On the melting behaviour of polymer single crystals in a mixture with a compatible polymer: 1. Poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Canalda, J. C.; Hoffmann, T.; Martínez‐Salazar, Javier

doi:10.1016/0032-3861(95)93598-g

Cited by 19 publications

(14 citation statements)

References 25 publications

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“…From the theoretical fit with the experimental melting points (Figure 4.11), a value of x aa 0.141 was estimated at 165 C (based on the x ca value of 0.345), which is smaller in magnitude (i.e., a lesser attractive interaction) than the reported value of x mp 0.31 obtained by Nishi from the melting point depression experiments in the vicinity of the melting temperature of pure PVDF [56]. In contrast, small-angle neutron scattering experiments gave much smaller values for the same PVDF/PMMA blends, for example, x aa 0.226 and 0.077 for two different concentrations of PVDF/ PMMA by Hadziioannou [72] and 0.14 by Canalda [73], and 0.03 to 0.16 from SAXS by Wendorff [74]. In the Flory diluent theory, the repulsive crystal-amorphous interaction x ca was completely ignored, and thus the x aa could have been overestimated as compared to those of other experiments.…”

Section: Matkarcontrasting

confidence: 43%

Phase Field Modeling on Polymer Crystallization and Phase Separation in Crystalline Polymer Blends

Kyu

Tai-ming

et al. 2010

Encyclopedia of Polymer Blends

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The solidification phenomenon of a liquid has been one of the most fascinating firstorder phase transitions, involving a complex interplay of many physical effects. The simplest solidification front is the planar interface. Usually, the solid-liquid interface is an active free boundary from which latent heat is liberated during solid-liquid phase transformation. Preferentially, this latent heat is conducted away from the convex solid-liquid tips, but it may be trapped in the case of concave interface, thereby leading to the directional growth of interfacial morphologies. Consequently, these interfaces are generally rough with convex and concave curvatures. Among them, the basic patterns are dendrites and seaweeds. A structure with pronounced orientational order is termed as dendrite, and without apparent orientational order it is called seaweed. The dendritic shape is a symmetric needle crystal with a parabolic tip, the sides of which are influenced by a secondary branching. The seaweed morphology was originally introduced on the basis of experimental observations under the name of dense-branching morphology, which is characterized by repeating tip splitting at the interface front [1]. The basic element of the seaweed structure is a doublon, which consists of two fingers with a liquid channel running along the axis of the symmetry between them. Experimentally, Akamatsu[2] showed that the seaweed growth involves a continual creation and elimination of doublons. In directional solidification, the solid-liquid interface is subjected to morphological instabilities in an externally imposed directional temperature gradient. Various interface morphologies have been observed [2-4] depending on the physical properties of the materials. Especially, the anisotropic properties of the solid-liquid interface play a particularly important role in deter mining the stability of the dendrites as well as the transformation between seaweed and dendrite patterns. Thus, an in-depth understanding of the interface morphology during solidification is essential to shed light on the pattern formation aspects of crystal solidification.Theoretical investigations of the solid-liquid phase transition have long been the subject of considerable interest. Among these, there are two main streams: one is the Edited by Avraam I. Isayev

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Section: Matkarcontrasting

confidence: 43%

Phase Field Modeling on Polymer Crystallization and Phase Separation in Crystalline Polymer Blends

Kyu

Tai-ming

et al. 2010

Encyclopedia of Polymer Blends

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“…PVDF possesses strong electric dipole moments associated with the C-F bonds in monomer units. Consequently, it is capable of interacting with a variety of polar polymers via dipole-dipole interactions [11,12]. For example, the miscibility of PVDF with poly(methyl methacrylate) (PMMA) has been extensively investigated.…”

Section: Introductionmentioning

confidence: 99%

Surface characteristics and blood compatibility of PVDF/PMMA membranes

Wang

et al. 2012

J Mater Sci

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Poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) membranes have important applications as biomaterials. In this study, PVDF/PMMA with varying ratios is blown into membranes, the surface property and blood compatibility of which are thoroughly investigated. Membrane surface characteristics including composition and topography exert considerable influence on the blood compatibility. Introduction of PMMA disturbs PVDF crystallization, however, favors the b phase crystal formation. PVDF content, crystallization ability, and surface enrichment have decisive effects on the membrane surface composition. Meanwhile, with increased PMMA fraction, the membrane surface roughness is also increased, and subsequently results in decreased hemocompatibility. While the membranes with PMMA content lower than 30 wt% show good blood compatibility, those with higher PMMA fraction exhibit obvious platelet adhesion to the surface. Thermal annealing promotes the formation of b phase PVDF and generates much smoother surface, thus endowing the membranes with greatly enhanced blood compatibility. These results show the prospect for optimization of processability, surface property, and blood compatibility of PVDF/PMMA membranes through facile modulation of PMMA content and fabrication process.

