
View
Online

Expo
Ci a ion
C ossMa k
RESEARCH ARTICLE | NOVEMBER 01 1998
Linea iscoelas ic p ope ies o suc ose es e -s abilized oil-
in-wa e emulsions
A. Gue e o; P. Pa al; C. Gallegos
Jou nal o Rheology 42, 1375–1388 (1998)
h ps://doi.o g/10.1122/1.550965
Rela ed Con en
S udy o geome ical and elec onic s uc u e o lan hanum doped PbTiO3 and PbZ TiO3: Fi s p inciples
calcula ion
AIP Con e ence P oceedings (No embe 2018)
Linea iscoelas ic beha io o comme cial and model mayonnaise
Jou nal o Rheology (Ap il 1992)
Rema ks on high ene gy muon collide
AIP Con e ence P oceedings (Augus 2000)
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd
Linea iscoelas ic p ope ies o suc ose es e -s abilized
oil-in-wa e emulsions
A. Gue e o
Depa amen o de Ingenie ı
´a Quı
´mica, Uni e sidad de Se illa, C/P. Ga cı
´a
Gonza
´lez s/n, 41012 Se illa, Spain
P. Pa ala) and C. Gallegos
Depa amen o de Ingenie ı
´a Quı
´mica, Uni e sidad de Huel a, Escuela
Poli e
´cnica Supe io , C a. de Palos de la F on e a s/n, 21819, Huel a, Spain
(Recei ed 22 Decembe 1997; inal e ision ecei ed 3 Augus 1998)
Synopsis
This pape deals wi h he in luence o composi ion @suc ose es e SE and oil O concen a ions#and
empe a u e on he linea iscoelas ici y p ope ies o highly concen a ed oil-in-wa e emulsions,
using a hyd ophilic suc ose palmi a e as emulsi ie . Di e en oil-in-wa e emulsions we e p epa ed
using a suc ose palmi a e (SE 51–5 w %) wi h a hyd ophilic–lipophilic balance o 15, sun lowe
oil (O 560–80 w %) and wa e . Oscilla o y measu emen s we e ca ied ou in he linea
iscoelas ici y egion. The elaxa ion ime spec a o he emulsions we e calcula ed using
egula iza ion echniques and we e i ed o an empi ical model p oposed by Madiedo ~1996!. The
esul s ob ained a e explained on he basis o he ela ionship among linea iscoelas ici y
p ope ies, d ople size dis ibu ion, and cha ac e is ics o he con inuous phase. Thus, an inc ease
in suc ose palmi a e concen a ion p oduces highe alues o he linea iscoelas ici y unc ions and
a b oade pla eau egion in he elaxa ion ime spec um, which sugges s a ce ain enhancemen o
he elas ic ne wo k. © 1998 The Socie y o Rheology. @S0148-6055~98!01206-1#
I. INTRODUCTION
Oil-in-wa e ~o/w!emulsions a e manu ac u ed by dispe sing he oil phase in o he
aqueous con inuous phase in he o m o small d ople s ~mos comme cial emulsions
ha e d ople sizes in he ange o 0.1–10
m
m!@Wals a ~1983!#. In o de o ob ain s able
emulsions wi h sui able d ople size dis ibu ions ~DSD!, he emulsi ica ion p ocess e-
qui es a conside able amoun o mechanical ene gy ~in he o de o 1–100 MJ/m3de-
pending on emulsi ica ion machine!@Wals a ~1993!#. I is wo h poin ing ou ha he
emulsi ica ion p ocess is a highly complex uni ope a ion which depends on many a i-
ables ~ empe a u e, esidence ime, agi a ion speed, e c.!@Gallegos and F anco ~1998!#.I
is in ol ed in many di e en indus ies o p oduce a wide a ie y o emulsions ~ ood-
s u s, cosme ics, pha maceu icals, pe ochemicals, ag ochemicals, e c.!@Walke ~1984!;
Yuki e al. ~1990!; Desai, 1990#, which may be o mula ed o co e a wide ange o
dispe se phase olume ac ions
om dilu e o highly concen a ed emulsions, wi h
app oaching a alue o 1.
a!Au ho o whom all co espondence should be add essed.
