It is since today the day man discovered fire that he preceded towards development very rapidly. Many of the Civilizations came into existence; technology went on advancing as per their requirements. Gradually came the days when man started imagining huge and started striving for bringing his imagination to the day of light. Today after having reached such heights of advancement we the human beings are still in thirst of technology indeed very desperately. One such field for current discussion and interest of brilliant brains is that “how small can we go?” the answer to this question is one billionth of a meter i.e. nothing but a nanometer. The prefix “nano” means one billionth. To get a sense of nano-scale a human hair measures few hundred nanometers across and so on. The smallest thing see-able with unaided human eye is 10000 nanometers across. Just ten hydrogen atoms in a line make up one nanometer. Nanoscience at its simplest is the study of the fundamental principles of molecules and structures with at least one dimension roughly between 1 and 100 nanometers. These structures are known, perhaps Nanostructures. Nanotechnology is the application of these nanostructures into various useful devices, their synthesis and fabrication1.
Anything smaller than a nanometer in size is just a loose atom or small molecule floating in space as a dilute spec of vapour. So nanostructures aren’t just smaller than anything we have made before, but they are the smallest thing it is possible to make2. Thus this ability to fabricate nanoscale materials with properties superior to those of bulk material has increased interest in recent years. The particles in the size range of 1-100 nm exhibit excellent and unique thermal, electrical, optical, chemical and magnetic properties which are absent in the bulk form. Say for example the bulk gold is yellow in colour but the same gold particles show somewhere around blue to violet colour at the nanoscale range. Similarly the carbon nanostructures became an interesting field of research in past fifteen years due to some fascinating facts. The experimental production of carbon nanoballs (fullerenes) was first observed in 1985 which opened the door for other carbon nanostructures3. In 1991 the carbon nanotubes were observed for the first time4. A wide range of potential applications like construction of light materials with extraordinary strength, gas storage within the cage structure, lubricants etc. were discovered depending on these carbon structures. These carbon nanotubes are nearly 100 times stronger in tensile strength than the steel in nanometric scale5,6. After knowledge of such properties of the materials at nanoscale the scientific world is moving towards the fabrication of such structures event at the individual level.
To produce such nanoscale materials there are many techniques available such as, Wet chemical process, Vapour phase reaction, Spray pyrolysis, Sol-gel processing etc.3,4. out of these techniques, wet chemical is more often undertaken when producing nanoparticles, as other methods are not yet commercially viable. The wet chemical technique involves the precipitation of metallic particles by a chemical reaction in the liquid medium between the starting inorganic precursor and a suitable reducing agent. Chemical methods for fabricating nanoparticles, allow the tailored designing of materials at molecular level, and offer a cost effective method of producing nanoparticles in large quantity. However a major drawback is that it is very difficult to prevent the progress of agglomeration as the reaction proceeds7. the major problem with the gel processing is that the preparation period of gels is a difficult job and takes a long time8. the alternative spray pyrolysis manufacturing process, also has disadvantages including low yield and non-uniform nanoparticles and the possibility of agglomeration.
One such method for the fabrication of Nanoparticles is LLSI technique. The Laser Liquid Solid Interface manufacturing technique was recently developed at the Penn State University Laboratory. This process utilizes less expensive liquid solutions or precursors and enables the production of high quality nanoparticles of relatively regular particle size and shape9. Thus in this seminar report the LLSI technique is studied for synthesis of nanoparticles and the building of nanostructures at micro gravity environment is also of prime interest. Both the topics are interdependent and are brought into focus over here.
OBJECTIVES
To acquaint the knowledge of smallest sizes of particles which can be produced i.e. nanoparticles.
To attain the know how? Of various techniques available for such nanoscale synthesis and to clear the idea of draw back of these techniques.
To visualize some new techniques currently introduced into the market i.e. to attain the knowledge and information about LLSI synthesis technique.
To study the various aspects of LLSI scheme to finds its reliability and accuracy for nanoparticles synthesis.
To study further the concept of micro gravity used in building of the large structures made up of these nanoparticles.
To make into complete view of this tiny material world (Nano World).
OVERVIEW OF VARIOUS SYNTHESIS TECHNIQUES
AVAILABLE
To start up with, first we are concerned at over viewing the some of familiar and frequently utilized techniques for the synthesis of the nanoparticles production. This will enable us to have a brief idea of the drawback of the currently available methods. We can come across variety of techniques in the market used for such synthesis, say wet chemical process, Sol-Gel method, Spray pyrolysis etc. The wet-chemical technique involves the precipitation of metallic particles by a chemical reaction in the liquid medium between the starting inorganic cursor and a suitable reducing agent. Chemical methods for fabricating nanoparticles, allow the tailored designing of materials at molecular level, and offer a cost effective method of producing nanoparticles in large quantity. However a major drawback is that it is very difficult to prevent the progress agglomeration as the reaction proceeds.
