84 research outputs found
Direct conversion of rheological compliance measurements into storage and loss moduli
We remove the need for Laplace/inverse-Laplace transformations of
experimental data, by presenting a direct and straightforward mathematical
procedure for obtaining frequency-dependent storage and loss moduli
( and respectively), from time-dependent experimental
measurements. The procedure is applicable to ordinary rheological creep
(stress-step) measurements, as well as all microrheological techniques, whether
they access a Brownian mean-square displacement, or a forced compliance. Data
can be substituted directly into our simple formula, thus eliminating
traditional fitting and smoothing procedures that disguise relevant
experimental noise.Comment: 4 page
Transient overshoot extensional rheology of long-chain branched polyethylenes: Experimental and numerical comparisons between filament stretching and cross-slot flow
This work analyses the high-strain extensional behavior of long-chain branched polyethylenes, employing two novel extensional rheometer devices, the filament stretching rheometer and the cross-slot extensional rheometer. The filament stretching rheometer uses an active feedback loop to control the imposed strain rate on a filament, allowing Hencky strains of around 7 to be reached. The cross-slot extensional rheometer uses optical birefringence patterns to determine the steady-state extensional viscosity from planar stagnation point flow. The two methods probe different strain-rate regimes and in this paper we demonstrate the agreement when the operating regimes overlap and explore the steady-state extensional viscosity in the full strain-rate regime that these two complimentary techniques offer. For long-chain branched materials, the cross-slot birefringence images show a double cusp pattern around the outflow centre line (named W-cusps). Using constitutive modeling of the observed transient overshoot in extension seen in the filament stretching rheometer and using finite element simulations we show that the overshoot explains the W-cusps seen in the cross-slot extensional rheometer, further confirming the agreement between the two experimental techniques. © 2013 The Society of Rheology
Scale-free static and dynamical correlations in melts of monodisperse and Flory-distributed homopolymers: A review of recent bond-fluctuation model studies
It has been assumed until very recently that all long-range correlations are
screened in three-dimensional melts of linear homopolymers on distances beyond
the correlation length characterizing the decay of the density
fluctuations. Summarizing simulation results obtained by means of a variant of
the bond-fluctuation model with finite monomer excluded volume interactions and
topology violating local and global Monte Carlo moves, we show that due to an
interplay of the chain connectivity and the incompressibility constraint, both
static and dynamical correlations arise on distances . These
correlations are scale-free and, surprisingly, do not depend explicitly on the
compressibility of the solution. Both monodisperse and (essentially)
Flory-distributed equilibrium polymers are considered.Comment: 60 pages, 49 figure
Branch-Point Motion in Architecturally Complex Polymers: Estimation of Hopping Parameters from Computer Simulations and Experiments
Arrested spinodal decomposition in polymer brush collapsing in poor solvent
We study the Brownian dynamics of flexible and semiflexible polymer chains
densely grafted on a flat substrate, upon rapid quenching of the system when
the quality of solvent becomes poor and chains attempt collapse into a globular
state. The collapse process of such a polymer brush differs from individual
chains, both in its kinetics and its structural morphology. We find that the
resulting collapsed brush does not form a homogeneous dense layer, in spite of
all chain monomers equally attracting each other via a model Lennard-Jones
potential. Instead, a very distinct inhomogeneous density distribution in the
plane forms, with a characteristic length scale dependent on the quenching
depth (or equivalently, the strength of monomer attraction) and the geometric
parameters of the brush. This structure is identical to the
spinodal-decomposition structure, however, due to the grafting constraint we
find no subsequent coarsening: the established random bundling with
characteristic periodicity remains as the apparently equilibrium structure. We
compare this finding with a recent field-theoretical model of bundling in a
semiflexible polymer brush.This work was funded by the Osk. Huttunen Foundation (Finland) and the Cambridge Theory of Condensed Matter Grant from EPSRC. Simulations were performed using the Darwin supercomputer of the University of Cambridge High Performance Computing Service provided by Dell Inc. using Strategic Research Infrastructure funding from the Higher Education Funding Council for England.This is the accepted manuscript. The final version is available at http://pubs.acs.org/doi/abs/10.1021/ma501985r
Interchain tube pressure effect in extensional flows of oligomer diluted nearly monodisperse polystyrene melts
Hydrolytic degradation of ROMP thermosetting materials catalysed by bio-derived acids and enzymes: from networks to linear materials
Comparison of the responsiveness of the Foot Health Status Questionnaire and the Manchester Foot Pain and Disability Index in older people
Dynamic Dilution Effect in Binary Blends of Linear Polymers with Well-Separated Molecular Weights
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