Category: NanoPaInt Blog

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Excited to share my latest interview featured in the LIMNI newsletter

In this interview, I discuss my journey into the fascinating world of nanoparticle research within capillary suspensions, under the guidance of Prof. Erin Koos.

I’m grateful for the opportunity provided by NanoPaint to contribute to our understanding of rheology and material behavior at the nanoscale. A special thanks to my peers and mentors for their support and inspiration!

https://us14.campaign-archive.com/?e=__test_email__&u=9d2b5793f6ef04b5f4288c1fc&id=7e73aa88d0

#MaterialScience #Nanotechnology #ResearchImpact #KULeuven

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Surface tension behavior of superspreading and non-superspreading trisiloxane surfactants

One parameter frequently considered to be relevant for superspreading of trisiloxane surfactants is surface tension kinetics. In the scientific literature, some experimental results reported for trisiloxane surfactants are in contradiction with fundamental concepts of surfactant monomer diffusion. Therefore, maximum bubble pressure tensiometry has been used to determine dynamic surface tension (DST) of two types of trisiloxane surfactants: superspreader and non-superspreader. Results show that both surfactants behave similarly at concentrations below critical micelle concentration (CMC), as expected. The CMC curves, as determined by drop shape analysis, confirmed that the more hydrophilic non-superspreader has a higher CMC as compared to the more hydrophobic superspreader. Accordingly, the lower surfactant monomer concentration of the superspreader results in a higher DST than the non-superspreader at the same surface age. So, in contrary to claims in the literature, there is nothing mysterious or unexpected concerning the surface tension behavior of trisiloxane surfactants.

More information about the subject is available on: https://doi.org/10.1007/s00396-023-05106-0

 

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The effect of diffusion coefficient on particles distribution during evaporation of drops deposited on superhydrophobic and parahydrophobic substrates

 

Introduction
The significance of nanofluid droplet evaporation is evident in its diverse applications, such as printing, coating, and supraparticle formation. Although both superhydrophobic and para-hydrophobic surfaces display high water contact angles, it’s important to note that the latter exhibits significantly higher contact angle hysteresis compared to the former. Simulating how nanoparticles are distributed within sessile droplets holds the potential for precise predictions regarding nanofluid drying and eventual deposition. It’s worth highlighting that the influence of the chosen diffusion coefficient model on nanoparticle dynamics has received limited attention in research so far.

Aim
Our objective is to develop a novel Computational Fluid Dynamics (CFD) framework using COMSOL Multiphysics to predict the influence of surface wettability and the solute diffusion model on the evaporation behavior of nanoparticle-laden droplets.

Diffusion Coefficient

Here we have applied the Stokes–Einstein equation, whose equation has been shown below:

D=kB ×T/(6πμrp)

Findings

CCA case

CCR case

 

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Exploring the Dynamic Behavior of a Water Droplet on a Vibrating Superhydrophobic Surface

The results of the dynamic behavior of a 10-microliter water droplet on a vibrating superhydrophobic surface at 40 Hz are presented in the video below. Key parameters essential for the study of droplet dynamics are obtained using a custom image processing code designed for this specific application. The video reveals the temporal evolution of critical parameters: maximum droplet width, maximum height, and lateral displacement of the center of mass. Playback of the video has been reduced to 5% of its original speed.

Additionally, a video that provides insight into the internal flow dynamics of an identical droplet undergoing the same conditions is also reported. This video showcases the transition from undisturbed flow, initially induced by evaporation, to a rotating internal flow resulting from the droplet’s rolling behavior caused by the applied vibration.

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Study of Vibrating Drops

A custom experimental setup has been developed by ESR 6 to investigate the dynamic behavior of liquid droplets on laterally vibrated substrate. This setup employs high-speed imaging techniques to capture and analyze the dynamic behavior of droplets. Additionally, Laser-Induced Fluorescence is used to visualize the internal flow patterns within the droplets. Below, is reported a sketch illustrating the core components of this setup.

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Adsorption of Dispersions of Silica Nanoparticles and anAmphiphilic Triblock Copolymer at Water‐Vapor Interface

This study is about the surface modification of hydrophilic silica nanoparticles by
non-chemical adsorption of an amphiphilic triblock copolymer (Pluronic F-127)
and its influence on surface tension and interfacial rheology. As copolymer
concentration increases, we observed an increment of the hydrodynamic diameter
and a reduction of the effective charge of the complexes. The presence of silica, at
low Pluronic F-127 concentration, increases surface tension and affects the
rheology: those results suggest that silica particles hinder Pluronic F-127
molecules reorganization at the interface, with subsequent increase in foam
stability.

 

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Effect of nanoparticles on the splashing of nanofluids

Liquid droplet splashing on various surfaces, including complex ones, is a widely studied topic in fluid mechanics. Recently, there has been growing interest in using nanofluids, which are created by adding nanoparticles to regular fluids, for applications like spray cooling. Despite the fact that a small nanoparticle addition doesn’t alter the fluid’s viscosity, it has a significant effect on splashing behavior. This means that we need to combine insights from studying nanosuspension rheology with this complex problem, as we deal with a seemingly simple material in a complex flow.

ESR05 is on a mission to explore the role of nanoparticles in the elongation and breakup of drops during the splashing of nanofluids. Below is a preliminary results video of a nanofluid drop splashing on a flat smooth surface. More details are published in the initial perspective paper “Role of Nanoparticles in Nanofluid Droplet Impact on Solid Surfaces” in Langmuir.

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Drop Impact Viscometry (DIV): Drop Impact on a Spherical Target

A novel method to measure viscosity has been developed by ESR05 using drop impact on a spherical target shown in the sketch below. It relies on high-speed imaging and analysis of the fluid mechanics using a theory developed specifically for this problem.  A water drop impact example is shown in the video below. The method is currently being upgraded to study nanosuspensions and nanoemulsions.

 

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Extensional Rheology and Dewetting of Nanosuspensions

The stretching of a liquid bridge is governed by inertia and the internal stresses which are determined by the liquid rheological properties. Some details on the flow, breakup, and flow instabilities can be found in our publications [1],[2][3]. A liquid bridge stretching setup capable of accelerating up to 20G is built specifically for this project. The phenomena are very fast and often fascinating.

A recent review article titled “Forced flows in liquid bridges” is now available for open access in the journal of Current Opinion in Colloid and Interface Science.

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