Glass transition temperature parameters affecting

The glass transition temperature can be measured in a variety of ways (DSC, dynamic mechanical analysis, thermal mechanical analysis), not all of which yield the same value [3,8,9,24,29], This results from the kinetic, rather than thermodynamic, nature of the transition [40,41], Tg depends on the heating rate of the experiment and the thermal history of the specimen [3,8,9], Also, any molecular parameter affecting chain mobility effects the T% [3,8], Table 16.2 provides a summary of molecular parameters that influence the T. From the point of view of DSC measurements, an increase in heat capacity occurs at Tg due to the onset of these additional molecular motions, which shows up as an endothermic response with a shift in the baseline [9,24]. 

Photophysical and photochemical processes in polymer solids are extremely important in that they relate directly to the functions of photoresists and other molecular functional devices. These processes are influenced significantly by the molecular structure of the polymer matrix and its motion. As already discussed in Section 2.1.3, the reactivity of functional groups in polymer solids changes markedly at the glass transition temperature (Tg) of the matrix. Their reactivity is also affected by the / transition temperature, Tp, which corresponds to the relaxation of local motion modes of the main chain and by Ty, the temperature corresponding to the onset of side chain rotation. These transition temperatures can be detected also by other experimental techniques, such as dynamic viscoelasticity measurements, dielectric dispersion, and NMR spectroscopy. The values obtained depend on the frequency of the measurement. Since photochemical and photophysical parameters are measures of the motion of a polymer chain, they provide means to estimate experimentally the values of Tp and Tr. In homogeneous solids, reactions are related to the free volume distribution. This important theoretical parameter can be discussed on the basis of photophysical processes. 

The glass transition temperature (Tg) of cellulose reinforced composites is an important parameter which influences different properties of the resulting composite such as mechanical behavior, matrix chains dynamics and swelling behavior. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are used to evaluate the Tg value of cellulose nanocomposites. In some cases, the addition of cellulose nanocrystals into polymer matrices does not seem to affect the... 

The glass-transition temperature, melting point, heat distortion temperature, thermal degradation temperature, ete. are important parameters affecting the application and processing of semicrystalline polymer materials. These thermal parameters can be obtained via differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, etc. 

Glass transition and melting behavior Glass transition temperature Tg is an important parameter used for identification of plastics. The Tg value is the temperature at which amorphous polymers change from hard to soft. The concentration of crystalline regions in amorphous (semicrystalline) polymers affects the rigidity of the polymer. The crystalline melting... 

The viscoelastic (see Viscoelasticity) nature of the adhesives means that all joints are affected by the rate and temperature of the test. A key parameter in the testing of such joints is the Glass transition temperature of the adhesive. When the joints are tested below this temperature, the adhesive will be a low-strain rigid material above this temperature, it will adopt a more rubber-like nature. 

Nickel acetate trihydrate pendant groups in the para-position of the pyridine ring could affect the glass transition temperature of P4VP. If this type of coordination occms for nickel acetate concentrations below 35 mol%, then this effect is contained in the parameter p. 

As biological systems have always been an inspiration for scientists, intracellular compartments (such as lysosomes or mitochondria) also have their artificial equivalents in polymer vesicles, called polymersomes. Polymersomes are spherical compartments with a bi- or monolayer membrane, generated by self-assembly of di- or triamphiphilic block copolymers in diluted aqueous conditions. To favor the formation of structures such as polymersomes, it is necessary to have a hydrophilic fraction of the copolymer mass of 25-40%, and polymer concentration above the critical micellar concentration. Other parameters that affect the self-assembly process, and therefore the final architecture of the polymer supramolecular assemblies, are the molecular weight of the copolymer (Af ), block lengths, solubility, and glass transition temperature (Tg) [21,22], The relative mass or volume fraction of each block is a key parameter in the formation of a self-assembled structure with a certain membrane curvature, and ultimately, with a specific architecture. The of the copolymer (and thus the block lengths) dictates the membrane thickness and polymersome properties, such as membrane fluidity, stabihty, and permeabihty [21,74],... 

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