potential of material giving new EPs. CNTs have found to be metallic or semiconducting depending on their structure. The tube length and diameter are also responsible for change in electrical property. An insulator can become a conductor at the nanoscale. Electrical conductivity decreases due to increased surface scattering and change of electronic structure Resistivity increases due to increase in band gap energy. But in some cases, resistivity decreases also. Eg.CNT  MECHANICAL PROPERTIES Strength, roughness, hardness, ductility. Decided by the size of the NP, surface atoms, grain size, grain boundary and porosity. The Young's modulus of the NM decreases in the low NP size range ie.20 nm The hardness of a material can increase at the nanoscale. Eg. nanocopper has shown to be a super hard material As grain size decreases, the grain boundary increases, which results in greater creep resistance. The type of fracture can change due to the grain size. The properties of polymers are tailored to a larger extent by addition of NPs called fillers. Large particle give poor mechanical properties. But by using CNTs it is possible to produce composite fibers with extremely high strength.  MAGNETIC PROPERTIES Dependent on size of NP, anisotropy of NPs, and modification of chemical bonding in nm range. The nanosize can alter the domain walls that can affect the magnetization process. A significant change in hysteresis loop is also reported at the nanoscale. A material in nanodomain can change from non-magnetic to magnetic. for eg. bulk gold and Pt are non-magnetic but at nanosize they are magnetic. Permanent magnetism was observed up to room temperature for thiol-capped Au NPs CATALYTIC PROPERTIES A change in no. of atoms on surface can change the CPs like catalytic activity, combustions, and state of matter. For eg. PT has shown to enhance catalytic activity at nanoscale and aluminium that is stable in bulk state shows combustible properties at nanoscale.