© 1998 by The Socie y o Rheology, Inc.
J. Rheol. 42~6!, No embe /Decembe 1998 13750148-6055/98/42~6!/1375/14/$20.00
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd
S abili y is a p ima y equi emen o he comme cial applica ion o emulsions. How-
e e , emulsions a e he modynamically uns able because o hei la ge in e acial a ea
and d ople s end o agg ega e spon aneously. An emulsion is conside ed s able when he
numbe , size dis ibu ion, and a angemen o d ople s do no unde go any disce nible
change o e he s o age ime scale.
An emulsi ie is ypically added o imp o e bo h he emulsi ica ion p ocess and he
emulsi ica ion s abili y. The emulsi ie molecules adso b a he oil–wa e in e ace and
educe he in e acial ension, he eby a o ing emulsi ica ion and o ming a p o ec i e
ba ie a ound he oil d ople s @Dickinson ~1994!#. This inc eases in e d ople in e ac ions
and p o ides enhanced s abili y agains coalescence. The ole o hese in e ac ions is
undamen al in highly concen a ed emulsions, in which e y close packing o d ople s is
ound and he con inuous phase consis s o a hin ilm sepa a ing adjacen d ople s. This
p oduces highly iscoelas ic esponses @O subo and P ud’homme ~1994!# and may lead o
he de elopmen o an ex ensi e loccula ion o d ople s o o m a weak gel-like pa icu-
la e ne wo k depending on he na u e and concen a ion o he emulsi ie @Dickinson
~1989!#. The ex ensi e loccula ion p ocess p o ides enhanced s abili y o he emulsion
since he c eaming a e is signi ican ly dec eased @F anco e al. ~1995a,b, 1997!#.
The iscoelas ic p ope ies o he emulsions depend on he s a e o loccula ion. Un-
loccula ed o weakly loccula ed emulsions show a c osso e poin be ween G8and G9,
which is ela ed o a cha ac e is ic elaxa ion ime o he onse o he e minal o low
egion. This elaxa ion ime inc eases sha ply wi h
because o he s onge in e ac ions
among d ople s @Tad os ~1993!#. Howe e , emulsions using a mix u e o suc ose es e
~SE!and egg yolk p o eins as emulsi ie s usually show ex ensi e loccula ion, depending
on he ene gy inpu and empe a u e du ing he emulsi ica ion p ocess, which has been
p e iously ela ed o he de elopmen o a pla eau egion in he elaxa ion ime spec um
@F anco e al. ~1995b, 1997!#. O he highly concen a ed emulsions s abilized only by
p o eins also show gel-like esponses (G8is much highe han G9, bo h a e almos
pa allel!wi h a wide pla eau egion @Gue e o and Ball ~1994!; Gallegos e al. ~1992!#.
In a p e ious pape , he abili y o a highly hyd ophilic ~hyd ophilic–lipophilic bal-
ance, HLB 515) suc ose palmi a e, used as he only emulsi ie , o o m highly s able
emulsions was es ablished @Pa al e al. ~1994!#. The low beha io and d ople size o
o/w emulsions s abilized by his suc ose palmi a e has also been s udied @Pa al e al.
~1997!#. An e olu ion owa ds smalle sizes and na owe dis ibu ions was obse ed as
suc ose palmi a e and oil concen a ions we e aised, which led o an inc ease in he
emulsion iscosi y.
The objec i e o he p esen pape is o s udy he in luence o composi ion ~suc ose
palmi a e and oil concen a ions!and empe a u e on he linea iscoelas ici y p ope ies
o highly concen a ed o/w emulsions using a hyd ophilic suc ose palmi a e as an emul-
si ie . The ela ionship among he linea iscoelas ici y unc ions, d ople size dis ibu-
ion, and s abili y is also analyzed.
