Cyclic motion and inversion of surface flow direction in a dense polymer brush under shear

Müller, Marcus; Pastorino, Claudio

doi:10.1209/0295-5075/81/28002

Cited by 49 publications

(84 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We also checked the existence of cyclic motion dynamics in semiflexible chains under shear, found in previous works for fully flexible isolated grafted chains and polymer brushes [20,22]. We analysed the effect of stiffness in the mechanism of cyclic motion, whose origin is attributed to spontaneous fluctuations of the polymer chains towards regions of higher velocity in the liquid.…”

Section: B Flow Propertiesmentioning

confidence: 84%

See 1 more Smart Citation

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Speyer

Pastorino

2015

Soft Matter

Self Cite

View full text Add to dashboard Cite

We performed molecular dynamics simulations to study equilibrium and flow properties of a liquid in a nano-channel with confining surfaces coated with a layer of grafted semiflexible polymers. The coverage spans a wide range of grafting densities from essentially isolated chains to dense brushes. The end-grafted polymers were described by a bead spring model with an harmonic potential to include the bond stiffness of the chains. We varied the rigidity of the chains, from fully flexible polymers to rigid rods, in which the configurational entropy of the chains is negligible. The brushliquid interaction was tuned to obtain a super-hydrophobic channel, in which the liquid did not penetrate the polymer brush, giving rise to a Cassie-Baxter state. Equilibrium properties such us brush height and bending energy were measured, varying the grafting density and the stiffness of the polymers. We studied also the characteristics of the brush-liquid interface and the morphology of the polymers chains supporting the liquid for different bending rigidities. Non-equilibrium simulations were performed, moving the walls of the channel in opposite directions at constant speed, obtaining a Couette velocity profile in the bulk liquid. The molecular degrees of freedom of the polymers were studied as a function of the Weissenberg number. Also, the violation of the no-slip boundary condition and the slip properties were analyzed as a function of the shear rate, grafting density and bending stiffness. At high grafting densities, a finite slip length independent of the shear rate or bending constant was found, while at low grafting densities a very interesting non-monotonic behaviour on the bending constant is observed.

show abstract

Section: B Flow Propertiesmentioning

confidence: 84%

“…The cyclic dynamics is indeed reduced upon increase of the chain stiffness and vanishes completely for the stiffest chains (k b = 80ε). A more comprehensive characterization of the effect and its consequences for flow inversion [20,22] could be an interesting future study.…”

Section: B Flow Propertiesmentioning

confidence: 99%

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Speyer

Pastorino

2015

Soft Matter

Self Cite

View full text Add to dashboard Cite

show abstract

“…A relatively large number of experimental investigations (see Klein, Perahia & Warburg 1991; Klein et al 1994; Baker et al 2000; Ivkov et al 2001; Anastassopoulos et al 2006), analytical studies (see e.g. Rabin & Alexander 1990; Milner 1991 a ; Barrat 1992; Kumaran 1993; Sevick & Williams 1994; Aubouy, Harden & Cates 1996; Harden & Cates 1996) as well as computational simulations (see Lai & Binder 1993; Peters & Tildesley 1995; Miao, Guo & Zuckermann 1996; Grest 1996, 1999; Doyle, Shaqfeh & Gast 1997; Irfachsyad, Tildesley & Malfreyt 2002; Wijmans & Smit 2002; Kreer, Binder & Muser 2003; Huang, Wang & Laradji 2006; Pastorino et al 2006; Müller & Pastorino 2008) have addressed the dynamics of polymer brushes exposed to fluid shear flow. However, it is still not well understood whether the polymer brushes show conformational changes, that is, swelling or collapse of the brush height at a certain value of shear rate.…”

Section: Introductionmentioning

confidence: 99%

Simulation and modelling of slip flow over surfaces grafted with polymer brushes and glycocalyx fibres

