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研究生： 趙君聖
Chao, Chun-Sheng
論文名稱： Polymer Nucleation via Segmental Bundling
指導教授： 蘇安仲
Su, An-Chung
口試委員:
學位類別： 碩士
Master
系所名稱： 工學院 - 化學工程學系
Department of Chemical Engineering
論文出版年： 2009
畢業學年度： 97
語文別： 英文
論文頁數： 20
中文關鍵詞： 高分子結晶 、冷結晶 、成核 、束狀核 、奈米晶粒 、聚合
外文關鍵詞： polymer crystallization, cold crystallization, nucleation, bundle, nanograin, coalescence
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    • Many phenomena observed in nucleation and growth of polymer crystals from the melt state remained unexplained by classical theories in terms of chain length dependence and fractionation effects. Also unexplained are morphological features of nanometer-sized nodules in melt-crystallized polymer crystals. Here we develop a molecular theory in terms of nanograin nucleation as bundled segments; this may then serve as the basis to describe the growth and coalescence of polymer crystals during cold crystallization. In our model, each bundle is composed of a limited portion of segments which may not all belong to one polymer chain, forming tight and loose loops and ordered stems; this allows for quantitative analysis via standard statistical mechanics. The model predicts increased strains around each nanograin during growth and (even more strongly) upon coalescence, the size of nanograins is therefore predicted to be limited at a given temperature as experimentally observed. It also predicts an upper temperature above which the coalesced nanograins are no longer capable of further coalescence. Qualitatively, the strain field developed around a nanograin is expected to result in an effective exclusion zone (reminiscent of brushes around micelles) that explains the experimentally observed FCC-like arrangement of nanograins during polymer cold crystallization. With the main feature of the balance between crystallization and elastic forces duly considered, this single-chain model appears to serve well as a simplified basis for the description of polymer crystallization in terms of multi-chain nanograins as units of morphological development.

    Chapter I.Introduction I.1 Experimental Results I.1-1 Nanograins I.1-2 Observations by SAXS/WAXS/DSC I.2 Bundle model proposed by Allegra et al I.2-1 The morphology of bundles I.2-2 Derivations by Allegra et al Chapter II. Objectives and Approaches Chapter III. Theoretical Derivation III.1 Definition of reference state III.2 Free energy change upon formation of a simple bundle III.2-1 Basic assumptions III.2-2 Derivation of Qnei III.2-3 Free energy change upon formation of a simple bundle III.2-4. Some brief comments III.3 A simple bundle in the frozen reptation limit III.3-1 Basic assumptions III.3-2 Free energy changes in the frozen reptation limit III.3-3 Preferred geometric ratio of bundles III.3-4 Some brief comments III.4 Coalescence III.4-1 Strain energy and contact energy III.4-2 Free energy change upon coalescence III.4-3 Some brief comments IV. Simulation results IV.1 Polyethylene-like chains IV.2 Free energy changes of polyethylene-like chains in cold crystallization IV.2-1 Bundle formation IV.2-2 Frozen reptation cases IV.2-3 Coalescence IV.3 Disentanglement and reptation effects IV.3-1 Disentanglement via chain-end motion IV.3-2 Reptation V. Concluding remarks References and Notes Appendix

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