Viscosity Behavior Research Articles

Effects of sugar molecules on the rheological and tribological properties and on the microstructure of agarose-based fluid gels

Introduction: Fluid gels exhibit a unique flow behaviour. Their pronounced viscoelastic behaviour arises from irregular microgel particles, leading to plasticity and yielding, as well as a characteristic transition from a solid to a fluid-like state. This is defined by both the core and the surface structures of the particles. Adding co-solutes such as sucrose alters the network properties at the molecular scale, affecting texture and lubrication. This study investigates how the microscopic changes due to sucrose addition correlate with macroscopic changes.Material and methods: Agarose fluid gels with varying sucrose concentrations were prepared and studied using the rheometer. Temperature dependent viscosity behaviour during gelation under shear was investigated in situ. Light microscopy and particle size measurements were examined, and complemented by amplitude, frequency and flow sweeps as well as tribological studies. These tests allow us to understand the influence of sucrose on the particle network formation.Results and discussion: Sucrose concentration influenced the sizes, shapes, and interconnected network structure of the microgel particles. These microstructural changes are closely related to the dynamic competition between gelation and disruption of the agarose chains during shear, which directly influences the rheological and tribological properties of the resulting fluid gels. Additionally, the association of the agarose chains and their gelation process is also influenced depending on whether the sucrose or agarose was first dissolved in water. The experimental observations suggest specific molecular mechanisms, explaining the role of sucrose in structure formation of agarose-based fluid gels. These results have the potential to expand the applications of fluid gels, which play a crucial role in modifying the texture and flow behaviour of foods and beverages, particularly in addressing challenges such as dysphagia.

Influence of Varying Oil-Water Contents on the Formation of Crude Oil Emulsion and Its Demulsification by a Lab-Grown Nonionic Demulsifier.

This study describes how varying oil/water contents affect emulsion formation and the impact they have on emulsion droplet size, viscosity, and interfacial behavior. Crude oil (continuous phase) volume fractions of 40, 50, 60, and 70 vol % were probed in the various W/O emulsions formed. Experimental results from optical morphology revealed the emulsion droplets kept reducing as the crude oil fraction kept increasing, while the droplets were nearly unnoticeable in the emulsions derived from 60 and 70% crude oil. The viscosity-shear rate of emulsions produced from 40, 50, and 60 vol % crude oil exhibited a non-Newtonian behavior owing to the substantial volume of water content in their emulsions, whereas the viscosity-shear rate of the emulsion with 70 vol % crude oil exhibited a Newtonian behavior similar to the pure crude oil, suggesting a thorough blending of oil-water at this crude oil fraction. Besides, the viscosity-temperature measurements revealed that the viscosity of these emulsions diminished as the temperature increased and the viscosity reduction became more noticeable in an emulsion comprising 70 vol % crude oil. In the interfacial assessment, the increased crude oil content in the produced emulsion led to a sharp reduction in the interfacial tension (IFT). The IFT values after 500 s contacts between the emulsion and water (surrounding phase) were 11.86, 10.02, 8.08, and 6.99 mN/m for 40, 50, 60, and 70 vol % crude oil, respectively. Demulsification experiments showed that water removal becomes more challenging with a large volume of crude oil and a small water content. Demulsification performances of the lab-grown nonionic demulsifier (NID) after 10 h of demulsification activity at room temperature (25 °C) were 98, 90, 17.5, and 10% for the emulsions formed from 40, 50, 60, and 70 vol % crude oil, respectively, indicating that the demulsification degree decreases with an increasing crude oil content. Viscosity-time determination was applied to affirm the activity of NID on the emulsion formulated with a 50% crude oil fraction. The injection of NID in this emulsion triggered a sharp viscosity reduction, indicating the adsorption of NID at the oil-water interface and disruption of emulsifiers, enabling emulsion stability.

