Deformation and Orientation of Flexible Polymers in Solution under Shear Flow: A New Picture for Intermediate Reduced Shear Rates

1995 ◽  
Vol 28 (14) ◽  
pp. 5097-5108 ◽  
Author(s):  
Carlo Pierleoni ◽  
Jean-Paul Ryckaert
Keyword(s):  
Shear Flow ◽  
Flexible Polymers ◽  
Shear Rates

In Situ Dynamics of Concentrated DNA Molecules in a Shear Flow

1999 ◽  
Author(s):  
Philip LeDuc ◽  
Bryan Pfister ◽  
Yangqing Xu ◽  
Denis Wirtz ◽  
Gang Bao
Keyword(s):  
Shear Flow ◽  
Conformational Changes ◽  
Flow Direction ◽  
Polymer Concentration ◽  
Polymer Dynamics ◽  
Dna Molecules ◽  
Flexible Polymers ◽  
Shear Rates ◽  
Dna Solutions

Abstract Polymer dynamics has been studied for many years because of its importance in many areas including materials, mechanics, biology, and medicine (Munk, 1989; Hoffman, et al., 1984). The dynamics of macromolecules in shear flow has been studied using light scattering and birefringence, but the effect of shear on the dynamics of individual polymers is not well understood (Doi & Edwards, 1986; de Gennes, 1991; de Gennes, 1997). Recently we studied the conformational changes of DNA molecules under shear in dilute concentration (LeDuc et al., 1998). Here we report the observations of the dynamics of fluorescently-labeled DNA molecules in a shear flow with increased concentration. Under a controlled shear flow, these flexible polymers exhibit various extended conformations, which range from parallel to perpendicular in orientation when compared to the flow direction. The amount of stretching that occurs in these experiments is found to be less than that for the dilute concentrations of the DNA solutions. Further, the stretching of the molecular solutions is found even at shear rates much smaller than the inverse of the relaxation time of the molecule. The in situ observations also reveal the effect of polymer concentration on the entanglement of macromolecules. These results provide insight into the behavior of individual and concentrated polymer molecules under shear and help further development of models for polymer dynamics (Perkins, et al., 1994; Smith, et al., 1992; Wirtz, 1995).

Role of membrane viscosity in the orientation and deformation of a spherical capsule suspended in shear flow

1985 ◽  
Vol 160 ◽  
pp. 119-135 ◽  
Author(s):  
D. Barthes-Biesel ◽  
H. Sgaier
Keyword(s):  
Relaxation Time ◽  
Shear Flow ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Liquid Droplets ◽  
Regular Perturbation ◽  
Shear Rates ◽  
Freely Suspended ◽  
Spherical Capsule

Red blood cells or artificial vesicles may be conveniently represented by capsules, i.e. liquid droplets surrounded by deformable membranes. The aim of this paper is to assess the importance of viscoelastic properties of the membrane on the motion of a capsule freely suspended in a viscous liquid subjected to shear flow. A regular perturbation solution of the general problem is obtained when the particle is initially spherical and undergoing small deformations. With a purely viscous membrane (infinite relaxation time) the capsule deforms into an ellipsoid and has a continuous flipping motion. When the membrane relaxation time is of the same order as the shear time, the particle reaches a steady ellipsoidal shape which is oriented with respect to streamlines at an angle that varies between 45° and 0°, and decreases with increasing shear rates. Furthermore it is predicted that the deformation reaches a maximum value, which is consistent with experimental observations of red blood cells.

Just a Drop of Blood: Exploration of Shear-Dependent Platelet Adhesion and Activation in Microfluidic Devices.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3650-3650 ◽  
Author(s):  
Ana Kasirer-Friede ◽  
Edgar Gutierrez ◽  
Brian Petrich ◽  
Sanford J. Shattil ◽  
Mark H. Ginsberg ◽  
...  
Keyword(s):  
Shear Rate ◽  
Shear Flow ◽  
Blood Sample ◽  
Platelet Adhesion ◽  
Thrombus Formation ◽  
Microfluidic Devices ◽  
Extracellular Matrices ◽  
Wild Type ◽  
Shear Rates ◽  
Platelet Thrombus

