A series of azobenzene containing side-on liquid crystalline ABA triblock copolymers were investigated.This triblock series possesses the same central liquid crystal block B and various lengths of the amorphous block A.Transmission electron microscopy(TEM),small angle X-rays and neutron scattering(SAXS and SANS) were used to study their morphologies.After annealing the samples over weeks at a temperature within the nematic temperature range of block B, different morphologies(disordered,lamellar,perforated layer and hexagonal cylinder) were observed by TEM.The alignment behavior of these azo triblock copolymers in the magnetic field for artificial muscle application,as well as the phase period and the order-disorder transition(ODT) were studied in situ by SANS. 相似文献
The deformation and fracture behaviour of symmetric and asymmetric styrene-b-(styrene-random-butadiene)-b-styrene (S-SB-S) triblock copolymers with variations in their molecular architectures in terms of their outer PS block and the random SB middle block composition ratios have been investigated using essential work of fracture approach based on post yield fracture mechanics concept. The present investigations on crack resistance behaviour of these S-(S/B)-S triblock copolymers where effective interaction parameter (χeff) is systematically varied through the variation of block compositions and architecture is in continuation to our earlier communicated short article highlighting the phase behaviour-morphology and mechanical property interrelation. The crack initiation and propagation behaviours are correlated to morphology and dynamic mechanical properties as obtained from TEM, SAXS and DMA measurements. The influence of interaction parameter (χ-parameter) space which has been manipulated through the variation of block compositions has clearly manifested in their morphologies and in their mechanical properties. Further the kinetic aspects of fracture mechanical response have also been investigated where all the materials have clearly revealed block composition dependence. SEM analysis was carried out to understand the fracture modes prior to failure. 相似文献
Symmetric styrene-b-styrene-co-butadiene-b-styrene (S-SB-S) tri-block copolymers with varying middle and outer block composition have been studied. We report our findings based on a systematic variation of the effective interaction parameter (χ) by adjusting the composition of the random copolymer in the middle block and of the outer blocks (in terms of PS-chain length) which allows us to explore the χ-parameter space with regard to molecular architecture more thoroughly than in SBS triblock copolymers. A variation in the S/B middle block composition or in the PS outer block content leads to a change in phase behaviour and morphology simultaneously accompanied by significant changes in mechanical properties, varying from elastomeric to thermoplastic property profile. Despite high PS contents of 55-75 wt.% these S-SB-S triblock copolymers reveal high strain at break values between 650% and 350% which is in striking contrast to the conventional SBS triblock copolymers where only about 10% strain at break have been reported to be achieved with similar PS-content (∼75 wt.%). 相似文献
EBE and BEB triblock copolymers were prepared and characterized. Microphase separation in the melt state was studied, and the results combined with those for EB and BEB copolymers reported previously. The microphase separation temperature (MST) was determined from the temperature dependence of SAXS. There was a large difference in MST between the diblock and triblock copolymers as expected from theory. The Flory‐Huggins parameter (χ) was independent of block architecture for all three series provided that the E block lengths in the EBE copolymers exceeded 65. 相似文献
Phenomena associated with the order-disorder transition (ODT) of block copolymers have been studied by optical light microscopy, SAXS, SEM, TEM and DSC. Observations have been made on almost symmetric polystyrene-block-poly(methyl methacrylate) samples of three molecular weights and their mixture. We observed non-equilibrium supermolecular structures several microns in diameter in the bulk of thick PS-b-PMMA films (ca. 100 μm thickness) prepared by vacuum drying of films cast from a non-selective solvent (after a short-term annealing above the Tg). Apparent LDOT (lower disorder-to-order transition) behaviour is observed for samples with non-equilibrium morphology surviving from solution as deduced from SAXS 1/Im vs 1/T and the full width at half-maximum vs 1/T plots.The measurements point to complex behaviour near the ODT, but