Primary surface measurement reported
Water contact angle of HPLC-grade water on Whatman® Grade 4 filter paper treated with four permanent-marker colors (blue, black, green, red).
At-a-Glance Summary
Dropometer attribution in the paper
Contact angle measurements were determined using the “Dropometer (Droplet Smart Tech Incorporation, Toronto, ON, Canada),” with images captured and analyzed using the installed Sessile mobile application.
How the surface-tension / contact-angle data were used in the study
Contact-angle results were used to compare marker-color hydrophobicity and guide selection of marker colors used to create hydrophobic barriers in the paper-based device, alongside leakage analysis.
Replication / reliability statement
Figure 4-1 caption states each bar represents the mean of three individual experiments ± standard deviation.
Paper Details
Title
Development of a Dual-Modal Microfluidic Paper-Based Analytical Device for the Quantitative and Qualitative Detection of The Total Hardness of Water.
Authors
Oyejide Damilola Oyewunmi
Journal
Thesis (Master of Applied Science, Mechanical Engineering)
Year
2020
License
© Oyejide Damilola Oyewunmi, 2020
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What Was Measured
Primary surface / interfacial measurement
Water contact angle measured on permanent-marker-treated Whatman® Grade 4 filter paper using HPLC-grade water, reported at a 10 s timepoint and as a mean over 60 s (Figure 4-1(b)).
Supporting measurements
Elution velocity of water in different grades of paper was measured to support paper-type selection (Figure 4-1(a)). Leakage analysis was performed by dipping marker-fabricated devices into colored water for 4 minutes to evaluate boundary resistance (Figure 4-2).
Role of the Dropometer
The Dropometer was used to determine the contact angle of HPLC-grade water on permanent-marker-treated paper substrates. Grade 4 Whatman filter paper was cut into 2×2 cm square sheets, four permanent marker colors were applied, HPLC water was fed into the sample application syringe and an aliquot was ejected on each square sample, and the droplet image was captured and analyzed using the installed Sessile mobile application to obtain contact-angle values.
The resulting contact-angle comparisons supported marker-color selection for creating hydrophobic barriers in the microfluidic paper-based device.
Key Findings
Marker color drives measured contact angle at 10 s
After 10 seconds, contact angles were observed as 144 deg. (black), 151 deg. (blue), 145 deg. (red), and 158 deg. (green) for HPLC-grade water on marker-treated Whatman® Grade 4 filter paper.
Hydrophobic strength ranking from contact-angle results
Based on the water contact-angle measurements, hydrophobic strength was reported as green marker > blue marker > red marker ≈ black marker.
Short time-window behavior matches the 10 s comparison
Contact angles investigated over 60 seconds showed similar results to the 10-second measurements, and this was linked to marker pigments retaining hydrophobicity over time.
Leakage outcomes differentiate barrier performance by marker color
Devices fabricated with green and blue marker boundaries did not show any sign of leakage, while black and red marker fabricated devices leaked after 4 minutes in colored water.
Contact-angle and leakage screening guided barrier choice
Following wettability and leakage evaluation, the green and blue markers were utilized to create hydrophobic barriers for flow through the device.
Figures & Visuals
Figure 4-1(b) — Contact-angle comparison used for marker screening
What it shows
Shows contact angle measurement over time for black, blue, red, and green markers on Whatman® Grade 4 filter paper, including a 10 s measurement and a mean over 60 s.
Figure 4-2 — Barrier leakage comparison by marker color
What it shows
Shows leakage analysis images for devices fabricated with green, blue, black, and red marker colors.
Why It Matters
In the fabrication optimization workflow for the microfluidic paper-based analytical device, the contact-angle measurements from the Dropometer provided a quantitative basis for comparing the hydrophobic behavior of different permanent-marker inks on the selected paper substrate.
These wettability results were used alongside leakage analysis to justify which marker colors were used to form hydrophobic barriers that support confined flow paths in the device.
Practical Takeaways
Marker inks can be screened by contact angle on the target paper
The study measured water contact angle on Whatman® Grade 4 filter paper after applying different marker colors to compare their hydrophobic strength.
Report both a fixed timepoint and a short-duration behavior check
Contact angles were evaluated at 10 seconds and also investigated over 60 seconds to compare marker performance over a short time window.
Pair contact-angle ranking with a boundary stress test
Leakage analysis by dipping devices into colored water for four minutes was used alongside contact-angle results to evaluate barrier resistance.
Use screening outcomes to select barrier materials for fabrication
The thesis uses the combined wettability and leakage outcomes to select green and blue markers for creating hydrophobic barriers in the device.