Chapter 01 - Surface Phenomena (2024-2025) - PDF

University of Setif-1 Faculty of Natural and Life Sciences Department of basic studies 2nd year CT Biology 2024-2025 Chapter 01 Surface phenomena play a significant role in the function of beings...

University of Setif-1 Faculty of Natural and Life Sciences Department of basic studies 2nd year CT Biology 2024-2025 Chapter 01 Surface phenomena play a significant role in the function of beings because they are the site of intense molecular activity Surfaces in the organism, they It is through them that the are essentially the exchanges necessary for cellular surfaces metabolism take place The creation of new surfaces always leads to energy consumption refers to the boundary or surface that separates interface two different phases of matter, such as solid-liquid, liquid-gas, or solid-gas.  Bringing a molecule which translates into an requires work from the bulk to the increase in surface energy surface 𝑑𝑊 = 𝜎. 𝑑𝑆 𝜎 is the surface tension MKSA system MKSA system 1 dyne = 10-5N 𝜎 = 𝐽/𝑚2 𝜎 = 𝑁/𝑚 CGSA system 1 erg = 10-7 J CGSA system 𝜎 = 𝑒𝑟𝑔/𝑐𝑚2 𝜎 = 𝑑𝑦𝑛𝑒/𝑚 Water has one of the highest surface primarily due to the strong hydrogen tensions among common liquids bonding between water molecules Polar liquids generally exhibit higher surface tensions than non-polar liquids because of the stronger hydrogen bonds. Surface tension varies significantly among different liquids, largely due to the nature and strength of the intermolecular forces Cohesion is an attraction between molecules of the Adhesion is an attraction between molecules same substance of different substances In this WC = 2 σ Wa=σL + σS – σL /S equation, 1 erg = 10-7 J only σL and [WC]=J/m2 𝑊𝑎 = 𝜎𝐿 1 + cos 𝜃 ϴ are known [WC]=erg/cm2 1 dyne = 10-5N [WC]=N/m [WC]=dyne/m  Incomplete wetting Poor wetting Good wetting Non wetting Complete wetting  Conditions for Spreading (Wetting) the spreading coefficient (S) If the energy of adhesion (𝑊𝑎 ​) is greater than the spreading coefficient (S) is the difference the energy of cohesion (𝑊𝑐 ), spreading occurs between Adhesion work and Cohesion work 𝑾𝒂 ≥ 𝑾𝒄 S=Wa-Wc 𝑆 = 𝜎𝑆 − (𝜎𝐿Τ𝑆 + 𝜎𝐿 ) If𝑾𝒂 ≥ 𝑾𝑪 , the liquid will spread, indicating good If 𝑺 > 𝟎, the liquid will spread, indicating good wetting. wetting. If𝑾𝒂 < 𝑾𝑪 , the liquid will not spread well, indicating If 𝑺 < 𝟎, the liquid will not spread well, indicating poor wetting. poor wetting. 𝑆 = 𝜎𝐿 cos 𝜃 − 1 Overpressure inside a droplet 𝛥𝑃 = 𝑃𝑖 − 𝑃𝑒 Spherical Surface Cylindrical Surface Soap Bubble 2𝜎 𝜎 4𝜎 𝛥𝑃 = 𝛥𝑃 = ∆𝑃 = 𝑅 𝑅 𝑟 𝟐𝝈 cos 𝜽 Jurin's Law 𝒉= 𝝆𝒈𝒓 The height h is to the surface tension The height 𝒉 is inversely proportional If the radius is smaller, σdirectly proportional to the radius 𝒓 of the tube the liquid rises higher A liquid with higher surface tension The height 𝒉 decreases with the increasing of the rises higher in the tube liquid density 𝝆  If the tube is perfectly wettable 𝟐𝝈 If the tube is non-wettable 𝟐𝝈 𝒉= 𝒉=− 𝝆𝒈𝒓 𝝆𝒈𝒓 Θ = 0° very clean glass and water Θ = 180° very clean glass, very clean mercury θ < Π/2 the liquid rises ℎ>0 θ > Π/2 the liquid falls ℎ 𝑃2 𝑃1 = 𝑃2 Smaller alveoli collapses into larger alveoli Smaller alveoli do not collapse into larger alveoli The air flows from the alveoli 1 to alveoli 2 The air do not flow from the alveoli 1 to alveoli 2  An emulsion is a dispersion of one liquid in A foam is a dispersion of a gas in a another liquid that is not miscible with the liquid first to create a foam It is necessary to vigorously agitate a liquid in the presence of a gas to obtain an emulsion It is necessary to vigorously shake together two immiscible liquids Pure liquids usually do not foam well, and their foams are unstable where one liquid is dispersed in the form of small droplets within the other To easily obtain abundant foamsThe surface tension must be significantly reduced Surfactants play a key role in stabilizing emulsions by reducing the interfacial tension we are dealing with surfactant between the two phases and forming a solutions protective layer around the droplets.