Dynamic Mechanical Analysis Techniques Research Articles

Slip-stick diffusion behavior caused by photo-polymerization-induced nano-gelation in highly heterogeneous photo-polymeric coatings

Herein, the diffusion behavior of the photo-polymeric coatings formed by various reactive diluents with different functionalities was studied using electrochemical impedance spectroscopy technique. Scanning electron microscopy, atomic force microscopy and dynamic mechanical analysis techniques were used to investigate the dynamic and structural heterogeneity of the photo-polymeric networks. It was found that the photo-polymerization-induced nano-gelation process leads to slip-stick diffusion of charge carriers through the photo-polymeric coatings. The lowest values of the apparent diffusion coefficient of the charge carriers through the nano-gel domains were obtained for the coatings formed by the highest amount of reactive diluent. The lowest and the highest value of the apparent diffusion coefficient were estimated to be 8 and 125 μm2/s, respectively.

Extension and application of dynamic mechanical analysis for the estimation of spatial distribution of material properties

The paper presents a unique extension and application of the dynamic mechanical analysis (DMA) technique for the determination of heterogeneous mechanical material properties. Their values as well as their spatial distribution are major interest when analysing properties of post-damage materials. The proposed procedure incorporates longer than typical beam-shaped test samples enclosing the zone with locally varied material properties. The mechanical properties are estimated for the extended sample at defined positions while the sample is iteratively shifted along its axis. The procedure was successfully validated in various tests incorporating standardised and extended samples.The preliminary investigations regarding the application of the proposed procedure were conducted on composite specimens with heterogeneous distribution of material properties introduced by impact load. The results show, on the one hand, a monotonic relation between the storage modulus and the damage extent. On the other hand, a non-monotonic relation between the loss modulus and damage severity has been observed.

Effect of the loading of organomodified clays on the thermal and mechanical properties of a model dental resin

Experimental dental resins composed of triethyleneglycol dimethacrylate, urethane dimethacrylate, ethoxylated bisphenol-A-dimethacrylate and bisphenol A glycidyl methacrylate containing an organoclay as filler were prepared by photopolymerization. The addition of organoclay fillers results in slower polymerization rates (0.59 and 0.24 mol L-1 min-1, for the formulations without and with 15% of organoclay, respectively) and lower degrees of conversion (0.50 and 0.35 for the formulations without and with 15% of organoclay), as determined by photocalorimetry. The influence of the organoclay on the thermal and mechanical properties of the resins was evaluated using thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) techniques. The (tan δ) and E´ curves indicate the formation of more rigid materials and the damping curve data indicates more homogeneous materials. An increase of storage modulus, E’, was observed for composites with the higher organoclay filler contents. These effects are due to the higher viscosity of the systems with organoclay, resulting in a lower mobility of the radicals during the propagation step of polymerization, as well as to the scattering of the incident photopolymerizing radiation, which lowers the amount of initiation centres.

Estudo de propriedades dinâmico-mecânicas de um compósito aeronáutico de CFRP com fios de ligas com memória de forma embebidos

Resumo Este trabalho trata-se de um estudo experimental do comportamento de propriedades termomecânicas de um compósito ativo, obtido através da introdução de diferentes frações volumétricas de fios de uma liga NiTi com efeito de memoria de forma em uma matriz polimérica reforçada com fibras de carbono (CFRP). Para tal estudo, inicialmente fez-se uma análise do módulo elástico de um pré preg de CFRP aeronáutico com diferentes posições de ângulo de fibras de carbono, a fim de determinar a matriz mais adequada para a introdução de fios de NiTi para obter compósito ativo. Verificou-se que a matriz com fibras alinhadas a 15º apresenta-se como uma boa opção para a obtenção de compósitos ativos, sendo utilizada para a fabricação de amostras de CFRP/NiTi. As amostras tiveram seu potencial de ativação avaliado através da análise da variação do módulo de elasticidade com o aumento da temperatura usando a técnica de Análise Dinâmico-Mecânica (DMA). Através dos resultados obtidos, verificou-se a capacidade de ativação dos compósitos CFRP/NiTi, os quais apresentam variação positiva de módulo de elasticidade ao serem aquecidos acima da temperatura de transformação dos fios NiTi.

