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Bamboriya OP, Tirumkudulu MS. Universality in the buckling behavior of drying suspension drops. SOFT MATTER 2023; 19:2605-2611. [PMID: 36947449 DOI: 10.1039/d2sm01688e] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Fast evaporation of particle-suspension drops results in complex morphologies of the final dried granules. Understanding the morphological transformations is important to industrial processes such as spray drying where droplets of particulate suspensions are dried at a fast rate to produce granules of thermally sensitive materials. The transformation of an initial spherical shell to complex morphologies of the final dried granule has been attributed to the buckling of particle-packed shells. Here, we demonstrate a universal scaling law for buckling that depends on the particle size, hardness, particle packing and size of drying drop. The critical transition for buckling is set by a dimensionless number that measures the competition between the compressive stress generated by capillary forces and the elastic strength of the packing. The same dimensionless number is also responsible for cracking of drying colloidal films, suggesting a universality in the mechanical behaviour of particle packings saturated with a solvent. These results should enable design of hierarchically structured, buckle-free granules with varying porosity, surface composition and internal structure.
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Affiliation(s)
- Om Prakash Bamboriya
- Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India.
| | - Mahesh S Tirumkudulu
- Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India.
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2
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Hegde O, Basu S. Spatio-temporal modulation of self-assembled central aggregates of buoyant colloids in sessile droplets using vapor mediated interactions. J Colloid Interface Sci 2021; 598:136-146. [PMID: 33895535 DOI: 10.1016/j.jcis.2021.04.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Revised: 04/03/2021] [Accepted: 04/04/2021] [Indexed: 11/24/2022]
Abstract
A functional sessile droplet containing buoyant colloids (ubiquitous in applications like chemical sensors, drug delivery systems, and nanoreactors) forms self-assembled aggregates. The particles initially dispersed over the entire drop-flocculates at the center. We attribute the formation of such aggregates to the finite radius of curvature of the drop and the buoyant nature of particles. Initially, larger particles rise to the top of the droplet (due to higher buoyancy force), and later the smaller particles join the league, leading to the graded size distribution of the central aggregate. This can be used to segregate polydisperse hollow spheres based on size. The proposed scaling analysis unveils insights into the distinctive particle transport during evaporation. However, the formation of prominent aggregates can be detrimental in applications like spray painting, sprinkling of pesticides, washing, coating, lubrication, etc. One way to avoid the central aggregate is to spread the droplets completely (contact angle ~ 00), thus theoretically creating an infinite radius of curvature leading to uniform deposition of buoyant particles. Practically, this requires a highly hydrophilic surface, and even a small inhomogeneity on the surface would pin the droplet giving it a finite radius of curvature. Here, we demonstrate using non-intrusive vapor mediated Marangoni convection (Velocity scale ~ O(103) higher than the evaporation-driven convection) can be vital to an efficient and on-demand manipulation of the suspended micro-objects. The interplay of surface tension and buoyancy force results in the transformation of flow inside the droplet leads to spatiotemporal disbanding of agglomeration at the center of the droplet.
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Affiliation(s)
- Omkar Hegde
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India
| | - Saptarshi Basu
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India.
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3
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Al Harraq A, Bharti B. Increasing aspect ratio of particles suppresses buckling in shells formed by drying suspensions. SOFT MATTER 2020; 16:9643-9647. [PMID: 32954396 DOI: 10.1039/d0sm01467b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Solvent evaporation in unpinned droplets of colloidal suspensions leads to the formation of porous shells which buckle under the pressure differential imposed by drying. We investigate the role of aspect ratio of rod-shaped particles in suppressing such buckling instabilities. Longer, thinner rods pack into permeable shells with consequently lower Darcy's pressure and thus avoid buckling.
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Affiliation(s)
- Ahmed Al Harraq
- Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
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Katiyar P, Singh JK. Evaporation induced self-assembly of different shapes and sizes of nanoparticles: A molecular dynamics study. J Chem Phys 2019; 150:044708. [DOI: 10.1063/1.5053974] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Parul Katiyar
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Jayant K. Singh
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India
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Bansal L, Sanyal A, Kabi P, Pathak B, Basu S. Engineering Interfacial Processes at Mini-Micro-Nano Scales Using Sessile Droplet Architecture. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:8423-8442. [PMID: 29470090 DOI: 10.1021/acs.langmuir.7b04295] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Evaporating sessile functional droplets act as the fundamental building block that controls the cumulative outcome of many industrial and biological applications such as surface patterning, 3D printing, photonic crystals, and DNA sequencing, to name a few. Additionally, a drying single sessile droplet forms a high-throughput processing technique using low material volume which is especially suitable for medical diagnosis. A sessile droplet also provides an elementary platform to study and analyze fundamental interfacial processes at various length scales ranging from macroscopically observable wetting and evaporation to microfluidic transport to interparticle forces operating at a nanometric length scale. As an example, to ascertain the quality of 3D printing we must understand the fundamental interfacial processes at the droplet scale. In this article, we review the coupled physics of evaporation flow-contact-line-driven particle transport in sessile colloidal droplets and provide methodologies to control the same. Through natural alterations in droplet vaporization, one can change the evaporative pattern and contact line dynamics leading to internal flow which will modulate the final particle assembly in a nontrivial fashion. We further show that control over particle transport can also be exerted by external stimuli which can be thermal, mechanical oscillations, vapor confinement (walled or a fellow droplet), or chemical (surfactant-induced) in nature. For example, significant augmentation of an otherwise evaporation-driven particle transport in sessile droplets can be brought about simply through controlled interfacial oscillations. The ability to control the final morphologies by manipulating the governing interfacial mechanisms in the precursor stages of droplet drying makes it perfectly suitable for fabrication-, mixing-, and diagnostic-based applications.
