Some recent illustrations of the phase behavior of polymer-amphiphile systems in solution are presented. Surfactant-polymer association is demonstrated for various amphiphilic synthetic and biological polymers both on a macroscopic and on a single molecular level

Dias, R

Khan, A

Lindman, B

Marques, E

Mel'nikov, SM

Miguel, MG

Progress in Colloid & Polymer Science

Repositório Aberto da Universidade do Porto

IntroductionMixed systems of macromolecules and amphiphiles areubiquitous in technical products (polymer–surfactantmixtures) and have a very broad role in biology(biopolymer–lipid mixtures) [1, 2]. Controlling theinteractions between macromolecules and low-molecu-lar-weight amphiphiles is the key to technical perfor-mance and biological function [3].Depending on the combination of a macromoleculeand an amphiphile, the interaction varies and, as aconsequence, the macroscopic behavior. Thus varioustypes of polymers behave quite dierently, i.e., chargedpolymers versus nonionic, cationic versus anionic,homopolymers versus graft or comb copolymers, etc.Early investigations focused on water-soluble homopol-ymers interacting with simple surfactants, but in recentyears much interest has concerned macromolecules withpronounced amphiphilic character. Amphiphilic syn-thetic polymers comprise a wide range of graft, blockand star copolymers, while biological examples includenucleic acids, proteins and lipopolysaccharides.Association and segregationBecause of the low entropic driving force of mixing,polymer–polymer–solvent systems have a strong ten-dency to segregative phase separation, i.e., two solutionphases enriched in either polymer result. Amphiphilesshow a strong tendency to self-assemble into micellesand other structures. Since these have a high eectivemolecular weight, segregation also becomes a typicalfeature of mixed polymer–surfactant solutions [4].The conditions for segregation are entirely dierentif one of the cosolutes, polymer or surfactant, is ionic.Then the large entropic contribution from the counter-ions becomes a strong driving force for mixing.An appreciable attractive interaction between poly-mer and surfactant will modify the situation and twoimportant phenomena are1. The binding of surfactant to the polymer.2. An associative phase separation.Piculell et al. [5] have identified three distinctly dierenttypes of surfactant binding to polymersProgr Colloid Polym Sci (1999) 112 : 157–162Ó Springer-Verlag 1999 POLYMERSM.G. MiguelE. MarquesR. DiasS.M. Mel’nikovA. KhanB. LindmanAssociating polymer±surfactant systemsInvited lecture, 12th Conference of theEuropean Colloid and Interface Society,Dubrovnik – Cavtat, 1998M.G. Miguel1 á E. Marques1 á R. Dias1S.M. Mel’nikov á A. KhanB. Lindman (&)Physical Chemistry 1Center for Chemistryand Chemical EngineeringP.O. Box 124, S-22100 Lund, SwedenPermanent address:1Departamento de Quı´micaUniversidade de CoimbraP-3049 Coimbra, PortugalAbstract Some recent illustrationsof the phase behavior of polymer–amphiphile systems in solution arepresented. Surfactant–polymer asso-ciation is demonstrated for variousamphiphilic synthetic and biologicalpolymers both on a macroscopic andon a single molecular level.Key words Polymer–surfactant sys-tems – Association and segregation –Phase behavior – Surfactant self-assembly – Catanionic vesicles1. An ionic surfactant associates with an oppositelycharged polymer.2. An ionic surfactant shows a strong tendency toassociate to a slightly hydrophobic, or a weaklypolar, polymer.3. All surfactants associate to polymers with stronglyhydrophobic parts, for example, hydrophobically-modified water-soluble polymers.In cases 1 and 2 the interactions are best described interms of a lowering of the critical micelle concentration(cmc) of the surfactant and in case 3 in terms of theformation of mixed micelles between polymer andsurfactant.Typical phase diagramsAn aqueous mixture of a rather hydrophobic polymerand a nonionic surfactant can phase-separate into onedilute solution and one concentrated isotropic phase. Asillustrated in Fig. 1, the extent of phase separationincreases with increasing temperature; this is due to thedecreased polarity of both surfactant and polymer athigher temperatures.A very strong tendency for associative phase separa-tion is displayed by polyelectrolytes mixed with oppo-sitely charged surfactants [7–13]. Here a correctrepresentation of the phase diagram is not possible inthe conventional triangular diagram, but a three-dimen-sional representation, representing the complete four-component system, is required. In Fig. 2 the typicalbehavior is given in the illustrative three-dimensionalpyramid diagram. Water is placed at the top and the foursides of the pyramid base are assigned to the four ioniccomponents of the system, with ions of the same chargelocated at opposite sides. As can be seen, there are twotwo-phase regions. In the low-salt one there is anassociative phase separation, i.e., the surfactant andthe polyelectrolyte form a concentrated phase in equi-librium with a very dilute solution. At high saltconcentrations there is a segregative phase separation,i.e., there is one surfactant-rich and one polymer-richsolution. At intermediate salt concentrations a homoge-nous solution is formed. The pyramid representationcertainly contains more information than the normallyused triangular representation, in which one dimensionis omitted, but due to the diculties to represent thepyramids, triangular phase diagrams are to be preferredin many cases.DNA and cationic surfactants phase-separateassociativelyThe phase diagrams of DNA in combination withdierent cationic surfactants have been investigated. Asillustrated in Fig. 3, there is, as for the analogousFig. 