Coassembly of Linear Diblock Copolymer Chains and Homopolymer Brushes on Silica Particles: A Combined Computer Simulation and Experimental Study

A combined computer simulation and experimental study on coassembly of poly­(2-(dimethylamino)­ethyl methacrylate)-<i>block</i>-polystyrene (PDMAEMA-<i>b</i>-PS) block copolymers and PS brushes on silica particles was performed. PS brushes on silica particles at two different grafting densities were prepared by the “grafting to” approach, and PDMAEMA-<i>b</i>-PS block copolymers with different molecular weights and compositions were synthesized by reversible addition–fragmentation chain transfer polymerization. In THF/methanol mixtures, block copolymer chains and PS brushes coassemble into surface micelles (s-micelles), with collapsed PS cores and PDMAEMA coronae. Meanwhile, block copolymer chains are able to self-assemble into block copolymer micelles (b-micelles). Computer simulation results and experimental results indicate that block copolymer concentration, PS and PDMAEMA block lengths, and PS grafting density exert significant influences on the coassembly process. In low BCP concentration regime, the average size of s-micelles increases with BCP concentration and keeps unchanged at high concentration. The PS block length has a significant influence on the size of s-micelles. The average size increases with an increase in PS block length. For a BCP with long solvophilic PDMAEMA block, it is energy favorable to self-assemble into b-micelles, but to coassemble into s-micelles. With an increase in PDMAEMA block length, the morphology of the s-micelles changes from wormlike/spherical structures to spherical structures and to smaller spherical structures. The average size of the s-micelles coassembled by PS brushes at a lower grafting density is smaller than those coassembled by PS brushes at a higher grafting density

Self-Assembly of Giant Amphiphiles Based on Polymer-Tethered Nanoparticle in Selective Solvents

We study the self-assembly and formation process of vesicles of giant molecular shape amphiphiles in a selective solvent using the Brownian dynamics approach. Each amphiphile is composed of one hydrophilic nanoparticle tethered with one to five hydrophobic polymer tail(s), and the number of coarse-grained beads in each polymer tail is comparable to the number of repeating units in shape amphiphile used in the experiments. The effects of various parameters, such as the number of polymer tails, the length of each tail, the concentration of amphiphile beads, the size of the nanoparticle, and the temperature of the system on the self-assembled aggregate morphologies, are investigated. Morphological phase diagrams are constructed in different parameter spaces, and multiple morphological transitions are predicted and explained based on packing parameter. The formation pathways of vesicles are examined systematically, and mechanism II is identified for the first time in such shape amphiphilic systems. Transition between mechanism I and mechanism II can occur by varying several parameters, and principles controlling the different pathways are elucidated. The simulation results are compared with available experimental and simulation results of related systems

Helical Vesicles, Segmented Semivesicles, and Noncircular Bilayer Sheets from Solution-State Self-Assembly of ABC Miktoarm Star Terpolymers

Multicompartment micelles, especially nanostructured vesicles, offer tremendous potential as delivery vehicles of therapeutic agents and nanoreactors. Solution-state self-assembly of miktoarm star terpolymers provides a versatile and powerful route to obtain multicompartment micelles. Here we report simulations of solution-state self-assembly of ABC star terpolymers composed of a solvophilic A arm and two solvophobic B and C arms. A variety of multicompartment micelles are predicted from the simulations. Phase diagrams for typical star terpolymers are constructed. It is discovered that the overall micelle morphology is largely controlled by the volume fraction of the solvophilic A arms, whereas the internal compartmented and/or segregated structures depend on the ratio between the volume fractions of the two solvophobic arms. The polymer−solvent and polymer−polymer interactions can be used to tune the effective volume fraction of the A-arm and, thereby, induce morphological transitions. For terpolymers with equal or nearly equal length of B and C arms, several previously unknown structures, including vesicles with novel lateral structures (helices or stacked donuts), segmented semivesicles, and elliptic or triangular bilayer sheets, are discovered. When the lengths of B and C arms are not equal, novel micelles such as multicompartment disks and onions are observed

Formation and Regulation of Multicompartment Vesicles from Cyclic Diblock Copolymer Solutions: A Simulation Study

The self-assembly of a cyclic AB copolymer system with relatively long A blocks and short B blocks in B-selective solvents is investigated using a simulated annealing method. By investigating the effect of the lengths and solubilities of A and B blocks (NA and NB, εAS and εBS), the incompatibility between A and B blocks (εAB), as well as the polymer concentration (Cp) and the conditions for the formation of multicompartment vesicles in cyclic diblock copolymer solutions, is predicted. The phase diagrams in terms of NB, εAS, and Cp are constructed. The mechanism of the morphological transition is elucidated. It is shown that for cyclic copolymers the change in the above factors relating to the polymer and solvent properties all can lead to the transition from simple vesicles to multicompartment vesicles, but two different transition mechanisms are revealed. In addition, our simulations demonstrate that the self-assembly of cyclic copolymers could provide a powerful strategy for regulating the compartment number and the wall thickness of the multicompartment vesicles by adjusting the block solubilities and block lengths, respectively. These findings will facilitate the application of multicompartment architectures in cell mimicry, drug delivery, and nanoreactors