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Yamada Y, Horibe A. Discontinuous contact line motion of evaporating particle-laden droplet on superhydrophobic surfaces. Phys Rev E 2018; 97:043113. [PMID: 29758695 DOI: 10.1103/physreve.97.043113] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Indexed: 11/07/2022]
Abstract
The three-phase contact line motion on a superhydrophobic surface through particle-laden sessile droplet evaporation was investigated. Sample surfaces with micro- and nanoscale structures were generated by various durations of chemical treatment and SiO_{2} spherical particles with different sizes were used as additives of test liquid. The contact angle and contact radius profiles were studied, and the discontinuous motion of those profiles on micro- and nanostructured hierarchical surfaces was observed, while it was not observed on a nanostructured superhydrophobic surface. Suspensions with low particle concentration induced a relatively large contact radius jump compared to the high-concentrated condition; in contrast, the previous report showed the opposite trend for flat surfaces. In order to explain this result, a simple explanation was provided-that the stacked particles at the contact line region suppressed to the deformation of the liquid-vapor interface near the contact line. This is confirmed by side-view images of the deposition results because the contact line region after evaporation of the dense suspension showed a large contact angle compared to that of the diluted suspension. In addition, deposition at the contact line region was observed by scanning electron microscopy to discuss the effect of the characteristic length scale of the surface structure and particles on the contact line motion. We believe that these results will help one to understand the deposition phenomenon during particle-laden droplet evaporation on the superhydrophobic surface and its applications such as evaporation-driven materials deposition.
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Affiliation(s)
- Yutaka Yamada
- Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
| | - Akihiko Horibe
- Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
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Kabi P, Chaudhuri S, Basu S. Micro to Nanoscale Engineering of Surface Precipitates Using Reconfigurable Contact Lines. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:2109-2120. [PMID: 29345953 DOI: 10.1021/acs.langmuir.7b04368] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Nanoscale engineering has traditionally adopted the chemical route of synthesis or optochemical techniques such as lithography requiring large process times, expensive equipment, and an inert environment. Directed self-assembly using evaporation of nanocolloidal droplet can be a potential low-cost alternative across various industries ranging from semiconductors to biomedical systems. It is relatively simple to scale and reorient the evaporation-driven internal flow field in an evaporating droplet which can direct dispersed matter into functional agglomerates. The resulting functional precipitates not only exhibit macroscopically discernible changes but also nanoscopic variations in the particulate assembly. Thus, the evaporating droplet forms an autonomous system for nanoscale engineering without the need for external resources. In this article, an indigenous technique of interfacial re-engineering, which is both simple and inexpensive to implement, is developed. Such re-engineering widens the horizon for surface patterning previously limited by the fixed nature of the droplet interface. It involves handprinting hydrophobic lines on a hydrophilic substrate to form a confinement of any selected geometry using a simple document stamp. Droplets cast into such confinements get modulated into a variety of shapes. The droplet shapes control the contact line behavior, evaporation dynamics, and complex internal flow pattern. By exploiting the dynamic interplay among these variables, we could control the deposit's macro- as well as nanoscale assembly not possible with simple circular droplets. We provide a detailed mechanism of the coupling at various length scales enabling a predictive capability in custom engineering, particularly useful in nanoscale applications such as photonic crystals.
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Affiliation(s)
- Prasenjit Kabi
- Interdisciplinary Centre for Energy Research, ‡Department of Mechanical Engineering, and §Department of Aerospace Engineering, Indian Institute of Science , Bangalore, Karnataka 560012, India
| | - Swetaprovo Chaudhuri
- Interdisciplinary Centre for Energy Research, ‡Department of Mechanical Engineering, and §Department of Aerospace Engineering, Indian Institute of Science , Bangalore, Karnataka 560012, India
| | - Saptarshi Basu
- Interdisciplinary Centre for Energy Research, ‡Department of Mechanical Engineering, and §Department of Aerospace Engineering, Indian Institute of Science , Bangalore, Karnataka 560012, India
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Pathak B, Hatte S, Basu S. Evaporation Dynamics of Mixed-Nanocolloidal Sessile Droplets. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:14123-14129. [PMID: 29160710 DOI: 10.1021/acs.langmuir.7b03578] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Evaporation dynamics of a particle-laden droplet has been a topic of interest in recent times owing to its widespread applications, ranging from surface patterning to drug delivery systems. The interplay of evaporation-induced internal flow dynamics, contact line dynamics, and nanoparticle self-assembly govern the morphologies of the residual structures. Fine-tuning of these residual structures is thus possible by controlling the governing parameters. A nanoparticle-laden sessile droplet placed on a hydrophobic substrate undergoes buckling phenomenon that results in a domelike structure with cavity on the surface. In the present work, it is shown that the addition of sodium dodecyl sulfate (SDS) surfactant in minute concentrations (0.005-0.02 wt %) can affect the contact line dynamics and subsequent buckling dynamics of a nanoparticle-laden droplet evaporating on a hydrophobic substrate. With increase in the initial SDS concentration, the morphologies of the residual structures show transition from a buckled dome structure to a flat flowerlike shape. Moreover, a critical SDS concentration (>0.0075 wt % in 20 wt % silica) is identified for the complete suppression of buckling instabilities. Last, the effects of droplet spreading on the surface crack dynamics are discussed.