homogenization of samples upon long-term annealing well above the Tg temperature call into existence common stacks of lamellae observable in SEM images of microphase-separated samples. This verifies the opinion that the observed apparent LDOT behaviour of samples II, III and II + III is associated with the frozen non-equilibrium morphology surviving from solution. This is confirmed by SAXS measurement on a homogenized sample displaying the expected UDOT behaviour. It has been demonstrated that self-assembled structures prepared by vacuum drying of films cast from a non-selective solvent are non-equilibrium structures and their successive ordering is difficult due to a relative narrow temperature interval between Tg and degradation temperature. The conditions under which BCP films are prepared thus have a pronounced effect on the microstructure and microphase ordering process. 相似文献
Summary: The crack toughness behaviour of binary styrene‐butadiene (SB) triblock copolymer blends of a thermoplastic block copolymer (LN3) and a thermoplastic elastomer (LN4) with different molecular architecture was studied using essential work of fracture (EWF) concept and was correlated to the morphological features from transmission electron microscopy (TEM). An increase in the crack toughness behaviour between 60 and 80 wt.‐% LN3 has been observed and is attributed to a change from cylindrical to lamellar morphology. The time‐resolved crack propagation studies have offered new dimensions to understand the kinetic aspects of fracture behaviour while the strain field analysis has explained the time‐dependent deformation behaviour to characterise the time dependence of the strain energy dissipation modes.
Load‐displacement diagrams of non essential work of fracture values of LN3/LN4 blends. 相似文献
Block copolymers are well‐known for their large number of microphase morphologies on mesoscopic length scales. After a short review of the different morphologies observed in binary block copolymers and ternary triblock copolymers, the self‐assembling in blends of different block copolymers into common superlattices is discussed in detail. Besides similar morphologies known for pure triblock and diblock copolymers, the blends can also show new morphologies. Examples of such new morphologies are periodic non‐centrosymmetric lamellae and multiple gyroid interface structures. The discussion of the superlattices is primarily based on investigations by transmission electron microscopy (TEM), which are supplemented in a few cases by small angle X‐ray scattering (SAXS) or results from computer simulations. 相似文献
Experiment finds that, for a chlorinated polyethylene (chlorine content 62.1% by weight)/poly(ethyl methacrylate) blend, a negative value of χ′2 3 is obtained, which indicates compatibility. With increasing temperature, χ′2 3 increases towards zero as required by the lower critical solution temperature behaviour of polymer blends. For chlorinated polyethylene/poly(butyl acrylate) blends however the specific retention volume is a linear function of composition and a positive χ′2 3 results if calculated by the conventional theory. The magnitude of χ′2 3 is determined by the difference between the retention volumes of the pure polymers and decreases with temperature. This effect is assumed to be a result of phase separation during coating the blend onto the support. A theoretical treatment is developed to explain this behaviour. 相似文献
The phase behavior of symmetric ABA triblock copolymers containing a semiflexible midblock is studied by lattice Monte Carlo simulation. As the midblock evolves from a fully flexible state to a semiflexible state in terms of increase in its persistence length, different phase behaviors are observed while cooling the system from an infinite high temperature to a temperature below T(ODT) (order-disorder transition temperature). Within the midblock flexibility range we studied (l(p)N(c)相似文献
