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

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 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

Janus Nanoparticles of Block Copolymers by Emulsion Solvent Evaporation Induced Assembly

We present a facile approach toward straightforward synthesis of Janus nanoparticles (NPs) of poly­(4-vinylpyridine)-based block copolymers by solvent evaporation induced assembly within emulsion droplets. Formation of the Janus NPs is arisen from the synergistic effect between solvent selectivity and interfacial selectivity. This method is robust without the requisites of narrow molecular weight distribution and specific range of block fraction of the copolymers. Janus NPs can also be achieved from mixtures of copolymers, whose aspect size ratio and thus Janus balance are finely tunable. The Janus NPs are capable to self-assemble into ordered superstructures either onto substrates or in dispersions, whose morphology relies on Janus balance

Effect of Chain Architecture on Self-Assembled Aggregates from Cyclic AB Diblock and Linear ABA Triblock Copolymers in Solution

The self-assembly behaviors of two block copolymers with the same chain length but different chain architectures (cyclic AB, linear ABA) in B-selective solvents are investigated using Monte Carlo simulations. A morphological transition sequence, from spherical micelles to cylindrical micelles, to vesicles and then to multicompartment vesicles, is observed for both copolymer systems when the interaction between the solvophobic A-block and the solvent is increased. In particular, toroidal micelles could be formed in triblock systems due to the presence of the bridging chains at the parameter region between cylindrical micelles and vesicles whereas disklike micelles are formed in cyclic systems. The simulation results demonstrated that the architecture of block copolymers could be used to regulate the structural characteristics and thermal stability of these self-assembled aggregates

Effect of Peptide Charge Distribution on the Structure and Kinetics of DNA Complex

The complexes formed by DNA or siRNA interacting with polycations showed great potential as nonviral vectors for gene delivery. The physicochemical properties of the DNA/siRNA complexes, which could be tuned by adjusting the characteristics of polycations, were directly related to their performance in gene delivery. Using 21 bp double-stranded oligonucleotide (ds-oligo) and two icosapeptides (with the repeating units being KKGG and KGKG, respectively) of the same charge density as model molecules, we investigated the effect of charge distribution on the kinetics of complexation and the structure of the final complexes. Even though the distribution of the charged groups in peptides was only adjusted by one position, the complexes formed by (KKGG)₅ and ds-oligo were larger in size and easier to precipitate than those formed by (KGKG)₅. Counterintuitively, it was not the charged groups but the hydrophilic neutral spacers that determined the kinetics and the structure of the complex. We attributed such an effect to the water-mediated disproportionation process. The hydrophilic spacers next to each other were better than that in the separated pattern in holding water molecules after forming the complex. The water-rich domains in the complex functioned as a lubricant and facilitated the relaxation of the polyelectrolyte, resulting in a fast complexation process. The resulting complex was thus larger in size and lower in surface energy