Thermomechanical Properties Of Polymers Research Articles

Thermomechanical Properties of Polymers for Use in Superconducting Magnets

The coefficient of thermal expansion (CTE) and the thermomechanical properties of the polymers used in superconducting magnets need to be known in order to predict their stress state under the different magnet assembly and operating conditions. We have measured Young's moduli of typically used polymers during in situ heat cycles with the dynamic resonance method. The dynamic test results are compared with Young's moduli determined from quasi-static stress-strain measurements at room temperature, 77 K and 4.2 K. A moderate elastic anisotropy is found for the fiber reinforced polymers. CTEs are compared based on dilation experiments. The CTEs of the fiber reinforced polymers studied are similar to those of copper or steel. In contrast, the pure resins exhibit relatively larger CTEs.

Влияние природы эпоксиизоцианатных связующих при их полимеризации на физико-механические и термомеханические свойства полимеров и композитов

Влияние природы эпоксиизоцианатных связующих при их полимеризации на физико-механические и термомеханические свойства полимеров и композитов

Metal–polymer and polymer–polymer microcantilevers: promising alternative to Si-based MEMS

Polymers are very attractive as thin films in emerging reel-to-reel manufacturing or as spin coated from liquid form in a quick and low cost process in standard microfabrication processes. There is a wide selection of materials available with many different thermal, electrical, and mechanical properties. With continuous growth in consumer electronics and sensors sectors, the range of potential application fields is further diversifying and integration of MEMS modules, as well as delivering IC functionality in thin foil-like packaging with proven reliability and reduction in cost is increasingly required. Furthermore, increased volume and decentralisation of testing within medical diagnostics field worldwide (IVD Point of Care and Patient Self Testing trends) require low cost solutions for disposable test cartridges and other supporting consumables. In majority of the emerging medical applications, integrated, low cost sensors need to operate in liquid environment, often rendering the use of standard Si-based solutions inadequate and costly. Polymer-based microcantilevers, realised by standard surface microfabrication techniques, were chosen for this study as the alternative approach to Si-based MEMS. Cantilevers are well understood microstructures and so provide an excellent vehicle for assessing both thermo-mechanical properties of polymers as MEMS materials and their potential for die-level packaging and integration into miniaturized systems. Due to the nature of processes involved and their thermal budget, substitution of Si substrate with e.g. flexible substrates or polymer films is foreseen in the near future. Fabricated cantilever beams consist of various combinations of thin metal/polymer and polymer/polymer films. Polyimides, as structural material, have been selected for this study due to inherently good mechanical properties, good chemical resistance, low dielectric constant and high thermal stability.

Prediction of structural and thermomechanical properties of polymers from multiscale simulations

We report mesoscale simulations of polymer melts and crosslinked polymer networks by using realistic coarse-grained (CG) models that are developed from atomistic simulations of polymer melts.

Glossary of Terms Relating to Thermal and Thermomechanical Properties of Polymers (IUPAC Recommendations 2013)

Article Glossary of Terms Relating to Thermal and Thermomechanical Properties of Polymers (IUPAC Recommendations 2013) was published on July 1, 2013 in the journal Chemistry International (volume 35, issue 4).

Nanomechanical thermal analysis of the effects of physical aging on glass transitions in PS/PMMA blend and PS-PMMA diblock copolymers

The effects of physical aging on the thermomechanical properties of polymers were investigated using silicon microcantilever deflection measurements. Polystyrene (PS), polymethylmethacrylate (PMMA), a PS/PMMA blend, or PS-PMMA diblock copolymer were applied to one side of a microcantilever, and the temperature-dependent thermal stress in the polymers was measured. A maximum compressive stress peak was observed for the PS- and PMMA-coated cantilevers during heating but not during cooling, which produced hysteresis. Physical aging of the polymers was found to contribute to the development of the hysteresis properties. The two distinct maximum compressive stress peaks in the PS/PMMA blend coincided with the temperatures at which the pure PS and PMMA peaks occurred, indicating that the glass transitions of each polymer were independent. In contrast, the thermal stress profiles of the PS-PMMA copolymer exhibited a single broad peak at a position intermediate between the peak positions of the pure PS and PMMA, indicating that the PS and PMMA polymers interacted during the glass transition.