1 Hydrophobic interactions between a surfactant and a polymermay induce an associative phase separation; typically this increaseswith increasing temperature. The phenomenon is exemplified by theaqueous mixture of an oxyethylene nonionic surfactant, C12E4, anda nonionic polymer, ethyl(hydroxyethyl) cellulose. F1 refers to anisotropic one-phase region and F2 to an isotropic two-phase region.From Ref. [6]Fig. 2 A polyelectrolyte and an oppositely charged surfactanttypically phase-separate associatively at low electrolyte concentrationsand segregatively in the presence of high salt contents; at intermediateelectrolyte concentrations, there is miscibility. The ‘‘sail’’ hangingfrom the pyramid top corresponds to the two-phase region. The dilutephase is located to the upper right side, and the concentrated phase tothe lower side of the ‘‘sail’’. The example shown is hyaluronan, ananionic polysaccharide, and tetradecyltrimethylammonium bromide,a cationic surfactant. From Ref. [14]158polyelectrolyte–surfactant systems [7], a strong tendencyfor associative phase separation. For DNA the role ofhydrophobic polymer–surfactant interactions has to befurther examined.DNA compaction in the presenceof cationic surfactants ± an illustration of associationWith fluorescence microscopy it is possible to visualizeindividual high-molecular-weight DNA molecules [15].Because of the high charge density, DNA in aqueoussolution exhibits a highly extended coil state at lowelectrolyte concentrations. DNA compaction to a glob-ule results on screening the electrostatics [16].On addition of cationic surfactant, DNA compactiontakes place [17]. At lower surfactant concentrations,there is a region of coexistence of coils and globules(Fig. 4).Cationic surfactant binding to DNA is stronglycooperative [18] and is best described as a DNA-inducedsurfactant self-assembly; direct support for this viewcomes, apart from from structural investigations, fromthe fact that the ‘‘binding isotherms’’ are shifted for thedierent surfactant alkyl chain lengths in the same wayas the normal cmc.Surfactant-induced compaction of a high-molecular-weight polymer molecule can be seen as a single-molecular analogy to the associative phase separation.The dierent parts of the DNA molecule strive in thepresence of the surfactant to form a concentrateddomain.Catanionic vesiclesMixed cationic–anionic surfactant systems, referred toas catanionic surfactants [19], oer excellent possibilitiesto control the charge density of self-assemblies [20]. Aparticularly interesting feature is the formation ofthermodynamically stable vesicles [21]. In the phasediagram, the water-rich part of which is schematicallyindicated in Fig. 5, there are two regions of vesicleformation. In one the vesicles have a net negative charge,in the other a net positive charge. One of our mainFig. 3 DNA phase-separates associatively with cationic surfactants.A simplified two-dimensional representation of the preliminary resultsis given for the hexadecyltrimethylammonium bromide–DNA systemFig. 4 Fluorescence microscopy visualizes that the compaction ofsingle DNA is induced by cationic surfactants. As shown for the caseof dodecyltrimethylammonium bromide, DNA has an extended coilstate at low surfactant concentrations a and a compact globule stateat high concentrations c; at intermediate concentrations there iscoexistence of coils and globules b159current interests concerns the interaction of catanionicvesicles with polymers [22].Vesicle±polymer interactionsThe interaction of vesicles with a net negative chargeand two cationic cellulose derivatives have been studied:one of these (LM 200, here denoted HMP+) was of thehydrophobically modified type, while the other (JR 400,or P+) was not.While the phase diagram (Fig. 6) is not yet wellinvestigated in detail, some general features can besingled out:1. With excess polymer or excess surfactant, a homoge-nous isotropic solution forms.2. In a broad intermediate range, associative phaseseparation results.3. There is a close analogy with respect to phaseseparation with previous studies of polymer–micellesystems.Rheological investigations with P+ show a viscoelasticbehavior (Fig. 7). For HMP+ the formation of gels isvery pronounced.Cryogenic transmission electron microscopic investi-gations (Fig. 8) display many notable features, such asthe direct visualization of the polymer-induced vesicleassociation and the formation