Search results for "Lamellar structure"

A quantitative electron-microscopic study of a linear polyethylene fraction crystallized at different temperatures

1981

Replica and thin-section electron microscopy was performed on a linear polyethylene fraction (Mw = 1.89 × 105, Mn = 1.79 × 10 5) which was either isothermally crystallized or quenched at difference temperatures. The results are numerically analyzed in such a manner so as to give the distribution of the total long spacing and of the crystallite and amorphous thicknesses. The quantitative information about the maximum and minimum values for these parameters at each crystallization temperature yields important clues as to possible molecular processes involved. Qualitative information regarding general morphology, molecular tilt with respect to the lamellar surface, and possible crystallographi…

A quantitative electron microscopic study of the crystallite structure of molecular weight fractions of linear polyethylene

1984

Utilizing thin-section techniques, transmission electron microscope studies were performed on a series of bulk-crystalized fractions of linear polyethylene covering the range M = 5 × 103−6 × 106. The crystallization conditions were varied from long-time isothermal to rapid quenching. Quantitative analysis could be carried out on such samples crystallized under controlled conditions. The crystallite thickness distributions and long periods are presented in terms of histograms. From these data the degree of crystallinity can be calculated and was found to compare favorably with that from other methods. The amorphous thickness increases significantly with molecular weight for all modes of crys…

Synthesis and characterization of nanomaterial based on halloysite and hectorite clay minerals covalently bridged

2021

Halloysite is an aluminosilicate clay with a predominantly hollow tubular structure (HNTs) able to act as a nanocontainer for the encapsulation of several chemicals. However, HNTs possess low affinity for metal ions in their pristine form and they need to be modified for improving their adsorption capabilities. Therefore, to overcome this issue herein we report a straightforward approach for the covalent modification of the external surface of halloysite nanotubes with hectorite clay. Compared to halloysite, hectorite possesses a lamellar structure with higher cation exchange capacity. The covalent linkage between the two clays was verified by several techniques (FTIR spectroscopy, 13C CP-M…

TEM studies on La2−2xCa1+2xMn2O7 (x=0.5 and 0.25)

2003

The nominal compositions and structures of the compounds La2-2xCa1+2xMn2O7 (x=0.5 and 0.25) prepared by solid-state reaction have been studied by transmission electron microscopy and high-resolution electron microscopy. Besides the observation of the major phase of a two-layer structure in the nominal composition La1.0Ca2.0Mn2O7, the embedded n = 3, n = 4 Ruddlesden-Popper phases and La rich phase in the two-layer structure were observed as defects. No layered structure was observed in the nominal composition La1.5Ca1.5Mn2O7. Instead, a major phase of orthorhombically distorted perovskite, a minor phase of an ideal cubic perovskite, and a small fraction of calcium-oxide were observed in the…

One-Step Anionic Copolymerization Enables Formation of Linear Ultrahigh-Molecular-Weight Block Copolymer Films Featuring Vivid Structural Colors in t…

2018

Ultrahigh-molecular-weight (UHMW) tapered block copolymers (BCPs) consisting of polyisoprene-block-poly(4-methylstyrene) featuring overall molar masses in the range of 1101–2033 kg mol–1 (Mw) are synthesized via a convenient one-step anionic copolymerization protocol. The obtained UHMW BCPs are investigated by differential scanning calorimetry, size exclusion chromatography, and 1H NMR spectroscopy. Microphase separation for the UHMW BCPs in the bulk state is investigated by transmission electron microscopy (TEM) measurements and scanning electron microscopy (SEM), revealing well-ordered lamellar and spherical domains with large domain sizes in the range of 100–200 nm. Excellent order and p…

“Ball at the wall” — A new lamellar multiphase morphology in a polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock copolymer

1994

Structural Characterization of the “Knitting Pattern” in Polystyrene-block-poly(ethylene-co-butylene)-block-poly(methyl methacrylate) Triblock Copoly…

1998

In a polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock copolymer (SBM) a morphological transition from a lamellar (ll) morphology (with sequence ABCB) to the knitting pattern (kp) morphology occurs upon hydrogenation of the center PB block. Structural information of the nonhydrogenated and the hydrogenated material is provided from small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). For the nonhydrogenated SBM sample the SAXS profile correlates well with a simple periodic lamellar structure. The hydrogenated sample forming the kp morphology displays a more complex SAXS pattern. From the TEM images of the knitting pattern the two-dimensional…

Rational design of ABC triblock terpolymer solution nanostructures with controlled patch morphology

2016

Block copolymers self-assemble into a variety of nanostructures that are relevant for science and technology. While the assembly of diblock copolymers is largely understood, predicting the solution assembly of triblock terpolymers remains challenging due to complex interplay of block/block and block/solvent interactions. Here we provide guidelines for the self-assembly of linear ABC triblock terpolymers into a large variety of multicompartment nanostructures with C corona and A/B cores. The ratio of block lengths NC/NA thereby controls micelle geometry to spheres, cylinders, bilayer sheets and vesicles. The insoluble blocks then microphase separate to core A and surface patch B, where NB co…

Development and In Vitro Evaluation of Lyotropic Liquid Crystals for the Controlled Release of Dexamethasone.

2017

Made available in DSpace on 2018-12-11T17:33:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-08-02 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) In this study, amphiphilic polymers were investigated as biomaterials that can control dexamethasone (DXM) release. Such materials present interfacial properties in the presence of water and an oily phase that can result in lyotropic liquid crystalline systems (LLCS). In addition, they can form colloidal nanostructures similar to those in living organisms, such as bilayers and hexagonal and cubic phases, which can be exploited to solubilize lipophilic drugs to sustain their release and enhance bioavailability. It was…

The effect of THF and the chelating modifier DTHFP on the copolymerisation of β-myrcene and styrene: kinetics, microstructures, morphologies, and mec…

2022

The statistical anionic copolymerisation of the biobased monomer β-myrcene with styrene in cyclohexane was investigated via in situ near-infrared (NIR) spectroscopy, focusing on the influence of the modifiers (i.e., Lewis bases) tetrahydrofuran (THF) and 2,2-di(2-tetrahydrofuryl)propane (DTHFP) on the reactivity ratios. With increasing [modifier]/[Li] ratio, the reactivity ratios in the system myrcene/styrene are adjustable from rS ≪ rMyrvia rS ≈ rMyr to rS ≫ rMyr. The bidentate modifier DTHFP affects the reactivity ratios much more than THF: minute amounts only (0.35 equivalent relative to Li) are required to randomize the copolymer, and one equivalent to invert the reactivity ratios. Usin…