The self-assembly in cylinder-forming diblock copolymer thin films upon solvent evaporation is studied by lattice Monte Carlo simulations under the assumption that the solvent evaporation starts from the free surface and gradually propagates toward the substrate. The effects of solvent selectivity, surface preference, and solvent evaporation rate on the morphology evolution during solvent evaporation are systematically investigated. It is found that the perpendicular cylinder morphology tends to form under weak surface preference, whereas under strong surface preference this morphology is promoted by the fast solvent evaporation rate and the strong solvent selectivity. The surface preference window for forming perpendicular cylinders with solvent evaporation is found to be wider than with thermal annealing, and especially much wider when the solvent evaporation starts from random (disordered) initial states. A new mechanism of perpendicular cylinder formation is proposed and elucidated. Hexagonally packed short perpendicular cylinders formed in the earlier stage of the solvent evaporation may remain to the dry film when the solvent selectivity for the majority block is strong or the solvent evaporation rate is fast, which results in the enlargement of the surface preference window of perpendicular cylinder morphology. Mix-orientated morphology with one or two layers of parallel cylinders at the top of the film and perpendicular cylinders throughout the remaining film is also predicted, and its formation mechanism is discussed.

The thermodynamic behaviors of a strongly charged polyelectrolyte chain in a poor solvent are studied using replica-exchange Monte-Carlo simulations on a lattice model, focusing on the effects of finite chain length and the solvent quality on the chain conformation and conformation transitions. The neutralizing counterions and solvent molecules are considered explicitly. The thermodynamic quantities that vary continuously with temperature over a wide range are computed using the multiple histogram reweighting method. Our results suggest that the strength of the short-range hydrophobic interaction, the chain length, and the temperature of the system, characterized by ε, N, and T, respectively, are important parameters that control the conformations of a charged chain. When ε is moderate, the competition between the electrostatic energy and the short-range hydrophobic interaction leads to rich conformations and conformation transitions for a longer chain with a fixed length. Our results have unambiguously demonstrated the stability of the n-pearl-necklace structures, where n has a maximum value and decreases with decreasing temperature. The maximum n value increases with increasing chain length. Our results have also demonstrated the first-order nature of the conformation transitions between the m-pearl and the (m-1)-pearl necklaces. With the increase of ε, the transition temperature increases and the first-order feature becomes more pronounced. It is deduced that at the thermodynamic limit of infinitely long chain length, the conformational transitions between the m-pearl and the (m-1)-pearl necklaces may remain first order when ε > 0 and m = 2 or 3. Pearl-necklace conformations cannot be observed when either ε is too large or N is too small. To observe a pearl-necklace conformation, the T value needs to be carefully chosen for simulations performed at only a single temperature.

Synthesis of ingenious nanoassemblies is pursued in materials science. Herein, the in situ synthesis of the self-assembled blends of AB/BAB block copolymers of poly(ethylene glycol)-block-polystyrene/polystyrene-block-poly(ethylene glycol)-block-polystyrene (PEG-b-PS/PS-b-PEG-b-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-b-PS/PS-b-PEG-b-PS blends such as high-genus compartmentalized vesicles, multilayer and bicontinuous nanoassemblies, and porous nanospheres are prepared. The parameters, such as PEG-b-PS/PS-b-PEG-b-PS molar ratio, polymerization degree of the PS block, and fed monomer concentration, affecting morphology/structure of PEG-b-PS/PS-b-PEG-b-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.

