Highly porous polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) diblock copolymer membranes are prepared using carbohydrates as additives. Therefore α‐cyclodextrine, α‐(D )‐glucose, and saccharose (cane sugar) are tested for the membrane formation of three different PS‐b‐P4VP polymers. The addition of the carbohydrates leads to an increasing viscosity of the membrane solutions due to hydrogen bonding between hydroxyl groups of the carbohydrates and pyridine units of the block copolymer. In all cases, the membranes made from solution with carbohydrates have higher porosity, an improved narrow pore distribution on the surface and a higher water flux as membranes made without carbohydrates with the same polymer, solvent ratio, and polymer concentration. 相似文献
The formation of channel membrane of polystyrene‐block‐poly(4‐vinyl pyridine) block copolymer is studied by computer simulations with the nonsolvent induced phase separation (SNIPS) method. Dissipative particle dynamics is employed to study the microphase separation process and the SNIPS mechanism. Simulation results indicate that polymer concentration has a significant effect on the membrane structure. Channel membranes form in the copolymer concentration range of 44–58%. Block ratio plays an important role in shaping the membrane structure. Solvent exchange rate also affects the degree of microphase separation at each evolution stage of simulation. The time evolution of morphologies shows that the microphase separation processes happen with the following sequences: the polymer self‐assembled and many small pores appear, then they form irregular cavities and cross‐link gradually, finally the channel membrane forms. These results throw light on the formation mechanism of polymer membranes and provide insightful guidance for future membrane design and preparation. 相似文献
The dispersion of single‐walled carbon nanotubes (SWNTs) in a non‐polar solvent is controlled with a series of polystyrene‐block‐polybutadiene‐block‐polystyrene (PSBS) block copolymers that contain cholesteryl chloroformate (CC) in side‐chains. Esterification of CC with the partially hydroxylated polybutadiene (PB) blocks allows one to tune the polarity of the block copolymers, which decreases with the amount of CC attached. An excellent dispersion of weak polar SWNTs is observed with PSBS that contains a partially hydroxylated PB block. The dispersion is then significantly deteriorated when the amount of non‐polar CC moieties increases in the block copolymers. A good dispersion is achieved with a polymer that gives rise to strong SWNT–polymer interactions, which ensures contact of the polymer molecules with the nanotube surface, rather than a good solubility of the polymer dispersant in solvent. The stability of the SWNTs in solution arises from unique needle‐like nanowires of the block copolymer aligned perpendicular to the nanotube axis.
Summary: Spherical micelles have been formed by mixing, in DMF, a poly(styrene)‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (PS‐block‐P2VP‐block‐PEO) triblock copolymer with either poly(acrylic acid) (PAA) or a tapered triblock copolymer consisting of a PAA central block and PEO macromonomer‐based outer blocks. Noncovalent interactions between PAA and P2VP result in the micellar core while the outer corona contains both PS and PEO chains. Segregation of the coronal chains is observed when the tapered copolymer is used.
Inclusion of comb‐like chains with short PEO teeth in the corona triggers the nanophase segregation of PS and PEO as illustrated here (PS = polystyrene; PEO = poly(ethylene oxide)). 相似文献
Summary: Pulse field gradient‐NMR (PFG‐NMR) spectroscopy is determined to be a more suitable method for the investigation of self‐association processes in multi‐component (co)polymer systems than light scattering methods. Here the co‐micellization of mixtures of the diblock copolymer polystyrene‐block‐(hydrogenated polyisoprene) (PS‐HPI) and the triblock copolymer polystyrene‐block‐(hydrogenated polybutadiene)‐block‐polystyrene (PS‐HPB‐PS) in decane is investigated by PFG‐NMR spectroscopy and the results compared to those experimentally determined by static (SLS) and dynamic (DLS) light scattering. As expected, diffusion coefficients determined by PFG‐NMR spectroscopy are systematically lower than those from DLS. The PFG‐NMR measurements provided higher values of cequation/tex2gif-stack-1.gif(X)/ctot than the model calculations, illustrating that the basic assumption used in the calculations, i.e., that the number concentration of co‐micelles in mixed solutions follows the dilution with a triblock copolymer solution, 1 − X, is not fully valid at high X (weight fraction of PS‐HPB) values.
Comparison of PFG‐NMR spectroscopy and SLS (cequation/tex2gif-stack-2.gif/ctot = equilibrium concentration of free PS‐HPB‐PS over the total concentration of copolymers in solution, X = weight fraction of PS‐HPB). 相似文献
The viscoelastic behavior, order-disorder transition, and phase equilibria in mixtures of a block copolymer and an endblock-associating resin were investigated. The block copolymer was a polystyrene-block-polyisoprene-block-polystyrene (KRATON® D-1107, Shell Development Co.) copolymer. The endblock-associating resins investigated were two different grades of a commercially available random copolymer of poly(α-methyl styrene) and polystyrene, one with a weight-average molecular weight \[\bar M_{\rm w}\] of 710 (KRISTALEX® 3085, Hercules Inc.) and the other with \[\bar M_{\rm w}\] = 4100 (KRISTALEX® 5140, Hercules Inc.). Mixtures of various proportions of the block copolymer and the endblock-associating resin were prepared in toluene solvent. With the mixtures, measurements of dynamic viscoelastic properties were made, namely, dynamic storage modulus G″ and dynamic loss modulus G″ as a function of temperature from temperature scans of the samples using a Rheometrics Mechanical Spectrometer. The following observations were made. (1) The plateau modulus of the block copolymer increased with increasing amount of KRISTALEX 3085 or KRISTALEX 5140, indicating that the low-molecular-weight resin was associated with the polystyrene microdomains of the block copolymer. (2) When KRISTALEX 3085 (up to 30 wt %) was added to the block copolymer, the glass transition temperature (Tg) of the polyisoprene midblock of the SIS block copolymer was shifted toward higher temperatures, indicating that part of the KRISTALEX 3085 added had associated with the rubbery midblock of the block copolymer. Also investigated was the order-disorder transition behavior of the mixtures, using a rheological technique (log G′ versus log G″ plots) recently introduced by Han and Kim. It has been found that the order-disorder transition temperature Tr of mixtures of the SIS block copolymer and KRISTALEX 3085 decreased steadily with increasing amount of KRISTALEX 3085, whereas the addition of KRISTALEX 5140 increased the Tr of the block copolymer. It was found by light scattering and hot-stage microscopy that macrophase separation occurred in the KRATON 1107/KRISTALEX 5140 mixtures while microdomains of polystyrene were present in the block copolymer. 相似文献
Block copolymers have been extensively studied over the last few decades because they can self‐assemble into well‐ordered nanoscale structures. The morphologies of block copolymers in confined geometries, however, are still not fully understood. In this work, the fabrication and morphologies of three‐dimensional polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) nanostructures confined in the nanopores of anodic aluminum oxide (AAO) templates are studied. It is discovered that the block copolymers can wet the nanopores using a novel solvent‐annealing‐induced nanowetting in templates (SAINT) method. The unique advantage of this method is that the problem of thermal degradation can be avoided. In addition, the morphologies of PS‐b‐PDMS nanostructures can be controlled by changing the wetting conditions. Different solvents are used as the annealing solvent, including toluene, hexane, and a co‐solvent of toluene and hexane. When the block copolymer wets the nanopores in toluene vapors, a perpendicular morphology is observed. When the block copolymer wets the nanopores in co‐solvent vapors (toluene/hexane = 3:2), unusual circular and helical morphologies are obtained. These three‐dimensional nanostructures can serve as naontemplates for refilling with other functional materials, such as Au, Ag, ZnO, and TiO2.