مطالعه اثر وزن مولکولی پلی دی ال-لاکتیک اسید بر پارامترهای حافظه شکلی به کمک شبیه‌سازی دینامیک مولکولی
محورهای موضوعی : فرآیندهای شبیه سازی
1 - دانشجوی مهندسی و علم مواد، دانشگاه خواجه نصیرالدین طوسی، تهران، ایران.
2 - دانشیار، دانشکده مهندسی و علم مواد، دانشگاه خواجه نصیرالدین طوسی، تهران، ایران.
کلید واژه: وزن مولکولی, شبیه‌سازی دینامیک مولکولی, پلی‌لاکتیک اسید, خاصیت حافظه شکلی, دمای انتقال شیشه‌ای,
چکیده مقاله :
پلیمرهای حافظه دار زیرمجموعه‌ای از مواد هوشمند هستند که می‌توانند شکل اولیه‌شان را بعد از تغییر شکل موقت بازیابی نمایند. این دسته از پلیمرها دارای کاربردهای فراوانی بوده و در سال های اخیر نظر بسیاری از صنایع (به‌خصوص پزشکی) را به خود جلب کرده‌اند. هدف اصلی این مطالعه، بررسی تأثیر وزن مولکولی بر پارامترهای مختلف حافظه شکلی پلیمر می‌باشد. علاوه بر این، مکانیزم های حاکم بر رفتار حافظه‌داری پلیمرها مورد مطالعه قرار می‌گیرد. محاسبه‌ی دمای انتقال شیشه ای و تأثیر این پارامتر بر رفتار حافظه شکلی پلیمر از دیگر اهداف این پژوهش می باشند. در این مطالعه، همه مدل‌ها با نرم‌افزار متریالز استودیو ساخته شده و تمامی شبیه‌سازی‌ها با استفاده از نرم‌افزار لمپس انجام شده است. طبق نتایج حاصل، دمای انتقال شیشه‌ای پلیمر با افزایش درجه پلیمریزاسیون افزایش می‌یابد. ادامه‌ی مطالعات در راستای دستیابی به ریزساختاری بهینه نشان داد که با افزایش وزن مولکولی از g/mol 36000 به g/mol108000، پارامتر تثبیت شکل از 90% به 94% افزایش می‌یابد. برخلاف تثبیت شکل، پارامتر بازیابی شکل روندی نزولی را با افزایش وزن مولکولی دنبال می‌کند. این روند کاهشی، ناشی از افزایش نسبت فاز ثابت به فاز بازگشت‌پذیر با افزایش وزن مولکولی پلیمر است.
Shape memory polymers are a subset of smart materials that can regain their original shape after a temporary deformation. In recent years, these polymers have been vastly utilized in many industries (especially biomedical). The main purpose of this study was to find the influence of the polymer molecular weight on the various shape memory parameters. Additionally, the mechanisms governing the shape memory behavior of polymers are thoroughly studied. Calculating the glass transition temperature and exploring its role on the shape memory behavior of polymeric materials are the other objectives of the current research. In this study, all models were built via Materials Studio and all the simulations were carried out using LAMMPS software. Based on the obtained results, the glass transition temperature of polymer increases with increasing the degree of polymerization. The attempts made to achieve an optimal microstructure revealed that the shape fixity parameter increases from 90% to 94% with increasing the molecular weight from 36000 g/mol to 108000 g/mol. In contrast to the shape fixity, the shape recovery parameter follows a descending trend with increasing the molecular weight. This is attributed to an increase in the ratio of the fixed phase to its reversible counterpart.
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