Measuring Water Droplet Contact Angle Using Contact Angle Goniometer

write the contact angle experiment lab report, given the instruction that included backgrounds and lab procedures. The results are included in the attachment. I will also upload a rubric for the paper. The paper should be full 2 pages without the reference and title. You don't have to include reference.

Contact Angle Assay - EBME 356Background 

In this lab you will measure the contact angle between a water droplet and a solid surface in order to determine the relative hydrophobicity of the solid surface. In order to understand the physical basis for what you observe, it is helpful to have a brief introduction to Young’s Equation, an equation that relates the surface energies of the water-solid, water-gas, and solid-gas interfaces to the contact angle of a water droplet as follows:γ_sl+γ_lg cosθ=γ_sg
γ_sl, γ_lg, and γ_sg are the surface energies for the solid-liquid, liquid-gas, and solid-gas interfaces respectively and θ is the angle between the droplet and the solid surface at the point where the two surfaces meet. Importantly, interfacial energies between gas phases and solid or liquid phases can be experimentally determined and are widely available. As a result, the contact angle of a droplet can be experimentally determined and used to determine the liquid-solid interfacial energy. In turn, the liquid-solid interfacial energy between water and a solid is a useful quantity for characterizing the hydrophobicity of a material.
To get a conceptual understanding of Young’s Equation, imagine a water droplet on a solid surface.
The shape of the droplet is primarily balanced by the surface energy of the liquid and the air (which is minimized by flattening the droplet to reduce external surface area) and the surface energy of the liquid and the solid (which is minimized by rounding the droplet to reduce the area of contact between these phases). Since the energy of the water-air interface is constant for all of our samples, the primary factor that will change the shape of the droplet is the surface energy of the water and the solid interface, where a higher surface energy causes the droplet to round out in order to minimize the water-solid surface area, corresponding to a greater contact angle and higher hydrophobicity. In summary, a larger contact angle between a water droplet and solid surface equates to a greater degree of hydrophobicity.
Contact angle is of interest because the hydrophobicity of a surface governs how biological tissues interact with it. Water molecules around highly hydrophobic surfaces get “trapped” into cage-like arrangements that have very low entropy relative to the freely moving water molecules in bulk solution. As a result, there is a strong entropic driving force for other compounds in the surrounding solution to replace water molecules at the surface of hydrophobic materials—this is known as the hydrophobic effect. As a common molecule available in biological solutions, this phenomenon causes proteins to accumulate at the surface of hydrophobic materials, where their interaction with hydrophobic surfaces can cause them to unravel and denature. Denaturation, in turn, causes epitopes to become exposed on the surface of a hydrophobic material that are not normally available, allowing it to be recognized by the immune system. Exposure of denatured protein epitopes may lead to inflammation or—for surfaces in contact with blood—platelet activation, both of which are typically undesirable for biocompatibility.
(Source: Wyatt Becicka)
In this lab, you will be using a contact angle goniometer (gonia → Greek for ‘angle’) to measure the water droplet contact angle. These devices help align the surface of interest so that accurate measurements of contact angle can be taken with a protractor. The sample surface is placed into the goniometer and aligned so that the water droplet is in line with the light source for visualization. Next, the tangent of the droplet is aligned with a protractor to measure contact angle. While making these measurements, it is desirable to keep liquid droplets on the order of the liquid’s capillary length, which indicates the length scale where gravitational forces begin to rival surface tension forces and the droplet size below which Young’s equation is most accurate. The capillary length for water is 2.71 mm.
A typical contact angle goniometer 
(Source: Wyatt Becicka)
Sample Preparation
Materials: Material Surfaces A and BDeionized waterContact Angle Goniometer
1) Turn on the light source on the contact angle goniometer.
2) Place the desired substrate surface on the platform.
3) Adjust the position of the microsyringe filled with DI water so that it is vertically above the substrate.
4) Using the microsyringe create a drop of the desired size.
5) Lower the microsyringe until the drop comes in contact with the substrate.
6) Raise the needle.
7) While looking through the eyepiece, adjust the position of the drop (in X-Y and Z directions) so that the base of the drop and the horizontal lines in the eyepiece are aligned.
8) By turning the knob on the eyepiece, move one of the horizontal lines to align the tangent of the drop profile at the contact point with the substrate surface and read the protractor through the eyepiece.
9) To get an accurate number for the contact angle, it is preferred to repeat the previous steps several times and average your measurements.