TY - JOUR
TI - Uniaxial extensional rheology of well-characterized comb polymers
AU - Lentzakis, H.
AU - Vlassopoulos, D.
AU - Read, D.J.
AU - Lee, H.
AU - Chang, T.
AU - Driva, P.
AU - Hadjichristidis, N.
JO - Journal of Rheology
PY - 2013
VL - 57
TODO - 2
SP - 605-625
PB - 
SN - 0148-6055, 1520-8516
TODO - 10.1122/1.4789443
TODO - Branched Polymer;  Comb polymers;  Combined effect;  Dynamic dilution;  Experimental datum;  Extensional rheology;  Hencky strains;  Large friction;  Linear chain;  Linear viscoelastic;  Long-chain branched polyolefins;  Molecular parameters;  Stretch relaxation;  Stretch time;  Systematic investigations;  Time-scales;  Uniaxial extension, Elasticity;  Friction;  Polymer blends;  Polystyrenes;  Rheology;  Strain hardening;  Tubes (components), Polymers
TODO - We present a detailed systematic investigation of the transient uniaxial extensional response of a series of well-characterized, anionically synthesized comb polystyrenes and polyisoprenes. The comb architecture consists of a linear chain backbone with multiple branches of equal molar mass, and represents an excellent model branched polymer. The linear viscoelastic response has been studied already in great detail. Our results indicate that the strain hardening becomes more important as the Hencky strain rate is increased. In general, the larger the number of entanglements of the segments between branches and/or of the branches, the stronger the strain hardening and the smaller the characteristic rate for its onset. The key molecular parameter appears to be the number of entanglements per branch. By varying it, one can tailor the amount and onset of strain hardening. This can be rationalized by accounting for the combined effect of backbone tube dilation and extra friction, brought about by the branches. In fact, we define an effective "stretch time" of the comb as the timescale for stretch relaxation along the dilated backbone tube when accounting for the large friction that comes from the branches and suggest that extension hardening occurs at rates equal to or greater than its inverse. The good comparison of this prediction to experimental data is a promising guide toward a universal framework for understanding the effects of branches on extensional rheology, and hence providing some insight into the behavior of long-chain branched polyolefins. © 2013 The Society of Rheology.
ER -