Simulations of Tetra-Tethered Organic/Inorganic Nanocube−Polymer Assemblies

Abstract

We perform molecular simulations to study the self-assembly of tetratethered nanoparticles with a cubic geometry. We develop a minimal model of the tethered nanoscale building block (NBB) to represent a polyhedral oligomeric silsesquioxane (POSS) molecule with polymeric functionalities based on information about the molecular structure and interactions obtained from ab initio density functional theory calculations. Using this model, we explore the rich nanostructures formed from self-assembly of the NBBs and make analogies with the morphologies observed in block copolymer, surfactant, and liquid crystalline systems. On the basis of the assembled structures produced and determination of the location and nature of the order-disorder transitions in the system, we propose phase diagrams to describe the behavior of these molecules. We find that qualitative similarities exist between the phase diagrams for the tetratethered NBBs and those for block copolymer and surfactant systems.

Geometry induced sequence of nanoscale Frank–Kasper and quasicrystal mesophases in giant surfactants

“…Nanophase separation between the hydrophilic POSS cages and the hydrophobic PS tails drives the formation of various highly ordered nanostructures in the bulk with feature sizes around 10 nm. When n = 1 or 2, the phase transitions display the conventional sequence as found in typical diblock copolymers, such as the usual BCC micellar phase, hexagonal cylindrical phase (HEX), and lamellar phase (LAM), but with shifted phase boundaries in terms of volume fraction of the PS tails (v f PS ) as previously predicted (28,29). More importantly, when n = 3 or 4, stable A15-, σ-, and DQC phases are identified in the spheroidal micelle region of the phase diagram, resulting in a distinct sequence of transitions from one phase to the next with increasing v f PS .…”

“…This is because the presence of multiple tails at the junction point creates shape asymmetry at the interfaces, and contributes to the interfacial curvature between immiscible nanodomains in addition to changing v f PS . Theoretical studies on polymer-tethered POSS conjugates with different architectures (28,29) and on linear-branched diblock copolymers (26,27) predict similar results. The phase diagrams of DPOSS-3PS m and DPOSS-4PS m include F-K and quasicrystal phases in the spheroidal micelle region of the phase diagram, resulting from the molecular geometric changes (Fig.…”

“…Although we do not expect to predict, with quantitative accuracy, volume fractions of specific phase, average micelle sizes, etc., we do expect our model to predict the experimentally observed phases and their relationship to molecular architecture. The model and simulation method are adapted from our previous studies of tethered nanoparticles (29,34,36); full details on the potentials used, and thermodynamic parameters, are available in SI Appendix, section 2.4. The DPOSS heads are modeled as cubes by bonding overlapping spheres with stiff harmonic springs.…”

Multiscale Simulation of the Synthesis, Assembly and Properties of Nanostructured Organic/Inorganic Hybrid Materials

“…[53][54][55] The model is constructed to retain the essential geometrical and energetic features of the tethered cubes and consequently the topological characteristics of the assembled structures. We have implemented the model in MD, BD, and off-lattice and on-lattice MC simulations.…”

“…We have conducted detailed simulation studies of monotethered POSS, 53 tetratethered POSS, 56 and POSS telechelics 56 via Brownian molecular dynamics by using a minimal model of tethered POSS cubes. Of primary interest in these studies is the prediction of equilibriumordered structures as a function of temperature, volume fraction, tether length and rigidity, number of tethers, and solvent quality.…”