Stretched Exponential Stress Relaxation in a Thermally Reversible, Physically Associating Block Copolymer Solution

2012 ◽  
Vol 1418 ◽  
Author(s):  
Kendra A. Erk ◽  
Jack F. Douglas
Keyword(s):  
Stress Relaxation ◽  
Polymer Materials ◽  
Copolymer Solution ◽  
Stretched Exponential ◽  
Glass Forming ◽  
Wide Range ◽  
Glass Forming Materials ◽  
Short Time ◽  
Associating Polymer ◽  
Shear Stress Relaxation

ABSTRACTThe shear stress relaxation of a thermally reversible, physically associating solution formed from a triblock copolymer in solvent selective for the mid-block was found to be well described over a broad temperature range by a stretched exponential function with a temperature independent ‘stretching exponent’, β ≈ 1/3. This same exponent value has been suggested to have particular significance in describing structural relaxation in a wide range of disordered viscoelastic materials ranging from associating polymer materials (‘gels’) to glass-forming liquids. We quantify the temperature dependence of the high frequency, or short time, shear modulus as function of temperature and find that this property also follows a variation often observed in gels and glass-forming materials.

scholarly journals Quantitative relations between cooperative motion, emergent elasticity, and free volume in model glass-forming polymer materials

2015 ◽  
Vol 112 (10) ◽  
pp. 2966-2971 ◽  
Author(s):  
Beatriz A. Pazmiño Betancourt ◽  
Paul Z. Hanakata ◽  
Francis W. Starr ◽  
Jack F. Douglas
Keyword(s):  
Free Volume ◽  
Glass Formation ◽  
Collective Motion ◽  
Configurational Entropy ◽  
Polymer Melt ◽  
Polymer Materials ◽  
Coarse Grained ◽  
Glass Forming ◽  
Cooperative Motion ◽  
Glass Forming Materials

The study of glass formation is largely framed by semiempirical models that emphasize the importance of progressively growing cooperative motion accompanying the drop in fluid configurational entropy, emergent elasticity, or the vanishing of accessible free volume available for molecular motion in cooled liquids. We investigate the extent to which these descriptions are related through computations on a model coarse-grained polymer melt, with and without nanoparticle additives, and for supported polymer films with smooth or rough surfaces, allowing for substantial variation of the glass transition temperature and the fragility of glass formation. We find quantitative relations between emergent elasticity, the average local volume accessible for particle motion, and the growth of collective motion in cooled liquids. Surprisingly, we find that each of these models of glass formation can equally well describe the relaxation data for all of the systems that we simulate. In this way, we uncover some unity in our understanding of glass-forming materials from perspectives formerly considered as distinct.

scholarly journals Wide range dielectric spectroscopy on glass-forming materials: An experimental overview

2001 ◽  
Vol 249 (1) ◽  
pp. 89-98 ◽  
Author(s):  
U. Schneider ◽  
P. Lunkenheimer ◽  
A. Pimenov ◽  
R. Brand ◽  
A. Loidl
Keyword(s):  
Dielectric Spectroscopy ◽  
Glass Forming ◽  
Wide Range ◽  
Glass Forming Materials

The Dynamics of Interacting Systems: Glassy Ionic Conductors and Glass-Forming Materials

1995 ◽  
Vol 411 ◽  
Author(s):  
K. L. Ngai ◽  
A. K. Rizos
Keyword(s):  
Correlation Function ◽  
Structural Relaxation ◽  
Time Range ◽  
Relaxation Techniques ◽  
Ionic Conductors ◽  
Time Dynamics ◽  
Glass Forming ◽  
Interacting Systems ◽  
Glass Forming Materials ◽  
Short Time

ABSTRACTThe dynamics of densely packed interacting systems including glass-forming materials and glassy ionic conductors of various chemical and micro structures have been investigated experimentally by many workers, covering an immense time range from microscopic times shorter than 10−12 s to macroscopic times as long as 104 s. The short time dynamics is fundamental because it can directly reveal the microscopic mechanism of the relaxation. Several experimental investigations of structural relaxation in glass-forming substances have found that the short time dynamics shows exponential relaxation with a correlation function well described by exp(−t/τo) for t<tc where tc is temperature insensitive and has the order of magnitude of a picosecond. The correlation function then crosses over at tc to assumes the stretched exponential form, exp[−(t/τ)β], for t>tc. The relaxation times τ and τo are related by the expression τ = [tc−(1−β)τo]1/β. In this work, we focus on glassy ionic conductors and ionic glass-forming materials and experiments that employ dielectric spectroscopic and conductivity relaxation techniques, the theme of this Symposium. We show that these experimental data exhibit the same feature as described above for structural relaxation and are in accord with the predictions of the coupling model proposed by one of the authors.

scholarly journals A simplified numerical method to determine the shear stress relaxation time parameters by the example of polymers

2017 ◽  
pp. 146-157
Author(s):  
М.С. Воронин
Keyword(s):  
Shear Stress ◽  
Relaxation Time ◽  
Stress Relaxation ◽  
Numerical Method ◽  
Yield Stress ◽  
Viscoelastic Model ◽  
Wide Range ◽  
Stress Point ◽  
Time Parameters ◽  
Shear Stress Relaxation

