【Basic Knowledge of Glossary Definitions for “Polymers and Materials”-027】Glossary definitions related to polymers
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1. θ temperature: At a certain temperature, a polymer dissolves in a solvent when the attractive forces between its molecular chains are equal to the repulsive forces resulting from solvation and the exclusion volume effect; there are no long-range interactions, and the polymer is in a perturbation-free state with an exclusion volume of 0. The behavior of such a solution corresponds to that of an ideal solution. At this point, the degree of superactivity of the solvent is 0, and the solution is known as a θ solution. This temperature is referred to as the θ temperature. 2. Equivalent freely jointed chain: A chain composed of several chemical bonds can be regarded as a unit that can move independently; this unit is called a chain segment. When these chain segments are freely joined to each other and arranged in a random manner, it is referred to as an equivalent freely jointed chain. 3. Silver-stripe texture (body) – bundles or highly oriented polymers that connect the two silver-stripe surfaces.
How are the voids formed in silver streak texture?
The silver streak phenomenon is unique to polymers; under tensile stress, stress concentration occurs in certain weak areas of the material, leading to local plastic deformation and orientation, which results in the formation of fine grooves or \"cracks\" on the surface or within the material, perpendicular to the direction of the stress. The silver streaks are not empty; the density of the material forming these streaks is 50% of that of the main material, and its refractive index is also lower than that of the polymer matrix. As a result, total internal reflection occurs at the interface between the silver streaks and the main material, giving rise to those shiny silver-colored patterns. Heating annealing will eliminate silver streaks.
Hollowing out can cause stress whitening; hollowing out is not considered to be silver streaks, as there are micro-fibers connecting the parts within silver streaks, whereas the interior of hollow areas is empty. As strain increases, these hollow areas can merge and grow larger, thus forming silver streaks – which are likely the preliminary stage of such structures.
Not all silver-streaked bodies disappear through annealing, right? Are there any that break?