Coating Process Regimes in Particulate Film Production by Forced-Convection-Assisted Drag-Out

Abstract

Operating conditions for the deposition of monolayer and bilayer particulate coatings from aqueous 20-nm-diameter silica dispersions are identified in the context of a drag-out operation assisted by forced convection. The dry film thickness, uniformity, and morphology are assessed within an operating window parametrized by the capillary number and silica dispersion weight fraction. Three film deposition regimes with respect to the capillary number are observed: convective film deposition at low process rates, film entrainment at moderate process rates, and a thin-film transition regime at intermediate process rates. Locally ordered particulate films of variable layering thickness, including (i) a discontinuous submonolayer or (ii) a mixed submonolayer and monolayer, (iii) a mixed monolayer and bilayer, and (iv) multilayers, are dominant under convective deposition conditions. A map of morphologies is presented within the capillary number-weight fraction operating window, where monolayer and mixed monolayer-bilayer films are demonstrated in the thin-film transition regime at an intermediate dispersion weight fraction. A complementary map of the morphologies formed by the drag-out of 110 nm silica dispersions reveals a broader applicability to this type of operability diagram. These operating maps are constructed using model silica dispersions and are therefore relevant to particulate coatings of other inorganic materials.

Spinodal decomposition in particle-laden Landau-Levich flow

“…3. Interestingly, the characteristic length scales of irregular aggregates found in many drying colloidal systems are also seen to be on the order of several particle diameters, 16,19,22 suggesting that capillary self-assembly of colloidal submonolayer aggregates may occur via a similar mechanism as that seen in our system.…”

“…Once particles are deposited on the wall, their surrounding liquid thins to less than a particle diameter, wetted particles distort the free surface, and capillary attraction acts to induce aggregation. (We note that a substantial body of literature exists in the area of self-assembly by evaporating colloidal suspensions, [16][17][18][19] coffee rings, 20 and gravitational drainage of thick suspension coatings. 21 These phenomena depend on concentration of solids via subsequent removal of liquid from the coating film, whereas in our system self-assembly occurs immediately and continuously upon passage through the bulk meniscus.)…”

Fabrication of non-close-packed colloidal monolayers by convective self-assembly using cationic polyelectrolyte-grafted silica particles

“…Convective self-assembly (CSA) is one of the most effective and widely used bottom-up techniques to form a colloidal layer basically with a CP structure [22][23][24][25][26][27][28]. In this process, a highly wettable (solvophilic) substrate is immersed into a colloidal suspension, and the temperature is controlled to allow the solvent to evaporate.…”

Controlled evaporative self‐assembly of polymer nanoribbons using oscillating capillary bridges

“…S5). In this regime, flow coating processes with a continuous velocity U , have been shown to deposit films with thickness scaling as: , where F is the evaporative flux and φ is the solute volume fraction and U is the characteristic velocity . For the oscillating blade method, the substrate moves with velocity u and blade tip oscillates with bending velocity u b .…”