Self-Assembled Blends of AB/BAB Block Copolymers Prepared through Dispersion RAFT Polymerization

Synthesis of ingenious nanoassemblies is pursued in materials science. Herein, the <i>in situ</i> synthesis of the self-assembled blends of AB/BAB block copolymers of poly­(ethylene glycol)-<i>block</i>-polystyrene/polystyrene-<i>block</i>-poly­(ethylene glycol)-<i>block</i>-polystyrene (PEG-<i>b</i>-PS/PS-<i>b</i>-PEG-<i>b</i>-PS) via two-macro-RAFT agent comediated dispersion polymerization is reported. The synthesis strategy combines the advantages of polymer blending and polymerization-induced self-assembly. Following this strategy, various nanoassemblies of PEG-<i>b</i>-PS/PS-<i>b</i>-PEG-<i>b</i>-PS blends such as high-genus compartmentalized vesicles, multilayer and bicontinuous nanoassemblies, and porous nanospheres are prepared. The parameters, such as PEG-<i>b</i>-PS/PS-<i>b</i>-PEG-<i>b</i>-PS molar ratio, polymerization degree of the PS block, and fed monomer concentration, affecting morphology/structure of PEG-<i>b</i>-PS/PS-<i>b</i>-PEG-<i>b</i>-PS self-assembled blends are revealed. Computer simulations of self-assembly of the AB/BAB blends are performed, and nanoassemblies similar to those observed in our experiments are obtained, indicating that these morphologies are close to thermodynamical equilibrium. The formation mechanism of compartmentalized vesicles is investigated. The proposed strategy of two-macro-RAFT agent comediated dispersion polymerization is considered to be an efficient approach to construct self-assembled blends of block copolymers

Accessing Structure and Dynamics of Mobile Phase in Organic Solids by Real-Time T_1C Filter PISEMA NMR Spectroscopy

The structure and dynamic behavior of mobile components play a significant role in determining properties of solid materials. Herein, we propose a novel real-time spectrum-editing method to extract signals of mobile components in organic solids on the basis of the polarization inversion spin exchange at magic angle (PISEMA) pulse sequence and the difference in ¹³C T₁ values of rigid and mobile components. From the dipolar splitting spectrum sliced along the heteronuclear dipolar coupling dimension of the 2D spectrum, the structural and dynamic information can be obtained, such as the distances between atoms, the dipolar coupling strength, the order parameter of the polymer backbone chain, and so on. Furthermore, our proposed method can be used to achieve the separation of overlapped NMR signals of mobile and rigid phases in the PISEMA experiment. The high efficacy of this 2D NMR method is demonstrated on organic solids, including crystalline l-alanine, semicrystalline polyamide-6, and the natural abundant silk fibroin

Soft Colloidal Molecules with Tunable Geometry by 3D Confined Assembly of Block Copolymers

We present with experiments and computer simulations that colloidal molecules with tunable geometry can be generated through 3D confined assembly of diblock copolymers. This unique self-assembly can be attributed to the slight solvent selectivity, nearly neutral confined interface, deformable soft confinement space, and strong confinement degree. We show that the symmetric geometry of the colloidal molecules originates from the free energy minimization. Moreover, these colloidal molecules with soft nature and directional interaction can further self-assemble into hierarchical superstructures without any modification. We anticipate that these new findings are helpful to extend the scope of our knowledge for the diblock copolymer self-assembly, and the colloidal molecules with new composition and performance will bring new opportunities to this emerging field

Self-Assembled Morphologies of Lamella-Forming Block Copolymers Confined in Conical Nanopores

Block copolymers (BCPs) under nanoscale confinement can self-assemble to form novel nanostructures that are not available in the bulk state. Particularly, the ordering process of block copolymers and the resulting morphologies depend sensitively on the dimensionality, geometry, and surface property of the confining environment. In this study, we report on the self-assembled morphologies of polystyrene-block-1,4-polybutadiene (PS-b-PB) confined in conical pores of various sizes, shapes, and surface properties. Based on the experimental observations from transmission electron microscopy and theoretical calculation using the simulated annealing method, we found that the phase separation of PS-b-PB under the conical confinement is competitively determined by three thermodynamic factors: (1) the interfacial energy between two blocks, (2) the surface energy between the blocks and the surrounding environment (i.e., air and substrates), and (3) the entropic penalty associated with the large curvature at the vertices of conical pores. In addition, three-dimensional imaging of transmission electron microtomography was also performed in an attempt to gain more detailed information on the internal nanostructures of the BCP