“…As seen from Table the A cmc values are independent of ( n ) m within the experimental error. This result is in agreement with findings of Yeates et al on the C n E 8 M series. On the other hand, the A cmc for Y surfactants C 14 G(E m /2 M) 2 increases with ( m ) n , but for V s surfactants (C 7 ) 2 GE m M the A cmc is almost independent of ( m ) n (Figure ). 4 Area per molecule A cmc at the air−water interface vs ( m ) n =14 for Y surfactants C n G(E m /2 M) 2 and V s surfactants (C n /2 ) 2 GE m M.…”
Section: Resultssupporting
confidence: 94%
“…The micellization and surface properties of (alkoxy)oligo(oxyethylenes) in water have been extensively studied . Only a few studies, however, exist dealing with the influence of the molecular geometry of the surfacant on surface and micellar properties. − …”
Section: Introductionmentioning
confidence: 99%
“…1 Only a few studies, however, exist dealing with the influence of the molecular geometry of the surfacant on surface and micellar properties. [2][3][4] The influence of the surfactant structure on the micelle organization is well-known. The factors controlling micellar shape are the average molecular area at the micelle surface, the length, the volume, and a structure parameter of the hydrocarbon part of the surfactant.…”
The influence of the molecular geometry of corresponding
differently branched nonionic surfactants on
surface and micellar properties in aqueous solution was investigated by
surface tension measurements.
The nonionic surfactants with a branched hydrophilic moiety are
described as Y surfactants
(C
n
G(E
m
/2M)2)
and with a branched lipophilic moiety as V surfactants: symmetrical
Vs
(C
n
/2)2GE
m
M
and asymmetrical
Va
(C
k
)(C
n
-k
)GE
m
M;
where C
n
and C
k
denote an
alkyl chain, G a triglyceryl unit, and E
m
M an
oligo(oxyethylene) monomethyl ether with k = 4, n =
10, 12, 14, 16, and m = 6, 8, 10. The critical
micelle
concentration (cmc), the standard free energy of micellization
(ΔG
m), the equilibrium surface tension
(γcmc),
and areas per molecule at cmc (A
cmc) at the
air−water interface were determined as a function of the
total
hydrocarbon number (n)
m
=const in
the lipophilic part and oxyethylene group number
(m)
n
=const, in the
hydrophilic part of the surfactant. The results are discussed on
the basis of structural factors for the
corresponding Y, Vs, Va surfactants and
compared with data of the conventional unbranched
surfactants
C
n
E8M (I surfactants). Within
these homologous series the increase of
(n)
m
leads to the lowering and
an
increase of (m)
n
to the increasing of
the cmc's and ΔG
m's. For the
corresponding surfactant series the
negative contribution to the cmc and ΔG
m of
each CH2 group promotes micellization and increases in
the
sequence I > Y > Vs. On the other hand the positive
contribution of each EO group opposes the micellization
and is larger for Y than for Vs surfactants. The
γcmc and A
cmc for Y surfactants
are significantly larger
than for V surfacants. In the gorup of the V surfactants the
cohesive forces of the hydrocarbon chains
significantly influence the γcmc's.
“…As seen from Table the A cmc values are independent of ( n ) m within the experimental error. This result is in agreement with findings of Yeates et al on the C n E 8 M series. On the other hand, the A cmc for Y surfactants C 14 G(E m /2 M) 2 increases with ( m ) n , but for V s surfactants (C 7 ) 2 GE m M the A cmc is almost independent of ( m ) n (Figure ). 4 Area per molecule A cmc at the air−water interface vs ( m ) n =14 for Y surfactants C n G(E m /2 M) 2 and V s surfactants (C n /2 ) 2 GE m M.…”
Section: Resultssupporting
confidence: 94%
“…The micellization and surface properties of (alkoxy)oligo(oxyethylenes) in water have been extensively studied . Only a few studies, however, exist dealing with the influence of the molecular geometry of the surfacant on surface and micellar properties. − …”
Section: Introductionmentioning
confidence: 99%
“…1 Only a few studies, however, exist dealing with the influence of the molecular geometry of the surfacant on surface and micellar properties. [2][3][4] The influence of the surfactant structure on the micelle organization is well-known. The factors controlling micellar shape are the average molecular area at the micelle surface, the length, the volume, and a structure parameter of the hydrocarbon part of the surfactant.…”
The influence of the molecular geometry of corresponding
differently branched nonionic surfactants on
surface and micellar properties in aqueous solution was investigated by
surface tension measurements.
