Coil-stretch transitions in mixed shear and extensional flows of dilute polymer solutions

Larson, Ronald G.; Magda, Jules J.

doi:10.1021/ma00197a022

Cited by 120 publications

(87 citation statements)

References 7 publications

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“…For example, dilute solution theory predicts a coilstretch transition under extensional flow at Wi = 0.5 based on the Zimm relaxation time. 53 The shear value is in reasonable agreement with Anwar et al 22 who observed the onset of FEN at Wi = 0.6 based on the center of mass diffusion time of a C20 molecule, rather than the Rouse relaxation time. The smaller critical strain rateε c observed under extension as compared to shear is likely due to the greater capacity for extensional flow to orient and stretch molecules, a phenomenon that has been observed in dilute solutions, 54 and can be observed in Fig.…”

Section: Discussionsupporting

confidence: 86%

Molecular simulation of flow-enhanced nucleation in n-eicosane melts under steady shear and uniaxial extension

Nicholson

Rutledge

2016

The Journal of Chemical Physics

118

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Non-equilibrium molecular dynamics is used to study crystal nucleation of n-eicosane under planar shear and, for the first time, uniaxial extension. A method of analysis based on the mean first-passage time is applied to the simulation results in order to determine the effect of the applied flow field type and strain rate on the steady-state nucleation rate and a characteristic growth rate, as well as the effects on kinetic parameters associated with nucleation: the free energy barrier, critical nucleus size, and monomer attachment pre-factor. The onset of flow-enhanced nucleation (FEN) occurs at a smaller critical strain rate in extension as compared to shear. For strain rates larger than the critical rate, a rapid increase in the nucleation rate is accompanied by decreases in the free energy barrier and critical nucleus size, as well as an increase in chain extension. These observations accord with a mechanism in which FEN is caused by an increase in the driving force for crystallization due to flow-induced entropy reduction. At high applied strain rates, the free energy barrier, critical nucleus size, and degree of stretching saturate, while the monomer attachment pre-factor and degree of orientational order increase steadily. This trend is indicative of a significant diffusive contribution to the nucleation rate under intense flows that is correlated with the degree of global orientational order in a nucleating system. Both flow fields give similar results for all kinetic quantities with respect to the reduced strain rate, which we define as the ratio of the applied strain rate to the critical rate. The characteristic growth rate increases with increasing strain rate, and shows a correspondence with the nucleation rate that does not depend on the type of flow field applied. Additionally, a structural analysis of the crystalline clusters indicates that the flow field suppresses the compaction and crystalline ordering of clusters, leading to the formation of large articulated clusters under strong flow fields, and compact well-ordered clusters under weak flow fields. Published by AIP Publishing. [http://dx

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Section: Discussionsupporting

confidence: 86%

Molecular simulation of flow-enhanced nucleation in n-eicosane melts under steady shear and uniaxial extension

Nicholson

Rutledge

2016

The Journal of Chemical Physics

118

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“…When the relaxation time is balanced against the characteristic strain rate ˙of the field, the result is the Deborah number, De= ˙, which is the governing dimensionless parameter for molecular deformation. It has been shown theoretically, 36 and confirmed experimentally, 15,37 that strong stretching occurs around De= 0.5.…”

Section: Background a Polymer Deformation In Field Gradientsmentioning

confidence: 73%

Simulation of electrophoretic stretching of DNA in a microcontraction using an obstacle array for conformational preconditioning

Trahan

Doyle

2009

Biomicrofluidics

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Recently our group has reported experiments using an obstacle array to precondition the conformations of DNA molecules to facilitate their stretch in a microcontraction. Based upon previous successes simulating electrophoretic stretching in microcontractions without obstacles, we use our simulation model to study the deformation of DNA chains in a microcontraction preceded by an array of cylindrical obstacles. We compare our data to the experimental results and find good qualitative, and even quantitative, agreement concerning the behavior of the chains in the array; however, the simulations overpredict the mean stretch of the chains as they leave the contraction. We examine the amount of stretch gained between leaving the array and reaching the end of the contraction and speculate that the differences seen are caused by nonlinear electrokinetic effects that become important in the contraction due to a combination of field gradients and high field strengths.

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“…9 has some similarity to this. Preference for higher extension at the centers than at the ends, proposed in recent models, 49,52,53 is only marginal. But this could be related to the limited segments employed in our chain model.…”

Section: B Non-free-draining Case "With Hi A‫…40؍‬mentioning

confidence: 88%

“…These jumps seem to be caused by Brownian motion caused fluctuations in coil size that also cause fluctuations in hydrodynamic drag. 12,49 For example, when in a random coil equilibrium conformation at a given ⑀ , a certain Brownian fluctuation could expand the coil size, thereby increasing the hydrodynamic drag sufficiently to stretch the chain to another local equilibrium ͑a partially extended conformation͒. Similarly, another sufficiently strong fluctuation reducing the coil size could lead the chain back to the random coil state.…”

Section: B Non-free-draining Case "With Hi A‫…40؍‬mentioning

confidence: 99%

Brownian dynamics simulation of a polymer molecule in solution under elongational flow

Agarwal¹,

Bhargava²,

Mashelkar³

1998

The Journal of Chemical Physics

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We use Brownian dynamics simulation to study coil-stretch transition of macromolecules in solution. Into a simple elongational flow field, we introduce freely jointed bead-rod chain model molecules in their coiled and stretched states, and follow the conformational changes. We find good agreement of our simulation results with the available theoretical predictions for low and high strain rates (⑀ ). At the intermediate elongation rates ͑near the onset of coil-stretch transition͒ of the flow field, we find that the residence time required for stretching of an initially coiled chain can be extremely large as compared to predicted (1ϩln(ͱN))⑀ Ϫ1, especially for the non-free-draining case. Hence, the chain conformation is dependent on the initial state of the chain molecule for residence time as long as 100⑀Ϫ1 . Thus, hysteresis is predicted when chain residence time in such an elongational flow field is limited, as in practical situations. Further, at such intermediate ⑀ , the chain molecule is seen to undergo Brownian fluctuation induced jumps between a randomly coiled state and another partially stretched state. This suggests the existence of more than one equilibrium conformation that is unstable to Brownian fluctuations.

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Coil-stretch transitions in mixed shear and extensional flows of dilute polymer solutions

Cited by 120 publications

References 7 publications

Molecular simulation of flow-enhanced nucleation in n-eicosane melts under steady shear and uniaxial extension

Molecular simulation of flow-enhanced nucleation in n-eicosane melts under steady shear and uniaxial extension

Simulation of electrophoretic stretching of DNA in a microcontraction using an obstacle array for conformational preconditioning

Brownian dynamics simulation of a polymer molecule in solution under elongational flow

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