If theta represents the angle of contact made by a liquid which completely wets the surface

https://chem.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FCourses%2FOregon_Institute_of_Technology%2FOIT%253A_CHE_202_-_General_Chemistry_II%2FUnit_7%253A_Intermolecular_and_Intramolecular_Forces_in_Action%2F7.1%253A_Surface_Tension%252C_Viscosity%252C_and_Capillary_Action When you pour a glass of water, or fill a car with gasoline, you observe that water and gasoline flow freely. But when you pour syrup on pancakes or add oil to a car engine, you note that syrup and motor oil do not flow as readily. The viscosity of a liquid is a measure of its resistance to flow. Water, gasoline, and other liquids that flow freely have a low viscosity. Honey, syrup, motor oil, and other liquids that do not flow freely, like those shown in Figure \(\PageIndex\] where • h is the height of the liquid inside the capillary tube relative to the surface of the liquid outside the tube, • T is the surface tension of the liquid, • θ is the contact angle between the liquid and the tube, • r is the radius of the tube, ρ is the density of the liquid, and • g is the acceleration due to gravity, 9.8 m/s 2. When the tube is made of a material to which the liquid molecules are strongly attracted, they will spread out completely on the surface, which corresponds to a contact angle of 0°. This is the situation for water rising in a glass tube. We will not concern ourselves with calculating capillary height in this course. Applications: Capillary Action is Used to Draw Blood...

If we observe the liquids around us carefully, some liquids partially wet solid surfaces, other liquids completely wet solid surfaces, while some liquids like mercury do not wet a solid surface at all. By studying the nature of the contact angle between the liquid and solid interface or by finding out whether the contact angle is acute, obtuse, or zero, we can determine whether the liquid will wet the solid surface or not. The property of a liquid to wet a solid surface is called wettability. Got a question on this topic? Let us consider the free surface of a liquid inside a capillary tube. The free surface of a liquid in contact with the walls of the capillary tube may be either concave upwards, concave downwards, or perfectly flat. The contact angle depends on cohesive and adhesive forces. Cohesive forces are the forces which act between molecules of the same type. For example, the intermolecular force between two water molecules is cohesive in nature. Adhesive forces act between different types of molecules. For example, the intermolecular force of attraction between molecules of the capillary tube and the molecule of water is adhesive in nature. The adhesive and cohesive forces help determine the contact angle. In the figure below, A is the adhesive force vector, C is the cohesive force vector, and R is the resultant force vector. Consider figure 2a. The free surface of the liquid is concave downwards. When we draw a tangent to the free surface of the liquid and measur...

Wetting, the process of water interacting with a surface, is critical in our everyday lives and in many biological and technological systems. The contact angle is the angle at the interface where water, air and solid meet, and its value is a measure of how likely the surface is to be wetted by the water. Low contact-angle values demonstrate a tendency of the water to spread and adhere to the surface, whereas high contact-angle values show the surface’s tendency to repel water. The most common method for surface-wetting characterization is sessile-drop goniometry, due to its simplicity. The method determines the contact angle from the shape of the droplet and can be applied to a wide variety of materials, from biological surfaces to polymers, metals, ceramics, minerals and so on. The apparent simplicity of the method is misleading, however, and obtaining meaningful results requires minimization of random and systematic errors. This article provides a protocol for performing reliable and reproducible measurements of the advancing contact angle (ACA) and the receding contact angle (RCA) by slowly increasing and reducing the volume of a probe drop, respectively. One pair of ACA and RCA measurements takes ~15–20 min to complete, whereas the whole protocol with repeat measurements may take ~1–2 h. This protocol focuses on using water as a probe liquid, and advice is given on how it can be modified for the use of other probe liquids. Open Access articles citing this article. • • ...

In surface free energy (also interfacial free energy or surface energy) quantifies the disruption of Cutting a solid body into pieces disrupts its bonds and increases the surface area, and therefore increases surface energy. If the cutting is done Assessment [ ] Measurement [ ] Contact angle [ ] The most common way to measure surface energy is through There are several different models for calculating the surface energy based on the contact angle readings. Contact angle method is the standard surface energy measurement method due to its simplicity, applicability to a wide range of surfaces and quickness. The measurement can be fully automated and is standardized. In general, as surface energy increases, the contact angle decreases because more of the liquid is being "grabbed" by the surface. Conversely, as surface energy decreases, the contact angle increases, because the surface doesn't want to interact with the liquid. Other methods [ ] The surface energy of a liquid may be measured by stretching a liquid δA, a quantity of γ δA, is needed (where γ is the surface energy density of the liquid). However, such a method cannot be used to measure the surface energy of a solid because stretching of a solid membrane induces elastic energy in the bulk in addition to increasing the surface energy. The surface energy of a solid is usually measured at high temperatures. At such temperatures the solid γ is the surface energy density of a cylindrical rod of radius r and length l at hi...

\( \newcommand\) • • • • • • • Contact angle is one of the common ways to measure the wettability of a surface or material. Wetting refers to the study of how a liquid deposited on a solid (or liquid) substrate spreads out or the ability of liquids to form boundary surfaces with solid states. The wetting, as mentioned before is determined by measuring the contact angle, which the liquid forms in contact with the solids or liquids. The wetting tendency is larger, the smaller the contact angle or the Introduction The contact angle is an angle that a liquid creates with a solid surface or capillary walls of a porous material when both materials come in contact together. This angle is determined by both properties of the solid and the liquid and the interaction and repulsion forces between liquid and solid and by the three phase interface properties (gas, liquid and solid). Those interactions are described by Figure \(\PageIndex\)​: Images used with permission from Wikipedia • The smaller the contact angle - cohesive forces are weaker then adhesive forces and molecules of the liquid tend to interact more with solid molecules then liquid molecules. • The larger the contact angle - cohesive forces are stronger then adhesive forces and the molecules of the liquid tend to interact more with each other then with the solid molecules. Thermodynamics Thomas Young (13 June 1773 – 10 May 1829) proposed treating the contact angle of a liquid with a surface as the mechanical equilibrium o...

HML 6) Wettability, non-wettability and contact angle hysteresis Wetting refers to the study of how a liquid deposited on a solid (or liquid) substrate spreads out. Understanding wetting enables us to explain why water spreads readily on clean glass but no on a plastic sheet. (i) Example: 'Total wetting' vs. 'Non-wetting' When a drop is placed down on very clean glass, it spreads completely. By contrast, the same drop deposited on a sheet of plastic remains stuck in its place. The conclusion is that there exist two regimes of wetting. Wetting can be characterized into two types: total wetting: when the liquid has a strong affinity for the solid; and partial wetting, the opposite case. water on cleaned glass slide on nanotube carpet Click here for the videos: (ii) Spreading Parameter Spreading parameter, S distinguishes the two different regimes of wetting. It measures the difference between the surface energy (per unit area) of the substrate when dry and wet: S = [E substrate] dry - E substrate] wet or S = γ solid - (γ liquid + γ solid-liquid) S > 0: Total wetting If the parameter S is positive, the liquid spreads completely in order to lower its surface energy. Condition favorable for this condition is a high value of γ solid (high energy surfaces like glass, clean silicon) and a lower value of γ liquid (ethanol, toluene). [See above figure] S 90°. (iii) Partially wetting and partially non-wetting Water on polymethylmethacrylate water on silanized silicon wafer Click her...

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