Special Issue "Complex Fluids and Interfaces"

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Analysis and Characterization".

Deadline for manuscript submissions: closed (5 May 2021) | Viewed by 7162

Special Issue Editors

Dr. Alexis Darras
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Guest Editor
Experimental Physics, Saarland University, 66123 Saarbruecken, Germany
Interests: colloids; aggregation; self-assembly; biophysics; fluid mechanics
Prof. Dr. Benoit Scheid
E-Mail Website
Guest Editor
TIPs, Université Libre de Bruxelles, C.P. 165/67, Avenue F. D. Roosevelt 50, 1050 Bruxelles, Belgium
Interests: interfacial dynamics; surface rheology; material processing; microfluidics

Special Issue Information

Dear Colleagues,

Complex fluids have attracted much attention from researchers thanks to their ominous presence in industrial and natural processes. For example, many drinks, paints or biological fluids fall within this category and are of the highest interest in practical applications such as food processing, printings and bio-medical devices. One of the aspects of these processes is the way the fluid behaves at its interface or interact with it.

For instance, deposition of colloidal particles on surfaces is a ubiquitous phenomenon, both in natural phenomena and industrial applications. It might be an undesired feature, as in apparition of deposits or clogs in food processing, or the direct purpose of an application, as in printing or blood smear tests. Understanding of the physico-chemical mechanisms underlying those processes is a key knowledge in order to prevent or enhance them. Evaporation of colloidal suspensions is a particular mechanism leading to such depositions. Since the seminal work of Deegan et al., this specific topic has received a particular attention from researchers, and the rate of publications in this domain is constantly increasing. Various processes have been highlighted as having a key contribution in the eventual dried pattern. Interactions between colloidal particles and surfaces are particularly relevant, as well as the flows in the continuous media containing the particles. This lead to an increased interest in topics such as evaporation of binary mixtures, interaction between polymers coatings and colloids deposition, Marangoni flows, self-assembly of anisotropic particles, resistivity of self-assembled particles, evaporative stresses, …

This special issue aims to gather the latest contributions from various research group which might help to understand the ways complex fluids behaves at or close to their interfaces. We hope it will offer both a state of the art of the current research interests in the field, and a good starting point for beginners to have a global insight of the field. Therefore, contributions to any topic related to the field, e.g. colloids-surface interactions, polymer coating, interfacial flows or self-assembled surface patterns, are welcome.

Dr. Alexis Darras and Prof. Benoit Scheid

Guest Editors


Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Colloids
  • Deposition
  • Evaporation
  • Self-assembly
  • Interface
  • Coating
  • Flow fields

Published Papers (6 papers)