The Sol-Gel technique gives more uniform particles of specific shape and size. In this method of synthesis the gels are used as the solutions with a specific precursor.
Then the gel is kept for settling under gravity conditions slightly a little more than the gravity on earth. The reason for this is the fact that some what higher than IG the particles do have a tendency of settling more rapidly, but if this gravitational field is increased more than 1.5G the gel particles tend to separate un-uniformly giving rise to improper size and shape. The further fact is that it takes a very long time for preparation of these gels is required and another limitation is multi directional fluid thermolysis puts an indenting barrier8.
We can also find the Spray pyrolysis technique available for the synthesis of these particles. At the initial stages of development the spray pyrolysis has result on uniform and uneven in sizes. Recently the process is being carried at higher temperature and the pyrolysis is being carried out using metal-salt solutions for gaining higher efficiency. But still the process is being carried at higher temperature and the pyrolysis is being carried out using metal-salt solutions for gaining higher efficiency. But still the process is being applied at very small level for commercial production as there can be uncertainties in the equal size distribution of the particles10. Here we can see that the each and every process currently available is having some of the major limitations, hence it is a necessary to find a new process which might give us a sigh of relief from some of the problems. The LLSI synthesis technique can prove itself to be more beneficial than current techniques available. It is studied in the next section of this report.
LLSI NONOPARTICLE SYNTHESIS TECHNIQUE
The LLSI setup is minimally composed of laser and a rotating substrate immersed in a precursor solution. Photon energy from the focused or defocused laser beam passes through the solution and impinges on the rotating substrate, heating the substrate and creating non-equilibrium conditions at the laser-liquid-substrate interface. This results in the formation of localized gas bubble on the order of 1 mm in size containing high temperature of gas (vaporized solution) and small particles (condensed metal species, like Ag and Ni). The presence of such a bubble has been observed in past experiments at Penn State. The bubble in anchored to a hot spot that like the laser beam in stationary. The substrate surface moves under the hot spot at a predetermined constant speed (on the order of 5 cm/s). The extremely high temperature vapor of the bubble, which is surrounded by room temperature solution to radiative cooling., causes nonparties to be produced in that, it is hypothesized to be a three step process:
Pre-nucleation : wherein the starting compound undergoes dissolution in the solvent. The laser-liquid-solid interaction generate a large number of metal atoms by reduction as well as by Pyrolytic and Photolytic process
Nucleation : wherein clustering of atoms forms he metal nuclei by diffusion, agglomeration, and radiative cooling.
Growth : Wherein the nuclei grow due to the supply of metal atoms in solution. The growth rate due depends on the residence time of the metal atoms in the bubble, radiative cooling of the nuclei, and heat and mass transfer form the convective flow field around the bubble.
Around the hot spot leads to the formation of nanoparticles or other forms of nanoscale materials, such as nanotubes or clusters. Once formed, the nanoparticles are swept out of, and away the form, the bubble by the forced and buoyancy-driven convective fluid flow of the liquid at the bubble boundary. The nanoscale materials may be separated from solution by centrifuging or, alternatively, may be allowed to settle on the substrate, as in laser-writing used in nanofabrication of microdevices10,11.
CONCEPT OF MICROGRAVITY
We rarely imagine gravity less environment being applied to the daily processes, to understand micro gravity let us first imagine this concept. Imagine of no gravity acting on the any of the unit operations or chemical processes, it is difficult to imagine it but if such thing happens almost all of our unit operations will fail, while our chemical processes or synthesis will be carried out at almost to the completion. The reason for this is the fact is that all of our unit operations are dependent on gravity. So if such is the case what if the gravitational field increases or crosses the earth’s gravity? It is really a very complex problem indeed. But this concept can just be imagined in space where micro gravity or very less gravity exists. The presence of such an environment is just not possible on the earth without advances equipments. Form the point of industrial production this concept is of no use, where as the same concept is more useful in processing of large or continuous nanostructures. One can ask as how is this possible?
The answer to this question is very simple. Every atomic particle and subatomic particle is made up of a string and this string is made of nothing but the energy in the form of waves12. One can imagine that are we made of no mass? In fact our mass is just a form of energy It is true. Now think of electromagnetism, when we supply electrical from of energy to any particle is gets magnetized and obviously it tries to attract and another particle.