A two-stage transition upon crossing the glass transition of polystyrene with increasing temperature was precisely determined and interpreted by using solid-state nuclear magnetic resonance (SSNMR), 1H-1H dipolar couplings based double quantum-filtered (DQF) and dipolar filter (DF) experiments and 13C chemical shift anisotropy (CSA) based centerband-only detection of exchange (CODEX) experiment are used to fully characterize the time scale of molecular motions during the glass transition. While differential scanning calorimetry (DSC) and CODEX experiment predicted the first stage of glass transiton, DQF and DF experiments provided the evidence for the second stage transition during which the time scale of molecular motions changed from very slow (t > ms) to very fast (t < µs). The first stage of glass transition begins with the occurrence of remarkable slow re-orientation motions of the polymer backbone segments and ends when the degree of slow motion reaches maximum. The onset and endpoint of the conventional calorimetric glass transition of polystyrene can be quantitatively determined at the molecular level by SSNMR. In the second stage, a subsequent dramatic transition associated with the melting of the glassy components was observed. In this stage liquid-like NMR signals appeared and rapidly increased in intensity after a characteristic temperature Tf (~1.1Tg). The signals associated with the glassy components completely disappeared at another characteristic temperature Tc (~1.2Tg).

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.

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.

The phase behavior of double-hydrophilic AB diblock copolymers in concentrated aqueous solutions is investigated using a simulated annealing technique. Phase diagrams of the system are constructed as a function of the volume fraction and concentration of the copolymer (Φ) as well as the hydrophilicity difference between the two blocks. Rich phase transition sequences, especially reentrant phase transitions, such as lamellae → gyroid → hexagonally packed cylinders → gyroid → lamellae → disorder, are observed for a given copolymer with decreasing Φ. By analyzing the variations of the average contact numbers between the A or B monomers and solvents, and of the effective volume fractions, the mechanisms of the reentrant, the order–order, and the order–disorder transitions are elucidated. The difference in hydrophilicity or in volume fraction can be used to tune the degree of swelling of the two blocks, resulting in a nonmonotonic variation of the effective volume fraction of the A (or B)-rich domain with the decrease of Φ, thus inducing the reentrant transitions. Our results are compared with those from available experiments, theory, and simulation and also with the simulation result of an amphiphilic diblock copolymer.

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.

The self-assembly of linear ABC triblock copolymers confined in spherical nanopores is studied using a simulated annealing technique. Morphological phase diagrams as a function of the pore diameter, the selectivity of the pore-wall to the terminal blocks, and the copolymer composition are constructed. A variety of patchy nanoparticles and multiple morphological transitions are identified. Janus nanoparticles, which can be regarded as particles with one patch, are observed inside small nanopores. With increasing the pore diameter, the number of patches on a nanoparticle surface increases from one to two, four, five, six, and seven. The size of each patch increases periodically. The number of patches also increases with increasing the wall selectivity. The distribution of the patches on the surface of a given particle is highly symmetric. The interior structures of the patchy nanoparticles and the morphological transition are investigated by calculating the bridging fraction, the mean square end-to-end distance and the average contact number between different components. A series of entropy-driven morphological transitions is predicted. Furthermore, it is found that the overall patchy morphology is largely controlled by the volume fraction of the middle B-block, while the internal structure is largely controlled by the volume fraction ratio of the two terminal blocks. Our study demonstrates that the size of nanopores, the pore-wall selectivity, and the copolymer composition could be utilized as effective means to tune the structure and properties of the anisotropic nanoparticles.

Polyurethane material is widely utilized in industry and daily life due to its versatile chemistry and relatively easy handling. Here, we focused on a novel thermally reversible cross-linked polyurethane with comprehensive remarkable mechanical properties as reported in our recent work (Adv. Mater. 2013, 25, 4912). The microphase-separated structure and heterogeneous segmental dynamics were well revealed by T2 relaxometry experiments, which was also first utilized to in situ monitor the reversible cross-linking associated with Diels–Alder (DA) and retro-Diels–Alder (RDA) reactions. On the basis of T2 relaxometry results, we determined the actual temperature of the (R)DA reaction as well as the corresponding activation energies of the motion of soft segments. Besides, the roles of the temperature and cross-linker contents on the microdomain structure and dynamics are discussed in detail. It is found that the microphase separation is enhanced by the increase of temperature as well as the incorporation of cross-linkers. Also, the polyurethane samples are still thermal-stable even at a high temperature beyond the disassociation of the cross-linkages. Furthermore, Baum–Pines and three-pulse multiple-quantum NMR experiments are utilized to investigate the heterogeneous structures and dynamics of the mobile and rigid segments, respectively. Both the results obtained from the T2 relaxometry and multiple-quantum NMR experiments are in good agreement with the macroscopic mechanical properties of the polyurethane. Finally, it is also well demonstrated that proton T2 relaxometry combined with multiple-quantum NMR is a powerful method to study the heterogeneous structures and dynamics of a multiphase polymer system.

