scholarly journals Relaxation Dynamics and Underlying Mechanism of a Thermally Reversible Gel from Symmetric Triblock Copolymer

2019 ◽  
Vol 52 (22) ◽  
pp. 8651-8661 ◽  
Author(s):  
Ya Nan Ye ◽  
Kunpeng Cui ◽  
Tsutomu Indei ◽  
Tasuku Nakajima ◽  
Dominique Hourdet ◽  
...  
Keyword(s):  
Triblock Copolymer ◽  
Underlying Mechanism ◽  
Relaxation Dynamics ◽  
Reversible Gel

scholarly journals The ultrafast onset of exciton formation in 2D semiconductors

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Chiara Trovatello ◽  
Florian Katsch ◽  
Nicholas J. Borys ◽  
Malte Selig ◽  
Kaiyuan Yao ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Transition Metal Dichalcogenides ◽  
Single Layer ◽  
Underlying Mechanism ◽  
Relaxation Dynamics ◽  
Electron Hole ◽  
Layer Transition ◽  
Coulombic Interactions ◽  
Formation Dynamics ◽  
Metal Dichalcogenides

Abstract The equilibrium and non-equilibrium optical properties of single-layer transition metal dichalcogenides (TMDs) are determined by strongly bound excitons. Exciton relaxation dynamics in TMDs have been extensively studied by time-domain optical spectroscopies. However, the formation dynamics of excitons following non-resonant photoexcitation of free electron-hole pairs have been challenging to directly probe because of their inherently fast timescales. Here, we use extremely short optical pulses to non-resonantly excite an electron-hole plasma and show the formation of two-dimensional excitons in single-layer MoS2 on the timescale of 30 fs via the induced changes to photo-absorption. These formation dynamics are significantly faster than in conventional 2D quantum wells and are attributed to the intense Coulombic interactions present in 2D TMDs. A theoretical model of a coherent polarization that dephases and relaxes to an incoherent exciton population reproduces the experimental dynamics on the sub-100-fs timescale and sheds light into the underlying mechanism of how the lowest-energy excitons, which are the most important for optoelectronic applications, form from higher-energy excitations. Importantly, a phonon-mediated exciton cascade from higher energy states to the ground excitonic state is found to be the rate-limiting process. These results set an ultimate timescale of the exciton formation in TMDs and elucidate the exceptionally fast physical mechanism behind this process.

scholarly journals Relaxation dynamics in bio-colloidal cholesteric liquid crystals confined to cylindrical geometry

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Sayyed Ahmad Khadem ◽  
Massimo Bagnani ◽  
Raffaele Mezzenga ◽  
Alejandro D. Rey
Keyword(s):  
Electric Fields ◽  
Cellulose Nanocrystals ◽  
Amyloid Fibrils ◽  
Underlying Mechanism ◽  
Stimuli Responsive ◽  
Relaxation Dynamics ◽  
Cholesteric Phase ◽  
Nematic Phases ◽  
Experimental Findings ◽  
Β Lactoglobulin

Abstract Para-nematic phases, induced by unwinding chiral helices, spontaneously relax to a chiral ground state through phase ordering dynamics that are of great interest and crucial for applications such as stimuli-responsive and biomimetic engineering. In this work, we characterize the cholesteric phase relaxation behaviors of β-lactoglobulin amyloid fibrils and cellulose nanocrystals confined into cylindrical capillaries, uncovering two different equilibration pathways. The integration of experimental measurements and theoretical predictions reveals the starkly distinct underlying mechanism behind the relaxation dynamics of β-lactoglobulin amyloid fibrils, characterized by slow equilibration achieved through consecutive sigmoidal-like steps, and of cellulose nanocrystals, characterized by fast equilibration obtained through smooth relaxation dynamics. Particularly, the specific relaxation behaviors are shown to emerge from the order parameter of the unwound cholesteric medium, which depends on chirality and elasticity. The experimental findings are supported by direct numerical simulations, allowing to establish hard-to-measure viscoelastic properties without applying magnetic or electric fields.