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Affiliation(s)
- Binita Pathak
- Department of Mechanical Engineering, Indian Institute of Science , Bangalore 560012, India
| | - Sandeep Hatte
- Department of Mechanical Engineering, Indian Institute of Science , Bangalore 560012, India
| | - Saptarshi Basu
- Department of Mechanical Engineering, Indian Institute of Science , Bangalore 560012, India
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Bansal L, Basu S, Chakraborty S. Confinement suppresses instabilities in particle-laden droplets. Sci Rep 2017; 7:7708. [PMID: 28794458 PMCID: PMC5550431 DOI: 10.1038/s41598-017-08126-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 07/10/2017] [Indexed: 11/09/2022] Open
Abstract
Tiny concentrations of suspended particles may alter the behavior of an evaporating droplet remarkably, leading to partially viscous and partially elastic dynamical characteristics. This, in turn, may lead to some striking mechanical instabilities, such as buckling and rupture. Here, we report certain non-trivial implications of the consequent morpho-dynamics (macro to nano scales), when such an evaporating droplet is encapsulated in a confined environment. Compared to unconfined scenario, we report non-intuitive suppression of rupturing beyond a critical confinement. We attribute this to confinement-induced dramatic alteration in the evaporating flux, leading to distinctive spatio-temporal characteristics of the internal flow leading to preferential particle transport and subsequent morphological transitions. We present a regime map quantifying buckling-non buckling pathways. These results may turn out to be of profound importance towards achieving desired morphological features of a colloidal droplet, by aptly tuning the confinement space, initial particle concentration, as well as the initial droplet volume.
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Affiliation(s)
- Lalit Bansal
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore, 560012, India
| | - Saptarshi Basu
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore, 560012, India.
| | - Suman Chakraborty
- Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, 721302, India.
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Bansal L, Chakraborty S, Basu S. Confinement-induced alterations in the evaporation dynamics of sessile droplets. SOFT MATTER 2017; 13:969-977. [PMID: 28078334 DOI: 10.1039/c6sm02429g] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Evaporation of sessile droplets has been a topic of extensive research. However, the effect of confinement on the underlying dynamics has not been well explored. Here, we report the evaporation dynamics of a sessile droplet in a confined fluidic environment. Our findings reveal that an increase in the channel length delays the completion of the evaporation process and leads to unique spatio-temporal evaporation flux and internal flow. The evaporation modes (constant contact angle and constant contact radius) during the droplet lifetime however exhibit global similarity when normalized by appropriate length and timescales. These results are explained in light of an increase in vapor concentration inside the channel due to greater accumulation of water vapor on account of increased channel length. We have formulated a theoretical framework which introduces two key parameters namely an enhanced concentration of the vapor field in the vicinity of the confined droplet and a corresponding accumulation lengthscale over which the accumulated vapor relaxes to the ambient concentration. Using these two parameters and modified diffusion based evaporation we are able to show that confined droplets exhibit a universal behavior in terms of the temporal evolution of each evaporation mode irrespective of the channel length. These results may turn out to be of profound importance in a wide variety of applications, ranging from surface patterning to microfluidic technology.
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Affiliation(s)
- Lalit Bansal
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India.
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Basu S, Bansal L, Miglani A. Towards universal buckling dynamics in nanocolloidal sessile droplets: the effect of hydrophilic to superhydrophobic substrates and evaporation modes. SOFT MATTER 2016; 12:4896-4902. [PMID: 27125247 DOI: 10.1039/c6sm00837b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The evaporation of a nanocolloidal sessile droplet exhibits preferential particle assembly, nanoporous shell formation and buckling to form cavities with unique morphological features. Here, we have established many universal trends that explain the buckling dynamics under one umbrella irrespective of hydrophobicity, evaporation mode and particle loading. We provide a regime map explaining the droplet morphology and buckling characteristics for droplet evaporation on various substrates. Specifically, we find that the final droplet volume and the radius of curvature at the buckling onset are universal functions of particle concentration. Furthermore, we establish that post-buckling cavity growth is evaporation driven regardless of the substrate.
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Affiliation(s)
- Saptarshi Basu
- Department of Mechanical Engineering, Indian Institute of Science, Bangalore, 560012, India.
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