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Research

Article
Experimental Validation of Falling Liquid Film Models: Velocity Assumption and Velocity Field Comparison
Polymers 2021, 13(8), 1205; https://doi.org/10.3390/polym13081205 - 08 Apr 2021
Cited by 1 | Viewed by 530
Abstract
This publication focuses on the experimental validation of film models by comparing constructed and experimental velocity fields based on model and elementary experimental data. The film experiment covers Kapitza numbers Ka = 278.8 and Ka = 4538.6, a Reynolds number range of 1.6–52, [...] Read more.
This publication focuses on the experimental validation of film models by comparing constructed and experimental velocity fields based on model and elementary experimental data. The film experiment covers Kapitza numbers Ka = 278.8 and Ka = 4538.6, a Reynolds number range of 1.6–52, and disturbance frequencies of 0, 2, 5, and 7 Hz. Compared to previous publications, the applied methodology has boundary identification procedures that are more refined and provide additional adaptive particle image velocimetry (PIV) method access to synthetic particle images. The experimental method was validated with a comparison with experimental particle image velocimetry and planar laser induced fluorescence (PIV/PLIF) results, Nusselt’s theoretical prediction, and experimental particle tracking velocimetry (PTV) results of flat steady cases, and a good continuity equation reproduction of transient cases proves the method’s fidelity. The velocity fields are reconstructed based on different film flow model velocity profile assumptions such as experimental film thickness, flow rates, and their derivatives, providing a validation method of film model by comparison between reconstructed velocity experimental data and experimental velocity data. The comparison results show that the first-order weighted residual model (WRM) and regularized model (RM) are very similar, although they may fail to predict the velocity field in rapidly changing zones such as the front of the main hump and the first capillary wave troughs. Full article
(This article belongs to the Special Issue Complex Fluids and Interfaces)
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Article
Molecular Dynamics Simulation of Nanocellulose-Stabilized Pickering Emulsions
Polymers 2021, 13(4), 668; https://doi.org/10.3390/polym13040668 - 23 Feb 2021
Viewed by 1565
Abstract
While the economy is rapidly expanding in most emerging countries, issues coupled with a higher population has created foreseeable tension among food, water, and energy. It is crucial for more sustainable valorization of resources, for instance, nanocellulose, to address the core challenges in [...] Read more.
While the economy is rapidly expanding in most emerging countries, issues coupled with a higher population has created foreseeable tension among food, water, and energy. It is crucial for more sustainable valorization of resources, for instance, nanocellulose, to address the core challenges in environmental sustainability. As the complexity of the system evolved, the timescale of project development has increased exponentially. However, research on the design and operation of integrated nanomaterials, along with energy supply, monitoring, and control infrastructure, has seriously lagged. The development cost of new materials can be significantly reduced by utilizing molecular simulation technology in the design of nanostructured materials. To realize its potential, nanocellulose, an amphiphilic biopolymer with the presence of rich -OH and -CH structural groups, was investigated via molecular dynamics simulation to reveal its full potential as Pickering emulsion stabilizer at the molecular level. This work has successfully quantified the Pickering stabilization mechanism profiles by nanocellulose, and the phenomenon could be visualized in three stages, namely the initial homogenous phase, rapid formation of micelles and coalescence, and lastly the thermodynamic equilibrium of the system. It was also observed that the high bead order was always coupled with a high volume of phase separation activities, through a coarse-grained model within 20,000 time steps. The outcome of this work would be helpful to provide an important perspective for the future design and development of nanocellulose-based emulsion products, which cater for food, cosmeceutical, and pharmaceutical industries. Full article
(This article belongs to the Special Issue Complex Fluids and Interfaces)
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Article
New Spectrophotometric Method for Quantitative Characterization of Density-Driven Convective Instability
Polymers 2021, 13(4), 661; https://doi.org/10.3390/polym13040661 - 23 Feb 2021
Cited by 1 | Viewed by 644
Abstract
CO2 convective dissolution has been regarded as one of the fundamental mechanisms to accelerate the mass transfer of CO2 into brine. We present a new spectrophotometric method to characterize the convective instability and measure the dissolved CO2 mass, which enables [...] Read more.
CO2 convective dissolution has been regarded as one of the fundamental mechanisms to accelerate the mass transfer of CO2 into brine. We present a new spectrophotometric method to characterize the convective instability and measure the dissolved CO2 mass, which enables the real-time quantitative visualization of CO2/brine transport mechanisms. Successive images were captured to identify the finger development regimes, and the convection morphologies were analyzed by the fingers length and affected area. CO2 solubility was experimentally studied, and the results are in agreement with the theoretical calculations. CO2 mass transfer flux was investigated as the Sherwood number changed. The increase in salinity and temperature has a negative effect on CO2 dissolution; here, numerical simulation and experimental phenomena are qualitatively consistent. In general, these findings confirm the feasibility of the method and improve the understanding of the physical process of CO2 convective dissolution, which can help assess the CO2 solubility trapping mass. Full article
