Journal of Non-Newtonian Fluid Mechanics最新文献

{"title":"Comparing flows of FENE-P, sPTT, and Giesekus model fluids in a helical static mixer","authors":"T.P. John ,&nbsp;J.T. Stewart ,&nbsp;R.J. Poole ,&nbsp;A. Kowalski ,&nbsp;C.P. Fonte","doi":"10.1016/j.jnnfm.2024.105249","DOIUrl":"10.1016/j.jnnfm.2024.105249","url":null,"abstract":"<div><p>Helical static mixers are used widely for mixing of non-Newtonian fluid flows in the laminar regime. We study flows of three viscoelastic constitutive models (sPTT, FENE-P, and Giesekus) in the helical static mixer using computational fluid dynamics. These three models have similarities in steady viscometric flows in that they all exhibit shear thinning and their planar extensional viscosities can be matched, but their responses can differ in complex geometries. We observe flow distribution asymmetries at the element intersections for all three models, which hinders the mixing performance of the device. These have previously been observed with the constant shear viscosity FENE-CR model. The asymmetry behaves similarly between the sPTT and Giesekus models, however the FENE-P model behaves in a distinct manner; beyond a critical degree of elasticity, the asymmetry sharply changes direction. This was also observed previously with the FENE-CR model. These results suggest that shear thinning and second-normal stress differences (present in the Giesekus model) do not significantly influence mixing performance in the range of conditions studied. We show that increasing the aspect (length/diameter) ratio of the mixer elements mitigates the poor mixing caused by elasticity. Overall, this study provides insight into the behaviour of these well-used constitutive models in complex, industrially-relevant flows.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"329 ","pages":"Article 105249"},"PeriodicalIF":3.1,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S037702572400065X/pdfft?md5=0eebb93da631ec40576abb91ba0feccf&pid=1-s2.0-S037702572400065X-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141026089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shear thickening of dilute suspensions of fractal silica aggregates","authors":"Sachidananda Barik ,&nbsp;Pradip K. Bera ,&nbsp;A.K. Sood ,&nbsp;Sayantan Majumdar","doi":"10.1016/j.jnnfm.2024.105246","DOIUrl":"10.1016/j.jnnfm.2024.105246","url":null,"abstract":"<div><p>The increase in viscosity under shear known as shear thickening (ST) is an inherent property of a wide variety of dense particulate suspensions. Recent studies indicate that ST systems formed by fractal particles are promising candidates for various practical applications. However, ST in fractal systems remains poorly explored. Here we experimentally study the ST behavior in suspensions of hydrophilic fumed silica (FS) particles in glycerol. Remarkably, unlike non-fractal systems, we observe a strong dependence of the onset stress for ST on the volume fraction of fractal objects and a reversible weakening of the ST response that depends strongly on the particle volume fraction as well as the properties of the FS system. Using in-situ boundary imaging, we map out the spatio-temporal flow properties during ST for different FS systems. We find that the fractal nature and structural properties like the internal branching of the particles can qualitatively explain the complex ST phase diagram of these systems.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"328 ","pages":"Article 105246"},"PeriodicalIF":3.1,"publicationDate":"2024-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140793778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamics of a thin film of viscoelastic fluid flowing down an inclined or vertical plane","authors":"S. Dholey,&nbsp;S. Gorai","doi":"10.1016/j.jnnfm.2024.105237","DOIUrl":"10.1016/j.jnnfm.2024.105237","url":null,"abstract":"&lt;div&gt;&lt;p&gt;The stability characteristics of a thin film of viscoelastic (Walters’ &lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;B&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;′&lt;/mo&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; model) fluid flowing down an inclined or vertical plane are analyzed under the combined influence of gravity and surface tension. A nonlinear free surface evolution equation is obtained by using the momentum-integral method. Normal mode technique and multiple scales method are used to obtain the results of linear and nonlinear stability analysis of this problem. The linear stability analysis gives the critical condition and critical wave number &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;k&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; which include the viscoelastic parameter &lt;span&gt;&lt;math&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, angle of inclination of the plane &lt;span&gt;&lt;math&gt;&lt;mi&gt;θ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, Reynolds number &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; and Weber number &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;W&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. The