Blends of isotactic propylene-ran-ethylene (EP) and propylene-ran-(1-butene) (BP) copolymers with various comonomer content (2-3.1 wt.% ethylene, 9.9 wt.% 1-butene), were prepared in Brabender internal mixer at various compositions (25/75, 50/50, 75/25). Static, impact and dynamic mechanical behavior of copolymers and their blends was investigated. The crystalline structure was studied by DSC and SAXS analysis. For all copolymers the lamellar thickness, crystallinity degree and glass transition temperature are lower than those of iPP homopolymer, depending on the comonomer content. It was found that the copolymers exhibit improved impact strength as compared to plain iPP, due to lower crystallinity and higher mobility of chains within amorphous component. Moreover, the elastic modulus as well as the yield behavior of the examined samples resulted to depend primarily on the amount of the crystalline phase and the thickness of the lamellar crystals, respectively. A linear dependence of yield stress on the logarithm of reciprocal lamellar thickness was observed for blends and copolymers, supporting the concept of thermal nucleation of dislocations which control the crystallographic slip processes initiated at the yield point. The blends of BPS with either EPS or EP2 display complete miscibility in the entire range of composition and their mechanical properties are intermediate between those of plain components, changing gradually with the composition. 相似文献
Self-assembly of binary blends of two triblock copolymers of poly(4-vinyl pyridine)-b-polystyrene-b-poly(4-vinyl pyridine), i.e., P4VP43-b-PS260-b-P4VP43 (P1) and P4VP43-b-PS366-b-P4VP43 (P2), in dioxane/water solution was studied. These two triblock copolymers individually tend to form vesicles (P2) and cylindrical micelles (P1) in dilute solution. It was found that copolymer components in the blend, sample preparation method, and annealing time had significant effect on hybridization aggregate morphology. By increasing P1 content in the copolymer blends, fraction of looped and stretched cylinders increased, while fraction of bilayers decreased. Nearly no bilayer was observed when P1 content was above 85 wt%. On the other hand, fraction of cylinders decreased while fraction of bilayers increased with the increase of P2 content in copolymer blends. Lamellar structures were obtained, when P2 content was 60 wt% in the copolymer blends, whereas cylinders were seldom found when P2 content was above 80 wt%. These results indicate that P1 and P2 copolymer molecules cooperatively participate in the formation of cylinders and vesicles. Some exotic structures, such as lamellae with protruding cylinders (LPC), incomplete vesicles with protruding cylinders (VPC), and cylindrical bilayers, have been kinetically trapped. These structures may result from intramicellar fusion processes in cylindrical micelles. The striking structures represent a compromise between bilayer and cylindrical geometries. 相似文献
The well-known bio-based and biocompostable poly(lactic acid), PLA, suffers from brittleness and a low heat distortion temperature. In this paper, we address a possible route to make PLA tough(er) by blending with ethylene-co-vinyl acetate (EVA) with different vinyl acetate contents. The compatibility and phase morphology of the PLA/EVA blends was controlled by the ratio of vinyl acetate and ethylene in the random copolymers. Tough PLA/EVA blends with increased impact toughness, up to a factor of 30, were obtained with a maximum toughness at a vinyl acetate content of approximately 50 wt.%. The local deformation mechanism was well studied by TEM, SAXS and SEM. It revealed that internal rubber cavitation in combination with matrix yielding is the dominant toughening mechanism for the PLA/EVA blends under both impact and tensile testing conditions. 相似文献
The crystallization behavior of a series of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO)
triblock copolymers (Pluronics) was investigated using time-resolved small-angle X-ray scattering (SAXS), thermal analysis,
and polarized optical microscopy. For comparison, a PEO homopolymer, PEO3K, was also included. Time-resolved SAXS during the
crystallization of PEO3K shows a typical “two-step” process, i.e., in the initial stage, a metastable crystal with nonintegral
folding (NIF) structure forms first, then, it transforms into integral folding (IF) structures, the IF(0) and the IF(1). In
contrast with PEO3K, the PEO–PPO–PEO triblock copolymers show a “one-step” crystallization process, i.e., the PEO blocks crystallize
directly into the final state and do not change with time. In thermal analysis, only one major solid–melt transition is observed
during isothermal crystallization and subsequent melting for triblock copolymers. In the full temperature range, a linear
crystal growth is observed. The crystal growth rates monotonously decrease with crystallization temperatures. Notches or breaks
due to the NIF–IF transition as clearly seen for PEO3K cannot be recognized for Pluronics. Based on these results, we conclude
that the crystallization of PEO–PPO–PEO triblock copolymers follows a “one-step” process; no metastable structure serving
as an intermediate state is formed during the crystallization process within the time scale of the current experiments (<120 min). 相似文献