摘要:

The new unified context for crystallization of linear macromolecules from the melt, established by recent work, is expounded. The morphology of spherulites shows that they form because of a short-range force operative at the branch points of dominant lamellae that causes them to diverge at noncrystallographic angles of about 20°. Work on monodispersen-alkanes has confirmed the identification of this short-range force with the pressure from dynamic cilia during growth. Accordingly, spherulites, like chain folding, are a direct consequence of molecular length. It is suggested that the tendency to form coarse spherulites even for extended-chain growth at lower temperatures may result from the increasing difference between the lengths of nucleus and molecule. Crystallization on linear nuclei has been used to maximize the concentration of segregants at the growth front and to demonstrate cellulation in undoped polymers for the first time. The behavior of branched polyethylenes differs from the uniform growth of the linear polymer in coarsening and developing protuberances at the growth front, all the while slowing continuously toward an asymptotic steady state; differences of detail may be useful in distinguishing polymers of different catalytic origin and branch content. Spherulitie growth is also nonlinear for these polymers, but is always faster than for rows. When there is sufficient segregation, spherulites themselves cellulate, increasingly so for higher branch content. Cellulation is thus an uncommon and secondary process may be superposed on regular spherulitie growth beyond a certain distance. Cell dimensions do not scale with the diffusion length; in so doing, the phenomenon displays new physics.

ISSN:0022-2348    

DOI:10.1080/00222349908248114

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In studies of spherulitic crystallization in polymers, many questions pertaining to the mechanism of the crystallization process have remained unanswered. A currently accepted view describes the development of spherulites from a framework of individual dominant lamellae that splay apart and branch (e.g., by a dislocation mechanism). This model, in addition, assumes that the space between the dominant lamellae is filled by subsidiary lamellae. In the center of a spherulitic entity, there is a hedritic core that occupies a relative volume that depends on the level of maturity of the spherulitic development. Typical hedritic views consist of lamellae that have a flat stack, or sheaflike, splaying appearance depending on the angle and depth of observation with respect to the central stack of lamellae. Visualization of the three-dimensional appearance of these hedrites by atomic force microscopy (AFM) and the observation of their growth in situ are the subjects of this article. First, we describe AFM studies of hedrites observed at etched surfaces of β-isotactic polypropylene (β-IPP). Evidence sup-porting splaying, branching via dislocations, and development of curved lamellae is presented. In the second part, we describe real-time hot-stage AFM in situ observations of the hedritic growth in poly(ethylene oxide) (PEO) and poly-(ε-caprolactone) (PCL).

ISSN:0022-2348    

DOI:10.1080/00222349908248115

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Polyethylene blends were studied by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Binary blends of commercial linear polyethylene (LPE) with two low-density polyethylenes (LDPEs) of melt indexes, about 20 and about 0.27 g/10 minutes, were investigated. The blends, with 10% and 50% LPE contents, and the pure LPE were isothermally crystallized at 124°C for up to 48 h under solid-liquid phase segregation conditions. Double melting endotherms were obtained for the blends. Results show that, despite differences in crystallization kinetics between both types of blends, the same depression in the LPE melting temperature and approximately the same LPE crystal thicknesses were found for the blend compositions. In addition, the extent of occurrence of lamellar thickening in LPE during crystallization is a function of its content in the blend.

ISSN:0022-2348    

DOI:10.1080/00222349908248116

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The effect of compatibilization on the adhesion, fracture toughness, morphology, and mechanical properties of isotactic polypropylene (PP)/polyamide 6 (PA) blends was investigated. Maleic anhydride (MAH) functionalized poly-(ethylene-co-vinyl acetate) (EVA-g-MAH) and nonreactive EVA copolymer were used as compatibilizers in binary blends. An attempt of in situ compatibilization via addition of pure maleic anhydride to PA/EVA/PP melt was also made. The blends containing maleated EVA copolymer showed more regular and finer dispersion of phases, better adhesion at the interface, and improved mechanical properties.