II. EXPERIMENT
Di e en oil-in-wa e emulsions we e p epa ed using a Ryo o suc ose palmi a e ~P-
1570, HLB 515) om he Mi subishi–Kasei Food Co po a ion ~Tokyo, Japan!. This
emulsi ie was used as ecei ed. Sun lowe oil was pu chased in a local s o e. Oil-in-
wa e emulsions we e p epa ed using an Ul a-Tu ax T-50 homogeneize . Sun lowe oil
was added o a solu ion o he emulsi ie in dis illed wa e a 55 °C, and mixed a a speed
o 5000 pm o 3.5 min. The suc ose palmi a e concen a ion ~SE! anged om 1% o
1376 GUERRERO, PARTAL, AND GALLEGOS
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd
5% ~w !and he oil con en ~O! om 60% o 80% ~w !(
50.59–0.77). Emulsions
we e s o ed a 5 °C.
Oscilla o y shea measu emen s we e pe o med in a Haake RS100 RheoS ess he-
ome e , using a cone-and-pla e senso sys em C35/4 ~4°, 35 mm!. The s ess ange o
linea iscoelas ici y was de e mined h ough a dynamic s ess sweep a a ixed equency
~6.28 ad/s!. All samples had he same ecen pas he mal and heological his o y. Rheo-
logical es s we e ca ied ou in he ange o 5–35 °C.
The elaxa ion ime spec um o each emulsion a each empe a u e was calcula ed by
using a comme cial so wa e p og am ~RHEOSPEC!, which is based on egula iza ion
echniques.
III. RESULTS AND DISCUSSION
A. In luence o suc ose palmi a e concen a ion
The e olu ion o he s o age and loss moduli wi h equency as a unc ion o he
suc ose palmi a e concen a ion is shown in Figs. 1~a!and 1~b!. Bo h moduli show a
con inuous inc ease wi h emulsi ie concen a ion. The s o age modulus G8is always
highe han he loss modulus G9wi hin he expe imen al equency ange. Hence, he
emulsions p esen a p edominan ly elas ic esponse, al hough a c osso e poin ends o
appea in he low- equency egime. Mo eo e , he e is a endency o G8 o exhibi a
pla eau egion @Fig. 1~a!#. This zone, a in e media e equencies, is known as he pla eau
egion and may be ela ed o he o ma ion o an elas ic s uc u al ne wo k due o in e -
ac ions among he emulsi ie molecules loca ed a he oil–wa e in e ace o adjacen
d ople s @Dickinson ~1989!; F anco e al. ~1995b!#. This beha io is ypical o highly
concen a ed emulsions such as comme cial o model mayonnaises @Gallegos e al.
~1992!; Gue e o and Ball ~1994!# and salad d essings @Mun
˜oz and She man ~1992!;
F anco e al. ~1995b!#. The pla eau egion has been ex ensi ely desc ibed in polyme
heology in e ms o an en anglemen ne wo k among polyme chains in which he
FIG. 1. In luence o suc ose palmi a e @~a!,~b!# on he s o age and loss moduli; and no malized linea iscoelas-
ici y unc ions o suc ose palmi a e-s abilized emulsions ~c!(T525°C).
1377OIL-IN-WATER EMULSIONS
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd
mo ion o molecules is cons ained by he neighbo ing molecules @Fe y ~1980!;Wu
~1989!#. When he emulsion is s abilized by p o eins @Gallegos e al. ~1992!; Gue e o
and Ball ~1994!#, he h ee-dimensional ne wo k is a o ed by en anglemen s among
p o ein segmen s adso bed a he oil–wa e in e ace. The same beha io was epo ed
when a suc ose s ea a e was used in combina ion wi h egg yolk @F anco e al. ~1995b!#.
Taking in o accoun ha he emulsions s udied a e s abilized exclusi ely by a low
molecula weigh su ac an ~suc ose palmi a e!and ha e high alues o dispe se phase
olume ac ion ~oil d ople s!, he pla eau egion was a ibu ed o an ex ensi e loc-
cula ion p ocess ha a o s emulsion s abili y by o ming a gel-like pa icula e ne -
wo k @Dickinson ~1989!# due o in e d ople in e ac ions. Simila e ec s we e epo ed
by Ebe e al. ~1988! o highly concen a ed emulsions s abilized by a
ce yl ime hylamonium-b omide su ac an .