A thermomechanical analysis based on a contact temperature measurement

Modern headlamps are made from thermoplasts, which are very convenient materials for headlamp design. However, the poor thermomechanical properties of polymers can cause deformations, problems with the photometric properties, and sealing difficulties. In order to predict these deformations, standard methods were used and combined in a new approach for a quick and efficient evaluation of such headlamps. Thin-film resistance temperature detectors were employed at significant points on the headlamp housing to measure the temperature. The results were then used to determine a three-dimensional temperature field for the headlamp housing. This temperature field was subsequently used in a finite element method analysis to determine the deformations in the housing of the headlamp.

Glossary of Thermal and Thermomechanical Properties of Polymers

Glossary of Thermal and Thermomechanical Properties of Polymers

Indentation testing of polystyrene through the glass transition

The determination of the thermomechanical properties of polymers is vitally important in their characterization. Indentation methods are especially attractive for polymer coatings, since the coatings do not need to be removed from the substrate. In this study, bulk polystyrene has been analysed by conventional cantilever testing and by spherical indentation at different temperatures. It was found that reasonable estimates of the glassy modulus, rubbery modulus and glass transition temperature could be obtained from simple load/unload indentation.

Thermomechanical Properties of Polymers at High Rates of Strain

The objective of this project was to develop a suitable testing technique which will allow the measurement of the bulk surface temperature of a specimen during high strain-rate compression testing. A fast response infra-red radiometer was developed which has the capability of measuring bulk surface temperature changes with an estimated accuracy of ±2°C and with a response time of 1.4μs. The radiometer is capable of measuring temperature changes above 20°C, when the signal-to-noise ratio becomes greater than 1. The properties of polymeric materials are extremely temperature sensitive, particularly when the glass transition temperature is approached. Models such as Eyring predict the yield of a polymer at constant temperature; the yield stress being unaffected by temperature rises. Temperature as well as mechanical data will allow models to be revised to include strain and dynamic temperature terms to predict the flow under adiabatic conditions. Strain-rates of ca. 2500s -1 were achieved when testing specimens and this rate was obtained using a split Hopkinson pressure bar. A substantial number of preliminary tests were conducted in order to obtain a suitable specimen size which was then used in the temperature measurement process. Quasistatic, intermediate and high strain-rate tests were performed; the last utilised the radiometer for temperature measurement. An Eyring plot was constructed from which fundamental values for activation volumes and enthalpies were obtained. Full descriptions of the testing techniques used have been included and a brief photoelastic analysis has been carried out on a partially deformed specimen which shows molecular alignment.

Stress measurement as a new technique for determining glass transition temperatures and other thermomechanical properties of polymers

Some of the most important properties of polymers include the glass transition temperature (T g), melting temperature (Tin), stress relaxation rate, coefficient of thermal expansion, biaxial elastic modulus and crystallization temperature. A method is presented here in which measurement of stress in a polymer film allows the experimenter to determine all of these properties. Growing interest in thin polymer films [1], which do not lend themselves well to traditional measurement techniques, has motivated this work. Poly(methyl methacrylate) (PMMA), a common amorphous commercial polymer, was tested for some of these properties to demonstrate the method. The values obtained for the properties studied were in excellent agreement with published results. If an initially unstressed film adhering to a substrate is subjected to a change in temperature, the difference in thermal expansion of the two materials will induce stress in the film. The amount of thermally generated stress can be calculated [2] as

Certain Regularities in Three-Dimensional Polycondensation of Oligomeric Compounds

Abstract The authors have studied certain regularities in the three-dimensional polycondensation of oligomeric ether acids with the common formula C[CH2OC(O)(CH2)nCOOH]4, where n = 2, 4, 8, with tri-and tetratomic silicoorganic alcohols, various glycols, and diamines. Problems have been considered relating to gel formation in systems containing oligomeric and monomeric branching units. The parameters obtained, which characterize gel formation in oligomeric systems, were compared with the values calculated in conformity with Flory's theory. Research was also carried out on the kinetic regularities of three-dimensional condensations of oligomers, and constants were calculated for the rates of esterifications and the rates of formation of the gel fraction. The thermomechanical properties of polymers were investigated during the condensation processes.