Crystallization and Melting of Oriented Parent - Daughter Lamellae in Sheared Isotactic Poly(propylene)

2010 ◽  
Vol 63 (8) ◽  
pp. 1179 ◽  
Author(s):  
Andrew Phillips ◽  
Peng-wei Zhu ◽  
Chitiur Hadinata ◽  
Graham Edward
Keyword(s):  
Flow Direction ◽  
Growth Direction ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Individual Contributions ◽  
Multiple Melting ◽  
The Individual ◽  
Poly Propylene ◽  
Induced Crystallization

Alpha isotactic poly(propylene) (α-iPP) exhibits a form of lamellar branching that is unique among semicrystalline polymers, where the branches have a distinct orientation relationship with the original crystalline lamellae. This is termed a parent–daughter relationship (PD). By allowing the structure to crystallize in an oriented form, a bimodal orientation of lamellae is developed and the individual contributions of PD lamellae can be observed using wide-angle X-ray scattering (WAXS). The present study investigated oriented PD lamellae during flow-induced crystallization and subsequent melting using time resolved rheo-WAXS. During crystallization the planes of the daughter lamellae were observed to curve towards the flow direction as they grew from their parent lamellae. This was explained by the influence of neighbouring daughter lamellae confining their growth direction. Oriented daughter lamellae were found to melt ~5°C lower than oriented parent lamellae, which provides a new explanation for the multiple melting behaviour observed in the melting thermograms of sheared α-iPP.

Following the structural changes during zinc-induced crystallization of charged membranes using time-resolved solution X-ray scattering

Soft Matter ◽  
2011 ◽  
Vol 7 (4) ◽  
pp. 1512-1523 ◽  
Author(s):  
Moshe Nadler ◽  
Ariel Steiner ◽  
Tom Dvir ◽  
Or Szekely ◽  
Pablo Szekely ◽  
...  
Keyword(s):  
Structural Changes ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Charged Membranes ◽  
Induced Crystallization ◽  
Ray Scattering

The Effect of Composition and Processing Conditions on the Structure Development in Injection Molded Dynamically Vulcanized PP/EPDM Blends

2000 ◽  
Vol 73 (4) ◽  
pp. 753-778 ◽  
Author(s):  
M. Cakmak ◽  
S. W. Cronin
Keyword(s):  
Flow Direction ◽  
Thin Layers ◽  
Processing Conditions ◽  
Axis Orientation ◽  
X Ray ◽  
X Ray Scattering ◽  
Rubber Particles ◽  
Injection Molded ◽  
Poly Propylene ◽  
Microscopy Techniques

Abstract The effect of composition and processing conditions on the spatial structural variation in dynamically vulcanized injection molded poly(propylene)/ethylene—propylene—diene rubber (PP/EPDM) was investigated using matrixing microbeam X-ray system and transmission optical microscopy techniques. The structure gradient in the thickness direction in these samples is composed of very thick, highly oriented, skin regions followed by core regions of lower preferential chain orientation. In these samples, the shear-crystallized layers are observed to be much thicker than the comparably processed pure PP. The nucleation densities in the PP phase were too high to allow for observation of individual crystallites in most of the regions except near the very core, where sparsely distributed PP crystallites, that appear bright under cross polars, were observed. The wide-angle X-ray scattering (WAXS) patterns taken at different distances from the skin indicate that chain axes are mostly oriented in the flow direction, and distinct bimodal c-axis and a* axis oriented dual population of orientation is observed in the PP phase. c-axis orientation factors, fc, start at intermediate values at the skin and increase steadily and after showing a maximum roughly in the middle of the shear crystallized region, decrease towards the core, and in most cases never achieve a state of isotropy. In the blends that contain very small polypropylene fractions (ca ∼ 15%), unusually high orientation levels were observed. This was attributed to the “shear amplification” phenomena that dominates the thin PP regions between the rubber particles and causes significant orientation levels in the thin layers of PP coating, the rubber particles with the relative motion of the particles in the shear flow field.

Microtubule nucleation sequence studied by time-resolved x-ray scattering and electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 766-767
Author(s):  
Eva-Maria Mandelkow ◽  
Eckhard Mandelkow ◽  
Joan Bordas
Keyword(s):  
Electron Microscopy ◽  
Dynamic Equilibrium ◽  
Time Resolved ◽  
X Ray ◽  
Additional Information ◽  
X Ray Scattering ◽  
Low Concentrations ◽  
Microtubule Growth ◽  
Ray Patterns ◽  
Ray Scattering

When a solution of microtubule protein is changed from non-polymerising to polymerising conditions (e.g. by temperature jump or mixing with GTP) there is a series of structural transitions preceding microtubule growth. These have been detected by time-resolved X-ray scattering using synchrotron radiation, and they may be classified into pre-nucleation and nucleation events. X-ray patterns are good indicators for the average behavior of the particles in solution, but they are difficult to interpret unless additional information on their structure is available. We therefore studied the assembly process by electron microscopy under conditions approaching those of the X-ray experiment. There are two difficulties in the EM approach: One is that the particles important for assembly are usually small and not very regular and therefore tend to be overlooked. Secondly EM specimens require low concentrations which favor disassembly of the particles one wants to observe since there is a dynamic equilibrium between polymers and subunits.

