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This work yields an inexpensive and fast process to replace the current standard of microscale periodic structure fabrication.
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Deposition: The experimental setup is shown in the following figure.  This apparatus is contained within a humidity controlled environment, where all experiments were performed at 53 %RH and 24 oC.  The deposition blade angle is placed at a set angle 25˚ to 80˚, and approximately 10  above the substrate, observed directly using a digital microscope camera (Dinolite AM311S).  Next the colloid suspension is injected to the wedge between the substrate and deposition plate with 10 um. The substrate is then pulled at a deposition speed ranging 20  to 200 um/s using a linear motor (Harvard Instruments). 
                                                     
                                            Fig. 1) Experiment Setup                                   Fig. 2) Meniscus Formation (blade corner)
                            
                                 
                                     

                                                                    Fig. 3) Thinfilm of 1um thick  after the deposition

                                                                

Meniscus Formation: The shape and curvature of the meniscus that resides between the deposition blade and the substrate has a large effect on the resulting deposition.  As shown in Figure 4, the blade angle and hydrophobicity of the deposition blade’s rear face determines the quasi-static shape of the droplet. The blade is highly hydrophilic after the initial cleaning process described above, and when the suspension is introduced, it flows under the blade wetting the underside of the blade along the full width of the substrate, as seen at the top row of images in Figure 6a. At this scale, surface tension dominates and the resulting meniscus wets both surfaces equally forming a concave free surface.  The degree of wetting to the backside of the blade increases with the deposition angle. At the deposition angle of 55o, the upper three phase contact line pins at the upper corner of the blade. Above 55°, less suspension resides on the backside of the blade.





Substrate Preparation: A plain glass microslide (76 x 25 x 1 , Fisher PA) is used as the deposition blade and glass cover slides (40 x 24 x 0.25 , Fisher PA) are used as the substrate for all samples prepared for analyzing the deposition process. All glassware is immersed in a Piranha solution, 5:1  sulfuric acid / hydrogen peroxide, used as a cleaning agent for 30 min. The glassware is then rinsed by DI water until no residual acid remains and the cleaned glassware is immersed in DI water before use. The back and bottom edges of the glass deposition blade are either left hydrophilic or treated to be hydrophobic by adding a thin coating with parafilm (Fisher PA) in order to control the wetting region of the meniscus droplet.
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Suspension Preparation: The primary colloid suspension used in this work is prepared by dispersing monosized microspheres in deionized water with the volume fraction of 0.20. The suspension is dispersed using a sonic dismembrator (model 550, Fisher Scientific, Pittsburg, PA) for 10 min and stirred for 30 minutes.  Various particles are used, primarily silica microspheres (Fuso Chemical Co, Japan) having a density of 2.2 g/cm3 and average diameter of 0.5±0.01 and 1.01 ± 0.02 um .  For the applications discussed, solutions of 0.1, 0.5 or 1.1 um  polystyrene (PS - supplied by the Emulsion Polymer Institute at Lehigh University)  prepared at  in DI water is used.  For binary suspensions, both SiO­2 and PS are dispersed in DI water to meet the desired volume fractions, and then sonicated for 10 min before use.