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Layer by Layer Nanofilm Assembly

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Layer-by-Layer Film Assembly
Rajan Arora, 13045069
Rajat Verma, 13045071
Rahul Verma, 13045068

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Background
 The performance of functional materials is governed by their
ability to interact with surrounding environment...

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Layer by Layer (LbL) Assembly
 LbL assembly is a cyclical process in which a charged
material is adsorbed onto a substrat...

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Layer by Layer Nanofilm Assembly

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Reference:
Joseph J. Richardson, Mattias Björnmalm and Frank Caruso: Technology-driven layer-by-layer assembly of nanofilms (2015) Science 348 (6233). doi: 10.1126/science.aaa2491

Reference:
Joseph J. Richardson, Mattias Björnmalm and Frank Caruso: Technology-driven layer-by-layer assembly of nanofilms (2015) Science 348 (6233). doi: 10.1126/science.aaa2491

Weitere Verwandte Inhalte

Layer by Layer Nanofilm Assembly

  1. 1. Layer-by-Layer Film Assembly Rajan Arora, 13045069 Rajat Verma, 13045071 Rahul Verma, 13045068
  2. 2. Background  The performance of functional materials is governed by their ability to interact with surrounding environments in a well- defined and controlled manner.  Coating technologies provide the means to control the surface of a material, thus creating composite materials where the interface and the bulk of the material can, to a large extent, be engineered and controlled independently.
  3. 3. Layer by Layer (LbL) Assembly  LbL assembly is a cyclical process in which a charged material is adsorbed onto a substrate, and after washing, an oppositely charged material is adsorbed on top of the first layer.  Thickness of a single bilayer is generally of the order of nanometres, and the deposition process can then be repeated  Apart from electrostatic interactions, other interactions such as covalent, hydrogen-bonding, host-guest are also used.
  4. 4. Types of LbL  Different technique offers different process properties (such as the time, scalability, and manual intervention) but also directly affects the physico-chemical properties of the films, such as (such as the thickness, homogeneity, and inter and intra-layer film organization, distinct-layer stratification, controlled roughness, and highly ordered packing.
  5. 5. LbL techniques can be condensed into the following categories: (i) Immersive, (ii) Spin, (iii) Spray, (iv) Electro-magnetic, and (v) Fluidic assembly.
  6. 6. Immersive Assembly
  7. 7. Immersive Assembly  Immersive assembly is typically performed by manually immersing a planar substrate into a solution of the desired material followed by three washing steps to remove unbound material.  Theoretically, any material capable of having a surface charge (such as metals, nonmetals, organics, and inorganics) could be applied for growing multilayers if suitable conditions are used. Further, the thickness of each layer corresponds to the thickness of the particles being adsorbed.
  8. 8. Immersive Assembly  Immersive assembly process can be improved by speeding up the process by automating labour-intensive steps using robots and replacing random-diffusion kinetics by faster kinetics of dewetting. In dewetting, solutions doped with organic solvents can be used to eliminate the need for rinsing and drying steps. It leads to a 30 fold reduction in assembly time because the adsorption process is no longer governed by diffusion but by evaporation and dewetting.  As immersive assembly typically requires more material than other technologies, especially to submerge large substrates on industrial scales, waste can be an issue
  9. 9. Applications of Immersive Assembly  Immersive assembly can be used for depositing conductive and flame-retardant coatings  Planar substrates coated with particle multilayers can be used for the detection of small particles invisible to the naked eye through color shifts in the multilayer films  Glass slides can also be coated with particle multilayers for the preparation of antireflective, antifogging, and self-cleaning surfaces.
  10. 10. Spin Assembly
  11. 11. Spin Assembly  This utilizes the common coating technology of spinning a substrate to facilitate the deposition of materials. The majority of spin assembly is performed by either casting the solution onto a spinning substrate or casting the solution onto a stationary substrate that is then spun.  It quickens the assembly process considerably, depositing layers in ~30 seconds. Furthermore, it allows for automation using commercially available spin coaters.
  12. 12. Spin Assembly  Spin assembly typically results in more homogenous films compared with immersive assembly. This is because assembly is driven by a collection of forces including electrostatic interactions, which cause the adsorption and rearrangement of polymers, and centrifugal, air shear, and viscous forces, which cause desorption of weakly bound polymers and dehydration of the films.  In the assembly process, faster speeds are tied to thinner films and vice-versa. On the whole, spin assembly produces thinner, smoother and more homogeneous films than immersive assembly. Since it produces more organized stratification and better transparency, it is used for preparing optical coatings and transparent films
  13. 13. Applications of Spin Assembly  It is useful tool in preparing optical coatings with controllable and homogenous color and for preparing transparent films  It is useful for preparing LEDs with higher luminance than immersive assembly
  14. 14. Spray Assembly
  15. 15. Spray Assembly  In this method, polymer solutions are aerosolized and sequentially sprayed onto substrates. It is much faster than immersive and spin assembly, as quick as ~6 seconds per layer. The resulting films are typically well organized with distinct layers.  Spray assembly is a quick and easy method to coat large or nonplanar substrates, although immersive assembly remains the method of choice for coating complex 3D substrates.