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“…Such discrepancy has been reported for numerous blends (Canalda et al, 1995), but there is no critical challenge as to why such a large discrepancy exists for the melting-temperature depression approach versus neutron scattering. Secondly, the meaning of the FH parameter based on the melting point depression is vague (Nishi & Wang, 1975); that is to say, whether it represents the amorphous-amorphous interaction as in the case of SANS or the crystal-amorphous interaction.…”

Section: Determination Of V Parameter Based On Melting Point Depressionmentioning

confidence: 92%

Discrepancy in determination of χ parameters by melting point depression versus small-angle neutron scattering in blends of deuterated polycarbonate and isotactic poly(methyl methacrylate)

et al. 2007

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Discrepancy in determination of v parameters by melting point depression versus small-angle neutron scattering in blends of deuterated polycarbonate and isotactic poly(methyl methacrylate) Thein Kyu,* Rushikesh A. Matkar, Dong Soo Lim and Chechian Ko Department of Polymer Engineering, University of Akron, Akron, OH-44325, USA. Correspondence e-mail: tkyu@uakron.eduThe discrepancy in the interaction parameters of deuterated polycarbonate/ isotactic poly(methyl methacrylate) blends as determined by the melting point depression approach and the small-angle scattering technique is reported. We have modified the Flory diluent theory by removing the inherent assumption of complete rejection of the solvent from the crystal solid by taking into consideration the crystal-amorphous, amorphous-crystal, and crystal-crystal interactions. The discrepancy in values obtained by the two methods is discussed. IntroductionThe tacticity of poly(methyl methacrylate) (PMMA) isomers has been recognized to exert profound effects on its miscibility with other polymers (Schurer et al., 1975;Silvestre et al., 1987). In our laboratory, blends of polycarbonate (PC)/PMMA isomers have been explored as a means of controlling the transparency of their blend films and the refractive index gradient (Lim & Kyu, 1991). It was found that PC/ syndiotactic poly(methyl methacrylate) (sPMMA) and PC/atactic poly(methyl methacrylate) (aPMMA) can be characterized as partially miscible with a cloud point phase diagram reminiscent of a lower critical solution temperature (LCST). The proximity of the aforementioned LCST to the glass transition temperatures of the constituents of the PC/PMMA blends, coupled with slow mutual diffusion of the polymer chains, impeded the exploration of the miscibility of PC/aPMMA and PC/sPMMA blends near their glass transition temperatures (T g ) by conventional techniques such as light scattering or optical microcopy. However, thermal reversibility of the LCST phase behavior could not be established for either of these blends. Hence, we shall focus on small-angle neutron scattering (SANS) experiments of deuterated polycarbonate (dPC)/isotactic poly(methyl methacrylate) (iPMMA) blends.In the present paper, SANS has been employed for the determination of the interaction parameter in the vicinity of the coexistence lines of the dPC/iPMMA blend using the Ornstein-Zernike approach (Kirste et al., 1975). The uniqueness of the present PC/ iPMMA blend is that both constituents can crystallize upon annealing above their glass transition temperatures. The melting point depression of PC was analyzed in the framework of the polymer diluent theory (Flory, 1953;Nishi & Wang, 1975). The value of the PC/ iPMMA blend obtained by the Flory diluent analysis was subsequently compared with that obtained by SANS. Materials and methodsThe deuterated PC (dPC) was obtained from Dr Steve Smith of the Procter & Gamble Company. The as-received dPC was purified by dissolving in tetrahydrofuran (thf) at a concentration of 2 wt% and filtered twice using a mi...

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On the melting behaviour of polymer single crystals in a mixture with a compatible polymer: 1. Poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Cited by 19 publications

References 25 publications

Phase Field Modeling on Polymer Crystallization and Phase Separation in Crystalline Polymer Blends

Phase Field Modeling on Polymer Crystallization and Phase Separation in Crystalline Polymer Blends

Surface characteristics and blood compatibility of PVDF/PMMA membranes

Discrepancy in determination of χ parameters by melting point depression versus small-angle neutron scattering in blends of deuterated polycarbonate and isotactic poly(methyl methacrylate)

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