晶體成長與形貌調控之粗粒化蒙地卡羅模擬

Coarse-grained modeling of crystal growth and morphology control by Monte Carlo simulations

侯采怡(Tsai-Yi Hou)

指導教授 ： 陳振中

共同指導教授 ： 陸駿逸(Chun-Yi Lu)

國立臺灣大學/理學院/化學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.02744

摘要

氟基磷灰石(Fluorine-substituted hydroxyapatite, FHAp)為目前常見的生醫替代材料。因其結構與牙齒組成成分相似，且具備良好的生物相容性與穩定性高，故已廣泛被研究利用於硬骨組織之替代品中。在實驗中未添加任何添加物時，FHAp晶體形貌為長柱狀；當溶液中存在有機添加物時，依據不同有機添加物會使FHAp產生相對應之晶體形貌。然而目前研究對於有機與無機物是如何作用、磷灰石的成長機制的了解仍相當有限。若能了解礦物之結晶成長過程，對生物材料發展將是一大突破，藉此提升硬骨組織替代品之應用性。本研究中，我們藉由建立一個二維粗粒化晶體成長之模擬系統，模擬晶體形貌變化情形，以便更進一步了解晶體成長、結晶機制。
本研究中將晶體單元設置為長方形，每次在模擬系統中加入一顆晶體單元以表示晶體成長過程。晶體單元加入系統之位置與旋轉角度由蒙地卡羅方法決定。由Debye length與排斥體積影響系統Helmholtz自由能。晶體單元間排列情形受模擬系統中有無添加物存在影響。無添加物之模擬系統中可得到長方形之晶體形貌，與實驗所觀察到之長柱狀晶體形貌相似。為了解有機物影響晶體結晶之過程：在模擬中加入較小方形之添加物影響晶體單元堆疊，以模型系統模擬觀察晶體形貌，可觀察到與實驗結果相似之晶體形貌。且當添加物吸附在晶體單元上，會使晶體單元堆疊時有組態競爭關係，進而影響晶體形貌。然而對於添加物如何吸附在晶體單元特定表面、調控晶體形貌之過程，仍需更進一步的觀察、分析與模擬證實。

關鍵字

蒙地卡羅模擬 ； 氟基磷灰石

並列摘要

Fluorine-substituted hydroxyapatite (FHAp) has been one of the most studied biomaterials due to its high stability and excellent biocompatibility. Crystallites of FHAp formed in ambient solution usually have rod-like shape, while various other morphologies would be observed in the presence of organic additives. To date, the growth mechanism of FHAp crystallites is still unclear. Therefore, we aim to build a two-dimensional crystal-growth model that can mimic the crystal morphology of FHAp in order to provide some insights into the crystallization mechanism.
In our model the basic structural unit is added one at a time to imitate the crystal growth process. For each addition, the orientation and position of the crystal unit is sampled by the Monte Carlo method. The interaction energy among the crystal units includes various terms accounting for the effects of Debye length, excluded volume, and crystal dislocation. As a validation of the simulation codes, we successfully obtained rod-like morphology for the resultant crystal. To mimic the effect of organic additive on the crystallization process of FHAp, we have also repeat the simulation in the presence of a set of blocks with smaller size, which would disturb the orientation of the neighboring crystal units. Starting from some judiciously prepared initial configurations, we are able to reproduce certain morphology observed experimentally. We believe that the results are due to the configuration competition of different crystal-unit stackings. Additional morphology analyses are currently underway to narrow down the physical principles governing the morphology selection in the crystallization process.

並列關鍵字

Monte Carlo simulations ； Fluorine-substituted hydroxyapatite ； FHAp

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