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Hoffman nucleation theory
Hoffman Nucleation Theory is a theory developed by John D. Hoffman and coworkers in the 1970s and 80's that attempts to describe the crystallization of a polymer in terms of the kinetics and thermodynamics of polymer surface nucleation. The theory introduces a model where a surface of completely crystalline polymer is created and introduces surface energy parameters to describe the process. Hoffman Nucleation Theory is more of a starting point for polymer crystallization theory and is better known for its fundamental roles in the Hoffman-Weeks Lamellar Thickening and Lauritzen-Hoffman Growth Theory.
==Polymer Morphology==
Polymers contain different morphologies on the molecular level which give rise to their macro properties. Long range disorder in the polymer chain is representative of amorphous solids, and the chain segments are considered amorphous. Long range polymer order is similar to crystalline material, and chain segments are considered crystalline.
The thermal characteristics of polymers are fundamentally different from those of most solid materials. Solid materials typically have one melting point, the Tm, above which the material loses internal molecular ordering and becomes a liquid. Polymers have both a melting temperature Tm and a glass transition temperature Tg. Above the Tm, the polymer chains lose their molecular ordering and exhibit reptation, or mobility. Below the Tm, but still above the Tg, the polymer chains lose some of their long-range mobility and can form either crystalline or amorphous regions. In this temperature range, as the temperature decreases, amorphous regions can transition into crystalline regions, causing the bulk material to become more crystalline over all. Below the Tg, molecular motion is stopped and the polymer chains are essentially frozen in place. In this temperature range, amorphous regions can no longer transition into crystalline regions, and the polymer as a whole has reached its maximum crystallinity.
Hoffman Nucleation Theory addresses the amorphous to crystalline polymer transition, and this transition can only occur in the temperature range between the Tm and Tg. The transition from an amorphous to a crystalline single polymer chain is related to the random thermal energy required to align and fold sections of the chain to form ordered regions titled lamellae, which are a subset of even bigger structures called spherulites. The Crystallization of polymers can be brought about by several different methods, and is a complex topic in itself.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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