Block copolymers are a class of soft matter that self-assemble to form ordered morphologies at nanometer scales, making them ideal materials for various applications. The self-assembly of block copolymers is mainly controlled by the monomer–monomer interactions, block compositions and molecular architectures. Besides these intrinsic parameters, placing block copolymers under confinement introduces a number of extrinsic factors, including the degree of structural frustration and surface–polymer interactions, which can strongly influence the self-assembled morphologies. Therefore confinement of block copolymers provides a powerful route to manipulate their self-assembled nanostructures. In this review, we discuss the relationship between confining conditions and the resulting structures, focusing on principles governing structural formation of diblock copolymers under two-dimensional and three-dimensional confinement. In particular, the effects of commensurability condition, surface–polymer interactions, and confining geometries on the self-assembled morphologies are discussed.

The CODEX (center-band only detection of exchange) NMR experiment is widely used for the detection of slow motions in organic solids, especially polymers. However, the RIDER (relaxation-induced dipolar exchange with recoupling) effect may result in artificial exchange signals in the CODEX pure exchange spectrum, which greatly limits the application of CODEX method. Herein, we investigate the distance range that the RIDER effect can reach by performing CODEX experiments on two typical organic solids, hexadecyltrimethylammonium bromide (CTAB) and semi-crystalline polyamide-6 (PA6) where there are no slow molecular motions at room temperature. Our experimental results demonstrate that generally two-bond distance is far enough to ignore the RIDER effect resulted from the dipolar interactions between 13C and the fast relaxing heteronucleus 14N. From the built-up curve of RIDER signals as a function of recoupling time and mixing time, it is clearly revealed that the RIDER effect can greatly affect the signal from 13C directly bonded with 14N. However, this RIDER effect accounts less than 3% of the reference intensity for signals from 13C not directly bonded with 14N if typical recoupling (∼0.5 ms) and mixing times (∼0.5 s) are used for the investigation of slow motions. When longer recoupling and mixing time are used, there are small RIDER signals even for the 13C far away from the 14N. These signals, to a large degree, result from the spin diffusion effect and/or the special microscopic molecule arrangement. However, they are so small compared to the reference signal (∼5%) that they can be ignored. Finally, according to the simulation results, it is worth noting that the RIDER signal is still generally negligible compared to the signals due to slow motions if the chemical shift anisotropy reorientation during the mixing time is not too small(larger than 20°) under the condition of 4tr recoupling time at the magic-angle-spinning speed of 6.5 kHz.Graphical abstractHighlights► Two-bond distance is far enough to suppress RIDER effect. ► For remote 13C, RIDER signal is rather small, generally no more than 5%. ► For remote 13C, RIDER signal is negligible to jump motions larger than 20°. ► CODEX can be used to detect slow motions in 14N-containing organic solids.

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.

