山东大学：《物理化学》课程教学资源（讲义资料）8.8 electric properties of colloid

88.8 Electric properties of colloids

§8.8 Electric properties of colloids

8.8.1 Electrokinetic phenomenon of colloid (I)Electropho the motion of colloidal particles under the action of an electric field sands (2) Electro-osmosis the motion of dispersion medium The experiments done by PeNce in 1809 under electric field demonstrated that both colloidal particles and dispersion medium are charged and can move under electric fields The colloidal particles of clay is negatively charged A colloidal particle may has hundreds of charge

The experiments done by PeNcc in 1809 demonstrated that both colloidal particles and dispersion medium are charged and can move under electric fields. The colloidal particles of clay is negatively charged. A colloidal particle may has hundreds of charge. 8.8.1 Electrokinetic phenomenon of colloids (1) Electrophoresis: the motion of colloidal particles under the action of an electric field. (2) Electro-osmosis: the motion of dispersion medium under electric field

8.8.2 The charge of colloids (1) Positively charged sols 3)Some sols, such as AgI sol, can be metallic oxide sols. metallic either positively charged or negatively hydroxide sols and some dyes harged depending on the preparation (4)Some lyophilic sols(protein solution) (2) Negatively charged sols: metal, metallic sulphide, sulfur can be positively, negatively or neutrally charged depending on the ph and the clay, paper, silicic acid colloids

(1) Positively charged sols: metallic oxide sols, metallic hydroxide sols and some dyes. (2) Negatively charged sols: metal, metallic sulphide, sulfur, clay, paper, silicic acid. (3) Some sols, such as AgI sol, can be either positively charged or negatively charged depending on the preparation. (4) Some lyophilic sols (protein solution): can be positively, negatively or neutrally charged depending on the pH and the colloids. 8.8.2 The charge of colloids

8.8.3 Origination of charge (I)Ionization and unequal dissolution: proteins Silica sol: H, SiO3=2H*+ SiO3 OH R-CH-COOH clay, glass, soap, biological R-CH-CO0 2R-CH-CO0 NH NH3 NH, macromolecules Agl sol: dissolution of Agt is more readily The pH at which protein does not move than that of i under electric field is named as isoelectric point

(1) Ionization and unequal dissolution: Silica sol: H2SiO3 = 2H+ + SiO3 2- clay, glass, soap, biological macromolecules AgI sol: dissolution of Ag+ is more readily than that of I￾proteins The pH at which protein does not move under electric field is named as isoelectric point. 8.8.3 Origination of charge

8.8.3 Origination of charge (2)Adsorption Agl sol: AgNO3+ KI: Agt, I,k, NO3- Agl, when prepared by adding ki into dilute AgNO, solution, positively charged AgI sol can be prepared. When adding AgNO3 into KI (AgI)m solution, negatively charged Agl sol was btained Fajans rule of preferential adsorption Co-ions/similiions: counterions Sols preferentially adsorb ions comprising itself, and then the ions with higher charges

AgI, when prepared by adding KI into dilute AgNO3 solution, positively charged AgI sol can be prepared. When adding AgNO3 into KI solution, negatively charged AgI sol was obtained. Fajans rule of preferential adsorption AgI sol: AgNO3 + KI: Ag+ , I− , K+ , NO3 − Sols preferentially adsorb ions comprising itself, and then the ions with higher charges. Co-ions /similiions; counterions (AgI)m I - I - I - (2) Adsorption 8.8.3 Origination of charge

8.8.3 Origination of charge (3)Substitution of crystal lattice: (4) Dielectric difference Carlin: Water droplet in petroleum is negatively m(Al3.34Mg06)(SO20)(OH)46m charged (0.66-x)Nax-xNa

(3) Substitution of crystal lattice: Caolin: {[m(Al3.34Mg0.66)(Si8O20)(OH)4 ] 0.66m- (0.66-x)Na+ } x- xNa+ (4) Dielectric difference Water droplet in petroleum is negatively charged. 8.8.3 Origination of charge

8.8.4 Structure of colloidal particle and electrokinetic potential Helmholtz double Gouy-Chappman Stern double layer(1853) layer(1910,1913) layer(1924) Electrokinetic potential/ s(zeta) potential Problems 1. Which model can be used to explain the charge of colloidal particle 2. Does the electrolyte concentration affect the structure of electric double layer

Holmholtz double layer (1853) Gouy-Chappman layer (1910, 1913) Stern double layer (1924) Electrokinetic potential /  (zeta) potential Problems: 1. Which model can be used to explain the charge of colloidal particle? 2. Does the electrolyte concentration affect the structure of electric double layer ? 8.8.4 Structure of colloidal particle and electrokinetic potential

8.8.4 Structure of colloidal particle and electrokinetic potential (n-xK- x K Colloidal core Surface charge Compact layer Diffusion layer Colloidal particle Colloid

[(AgI)m · n I – · (n-x)K+ ] x− x K+ Colloidal core Surface charge Compact layer Diffusion layer Colloidal particle Colloid (AgI)m I - I - I - 8.8.4 Structure of colloidal particle and electrokinetic potential

8.8.5 Factors on charge Compression of diffuse laver (K+ K Isoelectric state =0. Qc0.01 As the concentration of electrolyte increases, electrokinetic potential decreases. Overload adsorption and graham model

As the concentration of electrolyte increases, electrokinetic potential decreases. Overload adsorption and Graham model. Isoelectric state (AgI)m I - I - I -   c=0.01 c=0.001 c=0.004 Compression of diffuse layer 8.8.5 Factors on charge

8.8.6 Electrophoresis Electrophoretic mobility es =ge ff=nrv For electrophoresis with constant velocity E r77 q 4丌E-Eo 4兀EE052E1EE bTter 377 2E50 37 3 2E50

f es = qE f rv f = 6 For electrophoresis with constant velocity r qE v 6 = r q 4 r  0  =         3 2 6 4 r 0 r 0 E r r E v = = Electrophoretic mobility     3 2 r 0 U = 2 r 0 3     U = 8.8.6 Electrophoresis