Phase Transitions of Weakly Physisorbed Films

小科尔9705270 这个重点研究小组资助支持弱物理吸附薄膜相变的合作理论实验研究。调查的重点是薄膜的惰性气体氦，包括混合物的同位素质量4和3，吸附在基板上，提供最弱的可能的约束力。 这样的底物包括碱金属和分子氢。这种选择是为了更清楚地显示在亚单层二维膜中的超流起始和相分离领域的新行为; 在 润湿行为的变化;以及在吸附很厚的 薄膜. 在所有情况下，研究都是合作的，涉及 实验之间紧密耦合， 理论， 和仿真实验方法包括介电常数、体积法、毛细管上升法、扭振法、热容法和石英微天平法。该理论将涉及电影动力学，统计力学，货车德瓦尔斯力，和计算的潜力。巨正则模拟将主要针对润湿问题。 %此重点研究小组赠款支持气体分子薄膜粘附到几种类型的基板的合作研究，对分子润湿表面的能力感兴趣。正在研究的气体是相对惰性的稀有气体，特别是质量为3和4原子的氦原子。 质量单位，研究是在 出来 在接近绝对零度的温度下，氦原子可以以几种不同类型的超流体状态出现。 超流体状态是指在上述情况下，氦的运动完全不受其与周围容器或基底的相互作用的阻碍。例如，如果液体超流体旋转（就像玻璃杯中的水旋转），旋转运动将永远持续下去，这种效应是陀螺仪的基础，它可以检测到极慢的旋转。拟议的研究将澄清衬底对超流体行为首次发生时的温度的影响，并将这些行为探测到平均厚度小于一个原子层的层。结果可能会导致新的见解有用的各种情况下，如化学工程，聚合物科学，催化，和其他润湿现象是重要的。结果也将有助于一般知识的情况下，单层和亚单层覆盖表面的原子和分子发生。 国家的科学和工程研究基地将从该计划的研究生培训中受益匪浅，除了可能在单层润湿和相变方面取得的发现之外。 ***

9705270 Cole This Focused Research Group grant supports a collaborative theoretical-experimental study of phase transitions of weakly physisorbed films. The investigations focus on films of the noble gas helium, including mixtures of the isotopes of masses four and three, adsorbed on the substrates which offer the weakest possible binding. Such substrates include alkali metals and molecular hydrogen. This choice is made to more clearly display novel behaviors in the areas of superfluid onset and phase separation in submonolayer two dimensional films; in the varieties of wetting behavior; and in the adsorption of very thick films. In all cases the research is collaborative, involving close coupling between experiment, theory, and simulation. The experimental methods include dielectric constant, volumetric, capillary rise, torsional oscillator, heat capacity and quartz microbalance measurements. The theory will deal with film dynamics, statistical mechanics, van der Waals forces, and calculation of potentials. Grand canonical simulations will be directed primarily toward the wetting problem. %%% This Focused Research Group grant supports a collaborative study of the adherence of thin films of gas molecules to several types of substrates, with an interest in the ability of the molecules to wet the surfaces. The gases under study are relatively inert noble gases, specifically helium atoms of masses three and four atomic mass units, and the studies are carried out at temperatures near the absolute zero, where the helium atoms can appear in several different types of superfluid state. A superfluid state is one in which the motion of the helium is not at all impeded by its interaction with the surrounding container or substrate, in the case mentioned above. If, for example, the liquid superfluid is put into rotation (like swirling water in a glass) the swirl ing motion will persist forever, and this effect is the basis for a gyroscope which can detect extremely slow rotations. The proposed research will clarify the effects of the substrate on the temperature at which the superfluid behavior first occurs, and will probe these behaviors down to layers less than one atomic layer thick, on average. The results may lead to new insights useful in the variety of situations, such as chemical engineering, polymer science, catalysis, and others where wetting phenomena are important. The results will also contribute to general knowledge of situations where monolayer and submonolayer coverages of surfaces by atoms and molecules occur. The nation's science and engineering research base will benefit strongly from the training of graduate students in this program, in addition to the discoveries which may be made on monolayer wetting and phase transitions. ***