Phase behaviors of diblock copolymer/nanorod composites under oscillatory shear flow

Abstract

The phase behaviors of lamellar diblock copolymers (DBCPs) melts and lamellar DBCPs/nanorods (NRs) composites subjected to oscillatory shear flow, have been investigated using dissipative particle dynamics. The oscillatory shear is a quite common shearing mode used in experiments and manufacturing processes. The rich lamellar (LAM) reorientation and morphological transition of systems strongly depend on the shear amplitude and shear frequency. At very low frequency, the amplitude-induced phase behaviors of DBCPs melts or DBCPs/NRs composites are quite similar to those subjected to a steady shear. For DBCPs/NRs case, we control NRs concentration low 15% to preserve LAM morphology in the nanocomposites, and simultaneously consider both types of selective and nonselective NRs. Our aim is to compare the different inductions on DBCPs melts or nanocomposites caused by shear amplitude and frequency, and observe how the NRs are oriented and dispersed in phase-separated copolymers matrix while under oscillatory shear, and how the presence of selective/nonselective NRs affects the shear-induced LAM reorientations and rheological properties of systems. Our results show the NRs orientation not only directly depend on the imposed shear flow but also is interfered by the alignment of shear-stretched copolymer molecules. The shear viscosity decreases with the frequency decreases, also influenced by the NRs concentration and surface property.

Microphase transitions of block copolymer/homopolymer under shear flow

“…Further experiments also investigated the shear-induced phase behavior of block copolymer/homopolymer [44] and block copolymer/epoxy [45] blends. Later on, some researchers focused their attention on the phase behavior of block copolymer/nanoparticle [46][47][48][49][50][51] composites under shear flow. Hence, He et al systematically investigated the shear-induced reorientations and phase transitions of symmetric diblock copolymer/nanorod nanocomposites subjected to a steady shear flow [50] and oscillatory shear flow [51] via DPD.…”

“…Later on, some researchers focused their attention on the phase behavior of block copolymer/nanoparticle [46][47][48][49][50][51] composites under shear flow. Hence, He et al systematically investigated the shear-induced reorientations and phase transitions of symmetric diblock copolymer/nanorod nanocomposites subjected to a steady shear flow [50] and oscillatory shear flow [51] via DPD.…”

Understanding the microstructure of particle dispersion in confined copolymer nanocomposites

“…The microphase separation of block copolymers can direct special particle distribution and orientation so that copolymers can provide facile morphological control over homopolymers. 19,[21][22][23][24][25][26][27] With these methods, the phase behaviors have been extensively investigated and various structures such as lamellae, cylinders and bicontinuous morphologies have been analyzed. [15][16][17][18] In copolymer nanocomposites, the particle-copolymer interactions, copolymer conformation, the fraction of each block, particle size and volume fraction play important roles in determining their equilibrium structures.…”

“…In order to make clear different effects of entropic and enthalpic contributions, a multitude of theoretical approaches have been applied to understand the microstructures of copolymer nanocomposites. 19,[21][22][23][24][25][26][27] With these methods, the phase behaviors have been extensively investigated and various structures such as lamellae, cylinders and bicontinuous morphologies have been analyzed. Among these theoretical approaches, density functional theory (DFT) is a relatively simple and highly efficient one.…”

Computational Study of Nanoparticle Dispersion and Spatial Distribution in Polymer Matrix under Oscillatory Shear Flow

“…As described above, most of the existing computational explorations were conducted under quiescent and/or steady shear conditions. However, in experiments and manufacturing processes, the approach that is more commonly employed is oscillatory shear. − To the best of our knowledge, the only available report comes from the group of He, in which dissipative particles dynamics (DPD) simulations were performed to probe the phase behavior of diblock copolymer/nanorod composites under the oscillatory shear flow. Thus, it is quite necessary to put more efforts into this respect, which would in turn provide more comprehensive insights into the dispersion behavior of NPs at the molecular level, stimulating the rational design of new polymer composites with improved properties.…”