Thermal and viscous slip effects on electroosmotic Casson nanofluid flow with microorganisms in peristaltic porous media

Current work focuses on increasing heat transmission in thermal systems with the incorporation of gyrotactic motile microbes, promoting the creation of structured fluids useful for bio-cooling and nanotechnology. This study explores the effects of electroosmosis and slip boundary conditions in a non-Newtonian Casson nanofluid with mass transfer. Specifically, it looks at bio-convection peristaltic events and conducts a thermodynamic analysis. The Arrhenius activation energy in an asymmetric channel is considered in this study. In addition, the authors evaluate viscous resistance, thermophoresis diffusion, porous surface properties, coupled convection, Brownian diffusion, and thermal viscosity behavior. The results obtained from mathematical expressions together with surface conditions are handled by means of a numerical algorithm implemented by means of the shooting technique through traditional program Mathematica, with the aid of its built-in tool, NDSolve. Many physical parameters, such as entropy generation, the Bejan number, velocity profiles, the density of gyrotactic motile microbes, and the accumulation profile of nanoparticles, are depicted graphically. The graphical study shows that entropy generation increases with a greater Helmholtz-Smoluchowski factor by 10%, but declines as the heat generation/absorption factor increases with same percentage. The Bejan number tends to increase with stronger heat sources by 5%. Application possibilities include improved control and effectiveness in mechanisms that include microfluidic equipment, systems for delivering medications, and biotechnological operations.

Non-similar analysis of radially magnetized flow and heat transfer of Reiner–Philippoff based nanofluid over a curved stretching surface with viscous dissipation

The aim of this study is to conduct a non-similar analysis of flow and heat transfer rheology of non-Newtonian fluid over a radially magnetized curved stretching surface in the presence of multiple type of nanoparticles. Reiner–Philippoff viscosity and homogenous models are incorporated in the governing equation to study the effects of non-Newtonian fluid and nanoparticles respectively. Reiner–Philippoff viscosity model is a complicated non-Newtonian fluid model presenting an implicit stress-strain relationship. This fluid model has ability to present viscosity behavior in response to varying viscoelastic conditions of shear-thinning, shear-thickening as well as Newtonian fluid. The nanoparticles of nickel, molybdenum disulfide, and tantalum are used to study the enhancement of the thermal conductivity of the fluid with influences of radiative heat flux and viscous dissipation. To attain a more precise and generalized analysis of the heat transfer and flow, the governing boundary layer equations are converted to non-similar form. The local non-similarity method up to second level of truncation is employed to numerically solve the resulting non-similar PDEs via bvp4c in MATLAB tools. To examine the impact of physical factors on flow and heat transfer, numerical data are visually and tabulated displayed. It is worth mentioning that the thermal radiation, curvature parameter, and magnetic number play important role in controlling wall drag and heat flux.

3D printing of rice starch incorporated peanut protein isolate paste: Rheological characterization and simulation of flow properties

This study investigates the viscosity and creep behavior of peanut protein isolate (PPI) paste incorporated with rice starch (RS) for potential applications in 3D printing. The change in flow properties during the 3D printing was also studied by numerical simulation. The paste exhibited shear-thinning behavior with yield stress. The pressure predicted from the Herschel-Bulkley model showed higher values than those derived from the Power-Law model. The PPI and RS levels had negligible influence on velocity and shear rate; however, they showed greater dependence on the inflow rate. The fractional element model described the creep data well (R2 > 0.9). The addition of PPI resulted in increased viscosity, simulated pressure, and mean extrusion force, with similar effects observed for RS, except at higher PPI levels. Furthermore, the 3D-printed objects revealed that deformations were pronounced at low concentrations of PPI and RS, while resolution suffered when employing higher concentrations of PPI and RS. Industrial relevanceUsing peanut protein isolate, a plant-based high protein ingredient in 3D printing, reduces energy consumption, thereby reducing carbon footprints, offers improved functional properties, and diversifies dietary options by offering an alternative protein source from peanuts. The printing is influenced by the rheological properties of food ink. Thus, knowing the rheological properties of food ink can help researchers and industries to prepare food inks with desired properties. The observations of numerical simulation of this work have the potential to offer practical insights for designing 3D printing systems. In summary, this work has the potential to aid in improving and developing food ink for 3D printing, hence enhancing the performance of extrusion-based 3D food printers.