Cross-Linkable Epoxidized Maleinated Castor Oil: A Renewable Resin Alternative to Unsaturated Polyesters

As an alternative resin to conventional synthetic unsaturated polyesters (UPEs), epoxidized maleinated castor oil (EMACO) was synthesized in two steps. For this purpose, castor oil was reacted with maleic anhydride at 70°C to obtain maleinated castor oil (MACO). Then, epoxidation of MACO was carried out by using a mixture of formic acid and hydrogen peroxide at 0–5°C. Then, the free carboxyl groups of the synthesized EMACO were further reacted with free epoxide groups of EMACO at 90°C. At the end of the reaction, an unsaturated polyester precursor-prepolymer was obtained (P-EMACO). FTIR and1H NMR spectroscopic techniques were used to characterize the monomers synthesized. The P-EMACO was then mixed with styrene and cross-linked in the presence of AIBN at 50°C. Thermal and mechanical properties of the final cross-linked product were investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) techniques. The degradation onset temperature of the material at which cross-linked X-EMACO loses 5% of its weight was found to be 209°C. Its dynamicTgand storage modulus at 25°C were determined as 72°C and 1.08 GPa, respectively. These results are higher than some of the different oil based polymers reported in the literature.

Modeling physico-mechanical properties of an individual photopolymerization-induced urethane-based microgel particle

In this work, an individual microgel particle dispersed in a viscous-like matrix was synthesized through the in-situ photopolymerization process. The actual size of the individual microgel particle was calculated based on the microscopic techniques. The cooperative relaxation properties of the individual microgel particle were studied using dynamic mechanical analysis technique. A value of 18 of dynamic fragility index for the microgel network was obtained. The size of cooperatively rearranging region (CRR) at the glass transition temperature for the microgel particle was estimated to be 6. A value of 0.041 mol/cm3 of cross-link density of the individual microgel particle was predicted based on the atomic force microscopy results and stress-strain data. The microgel hardness was measured by a nano-indentation instrument with an indenter diameter of 150 nm. The value of the hardness of the microgel particle was found to be in a suitable agreement with the results obtained from the atomic force microscopy technique. On the basis of a proposed model, the apparent diffusion coefficient of Cl− through the photopolymerization-induced microgel particle was calculated to be about 10 μm2/sec.

34. Designing next generation protectants

In order to advance towards the vitrification of complex organs, further advances in cryoprotectant compositions will be necessary. Systematic solution optimization has enabled the identification of superior combinations of cryoprotectants for various cell and tissue types, yet the range of chemicals used as protectants is still quite narrow and it is oftentimes not well understood why some compositions work better than others. The White House recently launched a “Materials Genome Initiative” to catalyze an integrated design process that uses feedback from computational studies to improve the efficiency of advanced materials development. This approach is very suitable to the design of Next Generation Protectants. For vitrification applications the main materials optimization parameters are cryoprotectant toxicity and glassy state properties. While advances have been made in understanding and predicting CPA toxicity, it is much harder to predict the glassy state characteristics of complex mixtures. Additive mixing rules provide little insight, as superior compositions often exhibit strong deviations from ideal solution behavior. In recent work we have combined advanced thermal analysis techniques, specifically Dynamic Mechanical Analysis (DMA) and Differential Scanning Calorimetry (DSC), together with molecular modelling to explore the underling molecular mechanisms that give rise to Tg enhancements in protectant compositions in an effort to better understand the design rules that lead to improved compositions. Using molecular dynamics (MD) simulation, we have recently shown that divalent cations can strengthen the interacting network in electrolyte/glycerol mixtures via strong cation-dipole attractions, leading to an increase in T g 1 . In contrast, monovalent cations were observed to have little effect on Tg as the cation-dipole attraction was only slightly stronger than the original hydrogen-bonding network amongst glycerol molecules. The precursor of salt crystallization was also observed in these monovalent ion compositions, potentially contributing to weak Tg-enhancing ability. Using both thermal analysis and MD simulation we were also able to better understand the effects of phosphate anions on the glassy state properties of trehalose2. We observed that the addition of NaH2PO4 decreased both the glass transition temperature and the α -relaxation temperature of the dehydrated trehalose/NaH2PO4 mixture compared to trehalose alone while both Tg and Tα were increased by adding Na2HPO4 to pure trehalose. The hydrogen-bonding interactions between trehalose and HPO 4 2 - were found to be stronger than both the trehalose-trehalose hydrogen bonds and those formed between trehalose and H2 PO 4 - . The HPO 4 2 - ions also aggregated into smaller clusters than H2 PO 4 - ions, contributing to a more homogeneous glass network. Using DMA techniques we also demonstrated that when pure trehalose, a fragile glass-former, was diluted with a small amount of the strong glass-former, glycerol, the overall mixture was strengthened significantly. The fragility index (m) was observed to be minimized when glycerol was added at a 5–10 wt% concentration, the same formulation that has been shown by others to be maximally effective for preserving proteins in the glassy state. The combination of MD simulation and thermal analysis should prove to be very valuable for the development of Next Generation Protectants.