Multicompartment micelles, especially those with highly symmetric surfaces such as patchy-like, patchy, and Janus micelles, have tremendous potential as building blocks of hierarchical multifunctional nanomaterials. One of the most versatile and powerful methods to obtain patchy multicompartment micelles is by the solution-state self-assembly of linear triblock copolymers. In this article, we applied the simulated annealing method to study the self-assembly of ABC linear terpolymers in C-selective solvents. Simulations predict a variety of patchy and patchy-like multicompartment micelles with high symmetry and also yield a detailed phase diagram to reveal how to control the patchy multicompartment micelle morphologies precisely. The phase diagram demonstrates that the internal segregated micellar structure depends on the ratio between the volume fractions of the two solvophobic blocks and their incompatibility, whereas the overall micellar shape depends on the copolymer concentration. The relationship between the interfacial energy, stretching energy of chains and the micellar morphology, micellar morphological transition are elucidated by computing the average contact number among the species, the mean square end-to-end distances of the whole terpolymers, the AB blocks in the terpolymers, the AB diblock copolymers, and angle distribution of terpolymers. The anchoring effect of the solvophilic C block on micellar structures is also examined by comparing the morphologies formed from ABC terpolymers and AB diblock copolymers.

Binary blends of a diblock copolymer (AB) and an incompatible homopolymer (C) confined in spherical cavities are studied using a simulated annealing technique. The phase behavior of the blends is examined for four typical cases, representing the different selectivity of the pore surface to the A, B, and C species. The internal morphology of the spherical polymeric particles is controlled by the homopolymer volume fraction, the degree of confinement, and the composition of the copolymer. Inside a particle, the homopolymers segregate to form one or, under some conditions, two domains; thus, the homopolymers may act as an additional controlling parameter of the shape and symmetry of the copolymer domain. A rich array of confinement-induced novel diblock copolymer morphologies is predicted. In particular, core–shell particles with the copolymers as the shell wrapping around a homopolymer core or a copolymer–homopolymer combined core and Janus-like particles with the copolymers and the homopolymers on different sides are obtained.

Phase behavior of blends of two AB diblock copolymers, with the long one at relatively strong segregation, is studied using the self-consistent field theory, focusing on the effect of compositions of the two block copolymers and their length ratio. In order to carry out extensive calculations on the large parameter space, a unit-cell approximation is employed, in which the mean-field equations are solved using a Bessel function expansion. Phase diagrams are constructed for four typical series of blends by comparing the free energies of the different ordered phases including lamellae, cylinders, and spheres. The results reveal that the competition between macro- and microphase separation leads to complex phase behavior. When the length ratio of the two block copolymers is small, the short copolymers tend to segregate to the A/B interfaces, inducing multiple order−order phase transitions including reentrant phase transitions in some blends. When the length ratio of the two diblock copolymers is sufficiently large, macrophase separation may take place. The predicted phase diagrams are compared with available experiments. Density profiles of typical ordered structures are presented to understand the self-organization of the polymer chains. The energetics of the blends is introduced to account for the appearance of the macro- and microphase separations.

An efficient method for identifying different types of carbon groups (CH3, CH2, CH, and quaternary carbons) in organic solids is proposed by utilizing the combination of a two-dimensional (2D) 13C–1H polarization inversion spin exchange at magic angle (PISEMA) NMR experiment and numerical simulation results of simple isolated 13C–1H dipolar coupling models. Our results reveal that there is a unique line shape of the 13C–1H dipolar splitting pattern and a corresponding characteristic splitting value for each carbon group, based on which different carbon types can be distinguished unambiguously. In particular, by using this method, the discrimination and assignment of overlapped signals from different types of carbons can be achieved easily. The efficacy of this method is demonstrated on typical solid small molecules, polymers, and biomacromolecules.

The adsorption and charge inversion by flexible polyelectrolytes (PEs) onto an oppositely charged spherical surface from a bulk solution of finite PE concentration are studied via numerically solving the coupled ordinary differential equations derived from the continuum self-consistent field (SCF) theory under the ground-state dominance approximation. The effects of various parameters, including the particle radius (r0) and its surface charge density (σsf), PE charge fraction (p), short-range surface–PE interaction, solvent quality, and bulk PE concentration and salt concentration, on the amount of adsorbed PEs (Γ) and charge inversion ratio are investigated in detail. It is found that in salt-free solutions where the electrostatic interaction is dominant a relationship of Γ ≈ σsfr02/p is generally satisfied. The critical particle radius and its surface charge density for PE adsorption are computed as a function of the bulk salt concentration. It is also found that PE adsorption occurs in most cases, whereas strong charge inversion cannot occur either in salt-free solutions or for nonadsorbing surfaces. For attractive surfaces, increasing the bulk salt concentration, or decreasing the surface charge density and the particle radius, generally enhances the charge inversion. Our results on the charge inversion are consistent with previous SCF calculations for planar and cylindrical surfaces.

