Final Report for EPSRC Grants GR/S60402 and GR/S60419:
‘Self-Organised 2-D and 3-D Arrays of Stimulus Responsive Block
Copolymer Micelles’
Prof. S. Biggs, University of Leeds, UK and Prof. S. P. Armes, University of Sheffield, UK
Summary. This has been an outstandingly successful joint research grant that has generated twelve
primary papers and two secondary papers, plus a further four papers submitted for publication. This
has been achieved despite the inevitable disruption caused by Prof. Armes’s change of institution
during the grant period. All of the original objectives for this project have been achieved by the
team and especially the two hard-working, talented post-docs who have now secured further
academic employment. This work has been disseminated at various conferences and meetings, as
well as to individual industrial companies (e.g. Unilever, P & G, Kodak). Several informal
collaborations with non-UK scientists have also substantially enhanced the scientific quality of this
research programme. This project has also provided the scientific inspiration for a provisional
patent application and the formation of a University of Leeds spin-out company, Chamelic Ltd., to
commercialise some of the application opportunities for smart surface coatings. Thus this joint grant
has provided exceptional value for money to EPSRC and the UK tax-payer.
Primary Research Papers
This project was both fruitful and wide-ranging, and resulted in a large number of significant
publications. In the following sections, we have grouped these papers into various topics for clarity.
1. Synthesis of second-generation ‘weak acid’ zwitterionic diblock copolymers via ATRP
Prof. Armes invited two former group members (Prof. V. Bütün and Dr. M. Vamvakaki; both are
highly skilled synthetic polymer chemists who are now independent academics at the Universities
in Turkey and Crete, respectively) to visit his group during two summer vacations to carry out
extensive diblock copolymer syntheses using group transfer polymerization (GTP). This strategy
ensured a strong start to this joint grant, since the Biggs group had early access to multi-gram
quantities of both tertiary amine methacrylate-based cationic diblocks and also zwitterionic diblocks.
An improved two-step ATRP-based route was also developed by the EPSRC-supported PDRA (Dr.
Vo) to prepare a range of zwitterionic diblock copolymers in which both blocks are weak
polyelectrolytes. First, low polydispersity diblock copolymers of 2-hydroxypropyl methacrylate
(HPMA) with either 2-(diethylamino)ethyl methacrylate (DEA) or 2-(diisopropylamino)ethyl
methacrylate (DPA) were prepared by ATRP in protic media under mild conditions in a convenient
one-pot synthesis. Block copolymers with varying compositions were prepared by adjusting the
comonomer/initiator molar ratio. In the second step, the hydroxyl groups of the diblock copolymers
were esterified with excess succinic anhydride (SA) to produce the corresponding zwitterionic
diblock copolymers, which exhibit complex pH-dependent behavior (isoelectric points and
‘schizophrenic’-type micellization) in aqueous solution. The electrostatic adsorption of ‘cationic
corona’ micelles onto near-monodisperse anionic silica particles was successful at pH 3.5, as
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evidenced by aqueous electrophoresis, FT-IR studies, thermo-gravimetric analysis, and scanning
electron microscopy. The same ‘cationic corona’ micelles were also adsorbed onto planar mica at
pH 3.5. More surprisingly, inverted ‘anionic corona’ micelles prepared from the same diblock
copolymer could be adsorbed onto mica at pH 10. Presumably, this latter adsorption arises from
relatively weak hydrophobic interactions due to the micelle cores, rather than strong electrostatic
interactions due to the micelle corona. Both types of adsorbed micelles could be imaged by in situ
atomic force microscopy. This joint Armes/Biggs paper was published in Macromolecules.1 A
second paper describing the synthesis of related ‘third generation’ zwitterionic diblock copolymers
derived from the same HPMA-DEA and HPMA-DPA diblock copolymer precurors was also
published in Polymer by the Armes group.2 Here 2-sulfobenzoic acid cyclic anhydride was used
instead of succinic anhydride to produce sulfonic acid-based diblock copolymers (i.e. a strong
polyacid block).