In he pla eau egion, he loss angen passes h ough a minimum, which has been used
o calcula e an app oxima e alue o he pla eau modulus, GN
0@Wu ~1989!; A end e al.
~1994!; F anco e al. ~1995b!#. The pla eau modulus is a iscoelas ic pa ame e , de ined
as an ex apola ion o he en anglemen con ibu ion o G8o G9a high equency
@Baumgae el e al. ~1992!#. This pa ame e may be app oxima ed om he minimum in
an
d
as ollows @Wu ~1989!#:
GN
05@G8# an
d
→minimum.~1!
As a esul , he pla eau modulus GN
0unde goes an exponen ial inc ease when suc ose
palmi a e concen a ion is aised @Fig. 2~a!#, as co esponds o a mo e s uc u ed sys em.
The e olu ion o G8and G9, and also o he o he iscoelas ic unc ions wi h e-
quency ~i.e., loss angen !, is a he simila up o 3% suc ose palmi a e. This simila i y
allows one o supe pose all he iscoelas ic unc ions ~be ween 1% and 3% suc ose
palmi a e!by using he pla eau modulus as a no maliza ion ac o @Fig. 1~c!#. Howe e ,
he no maliza ion p ocedu e ails a he highes concen a ions o he emulsi ie ~4% and
5%!, because an inc ease in loss angen was obse ed om 3% o 5%.
As has been p e iously epo ed @Pa al e al. ~1997!#, an inc ease in SE concen a ion
p oduces a dec ease in d ople size and polydispe si y, which leads o an inc ease in he
speci ic in e acial a ea a@Fig. 2~b!#. Assuming sphe ical d ople s, ‘‘a’’ is ela ed o he
Sau e mean diame e as ollows:
a56/ds ,ds 5
(nidi
3
(nidi
2,~2!
whe e niis he numbe o d ople s ha ing diame e di.
Howe e , he e is a c i ical concen a ion ~3% SE!abo e which he slope o his
inc ease is lowe . To unde s and his change, he p ope ies o he con inuous phase used
o he p epa a ion o he emulsions should also be aken in o conside a ion. Thus, he
emulsions con aining 70% oil and 1%–3% SE we e p epa ed om a con inuous phase
con aining 3%–10% SE, which we e iso opic micella solu ions (L1) a he empe a u e
o emulsi ica ion ~50 °C!, as may be seen in he phase diag am shown in a p e ious pape
@Calaho o e al. ~1992!#. A concen a ions highe han 10% ~as co esponds o emul-
sions con aining 4% and 5% SE! he ini ial con inuous phase was always a dilu e dispe -
sion o lamella liquid-c ys alline (L
a
) po ions in an iso opic micella ma ix, a he
emulsi ica ion empe a u e ~50 °C!. The e o e, he abo e-men ioned c i ical concen a ion
co esponds o he ansi ion om L1micella solu ion o he L11L
a
dispe sion. As a
esul , a ema kable inc ease in he low-shea limi ing iscosi y
h
oc is obse ed o he
su ac an –wa e sys em @Fig. 2~c!#. This inc ease seems o impai he emulsi ica ion
p ocess, leading o a lowe inc ease in he in e acial a ea @Fig. 2~b!#.
1378 GUERRERO, PARTAL, AND GALLEGOS
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd

On he o he hand, he excess o su ac an o e he amoun necessa y o sa u a e he
in e ace as a monolaye (
e
SE) con inuously inc eases wi h SE concen a ion @Fig. 2~b!#.
The excess o su ac an has been calcula ed as ollows:
e
SE 5
~C
/a
!
Csa
21, ~3!
whe e Cis he suc ose palmi a e concen a ion,
is he emulsion densi y, ‘‘a’’ is he
speci ic in e acial a ea,
is he dispe se phase olume ac ion ~oil d ople s!, and Csa is
he concen a ion necessa y o sa u a e he in e ace as a monolaye . Taking in o accoun
he su ace p essu e-a ea iso he m ob ained by Ab an e al. ~1988! o he suc ose palmi-
a e, he Csa alue was es ima ed as 0.36531026g/cm2@Pa al e al. ~1997!#.
