Textile Chemistry II, Interfaces and Chemical Treatment 15 ECTS
Examination for Surface Chemistry
4.5 ECTS
Part of Course
Ladok code: AT2PL1
The exam is given to: Master students in Textile Technology
Date of exam: 19/02/2018 Time: 09:00 – 13:00 Means of assistance: Calculator Formula table Dictionary
Total points on exam: 40 Grades:
At least 20 points required to pass this part of the course. 20-23 points are required for grade E, 24-27 points for grade D, 28-31 points for grade C, 32-35 points for grade B, 36-40 points for grade A.
Additional information:
Your corrected examinations will be available from the student centre within 3 weeks after the examination date.
The results are posted no longer than three weeks after the exam Important! Do not forget to write your name on each paper you hand in. Good Luck!
Contact person during examination: Phone number:
Motivate all of your answers!
1 Various terms are used to describe different phenomena in surface chemistry. Describe
what is meant by the following terms. (12)
a) Foam
b) Electric double layer c) Ageing of a surface
d) Electrostatic patch flocculation
2a) What is the ccc? (3)
b) According to the DLVO theory, the total potential energy between two charged colloid
particles is the sum of the electrostatic and van der Waals potential energies. Sketch the
total potential energy, Vtot, as a function of the interparticle separation, H. Show on the
graph where coagulation and flocculation occur, as well as the energy barrier that
prevents coagulation. (4)
c) Use the graph drawn for question b) to describe how changes in the salt concentration
affect the rate of coagulation. (1)
d) What is the stability quotient for a dispersion? (1)
3a) What is the zeta potential? What is the difference between the zeta potential and the
surface electric potential? (4)
b) f1( a) 3 2 u o κ η ς εε
= is used to calculate the zeta potential using electrophoresis. What is
the correction factor when κa = 7? (2)
4a) Describe the three possible mechanisms for spreading of a liquid on another liquid
5 a) What is a micelle? (1) b) Sketch a typical distribution of the monomer / micelle concentration, An, against the
number of monomers in the micelle, n, for a system where the average number of monomers in the micelles is 90 (i.e., on average the micelles consist of 90 monomers). The total
surfactant concentration is slightly larger than CMC. Give typical concentrations (in molar)
for A1 and A90. (5)
c) Na-octylsulphate has 8 carbon atoms in its hydrophobic tail and Na-decylsulphate has 10 carbon atoms in its hydrophobic tail. Which of these surfactants has the lowest CMC? Why?
Table of Formulae: Surface and Colloid Chemistry Average values: ∑ ∑ = i i n i M i i n n M ∑ ∑ = i i w i M i i w w M m=ρV V=4/3πr3
Electric potential: Ψ =Ψ0exp(−κx) where
2 / 1 kT 2 o e 2 i z 0 i c ∑ = o εε κ
Counter-ion concentration profile for positive ions: Ψ − = kT ze exp c c 0 o
Electrostatic interactions: exp( H)
2 z 2 o e 2 2 ) a(kT 32 rep V = pεεo γo −κ ; 1 kT 2 0 o ze exp 1 kT 2 0 o ze exp + Ψ − Ψ = o γ
Van der Waals interactions:
12H Aa att V =− (spheres) 2 H 12 A att V p − = (planar surfaces) Stability quotient: 2 k 0 2 k W= Smoluchowski’s theory: η kT 3 4 0 2 k = Eletrophoretic mobility: f1( a) 3 2 u o κ η ς εε =
κa f1(κa) κa f1(κa)
0 1.000 5 1.160 1 1.027 10 1.239 2 1.066 25 1.370 3 1.101 100 1.460 4 1.133 ∞ 1.500 1 1 γ
Kelvin’s equation: rRT l v 2 o p g p ln = γ
Methods to measure surface tension:
Capillary method: γ =hr(cosθ)gρ/2 (h is height, r is the capillary’s internal radius, ρ is the density, g is acceleration due to gravity and θ is the contact angle)
Plate method:
Lcosθ netto w =
γ (wnetto is the nett force, L is the wetted length, θ is the contact
angle) Ring method: R 4 F ; ) ρ β α ( max mätt mätt mätt p = + = γ γ γ
γ (α, β are ring constants, Fmax is the
maximum force, R is the ring’s radius)
Drop-weight method: γ =Fmdropg/r(F is a correction factor, mdrop is the mass of the drop, r
is the capillary’s internal radius, g is acceleration due to gravity)
Maximum bubble pressure: γ =∆pmaxr/2(∆pmax is the pressure difference, r is the bubble
radius) Surface excess: T 2 c RT 2 c ) 1 ( 2 ∂ ∂ − = Γ γ
Tables for surface and colloid chemistry
Group numbers (according to Davies and Rideal) for some common groups Hydrophillic groups Group number Lipophillic groups Group number
Derived groups Group number -SO−4Na+ +38.7 -CH- -0.475 -(OCH2CH2)- +0.33 -COO-K+ +21.1 -CH2- -0.475 -(OCH2CH2 CH2)- -0.15 -COO-Na+ +19.1 -CH3 -0.475 N(tertiary amine) +9.4 =CH- -0.475 Ester -O-(CO)- +2.4 -CF2- -0.870 -COOH +2.1 -CF3 -0.870 -OH +1.9
Ether group -O- +1.3
Viscosity of water at different temperatures
ºC η (10-3 Pascal s) ºC η (10-3 Pascal s) 10 1.307 20 1.002 11 1.271 21 0.9779 12 1.235 22 0.9548 13 1.202 23 0.9325 14 1.169 24 0.9111 15 1.139 25 0.8904 16 1.109 26 0.8705 17 1.081 27 0.8513 18 1.053 28 0.8327 19 1.027 29 0.8148
Dielectric constant for water at different temperatures
ºC ε ºC ε 0 87.90 30 76.58 5 85.90 35 74.85 10 83.95 38 73.83 15 82.04 40 73.15 18 80.93 45 71.50 20 80.18 50 69.88 25 78.36 55 68.30
Some symbols and constants a,r: particle radius
ε: dielectric constant
ε0=8.85x10-12 C2J-1m-1: permittivity of vacuum
k=1.38x10-23 JK-1: Boltzmann’s constant R=8.314 JK-1mol-1: Gas constant
NA=6.022x1023 mol-1: Avogadro’s number
e0=1.602x10-19C: elementary charge (charge on an electron)
H: distance between particles Ψ: electric potential
Ψ0: surface electric potential
cio: concentration of species i in the bulk phase
A: Hamakar contant
k20: rate constant for rapid coagulation
η, η0: viscosity
φ: volume fraction γ: surface tension pg, p0: pressure
v: volume of the liquid phase
c2: concentration of the dissolved substance
u: electrophoretic mobility ζ: zeta potential