Curing and thermo-mechanical studies of a modified thermosetting clearcoat containing OH-functional POSS nanocages

Abstract This paper attempts to study the chemical, thermo-mechanical and rheological properties of an acrylic/melamine clearcoat modified with a polyhedral oligomeric silsesquioxane (POSS) macromolecule. OH-functional groups of the linear acrylic resin were stoichiometrically substituted with those of the POSS. This modification resulted in a drop in viscosity compared with the pristine sample, mainly because of the globular compact structure of the modifier. This lowered the chain entanglements and provided more mobile functional groups during curing. FTIR spectroscopy, dynamic mechanical thermal analysis (DMTA) and transmission electron microscopy (TEM) techniques were utilized to study the resultant clearcoats. It was illustrated that reduced viscosity facilitated curing reactions and lead to a more efficient and more extensive curing degree, leading to an enhanced cross-linking density in presence of the POSS nanostructure. It was also illustrated that compatibility of POSS and acrylic/melamine lead to a molecular-scale dispersion of POSS nanostructures within the matrix.

Effect of diisocyanates and chain extenders on the physicochemical properties and morphology of multicomponent segmented polyurethanes based on poly(l‐lactide), poly(ethylene glycol) and poly(trimethylene carbonate)

AbstractMulticomponent segmented polyurethanes (SPUs) based on poly(ethylene glycol), poly(l‐lactide) and poly(trimethylene carbonate) as macrodiols, 2,4‐toluene diisocyanate (2,4‐TDI) or 1,6‐hexane diisocyanate (HDI) as diisocyanate, and 1,4‐butanediol (BDO) or 2,2‐bis(hydroxymethyl)propionic acid (DMPA) as chain extenders were synthesized. The molecular, thermal, dynamic mechanical and morphological features of this set of uncrosslinked polyurethanes are characterized using 1H NMR, gel permeation chromatography, differential scanning calorimetry, dynamic mechanical thermal analysis (DMTA) and atomic force microscopy techniques. The lower reaction rate of HDI in comparison with 2,4‐TDI allows for better control of the SPU compositions, so that the intrinsic properties of each block can be better combined and modulated. HDI‐based SPUs are semi‐crystalline, while those based on 2,4‐TDI are amorphous, affecting the mechanical properties of these polyurethanes. All SPUs are heterogeneous, presenting morphologies of a disperse phase in a matrix which varies with the macrodiol ratios as well as with the nature of the diisocyanate and chain extender (a finer dispersion of the disperse phase is observed for SPUs of HDI and BDO). DMTA results indicate that the phases are complex mixtures of the different blocks with at least one rich in PLLA. The PEG content is shown to be the most important factor influencing the water sorption capability, while the incorporation of hindering carboxylic acid groups by the use of DMPA allows the water uptake of SPUs to be controlled by the solution pH. All SPUs show a significant loss of molar mass in hydrolytic degradation experiments and, in general, the PLLA‐rich SPUs are more susceptible to degradation. © 2015 Society of Chemical Industry

Influence of aggregate absorption and diffusion properties on moisture damage in asphalt mixtures

An experimental study was undertaken to characterise moisture sensitivity of asphalt mixtures by comparing certain physico-chemical properties of selected aggregates of different mineralogies to the moisture-induced strength degradation of the aggregate–mastic bonds. The aim of the study was to evaluate the effect of using different aggregate types (as substrates) with a single mastic type that had shown severe moisture sensitivity in the past when combined with a susceptible aggregate substrate. Four different aggregate types and an asphalt mastic (made with a 40/60 pen base bitumen) were used. Aggregate moisture sorption at ambient temperature was characterised using gravimetric techniques. Aggregate specific surface area was determined by octane adsorption using a dynamic vapour sorption device. Dynamic mechanical analysis techniques based on data from a dynamic shear rheometer were used to characterise the rheological properties of the asphalt mastic. Aggregate–mastic bond strength as a function of moisture conditioning time was determined using a tensile pull-off test set-up. The results were used to estimate equilibrium moisture uptake, diffusion coefficient, characteristic diffusion time, and aggregate ‘porosity’. The effect of moisture on bond strength was aggregate substrate-type-dependent with three out of the four aggregates performing well and the fourth performing poorly. The moisture absorption and diffusion properties of the poorly performing aggregates were worse than the ‘good’ performing aggregates. Susceptible aggregate–mastic bonds had high porosity, high moisture absorption, high diffusion coefficient and contained granite as substrates. Results of statistical analyses suggested that the differences in moisture sensitivity of the other three aggregates were not significant. Therefore, two unique damage models, one for ‘good’ performing and another for ‘poor’ performing were proposed to characterise moisture damage sensitivity of asphalt. The influence of aggregate moisture absorption and diffusion on asphalt mixture moisture damage was found to be aggregate-type-dependent. The results also suggested that in a susceptible mixture, the effect of the substrate aggregate may be more influential than the effect of mastic. The results have important implications for the selection of coarse aggregate for asphalt mix design.

