Construction of a closed polymer network for computer simulations

2016

Macromolecules

Self Cite

Stimuli-responsive core−shell nanogels display collapse properties which are determined by both the core and the shell. We examine the equilibrium properties and the detailed structural changes during a collapse transition of polymer core− shell nanoparticles using Brownian dynamics simulations. Gel particles with randomly distributed cross-linking nodes are created. The influence of the cross-linking degree, core/shell mass ratio, and the strength of the interparticle attractive interaction on the collapse behavior is investigated. Both collapsed core and collapsed shell structures are considered and compared with collapsed homopolymer networks. The transition time was found to be reduced with increasing cross-linking degree and inversely related to the depth of the Lennard-Jones potential. Similar to the kinetics of single chain collapse, there is an initial formation of clusters, in this case near cross-linking nodes, and a subsequent coarsening to form a compact globule. Where the nanogels were collapsed into a compact core, the deformation was found to be essentially symmetric, with a significantly slower relaxation time for the shell units compared to the core collapse transition time. Reducing the core size, the shell units were less affected by the presence of a collapsing core. For the system with a collapsing shell, our simulations reveal in some cases an inversion, with the shell compressing and eventually squeezing out the core units. This effect was more pronounced with decreasing cross-linking degree and core/shell mass ratio.

Section: ■ Model and Methodsmentioning

confidence: 99%

Section: Model and Methodsmentioning

confidence: 99%

Collapse Dynamics of Core–Shell Nanogels

Kamerlin

2016

Macromolecules

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“…Each node is then formally connected to four other nodes by finding the nearest neighbours that have at least one vacancy. It was noted in our previous work [45] that this procedure results in the presence of a number of long chains due to the lack of available nodes within proximity. We have corrected for the presence of these long chains by disconnecting long-distance connections and reconnecting these with nearby nodes and their associated neighbours such that the largest distances representing the node-node connections are reduced while tetra-valency is maintained (see supplementary material for details of network reconnection (stacks.iop.org/ JPhysCM/28/475101/mmedia)).…”

Section: Generating the Networkmentioning

confidence: 99%

“…For the purpose of illustrating the method of construction, a simple mapping is used here. Since a 3-sphere can be constructed by 'gluing' together the boundaries of a pair of 3-balls [45] such that the gluing surface will be the equatorial sphere, 'flattening' out one of the hemispheres will produce a ball (analogous to flattening out the hemisphere of a 2-sphere to form a flat disc), shown in figure 1. We note that since this captures only a part of the network, the full connectivity of all chains is not shown.…”

Section: Generating the Networkmentioning

confidence: 99%

“…In this work, we extend the use of SBC to simulate the diffusion of tracer particles in bulk gels. Our method is a further development of a previous study, in which we investigated different ways of constructing a 3D network on the 3-sphere [45]. We use a model of a defect-free (i.e., without loops and dangling ends), cross-linked polymer gel with randomly distributed cross-linking nodes.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Tracer diffusion in a polymer gel: simulations of static and dynamic 3D networks using spherical boundary conditions

Kamerlin

J. Phys.: Condens. Matter

2016

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We have investigated an alternative to the standard periodic boundary conditions for simulating the diffusion of tracer particles in a polymer gel by performing Brownian dynamics simulations using spherical boundary conditions. The gel network is constructed by randomly distributing tetravalent cross-linking nodes and connecting nearest pairs. The final gel structure is characterised by the radial distribution functions, chain lengths and end-to-end distances, and the pore size distribution. We have looked at the diffusion of tracer particles with a wide range of sizes, diffusing in both static and dynamic networks of two different volume fractions. It is quantitatively shown that the dynamical effect of the network becomes more important in facilitating the diffusional transport for larger particle sizes, and that one obtains a finite diffusion also for particle sizes well above the maximum in the pore size distribution.

An efficient linked list for molecular simulations on a spherical surface

Ramírez

J. Phys. A: Math. Theor.

2022

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The main part of the cpu time in molecular simulations is usually spent calculating the non-bonded interactions. To improve the efficiency, a neighbour list or a cell linked list is normally used, where the linked list is usually more efficient and requires less memory for a large number of particles or dense systems. The linked list, however, still suffers from including many pairs which will not be within the interaction distance, and this overhead becomes even more significant for higher dimensions. In this work, we consider specifically simulations of particles confined to move on a spherical surface, where the overhead using a cubic grid to form a linked list becomes even larger by also including many cells which do not intersect the sphere. We address this by setting up a linked list directly on the spherical surface, thus reducing the dimensionality of the resulting neighbour search. We show that one obtains not only a substantial reduction in cpu time, but also a significant decrease in memory requirement. We further show how to extend this procedure to the 3-sphere (hypersphere), which can be used to simulate bulk systems avoiding periodic boundaries. Also in this case, using a linked list directly on the 3-sphere, the reduction in cpu time is significant, and the decrease in memory requirement, compared with a regular grid in R4 , is even more pronounced. We finally comment on how the efficiency of the described method can be further improved