Dynamic Rigidity Percolation in AOT Micelles and Microemulsions

1989 ◽  
Vol 177 ◽  
Author(s):  
L. Ye ◽  
D. A. Weitz ◽  
Ping Sheng ◽  
J. S. Huang
Keyword(s):  
Frequency Dependence ◽  
Volume Fraction ◽  
Brillouin Scattering ◽  
Viscoelastic Behavior ◽  
Water Concentration ◽  
Hydrocarbon Chain ◽  
Acoustic Properties ◽  
Pronounced Increase ◽  
Hydrocarbon Chain Length ◽  
Consistent Picture

ABSTRACTWe study the acoustic properties of AOT micelles and microemulsions by measuring the velocity of sound as a function of droplet volume fraction and of frequency, using Brillouin scattering and ultrasonic techniques. These weakly attractive interparticle interactions lead to the formation of short–lived networks of droplets, which can support shear and result in a pronounced increase in the speed of sound at high frequencies. These networks do not persist for sufficiently long times to affect the sound velocity at lower frequencies. The increased rigidity due to the networks exhibits a percolation behavior with volume fraction, while the frequency dependence of the interactions depends on hydrocarbon chain length of the solvent. Increasing the water concentration results in an increase in interaction energy, but a decrease in the intrinsic droplet rigidity, which affects the magnitude and frequency dependence of the contribution of the microemulsion networks to the elastic constant of the suspension. A consistent picture of the viscoelastic behavior of these suspensions is obtained.

scholarly journals Structure and Interdigitation of Chain-Asymmetric Phosphatidylcholines and Milk Sphingomyelin in the Fluid Phase

Symmetry ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1441
Author(s):  
Moritz P. K. Frewein ◽  
Milka Doktorova ◽  
Frederick A. Heberle ◽  
Haden L. Scott ◽  
Enrico F. Semeraro ◽  
...  
Keyword(s):  
Chain Length ◽  
Hydration Shell ◽  
Fluid Phase ◽  
Hydrocarbon Chain ◽  
Specific Model ◽  
Glycerol Backbone ◽  
Membrane Composition ◽  
Membrane Structures ◽  
Hydrocarbon Chain Length ◽  
Dynamics Simulations

We addressed the frequent occurrence of mixed-chain lipids in biological membranes and their impact on membrane structure by studying several chain-asymmetric phosphatidylcholines and the highly asymmetric milk sphingomyelin. Specifically, we report trans-membrane structures of the corresponding fluid lamellar phases using small-angle X-ray and neutron scattering, which were jointly analyzed in terms of a membrane composition-specific model, including a headgroup hydration shell. Focusing on terminal methyl groups at the bilayer center, we found a linear relation between hydrocarbon chain length mismatch and the methyl-overlap for phosphatidylcholines, and a non-negligible impact of the glycerol backbone-tilting, letting the sn1-chain penetrate deeper into the opposing leaflet by half a CH2 group. That is, penetration-depth differences due to the ester-linked hydrocarbons at the glycerol backbone, previously reported for gel phase structures, also extend to the more relevant physiological fluid phase, but are significantly reduced. Moreover, milk sphingomyelin was found to follow the same linear relationship suggesting a similar tilt of the sphingosine backbone. Complementarily performed molecular dynamics simulations revealed that there is always a part of the lipid tails bending back, even if there is a high interdigitation with the opposing chains. The extent of this back-bending was similar to that in chain symmetric bilayers. For both cases of adaptation to chain length mismatch, chain-asymmetry has a large impact on hydrocarbon chain ordering, inducing disorder in the longer of the two hydrocarbons.

scholarly journals Factors Affecting Acoustic Properties of Natural-Fiber-Based Materials and Composites: A Review

Textiles ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 55-85
Author(s):  
Tufail Hassan ◽  
Hafsa Jamshaid ◽  
Rajesh Mishra ◽  
Muhammad Qamar Khan ◽  
Michal Petru ◽  
...  
Keyword(s):  
Sound Absorption ◽  
Natural Fiber ◽  
Volume Fraction ◽  
Fiber Type ◽  
Alkali Treatment ◽  
Acoustic Properties ◽  
Synthetic Fiber ◽  
Sound Insulation ◽  
Factors Affecting ◽  
Wide Range

Recently, very rapid growth has been observed in the innovations and use of natural-fiber-based materials and composites for acoustic applications due to their environmentally friendly nature, low cost, and good acoustic absorption capability. However, there are still challenges for researchers to improve the mechanical and acoustic properties of natural fiber composites. In contrast, synthetic fiber-based composites have good mechanical properties and can be used in a wide range of structural and automotive applications. This review aims to provide a short overview of the different factors that affect the acoustic properties of natural-fiber-based materials and composites. The various factors that influence acoustic performance are fiber type, fineness, length, orientation, density, volume fraction in the composite, thickness, level of compression, and design. The details of various factors affecting the acoustic behavior of the fiber-based composites are described. Natural-fiber-based composites exhibit relatively good sound absorption capability due to their porous structure. Surface modification by alkali treatment can enhance the sound absorption performance. These materials can be used in buildings and interiors for efficient sound insulation.

scholarly journals Effect of Hydrocarbon Chain Length of Amphiphilic Ruthenium Dyes on Solid-State Dye-Sensitized Photovoltaics

