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Technology >> Electrospray Deposition Method
Electrospray Deposition Method
Principles
The Electrospray Deposition Method is a process by means of which a liquid is transformed into a fine mist. This transformation is brought about by the application of a very high voltage electric field to the capillary in which the liquid is held. In recent years, this methodology is widely used as an ionizer for mass spectrometers.
The Electrospray Deposition Method (ESD method) is the technique of spraying various kinds of solution of biomacromolecules and/or synthetic polymers, to make them form nano-sized particles and fibers (nano-fiber), and to let them deposit and adhere on a substrate using electrostatic force. While electrospray is a very complicated physical process, which is not fully understood, generally what happens is as follows.
When a sample liquid stored in a thin capillary is supplied with from thousands to tens of thousand voltage relative to counter electrode, a strong electric field is generated at the tip of the capillary, due to the effect of electric field concentration. As the liquid begins to exit from the capillary, it forms a conical shape with the electrically charged ions gathered on its surface (This is called Taylor cone). Subsequently, when the electrostatic force becomes stronger than surface tension, the liquid erupts from the tip of the capillary to form a fine jet. Since the jet is highly charged, the liquid immediately turns into fine droplets to generate spray with each droplet spilt from the next by electrostatic force (This is called the Coulomb Explosion). The droplets formed by means of electrospray are tiny. Therefore, the solvent evaporates and dries in a very short period of time, and as a consequence, it forms very fine nano-particles. These charged tiny particles are attracted to the counter-electrode by electrostatic force, and are deposited in various patterns, which can be controlled by mask(s) made of insulating material and/or additional electrode(s).
Electrospray Deposition Example of structure
Electrospray Deposition
nano-fiber
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nano-particle
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nano-coating
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micro-patterning
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Features
The Electrospray Deposition Method can:
  1. spray various substances include solution and dispersion liquid, such as organic/inorganic compounds, biomacromolecules and/or synthetic polymers ,and deposit various nano structures.
  2. maintain the sample relatively free from damage, since the whole procedure is conducted under a room temperature and atmospheric pressure.
  3. create nano-sized particles and fibers.
  4. control depositions and patterns of the particle using electrostatic force.
  5. form the nano structures in a larger area can be possible.
  6. Since this is dry deposition, there will not be any problem which occurs as wet deposition. Of course, wet deposition can be also possible by ESD method just by changing the spray conditions.
Applications
Nano-fiber
For manufacture of synthetic fiber, the mainstream technique used is to squeeze out synthetic polymers under compression through fine nozzles. However, D. H. Reneker et al. reported the possibility of forming fibers using the process now known as electrospinning (this is the same technology as ESD technology). This is a technique by which a high voltage is applied to the nozzle and a liquid solution is sprayed forming nano-scaled fiber materials (1,2). Our Esprayer®, is capable of producing nano-metered levels of fibers (nano-fibers) by means of ESD method. Currently, with our Esprayers®, wide ranging research and development is being carried out to fabricate nano-fibers from synthetic polymers and/or biomacromolecules (3,4).
ESD method is applicable to almost all polymers, which is soluble in water or organic solvents. We provide various collectors and double/co-axial nozzles prepared and they can be used to many purposes.
The nano-fibers fabricated by the ESD method are already commercialized as a high performance filter. It can be used as catalytic carriers as well as high-performance membranes. They are not limited to high-performance filters and non-woven fabrics. A wide variety of products are being developed, not only for textile fabrics but also for electronic parts and high-performance batteries as well as for the materials used for biological research and medical treatments.
Our proprietary high-speed ESD-technology and system should contribute to industrialization of many nanofiber products.
Polyacrylonitrile(PAN) nanofiber
photo photo
average fiber diameter : 128 nm, CV : 12.8% nanofiber coating to the filter surface
Thin film
Nanofiber and micro/nano particles are used for various thin films, and its applications and demands are getting much broader and stronger. In addition, higher performance and lower costs are requested (5).