of faceted vesicles.Similarly DNA was observed to induce an associationof vesicles with a net positive charge.Forthcoming workPolymer–surfactant association in aqueous systems isa result of hydrophobic and electrostatic interactions.Surfactant self-assembly is a general feature of thesesystems. If the polymer itself is hydrophobically associ-ating, particularly strong polymer–surfactant associa-tion takes place resulting inter alia in viscosifying andgelation.In this account, we have presented some recentillustrations taken from an ongoing collaboration be-Fig. 5 Schematic representation of the approach used for the study ofthe phase behavior of polymer-cationic vesicle mixtures; the surfact-ants studied are didodecyldimethylammonium bromide (DDAB) andsodium dodecylsulfate (SDS). From Ref. [19]Fig. 6 Comparison of phase maps of mixed polyelectrolyte–surfact-ant systems show that anionic micellar (SDS) and vesicular (SDS–DDAB) systems behave similarly; the phase limits are given as afunction of polymer and surfactant charge for two cationic cellulosederivatives, JR 400 and LM 200. Lines at lower surfactant charge:coacervation/precipitation boundaries; lines at higher surfactantcharge: redissolution boundaries. For any given system, the regionbetween the two boundaries is a two-phase region. From Ref. [19],data for micellar systems from Refs. [23–24]Fig. 7 Mixtures of the cationic polymer JR 400, and catanionic SDS–DDAB vesicles have a much higher elastic (G¢) than loss modulus (G¢¢)over a wide range of frequencies; data are given for a total surfactantconcentration of 5 mM and three dierent polymer concentrations(0.50, 0.75, and 1.00 wt%) at 25 °C. From Ref. [19]160tween our groups in Coimbra and Lund. The work oncatanionic surfactant systems is from the PhD thesiswork of Eduardo Marques and an extensive account canbe found in his thesis [25]. The work just started on thephase behavior of DNA–surfactant and on DNA–catanionic vesicle interactions is the diploma work ofRita Dias. A full account of this work, with detailedexperimental findings and experimental techniques, willbe presented later.Acknowledgements The PhD studies of Eduardo Marques and hisstay in Lund were mainly supported by JNICT and Praxis XXIthrough a research studentship (BD/9295/96) and in part by theCentre of Amphiphilic Polymers (CAP) in Lund. The postdoctoralstay of Sergey Mel’nikov in Lund was supported by the RoyalSwedish Academy of Science and the Swedish Natural SciencesResearch Council. Rita Dias is an EU Erasmus exchange student.The visiting professorship of Maria Miguel was supported by theCAP.Fig. 8 Cryogenic transmissionelectron microscopy micro-graphs of aqueous mixtures of acationic polymer, LM 200, andcatanionic vesicles with a netnegative charge show a numberof interesting features, such aspolymer-induced vesicle clus-tering and faceted vesicles.Scale bar 100 nm. FromRef. [25]161References1. Jo¨nsson B, Lindman B, Holmberg K,Kronberg B (1998) Surfactants andpolymers in aqueous solution. Wiley,New York2. Kwak JCT (ed) (1998) Polymer–sur-factant systems. Surfactant science se-ries, vol 77. Dekker, New York3. Goddard ED, AnanthapadmanabhanKP (eds) (1993) Interactions of surfact-ants with polymers and proteins. CRCPress, Boca Raton4. Piculell L, Lindman B (1992) AdvColloid Interface Sci 41:1495. Piculell L, Lindman B, Karlstro¨m G(1998) In: Kwak JCT (ed) Polymer–surfactant systems. Dekker, New York1998, p 656. Zhang K, Karlstro¨m G, Lindman B(1994) J Phys Chem 98:44117. Lindman B, Thalberg K (1993) In:Goddard ED, AnanthapadmanabhanKP (eds) Interactions of surfactantswith polymers and proteins. CRCPress, Boca Raton, p 2038. Iliopoulos I, Wang TK, Audebert R(1991) Langmuir 7:6179. Magny B, Iliopoulos I, Audebert R,Piculell L, Lindman B (1992) ProgColloid Polym Sci 89:11810. Hansson P, Almgren M (1995) J PhysChem 99:1668411. Hansson P, Almgren M (1995) J PhysChem 99:1669412. Hansson P, Almgren M (1996) J PhysChem 100:903813. Anthony O, Zana R (1996) Langmuir12:196714. Thalberg K, Lindman B (1991) In:Mittal KL, Shah DO (eds) Surfactantsin solution, vol 11. Plenum, New York,p 24315. Bustamante C (1991) Annu Rev Bio-phys Biophys Chem 20:41516. Grosberg AYu, Khokhlov AR (1996)Giant molecules. Academic Press, Lon-don17. Mel’nikov SM, Sergeyev VG, Yoshika-waK (1997) In: Pandalai SG (ed) Recentresearch developments in chemical sci-ences, vol 1. Transworld Research Net-work, Trivandrum, India, p 6918. Hayakawa K, Kwak JCT (1991) In:Rubingh DN, Holland PM (eds) Cat-ionic surfactants: physical chemistry.Dekker, New York, p 18919. Khan A, Marques E (1997) In: RobbID (ed) Specialists surfactants. Chap-man & Hall, London, p 3720. Lindman B, Khan A, Marques E,Miguel MG, Piculell L, Thalberg K(1993) Pure Appl Chem 65:95321. Kaler EW, Murthy AK, Rodriguez BE,Zasadzinski JA (1989) Science 245:137122. Marques E, Regev O, Khan A, MiguelMG (1999) Langmuir 15:64223. Guillemet F, Piculell L (1995) J PhysChem 99:920324. Goddard ED, Hannan RB (1977) J AmOil Chem Soc 54:56125. Marques E (1998) PhD Thesis. Univ-ersidade de Coimbra, Portugal162