Once he emulsi ica ion p ocess is o e , he con inuous phase o hese highly concen-
a ed emulsions consis s o a e y hin ilm sepa a ing adjacen d ople s. The consis ency
o his ilm, a o ed by he inc ease in
e
SE, as well as he inc ease in he speci ic su ace
a ea, explain he la ge alues o he iscoelas ic unc ions and he exponen ial ise in he
pla eau modulus shown in Fig. 2~a!.
Figu e 3 shows he elaxa ion ime spec um o selec ed emulsions ob ained by means
o he Tikhono egula iza ion p ocedu e using he RHEOSPEC so wa e. As may be ob-
se ed in Fig. 1, he ecalcula ion o he iscoelas ic unc ions om he elaxa ion ime
spec um ob ained by he egula iza ion echnique ~RHEOSPEC so wa e!is e y accu a e.
FIG. 2. ~a!In luence o suc ose palmi a e concen a ion on he pla eau modulus; ~b!excess o su ac an o e
he amoun necessa y o sa u a e he in e ace as a monolaye and speci ic in e acial a ea as a unc ion o
suc ose palmi a e concen a ion; ~c! iscosi y o he ini ial su ac an -con aining solu ion ~SCS!a which oil is
added ~please no e ha he concen a ion o his solu ion is SCS 5SE33.3) a 50 °C.
1379OIL-IN-WATER EMULSIONS
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd
To exp ess quali a i ely he elaxa ion da a, De Rosa and Win e ~1994!p oposed an
empi ical model, de i ed om he Baumgae el–Schausbe ge –Win e ~BSW!spec um
@Baumgae el e al. ~1992!#, and he Chambon–Win e ~CW!spec um @Chambon and
Win e ~1985!#. Al hough his model was p oposed o desc ibe he elaxa ion p ocess o
polyme mel s, i has been also used o emulsions as salad d essings @F anco e al.
~1995b!#. This model equi es wo unc ions o desc ibe he ansi ion, pla eau, and e -
minal egions o he elaxa ion ime spec um. A simple empi ical equa ion, which com-
p ises he h ee egions o he spec um, has ecen ly been p oposed by Madiedo ~1996!
and Madiedo and Gallegos ~1997!:
H~l!5
a
lm1
b
ln
11~l/l !p,~4!
whe e m,nand (n–p) a e he slopes o he ansi ion, pla eau, and pseudo e minal zones,
espec i ely; and l is a cha ac e is ic elaxa ion ime ela ed o he bounda y o he
pla eau egion. Since he c osso e equency was no eached o he emulsions s udied,
l will be conside ed a i ing pa ame e in his pape . As may be no ed, hese pa ame e s
a e ela i ely simila o he pa ame e s o he BSW–CW model @Madiedo and Gallegos
~1997!#. Pa ame e s
a
and
b
ha e he ollowing exp essions:
a
5mH0
~m2n!l0
m,~5!
b
5nH0
l0
n~n2m!,~6!
whe e l0is a cha ac e is ic elaxa ion ime ela ed o he onse o he pla eau egion and
H0is he alue o he spec um co esponding o his elaxa ion ime. I he slope o he
pla eau egion is posi i e, n.0, Eq. ~4!p edic s a maximum alue o H(l) o a
elaxa ion ime lmax 5l @n/(n2p)#1/p, which was ela ed by De Rosa and Win e ~1994!
FIG. 3. In luence o suc ose palmi a e concen a ion on he elaxa ion ime spec a o suc ose palmi a e-
s abilized emulsions (T525°C).
1380 GUERRERO, PARTAL, AND GALLEGOS
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd
wi h he elaxa ion ime a which H(l) equals GN
0 imes n. Howe e , his maximum does
no always appea . Consequen ly, he elaxa ion ime spec um calcula ed om he egu-
la iza ion me hod o each emulsion was analyzed acco ding o he Madiedo and Gal-
legos ~1997!model @Eq. ~4!#.