Based on many experiences, we developed the equipment, ES-2000S series. It produces not only nanofiber but also high-quality thin film can also be produced.
Carbon black thin coating and its surface
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Instead of the solid-state reaction, which has been the most popular to prepare micro/nano-particles, the process to produce micro/nano-particles from solution directly, without using particles have been developed in recent years (6). The ESD method had also been tried (7), but, there were many problems in past ESD-equipments. We made various devices and developed the ES-2000HT series for a high temperature reaction, which can make micro/nano-particle thinfilms directly from precursor solutions. Since the equipment is customized, please contact us to discuss details.
Nano-coating
The particles of materials fabricated by the ESD method can be reduced to less than tens nano-meters. Using this technique, various types of coating are practicable, with the materials like synthetic polymers and biomacromolecules such as proteins. Thickness of the coating is controllable at the level of nano-meters, and with the electrostatic force, it is theoretically possible to coat the substrate both of flat surface and of complex shapes.
The section and surface coarseness of organic thin film coating
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Micro-Patterning
By using a mask of insulating material in the ESD method, electrostatic force controls the pattern of deposition and forms in desired shape, either spotted or striped. The resolution of pattern is possible to several micrometers depending on conditions. According to the nature of the substrate and the purpose of application, it carries out not only by using a mask but also by not using a mask. Deposition of various element materials and parts of electronics products, and the protein to a micro fluid chip, fixation in various form of biodegradable polymer, etc. can be performed using this patterning technology.
Micro patterning
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Nano-structure from protein
With the use of ESD method, freestanding protein films can be created (8). After treating the electrospray-deposited protein film with cross-linking reagents and removing from the substrate, a freestanding protein film is formed approximately 700um x 300um and with a thickness of 1 to 2um. Since the film is structured to be freestanding, it is possible to measure its mechanical properties and to detect a biochemical interaction as a parameter change of the mechanical property (mechanochemical methods, MC method) (9). This is a unique method of creating freestanding thinfilms from biological macromolecules, and therefore, it is a unique application of the ESD method. Such thin films are effective for various analytical purposes, materials for biological research, etc.
Protein film (300um x 700um x 1um)
protein film protein film
References
  1. Doshi,J. & Reneker,D.H., Electrospinning process and applications of electrospun fibers, J. Electrost. 35, 151-160 (1995).
  2. Reneker,D.H. & Chun,I., Nanometer diameter fibers of polymer produced by eletrospinning, Nanotechnology 7, 216-223 (1996).
  3. H.Matsumoto, T.Mizukoshi, K.Nitta, M.Minagawa, A.Tanioka and Y.Yamagata, Organic/inorganic hybrid nano-microstructured coatings on insulated substrates by electrospray deposition, Journal of Colloid and Interface Science 286, 414-416 (2005).
  4. T.Hayakawa, M.Yoshinari, K.Nitta and K.Inoue, Collagen Nanofiber on Titanium or Partially Stabilized Zirconia by Electrospray Deposition, Journal of Hard Tissue Biology 19, 5-12 (2010).
  5. Kikuo OKUYAMA, Nanoparticles Synthesis, Dispersion and Functionalization for Industrial Application, The Micromeritics No.51, 15-23 (2008).
  6. Wuled LENGGORO, Agus PURWANTO, Widiyastuti, Wei-Ning WANG, Kikuo OKUYAMA, Functionalization of Nanomaterials by Particle Processing Using Spray Merhod, The Micromeritics No.52, 43-47 (2009).
  7. A.Jaworek, A.T.Sobczyk, Electrospraying route to nanotechnology: An overview. Journal of Electrostatics 66, 197-219 (2008).
  8. Morozov,V.N. & Morozova,T.Y., Electrospray deposition as a method to fabricate functionally active protein films. Anal.Chem. 71, 1415-1420 (1999).
  9. Morozov,V.N. & Morozova,T.Y., Electrospray deposition as a method for mass fabrication of mono- and multicomponent microarrays of biological and biologically active substances. Anal.Chem. 71, 3110-3117 (1999).
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