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Pattern deposition of colloidal particles Manor, Ofer


Colloidal forces are known to influence the pattern deposition of nanoparticles off a volatile carrier liquid. Several experimental studies suggest a direct connection between colloidal forces and the morphology of the particulate deposit [1,2,3]. Specifically, variations in the zeta potential of the suspended particles and substrate; and variations in the ionic strength in the suspension were found to alter the geometry of the deposit. We use theory and experiment to investigate the connection between colloidal forces and the pattern deposition of colloidal particles off a volatile carrier liquid. We connect between colloidal forces and pattern deposition by considering the adhesion of particles to the solid substrate and the coagulation of particles in the suspension [4,5]. Our initial theoretical approach is based on an asymptotic â long wave type â model for the deposition process. In this model we employ the interactionâ force boundary layer theorem to account for the rate of adhesion of particles to the solid substrate. The theorem allows for manifesting the dynamic process of adhesion in a form that is reminiscent of a first order chemical reaction in a dynamic advection-diffusion equation for the transport of particle mass in the liquid. Similarly, we employ the augmented Smoluchowski theorem to account for particle aggregation. Hence, the rate of aggregation is manifested in a form that is reminiscent of multiple second order chemical reactions. The coefficients of the reaction terms are associated with the energy barriers for adhesion or coagulation. Comparing the predictions of our asymptotic model to experiment, we find that the rate of adhesion, coagulation, and diffusion of particles in the volatile liquid as well as the rate of liquid evaporation govern the deposition of particles. Moreover, fast adhesion of particles to the solid substrate and fast diffusion of particles in the liquid disperse the spatial distribution of the particulate deposit. Fast coagulation and fast evaporation support the deposition of denser patterns of particles of sharper spatial boundaries. A different theoretical approach for modelling the deposition problem, which we currently pursue, is to employ phase change type energy functional to account for particle coagulation and adsorption in the volatile liquid film. Such an approach should naturally incorporate the physics associated with concentrated particulate systems and particle volume effects that are not accounted for in the current asymptotic model. References 1. R. Bhardwaj, X. Fang, et al. Self-Assembly of Colloidal Particles from Evaporating Droplets: Role of DLVO Interactions and Proposition of a Phase Diagram, Langmuir 26 (7833â 7842) 2010 2. M. Anyfantakis, Z. Geng, et al. Modulation of the Coffee-Ring Effect in Particle/Surfactant Mixtures: the Importance of Particleâ Interface Interactions. Langmuir 31 ( 4113â 4120) 2015 3. E. Homede, A. Zigelman, et al. Signatures of van der Waals and electrostatic forces in the deposition of nanoparticle assemblies; J. Phys. Chem. Lett. 9 (5226â 5232) 2018 4. A. Zigelman and O Manor. Simulations of the dynamic deposition of colloidal particles from a volatile sessile drop, J. Colloids Interface Sci. 525 (282-290) 2018 5. A. Zigelman and O. Manor. The deposition of colloidal particles from a sessile drop of a volatile suspension subject to particle adsorption and coagulation, J. Colloids Interface Sci. 509 (195) 2018

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