Abstract Interactions of platelets and their adhesion receptors with extracellular matrices are essential for hemostasis. Platelets experience different shear rates as they circulate through the vasculature. Conventional studies of platelets in shear flow are performed in simple flow chambers with relatively large volumes of cells and reagents, limiting testing when these are in short supply. Microfluidics technology should enable the concurrent study of multiple small volume samples across a wide range of shear rates, thereby allowing trends to emerge that might be difficult to detect otherwise. To achieve this goal, we fabricated PDMS microfluidic devices that permit testing of dynamic platelet adhesion over a 100-fold span of shear rates from a single 200μl blood sample. Alternate device design permits synchronous monitoring of platelet adhesion from two genetically distinct blood samples or treatment groups. We have used this technology to gain new insights into integrin αIIbβ3 function in mepacrine-labeled platelets under shear flow. In whole blood, the adhesion of wild-type mouse platelets to a fibrinogen-coated substrate was shear rate-dependent, similarly to human platelets. In contrast, adhesion of αIIbβ3-deficient (β3−/−) platelets was virtually absent above a shear rate of 100 s−1. To distinguish between requirements for the presence of an intact extracellular αIIbβ3 ligand binding domain versus an intact integrin activation process, we used mice with a Y/A mutation at residue 747 in the β3 cytoplasmic tail (β3Y747A), that selectively blocks talin interaction with β3, agonist-induced αIIbβ3 activation, and platelet thrombus formation in vivo. When compared to wild-type and β3−/− platelets, a normal αIIbβ3 extracellular domain on β3Y747A platelets partially rescued dynamic adhesion to fibrinogen by 50–80% at ≤130 s−1, but by only 25% at 250 s−1. Treatment of wild-type platelets with PGE1 to inhibit platelet activation similarly reduced adhesion to fibrinogen at higher shear rates. On fibrillar type I collagen, wild-type platelets formed an initial monolayer and progressively larger thrombi over time. In addition, platelets supported rolling and firm adhesion of granulocytes in a manner dependent on shear rate, platelet P-selectin and granulocyte PSGL1. In contrast, no platelet thrombus growth on collagen was observed with αIIbβ3-deficient or β3Y747A platelets, or with wild-type platelets treated with PGE1. Furthermore, even the initial adhesion of αIIbβ3-deficient and β3Y747A platelets to collagen rapidly declined at increasing shear rates (120%, 30% and 7% of wild-type platelets at 70, 1000 and 4000 s−1, respectively (p < 0.01)). Taken together, these studies establish that microfluidics provides an efficient and high-throughput platform to study mechanisms of dynamic platelet adhesion, activation and thrombus formation on extracellular matrices. Furthermore, they demonstrate a role for talin-dependent αIIbβ3 activation in all of these processes. This platform will be particularly useful under conditions where blood sample volumes or reagents are limiting, such as in neonates, and genetically-modified model organisms.

Small-angle neutron scattering study of shear-induced phase separation in aqueous poly(N-isopropylacrylamide) solutions

e-Polymers ◽  
2004 ◽  
Vol 4 (1) ◽  
Author(s):  
Markus Stieger ◽  
Peter Lindner ◽  
Walter Richtering
Keyword(s):  
Phase Separation ◽  
Shear Flow ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Separation Process ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Strong Shear ◽  
Phase Separation Process

Abstract The influence of shear flow on the structure of concentrated aqueous poly(N-isopropylacrylamide) solutions near the lower critical solution temperature was investigated by means of small-angle neutron scattering. Two samples, both in the semi-dilute regime above the overlap concentration, were studied. The scattering curve of the less concentrated sample was not influenced by shear flow, although high shear rates were reached. The more concentrated 4 wt.-% sample, however, displayed shear-induced demixing under strong shear flow conditions. Experiments at different shear stresses indicated the existence of a threshold shear stress and the phase separation process became faster with increasing stress. The two-dimensional scattering patterns remained isotropic even during the phase separation process and the correlation length as obtained from an Ornstein- Zernike plot increased. The influence of shear flow on the phase separation process is thus similar to a temperature increase. The results are in excellent agreement with data from recent rheo-optical experiments where shear-induced phase separation was also observed for the concentrated solution at high shear rates. Apparently, strong shear flow exerts an effect analogous to a temperature increase.

A simple model to understand the effect of membrane shear elasticity and stress-free shape on the motion of red blood cells in shear flow

Soft Matter ◽  
2015 ◽  
Vol 11 (42) ◽  
pp. 8372-8382 ◽  
Author(s):  
Jules Dupire ◽  
Manouk Abkarian ◽  
Annie Viallat
Keyword(s):  
Simple Model ◽  
Shear Flow ◽  
Blood Cell ◽  
Red Blood Cells ◽  
Red Blood Cell ◽  
Time Variation ◽  
Blood Cells ◽  
Shear Rates ◽  
Shear Elasticity

Time variation of the inclination (θ) and the membrane rotation (ω) of a red blood cell tumbling in a shear flow for three shear rates.