The self-assembly of diblock copolymers under soft confinement is studied systematically using a simulated annealing method applied to a lattice model of polymers. The soft confinement is realized by the formation of polymer droplets in a poor solvent environment. Multiple sequences of soft confinement-induced copolymer aggregates with different shapes and self-assembled internal morphologies are predicted as functions of solvent–polymer interaction and the monomer concentration. It is discovered that the self-assembled internal morphology of the aggregates is largely controlled by a competition between the bulk morphology of the copolymer and the solvent–polymer interaction, and the shape of the aggregates can be non-spherical when the internal morphology is anisotropic and the solvent–polymer interaction is weak. These results demonstrate that droplets of diblock copolymers formed in poor solvents can be used as a model system to study the self-assembly of copolymers under soft confinement.

We report an extensive simulation study of the self-assembly of amphiphilic ABA triblock copolymers dissolved in solvents selective for the middle B-block. The effects of copolymer composition, copolymer concentration, and A-solvent interactions on the morphologies and morphological transitions of the aggregates are examined systematically. The simulations reveal that a rich variety of aggregates, ranging from spherical and rodlike micelles and vesicles to toroidal and net-cage micelles, can be formed spontaneously from a randomly generated initial state. Phase diagrams are constructed and rich morphological transitions are predicted. Chain packing in different micelles is investigated. The simulation results are compared with previous observations or predictions for related copolymer systems.

The self-assembly of gyroid-forming diblock copolymers confined in cylindrical geometry is studied using a combination of computer simulations and experiments. The simulations, based on a system qualitatively representative of poly(styrene-b-isoprene), are performed with cylindrical nanopores of different diameter (D) and surface selectivity. The effects of the pore size and surface selectivity on morphology are systematically investigated. Different morphological sequences are predicted for two gyroid-forming diblock copolymers. The experiments are carried out on two gyroid-forming poly(styrene-b-dimethylsiloxane) block copolymer samples confined in the core of continuous core−shell nanofibers of different diameters, which are obtained by a coaxial two-fluid electrospinning technique. The internal microphase-separated morphologies of these fibers are investigated by transmission electron microscopy (TEM). Both simulations and experiments demonstrate that a rich variety of structures spontaneously form for the gyroid-forming diblock copolymers, depending on the conditions of cylindrical confinement. Many of these confinement-induced structures are quite different from those of cylinder-forming or lamella-forming block copolymers. Simulations further show that these structures depend sensitively on the block copolymer composition, surface selectivity, and the ratio D/L0 where L0 is the period of the equilibrium gyroid phase. While the simulation and experimental systems are representative of different chemistries, the morphological predictions of simulations are qualitatively consistent with the experimental observations.

1H spin-diffusion solid-state NMR, in combination with other techniques, was utilized to investigate the effect of molecular architecture and temperature on the interphase thickness and domain size in poly(styrene)-block-poly(butadiene) and poly(styrene)-block-poly(butadiene)-block-poly(styrene) copolymers (SB and SBS) over the temperature range from 25 to 80 °C. These two block copolymers contain equal PS weight fraction of 32 wt%, and especially, polystyrene (PS) and polybutadiene (PB) blocks are in glass and melt state, respectively, within the experimental temperature range. It was found that the domain sizes of the dispersed phase and interphase thicknesses in these two block copolymers increased with increasing temperature. Surprisingly we found that the interphase thicknesses in these two block copolymers were obviously different, which was inconsistent with the theoretical predictions about the evolution of interphase in block copolymer melts by self-consistent mean-field theory (SCFT). This implies that the interphase thickness not only depends strongly on the binary thermodynamic interaction (χ) between the PS and PB blocks, but also is influenced by their molecular architectures in the experimental temperature range.

