Nanotechnology is all about the synthesis and manipulation of matter with at least one spatial dimension sized below 100 nm. Materials and technologies based on the nanoscale promise to considerably improve – even revolutionize – many industry sectors from: IT, domestic security, medicine, transportation, energy, amongst many others. Nanotechnology may be able to create many new materials and devices with a vast range of applications. This is achievable through reduced size that may allow for automation of tasks which were previously inaccessible due to physical restrictions, which in turn may reduce labour, land, or maintenance requirements. Moreover, due to greater efficiencies realizable from nanotech, sustainable manufacturing and products are more likely, in turn using less energy and with renewable inputs.
All of the above leverages the special properties associated with the nanoscale. There exists a relationship of such lengthscales with their special properties. Firstly, the surface-area-to-volume ratio is significantly increased. For the surface atoms, there is often an associated higher rate of reactivity, and because there are more surface atoms per gram of material, a correspondingly higher overall reactivity. In the nanoworld, the conventional threshold is taken as anything less than 100 nm. Each property has a size dependency at the nanoscale; however, not all are the same – and it strictly depends on the property in question.
Secondly, quantum effects such as confinement and tunneling also start to appear at the nanoscale. For example, we see with quantum dots of larger size, showing increasing wavelengths of photo-luminescence (green → red). With ever decreasing size towards the nanoscale, there is an evermore apparent discretization of energy levels and phenomena – this is quantum confinement at work. Tunneling is also a very strange effect where particles, such as electrons, can jump classical-energy barriers, and result in apparent new phenomena. This has been harnessed to increase electrical conductivity in very thin nanowire transistors.
In order to realize these useful properties in practical devices, attention has to be given to carefully synthesize such nanomaterials! This is because the special properties are sensitive functions of the exact size and shape of the nanodimensions. There are four main issues to address, in order to make commercially viable such state-of the art technologies. These comprise: (i) mass production, (ii) ease of self-assembly, (iii) fine-tuning nano-structures, and (iv) dispersion.
This is where the field of Chemical Engineering comes into play. Chemical Engineering is inherently multidisciplinary – very much like nanotechnology itself. By harnessing the integrated knowledge and understanding of the fundamentals, such as: catalysis, heat and mass transfer, and fluid dynamics, we are suitably placed to address issues associated with synthesis.
Various perspectives can be taken on the synthesis of nanomaterials – with the following class of problem-solving activities. Firstly, we need to be aware of the dimensionality of the types of materials – 0-D nanoparticles, 1-D nanowires, 2-D films, and nanostructured solids. Nanomaterials can also either be in aerosol free-form, or bounded to a substrate. Thirdly, the synthesis can be done in the liquid or gas phase – or in combination. Lastly, we mentioned synthesis, but there is also the important issue of how to assemble all the nanoparticles together to construct a coherent whole.
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