Chemistry Reference
In-Depth Information
7.4. Increasing the surfactant concentration in an emulsion polymerization usually
leads to the formation of more latex particles. If the rest of the reaction mixture
is unchanged, what will be the expected effect of the amount of surfactant on
the final average particle size, on the rate of polymerization, and on the
average degree of polymerization?
7.5. Many natural gums are used as thickeners and stabilizers in food products such
as ice cream. It is often found that a mixture of gums and other polymers gives
better results in terms of the final characteristics of the product than does any
one material alone. Suggest some possible reasons for such an apparently
synergistic effect.
7.6. A scientist wants to prepare a stable dispersion of a positively charged mineral
in a high-molecular-weight hydrocarbon carrier. One requirement of the
system is that it contain no low-molecular-weight components such as normal
surfactants. Suggest a relatively accessible synthetic pathway for a polymeric
surfactant that may suit her needs beginning with maleic acid and any
hydrocarbon materials that may be needed. Specific reaction conditions are
not required.
7.7. A series of A-B block copolymers, where A
POP chains,
were evaluated as solubilizers for a series of dyes. In the series, the molar
ratios of the two chains (A/B) were as follows:
¼
POE and B
¼
Surfactant
A/B
1
0.5
2
1.0
3
1.5
Which surfactant would you expect to perform better for each of the
following dye classes: (a) a hydrophobic dye; (b) a polar, uncharged dye;
(c) a positively charged dye?
7.8. On the basis of your conclusions in problem 7.7, where would you expect each
dye to be ''located'' in the corresponding micelle?
7.9. What would you expect to happen when the following polymer and surfactant
solution are mixed:
(a) Polyvinyl alcohol
þ
SDS
(b) Sodium polyacrylate
þ
SDS
Cl
(c) Sodium polyacrylate
þ
(CH
3
)
3
C
12
H
25
-N
þ
(d) Carboxymethyl cellulose
þ
glycerol monostearate
Ca
2
þ
(C
17
H
35
COO
)
2
(f) Gelatin (zpc
(e) Pectin
þ
Cl
¼
pH 4.8) at pH
¼
7.0
þ
(CH
3
)
3
C
12
H
25
-N
þ
(g) Gelatin (f)
þ
SDS
