Process Optimization of Ultrasonic Spray Coating of Polymer Films

Abstract

In this work we have performed a detailed study of the influence of various parameters on spray coating of polymer films. Our aim is to produce polymer films of uniform thickness (500 nm to 1 μm) and low roughness compared to the film thickness. The coatings are characterized with respect to thickness, roughness (profilometer), and morphology (optical microscopy). Polyvinylpyrrolidone (PVP) is used to do a full factorial design of experiments with selected process parameters such as temperature, distance between spray nozzle and substrate, and speed of the spray nozzle. A mathematical model is developed for statistical analysis which identifies the distance between nozzle and substrate as the most significant parameter. Depending on the drying of the sprayed droplets on the substrate, we define two broad regimes, "dry" and "wet". The optimum condition of spraying lies in a narrow window between these two regimes, where we obtain a film of desired quality. Both with increasing nozzle-substrate distance and temperature, the deposition moves from a wet state to a dry regime. Similar results are also achieved for solvents with low boiling points. Finally, we study film formation during spray coating with poly (D,L-lactide) (PDLLA). The results confirm the processing knowledge obtained with PVP and indicate that the observed trends are identical for spraying of other polymer films.

Application of Quality by Design (QbD) Approach to Ultrasonic Atomization Spray Coating of Drug-Eluting Stents

“…A lower nozzle-to-stent distance tended to result in smoother coatings, perhaps because this led to an even flow of the coating solution on the stent surface. Similar results were reported by Bose et al (35) for polyvinylpyrrolidone ultrasonically sprayed onto a 5×20 mm area, and Shanshan et al (17) also reported that higher flow rates resulted in smoother coatings of PLGA (LA/ GA=75/25, Mw 100000) containing 5%, 7%, or 9% PEG plasticizer (to reduce PLGA cracking) and PLGA:sirolimus ratios of 2:1; 3:1; or 4:1. Shanshan also found that changing the solvent (and presumably the evaporation rate) affected roughness, a relationship which we did not observe in our study.…”

Microcantilever sensors for fast analysis of enzymatic degradation of poly (d, l-lactide)

“…Spray coating of PDLLA was only done on the top surface of the cantilevers. The spray coating parameters were optimized to prepare uniform and non-uniform coating on the cantilever surface with an average roughness (R a ) of about R a = 200 nm and R a < 80 nm, respectively [36]. For preparing uniform film, the nozzlesubstrate distance was 15 mm with 10 spray-passes while for non-uniform film the nozzle-substrate distance was 45 mm with 20 spray-passes.…”

“…By changing the spray coating parameters [36] both uniform and non-uniform PDLLA films are deposited on the silicon cantilevers and the biodegradation of films with different surface morphologies is investigated. Image analysis of the optical microscope images is conducted to monitor the dimensions of the PDLLA coating during degradation.…”

Thermomechanical analysis of picograms of polymers using a suspended microchannel cantilever

“…17,18,21,22 Both of these techniques require special spray coating or ink jet printing to deposit nanograms of sample. 23 Another challenge (when using microstrings or microcantilevers) is sublimation of the sample during heating. In order to overcome these difficulties, we have developed a microchannel cantilever consisting of microuidic channel integrated on top of the cantilever.…”