L4-_Nanomaterial_Properties.pdf

L-5 NANOMATERIAL PROPERTIES Not a substitute for standard text books Materials Behave Differently At The Nanoscale Nanomaterial characteristics that can affect life-cycle interactions  Properties of Nanomaterials Properties Adjusting Optical...

L-5 NANOMATERIAL PROPERTIES Not a substitute for standard text books Materials Behave Differently At The Nanoscale Nanomaterial characteristics that can affect life-cycle interactions  Properties of Nanomaterials Properties Adjusting Optical Electrical Size Mechanical Composition Shape Magnetic Chemical  Unique Characteristics of Nanoparticles Large surface to volume ratio High percentage of atoms/molecules on the surface Surface forces are very important, while bulk forces are not as important Metal nanoparticles have unique light scattering properties and exhibit plasmon resonance Semiconductor nanoparticles may exhibit confined energy states in their electronic band structure (e.g., quantum dots) Can have unique chemical and physical properties Same size scale as many biological structures  Materials Behave Differently At The Nanoscale Two principal factors cause the properties of materials in nanoparticle size to differ significantly from their bulk form: increased relative surface area, and quantum size effects These factors can change or enhance properties such as reactivity, strength and electrical characteristics  One of the main reasons that properties are different at the nanoscale is an increased surface area to volume ratio As particle size gets smaller, the surface area to volume ratio gets larger. Nanoparticles are almost all surface!  The smaller the cubes, the higher your surface area to volume ratio for the same total volume of material. This means that there is more surface available for reactions to happen on. It is no surprise, therefore, that on the nanoscale, many materials are more reactive. For example, (do not try this at home!), if you throw some very finely ground sugar in the air, and the particles disperse, they become a lot more reactive and if a flame is added, will explode. The larger surface area to volume ratio does not just make things more explosive, but also means things heat up and cool down quicker.  Surface plasmon resonance SPR is a quantum electromagnetic phenomenon that occurs when light interacts with free electrons at the interface between the metal and dielectric This optical process happens when monochromatic and p-polarized light beam strikes the surface of metal (typically gold) At a certain angle of incidence, a portion of the light energy couples through the metal coating with the electrons in the metal surface layer, which then move due to excitation The electron movements are now called plasmon, and they propagate parallel to the metal surface  After that, the observed reflected light shows a dip in the intensity The electron coherent oscillations that were excited by exponentially decaying evanescent field of the incident light are called surface plasmons (SPs) and propagate parallel to the metallic surface The angle at which the reflected light shows the maximum loss of intensity is called resonance angle or SPR-dip The plasmon oscillation in turn generates an electric field whose range is around 300 nm from the boundary between the metal surface and sample solution  SPR-Applications Surface plasmon resonance (SPR) spectroscopy was widely used in biosensing SPR biosensors have multiple advantages such as easy preparation, no requirement of labeling, real-time detection capability, cost- effectiveness, and high specificity and sensitivity It has proven effective in medical diagnostics, food quality tests, detection of heavy metal ions, and others with respect to environmental protection  Localized surface plasmon resonance (LSPR) LSPR is an optical phenomenon that causes a collective oscillation of valence electrons and subsequent absorption within the ultraviolet-visible (UV-Vis) band, due to interactions between the incident photons and the conduction band of a noble metal nanostructure Localized surface plasmon resonance (LSPR) sensors offer high sensitivity, a small footprint and are reasonably affordable due to the simplicity of instrumentation  LSPR differs from SPR as the induced plasmons oscillate locally to the nanostructure, rather than along the metal- dielectric interface LSPR can be elegantly described by Mie’s solution to Maxwell’s equation, occurring as a consequence of the restriction to the movement of electrons through the internal lattice of a noble metal when the size of the noble metal structure is scaled down to the nano level (2nm  The color exhibited by metallic nanoparticles is due to the coherent excitation of all the “free” electrons within the conduction band, leading to an in phase oscillation and is known as surface plasmon resonance Optical properties (color) of gold and silver change, when the spatial dimensions are reduced and the concentration is changed VI) Mechanical Properties Mechanical properties of nanomaterials increase with decrease in size Most of the studies have been focused on the mechanical properties of one-dimensional structure such as nanowire The enhanced mechanical strength of nanocopper or any nanowire or nanorod is ascribed to the high internal perfection of nanowires Imperfections, such as dislocations, micro-twins, impurities that occur in bulk material gets eliminated at the nanoscale dimension CNM impregnated polymers which are being used for bulletproof fabric, airplane and car body, even a sky city i.e. wherever light weight, hard and non-corrosive material is needed. VII) Electrical Properties Nanoparticles are good conductor of electricity, which make the electrical devices faster with low power consumption and with reduced imperfections VIII) Thermal Properties Metal and semiconductor nanoparticles are found to have significantly lower melting point or phase transition temperature as compared to their bulk counterparts The lowering of the melting points is observed when the particle size is,