Spontaneous charging affects the motion of sliding drops

Water drops moving on surfaces are not only an everyday phenomenon seen on windows but also form an essential part of many industrial processes. Previous understanding is that drop motion is dictated by viscous dissipation and activated dynamics at the contact line. Here we demonstrate that these two effects cannot fully explain the complex paths of sliding or impacting drops. To accurately determine the forces experienced by moving drops, we imaged their trajectory when sliding down a tilted surface, and applied the relevant equations of motion. We found that drop motion on low-permittivity substrates is substantially influenced by electrostatic forces. Our findings confirm that electrostatics must be taken into consideration for the description of the motion of water, aqueous electrolytes and ethylene glycol on hydrophobic surfaces. Our results are relevant for improving the control of drop motion in many applications, including printing, microfluidics, water management and triboelectric nanogenerators

Enabling Marangoni flow at air-liquid interfaces through deposition of aerosolized lipid dispersions

Esta herramienta consiste en una síntesis en la que se ofrecen los elementos teóricos y/o prácticos más relevantes de análisis numérico. Se invita al estudiante para que se cuestione sobre sus propios procesos de aprendizaje. Consolida la comprensión, síntesis y reflexión crítica de los contenidos. Fomenta las habilidades de pensamiento: metacognición y pensamiento creativo

Oil Displacement in Calcite-Coated Microfluidic Chips via Waterflooding at Elevated Temperatures and Long Times

In microfluidic studies of improved oil recovery, mostly pore networks with uniform depth and surface chemistry are used. To better mimic the multiple porosity length scales and surface heterogeneity of carbonate reservoirs, we coated a 2.5D glass microchannel with calcite particles. After aging with formation water and crude oil (CRO), high-salinity Water (HSW) was flooded at varying temperatures and durations. Time-resolved microscopy revealed the CRO displacements. Precise quantification of residual oil presented some challenges due to calcite-induced optical heterogeneity and brine–oil coexistence at (sub)micron length scales. Both issues were addressed using pixel-wise intensity calibration. During waterflooding, most of the ultimately produced oil gets liberated within the first pore volume (similar to glass micromodels). Increasing temperature from 22 °C to 60 °C and 90 °C produced some more oil. Waterflooding initiated directly at 90 °C produced significantly more oil than at 22 °C. Continuing HSW exposure at 90 °C for 8 days does not release additional oil; although, a spectacular growth of aqueous droplets is observed. The effect of calcite particles on CRO retention is weak on flat surfaces, where the coverage is ~20%. The calcite-rich pore edges retain significantly more oil suggesting that, in our micromodel wall roughness is a stronger determinant for oil retention than surface chemistry

Effects of Fluid Aging and Reservoir Temperature on Waterflooding in 2.5D Glass Micromodels

To study improved oil recovery (IOR) via laboratory experiments at the pore scale, we performed waterflooding experiments in a glass 2.5D micromodel (dual depth: 12 and 27 μm) with crude oil (CRO) and brines of variable compositions at temperatures ranging from 22 °C (room temperature) to 90 °C. The time-dependent residual oil saturation (ROS) for various flooding and aging protocols was extracted from optical microscopy images of the entire pore space in the micromodel. Additionally, we used high-resolution images to examine the microscopic distributions of oil and brine at the subpore level. Variation of the fluid aging history (before the first flooding with high-salinity water, HSW) revealed that sequential aging with formation water and CRO led to significantly higher ROS values than aging with CRO only. Video analysis of the pore space showed that most of the oil was trapped via a complete bypassing of the deep pores. On increasing the waterflooding temperature, both the ROS and the fraction of bypassed pores became smaller. An increase in dewetting of tiny oil drops and films from the pore walls supports the notion of a ROS decrease via a wettability alteration. Subsequent flooding with low-salinity water (LSW) did not lead to recovery of additional oil, regardless of aging condition or temperature. Our results show the significance of fluid aging and temperature to design a successful microfluidic IOR strategy