scholarly journals Cross-Linker Control of Vitrimer Flow

2020 ◽  
Author(s):  
Bassil El-Zaatari ◽  
Jacob Ishibashi ◽  
Julia Kalow
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Bulk Material ◽  
Relaxation Rates ◽  
Exchange Reactions ◽  
Activation Barriers ◽  
Flow Activation Energy ◽  
Wide Range ◽  
Cross Linker ◽  
Frequency Sweeps

<div><p>Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that cross-linker reactivity represents an additional design parameter to tune stress relaxation rates in vitrimers. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition—elimination of thiols in a PDMS vitrimer. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.</p></div>

scholarly journals Cross-Linker Control of Vitrimer Flow

2020 ◽  
Author(s):  
Bassil El-Zaatari ◽  
Jacob Ishibashi ◽  
Julia Kalow
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Bulk Material ◽  
Relaxation Rates ◽  
Exchange Reactions ◽  
Activation Barriers ◽  
Flow Activation Energy ◽  
Wide Range ◽  
Cross Linker ◽  
Frequency Sweeps

<div><p>Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that cross-linker reactivity represents an additional design parameter to tune stress relaxation rates in vitrimers. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition—elimination of thiols in a PDMS vitrimer. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.</p></div>

scholarly journals Cross-Linker Control of Vitrimer Flow

2019 ◽  
Author(s):  
Bassil El-Zaatari ◽  
Jacob Ishibashi ◽  
Julia Kalow
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Bulk Material ◽  
Relaxation Rates ◽  
Exchange Reactions ◽  
Activation Barriers ◽  
Flow Activation Energy ◽  
Constant Stiffness ◽  
Wide Range ◽  
Cross Linker

Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that the use of an associative mechanism additionally enables decoupling of stiffness and stress relaxation. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition–elimination of thiols in a PDMS vitrimer, and demonstrate modulation of stress relaxation rate while maintaining constant stiffness. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.

Chemical Stress-Relaxation and Other Studies on Styrene-Butadiene Rubber

1974 ◽  
Vol 47 (5) ◽  
pp. 1265-1274 ◽  
Author(s):  
S. H. Kalfayan ◽  
R. Rakutis ◽  
R. H. Silver
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Activation Energies ◽  
Hydroxyl Group ◽  
Styrene Butadiene Rubber ◽  
Chemical Stress ◽  
Butadiene Rubber ◽  
Relaxation Rates ◽  
Relaxation Measurements ◽  
Styrene Butadiene

Abstract The aging of styrene—butadiene rubber (SBR) was studied by three methods: stress relaxation, infrared spectroscopy, and swelling measurements, with the purpose of supplying information pertinent to understanding the basic mechanism of its aging. Stress-relaxation measurements in air and nitrogen at elevated temperatures indicated that atmospheric oxygen is the principal cause of chemical stress relaxation of SBR, rather than heat. Intermittent stress-relaxation measurements showed scission and crosslinking occurring simultaneously during network breakdown, and it was concluded that random scission in the backbone is indicated to take place in preference to scission in the crosslinks. Activation energies obtained from relaxation rates at several temperatures was 28 ± 0.5 kcal, comparable to literature values of 30 ± 2 kcals. The rates of carbonyl and hydroxyl group formation in SBR in air at various temperatures were determined by ir spectroscopy, both induction and maximum rates, νm, being measured. Activation energies calculated from these rates showed lower values compared to those obtained from stress-relaxation measurements. This may be due to the possibility that the processes being measured are not the same in each case. The three peaks appearing in the carbonyl region were ascribed to carboxyl, ketone, or aldehyde, and perester. The presence of these groups was confirmed by microanalytical methods. The absorption centered at 3450 cm−1 was attributed to hydrogen-bonded OH groups, i.e., alcohols and hydroperoxides. Positive chemical tests were obtained for hydroperoxide. The number of new network chains formed, νe, obtained from swelling measurements agreed well with those obtained from stress-relaxation measurements. It was found that the rate of the number of new network chains formed increased rapidly during the latter states of oxidation.

scholarly journals Laser Ablation Deposition of Ga2S3-La2S3 Glass Films

1995 ◽  
Vol 397 ◽  
Author(s):  
R. Asal ◽  
P.E. Rivers ◽  
H.N. Rutt
Keyword(s):  
Refractive Index ◽  
Laser Ablation ◽  
Laser Fluence ◽  
Bulk Material ◽  
Relaxation Rates ◽  
Radiative Relaxation ◽  
Urbach Tail ◽  
Wide Range ◽  
Gallium Lanthanum Sulphide ◽  
Novel Method

ABSTRACTGallium - lanthanum sulphide glasses (GLS) show wide range transparency and low non radiative relaxation rates for dopant ions such as Ho3+, Er3+ etc. They also show permanent photomodification of the refractive index under visible illumination. We report laser ablation deposition of these glasses and preliminary results on film stoichiometry and deposition rate as a function of excimer laser fluence. The sulphur to metal and Ga/La ratios are found to have marked fluence dependencies. The films show considerably more Urbach tail absorption than bulk material. A novel method has been developed for mapping the permanent photomodified index.

Mechanical Properties and Dislocation Structure of Single Crystal Cdte Deformed in Compression at 300°C

1976 ◽  
Vol 34 ◽  
pp. 592-593
Author(s):  
Ernest L. Hall ◽  
J. B. Vander Sande
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Dislocation Structure ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Strain Curve ◽  
Optical Devices ◽  
Semiconductor Compound ◽  
Wide Range ◽  
Sample Orientation

The present paper describes research on the mechanical properties and related dislocation structure of CdTe, a II-VI semiconductor compound with a wide range of uses in electrical and optical devices. At room temperature CdTe exhibits little plasticity and at the same time relatively low strength and hardness. The mechanical behavior of CdTe was examined at elevated temperatures with the goal of understanding plastic flow in this material and eventually improving the room temperature properties. Several samples of single crystal CdTe of identical size and crystallographic orientation were deformed in compression at 300°C to various levels of total strain. A resolved shear stress vs. compressive glide strain curve (Figure la) was derived from the results of the tests and the knowledge of the sample orientation.