  16. 16. Spray Assembly  The film thickness is influenced by suspension concentration, spray flow rate, spray duration, resting duration, whether or not the substrate is washed and for how long, and whether the solution is sprayed vertically or horizontally.  A disadvantage of spray LbL assembly is that the obtained films may not be homogeneous due to the effects of gravity draining, causing increased deposition in the vicinity of the solution drips, and because of irregular patterns caused by the spray nozzles at certain distances
  17. 17. Spray Assembly  To address this problem, rotating the substrate during spray assembly allows for the preparation of more homogeneous films. One advantage of this method is that polymer concentrations 10 to 50 times less than that in immersive assembly can be used as most of it is absorbed in spraying but majority remains in solution while in immersion.  Another advantage is that structure of the films can be controlled at the nanometer-level by the spray time.
  18. 18. Applications of Spray Assembly  it can be used to coat industrial-scale substrates with relative ease and is not limited to planar substrates  It used to prepare flame-retardant films over cotton cloth  It is used to prepare anti-reflective coatings, and similarly, car tinting with structured coloring to reduce heating from infrared light
  19. 19. Electromagnetic Assembly
  20. 20. Electromagnetic Assembly  Electromagnetic assembly uses electric or magnetic fields, typically in the form of electrodes in polymer solutions (electrodeposition) or magnetic particulate substrates, to deposit films. Electromagnetic assembly can exploit current- induced changes in pH or redox-reactions to effect film assembly, thus using a driving force substantially different from that of the other main assembly categories.  Generally, electromagnetic-assembled films are thicker and more densely packed than films prepared using other LbL assembly methods.
  21. 21. Electromagnetic Assembly  In the standard electrodeposition setup, two electrodes are immersed in polymer solution, then an electric current is applied. The electrodes are then washed and placed into solution of an oppositely charged polymer; the polarities of the electrodes are reversed, and the process is repeated.  The thicknesses of the electrodeposited films are directly related to the voltage used during assembly as well as electrodeposition time.
  22. 22. Applications of Electromagnetic Assembly  Electromagnetic assembly has found use in several different applications, as it can be used to form LbL films with compositions that are not readily assembled using other technologies.  Bimetallic films of Pt and Pd layers exhibit enhanced electrochemical activity in the methanol oxidation reaction, compared with single- layer films  Hollow polymer capsules (from micrometers to sub–100 nm in diameter) can also be prepared using electrodeposition on immobilized particles
  23. 23. Fluidic Assembly
  24. 24. Fluidic Assembly  Fluidic assembly can be used to deposit multilayers with fluidic channels, both by coating the channel walls and by coating a substrate placed or immobilized in a fluidic channel.  The general method involves using pressure or vacuum to sequentially move polymer and washing solutions through the channels such as tubing or capillaries  Pipetting, static incubation, spinning and capillary forces can also be used.
  25. 25. Fluidic Assembly Advantages  Fluidic assembly provides the means to assemble multilayers on surfaces not easily accessible to other methods (e.g., inside capillaries),  Provides new ways for region-specific patterning (e.g., by masking a surface with a fluidic channel),  Increases the industrial capacity of multilayer assemblies (e.g., through parallelization of film assembly and decrease of reagent consumption).
  26. 26. Applications of Fluidic Assembly  Fluidic assembly can also be used to engineer complex flow, such as having flow in opposite directions in the same capillary, by changing the outer coating of the capillary walls  Similarly, catheter tubing can be coated with antifungal multilayers to reduce fouling  Chromatography beads coated with multilayers of particles increase the surface area of the beads, thereby improving chromatography  Fragile particulate substrates like emulsions can also be coated with lipids, using fluidic assembly for the generation of synthetic cells  Fluidic assembly functions as a valuable tool for coating sensitive particulate substrates, like mammalian cells, that may be damaged in centrifugation based assembly.
  27. 27. Comparison
  28. 28. Conclusion  Over the past two decades, LbL assembly has undergone an explosive growth in usable materials and substrates. Now, LbL assembly is a firmly established technology and shows great promise in diverse fields.  Two main themes can be identified for current developments in assembly technologies: The first is the move away from random diffusion-driven kinetics for layer deposition, and the second is the advancement from manual assembly toward automated systems.
  29. 29. Conclusion  Much of the development up until now has focused on using new molecular driving forces for film assembly. Despite this extensive toolbox of LbL techniques, relatively few multilayer films have had widespread impact outside of research environments.  Thus, focus should be on developing robust and scalable techniques with industrial applications, and developing these would require technological and methodological innovation.
  30. 30. Thanks References:  Joseph J. Richardson, Mattias Björnmalm and Frank Caruso: Technology-driven layer-by-layer assembly of nanofilms (2015) Science 348 (6233). doi: 10.1126/science.aaa2491

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