Introduction:
? Thermodynamics is derived from two words: ‘Thermo’ which means ‘Heat energy’ and ‘Dynamics’ which means ‘conversion’ or ‘transformation’
Performance of polymer blends depends on the properties of polymeric components, as well as how they are arranged in space. The spatial arrangement is controlled by the thermodynamics and flow-imposed morphology.
Determination of thermodynamic properties such as the phase diagram or the Huggins-Flory binary interaction parameter, ?12, is difficult.
The difficulties originate in high viscosity of macromolecular species, thus slow diffusion toward the equilibrium, heat generation when mixing and dangers of degradation.
For these reasons, there is a tendency to use low molecular homologues or solutions. Furthermore, it is an accepted practice to purify the polymers before measuring their thermodynamic properties. However, the industrial polymers have high molecular weights, and are modified by incorporating low molecular weight additives. Furthermore they are processed under high flow rates and stresses that preclude the possibility of thermodynamic equilibrium. For these and other reasons, a direct application of the laboratory data to industrial systems may not always
be advisable.
Another difficulty originates in the lack of theories able to predict variation of thermodynamic properties for commercially attractive systems with modifiers.
Polymeric Liquid Mixtures:
Polymeric liquid mixtures are conveniently divided into:
1- Solutions (containing a low molecular weight liquid)
2- Blends(containing only macromolecular species)
Polymer Solutions:
?Concentration of polymer solution is given either as:
- volume fraction, ?i, or
- wt/vol concentration, c (g/100 mL) ,(for dilute solutions)
?In solutions, the solubility originates mainly from the entropic effects(there is a large number of possible arrangements of macromolecules in space containing small solvent molecules)
?Traditionally, solutions have been used to characterize the polymer:
to measure its molecular weight averages, e.g., number, weight and z- average: Mn, Mw, and Mz, or the size of its macromolecular coil
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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