Dynamic mechanical response of a Ni45.7Ti29.3Hf20Pd5 alloy

Phase transformation and damping properties of a Ni45.7Ti29.3Hf20Pd5 (at%) alloy was studied through Dynamic Scanning Calorimetry and Dynamic Mechanical Analysis techniques. Damping properties were characterized as functions of aging, temperature cycling, frequency and heating rate. The maximum damping capacity of the alloy was determined to be 0.215 during thermoelastic martensitic phase transformation, that is comparable to NiTi alloys. It was found that aging at temperatures ranging from 300°C to 900°C for 1.5h was effective in controlling damping capacity of the alloy as well as altering the phase transformation temperatures. The damping capacity of the Ni45.7Ti29.3Hf20Pd5 alloy increased with heating rate and decreased with frequency.

Development of Functional Polyurethane–ZnO Hybrid Nanocomposite Coatings from Thevetia peruviana Seed Oil

AbstractThe present article reports eco‐friendly multi‐functional polyurethane–ZnO hybrid nanocomposite coatings obtained from Thevetia peruviana seed oil (TPSO). Initially, the polyols were prepared by treating TPSO with glycerol and the formation was supported by Fourier transform infrared (FT‐IR) and 1H‐NMR studies. In the next stage, siloxane functionalized ZnO nanoparticles were added to the polyol mixture in different weight percentages (0, 1 and 2 %) and then treated with excess 4,4′‐diisocyanatodicyclohexylmethane (H12MDI) in order to synthesize isocyanate terminated polyurethane nanocomposites. The polyurethane hybrids were then casted as thin films and cured under atmospheric moisture. After complete curing they were characterized by using FT‐IR, 1H‐NMR, 13C‐NMR, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and dynamic mechanical thermal analysis techniques. The hybrid nanocomposites showed superior thermo‐mechanical and anti‐corrosive properties compared to pristine polyurethane. Also, due to the presence of nano ZnO in the polyurethane matrix, the composite coatings are showing excellent resistance towards various bacterial and fungal stains.

Influence of Thermal Treatment on Mechanical and Morphological Characteristics of Polyamide 11/Cellulose Nanofiber Nanocomposites

Nanocomposite films were prepared from polyamide 11 (PA11) and cellulose nanofibers (CN) by melt compounding and compression molding. The impact of thermal treatment on the morphology and mechanical behavior of PA11 and nanocomposite films was studied using dynamic mechanical analysis, tensile tests, X-ray diffraction (XRD), and peak force (PF) QNM technique. Slightly higher storage modulus values were obtained for nanocomposites compared to the matrix before the treatment, but a noticeable increase was observed after the treatment. Although CN addition determined increased tensile strength and modulus both before and after the treatment, the increase was much more significant in the case of treated films. The best mechanical properties were shown by treated PA11 films containing 5 wt% CN, with 40% higher Young’s modulus and with 35% higher tensile strength compared to the matrix. Some of the changes pointed out by static and dynamic mechanical tests were explained by the morphological changes determined by the thermal treatment and emphasized by PF QNM and by the increase of XRD crystallinity. A transition from lamellar stack morphology to one involving spherulites was highlighted by AFM. Thermal treatment has proved a valuable method for improving the mechanical properties of PA11/CN composites.

