Autonomous Capillary Microfluidic Devices with Constant Flow Rate and Temperature-Controlled Valving

<p>In this work, we introduce a Poly(N-isopropylacrylamide) (PNIPAm) grafted PDMS (PNIPAm-g-PDMS) capillary flow-driven microfluidic device with integrated valving function. Due to the thermo-sensitive properties of PNIPAm, the device possesses a temperature-switchable surface wettability between 20 and 36 °C. By locally integrating a heating wire, a hydrophobic valving function can thus be obtained. The device provides large operational freedom, enables single-valve control, and operates in a convenient temperature range. In addition, this device is characterized by a capillary filling rate that is constant in time. The constant flow velocities ranging from 1 µm/s to 240 µm/s can be obtained in dry PNIPAm-g-PDMS and freshly treated PNIPAm-g-PDMS devices with different channel geometry. We explained the constant flow rate with diffusive hydration of PNIPAm at the liquid front. This device thus provides both stop valving and accurate flow control functions, being potentially applied for diagnostic assay performance.</p><div><br></div>

Autonomous Capillary Microfluidic Devices with Constant Flow Rate and Temperature-Controlled Valving

<p>In this work, we introduce a Poly(N-isopropylacrylamide) (PNIPAm) grafted PDMS (PNIPAm-g-PDMS) capillary flow-driven microfluidic device with integrated valving function. Due to the thermo-sensitive properties of PNIPAm, the device possesses a temperature-switchable surface wettability between 20 and 36 °C. By locally integrating a heating wire, a hydrophobic valving function can thus be obtained. The device provides large operational freedom, enables single-valve control, and operates in a convenient temperature range. In addition, this device is characterized by a capillary filling rate that is constant in time. The constant flow velocities ranging from 1 µm/s to 240 µm/s can be obtained in dry PNIPAm-g-PDMS and freshly treated PNIPAm-g-PDMS devices with different channel geometry. We explained the constant flow rate with diffusive hydration of PNIPAm at the liquid front. This device thus provides both stop valving and accurate flow control functions, being potentially applied for diagnostic assay performance.</p><div><br></div>

Physicochemical method of fixing mobile sands with local materials

Impregnating composition with water-soluble binders has been elaborated, with the help of which the source of deflation of mobile sands is blocked, and the protective crust obtained on the sandy surface is characterized by resistance to the effects of wind-sand flow, assessed by plastic strength and thickness. The free-flow movement of a binder in a porous body of sand depends mainly on the equivalent diameter of the particles obtained by the joint solution of the internal and external problems of hydrodynamics and the shape factor of the particles. To interpret the experimental results empirically, an indicator of the saturation of the protective crust sand characterizing the impregnation as an unstable process proceeding under the predominant influence of the gravity field with an uneven movement of the liquid front was revealed. The prevalence of the elastic-plastic properties of the protective crust is evidenced by a slight and smooth change in physical and mechanical indicators over time by the third year of operation.

Liquid Transport During Evaporation of Water From a Small Simulated Soil Column

The food-energy-water nexus considers critical resource challenges which must be resolved in order to meet the needs of a growing population. Agriculture is the largest global water user, accounting for two-thirds of global water withdrawals, including water for crop irrigation. Understanding and therefore reducing evaporation of water from soil is an approach to conserve water resources globally. This work studies evaporation of water from a simulated soil column and employs x-ray imaging to determine the location of water in the porous media. A 30-mL beaker was filled with approximately 1700 2-mm hydrophilic glass beads. Water (i.e., 5.5 mL) was added to the simulated soil, comprised of glass beads and a heat flux (i.e., 1500 W/m2) was applied to the beaker using a solar simulator and the intensity was measured with a light meter. Real-time mass measurements were recorded during evaporation and X-ray imaging was utilized to capture liquid transport during evaporation. Images were post-processed using Matlab; the position of the liquid front was determined from this imaging. Across three replications, it took 47 hours on average to evaporate 5 mL of the total 5.5 mL of water. The transitions between evaporation Stage I, II, and III evaporation rates were determined using mass data and x-ray imaging; transition between Stages I and II occurred between approximately 4 and 9 hours, and the transition from Stage II to III evaporation occurred between approximately 18 and 24 hours. The result of this experiment will be useful to understand the liquid transport and formation of liquid bridges during evaporation from soil.

Foam–liquid front motion in Eulerian coordinates

A mathematical model formulated as a system of Hamilton–Jacobi equations describes implicitly the propagation of a foam–liquid front in an oil reservoir, as the zero-level set of the solution variable. The conceptual model is based on the ‘pressure-driven growth’ model in Lagrangian coordinates. The Eulerian mathematical model is solved numerically, where the marching is done via a finite volume scheme with an upwind flux. Periodic reinitialization ensures a more accurate implicit representation of the front. The numerical level set contour values are initially formed to coincide with an early time asymptotic analytical solution of the pressure-driven growth model. Via the simulation of the Eulerian numerical model, numerical data are obtained from which graphical representations are generated for the location of the propagating front, the angle that the front normal makes with respect to the horizontal and the front curvature, all of which are compared with the Lagrangian model predictions. By making this comparison, it is possible to confirm the existence of a concavity in the front shape at small times, which physically corresponds to an abrupt reorientation of the front over a limited length scale.

Bioinspired polymer microstructures for directional transport of oily liquids

Nature has always served as an inspiration for scientists, helping them to solve a large diversity of technical problems. In our case, we are interested in the directional transport of oily liquids and as a model for this application we used the flat bug Dysodius lunatus . In this report, we present arrays of drops looking like polymer microstructures produced by the two-photon polymerization technique that mimic the micro-ornamentation from the bug's cuticle. A good directionality of oil transport was achieved, directly controlled by the direction of the pointed microstructures at the surface. If the tips of the drop-like microstructures are pointing towards the left side, the liquid front moves to the right and vice versa. Similar effects could be expected for the transport of oily lubricants. These results could, therefore, be interesting for applications in friction and wear reduction.