Miscibility of Polymer Blends
Miscibility: Capability of a mixture to form a single phase over certain ranges of temperature, pressure, and composition.
The miscibility term describes the homogeneity of polymer mixtures at some temperatures. Miscibility can be influenced by various factors such as morphology, crystalline phase, intermolecular interaction, and reduction of surface tension.
Notes:
1. Whether or not a single phase exists depends on:
? The chemical structure
? Molar-mass distribution
? Molecular architecture of the components present.
2. The single phase in a mixture may be confirmed by:
? Light scattering
?X- ray scattering
? Neutron scattering
The miscibility of two polymers is depending on the specific interactions between polymer chains. This can be explained by the factor of entropy in the following equation, which represents the second law of thermodynamics.
?GM = ?HM - T?SM
where, ?G = change in free energy, ?H = change in enthalpy, ?S = change in entropy, T = absolute temperature.
For a homogeneous miscible blend the Gibbs free energy of mixing requires a negative value. For high molecular weight polymer blends, the gain in entropy is negligible. Hence, the free energy of mixing can only be negative if the heat of mixing is negative. This means that the mixing must be exothermic, which usually requires specific interactions between the blend components. These interactions may range from strongly ionic to weak and non-bonding, including hydrogen bonding, ion-dipole, dipole-dipole, and donor-acceptor interactions.
Based on the miscibility, three types of blends can be distinguished;
1- Completely miscible blends
2- Partially miscible blends
3- Fully immiscible blends
Partially miscible blends, in which a part of one blend component is dissolved in the other, exhibits normally good compatibility and fine phase morphologies. However, fully immiscible blends exhibit a coarse phase morphology having a sharp interface and a poor adhesion between both blend phases. This is the reason for often observed poor properties
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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