A Dynamic Mechanical Analysis Technique for Porous Media

Dynamic mechanical analysis (DMA) is a common way to measure the mechanical properties of materials as functions of frequency. Traditionally, a viscoelastic mechanical model is applied and current DMA techniques fit an analytical approximation to measured dynamic motion data by neglecting inertial forces and adding empirical correction factors to account for transverse boundary displacements. Here, a finite-element (FE) approach to processing DMA data was developed to estimate poroelastic material properties. Frequency-dependent inertial forces, which are significant in soft media and often neglected in DMA, were included in the FE model. The technique applies a constitutive relation to the DMA measurements and exploits a nonlinear inversion to estimate the material properties in the model that best fit the model response to the DMA data. A viscoelastic version of this approach was developed to validate the approach by comparing complex modulus estimates to the direct DMA results. Both analytical and FE poroelastic models were also developed to explore their behavior in the DMA testing environment. All of the models were applied to tofu as a representative soft poroelastic material that is a common phantom in elastography imaging studies. Five samples of three different stiffnesses were tested from 1-14 Hz with rough platens placed on the top and bottom surfaces of the material specimen under test to restrict transverse displacements and promote fluid-solid interaction. The viscoelastic models were identical in the static case, and nearly the same at frequency with inertial forces accounting for some of the discrepancy. The poroelastic analytical method was not sufficient when the relevant physical boundary constraints were applied, whereas the poroelastic FE approach produced high quality estimates of shear modulus and hydraulic conductivity. These results illustrated appropriate shear modulus contrast between tofu samples and yielded a consistent contrast in hydraulic conductivity as well.

Measurement for mechanical behavior and fatigue property of Cu films by nanoscale dynamic load method

Mechanical behavior and fatigue properties greatly influence the reliability and life of film materials. Quantitative testing of film fatigue property under dynamic load is realized on the basis of nanometers thick Cu films deposited on monocrystalline silicon substrates by magnetron sputtering system. Microstructure and surface pattern of copper films are characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Film hardness and modulus are measured by quasi-static test and continuous measurements (CMX) systems of nanomechanical testing instrument. Fatigue damage behaviors are investigated by nanoscale dynamic mechanical analysis (nanoDMA) technique. The results indicate that Cu films prepared by magnetron sputtering system present (111) preferred orientation and contain a large number of nanoscale grains with uniform texture and low roughness. As is affected by substrate and small scale effect, CMX method is more suitable than quasi-static method for the measurement of micro-mechanical properties of ultra-thin films. Fatigue dominantly happens in thinner films. Factors, like thickness, inner stress, modulus and hardness, can influence fatigue life of nanoscale Cu films.

Curing behaviour and mechanical properties of pigmented UV-curable epoxy acrylate coatings

Purpose – The purpose of this work was to study the effect of chemical structure of reactive diluents on the curing behaviour and physical–mechanical properties of a titanium dioxide pigmented UV-curable epoxy acrylate system. Design/methodology/approach – Two different tri-functional and two different tetra-functional acrylate monomers were used as reactive diluents in the formulations. The curing behaviour of the formulations was studied by using photo-differential scanning calorimetry analysis. The rate of curing, conversion at the maximum rate and ultimate conversion for different formulations were calculated. In addition, the physical and mechanical characteristics of the cured films, including glass transition temperature and modulus, were measured by using a dynamic mechanical analysis technique. Findings – The results showed that the ultimate conversion for non-pigmented pentaerythritol triacrylate (PETA) and trimethylol propane triacrylate (TMPTA) formulations were almost similar, but the interference effect of titanium dioxide particles on the curing of the PETA formulations was found to be more considerable in comparison to the TMPTA formulations. The extent of reaction for tetra-functional acrylate monomers was considerably less than those for tri-functional acrylate monomers. The Tg and storage modulus of non-pigmented PETA, TMPTA and pentaerythritol tetraacrylate (PE4TA) formulations were almost the same and higher than that for ditrimethylol propane tetraacrylate (DiTMP4TA) formulations. However, Tg and storage modulus of pigmented tetra-functional acrylate monomer formulations were higher than those for tri-acrylate monomer formulations. Research limitations/implications – The curing conditions (temperature and UV intensity) can affect the network formation and consequently will affect on the properties of the cured films. Practical implications – The pigmented UV-curable coatings are interested for many industries such as wood and automotive industries. The reported data can be used by the formulators working in the R&D departments. In addition, the results obtained can be used by the researchers who are active in the field of structure–property relationship for UV-curable coatings. Social implications – UV-curing systems are considered as one of the most environment-friendly coatings system. Therefore, the developing of its knowledge can help to extend its usage to different applications. Originality/value – The photopolymerisation of pigmented coatings is a great challenge and is hardly investigated in the literature. Therefore, in this research, the effect of chemical structure and functionality of different multifunctional acrylate monomers on the curing behaviour of pigmented formulations was investigated.