ISSN:0022-2348    

DOI:10.1080/00222349908248117

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Different methods for characterizing the morphology of multiphase blends were applied to a blend of thermoplastic polyurethane with 20 wt% polypropylene as the dispersed phase. Optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and light scattering were compared. The microscopy methods were evaluated with respect to their suitability for quantitative image analysis for determination of the particle size distribution. Comparison of the particle size distributions revealed that the dependence of the measured particle size on the method of preparation and technique was not very pronounced. The main difference resulted from cutting the particles outside their maximum diameter. The measured particle sizes determined with methods that analyze the whole particles, such as SEM on separated particles and laser light scattering, are larger than those measured on cut specimens. The factor 4/π valid in monodisperse systems for the ratio between the real particle size and that measured on sections was found also to be applicable to this polydisperse blend system. Although light micros-copy requires the least preparation efforts, it is a reliable method for this blend system.

ISSN:0022-2348    

DOI:10.1080/00222349908248118

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The morphology of an interpenetrating network-like (IPN-like) system consisting of polyethylene (PE) and polystyrene (PS) is compared with an IPN system consisting of PE and polymethacrylate copolymers with different lengths of alkyl groups. In the presence of dodecyl methacrylate (DMA) units in the copolymer network of the IPN-like system, increased homogeneity of the interphase was observed.

ISSN:0022-2348    

DOI:10.1080/00222349908248119

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Multiblock copolymers (MBCPs) consisting of polysulfone (PSU) segments and segments of the liquid crystalline poly(ethyleneterephthalate-co-oxybenzoate) (PET/HBA) form rather complex morphologies. Scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), and atomic force microscopy (AFM) investigations of two block copolymers with significantly different block molecular weights proved the existence of both macro-and microphase separation. These morphologies, existing on different length scales, were found to be superimposed in the samples. A suitable fractionation procedure was used to suppress macrophase separation. Then, it was found that microphase separation is controlled by the segment molecular weights.

ISSN:0022-2348    

DOI:10.1080/00222349908248120

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Thin films of incompatible polymer blends can form a variety of structures on preparation. For the polymer blend system consisting of two poly(styrene-co-para-bromo-styrene)s at different degrees of bromination, PBrxS/PBryS, the compatibility can be tuned through a variation of the difference in the degree of bromination. Within this blend system, two series of samples with different compatibilities were investigated at various blend compositions. The surface morphology of the thin films was investigated by atomic force microscopy (AFM) measurements, while diffuse X-ray scattering provided additional depth sensitivity at a comparable lateral resolution. The results are indicative for phase separation lateral, as well as perpendicular, to the sample surface.

ISSN:0022-2348    

DOI:10.1080/00222349908248121

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

By control of phase separation and dewetting of thin blend films of weakly incompatible polymers, particular surface patterns may be generated. These patterns cover a typical height scale from 0.3 nm to 300 nm and most prominent in-plane length scale from 0.1 μm to 100 μm. Characteristic features are holes, regular continuous structures, and drops of these sizes. In addition, conformal rough surfaces with a morphology dominated by one of the underlying substrates can be prepared. The surface morphology was investigated with scanning force microscopy (SFM), while the interface correlation was measured with diffuse X-ray scattering. Both methods together yield a topological description of the examined samples. Observed morphologies originated from phase separation of the thin blend film and from the dewetting of one blend component on top of a continuous film formed by the other component.

ISSN:0022-2348    

DOI:10.1080/00222349908248122

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Cross-linked ferroelectric liquid crystalline (FLC) polymers were studied by atomic force microscopy (AFM). Polysiloxane copolymers were synthesized with mesogenic and photo-cross-linkable side groups, the latter connected either directly to the backbone via a short spacer or as a terminal group on a part of the mesogens. These elastomers were prepared as thin, freely suspended films in homeotropic orientation. Topographic measurements depict plateaus separated by steps of characteristic height corresponding to the surfaces and edges of smectic layers. From the temperature behavior, as well as from the reaction to mechanical deformation, a model for the network architectures is proposed. In the first case (“intralayer cross-linking”), a predominantly two-dimensional network is formed within the backbone layers separating the smectic layers; in the second case (“interlayer cross-linking”), a three-dimensional network is established that is dependent on the mesophase present during cross-linking.

ISSN:0022-2348    

DOI:10.1080/00222349908248123

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor