Application Of Dynamic Mechanical Analysis Research Articles

Advancing the dynamic mechanical analysis of organic semiconductor materials.

Dynamic mechanical analysis (DMA) is a powerful technique for characterizing the mechanical properties of a wide range of materials. However, the importance of DMA in studying organic/polymer semiconductors has not been fully appreciated. In this Highlight, we explore recent advancements in the use of DMA in understanding the viscoelastic and mechanical properties and thermal transitions of organic semiconductor materials. In particular, the insights gained from DMA can serve as new guides for the device optimisation of organic solar cells towards stable operation. Furthermore, we present key findings, challenges, and future directions to advance the application of DMA in organic electronics.

The Development of a Novel Thin Film Test Method to Evaluate the Rain Erosion Resistance of Polyaspartate-Based Leading Edge Protection Coatings

The relationship between the bulk thermomechanical properties and rain erosion resistance of development polyaspartate-based coatings as candidate leading edge protection (LEP) materials for wind turbine blades is investigated by the combined application of dynamic mechanical analysis (DMA) and rain erosion testing (RET) within a novel test method (DMA+RET). This method introduces the use of DMA+RET to both monitor the change in thermomechanical properties with respect to raindrop impact and subsequently rationalise differences in rain erosion resistance between coating formulations of comparable composition. The application of this combined process has demonstrated the importance of relatively high viscoelastic moduli at increased strain rates and creep recovery after RET as key material properties to be considered for LEP material development, whereas previous research presented in the scientific literature has primarily focussed on the use of routine characterisation procedures by tensile testing or stand-alone DMA to evaluate coating formulations prior to rain erosion testing. This journal article therefore presents a novel method to evaluate key material properties relevant to rain erosion resistance before and after subjection to raindrop impact using standard ASTM G73 RET equipment. The test method is demonstrated on a novel polyaspartate-based coating, PA-U, that exhibits notable rain erosion resistance in comparison to commercial LEP products. PA-U exhibited negligible mass loss after 30 h of rain erosion testing and favourable thermomechanical properties (E″ = 35 MPa at critical strain; equilibrium recoverable compliance of 0.05 MPa−1) in comparison to alternative formulations.

Application of dynamic mechanical analysis and linear dilatometry in the study of the mechanisms of climatic aging of transparent thermoplastics in natural conditions

The volume, assortment and application areas of transparent thermoplastics, including as construction materials in modern hightech products and devices, are expanding every year. At the same time, parts of products made from these materials are one of the most sensitive elements of the product exposed to the environment. Assessment of material performance under the influence of environmental factors is carried out by conducting tests in full-scale and laboratory conditions. The use of physical research methods makes it possible to understand the mechanism and kinetics of the aging processes of thermoplastic materials and to increase the reliability of predicting performance under natural conditions. In addition, the use of the proposed research methods makes it possible to more reliably evaluate and, if necessary, correct the methods of accelerated climatic tests when comparing the aging mechanisms in natural and artificial conditions.

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.

Use of dynamic mechanical analysis (DMA) to determine critical transition temperatures in frozen biomaterials intended for lyophilization

Dynamic mechanical analysis is widely used to determine glass transitions in solid state materials. However, here we demonstrate the application of DMA for the determination of glass transitions (Tg ’) in the frozen liquid state by means of a steel sample pocket. The use of the pocket allows frozen material to be analysed and glass transition events demonstrated. In addition, it allows weak glass transitions to be detected clearly in some complex formulations where they can be obscured by eutectic and other strong thermal events when other methods such as DSC or DTA are used. Classical excipients (trehalose, lactose, dextran) were analysed and shown to give reproducible Tg ’ values, though with values slightly higher than those obtained by DSC. Finally, several complex real biological materials, typical of those encountered when freeze drying biological and biopharmaceutical materials, were analysed and the potential value of DMA demonstrated to determine the relevant glass transition temperatures for use in cryobiology and freeze drying.