Associating polymer-surfactant systems

Open Repository of the University of Porto

Introduction
Mixed systems of macromolecules and amphiphiles are
ubiquitous in technical products (polymer–surfactant
mixtures) and have a very broad role in biology
(biopolymer–lipid mixtures) [1, 2]. Controlling the
interactions between macromolecules and low-molecu-
lar-weight amphiphiles is the key to technical perfor-
mance and biological function [3].
Depending on the combination of a macromolecule
and an amphiphile, the interaction varies and, as a
consequence, the macroscopic behavior. Thus various
types of polymers behave quite dierently, i.e., charged
polymers versus nonionic, cationic versus anionic,
homopolymers versus graft or comb copolymers, etc.
Early investigations focused on water-soluble homopol-
ymers interacting with simple surfactants, but in recent
years much interest has concerned macromolecules with
pronounced amphiphilic character. Amphiphilic syn-
thetic polymers comprise a wide range of graft, block
and star copolymers, while biological examples include
nucleic acids, proteins and lipopolysaccharides.
Association and segregation
Because of the low entropic driving force of mixing,
polymer–polymer–solvent systems have a strong ten-
dency to segregative phase separation, i.e., two solution
phases enriched in either polymer result. Amphiphiles
show a strong tendency to self-assemble into micelles
and other structures. Since these have a high eective
molecular weight, segregation also becomes a typical
feature of mixed polymer–surfactant solutions [4].
The conditions for segregation are entirely dierent
if one of the cosolutes, polymer or surfactant, is ionic.
Then the large entropic contribution from the counter-
ions becomes a strong driving force for mixing.
An appreciable attractive interaction between poly-
mer and surfactant will modify the situation and two
important phenomena are
1. The binding of surfactant to the polymer.
2. An associative phase separation.
Piculell et al. [5] have identified three distinctly dierent
types of surfactant binding to polymers
Progr Colloid Polym Sci (1999) 112 : 157–162
Ó Springer-Verlag 1999 POLYMERS
M.G. Miguel
E. Marques
R. Dias
S.M. Mel’nikov
A. Khan
B. Lindman
Associating polymer±surfactant systems
Invited lecture, 12th Conference of the
European Colloid and Interface Society,
Dubrovnik – Cavtat, 1998
M.G. Miguel1 á E. Marques1 á R. Dias1
S.M. Mel’nikov á A. Khan
B. Lindman (&)
Physical Chemistry 1
Center for Chemistry
and Chemical Engineering
P.O. Box 124, S-22100 Lund, Sweden
Permanent address:
1Departamento de Quı´mica
Universidade de Coimbra
P-3049 Coimbra, Portugal
Abstract Some recent illustrations
of the phase behavior of polymer–
amphiphile systems in solution are
presented. Surfactant–polymer asso-
ciation is demonstrated for various
amphiphilic synthetic and biological
polymers both on a macroscopic and
on a single molecular level.
Key words Polymer–surfactant sys-
tems – Association and segregation –
Phase behavior – Surfactant self-
assembly – Catanionic vesicles
1. An ionic surfactant associates with an oppositely
charged polymer.
2. An ionic surfactant shows a strong tendency to
associate to a slightly hydrophobic, or a weakly
polar, polymer.
3. All surfactants associate to polymers with strongly
hydrophobic parts, for example, hydrophobically-
modified water-soluble polymers.
In cases 1 and 2 the interactions are best described in
terms of a lowering of the critical micelle concentration
(cmc) of the surfactant and in case 3 in terms of the
formation of mixed micelles between polymer and
surfactant.
Typical phase diagrams
An aqueous mixture of a rather hydrophobic polymer
and a nonionic surfactant can phase-separate into one
dilute solution and one concentrated isotropic phase. As
