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The morphology of blends of linear and branched polyethylenes in solid state by SANS

Description: In a previous paper, the authors have shown how small-angle neutron and X-ray scattering (SANS, SAXS) can be used to determine the melt compatibility of different polyolefins, including high-density (HD), low-density (LD), and linear low density (LLD) polyethylene. Such blends have attained widespread commercial applications, though the understanding of the mechanical and melt-flow properties of such blends has hitherto been handicapped by the absence of a consensus concerning the degree of mixing of the components, both in the melt and solid states. Recent SANS data indicate that for HDPE/LDPE blends, the melt is homogeneous for all compositions after proper accounting for H/D isotope effects. In this publication the authors use complementary SANS, DSC, and SAXS to examine the types of morphologies and the different degrees of phase separation which may arise via crystallization effects on cooling from a homogeneous melt.
Date: March 1, 1995
Creator: Wignall, G.D.; Londono, J.D.; Alamo, R.G. & Mandelkern, L.
Partner: UNT Libraries Government Documents Department

The morphology of blends of linear and branched polyethylenes in solid state by SANS

Description: In a previous paper the authors have shown how small-angle neutron and X-ray scattering (SANS, SAXS) can be used to determine the melt compatibility of different polyolefins, including high-density (HD), low-density (LD), and linear low density (LLD) polyethylene. Such blends have attained widespread commercial applications, though the understanding of the mechanical and melt-flow properties of such blends has hitherto been handicapped by the absence of a consensus concerning the degree of mixing of the components, both in the melt and solid states. Recent SANS data indicate that for HDPE/LDPE blends, the melt is homogeneous for all compositions after proper accounting for H/D isotope effects. In this publication the authors use complementary SANS, DSC, and SAXS to examine the types of morphologies and the different degrees of phase separation which may arise via crystallization effects on cooling from a homogeneous melt.
Date: December 31, 1994
Creator: Wignall, G.D.; Londono, J.D.; Alamo, R.G.; Mandelkern, L. & Stehling, F.C.
Partner: UNT Libraries Government Documents Department

Phase Behavior of Blends of Linear and Branched Polyethylenes on Micron-Length Scales via Ultra-Small-Angle Neutron Scattering (USANS)

Description: SANS experiments on blends of linear, high density (HD) and long chain branched, low density (LD) polyethylenes indicate that these systems form a one-phase mixture in the melt. However, the maximum spatial resolution of pinhole cameras is approximately equal to 10<sup>3</sup>Å and it has therefore been suggested that data might also be interpreted as arising from a bi-phasic melt with large a particle size (~ 1 µm), because most of the scattering from the different phases would not be resolved. We have addressed this hypothesis by means of USANS experiments, which confirm that HDPEILDPE blends are homogenous in the melt on length scales up to 20 µm. We have also studied blends of HDPE and short-chain branched linear low density polyethylenes (LLDPEs), which phase separate when the branch content is sufficiently high. LLDPEs prepared with Ziegler-Natta catalysts exhibit a wide distribution of compositions, and may therefore be thought of as a �blend� of different species. When the composition distribution is broad enough, a fraction of highly branched chains may phase separate on µm-length scales, and USANS has also been used to quantify this phenomenon.
Date: May 17, 1999
Creator: Agamalian, M.M.; Alamo, R.G.; Londono, J.D.; Mandelkern, L. & Wignall, G.D.
Partner: UNT Libraries Government Documents Department

SAXS and SANS studies of surfactants and reverse micelles in supercritical CO{sub 2}

Description: Surfactants promise to extend the applicability of supercritical CO{sub 2} (SC-CO{sub 2}) to processing of insoluble materials such as polymers and aqueous systems. In this short paper the authors summarize the techniques for studying surfactants and reverse micelles in SC-CO{sub 2} using SAXS and SANS; they will describe the scattering instruments and the pressure cells for conducting these studies; they will describe the types of measurement that yield the desired characterizations; they will describe the methods of data analysis and interpretation; and they will provide illustrative results from this laboratory. Industry seeks to replace common organic solvents now used in many reaction and separation processes; SC-CO{sub 2} is a potential solvent substitute widely favored by both government and industry. The currently available surfactants are limited in number and performance. In ongoing work the authors are coupling their SAXS and SANS scattering studies with complementary molecular simulations in efforts to understand, at a molecular level, what surfactant characteristics lead to improved performance. They hope that superior surfactants for use in SC-CO{sub 2} can be designed and synthesized based on this new level of understanding.
Date: March 1, 1997
Creator: Londono, J.D.; Dharmapurikar, R.S.; Wignall, G.D. & Cochran, H.D.
Partner: UNT Libraries Government Documents Department