Yuri Sikorski

Sessile droplet spread into porous substrates—Determination of capillary pressure using a continuum approach

The problem of primary and secondary spread of sessile droplets into a porous substrate was formulated and solved numerically. A continuum approach for liquid- and gas-phases was utilized. The governing equations were discretized by finite difference method and solutions for both phases are obtained by marching in time using the fourth-order Runge-Kutta integration algorithm. This type of spread is a purely momentum-driven process that is caused by gradients both in capillary pressure and in saturation. A methodology was developed for finding the capillary pressure function for sessile droplets, which has not been described before. This approach was based on experimental data for a liquid/porous medium pair, and using universal, non-dimensional curves. Similar solutions were generated by the continuum approach and validated using experimental results. The model shows qualitative and quantitative agreement with experimental data. Although the focus of this work was to understand the interaction of chemical warfare agents with porous media, the approaches are universal and can be applied to determining the spread of any liquid into a porous material.

Infiltration time and imprint shape of a sessile droplet imbibing porous medium

The infiltration of a sessile droplet into a homogeneous porous medium for a constant droplet base radius case is solved numerically, where the porous medium is represented as a capillary network consisting of pores and throats. For a homogeneous medium, the network is built of the spherical pores of constant radius, and the cylindrical throats of constant radius and height. Having such defined network, the droplet imbibes porous medium in a single-phase flow for which the free interface in porous medium is smooth, and the liquid phase permeability and the capillary pressure are constant. Using the numerical solution we carry out the parametric study in which: (i) liquid viscosity and surface tension, (ii) droplet volume and base radius, and (iii) porous medium porosity and permeability are varied. The droplet infiltration time, and the imprint shape that is given with two spheroid half-axes are calculated. The dimensionless analysis is utilized to correlate the droplet infiltration parameters from which master curves for the droplet infiltration time and the droplet imprint shape are obtained. Using the infiltration time correlation, both numerical and experimental results show a linear behavior.

Fabrication and characterization of microstructures with optical quality surfaces in fused silica glass using femtosecond laser pulses and chemical etching

We present a study of the sidewall surface quality inside microchannels fabricated in fused silica glass by femtosecond laser pulses and chemical etching. Multiple combinations of laser exposure and etching solution parameters were examined. Results of scanning electron microscopy, atomic force microscopy, and optical reflection analyses of the surfaces are presented. The results obtained demonstrate the feasibility of optical quality surface fabrication, which in turn demonstrates the feasibility of fabricating complex integrated devices containing microfluidic channels and optical waveguides in the glass substrates.

Preparation of hydroxylated polyethylene surfaces

The surfaces of high-density or ultra-high-molecular-weight polyethylenes were hydroxylated using a two-step process. The wetting and wear properties of the untreated (virgin) and surface hydroxylated polyethylenes were compared. The introduction of hydroxyl groups provided an increase in surface hydrophilicity resulting in reduced wear. Hydrophilicity was analyzed by optical analysis of water contact angle. Wear was determined by weight loss under conditions of a reciprocating pin-on-plate apparatus with the panels immersed in water or calf serum. These results suggest that hydroxylation of polyethylene friction-bearing orthopedic surfaces may lead to a longer joint life.

Urban Greenhouse Solar/Geothermal Research and Community Outreach Project

The need for developing a self-sustaining urban farm greenhouse project in a cold-weather climate is discussed. A greenhouse heating system solution based on a hybrid geothermal -solar photovoltaic system is proposed. Specific greenhouse heat loss mechanisms are investigated. Implementation of a community outreach website information dissemination plan is outlined.

Simple and effective method to measure the diffusion coefficient of organic vapors in porous media

A quick and reliable method to measure a vapor concentration within porous substrate was developed. The technique consists of two steps, where a modified head space single drop microextraction (HS-SDME) sampling is used to entrap the vapor phase. In the second step, the entrapped vapor concentration is measured by gas chromatography (GC-FID). The technique is used to measure an effective diffusion coefficient of n-pentane in dry medium grain sand, with the sand partially saturated with water as an inert liquid. The measurements are carried out in a cylindrical sand holder on which the HS-SDME sampling ports are mounted. A linear vapor concentration profile along the bed thickness is found. From known concentration gradient and measuring the mass flux gravimetrically, the effective diffusion coefficient is determined. It turns out that the diffusion coefficient decreases from 8.49 × 10−6 for dry sand to 7.13 × 10−6 m2 s−1 as a function of water saturation. Additional hindrance to the vapor transport is observed from both the simple volumetric effect due to the porous medium void space reduction caused by the presence of water and increase of the tortuosity.