Visualization of a gas flow instability in spin coating systems

Wahal, Sanjay; Öztekin, Alparslan; Bornside, David E.; Brown, Robert A.; Seidel, Philip K.; Ackmann, Paul; Geyling, F. T.

doi:10.1063/1.109304

Cited by 17 publications

(9 citation statements)

References 10 publications

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“…Spin-coating technique has been introduced in colloids to fabricate thin films and colloidal crystals since long [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. It is simple, reproducible and requires little material to get results in a very short time [15].…”

Section: Introductionmentioning

confidence: 99%

Spin-coating of moderately concentrated superparamagnetic colloids in different magnetic field configurations

Aslam

González-Viñas

2017

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Spin-coating technique is very fast, cheap, reproducible, simple and needs less material to fabricate films of particulate systems/colloids. Their thickness and uniformity may be controlled by means of external fields. We apply magnetic fields during the spin-coating of a moderately concentrated superparamagnetic colloid (made of silica coated magnetite particles). We study the influence of different magnetic field configurations (homogeneous and inhomogeneous) on the resulting spincoated deposits and compare experimental results under various conditions. Superparamagnetic colloids behave as, non-Newtonian, magnetorheological fluids. Their viscosity vary significantly under applied magnetic fields. We measure and compare the effect of uniform and non-uniform magnetic fields on their relative effective viscosity, using the spin-coated deposits and a previously existing model for simple colloids. The mechanisms involved in the deposits formation under different experimental conditions are also discussed. In particular, we show that the magnetophoretic effect plays an important role in the spin-coating of magnetic colloids subjected to non-uniform magnetic fields. We characterize an effective magnetoviscosity in non-uniform magnetic fields that is largely influenced by the magnetophoretic effect that enhances the flow of the magnetic fluid.

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Section: Introductionmentioning

confidence: 99%

Spin-coating of moderately concentrated superparamagnetic colloids in different magnetic field configurations

Aslam

González-Viñas

2017

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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“…While the results presented here pertain to experiments using methyl ethyl ketone (MEK) as solvent, similar results were found with acetone as solvent. This phase is characterized ( Figure 1a) by a set of von K arm an spirals 13,14 that disappear when no more suspension is pipetted into the rotating substrate. Long-range orientational order with 6-fold symmetry extending over the whole surface is observed immediately after pouring of the suspension ceased.…”

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confidence: 99%

Dynamics of Crystal Structure Formation in Spin-Coated Colloidal Films

Giuliani

González-Viñas

Poduska

et al. 2010

J. Phys. Chem. Lett.

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The spin-coating of colloidal suspensions is an inherently nonequilibrium process that gives rise to highly reproducible, but polycrystalline, films with different symmetries depending on experimental parameters. In this study, we explore the transient dynamics of evaporative colloid spin-coating for the first time, via a combination of high-speed imaging, atomic force microscopy, static photography, and scanning electron microscopy. As the wet colloidal film thins and dries, we observe several symmetry transitions, while at the same time remarkably, the thinning rate (in nondimensional time units) collapses to one universal curve for all rotation rates. We correlate static and dynamic measures of crossovers in ordering regimes, and obtain an estimate of the evaporation rate in the late stage of drying. We conclude that the thinning dynamics controls the local volume fraction and stress profiles, which in turn drives the structural transitions. SECTION Macromolecules, Soft Matter C olloidal self-assembly is a facile and promising method for making photonic crystals, 1 but the control of defects is a challenge. Nonequilibrium approaches to colloidal self-assembly are likely crucial to the making of large-area colloidal crystals.2,3 Colloid spin-coating has recently emerged as a highly robust and reproducible nonequilibrium method to make multilayer colloidal crystalline films. [4][5][6] However, in spite of its robustness, the spin-coating route to colloidal crystals is fraught with challenges. The highly uniform structural colors exhibited by these films have been shown to arise from a polycrystal where different crystallites exhibit longrange orientational order. 7 In order to develop strategies to produce crystals with a greater degree of translational order, a deeper understanding of the dynamical mechanisms of structure formation is required.While the dynamics of spin-coating has been studied extensively and quantitatively in simple one-component fluids 8,9 as well as in polymer solutions, 10,11 the study of the dynamics of colloid spin-coating has been limited to numerical studies of thinning rates.12 A recent work demonstrates that spin-coating flows (in the absence of evaporation) control the local stress profiles, and drive crystallization when the Peclet number exceeds a critical value. 6 Two questions that have remained unaddressed;how the dynamics interlinks with the emergence of different symmetries, and the role played by evaporation;are the focus of the experiments reported here.We begin with our observations of the transient dynamics. Using high-speed imaging and the lighting configuration A (Figure 6), we are sensitive to changes in long-range orientational order via the appearance of symmetries in the optical reflections. In all experiments (at varying rotation speeds) common dynamical features are observed in the fluid phase. While the results presented here pertain to experiments using methyl ethyl ketone (MEK) as solvent, similar results were found with acetone as solvent. This phase...

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“…Furthermore, the frequency in the low frequency band shifts considerably with increasing the orbital speed. Velocity fluctuation at low frequency is observed from the inward regions of the disk, as shown in Figure 8 et al th vortices of streamline-curvature instability are likely to travel [11]. A detailed investigation will be conducted in future work.…”

Section: Fluctuating Tangential Velocitymentioning

confidence: 92%

Effects of Orbital Motion on the Boundary Layer Flow on a Spinning Disk

Munekata¹,

Jobi²,

Ikebe³

et al. 2012

OJFD

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The objective of this study is to experimentally examine the effects of orbital motion on the boundary layer flow on a spinning disk. The boundary layer flow on the disk is visualized by the oil flow method, and velocity in the boundary layer is measured by the hot-wire method. For the oil flow pattern in the case of spinning motion only, streaks are clearly observed on the disk as transient vortices, but by adding orbital motion to the spinning motion, we find that streaks are not observed in a certain range of orbital conditions. With increasing orbital motion speed, the laminar region becomes narrower and transition is promoted from the inward region of the disk, regardless of the direction of rotation. Also, with the addition of orbital motion, the velocity profile in the boundary layer becomes more asymmetric with respect to the spin axis of the disk. Furthermore, stationary vortices do not appear on the disk when the orbital speed is beyond a certain critical value. Therefore, the lack of streaks in the oil film pattern when orbital motion is added is due to the spatiotemporal unsteadiness of the flow field on the disk.

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Visualization of a gas flow instability in spin coating systems

Cited by 17 publications

References 10 publications

Spin-coating of moderately concentrated superparamagnetic colloids in different magnetic field configurations

Spin-coating of moderately concentrated superparamagnetic colloids in different magnetic field configurations

Dynamics of Crystal Structure Formation in Spin-Coated Colloidal Films

Effects of Orbital Motion on the Boundary Layer Flow on a Spinning Disk

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