Friction of colloidal monolayers on periodic and quasiperiodic surfaces

点击翻译按钮获取中文摘要

Friction is an important process encountered at a wide range of length scales and in almost any material. Depending on the specific situation, either strong or low friction coefficients are desirable, e.g. to enhance adherence of adlayers or to reduce wear between moving components in engines. Despite its long history, however, many aspects of friction are not well understood. In this proposal we will investigate the basic relationship between friction and the structural properties of the surfaces in contact. Exemplarily, we will study surfaces with periodic and quasiperiodic order which are known to behave rather differently regarding their friction coefficients. The studies will be performed with a colloidal model system of micron-sizes particles which is driven across periodic and quasiperiodic substrates, the latter created by optical interference patterns. Due to optical gradient forces, such patterns play the role of a substrate potential whose length scale, interaction strength and even geometry can be continuously varied. An additional advantage of this approach is the possibility to have unobstructed optical access to the interface where the friction process occurs. This allows to study how elastic and plastic deformations or creeping motion occurs with single particle resolution. Depending on whether the two bodies are in registry (commensurate) or not (incommensurate), either a stick-slip or a continuous sliding motion is expected. Since the latter is strongly related to low friction coefficients, our research will not only add valuable insights into the microscopic mechanisms of friction but also help to understand the conditions under which ultralow friction coefficients (superlubricity) can be expected.