14,238 research outputs found
A Scaling Theory of the Competition between Interdiffusion and Cross-Linking at Polymer Interfaces
We study theoretically situations where competition arises between an
interdiffusion process and a cross-linking chemical reaction at interfaces
between pieces of the same polymer material. An example of such a situation is
observable in the formation of latex films, where, in the presence of a
cross-linking additive, colloidal polymer particles initially in suspension
come at contact as the solvent evaporates, and, optimally, coalesce into a
continuous coating. We considered the low cross-link density situation in a
previous paper (A. Aradian, E. Raphael, P.-G. de Gennes, Macromolecules 33,
9444 (2000)), and presented a simple control parameter that determines the
final state of the interface. In the present article, with the help of simple
scaling arguments, we extend our description to higher cross-link densities. We
provide predictions for the strength of the interface in different favorable
and unfavorable regimes, and discuss how it can be optimized.Comment: 19 pages, 5 figures. To appear in Macromolecule
A Laplace Transform Method for Molecular Mass Distribution Calculation from Rheometric Data
Polydisperse linear polymer melts can be microscopically described by the
tube model and fractal reptation dynamics, while on the macroscopic side the
generalized Maxwell model is capable of correctly displaying most of the
rheological behavior. In this paper, a Laplace transform method is derived and
different macroscopic starting points for molecular mass distribution
calculation are compared to a classical light scattering evaluation. The
underlying assumptions comprise the modern understanding on polymer dynamics in
entangled systems but can be stated in a mathematically generalized way. The
resulting method is very easy to use due to its mathematical structure and it
is capable of calculating multimodal molecular mass distributions of linear
polymer melts
Analysis and optimisation of the tuning of the twelfths for a clarinet resonator
Even if the tuning between the first and second register of a clarinet has
been optimized by instrument makers, the lowest twelfths remain slightly too
large (inharmonicity). In this article, we study the problem from two different
points of view. First, we systematically review various physical reasons why
this inharmonicity may take place, and the effect of different bore
perturbations inserted in cylindrical instruments. Applications to a real
clarinet resonator and comparisons with impedance measurements are then
presented. A commonly accepted idea is that the register hole is the dominant
cause for this inharmonicity: it is natural to expect that opening this hole
will raise the resonance frequencies of the instrument, except for the note for
which the hole is at the pressure node. We show that the real situation is
actually more complicated because other effects, such as open holes or bore
taper and bell, introduce resonance shifts that are comparable but with
opposite sign, so that a relatively good overall compensation takes place. The
origin of the observed inharmonicity in playing frequencies is therefore
different. In a second part, we use an elementary model of the clarinet in
order to isolate the effect of the register hole: a perfect cylindrical tube
without closed holes. Optimization techniques are then used to calculate an
optimum location for the register hole; the result turns out to be close to the
location chosen by clarinet makers. Finally, attempts are made numerically to
improve the situation by introducing small perturbations in the higher part of
the cylindrical resonator, but no satisfactory improvement is obtained.Comment: 28 June 2004 (submitted to Applied Acoustics
Polymer Reactor Modeling, Design and Monitoring
Polymers range from synthetic plastics, such as polyacrylates, to natural biopolymers, such as proteins and DNA. The large molecular mass of polymers and our ability to manipulate their compositions and molecular structures have allowed for producing synthetic polymers with attractive properties. new polymers with remarkable characteristics are synthesized. Because of the huge production volume of commodity polymers, a little improvement in the operation of commodity-polymer processes can lead to significant economic gains. On the other hand, a little improvement in the quality of specialty polymers can lead to substantial increase in economic profits
Phase Separation and Self-Assembly in a Fluid of Mickey Mouse Particles
Recent developments in the synthesis of colloidal particles allow for control
over shape and inter-particle interaction. One example, among others, is the
so-called "Mickey Mouse" (MM) particle for which the self-assembly properties
have been previously studied yielding a stable cluster phase together with
elongated, tube-like structures. Here, we investigate under which conditions a
fluid of Mickey Mouse particles can yield phase separation and how the
self-assembly behaviour affects the gas-liquid coexistence. We vary the
distance between the repulsive and the attractive lobes (bond length), and the
interaction range, and follow the evolution of the gas-liquid (GL) coexistence
curve. We find that upon increasing the bond length distance the binodal line
shifts to lower temperatures, and that the interaction range controls the
transition between phase separation and self-assembly of clusters. Upon further
reduction of the interaction range and temperature, the clusters assume an
increasingly ordered tube-like shape, ultimately matching the one previously
reported in literature. These results are of interest when designing particle
shape and particle-particle interaction for self-assembly processes
Real-space analysis of branch point motion in architecturally complex polymers
By means of large-scale molecular dynamics simulations, we investigate branch point motion in pure branched polymers and in mixtures of stars and linear chains. We perform a purely geometrical density-based cluster analysis of the branch point trajectories and identify regions of strong localization (traps). Our results demonstrate that the branch point motion can be described as the motion over a network of traps at the time scales corresponding to the reptation regime. Residence times within the traps are broadly distributed, even extending to times much longer than the side-arm relaxation time. The distributions of distances between consecutively visited traps are very similar for all the investigated branched polymers, even though tube dilation is much stronger in the star/linear mixtures than in the pure branched systems. Our analysis suggests that the diffusivity of the branch point introduced by hierarchical models must be understood as a parameter to account for the effective friction associated with the relaxed side arm, more than the description of a hopping process with a precise time scale.We acknowledge support from projects FP7-PEOPLE-2007-1-1-ITN (DYNACOP, EU), MAT2012-31088 (Spain), and IT654-13 (GV, Spain). We acknowledge the programs
PRACE, HPC-Europa2 and ESMI (EU), and ICTS (Spain) for generous allocation of CPU time at GENCI (France), HLRS and FZJ-JSC (Germany), and CESGA (Spain).Peer Reviewe
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