weakly nonlinear stability analysis that is based on the second Landau constant &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;J&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, reveals the condition for the existence of explosive unstable and supercritical stable zone along with the other two (unconditional stable and subcritical unstable) flow zones of this problem which is &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;mi&gt;o&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mi&gt;θ&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mi&gt;W&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;k&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; = 0. It is found that all the four distinct flow zones of this problem exist in &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;-&lt;span&gt;&lt;math&gt;&lt;mi&gt;k&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;-, &lt;span&gt;&lt;math&gt;&lt;mi&gt;θ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;-&lt;span&gt;&lt;math&gt;&lt;mi&gt;k&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;- and &lt;span&gt;&lt;math&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;-&lt;span&gt;&lt;math&gt;&lt;mi&gt;k&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;-plane after the critical value of &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;θ&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, respectively. A novel result of this analysis is that the film flow is stable (unstable) for a negative (positive) value of &lt;span&gt;&lt;math&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; irrespective of the values of &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&gt;&lt;mi&gt;θ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, as for example, a solution of polyisobutylene in cetane, compared with the viscous &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; film flow case. Finally, we scrutinize the effect of &lt;span&gt;&lt;math&gt;&lt;mi&gt;Γ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; on the threshold amplitude and nonlinear wave speed by depicting some numerical exa","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"329 ","pages":"Article 105237"},"PeriodicalIF":3.1,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140757978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical study of collective motion of microswimmers in Giesekus viscoelastic fluids","authors":"Minkang Zhang ,&nbsp;Zhaosheng Yu ,&nbsp;Zhenyu Ouyang ,&nbsp;Yan Xia ,&nbsp;Zhaowu Lin","doi":"10.1016/j.jnnfm.2024.105245","DOIUrl":"10.1016/j.jnnfm.2024.105245","url":null,"abstract":"<div><p>Few simulations currently explore the dynamics of microswimmers swimming through viscoelastic environments. In this study, we employ a direct-forcing fictitious domain method to investigate the collective behavior of spherical squirmers within viscoelastic fluids at low Reynolds numbers. Our findings reveal clear differences between pusher and puller swimmers: puller swimmers exhibit a tendency to aggregate into clusters, particularly noticeable in suspensions with high concentrations, which increases the average speed of the swimmers. Through an analysis of the cluster-size distribution function, we observe the larger-scale clusters of puller swimmers with increasing concentration. Moreover, the presence of fluid elasticity significantly reduces both the average swimming speed of squirmers and the fluid’s kinetic energy.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"329 ","pages":"Article 105245"},"PeriodicalIF":3.1,"publicationDate":"2024-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140770245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamics of a viscoelastic droplet migrating in a ratchet microchannel under AC electric field","authors":"Anant Kumar Nema,&nbsp;Manoj Kumar Tripathi","doi":"10.1016/j.jnnfm.2024.105236","DOIUrl":"https://doi.org/10.1016/j.jnnfm.2024.105236","url":null,"abstract":"<div><p>Droplet-based microfluidic devices can be powered or manipulated by applying an external electric field, and the ability to precisely control the flow in such devices is essential for various engineering and biomedical applications. In this numerical study, we investigate the deformation dynamics of a viscoelastic droplet in a ratchet microchannel under the influence of an AC electric field. We employ the leaky-dielectric electrohydrodynamic model for both the immiscible fluid phases coupled with the Oldroyd-B model for the droplet fluid. The effect of geometrical parameters such as the type of ratchet and the wavenumber of the ratchets along with the flow parameters such as the electrocapillary number, Weissenberg number and the capillary number significantly affect the droplet shape dynamics and the polymer chain extension. For the parameters considered in this work, the electric force tends to stretch the droplet in the streamwise direction and enhances the droplet deformation and polymer extension. Several interesting effects arise as a result of the coupling of the periodic hydrodynamic forcing of the ratchet walls and the electric field. Specifically, an exponential rise in the polymer chain extension for higher ratchet wavenumbers is observed, along with the cross-stream migration of the droplet for higher electrocapillary numbers when it reaches the outlet of the ratchet constriction.