Deng

Liang

et al. 2012

J. Fluid Mech.

View full text Add to dashboard Cite

Fabrication of functionalized surfaces using polymer brushes is a relatively simple process and parallels the presence of glycocalyx filaments coating the luminal surface of our vasculature. In this paper, we perform atomistic-like simulations based on dissipative particle dynamics (DPD) to study both polymer brushes and glycocalyx filaments subject to shear flow, and we apply mean-field theory to extract useful scaling arguments on their response. For polymer brushes, a weak shear flow has no effect on the brush density profile or its height, while the slip length is independent of the shear rate and is of the order of the brush mesh size as a result of screening by hydrodynamic interactions. However, for strong shear flow, the polymer brush is penetrated deeper and is deformed, with a corresponding decrease of the brush height and an increase of the slip length. The transition from the weak to the strong shear regime can be described by a simple ‘blob’ argument, leading to the scaling γ̇0 ∝ σ3/2, where γ̇0 is the critical transition shear rate and σ is the grafting density. Furthermore, in the strong shear regime, we observe a cyclic dynamic motion of individual polymers, causing a reversal in the direction of surface flow. To study the glycocalyx layer, we first assume a homogeneous flow that ignores the discrete effects of blood cells, and we simulate microchannel flows at different flow rates. Surprisingly, we find that, at low Reynolds number, the slip length decreases with the mean flow velocity, unlike the behaviour of polymer brushes, for which the slip length remains constant under similar conditions. (The slip length and brush height are measured with respect to polymer mesh size and polymer contour length, respectively.) We also performed additional DPD simulations of blood flow in a tube with walls having a glycocalyx layer and with the deformable red blood cells modelled accurately at the spectrin level. In this case, a plasma cell-free layer is formed, with thickness more than three times the glycocalyx layer. We then find our scaling arguments based on the homogeneous flow assumption to be valid for this physiologically correct case as well. Taken together, our findings point to the opposing roles of conformational entropy and bending rigidity – dominant effects for the brush and glycocalyx, respectively – which, in turn, lead to different flow characteristics, despite the apparent similarity of the two systems.

show abstract

“…For instance, this choice gives rise to a discontinuous non-bonded force, −∂H nb ({r i,s })/∂r j,t that acts on the t th segment of polymer j . The first-order assignment function, which is defined by [17,130] Π (1) …”

Section: Non-bonded Interactions: Collocation Grid Versus Weighting Fmentioning

confidence: 99%

“…Thus we can choose w 1,1 = 0 and match the pre-weighting factors at the interval boundaries, w p,mp = w p+1,1 . The partition function of the simulation is given by [130] …”

Section: Reversible Transformation Of Self-assembled Morphologiesmentioning

confidence: 99%

Studying Amphiphilic Self-assembly with Soft Coarse-Grained Models

2011

View full text Add to dashboard Cite

Highly coarse-grained models for investigating the self-assembly of lipids and copolymer materials are discussed. Soft interactions between segments that represent many atoms naturally arise in the course of systematic coarse-graining, and they are necessary for modeling fluctuation effects whose strengths is dictated by a large invariant degree of polymerization. The soft non-bonded interactions of the coarse-grained models are related to the excess free-energy functional of an equivalent field-theoretic description. The connection between the particle-based model and the field-theoretic description helps to identify the physical significance of the model interactions. Non-bonded interactions, which describe the complex phase behavior of compressible mixtures or include local fluid-like packing effects of the coarse-grained segments, can be systematically constructed based on liquid-state theory or classical density functional theory. Details of the computational implementation and limitations of soft coarse-grained models are discussed. Two computational techniques-field-theoretic force-matching and umbrella sampling-are devised for computing a free-energy functional from a particle-based description. They can be employed to (i) derive the non-bonded free-energy functional of a soft coarse-grained model from a more detailed computational model or to (ii) derive a field-theoretic description from a particle-based model. Moreover, different strategies for accurately calculating free energies of self-assembled systems are described and selected applications presented.

show abstract

Cyclic motion and inversion of surface flow direction in a dense polymer brush under shear

Cited by 49 publications

References 38 publications

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime

Simulation and modelling of slip flow over surfaces grafted with polymer brushes and glycocalyx fibres

Studying Amphiphilic Self-assembly with Soft Coarse-Grained Models

Contact Info

Product

Resources

About