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

Efficient Identification of Different Types of Carbons in Organic Solids by 2D Solid-State NMR Spectroscopy

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

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

Gyroid-Forming Diblock Copolymers Confined in Cylindrical Geometry: A Case of Extreme Makeover for Domain Morphology

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

Various Types of Hydrogen Bonds, Their Temperature Dependence and Water−Polymer Interaction in Hydrated Poly(Acrylic Acid) as Revealed by ¹H Solid-State NMR Spectroscopy

Various types of hydrogen bonds, their temperature dependence and water−polymer interaction in hydrated poly(acrylic acid) (PAA) were systematically investigated using 1H CRAMPS solid-state NMR techniques in the temperature range from 25 to 110 °C. The 1H CRAMPS NMR methods are based on a recently developed continuous phase modulation technique for 1H−H homonuclear dipolar decoupling. The 1H CRAMPS experiments revealed four types of protons in hydrated PAA which are assigned to protons from the mutually hydrogen-bonded COOH groups (1), from the free COOH groups (2), from the COOH groups bounded with water or from water bounded with COOH groups which are undergoing fast chemical exchange mutually (3), and from main chain groups (4), respectively. Furthermore, we proposed double-quantum filtered and dipolar filtered 1H CRAMPS experiments to further assign the protons according to their dipolar coupling strength. In addition, high-resolution spin echo 1H CRAMPS experiments were further employed to accurately determine the chemical shift of these protons. These NMR techniques were also used to elucidate the molecular mobility of the different groups. It was found that dehydration in PAA promotes the formation of hydrogen bonds between COOH groups. Variable-temperature 1H CRAMPS experiments demonstrated that the dissociation of the hydrogen bonds between COOH groups occurs dramatically at lower temperature in hydrated PAA and slowly over a wide range of temperature in dehydrated PAA. It was also found that the dehydration of water bounded with COOH groups in hydrated PAA occurs significantly at high temperature. The NMR results were compared with previous work using DSC and other techniques. Besides undergoing fast chemical exchange, the adsorbed water was also demonstrated in proximity with the free COOH groups and far from the hydrogen bonds between COOH groups by using two-dimensional 1H−1H spin-exchange NMR experiments