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"328 ","pages":"Article 105236"},"PeriodicalIF":3.1,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140631251","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Smoothed Particle Hydrodynamics simulations of integral multi-mode and fractional viscoelastic models","authors":"Luca Santelli ,&nbsp;Adolfo Vázquez-Quesada ,&nbsp;Marco Ellero","doi":"10.1016/j.jnnfm.2024.105235","DOIUrl":"https://doi.org/10.1016/j.jnnfm.2024.105235","url":null,"abstract":"<div><p>To capture specific characteristics of non-Newtonian fluids, during the past years fractional constitutive models have become increasingly popular. These models are able to capture, in a simple and compact way, the complex behaviour of viscoelastic materials, such as the change in power-law relaxation pattern during the relaxation process of some materials. Using the Lagrangian Smoothed-Particle Hydrodynamics (SPH) method we can easily track particle history; this allows us to solve integral constitutive models in a novel way, without relying on complex tasks.</p><p>Hence, we develop here a SPH integral viscoelastic method which is first validated for simple Maxwell or Oldroyd-B models under Small Amplitude Oscillatory Shear (SAOS) and start-up channel flows. By exploiting the structure of the integral method, a multi-mode Maxwell model is then implemented. Finally, the method is extended to include fractional constitutive models, validating the approach by comparing results with theory.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"329 ","pages":"Article 105235"},"PeriodicalIF":3.1,"publicationDate":"2024-04-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140816637","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reversal of particle Migration for viscoelastic solution at high solvent viscosity","authors":"Xavier Salas-Barzola ,&nbsp;Guillaume Maîtrejean ,&nbsp;Clément de Loubens ,&nbsp;Antoine Naillon ,&nbsp;Enric Santanach Carreras ,&nbsp;Hugues Bodiguel","doi":"10.1016/j.jnnfm.2024.105234","DOIUrl":"10.1016/j.jnnfm.2024.105234","url":null,"abstract":"<div><p>The imbalance of normal stress around a particle induces its transverse migration in pressure-driven viscoelastic flow, offering possibilities for particle manipulation in microfluidic devices. Theoretical predictions align with experimental evidence of particles migrating towards the center-line of the flow. However, these arguments have been challenged by both experimental and numerical investigations, revealing the potential for a reversal in the direction of migration for viscoelastic shear-thinning fluids. Yet, a significant property of viscoelastic liquids that remains largely unexplored is the ratio of solvent viscosity to the sum of solvent and polymer viscosities, denoted as <span><math><mi>β</mi></math></span>. We computed the lift coefficients of a freely flowing cylinder in a bi-dimensional Poiseuille flow with Oldroyd-B constitutive equations. A transition from a negative (center-line migration) to a positive (wall migration) lift coefficient was demonstrated with increasing <span><math><mi>β</mi></math></span> values. Analogous to inertial lift, the changes in the sign of the lift coefficient were strongly correlated with abrupt (albeit small) variations in the rotation velocity of the particle. We established a scaling law for the lift coefficient that is proportional, as expected, to the Weissenberg number, but also to the difference in rotation velocity between the viscoelastic and Newtonian cases. If the particle rotates more rapidly than in the Newtonian case, it migrates towards the wall; conversely, if the particle rotates more slowly than in the Newtonian case, it migrates towards the center-line of the channel. Finally, experiments in microfluidic slits confirmed migration towards the wall for viscoelastic fluids with high viscosity ratio.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"329 ","pages":"Article 105234"},"PeriodicalIF":3.1,"publicationDate":"2024-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140407132","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Slot coating of viscoplastic materials: A computational study of the effects of viscoplasticity on the flow dynamics and low-flow limit","authors":"I.R. Siqueira ,&nbsp;R.L. Thompson ,&nbsp;M.S. Carvalho ,&nbsp;P.R. de Souza Mendes","doi":"10.1016/j.jnnfm.2024.105222","DOIUrl":"https://doi.org/10.1016/j.jnnfm.2024.105222","url":null,"abstract":"<div><p>Yield-stress materials such as structurally complex formulations of paints, slurries, and waxes have been long ubiquitous in the coating industry, though the practice of coating engineering remains largely empirical as the fundamental role of viscoplasticity due to the yield stress of the coating material in most coating applications is still unclear. Here, we