(This article belongs to the Special Issue Complex Fluids and Interfaces)
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Article
Molecular Dynamics Simulations of Crystal Nucleation near Interfaces in Incompatible Polymer Blends
Polymers 2021, 13(3), 347; https://doi.org/10.3390/polym13030347 - 22 Jan 2021
Cited by 3 | Viewed by 1869
Abstract
We apply molecular dynamics (MD) simulations to investigate crystal nucleation in incompatible polymer blends under deep supercooling conditions. Simulations of isothermal nucleation are performed for phase-separated blends with different degrees of incompatibility. In weakly segregated blends, slow and incompatible chains in crystallizable polymer [...] Read more.
We apply molecular dynamics (MD) simulations to investigate crystal nucleation in incompatible polymer blends under deep supercooling conditions. Simulations of isothermal nucleation are performed for phase-separated blends with different degrees of incompatibility. In weakly segregated blends, slow and incompatible chains in crystallizable polymer domains can significantly hinder the crystal nucleation and growth. When a crystallizable polymer is blended with a more mobile species in interfacial regions, enhanced molecular mobility leads to the fast growth of crystalline order. However, the incubation time remains the same as that in pure samples. By inducing anisotropic alignment near the interfaces of strongly segregated blends, phase separation also promotes crystalline order to grow near interfaces between different polymer domains. Full article
(This article belongs to the Special Issue Complex Fluids and Interfaces)
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Article
Change in Convection Mixing Properties with Salinity and Temperature: CO2 Storage Application
Polymers 2020, 12(9), 2084; https://doi.org/10.3390/polym12092084 - 14 Sep 2020
Cited by 3 | Viewed by 954
Abstract
In this study, we visualised CO2-brine, density-driven convection in a Hele-Shaw cell. Several experiments were conducted to analyse the effects of the salinity and temperature. The salinity and temperature of fluids were selected according to the storage site. By using charge [...] Read more.
In this study, we visualised CO2-brine, density-driven convection in a Hele-Shaw cell. Several experiments were conducted to analyse the effects of the salinity and temperature. The salinity and temperature of fluids were selected according to the storage site. By using charge coupled device (CCD) technology, convection finger formation and development were obtained through direct imaging and processing. The process can be divided into three stages: diffusion-dominated, convection-dominated and shutdown stages. Fingers were formed along the boundary at the onset time, reflecting the startup of convection mixing. Fingers formed, moved and aggregated with adjacent fingers during the convection-dominated stage. The relative migration of brine-saturated CO2 and brine enhanced the mass transfer. The effects of salinity and temperature on finger formation, number, and migration were analysed. Increasing the salinity accelerated finger formation but suppressed finger movement, and the onset time was inversely related to the salinity. However, the effect of temperature on convection is complex. The dissolved CO2 mass was investigated by calculating the CO2 mass fraction in brine during convection mixing. The results show that convection mixing greatly enhanced mass transfer. The study has implications for predicting the CO2 dissolution trapping time and accumulation for the geological storage of CO2. Full article
(This article belongs to the Special Issue Complex Fluids and Interfaces)
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Article
Influence of the Architecture of Soft Polymer-Functionalized Polymer Nanoparticles on Their Dynamics in Suspension
Polymers 2020, 12(8), 1844; https://doi.org/10.3390/polym12081844 - 17 Aug 2020
Cited by 3 | Viewed by 1106
Abstract
The behavior of nanogels in suspension can be dramatically affected by the grafting of a canopy of end-tethered polymer chains. The architecture of the interfacial layer, defined by the grafting density and length of the polymer chains, is a crucial parameter in defining [...] Read more.
The behavior of nanogels in suspension can be dramatically affected by the grafting of a canopy of end-tethered polymer chains. The architecture of the interfacial layer, defined by the grafting density and length of the polymer chains, is a crucial parameter in defining the conformation and influencing the dynamics of the grafted chains. However, the influence of this architecture when the core substrate is itself soft and mobile is complex; the dynamics of the core influences the dynamics of the tethered chains, and, conversely, the dynamics of the tethered chains can influence the dynamics of the core. Here, poly(styrene) (PS) particles were functionalized with poly(methyl acrylate) (PMA) chains and swollen in a common solvent. NMR relaxation reveals that the confinement influences the mobility of the grafted chain more prominently for densely grafted short chains. The correlation time associated with the relaxation of the PMA increased by more than 20% when the grafting density increased for short chains, but for less than 10% for long chains. This phenomenon is likely due to the steric hindrance created by the close proximity to the rigid core and of the neighboring chains. More interestingly, a thick layer of a densely grafted PMA canopy efficiently increases the local mobility of the PS cores, with a reduction of the correlation time of more than 30%. These results suggest an interplay between the dynamics of the core and the dynamics of the canopy. Full article
(This article belongs to the Special Issue Complex Fluids and Interfaces)
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