polymers-10-01301.pdf

Polymers

Coarse-grained molecular dynamics simulations of a diblock copolymer consisting of a flexible and semi-flexible block in a dense array of parallel nanoposts with a square lattice packing were performed. The mutual interactions between the two blocks of the confined diblock chain were investigated through a comparison of their size, structure, and penetration among nanoposts with the corresponding separate chains. The geometry of a nanopost array was varied at constant post separation or at constant width of the passage between nanoposts. The size of a single interstitial volume was comparable to or smaller than the size of the diblock chain. A comparison of the blocks with their separate analogous chains revealed that the mutual interactions between the blocks were shielded by the nanoposts and, thus, the blocks behaved independently. At constant passage width, competitive effects of the axial chain extension in interstitial volumes and the lateral chain expansion among interstitial...

Polymers, 2020, 12(5), 1064, 2020

The conformation and distribution of a flexible and semiflexible chain confined in an array of nanoposts arranged in parallel way in a square-lattice projection of their cross-section was investigated using coarse-grained molecular dynamics simulations. The geometry of the nanopost array was varied at the constant post diameter dp and the ensuing modifications of the chain conformation were compared with the structural behavior of the chain in the series of nanopost arrays with the constant post separation Sp as well as with the constant distance between two adjacent post walls (passage width) wp. The free energy arguments based on an approximation of the array of nanopost to a composite of quasi-channels of diameter dc and quasi-slits of height wp provide semiqualitative explanations for the observed structural behavior of both chains. At constant post separation and passage width, the occupation number displays a monotonic decrease with the increasing geometry ratio dc/wp or volume fraction of posts, while a maximum is observed at constant post diameter. The latter finding is attributed to a relaxed conformation of the chains at small dc/wp ratio, which results from a combination of wide interstitial volumes and wide passage apertures. This maximum is approximately positioned at the same dc/wp value for both flexible and semiflexible chains. The chain expansion from a single interstitial volume into more interstitial volumes also starts at the same value of dc/wp ratio for both chains. The dependence of the axial chain extension on the dc/wp ratio turns out to be controlled by the diameter of the interstitial space and by the number of monomers in the individual interstitial volumes. If these two factors act in the same way on the axial extension of chain fragments in interstitial volumes the monotonic increase of the axial chain extension with the dc/wp in the nanopost arrays is observed. At constant wp, however, these two factors act in opposite way and the axial chain extension plotted against the dc/wp ratio exhibits a maximum. In the case of constant post diameter, the characteristic hump in the single chain structure factor whose position correlates with the post separation is found only in the structure factor of the flexible chain confined in the nanopost array of certain value of Sp. The structure factor of the flexible chain contains more information on the monomer organization and mutual correlations than the structure factor of the semiflexible chain. The stiffer chain confined in the nanopost array is composed of low number of statistical segments important for the presence of respective hierarchical regimes in the structure factor.

Macromolecular Theory and Simulations, 2011

Polymers

The structural properties of a flexible and semiflexible circular chain confined in an array of parallel nanoposts with a square lattice cross-sectional projection were studied using coarse-grained molecular dynamics simulations. To address the effect of the circular topology, a comparison with linear analogs was also carried out. In the interpretation of the chain structural properties, the geometry of the post array is considered as a combination of a channel approximating the interstitial volume with the diameter d c and a slit approximating the passage aperture with the width w p. The number of interstitial volumes occupied by a chain monotonically increases with the decreasing ratio d c /w p regardless of the way the geometry of the post array is varied. However, depending on how the array geometry is modified, the chain span along the posts displays a monotonic (constant post separation) or a non-monotonic behavior (constant passage width) when plotted as a function of the post diameter. In the case of monotonic trend, the width of interstitial spaces increases with the increasing chain occupation number, while, in the case of non-monotonic trend, the width of interstitial spaces decreases with the increasing chain occupation number. In comparison with linear topology, for circular topology, the stiffness affects more significantly the relative chain extension along the posts and less significantly the occupation number. The geometrical parameters of the post arrays are stored in the single-chain structure factors. The characteristic humps are recognized in the structure factor which ensue from the local increase in the density of segments in the circular chains presented in an interstitial volume or from the correlation of parallel chain fragments separated by a row of posts. Although the orientation correlations provide qualitative information about the chain topology and the character of confinement within a single interstitial volume, information about the array periodicity is missing.

Journal of Materials Chemistry, 2010

Mixing microphase-separating diblock copolymers and nanoparticles can lead to the self-assembly of organic/inorganic hybrid materials that are spatially organized on the nanometre scale. Controlling particle location and patterns within the polymeric matrix domains remains, however, an unmet need. Computer simulation of such systems constitutes an interesting challenge since an appropriate technique would require the capturing of both the formation of the diblock mesophases and the copolymer-particle and particle-particle interactions, which can affect the ultimate structure of the material. In this work we discuss the application of Dissipative Particle Dynamics (DPD) to the study of the distribution of nanoparticles with different degree of functionality and volume fraction in a lamellar microsegregated copolymer template. The DPD parameters of the systems were calculated according to a multi-step modelling approach, i.e., from lower scale (atomistic) simulations. The results show that positioning and ordering of the nanoparticles, as well as the dimensions of the block domains depend on covering extent and volume fraction, in full agreement with experiments. The overall results provide molecular-level information for the rational, a priori design of new polymer-particle nanocomposites with ad hoc, tailored properties.