The nonionic surfactants with a branched hydrophilic moiety are
described as Y surfactants
(C
n
G(E
m
/2M)2)
and with a branched lipophilic moiety as V surfactants: symmetrical
Vs
(C
n
/2)2GE
m
M
and asymmetrical
Va
(C
k
)(C
n
-k
)GE
m
M;
where C
n
and C
k
denote an
alkyl chain, G a triglyceryl unit, and E
m
M an
oligo(oxyethylene) monomethyl ether with k = 4, n =
10, 12, 14, 16, and m = 6, 8, 10. The critical
micelle
concentration (cmc), the standard free energy of micellization
(ΔG
m), the equilibrium surface tension
(γcmc),
and areas per molecule at cmc (A
cmc) at the
air−water interface were determined as a function of the
total
hydrocarbon number (n)
m
=const in
the lipophilic part and oxyethylene group number
(m)
n
=const, in the
hydrophilic part of the surfactant. The results are discussed on
the basis of structural factors for the
corresponding Y, Vs, Va surfactants and
compared with data of the conventional unbranched
surfactants
C
n
E8M (I surfactants). Within
these homologous series the increase of
(n)
m
leads to the lowering and
an
increase of (m)
n
to the increasing of
the cmc's and ΔG
m's. For the
corresponding surfactant series the
negative contribution to the cmc and ΔG
m of
each CH2 group promotes micellization and increases in
the
sequence I > Y > Vs. On the other hand the positive
contribution of each EO group opposes the micellization
and is larger for Y than for Vs surfactants. The
γcmc and A
cmc for Y surfactants
are significantly larger
than for V surfacants. In the gorup of the V surfactants the
cohesive forces of the hydrocarbon chains
significantly influence the γcmc's.
“…12 we replot the data for the EB diblock copolymers and include results for two other important poly-(oxyethylene)-based diblock copolymer systems: (i) commercially-important alcohol ethoxylates (CE, C = CH 2 or CH 3 ) and related EC block copolymers 115) ; (ii) biodegradable diblock copolymers of ethylene oxide and D,L-lactide (EL, L = carbonyloxymethylmethylene, COOCH-(CH 2 )). For the former system there are a number of results available in the literature, but we have chosen to plot our own for which the characterisation of the copolymers is secure [116][117][118] . For the latter system there are two reports which are not in good agreement 119,120) , and again, and for the same reason, we have chosen to plot our own data 119) .…”
Section: Effect Of Composition and Block Lengthmentioning
“…They can as well be classified as di- and triblock amphiphiles. The influence of the number of methylene groups in the linear hydrophobic part − and the number of ethylene oxide groups in the hydrophilic part − on the micelle organization are well established. The interfacial area per molecule, the CMC, chain geometry, and tendency to self coil have been reported for surfactants with polar or aromatic groups either at the alkyl terminus or along the hydrocarbon chain .…”
The micellization characteristics of nonionic surfactants of the
type C7E26 and symmetric
C7E26C7 where
C7 = the heptanoic acid
(C7H14O2) or the
cyclohexanecarboxylic acid
(C7H12O2) group is
investigated.
Structural formulas being nearly the same, the linear and cyclic
analogues possess roughly the same
molecular weights and hydrophilic−lipophilic balance (HLB) values.
Surface tension and fluorescence
experiments provide information on the thermodynamics of micellization,
interfacial adsorption, mean
aggregation number, etc. Comparisons are made between linear and
cyclic analogues and between diblocks
and triblocks. The results indicate that, compared to their linear
counterparts, amphiphiles with cyclic
hydrophobes possess higher CMC values and the micelles formed are less
compact with lower aggregation
number. A qualitatively similar trend is seen between diblock and
triblock surfactants. The results for
triblocks are consistent with a micellar structure in which the PEG
chain folds to insert both the terminal
hydrophobic segments into the micellar core.
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