A deep look into the spray coating process in real-time—the crucial role of x-rays

Abstract

Tailoring functional thin films and coating by rapid solvent-based processes is the basis for the fabrication of large scale high-end applications in nanotechnology. Due to solvent loss of the solution or dispersion inherent in the installation of functional thin films and multilayers the spraying and drying processes are strongly governed by non-equilibrium kinetics, often passing through transient states, until the final structure is installed. Therefore, the challenge is to observe the structural build-up during these coating processes in a spatially and time-resolved manner on multiple time and length scales, from the nanostructure to macroscopic length scales. During installation, the interaction of solid-fluid interfaces and between the different layers, the flow and evaporation themselves determine the structure of the coating. Advanced x-ray scattering methods open a powerful pathway for observing the involved processes in situ, from the spray to the coating, and allow for gaining deep insight in the nanostructuring processes. This review first provides an overview over these rapidly evolving methods, with main focus on functional coatings, organic photovoltaics and organic electronics. Secondly the role and decisive advantage of x-rays is outlined. Thirdly, focusing on spray deposition as a rapidly emerging method, recent advances in investigations of spray deposition of functional materials and devices via advanced x-ray scattering methods are presented.

Morphological properties of airbrush spray-deposited enzymatic cellulose thin films

“…For spraying of cellulose thin films, a commercial airbrush spray nozzle (Harder & Steenbeck, model Grafo T3) was installed above the sample position. [52][53][54][55][56][57] The sample-to-nozzle distance (SND) was set to 15 cm. We used an N 2 pressure of p = 1 bar and a spray rate of (0.10 ± 0.01) mL/s.…”

Structural stability of naphthyl end-capped oligothiophenes in organic field-effect transistors measured by grazing-incidence X-ray diffraction in operando

“…As the performance of OFETs depends on the thin-film structures, various aspects and processing steps of conjugated oligomers and polymers have been studied by GIXRD including alignment [24], phase behavior [25,26], solution shearing [27], solvent vapour annealing [28], roll-to-roll processing [29], doctor-blading [30] and spray-processing in real time [31]. However, apart from the GIXRD studies of Liscio and co-workers [13] the GIXRD literature of OFETs in operando is less comprehensive.…”

Investigating Polymer–Metal Interfaces by Grazing Incidence Small-Angle X-Ray Scattering from Gradients to Real-Time Studies

“…The efficient preparation techniques of polymer and nanoparticle thin films incorporates a wealth of methods [ 6 ]. Among them are spray-coating [ 7 , 8 , 9 , 10 , 11 , 12 ], spin-coating [ 13 , 14 , 15 , 16 , 17 , 18 ], Langmuir-Blodgett [ 19 , 20 , 21 ], dip-coating [ 22 , 23 , 24 ], printing [ 25 , 26 , 27 ], and flow stream deposition. Concerning the latter, exploiting the selective interaction of metal with polymers, Metwalli et al investigated the growth of necklace metal nanostructures by laminar flow of gold colloidal dispersions onto block-copolymer (BCP) thin films as templates [ 28 ].…”