Surface Chemistry Jurusan Kimia Fakultas MIPA Universitas Jember
Surface Chemistry The study of physical and chemical phenomena that occur at the interface of two phases, including solid-liquid interfaces, solid-gas interfaces, solid-vacuum interfaces, and liquid-gas interfaces
Gas-Liquid and Liquid-liquid Interfaces
Phenomena in Surface Chemistry Wetting, Spreading and Penetration Foam Breaking in Aqueous Systems Solubilization Rheological Effects in Surfactant Phases
Surface Tension, an effect within the surface layer of a liquid that causes that layer to behave as an elastic sheet
Surface Tension, Ketika mengisi gelas dengan air, air tidak tumpah meskipun permukaannya sedikit melebihi bibir gelas Kenapa air tidak dapat tumpah? A reason is that water has force to round of itself and remains at the border of cup by shaping an arch. The force to round of itself (to reduce area of surface) is Surface Tention. Unit of surface tentions is “mN/m” now. Once “dyne/cm” was being used and the scale of those units are same
Surface Tension Water Bead or Dome Penny Water Molecule O O O H Water Molecule O H O H O H Water molecules are too small for us to see with our eyes alone, but they are composed of one Oxygen (O) atom and two Hydrogen (H) atoms. This is why water is commonly called H2O. O H O H O H O H O H O H O H O H Penny Have you heard the saying opposites attract? In a way the atoms that make up a water molecule are kind of like magnets. The hydrogen atoms are positively charged and the oxygen atoms are negatively charged so the water molecules are attracted to each other. This attraction causes the molecules to want to “stick” together and form a dome on a waterproof surface. O H -- Attraction O H +
Surface Tension Soapy Water Plain Water Penny Penny O O O O O O O O O H O H O H O H O H O H O H O H O H O H O H O H O H O H O H O H O H O H O H O H O H O H Penny Penny Soap Molecule In our new model, the blue rectangle represents a soap molecule. Soap molecules act as a “barrier.” When soap is present in the water, the water molecules have a harder time attracting each other so surface tension is reduced. As a result, fewer water molecules will fit on the same penny.
Surface Tension as a Force caused by the attraction between the molecules of the liquid by various intermolecular forces
Surface Tension as a Surface Exess Free Energy γ= 𝜕G 𝜕A P,T
Essential of Surface Tension It originates in Intermolecular forces between molecules. In the bulk, intermolecular forces work every direction and keep balance On Surface, the balance is off and molecules exposed in the surface are pulled inside The surface molecules demand others for interaction and surplus energies generated there, which is Surface Tension. Surface tension is peculiar physical property of each material has
Surface Tension and Wettability If the surface tension of a target liquid is large... Force to make the liquid round of itself will be strong The liquid will be apt to be repelled by solid surfaces Contact angle results larger wetting becomes worse If the surface tension of a target liquid is small... The liquid will allow to wet over the solid surface Contact angle results smaller wetting becomes better. It will contribute better sreading and permeating
Applications of Surface Tension Evaluation focusing to liquids Abality of surfactant to decrease S.T. Wettability, permeability between solid and liquid Permeation to clearance, fibers Ink, surfactant Coating Characterization of liquids Emulsification Dressing, mayonaise, cosmetics Quality control of detergent, guilt Management of change cycle
Liquid Interfaces For lotions with mineral oil base to spread freely and evenly on the skin, its polarity and spreading coefficient should be increase by the addition of surfactant
ℎ= 2 𝛾 𝑙𝑎 𝑐𝑜𝑠𝜃 𝜌𝑔𝑟 Determination Methods Capillary Rise Method Where: h = the height the liquid is lifted, la = the liquid-air surface tension (J/m² or N/m) θ = contact angle ρ = density of liquid (kg/m3) g = acceleration due to gravity (m/s²) r = radius of tube (m)
The Ring Method where = constant (Du Noűy Tensiometer)
Principle of du Noűy Ring methods A detecting platinum ring is hanged on the balance and the ring bottom is touched to the liquid surface Same system can be used for plate and ring in common Surface tension of liquid does not work along the ring bottom at this condition. Than, let the liquid surface down to detach it from the ring The peak downward force detected by the balance before detaching the ring from the liquid surface is converted to surface tension.
mg = 3a cos() Pendant Drop Method is the surface tension of liquid is the contact angle at which a liquid/vapor interface meets the solid surface. Contact Angle Goniometer.
Pendant Drop Method
Surface Tension (mNm-1) of some liquids 0oC 20oC 40oC 60oC 80oC 100oC H2O 75.64 72.75 59.56 66.18 62.61 58.85 Ethanol 24.05 22.27 20.60 19.01 - - Acetone 26.20 23.70 21.20 18.60 16.20 Toluene 30.74 28.43 26.13 23.81 21.53 19.39 Benzene 31.60 28.90 26.30 23.70 21.30 Hg (0oC) 480 Ag (970oC) 800 NaCl (1080oC) 94 AgCl (452oC) 125 Intermolecular forces
Surface Tension Directly depends on intermolecular forces in the solution Inversely depends on temperature of metallic liquid > ionic liquid > covalent liquid
ls = la cosθ Liquid in The Vertical tube ls = liquid-solid surface tension la = liquid-air surface tension = contact angle Concave Concave Adhesive>>Cohesive Convex Adhesive<<Cohesive Convex
Interface Tension and Sprading
Spreading Coefficient, S in Water at 20 °C liquid B n-hexadecane 72.8-(30.0+52.1) = - 9.3 Drop on water surface n-octane 72.8-(21.8+50.8) = + 0.2 Spreading n-octanol 72.8-(27.5+8.5) = +36.8 Spreading against inpurity
Use the following data of the surface/interface tensions (mN m-1) at 20oC A B A B AB H2O C6H6 72.75 28.88 35.0 H2O CCl4 72.75 26.28 45.0 H2O Hg 72.75 470 375 H2O C8H15OH 72.75 17.0 10.7 predicts the spreading behavior of B on A
Surface Tension of Solution Substances in solution : Surface active agent “Surfactant” (<o) hydrophilic part hydrophobic part Surface inactive agent (>o) such as ionic compounds, acids, bases etc.
Surface Tension of Some Alcohols in Water at 20 °C
Surfactants in Solution Micelle formation when C > CMC
CMC determination CMC = critical micelle concentration
Surface tension in Surfactant Surfactants have characteristics to change surface tension over time and the curves very depended on surfactant concentration Surfactants have a point of critical comcentration the surface tension does not get lower. That point is called “CMC” In the lower concentration than CMC, the surface tension will change untill equilibration
Effect of Concentration on surface tension Adsorption On surface Gibbs isotherm is known as surface concentration (mol/m2) C is the concentration of the substance in the bulk solution. R is the gas constant T the temperature
Tugas Mencari Jurnal tentang Surface Chemistry in Important Technologies dalam web EBSCO. 2. Membuat rangkuman dalam 1 halaman A4 Dikumpulkan Kamis 7 April 2016.