illustrated in Fig. 1, the extent of phase separation
increases with increasing temperature; this is due to the
decreased polarity of both surfactant and polymer at
higher temperatures.
A very strong tendency for associative phase separa-
tion is displayed by polyelectrolytes mixed with oppo-
sitely charged surfactants [7–13]. Here a correct
representation of the phase diagram is not possible in
the conventional triangular diagram, but a three-dimen-
sional representation, representing the complete four-
component system, is required. In Fig. 2 the typical
behavior is given in the illustrative three-dimensional
pyramid diagram. Water is placed at the top and the four
sides of the pyramid base are assigned to the four ionic
components of the system, with ions of the same charge
located at opposite sides. As can be seen, there are two
two-phase regions. In the low-salt one there is an
associative phase separation, i.e., the surfactant and
the polyelectrolyte form a concentrated phase in equi-
librium with a very dilute solution. At high salt
concentrations there is a segregative phase separation,
i.e., there is one surfactant-rich and one polymer-rich
solution. At intermediate salt concentrations a homoge-
nous solution is formed. The pyramid representation
certainly contains more information than the normally
used triangular representation, in which one dimension
is omitted, but due to the diculties to represent the
pyramids, triangular phase diagrams are to be preferred
in many cases.
DNA and cationic surfactants phase-separate
associatively
The phase diagrams of DNA in combination with
dierent cationic surfactants have been investigated. As
illustrated in Fig. 3, there is, as for the analogous
Fig. 1 Hydrophobic interactions between a surfactant and a polymer
may induce an associative phase separation; typically this increases
with increasing temperature. The phenomenon is exemplified by the
aqueous mixture of an oxyethylene nonionic surfactant, C12E4, and
a nonionic polymer, ethyl(hydroxyethyl) cellulose. F1 refers to an
isotropic one-phase region and F2 to an isotropic two-phase region.
From Ref. [6]
Fig. 2 A polyelectrolyte and an oppositely charged surfactant
typically phase-separate associatively at low electrolyte concentrations
and segregatively in the presence of high salt contents; at intermediate
electrolyte concentrations, there is miscibility. The ‘‘sail’’ hanging
from the pyramid top corresponds to the two-phase region. The dilute
phase is located to the upper right side, and the concentrated phase to
the lower side of the ‘‘sail’’. The example shown is hyaluronan, an
anionic polysaccharide, and tetradecyltrimethylammonium bromide,
a cationic surfactant. From Ref. [14]
158
polyelectrolyte–surfactant systems [7], a strong tendency
for associative phase separation. For DNA the role of
hydrophobic polymer–surfactant interactions has to be
further examined.
DNA compaction in the presence
of cationic surfactants ± an illustration of association
With fluorescence microscopy it is possible to visualize
individual high-molecular-weight DNA molecules [15].
Because of the high charge density, DNA in aqueous
solution exhibits a highly extended coil state at low
electrolyte concentrations. DNA compaction to a glob-
ule results on screening the electrostatics [16].
On addition of cationic surfactant, DNA compaction
takes place [17]. At lower surfactant concentrations,
there is a region of coexistence of coils and globules
(Fig. 4).
Cationic surfactant binding to DNA is strongly
cooperative [18] and is best described as a DNA-induced
surfactant self-assembly; direct support for this view
comes, apart from from structural investigations, from
the fact that the ‘‘binding isotherms’’ are shifted for the
dierent surfactant alkyl chain lengths in the same way
as the normal cmc.