Effect of Basicity and MgO/Al2O3 Ratio on Viscosity and Crystallization Behavior of HIsmelt Titanium‐Containing Slag

Numerous challenges persist in the smelting of vanadium–titanium magnetite using the blast furnace process. These challenges can be overcome by adopting the HIsmelt process, without the need for additional ore or enhanced slag operations. In this study, the effects of basicity and the MgO/Al2O3 ratio on slag viscosity and crystallization behavior are investigated through thermodynamic calculations and experiments. In the results, a decrease in slag viscosity with an increase in basicity and MgO/Al2O3 ratio is demonstrated. Notably, MgO/Al2O3 ratios have a minor impact on the viscosity and break temperature of the slag. With a TiO2 content of 40 wt% in the slag, perovskite phases are identified as the main equilibrium solid precipitates during the crystallization process under various basicity and MgO/Al2O3 ratios. As the slag temperature decreases further, the liquid phase content in the slag progressively decreases, reaching complete crystallization at 1159.0 °C. For industrial production, it is advisable to maintain the binary basicity of the slag within the range of 1.0–1.1, with the MgO/Al2O3 ratio around 0.6. Herein, the research findings contribute to a deeper understanding of the viscosity and crystallization behavior of HIsmelt titanium‐containing slag.

A theoretical study on the bulk viscosity in a compressible flow of an electrically conducting gas in the presence of magnetoacoustic waves

Only a few studies in the current literature are dedicated to the analysis of the effect of a bulk viscosity (i.e., second viscosity coefficient), and little is known about how to determine this quantity for high frequency compressible flows involving magnetic effect. The dissipation phenomenon associated with rapid expansions in the flow and the consequent attenuation of magnetoacoustic waves by the bulk viscosity has been neglected by several works on gas dynamics at high frequency. In this paper, we present a theoretical study on a compressible flow of an electrically conducting barotropic gas in the presence of a bulk viscosity. The governing equations represent a coupling between hydrodynamics and Maxwell's equations in the context of magnetohydrodynamics (MHD), and the relevant physical parameters of the flow are presented after an appropriate dimensional analysis of these equations. First, an analysis of small perturbations around an equilibrium state of the electrically conducting gas results in a system of linearized equations in the frequency-wavenumber space. The dispersion relation for magnetic waves is determined in terms of magnetic and the bulk viscosity effects. Second, based on the dispersion relation for magnetoacoustic waves, we propose a new expression to estimate the bulk viscosity in terms of the gas barotropic coefficient, the wavenumber, the wave frequency, the orientation of the applied field, and the Euler magnetic parameter, which measures the relative importance between magnetic and thermodynamic pressures. The behavior of the bulk viscosity is examined as a function of the wavenumber for different magnetic Euler numbers and field orientation, revealing how the rate of energy dissipation associated with the bulk viscosity can be controlled by varying the intensity of an applied magnetic field and its orientation. We show that understanding magnetoacoustic waves not only provides a tool for estimating the bulk viscosity in plasma flows in terms of these wave parameters, but also offers a potential pathway to manipulating both the magnitude and orientation of a magnetic field in order to reduce the rate of energy dissipation in most of plasma flows. This rate of dissipation produced by the rapid expansion of a recombining gas can be orders of magnitude larger than the one produced by the standard shear viscosity. These insights into bulk viscosity in compressible MHD flow at high frequency have potential applications in reacting plasmas where magnetoacoustic waves are damped by bulk viscosity, in production and dissipation of turbulence and in phenomenon of sonoluminescence as occurs in liquid containing gas bubble oscillating at fairly high frequency.

