NANO CLUSTERS AND NANOCOMPOSITES

 

Clusters are collections of atoms lying between individual atoms/molecules and bulk materials. In some materials, certain collections of atoms are more preferred due to energy minimization and exhibiting stable structures and providing unique properties to the materials. These collections of atom providing stable structures to the materials are called as MAGIC NUMBER. For example, one of the combination of 55 atoms of gold provides stable structure and hence its magic number is 55

What is cluster in nanotechnology?

Clusters are small aggregates of atoms and molecules. Small means really tiny pieces of matter—they are composed of a few to thousands of units and have a diameter of nanometers. Nanoclusters have at least one dimension between 1 and 10 nm and a narrow size distribution. Nanoclusters are composed of up to 100 atoms, but bigger ones containing 1000 or more are called nanoparticles.

What are nanoclusters used for?

Nanoclusters have potential uses in chemical reactors, telecommunications, microelectronics, optical data storage, catalysts magnetic storage, spintronic devices, electroluminescent displays, sensors, biological markers, switches, transducers and many other fields. The florescence silver nanoclusters have been extensively used as biological markers for photodynamic therapy.

What are metal nanoclusters?

Metal nanoclusters (NCs) are composed of a small number of atoms, up to dozens. These nanoclusters can consist of a single element or multiple elements, usually smaller than 2 nm. Compared with their larger counterparts, this nanocluster exhibits attractive electronic, optical and chemical properties. These particles have quasi-continuous energy levels and display intense colors due to surface plasmon resonance. If their dimension is further reduced to the size approaching the Fermi wavelength of electrons, the band structure becomes discrete energy levels. The ultrasmall metal nanoparticles display molecule-like properties and no longer exhibit plasmonic behavior. Metal NCs, such as AuNCs, AgNCs, CuNCs, and PtNCs, exhibit a marked photoluminescence property due to quantum confinement. The most studied among these metal NCs are AuNCs, AgNCs, and CuNCs.

What are gold nanoclusters?

Nanocluster are collective groups composed of a specific number of atoms or molecules held together through a certain interaction mechanism. Gold nanoclusters attract increasing attention due to their potential applications in sensing, catalysis, optoelectronics, and biomedicine.

How are gold nanoclusters made?

In one example, green-emitting gold nanoclusters could be prepared by adding mercaptoundecanoic acid (MUA) into small AuNP solutions prepared by the reduction of HAuCl4 with tetrakis(hydroxymethyl)phosphonium chloride (THPC).

Size 

Nanoclusters: Typically have at least one dimension between 1–10 nanometers (nm).

Quantum dots: Typically have a diameter of 2–10 nm.

Composition 

Nanoclusters: Made up of up to 100 atoms, but larger ones can contain 1000 or more atoms.

Quantum dots: Made of a semiconducting material.

Properties 

Nanoclusters: Have strong fluorescence emission, good photostability, and high conductivity.

Quantum dots: A type of semiconductor nanocrystal.

Nanocomposites

Composite materials are prepared from the combination of two or more different materials with distinct chemical or physical characteristics. The resultant composite exhibits properties which are superior to its constituent materials. 

Nanocomposites are broad range of materials consisting of two or more components, with at least one component having dimensions in the nm range (i.e. between 1 and 100 nm)

Nanocomposites consist of two phases (i.e nanocrystalline phase + matrix phase)

Nanocomposite means nanosized particles (i.e metals, semiconductors, dielectric materials, etc) embedded in different matrix materials (ceramics, glass, polymers, etc).

Nanocomposites differ from traditional composites in the smaller size of the particles in the matrix materials.

Classification: 

nanocomposites can also be classified into three categories based on the matrix material type:

Polymer-matrix Nanocomposites -  These nanocomposites are made from polymer matrix materials such as thermoplastic, thermoset polymers, layered silicates, and polyester

Ceramic-matrix Nanocomposites - These nanocomposites are made from ceramic matrix materials such as Al2O3 or SiC.

Metal-matrix Nanocomposites - These nanocomposites are made from a ductile metal or alloy matrix with nanosized reinforcement material.

Prepration:

Synthetic methods are commonly employed to prepare nanocomposites, such as lamination, soft lithography, solution casting, and spin-coating. Homogenous nanoparticle dispersion is a primary challenge during preparation. Dispersion affects phase interfaces and the final nanocomposite properties.

Different materials, structures, and compositions allow for fine-tuning of nanocomposite properties, such as electrical, mechanical, thermal, acoustical, and magnetic properties. Nanocomposites have given rise to the field of multifunctional materials.

Application Areas

Application areas in the automotive industry include engine covers, intake manifolds, door handles, mirror housings, and timing belt covers in various vehicle types. Applications in other commercial areas include vacuum impellers and blades, mower hoods, mobile phone covers, and power tool housings.

Nanocomposites in Food Packaging

Nanoclays, which are added to,polypropylene or polylactic acid packaging films, prevent the diffusion of oxygen or flavorings and thus prolong the shelf life of foods. Nanosilver has an antimicrobial effect and can be used in plastics composites, for example to manufacture food packaging such as films or containers to protect food from spoilage.