Automated Spray-LbL Technology

Technology #12307

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Inventors
Professor Paula Hammond
Department of Chemical Engineering, MIT
External Link (hammondlab.mit.edu)
Kevin Krogman
Department of Chemical Engineering, MIT
Nicole Zacharia
Department of Materials Science and Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Automated layer by layer spray technology

US Patent US 8,234,998

Automated layer by layer spray technology

US Patent US 8,689,726
Publications
Automated process for improved uniformity and versatility of layer-by-layer deposition
Langmuir, 2007, 23 (6), p. 3137-3141
Spraying asymmetry into functional membranes layer-by-layer
Nature Materials, 19 April 2009, p. 512 - 518
Building biomedical materials layer-by-layer
Materials Today, May 2012, Pages 196–206

Application

Automated Spray-LbL (Layer-by-Layer) technology consists of an automated apparatus that can be used to deposit Spray-LbL thin films, thus allowing a decrease in process time while eliminating human interaction/error. This technology is capable of depositing both weak and strong polyelectrolyte films, hydrogen bonded films, dendritic compounds, and nanoparticles - broadening its range of future applications. This system is only constrained by substrate size, rather than deposition technique, making Spray-LbL technology an attractive invention on an industrial scale.  Some industrial applications include the rapid deposition on cotton textiles and the technology can be scaled-up for commercial applications.

Problem Addressed

Current LbL deposition is a time-consuming process involving the submersion of a substrate with an inherent surface charge into a series of liquid solutions. The first exposure to an oppositely charged polyion bath results in charged species near the surface being adsorbed quickly until a sufficient layer has developed to reverse the net charge of the surface.  The substrate is then exposed to a series of water baths to remove any physically entangled or loosely bound polyelectrolyte, followed by the addition of a solution of polyion of the opposite charge. This sequence is repeated to build up a 'layer pair' of deposition and can be repeated as desired to achieve a certain amount of layers on a film. Although this method does produce extremely uniform films as thin as one nanometer per layer pair, this process may require upwards of thirty minutes to deposit. Automated Spray-LbL technology yields similar results but at a much faster rate and without the possibility for operator induced nonuniformities. 

Technology

The proposed apparatus consists of three identical solenoid valves, each with a constant head of fluid from either of two polyelectrolyte supply vessels or a rinse water supply vessel. The polyelectrolyte vessels are inverted, allowing a constant delivery pressure in the vapor space of each vessel which is regulated by a nitrogen source. With a constant liquid supply available, the spray is then controlled by sequentially closing and opening the solenoid values through the use of a logic relay capable of 10 ms of accuracy in response time. The elimination of mass transfer by diffusion reduces the interpenetration of layer pairs within the film, which allows for reproducible, linear rates. 

While the apparatus is delivering a Spray-LbL deposit, the substrate is rotated at a rate of 10 RPM to minimize the effects of gravity and to avoid drip patterns from the spray.  The apparatus is designed to make traditional LbL technology function at a faster pace. As a result, the apparatus is made to be more industrially viable.

Advantages

  • 25-fold decrease in processing time, making LbL-technology more industrially viable
  • Atomization of the solution before it contacts the substrate allows for uniform coating of extremely hydrophobic surfaces, even from aqueous solutions of charged species
  • Easily scalable and has other potential applications (i.e. rapid coating of large bolts of material using a roll-to-roll process, conformal coating of 3D objects through array configurations)
  • Automated system requiring  no human interaction