The elaxa ion ime spec a calcula ed om he Tikhono egula iza ion me hod, o
each suc ose palmi a e concen a ion, a e shown in Fig. 3. As may be seen, he abo e-
men ioned model sa is ac o ily desc ibes he elaxa ion ime spec a ob ained o hese
emulsions. The shape o he spec um is always simila . A pla eau egion is always
clea ly obse ed. Likewise, a egion cha ac e ized by a end o each he e minal zone
o low egion may be no ed. The inc ease in emulsi ie concen a ion p oduces an in-
c ease in he elaxa ion ime spec um highe han one o de o magni ude, which is
app oxima ely he same inc ease unde gone by GN
0and indica es ha an enhancemen o
he elas ic ne wo k is p oduced.
Howe e , Table I shows a maximum alue in l ollowed by a dec ease, which
co esponds o a displacemen o he pla eau egion owa ds a sho e elaxa ion ime o
highe equency. This displacemen has also been ound o salad d essing emulsions
s abilized by p o eins and suc ose es e @F anco e al. ~1997!#. The slope o he pla eau
egion does no change wi h SE concen a ion showing alues close o ze o. The only
excep ion was he emulsion con aining 5% SE, which shows a posi i e alue o n,
indica i e o a highe deg ee o s uc u e. A signi ican inc ease in he s abili y o hese
emulsions was also ound as SE became highe @Pa al e al. ~1994!#.
B. In luence o oil concen a ion
The e olu ion o he s o age and loss moduli wi h equency is simila o all he oil
concen a ions s udied, G8always being highe han G9@Figs. 4~a!and 4~b!#. Thus, he
loss angen is oughly independen o he oil concen a ion. As a esul , he pla eau
modulus @which is shown in Fig. 5~a!# was success ully used o no malize bo h s o age
and loss moduli as a unc ion o equency (a
8
), leading o a mas e cu e o each o
hem @Fig. 4~c!#. Howe e , some sca e may be obse ed in G9a high equencies @Fig.
4~c!#. An empi ical ho izon al shi ac o , (a
850.4) was necessa y o he smalles oil
concen a ion because o a equency displacemen o he pla eau egion as was p e i-
ously ound o salad d essing emulsions @F anco e al. ~1997!#.
Figu e 5~a!shows he alues o pa ame e GN
0as a unc ion o he dispe se phase
olume ac ion. An inc ease in his pa ame e , wi h a end o each an almos cons an
TABLE I. In luence o concen a ion on bo h he pseudo e minal elax-
a ion ime (l ) and slope o he pla eau egion ~n!, o suc ose palmi a e-
s abilized emulsions.
%SE %O nl
~s!
1% 70% 0.017 59
2% 70% 20.006 80
3% 70% 20.013 84
4% 70% 20.025 66
5% 70% 0.045 18
3% 60% 0.003 28
3% 65% 20.035 93
3% 75% 0.004 62
3% 80% 20.002 144
1381OIL-IN-WATER EMULSIONS
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd
alue abo e 70% (
50.68), was obse ed. Simila ly, he iscoelas ic moduli inc ease
wi h oil concen a ion bu only up o a ce ain alue which depends on equency. Thus,
a low equencies, he emulsion con aining 80% oil has he highes alues o G8and G9
@Figs. 4~a!and 4~b!#, while a in e media e and high equencies he e a e no di e ences
in G8 om 70% o 80% and he highes alues o G9co espond o 70% oil. This
FIG. 4. In luence o oil concen a ion @~a!,~b!# on he s o age and loss moduli; and no malized linea iscoelas-
ici y unc ions o suc ose palmi a e-s abilized emulsions ~c!(T525°C).
FIG. 5. ~a!In luence o dispe se phase olume ac ion ~oil!on he pla eau modulus; ~b!excess o su ac an
o e he amoun necessa y o sa u a e he in e ace as a monolaye and speci ic in e acial a ea as a unc ion o
dispe se phase olume ac ion.
1382 GUERRERO, PARTAL, AND GALLEGOS
Downloaded om h p://pubs.aip.o g/so /jo /a icle-pd /42/6/1375/12481961/1375_1_online.pd