Miscibility

About: Miscibility is a research topic. Over the lifetime, 5521 publications have been published within this topic receiving 133547 citations. The topic is also known as: miscible.

Mapping phases of poly(vinyl alcohol) and poly(vinyl acetate) blends by FTIR microspectroscopy and optical fluorescence microscopy

Abstract: Fluorescence optical microscopy (FOM) of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) blends in compositions 9/1, 1/1, and 1/9 (w/w) show that these blends present phase separation in the solid state. Each domain of the solid samples was identified by FOM as PVA-richer domains by green fluorescence of fluorescein and PVAc-richer domains by the blue fluorescence of anthracene. The dimensions, shapes, and distributions of these domains were dependent on the initial composition of the polymeric mixtures in the solution. Specific interactions between both homopolymers were studied using FTIR microspectroscopy, which allowed us to obtain spectra for both PVA-richer and PVAc-richer domains. These spectra demonstrated that partial miscibility could occur only for blends with a higher PVAc content and, in these cases, we observed interchain hydrogen-bonded carbonyl groups. Fluorescence microscopy of blends with this partial miscibility exhibited small interconnected domains produced by coalescence of droplets during the polymer phase separation process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 645–655, 1998

Investigation of Chitosan-PVA Composite Films and Their Adsorption Properties

Abstract: Viscous aqueous solutions of chitosan and polyvinyl alcohol (PVA) were blended to enhance miscibility and avoid polymer phase separation. The mixtures were drop-casted and air dried to yield composite film materials that were characterized by equilibrium water uptake, physical stability in aqueous solution, and thermal stability. Chitosan/PVA blends have greater thermal stability, unique morphology, and reduced solubility in acidic solution, thus extending the useful pH range for chitosan as a sorbent material. The uptake properties of the films was investigated using methylene blue (MB) and a p-nitrophenol (PNP) dyes, where it was found that each single component polymer has greater uptake toward MB than PNP. A direct relationship between film composition (chitosan:PVA) with solution pH and the uptake of MB was observed. The results are in agreement with electrostatic interactions and contributions due to the hydrophobic effect for such composite materials.

Investigation of Polymer-Surfactant and Polymer-Drug-Surfactant Miscibility for Solid Dispersion

Abstract: In a solid dispersion (SD), the drug is generally dispersed either molecularly or in the amorphous state in polymeric carriers, and the addition of a surfactant is often important to ensure drug release from such a system. The objective of this investigation was to screen systematically polymer-surfactant and polymer-drug-surfactant miscibility by using the film casting method. Miscibility of the crystalline solid surfactant, poloxamer 188, with two commonly used amorphous polymeric carriers, Soluplus® and HPMCAS, was first studied. Then, polymer-drug-surfactant miscibility was determined using itraconazole as the model drug, and ternary phase diagrams were constructed. The casted films were examined by DSC, PXRD and polarized light microscopy for any crystallization or phase separation of surfactant, drug or both in freshly prepared films and after exposure to 40°C/75% RH for 7, 14, and 30 days. The miscibility of poloxamer 188 with Soluplus® was <10% w/w, while its miscibility with HPMCAS was at least 30% w/w. Although itraconazole by itself was miscible with Soluplus® up to 40% w/w, the presence of poloxamer drastically reduced its miscibility to <10%. In contrast, poloxamer 188 had minimal impact on HPMCAS-itraconazole miscibility. For example, the phase diagram showed amorphous miscibility of HPMCAS, itraconazole, and poloxamer 188 at 54, 23, and 23% w/w, respectively, even after exposure to 40°C/75% RH for 1 month. Thus, a relatively simple and practical method of screening miscibility of different components and ultimately physical stability of SD is provided. The results also identify the HPMCAS-poloxamer 188 mixture as an optimal surface-active carrier system for SD.

Influence of Composition Distribution and Branch Content on the Miscibility of m-LLDPE and HDPE Blends: Rheological Investigation †

Abstract: The miscibility of metallocene linear low-density polyethylene (m-LLDPE) and Ziegler- Natta LLDPE (ZN-LLDPE) with linear high-density polyethylene (HDPE) was studied. The influences of composition distribution (CD) and branch content (BC) on the miscibility of m-LLDPE and ZN-LLDPE with HDPE were investigated with rheological methods. The m-LLDPEs (BC ) 13.2 CH3/1000 C) and ZN-LLDPE (BC ) 14.5 CH3/1000 C) of similar molecular weights were paired to study one molecular variable at a time. Melt blending was carried out in a Haake PolyDrive at 190 °C in the presence of 1000 ppm of antioxidants. Dynamic and steady shear measurements were performed in a Rheometrics ARES at 190 °C. The miscibilities of blends were revealed by the dependence of their o, ', N1 and Gon blend composition and from predictions of rheological models. The CD was found to have no effect on the miscibility of low-BC ZN-LLDPE and m-LLDPE blends with linear HDPE, and both blends were miscible at all compositions. Increasing the branch content (BC ) 42.0 CH3/1000 C) resulted in an increased immiscibility of m-LLDPE-rich blends with linear HDPE. The rheology of immiscible blends suggests a layered morphology and agreement with Bousmina-Palierne-Utracki's and Lin's models was obtained with slip parameters k ) 2.85 10 -5 and I ) 0.72, respectively.

Microstructure and phase selection in supercooled copper alloys exhibiting metastable liquid miscibility gaps

Abstract: The influence of both bulk supercooling and cooling rate on the microstructure and phase selection during solidification of Cu–Co, Cu–Co–Fe, and Cu–Nb alloys exhibiting metastable liquid miscibility gaps were investigated using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Containerless electromagnetic levitation was used to achieve large bulk supercoolings in the specimens. Supercooling of these alloys below a certain temperature resulted in metastable separation of the melt into two liquids, a Cu-lean (Co, Co + Fe, or Nb enriched) melt (L1) and a Cu-rich melt (L2). Usually, the microstructure of the phase-separated alloys consisted of spherulites corresponding to one of the phase-separated liquids embedded in a matrix corresponding to the other. The microstructure and phase selection are found to depend on factors such as: alloy composition, supercooling level, whether the material was dropped before or after recalescence, and the cooling rate during solidification. The following results were observed: (1) solidification of metastable e-Cu with enhanced Co (or Co + Fe, or Nb) solubility; (2) partitionless solidification of the L1 and L2 liquids; (3) spinodal decomposition of the supercooled liquid, and (4) secondary melt separation. The results are discussed and related to current solidification theories regarding solidification paths for the different conditions examined. The miscibility gap boundaries for the different alloys were determined and compared with those reported in the literature.