Análise dinâmico-mecânica: aplicações em filmes comestíveis

Edible films are thin materials based on biopolymers and food additives. The aim of this work is a review on the application of dynamic mechanical analysis in edible film technology. After a brief review of the linear visco-elasticity theory, a description of some practical aspects related to dynamic mechanical analysis, such as sample fixation and sample dehydration during analysis and types and modes of tests are presented. Thus, the use of temperature scanning analysis for glass transition and for plasticizer-biopolymer compatibility studies and frequency scanning tests, less common in edible film technology, are critically reviewed.

Application of Dynamic Mechanical Analysis (DMA) to the determination of the mechanical properties of coated pellets

Pellets containing a model drug, paracetamol, and microcrystalline cellulose (MCC) were designed to vary their mechanical properties by the incorporation of lactose, glyceryl monostearate (GMS), ethanol, or glycerol, and were produced by the process of extrusion and spheronization. The pellets were coated with an aqueous dispersion of ethyl cellulose (Surelease ®) to different levels of weight gain (5, 10, and 20%). The tensile strength, deformability, linear strain, elastic modulus, and shear strength of the coated and uncoated pellets were determined by conventional techniques, which are obtained from diametral compression test of individual pellets and compaction of a bed of pellets. Dynamic Mechanical Analysis (DMA) was performed on single pellets to determine the storage modulus and phase angle of the coated pellets. This work demonstrated that the coating film affected the mechanical properties of the pellets differently depending on the properties of the core pellets. Analysis of variance established a significant increase in the strength of the soft GMS- or glycerol-containing pellets with coating, while the effect of the coating material was not significant with respect to the elastic modulus, storage modulus, and phase angle of such pellets. The effects of the coating material on the elastic modulus, deformability, storage modulus, and phase angle of the rigid lactose-containing pellets were significant. The sinusoidal stress–relaxation cycle of the DMA illustrated the increase in the viscoelasticity of all the pellets after coating. Finally, the work demonstrate the advantages of DMA in determining the reversible or dissipated energy by means of storage modulus or phase angle when compared with the irreversible structural destruction of the pellets by conventional techniques.

Application of dynamic mechanical analysis (DMA) to determine the mechanical properties of pellets.

Pellets of a wide range of mechanical properties were produced by the process of extrusion and spheronisation using various formulation factors. A range of mechanical properties from a simple fracture load to detailed load/displacement curves obtained when pellets were subjected to diametral compression test and a bed of pellets was compacted, were used to provide measure of tensile strength, deformability, linear strain, elastic modulus, yield and shear strength. Such conventional techniques resulted in irreversible damage to the structure of the pellets and were unable to establish the viscoelastic properties of the pellets. The application of the dynamic mechanical analysis (DMA), however, allowed the determination of (1) an accurate Young's modulus of elasticity, which was found to be between 8.4 and 24-fold higher than that determined from the diametral compression test, (2) the presence of a reversible elastic deformation even after the yield point in terms of storage modulus and (3) a change in the values of the phase angle, which illustrates the increase in viscoelasticity of the pellets formed with ethanol, glyceryl monostearate (GMS) or glycerol, while a decrease in viscoelasticity with the incorporation of lactose into the microcrystalline cellulose (MCC) pellets. This work further demonstrated that the only feasible technique for determining the elastic and plastic deformability of the pellets is the one which subjects the specimen to stress/relaxation cycles and can determine the dissipated energy in terms of loss modulus or phase angle, and that is DMA.

The formation of colonic digestible films of amylose and ethylcellulose from aqueous dispersions at temperatures below 37°C

The film forming properties of a commercial aqueous ethylcellulose dispersion (Surelease) mixed with a range of ratios of an amylose/butanol complex in the presence of a range of concentrations of a plasticiser has been studied by measuring the minimum film forming temperature (MFFT). Contrary to what was to be anticipated from the literature, it was found that an additional 4% of the plasticiser (dibutyl sebacate), normally present in the standard formulation of the ethyl cellulose dispersion, was sufficient to lower the MFFT to allow the formation of films at 35°C. This was confirmed by assessment of the glass transition temperature of free films prepared by casting and drying at 35°C by the application of dynamic mechanical analysis. This technique also demonstrated that the ethylycellulose and the amylose were not miscible. The ability of faecal slurry to digest the films formed at low temperatures was confirmed by the use of a batch fermenter. The extent of digestion was directly related to the amylose content of the films, ensuring the potential to provide films, which could function as colon specific coatings.