Nano Letters ◽  
2005 ◽  
Vol 5 (7) ◽  
pp. 1315-1320 ◽  
Author(s):  
Lukas Schmidt-Mende ◽  
Jessica E. Kroeze ◽  
James R. Durrant ◽  
Md. K. Nazeeruddin ◽  
Michael Grätzel
Keyword(s):  
Solid State ◽  
Chain Length ◽  
Hydrocarbon Chain ◽  
Dye Sensitized ◽  
Hydrocarbon Chain Length ◽  
Ruthenium Dyes

Formation mechanism of self-assembled unilamellar vesiclesSpecial issue on Neutron Scattering in Canada

2010 ◽  
Vol 88 (10) ◽  
pp. 735-740 ◽  
Author(s):  
Mu-Ping Nieh ◽  
Norbert Kučerka ◽  
John Katsaras
Keyword(s):  
Neutron Scattering ◽  
Hydrocarbon Chain ◽  
Lipid Concentration ◽  
Uniform Size ◽  
Lipid Mixtures ◽  
Hydrocarbon Chain Length ◽  
Membrane Rigidity ◽  
Self Assembled ◽  
Best Fit ◽  
Sans Data

Uniform size self-assembled unilamellar vesicles (ULVs) can be produced from mixtures of weakly charged short- and long-chain phospholipids. These lipid mixtures self-assemble into bilayered micelles (so-called bicelles), and a bicelle to ULV transition has been previously reported. Here, we discuss the effect of various parameters (i.e., lipid concentration, charge density, membrane rigidity, lipid composition, and lipid hydrocarbon chain length) on ULV radius as determined by small angle neutron scattering (SANS). SANS data were best fit using a core-shell disk and a spherical-shell model to obtain the size of bicelles and ULVs, respectively. From the present experiments we conclude that a previously proposed mechanism of ULV formation, where bicelles coalesce into large precursor and self-fold into ULVs, is able to explain the present SANS data.

Viscoelastic behavior of epoxy resin reinforced with shape-memory-alloy wires

2020 ◽  
pp. 1045389X2097549
Author(s):  
Niloufar Bagheri ◽  
Mahmood M Shokrieh ◽  
Ali Saeedi
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Epoxy Resin ◽  
Volume Fraction ◽  
Niti Alloy ◽  
Micromechanical Model ◽  
Viscoelastic Behavior ◽  
Mechanical Analysis ◽  
Reinforced Polymer ◽  
Small Volume Fraction

The effect of NiTi alloy long wires on the viscoelastic behavior of epoxy resin was investigated by utilizing the dynamic mechanical analysis (DMA) and a novel micromechanical model. The present model is capable of predicting the viscoelastic properties of the shape-memory-alloy (SMA) reinforced polymer as a function of the SMA volume fraction, initial martensite volume fraction, pre-strain level in wires, and the temperature variations. The model was verified by conducting experiments. Good agreement between the theoretical and experimental results was achieved. A parametric study was also performed to investigate the effect of SMA parameters. According to the results, by the addition of a small volume fraction of SMA, the storage modulus of the composite increases significantly, especially at higher temperatures. Moreover, applying a 4% pre-strain caused a 10% increase in the maximum value of the loss factor of the SMA reinforced epoxy in comparison with the 0% pre-strained SMA reinforced epoxy.

scholarly journals Crystal Memory near Discontinuous Triacylglycerol Phase Transitions: Models, Metastable Regimes, and Critical Points

Molecules ◽  
2020 ◽  
Vol 25 (23) ◽  
pp. 5631
Author(s):  
David A. Pink ◽  
Marjorie Ladd-Parada ◽  
Alejandro G. Marangoni ◽  
Gianfranco Mazzanti
Keyword(s):  
Phase Transition ◽  
Critical Point ◽  
Single Phase ◽  
Hydrocarbon Chain ◽  
Temperature Data ◽  
Recent Time ◽  
Recent Experimental Data ◽  
Hydrocarbon Chain Length ◽  
Discontinuous Phase ◽  
Solid Liquid

It is proposed that “crystal memory”, observed in a discontinuous solid-liquid phase transition of saturated triacylglycerol (TAG) molecules, is due to the coexistence of solid TAG crystalline phases and a liquid TAG phase, in a superheated metastable regime. Such a coexistence has been detected. Solid crystals can act as heterogeneous nuclei onto which molecules can condense as the temperature is lowered. We outlined a mathematical model, with a single phase transition, that shows how the time-temperature observations can be explained, makes predictions, and relates them to recent experimental data. A modified Vogel-Fulcher-Tammann (VFT) equation is used to predict time-temperature relations for the observation of “crystal memory” and to show boundaries beyond which “crystal memory” is not observed. A plot of the lifetime of a metastable state versus temperature, using the modified VFT equation, agrees with recent time-temperature data. The model can be falsified through its predictions: the model possesses a critical point and we outline a procedure describing how it could be observed by changing the hydrocarbon chain length. We make predictions about how thermodynamic functions will change as the critical point is reached and as the system enters a crossover regime. The model predicts that the phenomenon of “crystal memory” will not be observed unless the system is cooled from a superheated metastable regime associated with a discontinuous phase transition.

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