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A dynamic slip velocity model for molten polymers based on a network kinetic theory

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Abstract

In this paper the slip phenomenon is considered as a stochastic process where the polymer segments (taken as Hookean springs) break off the wall due to the excessive tension imposed by the bulk fluid motion. The convection equation arising in network theories is solved for the special case of a polymer/wall interface to determine the time evolution of the configuration distribution function ψ (Q, t). The stress tensor and the slip velocity are calculated by averaging the proper relations over a large number of polymer segments. Due to the fact that the model is probabilistic and time dependent, dynamic slip velocity calculations become possible for the first time and therefore some new insight is gained on the slip phenomenon. Finally, the model predictions are found to match macroscopic experimental data satisfactorily.

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Abbreviations

ĝ :

rate of creation of polymer segments

g(Q) :

constant of rate of creation of polymer segments

ĥ :

rate of loss of polymer segments

h(Q) :

constant of rate of loss of polymer segments

h′(Q) :

constant of rate of loss of polymer segments due to destruction of its B-link

H :

Hookean spring constant

k :

Boltzmann's constant

n :

unit vector normal to the polymer/wall interface

n 0 :

number density of polymer segments

n 0 :

surface number density of polymer segments

Q :

vector defining the size and orientation of a polymer segment

Q * :

critical length of a segment beyond which the tension may overcome the W adh

t :

time

t h :

howering time of broken polymer segments

T :

absolute temperature

W adh :

work of adhesion

γ n :

nominal strain

γ:

strain

\(\dot \gamma _n \) n :

nominal shear rate

\(\dot \gamma \) :

shear rate

ɛ:

dimensionless constant in the expressions of h(Q), g(Q)

η:

viscosity

κT :

velocity gradient tensor

λ0 :

time constant

σ:

standard deviation of vectors Q at equilibrium

σ w :

wall shear stress

τ:

stress tensor

Ψ0 :

equilibrium configuration distribution function of Q

Ψ:

configuration distribution function of Q

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Hatzikiriakos, S.G., Kalogerakis, N. A dynamic slip velocity model for molten polymers based on a network kinetic theory. Rheola Acta 33, 38–47 (1994). https://doi.org/10.1007/BF00453462

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  • DOI: https://doi.org/10.1007/BF00453462

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