Приводится метод расчета параметров функции времени релаксации касательных напряжений, являющейся одним из замыкающих соотношений для модели вязкоупругого тела максвелловского типа. Метод основан на упрощении системы уравнений, описывающей деформирование тонкого стержня в рамках модели, если рассматривать эту систему в точке начала пластической деформации. Метод позволяет отыскать те параметры времени релаксации, которые ответственны за описание предела упругости материала в широком диапазоне температур и скоростей деформации. Результаты применения метода демонстрируются сравнением с экспериментальными данными для трeх полимерных материалов: ПММА (полиметилметакрилат), ПТФЭ (политетрафторэтилен) и эпоксидной смолы. A numerical method to determine the parameters of the shear stress relaxation time is discussed. This function is one of the constitutive equations of a Maxwellian viscoelastic model. The method is based on a simplification of the system of equations describing the deformation of a thin rod when this system is considered at the yield stress point. The method allows one to find the relaxation time parameters responsible for the yield stress description in a wide range of temperatures and strain rates. The numerical results obtained by the method are compared with experimental data for polymethylmethacrylate, polytetrafluoroethylene, and epoxy resin.

scholarly journals Effects of local isolates of Beauveria bassiana (Balsamo) Vuillemin on the two-spotted spider mite, Tetranychus urticae (Koch) (Acari: Tetranychidae)

2021 ◽  
Vol 31 (1) ◽  
Author(s):  
Cenk Yucel
Keyword(s):  
Tetranychus Urticae ◽  
Beauveria Bassiana ◽  
Spider Mite ◽  
Lethal Effect ◽  
Probit Analysis ◽  
Plant Feeding ◽  
Wide Range ◽  
Two Spotted Spider Mite ◽  
Short Time ◽  
Tetranychus Urticae Koch

Abstract Background The two-spotted spider mite, Tetranychus urticae (Koch) (Acari: Tetranychidae), is a widely distributed plant-feeding pest that causes significant yield losses in a wide range of crops. Newly developed or improved environmentally friendly biocontrol agents serve as an alternative to traditional pest control tools. Experiment of the effects of 2 local fungal isolates of Beauveria bassiana (BGF14 and BCA32) was carried out against T. urticae under laboratory conditions. Results Both tested isolates had lethal effect in a short time after application, and this effect increased as time progressed. BGF14 and BCA32 isolates caused T. urticae mortality rates ranging from 25.88 to 61.92 and 32.36 to 62.03% when applied at the concentrations between 1×105 and 1×108 conidia/ml, respectively. According to the Probit analysis performed on the effect of fungi on T. urticae adults, the LC50 values of BGF14 and BCA32 isolates on the 7th day after inoculation were 2.6×106 and 6.3×104 conidia/ml, respectively, and the LT50 values for both fungi applied at a concentration of 108 conidia/ml were 2.14 and 2.23 days, respectively. Conclusions The 2 isolates of B. bassiana (BGF14 and BCA32) had the potentials to suppress T. urticae population and can be recommended as promising biocontrol agent candidates for control of T. urticae.

scholarly journals Breeding Strategies to Improve Miscanthus as a Sustainable Source of Biomass for Bioenergy and Biorenewable Products

Agronomy ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 673 ◽  
Author(s):  
John Clifton-Brown ◽  
Kai-Uwe Schwarz ◽  
Danny Awty-Carroll ◽  
Antonella Iurato ◽  
Heike Meyer ◽  
...  
Keyword(s):  
Significant Contribution ◽  
Perennial Grass ◽  
Time Frame ◽  
Eastern Asia ◽  
Germplasm Collections ◽  
Naturally Occurring ◽  
Wide Range ◽  
Yield Quality ◽  
Short Time ◽  
Commercial Expansion

Miscanthus, a C4 perennial grass native to Eastern Asia, is being bred to provide biomass for bioenergy and biorenewable products. Commercial expansion with the clonal hybrid M. × giganteus is limited by low multiplication rates, high establishment costs and drought sensitivity. These limitations can be overcome by breeding more resilient Miscanthus hybrids propagated by seed. Naturally occurring fast growing indigenous Miscanthus species are found in diverse environments across Eastern Asia. The natural diversity provides for plant breeders, the genetic resources to improve yield, quality, and resilience for a wide range of climates and adverse abiotic stresses. The challenge for Miscanthus breeding is to harness the diversity through selections of outstanding wild types, parents, and progenies over a short time frame to deploy hybrids that make a significant contribution to a world less dependent on fossil resources. Here are described the strategies taken by the Miscanthus breeding programme at Aberystwyth, UK and its partners. The programme built up one of the largest Miscanthus germplasm collections outside Asia. We describe the initial strategies to exploit the available genetic diversity to develop varieties. We illustrate the success of combining diverse Miscanthus germplasm and the selection criteria applied across different environments to identify promising hybrids and to develop these into commercial varieties. We discuss the potential for molecular selections to streamline the breeding process.

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