scholarly journals Gel Characteristics of Urea-Formaldehyde Resin under Shear Flow Conditions

2013 ◽  
Vol 2013 ◽  
pp. 1-5
Author(s):  
Dang-liang Wang ◽  
Han-ying Bai ◽  
Gao Yue
Keyword(s):  
Shear Flow ◽  
Urea Formaldehyde ◽  
Urea Formaldehyde Resin ◽  
Formaldehyde Resin ◽  
Flow Conditions ◽  
Shear Rates ◽  
Magnetic Stirrer ◽  
Gelling Time ◽  
Chinese Coal ◽  
Static Conditions

Urea-formaldehyde resin (UFR), one of chemical grouts in which the major ingredients are urea-formaldehyde and resin, is widely used in Chinese coal mines grouting. The gel characteristics of urea-formaldehyde resin (UFR) chemical grout under static conditions have been studied by many researchers. However, there is little research carried out on the gel characteristics under shear flow conditions. In fact, chemical grout like UFR keeps in shear flow conditions before gelling in the grouting process. In order to investigate the gel characteristics of UFR in shear flow conditions, an apparatus which consists of a magnetic stirrer and a viscometer was established. Magnetic stirrer was used to shear UFR at different velocity. Then the changes of UFR viscosity could be recorded by viscometer. As a result, the gel characteristics were summarized under different shear rates, and a formula of gelling is derived. The results show that the grouting flow rate influences the gelling time. Faster flow rates will cause longer gelling time, which means that the time for the grout to gel during the flowing process under shear flow conditions is longer than that under static conditions.

scholarly journals Competition Between Red Blood Cell Aggregation and Breakup: Depletion Force due to Filamentous Viruses vs. Shear Flow

2021 ◽  
Vol 9 ◽  
Author(s):  
O. Korculanin ◽  
T. Kochetkova ◽  
M. P. Lettinga
Keyword(s):  
Shear Flow ◽  
Flow Direction ◽  
Cell Aggregation ◽  
Interaction Force ◽  
Range Interaction ◽  
Microscopy Imaging ◽  
Shear Rates ◽  
Critical Range ◽  
Full Contact ◽  
Tumbling Motion

Human blood is a shear-thinning fluid with a complex response that strongly depends on the red blood cell’s (RBC’s) ability to form aggregates, called rouleaux. Despite numerous investigations, microscopic understanding of the break up of RBC aggregates has not been fully elucidated. Here, we present a study of breaking up aggregates consisting of two RBCs (a doublet) during shear flow. We introduce the filamentous fd bacteriophage as a rod-like depletant agent with a very long-range interaction force, which can be tuned by the rod’s concentration. We visualize the structures while shearing by combining a home-build counter-rotating cone-plate shear cell with microscopy imaging. A diagram of dynamic states for shear rates versus depletant concentration shows regions of different flow responses and separation stages for the RBCs doublets. With increasing interaction forces, the full-contact flow states dominate, such as rolling and tumbling. We argue that the RBC doublets can only undergo separation during tumbling motion when the angle between the normal of the doublets with the flow direction is within a critical range. However, at sufficiently high shear rates, the time spent in the critical range becomes too short, such that the cells continue to tumble without separating.

Dynamics of individual flexible polymers in a shear flow

Nature ◽  
10.1038/21148 ◽  
1999 ◽  
Vol 399 (6736) ◽  
pp. 564-566 ◽  
Author(s):  
Philip LeDuc ◽  
Charbel Haber ◽  
Gang Bao ◽  
Denis Wirtz
Keyword(s):  
Shear Flow ◽  
Flexible Polymers

Morphological Evolution of SCN Crystals in a Shear Flow

2014 ◽  
Vol 217-218 ◽  
pp. 83-90
Author(s):  
Mehdi Reisi ◽  
Behzad Niroumand ◽  
Ebrahim Shirani
Keyword(s):  
Shear Flow ◽  
Morphological Evolution ◽  
Solid Particles ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Cluster Morphology ◽  
Size And Morphology ◽  
Low Shear

Morphological evolution of a transparent model succinonitrile (SCN) material during solidification was investigated in an apparatus resembling a shearing-disc viscometer. The in situ microscopic observations showed that fragmentation decreased the average particles size, but did not result in transition of dendritic to spherical morphology. At low shear rates, the degenerated dendrites and at high shear rates, the pseudo-cluster morphology was observed. It was revealed that coarsening has the most important effect on the final morphology of solid particles. The quantitative influences of shearing rate and intensity on the size and morphology of solid crystals were also discussed based on the measurements on the microstructures.

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