Solid propellant burn rate characterization: Effect of copper chromite blend with oxidiser and its storage

This work details the study conducted on composite solid propellants with activated copper chromite (ACR) as burn catalyst for its burn rate change with time due to the interaction of ammonium perchlorate (AP) with ACR. One of the hypotheses cited for burn rate reduction is the conversion of chromite in ACR to chromate by an electrolytic reaction with moisture in the presence of ammonium perchlorate. This hypothesis was studied by a design of experiments which includes blending ammonium perchlorate and ACR, Aluminum and ACR, stand alone ACR in raw material stage and the blends storage with time. The effect of moisture in AP is addressed by comparing undried and dried AP in the blends. The blended raw materials were characterized by Thermo-gravimetric analysis, Particle Size Distribution, surface area measurement, Scanning Electron Microscopy and chromium estimation. Results show that the conversion of chromium from chromite to chromate is very minimum in the presence of AP. Propellant samples are prepared with these blends at different time intervals to understand viscosity, mechanical properties and burn rate behavior with raw material storage. Experimental results show burn rate shows an opposite trend of increase with blend storage of 6 months. A plausible explanation for this observation is presented in the paper correlating the experimental conditions.

Influence of temperature, time, and moisture content on rheology of tomatoes and pepper purees

This study explored how temperature, time, and moisture content affect the rheological properties (apparent viscosity, flow behavior index, and consistency coefficient) of stored tomato and pepper purees. These purees were prepared with moisture contents of 85%, 90%, and 95% (w/v) using the hot-break method and tested over 6 days at 2-day intervals and temperatures of 5°C, 10°C, and 15°C. Results displayed distinct ranges for apparent viscosity, consistency coefficient, and flow behavior indices: tomato puree (2,519.9-4,324.6 mPa · s, 258.0-550.6 mPa · Sn, 1.80-0.48) and pepper puree (2,105.6-4,562.0 mPa · s, 268.4-580.4 mPa · Sn, 0.22-0.48). The temperature and storage time had significant (p≤0.05) effects, but moisture content did not affect these properties. Flow behavior and consistency coefficients demonstrated relative variation with apparent viscosity, indicating pseudoplastic behavior. Optimal processing and storage conditions were identified within specific ranges: 13.21-14.42°C for 2 days with 92.22-94.23% (w/v) moisture content for pepper, and 8.42-11.77°C for 2-6 days with 85% (w/v) moisture for tomato.

Diving deep into the superior lubrication efficiency: A dynamic approach incorporating covalent organic polymer as strengthening booster in paraffin oil through a holistic blend of experimental and computational approaches

This research addresses the paramount importance of enhancing surface protection and minimizing friction in mechanical systems through the novel design of covalent organic polymer additive (COPA). COPA-1 and COPA-2 were intricately designed to enhance surface protection and minimize wear. Tribological analysis revealed that the addition of an optimized concentration of COPA-1 (25 ppm) to base oil significantly reduced friction (∼60.49% decrease) and wear (∼79.23% decrease) while increasing load-bearing capacity to 588 N. Rheological analysis confirmed excellent shear stability and desirable viscosity behavior. Furthermore, computational tools like density functional theory and molecular dynamics simulations provided valuable insights into the adsorption mechanisms and tribological performance. This integration of experimental and computational insights highlights the transformative potential of COPA in revolutionizing lubrication technology.

