سمینار عمومی
آب محصور شده در دو بعد(یخ دوبعدی؟)
سخنران: دکتر مهدی نیک‌عمل(رزومه)
زمان: سه شنبه ۱۹ آبان ۹۴ – ساعت ۱۵ الی ۱۶
مکان: دانشگاه شهید بهشتی، دانشکده فیزیک، تالار ابن هیثم
در ده های اخیر آب محصور شده بین صفحات آبگریز و ساختار فیزیکی آن به لحاظ نظری مورد مطالعه و علاقه بسیاری در علوم و مهندسی بوده است. اخیرا آزمایشی که تاییدی بر وجود فازی از آب که شبه دو بعدی و محصور شده بین دو صفحه آب گریز از جنس گرافن بوده است با همکاری تیم بین المللی گزارش شده است.
G. Algara- Siller et al. Nature 519, 443445 (2015)
در این سمینار به بیان این مساله و شبیه سازی های تمام اتمی می پردازیم که سعی دارند توجیه ای برای برخی جنبه های ناشناخته این پدیده ارائه دهند.
Quasi two-dimensional Ice
Abstract
The phase diagram of water and its extraordinary properties have been an interesting topic of research in biology, chemistry, and physics for many decades. Depending on the hydrophobic confinement width several two-dimensional ice structures can be formed. Different theoretical methods, e.g. molecular dynamics (MD) simulations using different force fields, density functional theory , and Monte Carlo simulations , have been used to study ice formation in the presence of high pressure. In particular, monolayer ice was proposed by Zangi and Mark [Phys. Rev. Lett. 91, 025502 (2003)] using MD simulations by applying a five site and tetrahedrally coordinated model, i.e. TIP5P. They confined water between two parallel plates and applied a high lateral pressure (Pl) of about 1 GPa and found a non-flat monolayer of ice.
Recently, it was found experimentally that confined water exists as a quasi two-dimensional layer with different properties than those of bulk water. Graphene, the two-dimensional allotrope of carbon , was used in a recent experiment to confine water into monolayer, bilayer and three layers. Using transmission electron microscopy(TEM) square lattice structures was observed [Nature 519, 443445 (2015)].
Water confined between two layers with separation of a few Angstrom forms layered two- dimensional ice structure. Using large scale molecular dynamics simulations with the adoptable ReaxFF interatomic potential we found that flat monolayer ice with a rhombic-square structure nucleates between graphene layers which is non-polar and non-ferroelectric. Two layers of water are found to crystallize into a square lattice close to the experimental found AA-stacking [G. Algara- Siller et al. Nature 519, 443445 (2015)]. Each layer has a net dipole moment which are in opposite direction. Bilayer ice is also non-polar and non-ferroelectric. For three layer ice we found that each layer has a crystal structure similar to monolayer ice.
