Laboratoire de Physique et Mécanique des Milieux Hétérogènes (PMMH UMR 7636) CNRS, ESPCI Paris, PSL Research University, Sorbonne Université, Université Paris Diderot, 10 rue Vauquelin, 75005 Paris, France.
Centro de Investigación y de Estudios Avanzados, Unidad Monterrey, PIIT Autopista al Aeropuerto Km. 9.5, Apodaca, Nuevo León, 66600, Mexico.
Sci Rep. 2018 Mar 16;8(1):4668. doi: 10.1038/s41598-018-22960-z.
Brownian or self-propelled particles in aqueous suspensions can be trapped by acoustic fields generated by piezoelectric transducers usually at frequencies in the megahertz. The obtained confinement allows the study of rich collective behaviours like clustering or spreading dynamics in microgravity-like conditions. The acoustic field induces the levitation of self-propelled particles and provides secondary lateral forces to capture them at nodal planes. Here, we give a step forward in the field of confined active matter, reporting levitation experiments of bacterial suspensions of Escherichia coli. Clustering of living bacteria is monitored as a function of time, where different behaviours are clearly distinguished. Upon the removal of the acoustic signal, bacteria rapidly spread, impelled by their own swimming. Nevertheless, long periods of confinement result in irreversible bacteria entanglements that could act as seeds for levitating bacterial aggregates.
在水溶液中，布朗运动或自主运动的粒子可以被通常在兆赫兹频率下产生的压电换能器产生的声场捕获。这种获得的限制允许研究丰富的集体行为，如在微重力条件下的聚集或扩散动力学。声场诱导自主运动的粒子悬浮，并提供次级侧向力以在节点平面捕获它们。在这里，我们在受限活性物质领域迈出了一步，报告了大肠杆菌细菌悬浮液的悬浮实验。作为时间的函数，监测活细菌的聚集，清楚地区分不同的行为。在去除声信号后，细菌迅速扩散，被自身游动推动。然而，长时间的限制会导致不可逆转的细菌缠绕，这可能成为悬浮细菌聚集体的种子。