Morphological transformations in solution-cast Styrene-Butadiene-Styrene (SBS) triblock copolymer thin films

1995 ◽  
Vol 53 ◽  
pp. 184-185
Author(s):  
Ginam Kim ◽  
W. Marsillo ◽  
M. Libera
Keyword(s):  
Thin Films ◽  
Triblock Copolymer ◽  
Annealing Treatment ◽  
Minor Component ◽  
Solvent Evaporation ◽  
Single Crystal Substrate ◽  
Transparent Films ◽  
Crystal Substrate ◽  
Solution Cast ◽  
Morphological Transformations

The fact that block copolymers can assume a range of morphologies depending upon such variables as relative block length and molecular weight is now well known. In the case of poly(styrene)[PS]-poly(butadiene)[PB]-poly(styrene) (SBS) triblock copolymer, the morphologies range from spheres (roughly ~20% minor component), to cylinders (roughly 20%~35% minor component), to lamellae (roughly equal component fractions) Most recently, there has been increasing interest in transformations between morphologies by thermal annealing. This paper describes initial results studying the effect of solvent evaporation rate and post-casting annealing treatment on the morphology of SBS thin films.TEM specimens were prepared by solution casting electron transparent films. 50 μl of 0.1 wt% SBS (30% styrene, Mw=14,000, Scientific Polymer Products, Inc.) dissolved in toluene was deposited on a polished NaCl single crystal substrate placed in a small dish. After solvent evaporation the film was cut into small squares, floated from the salt in water, and each square was collected on a Cu grid.

Face Inversion Effect Emerges Under Critical Configural Discrepancy

2010 ◽  
Vol 69 (3) ◽  
pp. 161-167 ◽  
Author(s):  
Jisien Yang ◽  
Adrian Schwaninger
Keyword(s):  
Face Recognition ◽  
Face Processing ◽  
Underlying Mechanism ◽  
Inversion Effect ◽  
Configural Processing ◽  
Major Contributor ◽  
Face Inversion Effect ◽  
Configural Information ◽  
Face Inversion ◽  
The Face

Configural processing has been considered the major contributor to the face inversion effect (FIE) in face recognition. However, most researchers have only obtained the FIE with one specific ratio of configural alteration. It remains unclear whether the ratio of configural alteration itself can mediate the occurrence of the FIE. We aimed to clarify this issue by manipulating the configural information parametrically using six different ratios, ranging from 4% to 24%. Participants were asked to judge whether a pair of faces were entirely identical or different. The paired faces that were to be compared were presented either simultaneously (Experiment 1) or sequentially (Experiment 2). Both experiments revealed that the FIE was observed only when the ratio of configural alteration was in the intermediate range. These results indicate that even though the FIE has been frequently adopted as an index to examine the underlying mechanism of face processing, the emergence of the FIE is not robust with any configural alteration but dependent on the ratio of configural alteration.

Relaxation dynamics in confined glasses

2000 ◽  
Vol 10 (PR7) ◽  
pp. Pr7-227-Pr7-232 ◽  
Author(s):  
B. Jérôme ◽  
E. Cecchetto ◽  
N. R. de Souza ◽  
A. L. Demirel
Keyword(s):  
Relaxation Dynamics

Contrasting underlying mechanisms of different barrier coating types

TAPPI Journal ◽  
2018 ◽  
Vol 17 (01) ◽  
pp. 31-37
Author(s):  
Bryan McCulloch ◽  
John Roper ◽  
Kaitlin Rosen
Keyword(s):  
Food Packaging ◽  
Underlying Mechanism ◽  
Consumer Products ◽  
Mechanical Degradation ◽  
Design Rules ◽  
Barrier Coatings ◽  
Barrier Materials ◽  
Barrier Coating ◽  
Coating Type ◽  
Underlying Mechanisms

Barrier coatings are used in applications including food packaging, dry goods, and consumer products to prevent transport of different compounds either through or into paper and paperboard substrates. These coatings are useful in packaging to contain active ingredients, such as fragrances, or to protect contents from detrimental substances, such as oxygen, water, grease, or other chemicals of concern. They also are used to prevent visual changes or mechanical degradation that might occur if the paper becomes saturated. The performance and underlying mechanism depends on the barrier coating type and, in particular, on whether the barrier coating is designed to prevent diffusive or capillary transport. Estimates on the basis of fundamental transport phenomena and data from a broad screening of different barrier materials can be used to understand the limits of various approaches to construct barrier coatings. These estimates also can be used to create basic design rules for general classes of barrier coatings.

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