Time-Resolved Cryo-Electron Microscopy of Oscillating Microtubules

1990 ◽  
Vol 48 (1) ◽  
pp. 502-503
Author(s):  
Eva-Maria Mandelkow ◽  
Ron Milligan
Keyword(s):  
Electron Microscopy ◽  
Dynamic Instability ◽  
Entire Solution ◽  
Reaction Scheme ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
A Chain ◽  
Ray Scattering

Microtubules form part of the cytoskeleton of eukaryotic cells. They are hollow libers of about 25 nm diameter made up of 13 protofilaments, each of which consists of a chain of heterodimers of α-and β-tubulin. Microtubules can be assembled in vitro at 37°C in the presence of GTP which is hydrolyzed during the reaction, and they are disassembled at 4°C. In contrast to most other polymers microtubules show the behavior of “dynamic instability”, i.e. they can switch between phases of growth and phases of shrinkage, even at an overall steady state [1]. In certain conditions an entire solution can be synchronized, leading to autonomous oscillations in the degree of assembly which can be observed by X-ray scattering (Fig. 1), light scattering, or electron microscopy [2-5]. In addition such solutions are capable of generating spontaneous spatial patterns [6].In an earlier study we have analyzed the structure of microtubules and their cold-induced disassembly by cryo-EM [7]. One result was that disassembly takes place by loss of protofilament fragments (tubulin oligomers) which fray apart at the microtubule ends. We also looked at microtubule oscillations by time-resolved X-ray scattering and proposed a reaction scheme [4] which involves a cyclic interconversion of tubulin, microtubules, and oligomers (Fig. 2). The present study was undertaken to answer two questions: (a) What is the nature of the oscillations as seen by time-resolved cryo-EM? (b) Do microtubules disassemble by fraying protofilament fragments during oscillations at 37°C?

In situ Time-Resolved Small-Angle X-ray Scattering Reveals the Formation Kinetics of Polyelectrolyte Complex Micelles

2019 ◽  
Author(s):  
Hao Wu ◽  
Jeffrey Ting ◽  
Siqi Meng ◽  
Matthew Tirrell
Keyword(s):  
Small Angle ◽  
Self Assembly ◽  
Electrostatic Interactions ◽  
Polyelectrolyte Complex ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Kinetics Of ◽  
Ray Scattering

We have directly observed the <i>in situ</i> self-assembly kinetics of polyelectrolyte complex (PEC) micelles by synchrotron time-resolved small-angle X-ray scattering, equipped with a stopped-flow device that provides millisecond temporal resolution. This work has elucidated one general kinetic pathway for the process of PEC micelle formation, which provides useful physical insights for increasing our fundamental understanding of complexation and self-assembly dynamics driven by electrostatic interactions that occur on ultrafast timescales.

scholarly journals Osmotic shrinkage of sterically stabilized liposomes as revealed by time-resolved small-angle X-ray scattering

2014 ◽  
Vol 47 (1) ◽  
pp. 35-40 ◽  
Author(s):  
Zoltán Varga ◽  
András Wacha ◽  
Attila Bóta
Keyword(s):  
Form Factor ◽  
Small Angle ◽  
Freeze Fracture ◽  
Initial Step ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Sterically Stabilized Liposomes ◽  
Liposome Size ◽  
Ray Scattering

Time-resolved synchrotron small-angle X-ray scattering (SAXS) was used to study the structural changes during the osmotic shrinkage of a pharmacologically relevant liposomal drug delivery system. Sterically stabilized liposomes (SSLs) with a diameter of 100 nm and composed of hydrogenated soy phosphocholine, cholesterol and distearoyl-phosphoethanolamine-PEG 2000 prepared in a salt-free buffer were mixed with a buffered 0.3 MNaCl solution using a stopped flow apparatus. The changes in the liposome size and the bilayer structure were followed by using SAXS with a time resolution of 20 ms. A linear decrease in liposome size is observed during the first ∼4 s of the osmotic shrinkage, which reveals a water permeability value of 0.215 (15) µm s−1. The change in the size of the liposomes upon the osmotic shrinkage is also confirmed by dynamic light scattering. After this initial step, broad correlation peaks appear on the SAXS curves in theqrange of the bilayer form factor, which indicates the formation of bi- or oligolamellar structures. Freeze-fracture combined with transmission electron microscopy revealed that lens-shaped liposomes are formed during the shrinkage, which account for the appearance of the quasi-Bragg peaks superimposed on the bilayer form factor. On the basis of these observations, it is proposed that the osmotic shrinkage of SSLs is a two-step process: in the initial step, the liposome shrinks in size, while the area/lipid adapts to the decreased surface area, which is then followed by the deformation of the spherical liposomes into lens-shaped vesicles.

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