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prepared by Justyna Iwaczuk University of Natural Sciences - - PowerPoint PPT Presentation
prepared by Justyna Iwaczuk University of Natural Sciences - - PowerPoint PPT Presentation
prepared by Justyna Iwaczuk University of Natural Sciences Humanities in Siedlce Supervisor of the project: Aldona Rajewska, PhD Surfactants (Surface active agent) are compounds that are amphiphilic, meaning they contain both hydrophobic
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Surfactants (Surface active agent) are compounds that are amphiphilic, meaning they contain both hydrophobic groups (their tails) and hydrophilic groups
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Example
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The concentration at which surfactants start forming micelles is called the "critical al micelle le concentra centration tion (CMC)" )". Kraft t point is the minimum temperature at which surfactants form micelles. The Krafft temperature is a point of phase change below which the surfactant remains in crystalline form, even in aqueous solution. Micellization
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1 – two reflectors; 2 – zone of reactor with moderator; 3 – chopper; 4 – first collimator; 5 – vacuum tube; 6 – second collimator; 7 – thermostate; 8 – samples table; 9 – goniometer; 10-11 – Vn-standard; 12 – ring-wire detector; 13 – position-sensitve edetector "Volga"; 14 – direct beam detector.
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Why
Why use neutrons rons?
- Neutrons interact through short-range nuclear
- interactions. They have no charge and are very penetrating
and do not destroy samples.
- Neutron wavelengths are comparable to atomic sizes and
interdistance spacings
In this technique radiation is elastically scattered by a
sample and the resulting scattering pattern is analysed to provide information about the size, shape and orientation
- f some component of the sample.
SANS are used in situations where the important physical
aspects ( size, range of interaction etc.) occur at distances extanding typically from 10 to 1000 Å
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Monodisperse, homogeneous, globular
particles, the total scattering intensity can be expressed by this equation I(q)=NS(q)P(q) Where N- number of parcitles S(q)- structure factor P(q)-form factor
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In experiment determined the temperature and concentration influence on the micelle shape of two nonionic surfactants:
Pentaethylene glycol monododecyl ether (C12E5) ,
CMC=7*10-5M at 25oC
Octaethylene glycol monododecyl ether (C12E8),
CMC= 8*10-5 M at 25oC
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0.01 0.1 0.1 1
d (Q)/d , cm
- 1
Q[A
- 1]
nonionic classic surfactant c=1% 10
- C
15
- C
20
- C
25
- C
30
- C
35
- C
Fig.1. Intensity of neutron scattering vs scattering vector for concentration c1=1% at temperatures: 10o, 15o, 20o, 25o, 30o and 35oC.
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1 2 3 4 5 6 7 8 9 10 0.02 0.04 0.06 0.08
p(r) r [nm]
c=1% 10
- C
15
- C
20
- C
25
- C
30
- C
35
- C
- Fig. 2. Pair distance distributon function (PDDF) for the …
(c=0,17%) system from SANS measurements for temperatures 10, 15, 20, 25 30 and 35 Celsius degree
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0.01 0.1 1E-4 1E-3 0.01 0.1 1 10 100
d (Q)/d , cm
- 1
Q [A
- 1]
nonionic classic surfactant 6
- C
10
- C
15
- C
20
- C
25
- C
30
- C
35
- C
- Fig. 3 Intensity of neutron scattering vs scattering vector
for concentration c1=1% at temperatures: 10o, 15o, 20o, 25o, 30o and 35oC
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- Fig. 4 Pair distance distributon function (PDDF) for the C17
(c=1 %) system from SANS measurements for temperature 6 Celsius degree
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- Fig. 5 Pair distance distributon function (PDDF) for the C17
(c=1 %) system from SANS measurements for temperature 15 Celsius degree
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If intensity of neutrons scattering increases the
number of micelles grow up in micellar solution
For the bigger concentrations and temperatures
the maximum have a higher value
If the curve p(r) is symmetric – micelles have
spherical shape
If the curve p(r) is asymmetric – micelles have
cylindrical shape
Distance between zero point and point where
curve p(r) cross axis r is equal to diameter of micelle
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