Surfactant-induced compaction of a high-molecular-
weight polymer molecule can be seen as a single-
molecular analogy to the associative phase separation.
The dierent parts of the DNA molecule strive in the
presence of the surfactant to form a concentrated
domain.
Catanionic vesicles
Mixed cationic–anionic surfactant systems, referred to
as catanionic surfactants [19], oer excellent possibilities
to control the charge density of self-assemblies [20]. A
particularly interesting feature is the formation of
thermodynamically stable vesicles [21]. In the phase
diagram, the water-rich part of which is schematically
indicated in Fig. 5, there are two regions of vesicle
formation. In one the vesicles have a net negative charge,
in the other a net positive charge. One of our main
Fig. 3 DNA phase-separates associatively with cationic surfactants.
A simplified two-dimensional representation of the preliminary results
is given for the hexadecyltrimethylammonium bromide–DNA system
Fig. 4 Fluorescence microscopy visualizes that the compaction of
single DNA is induced by cationic surfactants. As shown for the case
of dodecyltrimethylammonium bromide, DNA has an extended coil
state at low surfactant concentrations a and a compact globule state
at high concentrations c; at intermediate concentrations there is
coexistence of coils and globules b
159
current interests concerns the interaction of catanionic
vesicles with polymers [22].
Vesicle±polymer interactions
The interaction of vesicles with a net negative charge
and two cationic cellulose derivatives have been studied:
one of these (LM 200, here denoted HMP+) was of the
hydrophobically modified type, while the other (JR 400,
or P+) was not.
While the phase diagram (Fig. 6) is not yet well
investigated in detail, some general features can be
singled out:
1. With excess polymer or excess surfactant, a homoge-
nous isotropic solution forms.
2. In a broad intermediate range, associative phase
separation results.
3. There is a close analogy with respect to phase
separation with previous studies of polymer–micelle
systems.
Rheological investigations with P+ show a viscoelastic
behavior (Fig. 7). For HMP+ the formation of gels is
very pronounced.
Cryogenic transmission electron microscopic investi-
gations (Fig. 8) display many notable features, such as
the direct visualization of the polymer-induced vesicle
association and the formation of faceted vesicles.
Similarly DNA was observed to induce an association
of vesicles with a net positive charge.
Forthcoming work
Polymer–surfactant association in aqueous systems is
a result of hydrophobic and electrostatic interactions.
Surfactant self-assembly is a general feature of these
systems. If the polymer itself is hydrophobically associ-
ating, particularly strong polymer–surfactant associa-
tion takes place resulting inter alia in viscosifying and
gelation.
In this account, we have presented some recent
illustrations taken from an ongoing collaboration be-
Fig. 5 Schematic representation of the approach used for the study of
the phase behavior of polymer-cationic vesicle mixtures; the surfact-
ants studied are didodecyldimethylammonium bromide (DDAB) and
sodium dodecylsulfate (SDS). From Ref. [19]
Fig. 6 Comparison of phase maps of mixed polyelectrolyte–surfact-
ant systems show that anionic micellar (SDS) and vesicular (SDS–
DDAB) systems behave similarly; the phase limits are given as a
function of polymer and surfactant charge for two cationic cellulose
derivatives, JR 400 and LM 200. Lines at lower surfactant charge:
coacervation/precipitation boundaries; lines at higher surfactant
charge: redissolution boundaries. For any given system, the region
between the two boundaries is a two-phase region. From Ref. [19],
data for micellar systems from Refs. [23–24]
Fig. 7 Mixtures of the cationic polymer JR 400, and catanionic SDS–