The phase behavior of binary blends of a long symmetric AB diblock copolymer and a short asymmetric AB diblock copolymer is studied using the self-consistent mean-field theory. The investigation focuses on blends with different short diblocks by constructing phase diagrams over the whole blending compositions and a large segregation regime. The influences of the chain length ratio (R) of the long and short diblock copolymers on their miscibility and on the stability of various ordered structures are explored. The theoretical results reveal that the blends have a much more complex phase behavior than each constituent copolymer. With the increase of the volume fraction of the short diblocks in the blends, multiple transitions from a long-period lamellar phase to phases with nonzero interfacial curvatures including cylindrical and spherical phases, and finally to a short-period lamellar phase or disordered phase, are predicted. In particular, consistent with experiments, the theory predicts that the cylindrical phase is stabilized over a wide blending compositions region in the strong segregation region, even though the two constituent diblock copolymers are both lamella-forming. When the ratio R is large enough, macrophase separation occurs over a wide range of blending compositions in a relatively strong segregation regime. Various coexisting phases, including those of lamellar and disorder, lamellar and cylindrical, cylindrical and cylindrical, cylindrical and disorder, spherical and disorder, and cylindrical and spherical, are predicted. In addition, the density profiles of the typical ordered structures are presented in order to understand the self-organization of the different copolymer chains.

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.

Self-assembly of cylinder-forming diblock copolymers confined in cylindrical nanopores is studied systematically using a simulated annealing method. The diblock copolymers form hexagonally packed cylinders in the bulk with a period L0, whereas novel structures spontaneously form when the copolymers are confined inside cylindrical pores. It is discovered that the sequence of structures is controlled by the ratio between the pore diameter (D) and L0, as well as the selectivity of the pores. For selective small pores (D/L0 < 2.7), the following structural sequence occurs as the pore size is increased: a string of spheres, a single cylinder, a straight band, a twisted band or stacked disks, a single helix, a set of degenerate structures (includes single helix, stacked toroids and double helices), and double helices. For larger pores (D/L0 > 2.7), the outer ring of the minority block-domain forms helices or stacked toroids, while the inner structure repeat the sequence of structures observed in smaller pores. For neutral pores, cylinders oriented parallel and nearly perpendicular to the cylindrical pore are observed besides helical or toroidal structures. These morphologies are consistent with available experiments and theoretical studies. Mechanisms of the morphological transitions can be understood based on the degree of commensurability between the pore diameter and bulk period of the copolymer L0, parametrized by the ratio D/L0. The effect of the cylindrical pore length on final morphologies is investigated. The chain conformations as a function of morphologies are calculated and analyzed. A mechanism for the formation of helices is proposed based on a packing model, which gives a reasonable description of the radius and pitch of the observed helices.

A multiblock model is developed for the study of the phase behavior of gradient copolymers. The model is able to describe gradient copolymer chains with arbitrary composition profiles. The validity of the multiblock model of gradient copolymers is established by good agreement between RPA (random phase approximation) results for a continuous composition distribution and a multiblock model. The phase behavior of gradient copolymers is examined using self-consistent mean-field theory (SCMFT) for multiblock copolymers. Phase diagrams of gradient copolymer melts with different gradient profiles are constructed by solving the SCMFT equations. It is discovered that the phase behavior depends sensitively on the gradient profiles. In particular, new triple points are observed, and the stability region of phases with curved interfaces shrinks as the gradient profile becomes smooth. For linear gradient copolymers, the lamellar phase is predicted to be the only stable ordered phase.