WIELAND-K88

Alloy Digest ◽  
2005 ◽  
Vol 54 (12) ◽  
Keyword(s):  
Thermal Conductivity ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Stress Relaxation ◽  
Copper Alloy ◽  
Elevated Temperatures ◽  
Heat Treating ◽  
Relaxation Resistance ◽  
Temperature Performance ◽  
Very High

Abstract Wieland K-88 is a copper alloy with very high electrical and thermal conductivity, good strength, and excellent stress relaxation resistance at elevated temperatures. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: CU-738. Producer or source: Wieland Metals Inc.

USS TENELON

Alloy Digest ◽  
1975 ◽  
Vol 24 (5) ◽  
Keyword(s):  
Corrosion Resistance ◽  
Elevated Temperatures ◽  
Stress Rupture ◽  
High Strength ◽  
Heat Treating ◽  
Creep Properties ◽  
United States Steel Corporation ◽  
Excellent Corrosion Resistance ◽  
Wide Range ◽  
Mild Acid

Abstract USS TENELON is a completely austenitic, nickel-free stainless steel with exceptionally high strength which is retained at elevated temperatures. It has excellent corrosion resistance in atmospheric and mild acid exposures and maintains nonmagnetic characteristics even when 60% cold reduced. It also has good stress-rupture and creep properties in the range 1200-1500 F. It has a wide range of applications. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness, creep, and fatigue. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SS-311. Producer or source: United States Steel Corporation.

The Future of Plasma-Based Surface Engineering Techniques in Tribology (Keynote)

2005 ◽  
Author(s):  
Allan Matthews ◽  
Adrian Leyland
Keyword(s):  
Surface Engineering ◽  
Performance Enhancement ◽  
Bulk Material ◽  
Cost Savings ◽  
Cost Effective ◽  
Ceramic Coatings ◽  
Performance Improvements ◽  
Treatment Techniques ◽  
Wide Range ◽  
Macro Scale

Over the past twenty years or so, there have been major steps forward both in the understanding of tribological mechanisms and in the development of new coating and treatment techniques to better “engineer” surfaces to achieve reductions in wear and friction. Particularly in the coatings tribology field, improved techniques and theories which enable us to study and understand the mechanisms occurring at the “nano”, “micro” and “macro” scale have allowed considerable progress to be made in (for example) understanding contact mechanisms and the influence of “third bodies” [1–5]. Over the same period, we have seen the emergence of the discipline which we now call “Surface Engineering”, by which, ideally, a bulk material (the ‘substrate’) and a coating are combined in a way that provides a cost-effective performance enhancement of which neither would be capable without the presence of the other. It is probably fair to say that the emergence and recognition of Surface Engineering as a field in its own right has been driven largely by the availability of “plasma”-based coating and treatment processes, which can provide surface properties which were previously unachievable. In particular, plasma-assisted (PA) physical vapour deposition (PVD) techniques, allowing wear-resistant ceramic thin films such as titanium nitride (TiN) to be deposited on a wide range of industrial tooling, gave a step-change in industrial productivity and manufactured product quality, and caught the attention of engineers due to the remarkable cost savings and performance improvements obtained. Subsequently, so-called 2nd- and 3rd-generation ceramic coatings (with multilayered or nanocomposite structures) have recently been developed [6–9], to further extend tool performance — the objective typically being to increase coating hardness further, or extend hardness capabilities to higher temperatures.

scholarly journals Properties of Silicone Rubber-Based Composites Reinforced with Few-Layer Graphene and Iron Oxide or Titanium Dioxide

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1550
Author(s):  
Vineet Kumar ◽  
Anuj Kumar ◽  
Minseok Song ◽  
Dong-Joo Lee ◽  
Sung-Soo Han ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Titanium Dioxide ◽  
Iron Oxide ◽  
Stress Relaxation ◽  
Silicone Rubber ◽  
Room Temperature ◽  
Relaxation Rates ◽  
Layer Graphene ◽  
Few Layer Graphene ◽  
Mechanical Actuation

The increasing demand for polymer composites with novel or improved properties requires novel fillers. To meet the challenges posed, nanofillers such as graphene, carbon nanotubes, and titanium dioxide (TiO2) have been used. In the present work, few-layer graphene (FLG) and iron oxide (Fe3O4) or TiO2 were used as fillers in a room-temperature-vulcanized (RTV) silicone rubber (SR) matrix. Composites were prepared by mixing RTV-SR with nanofillers and then kept for vulcanization at room temperature for 24 h. The RTV-SR composites obtained were characterized with respect to their mechanical, actuation, and magnetic properties. Fourier-transform infrared spectroscopy (FTIR) analysis was performed to investigate the composite raw materials and finished composites, and X-ray photoelectron spectroscopy (XPS) analysis was used to study composite surface elemental compositions. Results showed that mechanical properties were improved by adding fillers, and actuation displacements were dependent on the type of nanofiller used and the applied voltage. Magnetic stress-relaxation also increased with filler amount and stress-relaxation rates decreased when a magnetic field was applied parallel to the deformation axes. Thus, this study showed that the inclusion of iron oxide (Fe3O4) or TiO2 fillers in RTV-SR improves mechanical, actuation, and magnetic properties.

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