Trisilanolisobutyl POSS/polyurethane hybrid composites: preparation, WAXS and thermal properties

Trisilanolisobutyl polyhedral oligomeric silsesquioxane (TSI-POSS) with three hydroxyl functional groups pendent to an open cage, was incorporated in concentrations of 7, 13 and 22 wt% into 4,4′-methylenebis(phenyl isocyanate) and glycerol propoxylate to prepare TSI-POSS–PU hybrid composites as a heavy linking node in polymer backbone, respectively. These composites were characterized by FTIR, wide-angle X-ray scattering (WAXS), dynamic mechanical analysis and thermogravimetry techniques. In WAXS profiles, above 22 wt% TSI-POSS concentration, the morphology of composite is significantly altered and distinct crystallite clusters are formed, which increase the volume of hard segment in polyurethane (PU) hybrid composite. As TSI-POSS concentration rises, the glass transition temperature (T g) of composites is increased while the decomposition temperature is slightly decreased due to the oxysensitive isobutyl groups in structure. Meanwhile, the activation energy of hybrid composites is nearly unchanged indicating that the formation of crystallite cluster, which restricts motion of surrounding chains, is the predominant effect in T g increasing. It can be concluded that the morphology and the thermal property of polyurethane can be tailored by TSI-POSS incorporation, whereas functional group in TSI-POSS structure is the decisive factor for the thermostability of designed composites.

Correlation between dynamic mechanical thermo-analysis and composition-based models for C-S-H in hydrated portland cement paste

A dynamic mechanical analysis (DMTA) technique was used to assess the mechanical performance of 1.4 nm tobermorite (T), jennite (J) and mixtures of tobermorite and jennite and tobermorite and calcium hydroxide (CH). A comparison of E′ (storage modulus) and tan∂ (internal friction) versus temperature curves for compacted solid bodies of these mineral systems with corresponding curves for cement paste hydrated for 2 month and 3 years (both referred to as ‘young’) and 45-year-old paste (referred to as ‘old’) was made. Original data was provided to assess the practical validity of the Richardson–Groves composition-based models for the C-S-H in cement paste. Differences in mechanical performance between the ‘young’ paste and the ‘old’ paste could be accounted for by application of a T/J dominant model (‘young’ paste) and a J–T/CH structural model with a minor amount of T (‘old paste’).

Impact of the structural state on the mechanical properties in a Zr–Co–Al bulk metallic glass

This paper reports on the use of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and nanoindentation technique to investigate atomic mobility in Zr56Co28Al16 bulk metallic glass in the as-cast state, after thermal annealing and after cold rolling. From the DMA results together with nanoindentation data point of view, the atomic mobility is significantly modified by the thermo-mechanical history. On the one hand, atomic mobility in bulk metallic glass is reduced after physical aging or crystallization. On the other hand, the atomic mobility in metallic glass is enhanced by cold rolling. To analyze the atomic mobility in amorphous materials, a physical theory is introduced. This model invoked the concept of quasi-point defects, which correspond to the density fluctuations in the glassy materials. Correlated movements of atoms are assisted by these quasi-point defects and the correlation factor χ is connected to the concentration of these “defects” in metallic glasses: (i) physical aging and crystallization decreases the parameter χ and (ii) the concentration of defects augments via plastic deformation (i.e. cold-rolling), suggesting that the correlation factor χ reflects the atomic mobility for glassy materials in a quantitative manner. This correlation bridges the gap between the mechanical properties on macroscopic scale and atomic mobility in microstructural regions in metallic glasses.

Sequential Thiol Click Reactions: Formation of Ternary Thiourethane/Thiol–Ene Networks with Enhanced Thermal and Mechanical Properties

We report the physical properties of thiol-ene networks modified with thiourethane or urethane linkages, either along the main chain or as a branched component in the network, respectively. Because of the robust and orthogonal nature of thiol-isocyanate and thiol-ene reactions, these networks can be formed in a two-step, one-pot synthesis. Resultant networks were characterized using dynamic mechanical analysis, mechanical testing and other complementary techniques. It was found that incorporating (thio)urethanes into the networks increased Tg, but also increased strain at break and toughness while decreasing cross-link density. The changes in physical properties are discussed in terms of a proposed dual network morphology. These facile modifications to thiol-ene networks demonstrate how molecular-level, nanoscale changes can have a profound influence on the macroscale properties through hierarchical development of network morphology.