Nature Materials, 2004

The Journal of chemical physics, 2017

Equilibrium conformation of a semiflexible macromolecule in an array of nanoposts exhibits a non-monotonic behavior both at variation of the chain stiffness and increased crowding imposed by nanoposts. This is a result of the competition between the axial chain extension in channel-like interstitial volumes between nanoposts and the chain partitioning among these volumes. The approximation of a nanopost array as a combination of a quasi-channel and a quasi-slit like geometry semi-qualitatively explains the behavior of a chain in the array. In this approximation, the interstitial spaces are viewed as being of the channel geometry, while the passages between two adjacent posts are viewed as being of the slit geometry. Interestingly, the stiffer chains tend to penetrate more readily through the passage apertures, in the direction perpendicular to the post axes, and thus to occupy more interstitial volumes. This is consistent with the prediction of the free-energy penalty that is lower ...

Macromolecular Theory and Simulations, 2016

The presence of nanoparticles in a diblock copolymer leads to changes in the morphology and properties of the matrix and can produce highly organized hybrid materials. The resulting material properties depend not only on the polymer composition, but also on the size, shape and surface properties of the colloids. We study the dynamics of this kind of systems using a hybrid mesoscopic approach. A continuum description for the polymer is used, while colloids are individually resolved. The method allows for a variable preference of the colloids, which can have different sizes, to the different components the block copolymer is made of. We can analyze the impact that the nanoparticle preference for either, both or none of the blocks have on the collective properties of nanoparticleblock copolymer composites. Several experimental results are reproduced covering colloid-induced phase transition, particles' placement within the matrix and the role of incompatibilities between colloids and monomers.

Progress in Polymer Science, 2003

The solid-state supramolecular organization of block copolymers containing one p-conjugated block and one nonconjugated block is elucidated with a joint experimental and theoretical approach. This approach combines atomic force microscopy (AFM) measurements on thin polymer deposits, which reveal the typical microscopic morphologies, and molecular modeling, which allows one to derive the models for chain packing that are most likely to explain the AFM observations. The conjugated systems considered in this study are based on aromatic building blocks (i.e. phenylene, phenylene ethylene, fluorene, or indenofluorene), substituted with alkyl groups to provide solubility; they are attached to non-conjugated blocks such as polydimethylsiloxane, polyethylene oxide, or polystyrene. Films are prepared from solutions in solvents which are good for both blocks, in order to prevent aggregation processes in solution. Therefore, the morphology observed in the solid state is expected to result mostly from the intrinsic self-assembly of the chains, with little specific influence of the solvent. In such conditions, the vast majority of compounds show deposits made of fibrilar objects. Closer examination of single fibrils on the substrate surface indicates that the objects are ribbon-like, i.e. their width is significantly larger than their height, with typical dimensions of a few tens of nanometers and a few nanometers, respectively. These results suggest that a single type of packing process, governed by the p-stacking of the conjugated chains, is at work in those block copolymers. This prevalence of such a type of packing is supported by the theoretical simulations. Molecular mechanics/dynamics calculations show that the conjugated segments tend to form stable p-stacks. In these assemblies, the block copolymer molecules can organize in either a head-to-tail or head-to-head configuration. The former case appears to be most likely because it allows for significant coiling of the non-conjugated blocks while maintaining the conjugated blocks in a compact, regular assembly. Such supramolecular organization is likely responsible for the formation of the thin, 'elementary' ribbons, which can further assemble into larger bundles. The issue of chain packing in fluorene-based systems has been modeled separately, since in these compounds, the alkyl groups attached to sp 3-hybridized sites inherently accommodate out of the plane of the conjugated backbone, which can disturb the chain packing. Various possibilities of chain packing have been explored, starting from short alkyl substituents and extending the size of the side groups to n-octyl. The calculations indicate that, when in zigzag planar conformation, linear alkyl side groups can orient in such a way that close p-stacking of the conjugated chains is preserved. In contrast, branched alkyl groups are too bulky to allow close packing of the conjugated backbones to take place. This difference is consistent with the presence or absence of fibrilar structures observed in thin deposits of the corresponding polymers; it can also account for the differences observed in the optical properties.

Molecular Physics, 2005

We propose a systematic coarse-grained representation of block copolymers, whereby each block is reduced to a single "soft blob" and effective intra-as well as intermolecular interactions act between centres of mass of the blocks. The coarse-graining approach is applied to simple athermal lattice models of symmetric AB diblock copolymers, in particular to a Widom-Rowlinson-like model where blocks of the same species behave as ideal polymers (i.e. freely interpenetrate), while blocks of opposite species are mutually avoiding walks. This incompatibility drives microphase separation for copolymer solutions in the semi-dilute regime. An appropriate, consistent inversion procedure is used to extract effective inter-and intramolecular potentials from Monte Carlo results for the pair distribution functions of the block centres of mass in the infinite dilution limit. PACS numbers: 61.25.Hq,61.20.Gy,05.20Jj