DDAB vesicles have a much higher elastic (G¢) than loss modulus (G¢¢)
over a wide range of frequencies; data are given for a total surfactant
concentration of 5 mM and three dierent polymer concentrations
(0.50, 0.75, and 1.00 wt%) at 25 °C. From Ref. [19]
160
tween our groups in Coimbra and Lund. The work on
catanionic surfactant systems is from the PhD thesis
work of Eduardo Marques and an extensive account can
be found in his thesis [25]. The work just started on the
phase behavior of DNA–surfactant and on DNA–
catanionic vesicle interactions is the diploma work of
Rita Dias. A full account of this work, with detailed
experimental findings and experimental techniques, will
be presented later.
Acknowledgements The PhD studies of Eduardo Marques and his
stay in Lund were mainly supported by JNICT and Praxis XXI
through a research studentship (BD/9295/96) and in part by the
Centre of Amphiphilic Polymers (CAP) in Lund. The postdoctoral
stay of Sergey Mel’nikov in Lund was supported by the Royal
Swedish Academy of Science and the Swedish Natural Sciences
Research Council. Rita Dias is an EU Erasmus exchange student.
The visiting professorship of Maria Miguel was supported by the
CAP.
Fig. 8 Cryogenic transmission
electron microscopy micro-
graphs of aqueous mixtures of a
cationic polymer, LM 200, and
catanionic vesicles with a net
negative charge show a number
of interesting features, such as
polymer-induced vesicle clus-
tering and faceted vesicles.
Scale bar 100 nm. From
Ref. [25]
161
References
1. Jo¨nsson B, Lindman B, Holmberg K,
Kronberg B (1998) Surfactants and
polymers in aqueous solution. Wiley,
New York
2. Kwak JCT (ed) (1998) Polymer–sur-
factant systems. Surfactant science se-
ries, vol 77. Dekker, New York
3. Goddard ED, Ananthapadmanabhan
KP (eds) (1993) Interactions of surfact-
ants with polymers and proteins. CRC
Press, Boca Raton
4. Piculell L, Lindman B (1992) Adv
Colloid Interface Sci 41:149
5. Piculell L, Lindman B, Karlstro¨m G
(1998) In: Kwak JCT (ed) Polymer–
surfactant systems. Dekker, New York
1998, p 65
6. Zhang K, Karlstro¨m G, Lindman B
(1994) J Phys Chem 98:4411
7. Lindman B, Thalberg K (1993) In:
Goddard ED, Ananthapadmanabhan
KP (eds) Interactions of surfactants
with polymers and proteins. CRC
Press, Boca Raton, p 203
8. Iliopoulos I, Wang TK, Audebert R
(1991) Langmuir 7:617
9. Magny B, Iliopoulos I, Audebert R,
Piculell L, Lindman B (1992) Prog
Colloid Polym Sci 89:118
10. Hansson P, Almgren M (1995) J Phys
Chem 99:16684
11. Hansson P, Almgren M (1995) J Phys
Chem 99:16694
12. Hansson P, Almgren M (1996) J Phys
Chem 100:9038
13. Anthony O, Zana R (1996) Langmuir
12:1967
14. Thalberg K, Lindman B (1991) In:
Mittal KL, Shah DO (eds) Surfactants
in solution, vol 11. Plenum, New York,
p 243
15. Bustamante C (1991) Annu Rev Bio-
phys Biophys Chem 20:415
16. Grosberg AYu, Khokhlov AR (1996)
Giant molecules. Academic Press, Lon-
don
17. Mel’nikov SM, Sergeyev VG, Yoshika-
waK (1997) In: Pandalai SG (ed) Recent
research developments in chemical sci-
ences, vol 1. Transworld Research Net-
work, Trivandrum, India, p 69
18. Hayakawa K, Kwak JCT (1991) In:
Rubingh DN, Holland PM (eds) Cat-
ionic surfactants: physical chemistry.
Dekker, New York, p 189
19. Khan A, Marques E (1997) In: Robb
ID (ed) Specialists surfactants. Chap-
man & Hall, London, p 37
20. Lindman B, Khan A, Marques E,
Miguel MG, Piculell L, Thalberg K
(1993) Pure Appl Chem 65:953
21. Kaler EW, Murthy AK, Rodriguez BE,
Zasadzinski JA (1989) Science 245:
1371
22. Marques E, Regev O, Khan A, Miguel
MG (1999) Langmuir 15:642
23. Guillemet F, Piculell L (1995) J Phys
Chem 99:9203
24. Goddard ED, Hannan RB (1977) J Am
Oil Chem Soc 54:561
25. Marques E (1998) PhD Thesis. Univ-
ersidade de Coimbra, Portugal
162


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