Effect of bioactive borate glass on printability and physical properties of hydrogels

Hydrogels are a key component in bioinks and biomaterial inks for bioprinting due to their biocompatibility and printability at room temperature. The research described in the present paper contributes to the advancement of bioprinting by studying the effect of bioactive borate glass (BBG) incorporated into hydrogels on printability and physical properties. In this study, we fabricated 3D-printed hydrogel scaffolds using gelatin and alginate hydrogel mixture incorporated with various amounts of BBG, a bioceramic rich in therapeutic ions including boron, calcium, copper, and zinc. We investigated the effect of incorporating BBG on the density, viscosity, physical interactions, chemical structure, and shear thinning behavior of gelatin-alginate hydrogel biomaterial ink at different temperatures. After 3D printing and crosslinking of scaffolds, we measured mechanical properties and printing outcomes. The near-optimal extrusion temperature and pressure for uniform extrusion of hydrogel filaments at various BBG contents were determined. We compared the printing outcomes by quantifying the uniformity of printed filaments and shape fidelity of printed scaffolds. The rheological analysis showed that the addition of BBG increased the viscosity of the biomaterial inks and Young’s modulus of the 3D-printed scaffolds. Biomaterial inks with a dynamic viscosity within the range of 4.5 – 6.5 Pa·s showed the best printability across all samples. In conclusion, the inclusion of BBG contributes to a substantial improvement in the physical properties and printability of 3D-printed gelatin-alginate hydrogels.

Machine Learning-Based Predictive Model to Assess Rheological Dynamics of Eco-Friendly Oils as Biolubricants Enriched with SiO2 Nanoparticles

Efficient machinery operation relies on the performance of high-quality lubricants. Currently, mineral oils of different grades are widely employed for lubricating machine components, but their environmental impact is a concern. Biolubricants are potential alternatives to mineral oils due to environmental factors. The present study focuses on assessing the rheological characteristics of SiO2 nanoparticle (NP)-enhanced ecofriendly biolubricants for near zero and high-temperature conditions. Pure neem oil, pure castor oil and a 50:50 blend of both oils were considered as the base oils. Nanobiolubricants with enhanced dispersion stability were prepared for varied concentrations of NPs using an ultrasonification method. Viscosity analysis was conducted using an MCR-92 rheometer, employing the Herschel Bulkley model to precisely characterize the viscosity behavior of bio-oils. Due to the fluid–solid interaction between SiO2 NPs and bio-oils, a crossover trend was observed in the flow curves generated for different base oils enriched with SiO2 NPs. For neem oil, a significant increase in viscosity was noted for 0.2 wt% of NPs. Using the multilayer perceptron (MLP) algorithm, an artificial neural network (ANN) model was developed to accurately predict the viscosity variations in nanobiolubricants. The accuracy of the predicted values was affirmed through experimental investigations at the considered nanoSiO2 weight concentrations.

Wetting dynamics and adhesion of polyether ether ketone

Better understanding of how thermoplastics like polyether ether ketone (PEEK) spread on fiber surfaces within a composite, or themselves during fused filament fabrication is crucial for high-quality part production. Yet, due to its high melting temperature, the properties of molten PEEK have been rarely investigated. In this study, the viscosity, surface tension, and spreading dynamic behavior of molten PEEK on different substrates (glass, silicon wafer, and steel) were systematically explored. The analysis of the contact angle dynamics showed that both the classical hydrodynamics approach (HD) and molecular-kinetic theory (MKT) could model the experimental data satisfactorily. The relative contribution of the viscosity, as depicted by the MKT, to the energy dissipation process was found to dominate the contact-line friction contribution. In addition, a good agreement was found when calculating the physical work of adhesion between PEEK and the substrates in three different ways: at high temperatures (molten state), at room temperature (solid state), and using a combination of both states. This is a promising result indicating that the bonding ability of PEEK during processing could be predicted by characterizing its surface properties in the solid state.

