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.
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.
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.
- 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