To have a broader sense of this the gravitational pull is nothing but a paramagnetic pull and push between two bodies13. Hence is cleat that in space a very loess gravitational field exists. At the nanoscale of particles this effect sets the bodies free to acquire additional gravitational field by the another particle when the both come into to vicinity of each other14. The try to form a combined the both come into to vicinity of each other The try to form a combined gravitational field of their own due to the fact that each and every body tries to attain stability in all the manners15. Where as in the gravitational environment this case does not exist due to the fact as concentration gradient causes density gradient and consequently causes complex motion of fluids. The gravitational effect causes the particles to agglomerate, but to build large nanostructures this effect is just a devastation.
NANOPARTICLE CRYSTAL GROWTH IN MICROGRAVITY
Several of the recent crystal growth experiments under sustained micro gravity conditions have shown that that such an environment has led to an improvement on the size, morphology, and internal order of macromolecular crystals. Among crystal growth scientists it of great interest t understand the phenomenon affection the growth. The more obvious direct mechanical action on the nanoparticles orientation, deformation, and attachment kinetics by naturally occurring, gravitationally induced convective flows have been theoretically estimated. They have been found to be insignificant results have been some others who have invoked more complicated mechanisms for growth. Thus, the influence of gravity-induced flows on the growth of protein crystal appear to be more indirect, and it’s understanding will ideally required the identification of a specific, experimentally observable characteristics tat can be correlated to both the flow of conditions as well as to the resultant crystal morphology. The depletion zone, in neighborhood of the crystal surface, is believed to be an important participant in affecting nanoparticles crystal quality. The formation of stable depletion zones around growing nanoparticles crystals could play ‘self-regulation role’s by decreasing the growth rate and thus indirectly reducing instant of discrete crystallographic defects and dislocations. Evidence of the existence of such depletions zone appears have already been obtained during a space-based experiment, and interferometer holography has allowed it’s visualization by researchers practicing Earth-based crystal growth in gels16.
CASE STUDY : SYNTHESIS OF NANOSIZES POWDERS
Advances in power-based processing long have been focused on reducing particle size and improving the particle uniformity. Nanosized powders particles at the nanoscale, or a approximately I nanometer (nm) to 100 nm size are becoming increasingly critical to innovations in numerous application, including catalysis, coating, cosmetics, electronic, sensors and drug delivery. Nanopowders offer controlled functionality, increased reactivity and a number of other advantages over existing materials. Moreover, new production and synthesis methods promise to further improve particle capabilities and push particle sizes to new lows.
Xerox has reinvented toner production through its emulsion aggregation (EA) process, which creates 1 micron (nm) to 15 um particles from smaller nanometer-sized particles. This technology has potential applications in biotech, personal-hygiene and related applications. The smaller particle size will give improved image resolution, and end up using about 40% less toner on a page. Conventionally the has to be brittle enough to break in the grinding process.
The environmentally friendly EA process starts with monomers, and uses emulsion polymerization to grow tiny polymer particles in an aqueous environment. The toner particles then are combined with pigment particles and wax particles, which are also in water and very small (after pour them together) it’s not very viscous: (it’s) like water. Then is added reagent to cause the particles to flocculate. Basically, most of the particles are stabilized with a negative charge, so we can put in a positively charge material. That causes destabilization, and it causes the particles to flocculate together. By controlling the physical chemistry of the mixture, we determine the temperature time and stirring. And obviously the amount of flocculent added. That causes the particles to come together in a controlled fashion.
APPLICATIONS
- To synthesize carbon nanoparticles up to 100 nm.
- To synthesize nanoparticles of noble metals up to 100 nm.
- To synthesize nanoparticles of inorganic compounds lead oxide, tin oxide up to 80 nm.
- To synthesize fibre composite nanoparticles up to 30 nm.
- To synthesize silicon related nanoparticles up to 60 nm.
- To synthesize pharma drugs size is dependent on the size of drug molecule.
- To synthesize matrix composites of many metals from 50-70 nm
- To synthesize nanolevel bio particles of complex organic chemistry up to 15nm.
CONCLUSION
In recent years of technological development the nanoparticles synthesis is gaining interest due to immense potential of this field to produce materials with almost the properties beyond our imagination. It is obviously a tough and challenging job to synthesized material. But not ever in response of this need the modern synthesis technique of LLSI technique has proven to be more economical since it utilizes cheap precursors. For the next level of building of large nanostructures of the minute particles the micro gravity processing is proving itself to be a useful tool. But still the future research work should be carried out to make this process more and more efficient.
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