Temperature and coefficient of thermal expansion

The nanodispersion of Si and O throughout the polyimide polymer matrix leads to the formation of a protective silica layer on the polyimide surface when the material reacts with AO [15]. Our data indicates that upon AO exposure, the organic material in the polymer surface erodes, while the atomic oxygen reacts with the nanodispersed POSS to form a silica layer. Therefore, when POSS is copolymerized to form POSS-PI, it imparts remarkable AO resistance, and does so with minor effects in the storage modulus, glass transition temperature, and coefficient of thermal expansion [15]. 

Properties relating to performance of completely cured adhesive were determined by mechanical spectroscopy and thermomechanical analysis. Measurement of glass transition temperature and coefficient of thermal expansion was obtained from temperature scanning. 

Glass Transition Temperature and Coefficients of Thermal Expansion... 

Thermal ejfects, such as extreme heat or cold, or rapid changes in temperature, can cause temporary or permanent changes in the physical characteristics of optical materials. The critical material characteristics are melting temperature and coefficient of thermal expansion. For example, thermal expansion of a material can be particularly important in applications in which the optical component is subjected to localized heating, caused by high laser light power. As a result, non-uniform material density introduces distortion of the beam paths (e.g. thermal leasing). 

Where mo and m are the weight of bobs in air and high temperamre molten slag, respectively. The weight of bob was measured using an electric balance. V is the volume of the bob at the determined temperature, which was calculated from the volume at room temperature and coefficient of thermal expansion of molybdenum. 

Singh, L., Ludovice, P.J., Hendaxon, C.L. Influence of molecular weight and film thickness on the glass transition temperature and coefficient of thermal expansion of supported ultrathin polymer films. Thin Solid Films 449(12), 231-241 (2004)... 

There are two main types of mechanical thermal analysis instruments, namely thermomechanical analysis and dynamic mechanical analysis, TMA and DMA respectively. The first is a simple technique that has been available for many years and simply records change of sample length as a function of changing temperature. Despite this simplicity it enables the measurement of phase transitions, glass transition temperature and coefficient of thermal expansion. It has the advantage of being simple to use and perhaps more importantly the interpretation of results is quite straightforward. 

Material Properties. The properties of materials are ultimately deterrnined by the physics of their microstmcture. For engineering appHcations, however, materials are characterized by various macroscopic physical and mechanical properties. Among the former, the thermal properties of materials, including melting temperature, thermal conductivity, specific heat, and coefficient of thermal expansion, are particularly important in welding. 

Shrinkage and coefficient of thermal expansion are those of semi-crystalline polymers, that is to say, rather high. The absorption and swelling by moisture exposure are high (see Figure 4.54). Creep depends on reinforcement, moisture content and temperature. 

Alterations by moisture exposure are weak shrinkage and coefficients of thermal expansion are low, as for other amorphous polymers creep resistance is rather good at room temperature. 

Crosslinked low-density polyethylene foams with a closedcell structure were investigated using differential scanning calorimetry, scanning electron microscopy, density, and thermal expansion measurements. At room temperature, the coefficient of thermal expansion decreased as the density increased. This was attributed to the influence of gas expansion within the cells. At a given material density, the expansion increased as the cell size became smaller. At higher temperatures, the relationship between thermal expansion and density was more complex, due to physical transitions in the matrix polymer. Materials with high density and thick cell walls were concluded to be the best for low expansion applications. 16 refs. 

It should be remembered that density refers to the weight per unit volume of product and specific gravity is the ratio of the density of a product to that of water at some specified temperature. The coefficient of thermal expansion is the effect of temperature on density, and each substance has its own coefficient. Thus, when speaking of specific gravity, it is desirable to state both the sample and water temperatures frequently, they are the same. 

For the calculation of the thermal shock-induced stresses, we consider the plate shown in Fig. 15.1 with Young s modulus E, Poisson s ratio v, and coefficient of thermal expansion (CTE) a, initially held at temperature /j. If the top and bottom surfaces of the plate come into sudden contact with a medium of lower temperature T they will cool and try to contract. However, the inner part of the plate initially remains at a higher temperature, which hinders the contraction of the outer surfaces, giving rise to tensile surface stresses balanced by a distribution of compressive stresses at the interior. By contrast, if the surfaces come into contact with a medium of higher temperature Tm, they will try to expand. As the interior will be at a lower temperature, it will constrain the expansion of the surfaces, thus giving rise to compressive surface stresses balanced by a distribution of tensile stresses at the interior. 

Fractional Free Volume and Coefficient of Thermal Expansion. The shift constants c and C2 from the WLF equation are not only fitting parameters that describe the frequency-temperature relation of a given polymer, but they are also related to chemical structure. Ferry has shown (6) that these constants can be related to the fractional free volume and coefficient of thermal expansion of the free volume, which have physical meaning in terms of the polymer structure. One can define the free volume at the glass transition divided by the total volume as fg and the coefficient of thermal expansion of... 

The coefficient of thermal expansion of glass is a most important physical property. It is defined, for all solids, as the increase in length per unit length per degree rise in temperature. The coefficient of thermal expansion is a ratio and so has no units. It is, however, necessary to quote the temperamre scale used. 

Experimental results and modeling strategy for the determination of stresses in thermosets used in microelectronics are presented. The bending beam technique for in situ stress measurement is particularly emphasized. This technique is here extended to determine the glass transition temperature, Tg, and the product of the elastic modulus and coefficient of thermal expansion,... 

Correlations for the key volumetric properties (the van der Waals volume and the molar volumes, densities and coefficients of thermal expansion of amorphous polymers) will be developed in Chapter 3 followed by discussions of pressure-volume-temperature relationships and of the effects of crystallinity on the density. 

Values of the density, isothermal compressibility, and coefficient of thermal expansion for some common fluids are listed in App. A. 10. Notice that for most fluids the effect of a change in temperaturej is more significant than the effect of a change in pressure. Normally a temperature decrease of 1°F will have the same effect as a pressure increase of 100 psi. 

Thermomechanical Analysis. A thermomechanical analyzer (Perkln-Elmer TMS 2) was used to measure glass transition temperature (Tg) and coefficient of thermal expansion (a ) of completely cured samples In the penetration and expansion modes respectively. Experimental conditions are listed In Table I. 

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