Top-Down and Bottom_Up Approches

Methods of preparing Nano-particles.

1. TOP-DOWN and BOTTOM-UP approaches IGNTU AMARKANTAK DEPARTMENT OF BIOTECHNOLOGY Submitted By Dileep Kumar Banjare B.Sc. 5 th Sem Enrollment no. 17120006 Submitted To Pooja Singh

2. TOP DOWN and BOTTOM UP APPROCHES This is two different methods of design and preparation of nano -particles with high functionality. The fabrication of nano -materials of tailored properties involve the control of size, structure, composition and purity of their constituents. I,e to fabricate nano -materials which have the suitable properties for application.

3. TOP-DOWN APPROACHES The top down approach refers to slicing or successive cutting of a bulk materials to get nano - sized particles. In top down method or technique the starting materials is solid state. Nano - materials are synthesized by breaking down bulk solid into nano - sized and provides desired shape and order.

4. BALL MILLING METHOD This method is popular, simple, inexpensive or extremely scalable material to synthesize all classes of nano - particle . Can produce amorphous or nano - crystalline materials. Can use either re-factory balls or steel balls or plastic balls depending on the material to be synthesized. When the balls rotate at particular rpm, the necessary energy is transferred to the powder which in turn reduce the powder of coarse grain sized structure to ultrafine nano -range particles.

5. TOP-DOWN METHOD

6. The energy transferred to the powder from the balls depends on many factors such as Rotational speed of the balls. Size of the balls. Numbers of the balls. Milling time. Ratio of ball to powder mass. Milling medium/atmosphere. Cryogenic liquid can be used to increase the brittleness of the product.

7. One has to take necessary step to prevent oxidation during milling process. The selection of ball material influence the type of material obtained. Alpha-alumina and zirconia are widely used ball materials due to their high grinding resistance values.

8. ADVANTAGE and DISADVANATGE Screening can be achieved up to tonnage quantity materials for wider application. Large scale production. Contamination of the milling mill. Non metal oxides requires an inert medium and vacuum or glove box to use powder particles so this milling process is re-constrictive.

9. BOTTOM-UP APPROACHES Bottom-up approach refers to the build up of a materials from the bottom : atom by atom, molecule by molecule. Atom by atom deposition leads to formation of self- assembly of atoms/molecule and clusters. This clusters come together to form self-assembled monolayer on the surface of substrate. All the bottom-up technique, the starting material is either gaseous state or liquid state of matter.

10. BOTTOM-UP METHOD

11. NUCLEATION METHOD S ynthesis of nano -particles is a combination of two stage process : Nucleation and Growth. Most phase transformation begin with the formation of numerous small particles (clusters) of the new phase that increase in size until the transformation is complete. Nucleation is the process whereby nuclei (seeds) act as template for crystal growth.

12. NUCLEATION

13. There are two different categories of nucleation Heterogeneous nucleation The nucleation of critical nuclei forming at defects such as surface imperfection, grain boundaries is called heterogeneous nucleation. Nucleation is much easier since stable “Nucleating Surface” is already present. Requires slight super c0oling (0.1-10 ℃ )

14. 2. Homogenous ⃰ This happens spontaneously. ⃰ Nucleation that randomly occurs away from a surface nuclei form uniformly throughout the parent phase. ⃰ Requires considerable super-cooling (30-300 ℃ )

15. ⃰ Super-cooling During a cooling of a liquid solidification (nucleation) will begin only after the temperature has been lowered below the equilibrium solidification (or melting) temperature to this phenomenon is termed super-cooling (under-cooling). The driving force to nucleate increase as Δ T increases. Small super-cooling → slow nucleation rate → few nuclei →large crystal. Large super-cooling →rapid nucleation rate →many nuclei →small crystal.

16. ADVANTAGE and DISADVANATGE Ultra-fine nano -particles, nano -shells, nano -tubes, can be prepared. Deposition parameter can be controlled. Narrow size distribution is possible (1-20nm). Cheap technique. Large scale production is difficult. Chemical purification of nano -particles is required.