Structural and flow rheological properties of pumpkin pectic polysaccharide extracted by citric acid

The present study aimed to investigate the structural and physicochemical characteristics of acid-extracted pumpkin pectic polysaccharide (AcPP) and to evaluate their flow rheological properties. AcPP was extracted from pumpkin pulp using the citric acid extraction method. The physicochemical and structural properties were analyzed by chemical methods and instrumental analyses. The obtained results showed that AcPP consisted predominantly of GalA (85.99 %) and small amounts of Rha, Gal, and Ara, with the ratio of HG/RG-I being 81.39/16.75. In addition, AcPP had medium DE (45.34 %) and contained four macromolecular populations with different Mw of 106.03 (main), 10.15, 4.99, and 2.90 kDa. The NMR analysis further confirmed that AcPP contained a linear backbone consisting of α-1,4-linked GalA residues, some of which were partially methyl-esterified. Furthermore, AcPP was amorphous in nature and had favorable thermal stability. The effects of extrinsic factors on the flow rheological properties of AcPP were evaluated. In particular, the high concentrations of CaCl2 (8 mM) and MgCl2 (10 mM) were effective in enhancing the viscosity and non-Newtonian shear-thinning behavior of the AcPP solution. This study elucidates the unique molecular structure of AcPP and suggests the potential of AcPP as a rheology modifier in low-viscous and mineral-reinforced beverages.

Investigating the Potential of a Transparent Xanthan Polymer for Enhanced Oil Recovery: A Comprehensive Study on Properties and Application Efficacy

This study delves into the properties and behavior of xanthan TNCS-ST, a specialized variant designed for enhanced oil recovery (EOR) purposes. A notable aspect of this polymer is its transparency and capability to dissolve in high salt concentrations, notably up to 18% total dissolved solids. Various laboratory methods are employed to assess the polymer’s distinctive traits, including transparency, salt tolerance, and high pyruvylation. These methods encompass preparing xanthan solutions, conducting filtration tests, assessing energy consumption, and measuring rheological properties. The findings highlight the influence of salt concentration on xanthan’s filterability, indicating increased energy requirements for dissolution with higher salt and xanthan concentrations. Additionally, this study observes temperature-dependent viscosity behavior in different solutions and evaluates the shear stability of xanthan. A significant and novel characteristic of TNCS-ST is its high salt tolerance, enabling complete dissolution at elevated salt concentrations, thus facilitating the filterability of the xanthan solution with sufficient time and energy input. Core flooding experiments investigate fluid dynamics within porous rock formations, particularly sandstone and carbonate rocks, while varying salinity. The results underscore the substantial potential of the new xanthan polymer, demonstrating its ability to enhance oil recovery in sandstone and carbonate rock formations significantly. Remarkably, the study achieves a noteworthy 67% incremental recovery in carbonate rock under the high salinity level tested, suggesting promising prospects for advancing enhanced oil recovery applications.

Numerical modeling of magnetohydrodynamic non‐Newtonian flow in a cross‐slot

AbstractThis study numerically investigates the characteristics of a non‐Newtonian magnetohydrodynamic flow in a cross‐slot. Numerical simulations are performed using power law, Bird–Carreau and Casson non‐Newtonian fluid models. The flow characteristics and shear viscosity behavior in the flow region are analyzed for different values of magnetic field. Additionally, the dynamic behavior of the bifurcated flow in the cross‐slot is studied in detail, and the computational results are compared with existing models. It is shown that the fluid velocity is reduced in both the inlet and outlet channels of the cross‐slot due to the magnetic field, regardless of the viscosity model. Moreover, it is found that the fluid viscosity increases along the centerline of the inlet channels and decreases in the outlet channels of the cross‐slot for all non‐Newtonian fluid models tested here. Furthermore, this study shows that the flow properties of the non‐Newtonian fluids can be controlled by changing the magnetic field strength. The results of this study will be useful for analyzing the flow behavior of blood in a microfluidic cross‐slot and other rheological fluids used in biochemical engineering and industrial processes, where higher mass transfer and mixing efficiency can be achieved by imposing an external magnetic field.Highlights Simulation of non‐Newtonian magnetohydrodynamic flow in a cross‐slot is conducted. Analysis of the flow and shear viscosity behavior for different Hartman number is performed. Flow properties were successfully controlled with the imposed external magnetic field.