Two‐dimensional step‐scan FTIR: a tool to unravel the OH‐valency‐range of the spectrum of Cellulose I

This article presents the results of the first application of dynamic mechanical analysis (DMA) coupled with 2D step‐scan Fourier transform infrared (FTIR) spectroscopy, to cellulose. It is demonstrated that the broad hydroxyl infrared absorption band between 3700 and 3000 cm−1 in the cellulose infrared spectra could be separated into distinct bands by this dynamic rheo‐optical investigation using FTIR‐spectroscopy as detecting system. The responses of the OH‐groups to an external perturbation were recorded as in‐phase and out‐of‐phase spectra. The cross correlation of these spectra gave the 2D synchronous and asynchronous plots, which showed clearly separated bands in the OH‐vibration range and the relation of the OH‐groups to each other. It is demonstrated that it is possible to establish relations between the OH‐bands and the cellulose structure.

Mechanical performance of polyurethane ureteral stents in vitro and ex vivo

A serious problem associated with the use of ureteral stents is fracture in situ. Following clinical observations of fracture of polyurethane stents in vivo, this study examined the mechanical properties of 17 polyurethane stents (double-J containing drainage holes) retrieved from patients over a 24-week period of insertion. In addition, stents were immersed in human and artificial urine in an in vitro model at 37 °C to determine their general propensity to fracture. Mechanical properties of ureteral stents were examined using the standard ASTM D-412 tensile test and by the novel application of dynamic mechanical analysis (DMA). The ultimate tensile strength and elongation at break (but not the Young's modulus) of unused polyurethane stent sections containing side-drainage holes were greater than stent sections devoid of side-drainage holes. No correlations were observed between increased or decreased Young's modulus, ultimate tensile strength or elongation at break of polyurethane stents and their time of immersion in either human urine or artificial urine in simulated upper urinary tract conditions of 37 °C and 5% CO 2. Similarly, no correlations were observed between Young's modulus, ultimate tensile strength or elongation of polyurethane stents and stent dwell time in situ. DMA of retrieved stents revealed that their tan δ value and storage modulus did not differ significantly from unused stents following dwell times in situ of up to 24 weeks. No changes in the glass transition temperatures were observed in retrieved stents. Although patient variation was observed, the results indicate that the polyurethane stents examined in vitro and following removal from patients did not exhibit any greater propensity to fracture than their unused counterparts. Fracture of retrieved polyurethane stents, arising in vivo and also during subsequent tensile testing, was observed to occur along the drainage holes, suggesting that elimination of these holes will reduce the incidence of polyurethane ureteral stent fracture in use.

Application of dynamic mechanical analysis for the study of the interfacial region in carbon fiber/epoxy composite materials

AbstractThe application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.

Theory and application of dynamic mechanical thermal analysis

The dynamic mechanical technique of applying a sinusoidally oscillating stress to a material and the analysis of the resultant strain is now widely practised. The basic theory underlying this method is discussed and the application of dynamic mechanical analysis (DMTA) to a wide range of materials ranging from solid composites through to polymer melts is considered. Data may be collected under computer control in the temperature plane; in the frequency plane at a set of preselected temperatures; or isothermally as a function of time. Thus, the dynamic mechanical technique has been applied to a wide variety of different systems. Examples which are considered in this paper include; The study of polymer blends and phase morphology; The effect of orientation on the mechanical properties of solid polymers; The deviation of master curves using the time-temperature superposition principle; Investigation of the cure properties of thermosetting resins and fibre reinforced composites and finally, the study of melting semi-crystalline polymers. This list of applications is by no means exhaustive but will serve to illustrate the flexibility of this method for materials characterisation.