We report many different nano-structures which are formed when model nano-particles of different sizes (diameter σn) are allowed to aggregate in a background matrix of semi-flexible self assembled polymeric worm like micellar chains. The different nano-structures are formed by the dynamical arrest of phase-separating mixtures of micellar monomers and nano-particles. The different morphologies obtained are the result of an interplay of the available free volume, the elastic energy of deformation of polymers, the density (chemical potential) of the nano-particles in the polymer matrix and, of course, the ratio of the size of self assembling nano-particles and self avoidance diameter of polymeric chains. We have used a hybrid semi-grand canonical Monte Carlo simulation scheme to obtain the (non-equilibrium) phase diagram of the self-assembled nano-structures. We observe rod-like structures of nano-particles which get self assembled in the gaps between the nematically ordered chains as well as percolating gel-like network of conjoined nanotubes. We also find a totally unexpected interlocked crystalline phase of nano-particles and monomers, in which each crytal plane of nanoparticles is separated by planes of perfectly organized polymer chains. We identified the condition which leads to such interlocked crystal structure. We suggest experimental possibilities of how the results presented in this paper could be used to obtain different nano-structures in the lab. There is persistent interest in the controlled self assembly and growth of nano-structures of predefined morphology and size starting from small constituent nanoparticles (NP) . A separate non-alligned interest of physicists is in the formation and properties of topological defects when large particles (large compared to the size and spacing between nematogens) are introduced in ordered liquid crystalline nematic and smectic phases [29][30][31][32][33][34][35][36][37][38][39][40][41]. Recents experiments have also explored the self organization of nano-particles in a background matrix of nematically ordered micellar phase, but constraints in the choice of size of NPs led to the following two scenarios: small NPs of 2 − 3 nm diameter pervade the nematic chains themselves and form a dispersion/solution, whereas, larger NPs of size 8 − 26 nm get expelled by the elastic energy of ordered nematic phases and aggregate at the grain boundaries between nematic domains [42][43][44]. The distance between adjacent nematic chains was 5.7 nm in the experiments.Our present study spans across these two different research domains and we use computer simulations to investigate the heirarchical self assembly of NPs in the free volume between parallel chains of nematically ordered worm-like micelles (WM). The micellar polymers are selfassembled themselves from monomeric beads and have a length and size distribution controlled by monomer density and temperature [45][46][47]. In a computer simulation, we are able to systematically vary the diameter, chemical potential of the spher...
Using Monte carlo simulations, we investigate the self-assembly of model nanoparticles inside a matrix of model equilibrium polymers (or matrix of Wormlike micelles) as a function of the polymeric matrix density and the excluded volume parameter between polymers and nanoparticles. In this paper, we show morphological transitions in the system architecture via synergistic self-assembly of nanoparticles and the equilibrium polymers. In a synergistic self-assembly, the resulting morphology of the system is a result of the interaction between both nanoparticles and the polymers, unlike the polymer templating method. We report the morphological transition of nanoparticle aggregates from percolating network-like structures to non-percolating clusters as a result of the change in the excluded volume parameter between nanoparticles and polymeric chains. In parallel with the change in the self-assembled structures of nanoparticles, the matrix of equilibrium polymers also shows a transition from a dispersed state to a percolating network-like structure formed by the clusters of polymeric chains. We show that the shape anisotropy of the nanoparticle clusters formed is governed by the polymeric density resulting in rod-like, sheet-like or other anisotropic nanoclusters. It is also shown that the pore shape and the pore size of the porous network of nanoparticles can be changed by changing the minimum approaching distance between nanoparticles and polymers. We provide a theoretical understanding of why various nanostructures with very different morphologies are obtained.
We use a hybrid method that combines the Multiparticle collision dynamics (MPCD) for solvent particles with the molecular dynamics for equilibrium polymers to simulate the shearing of the equilibrium polymers (or Wormlike micelles) at a mesoscopic length scale. The MPCD method incorporates the hydrodynamic interaction with the polymeric chains. We show successful implementation of the method on the model equilibrium polymers (or Wormlike micelles) and observe that the order of the Iso-Nem transition of the polymeric system is affected by the shear rate. Moreover, the chains of the equilibrium polymers first increase in their average length with the increase in shear rate but then show a decrease in their average length after crossing a particular value of the shear rate which shows the breaking of chains due to shear stress when their nematic order remains unchanged. This model and method can be further used to investigate the shear banding in Wormlike micelles or other interesting properties of such systems.
The nanoparticle-Equilibrium polymer (or Wormlike micellar) system shows morphological changes from percolating network-like structures to non-percolating clusters with a change in the minimum approaching distance (EVP-excluded volume parameter) between nanoparticles and the matrix of equilibrium polymers. The shape anisotropy of nanoparticle clusters can be controlled by changing the polymer density. In this paper, the synergistic self-assembly of nanoparticles inside equilibrium polymeric matrix (or Wormlike micellar matrix) is investigated with respect to the change in the strength of attractive interaction between nanoparticles. A shift in the point of morphological transformation of the system to lower values of EVP as a result of a decrease in the strength of the attractive nanoparticle interaction is reported. We show that the absence of the attractive interaction between nanoparticles leads to the low packing of nanoparticle structures, but does not change the morphological behavior of the system. We also report the formation of the system spanning sheet-like arrangement of nanoparticles which are arranged in alternate layers of matrix polymers and nanoparticles.
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