couple a recent harmonic mean viscosity regularization for the Bingham model with a well-established finite element/elliptic mesh generation method for free surface flows to present a detailed computational study of slot coating applications of viscoplastic materials. By neglecting inertia and focusing on the downstream section of a slot coater, we introduce suitable dimensionless parameters to discuss a comprehensive set of results that unravels a striking impact of viscoplasticity on the flow dynamics and low-flow limit. We show that viscoplastic effects have major implications to the velocity field and recirculation pattern in the coating bead as well as to the development length and free surface in the film formation region. Most importantly, we find that viscoplastic effects markedly widen the operating window of the process, delaying the onset of the low-flow limit and thereby suggesting that structurally complex yield-stress materials may be used to coat thinner films and/or at higher speeds than predicted by the standards far established for simple Newtonian liquids.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"327 ","pages":"Article 105222"},"PeriodicalIF":3.1,"publicationDate":"2024-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140341896","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact of drops of a nanoparticle dispersion in a viscoelastic liquid","authors":"Takshak Shende,&nbsp;Ian Eames,&nbsp;Mohammad Hadi Esteki,&nbsp;Yousef Javanmardi,&nbsp;Emad Moeendarbary","doi":"10.1016/j.jnnfm.2024.105221","DOIUrl":"10.1016/j.jnnfm.2024.105221","url":null,"abstract":"<div><p>The evaluation of nanoparticle dispersion within viscoelastic fluids upon impact on hydrophobic and hydrophilic surfaces is conducted using the Euler-Lagrangian technique. The volume-of-fluid approach is employed in conjunction with the Lagrangian method to model the transport of nanoparticles in a three-phase system (particles-air-viscoelastic fluid). The assessment of nanoparticle dispersion was conducted over a range of Péclet numbers and contact angles (<span><math><mrow><mi>θ</mi><mo>=</mo><mn>30</mn><mo>°</mo></mrow></math></span> and <span><math><mrow><mn>120</mn><mo>°</mo></mrow></math></span>) in three-dimensional (3D) space using the mean square displacement method. The findings suggest that the dispersion of nanoparticles is mainly influenced by normal stress. During droplet impact, nanoparticles exhibit non-Fickian superdiffusive behaviour due to the viscoelastic fluid’s non-Gaussian distribution of velocity and stresses (normal and shear) fields. The wettability of the fluid with solid surfaces substantially affected the dispersion of nanoparticles in the viscoelastic fluid.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"327 ","pages":"Article 105221"},"PeriodicalIF":3.1,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0377025724000375/pdfft?md5=330f024441ea0bfebfed29addc47af18&pid=1-s2.0-S0377025724000375-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140273938","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modeling Elongational Rheology of Model Poly((±)-lactide) Graft Copolymer Bottlebrushes","authors":"Manfred H. Wagner ,&nbsp;Aristotelis Zografos ,&nbsp;Valerian Hirschberg","doi":"10.1016/j.jnnfm.2024.105220","DOIUrl":"https://doi.org/10.1016/j.jnnfm.2024.105220","url":null,"abstract":"<div><p>The shear and elongational rheology of graft polymers with poly(norbornene) backbone and one poly((<em>±</em>)-lactide) side chain of length N_sc = 72 per two backbone repeat units (grafting density <em>z</em> <em>=</em> <em>0.5</em>) was investigated recently by Zografos et al. [Macromolecules 56, 2406–2417 (2023)]. Above the star-to-bottlebrush transition at backbone degrees of polymerization of N_bb&gt;70, increasing strain hardening was observed with increasing N_bb, which was attributed to side-chain interdigitation resulting in enhanced friction in bottlebrush polymers. Here we show that the elongational rheology of the copolymers with entangled side chains and an unentangled backbone can be explained by the Hierarchical Multi-mode Molecular Stress Function (HMMSF) model, which takes into account hierarchical relaxation and dynamic dilution of the backbone by the side chains, leading to constrained Rouse relaxation. In nonlinear viscoelastic flows with larger Weissenberg numbers, the effect of dynamic dilution is increasingly reduced leading to stretch of the backbone chain caused by side chain constraints and resulting in strain hardening. If the backbone is sufficiently long, hyperstretching is observed at larger strain rates, i.e. the stress growth is greater than expected from affine stretch.</p></div>","PeriodicalId":54782,"journal":{"name":"Journal of Non-Newtonian Fluid Mechanics","volume":"327 ","pages":"Article 105220"},"PeriodicalIF":3.1,"publicationDate":"2024-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0377025724000363/pdfft?md5=aabbc6a2887aaa174356ee61436c0f47&pid=1-s2.0-S0377025724000363-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140195897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}