Near-surface viscosity and complex crystal growth behavior in Se90Te10 thin films and bulk surface

Considering the resurgence of interest in selenium and tellurium-based solar cells and the inter alia related relationship between the device efficiency and post-growth annealing for crystallization, increased attention should be given to the understanding of crystallization process (formation of crystals, crystal positions, and nucleation and crystal growth kinetics). This work summarizes an extensive study of the crystal growth rates and near-surface viscosity at the Se90Te10 bulk surface and in thin films using nanoindentation and measurements of thermal grating decay. The crystal growth in Se90Te10 thin films occurs at two positions – at the thin film-substrate interface and the free surface of the thin film. Here, the crystallization of the interface crystals was quantitatively studied using microscopy down to the Tg and below. The influence of different substrates, illumination, and aging on crystal growth rates was tested in the studied thin films to understand the crystal growth properly. Regarding the crystal growth at the bulk surface, the sample size-dependent crystal growth rates were found. The values can be found in the region limited by growth rates of volume crystals (lower limit) and those found in thin films (upper limit). The growth data are combined with the near-surface viscosities measured in bulk samples and thin films to assess a suitable growth model for the description and prediction of the growth data in a wide temperature range.

Late time cosmological solutions in f(R,T) gravity in a viscous universe

Considering the condition on conservation of energy–momentum tensor (EMT), we study late time cosmological solutions in the context of [Formula: see text] gravity (where [Formula: see text] and n are constants) in a flat Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime. The present model discusses the case of a barotropic perfect fluid as the matter content of the Universe, along with the case when dissipative effects are taken into account. Briefly, assuming a single perfect fluid, we find that the mentioned model is not capable of presenting an observationally consistent picture of the late time accelerated expansion of the Universe; nevertheless, the model leads to admissible solutions when the bulk viscosity is included. In this regard, a consistent setting is found considering the Eckart, Truncated and Full Israel–Stewart theories which determine the behavior of bulk viscosity. In the presence of bulk viscosity, the behavior of the deceleration parameter (DP) shows that the underlying model can describe an acceptable evolution even if the isotropic pressure of matter content of the Universe is negligible.

Free volume theory explains the unusual behavior of viscosity in a non-confluent tissue during morphogenesis.

A recent experiment on zebrafish blastoderm morphogenesis showed that the viscosity (η) of a non-confluent embryonic tissue grows sharply until a critical cell packing fraction (ϕS). The increase in η up to ϕS is similar to the behavior observed in several glass-forming materials, which suggests that the cell dynamics is sluggish or glass-like. Surprisingly, η is a constant above ϕS. To determine the mechanism of this unusual dependence of η on ϕ, we performed extensive simulations using an agent-based model of a dense non-confluent two-dimensional tissue. We show that polydispersity in the cell size, and the propensity of the cells to deform, results in the saturation of the available free area per cell beyond a critical packing fraction. Saturation in the free space not only explains the viscosity plateau above ϕS but also provides a relationship between equilibrium geometrical packing to the dramatic increase in the relaxation dynamics.

Free volume theory explains the unusual behavior of viscosity in a non-confluent tissue during morphogenesis

A recent experiment on zebrafish blastoderm morphogenesis showed that the viscosity (η) of a non-confluent embryonic tissue grows sharply until a critical cell packing fraction (ϕS). The increase in η up to ϕS is similar to the behavior observed in several glass-forming materials, which suggests that the cell dynamics is sluggish or glass-like. Surprisingly, η is a constant above ϕS. To determine the mechanism of this unusual dependence of η on ϕ, we performed extensive simulations using an agent-based model of a dense non-confluent two-dimensional tissue. We show that polydispersity in the cell size, and the propensity of the cells to deform, results in the saturation of the available free area per cell beyond a critical packing fraction. Saturation in the free space not only explains the viscosity plateau above ϕS but also provides a relationship between equilibrium geometrical packing to the dramatic increase in the relaxation dynamics.