2. Adsorption characteristics of cationic diblock copolymer micelles onto anionic substrates
We used a series of novel cationic diblock copolymers that undergo reversible self-assembly in
aqueous solution in response to stimuli such as solution pH or temperature as the fundamental
building blocks for the preparation of smart surface coatings. Under appropriate conditions, these
cationic diblock copolymers formed micelles in aqueous solution whose physicochemical properties
[critical micelle concentration (cmc), micelle size and  potential] could be controlled by adjusting
block copolymer characteristics such as block composition and overall copolymer molecular weight.
Preliminary studies of these cationic diblock copolymer micelles were conducted by Dr. G. B.
Webber, a former PhD student of Prof. Biggs who was awarded a prestigious two-year AngloAustralian post-doctoral fellowship from the Royal Academy of Engineering to work with Prof.
Biggs at U. Leeds in support of this project. Dr. Webber found that these copolymer micelles
undergo remarkable morphology changes when electrostatically adsorbed as micelle monolayers at
an anionic planar substrate such as mica.3 Unlike the acid-induced break-up of micelles observed in
bulk solution, these surface-adsorbed micelles did not dissociate on lowering the pH of the
surrounding solution. Instead, various morphological changes were observed that were dependent
on the precise nature of the block copolymer (block composition, cationic charge density, molecular
weight etc.). These changes suggested a number of possible applications as ‘smart’ surface coatings.
However, before exploiting these effects, it was necessary to fully characterise the fundamental
aspects of the adsorption process, as well as exploring the effects of washing, drying and repeated
pH cycles on the behaviour of the surface-adsorbed block copolymer micelles.
In a series of published articles,4-8 we have thoroughly investigated the adsorption properties of
poly(2-(dimethylamino)ethyl
methacrylate)-block-poly(2-(diethylamino)ethyl
methacrylate)
(XqPDMA-PDEA, where X refers to a mean degree of quaternisation of the PDMA block) diblock
copolymer micelles at the solid/aqueous solution interface. XqPDMA-PDEA shows stimulusresponsive behaviour in aqueous solution: it is molecularly dissolved in acidic solution while in
alkaline solution it forms core-shell micelles, with the PDEA chains being located in the
hydrophobic cores and the hydrophilic PDMA chains forming the cationic micelle coronas. These
micelles spontaneously form a structured adsorbed layer at a mica/aqueous solution interface due to
strong electrostatic interactions. In situ atomic force microscopy (AFM) studies have confirmed
that the mean spacing and the dimension of the adsorbed micelles depend on both the substrate (i.e.
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mica or silica)4 and the mean degree of quaternisation.8 In particular, the adsorbed layer
morphology of the non-quaternised copolymer is clearly influenced by the substrate type: these
micelles form a disordered layer on silica, while much more close-packed, highly ordered layers are
obtained on mica.4 The key reasons for this difference are suggested to be the ease of lateral
rearrangement for the copolymer micelles attached to the solid substrates and the relative rates of
relaxation of the coronal PDMA chains (which are in turn controlled by the relative charge densities
on the micelles and the substrate). The adsorption kinetics and equilibrium adsorbed structures at
the silica/aqueous solution interface have been studied using a quartz crystal microbalance with
dissipation monitoring (QCM-D) and an optical reflectometer (OR).5-7
The pH-responsive behaviour of the XqPDMA-PDEA films adsorbed on silica has also been
characterised as a function of copolymer concentration, chain length and mean degree of
quaternisation.3,6 The micellar morphology of these copolymers, initially adsorbed at pH 9, can be
dramatically altered by lowering the solution pH. The original micelle-like morphology of the
adsorbed copolymer chains at pH 9 completely disappears as the pH is decreased to 4, and a brushlike layer structure is produced. This change results from protonation of the copolymer chains: the
subsequent electrostatic repulsions within the film drive the copolymer chains to expand into the
aqueous phase. Returning the solution pH from 4 to 9 causes this brush-like layer to collapse, with
AFM images suggesting some degradation of the film. This is in contrast to the fully reversible
behaviour observed for mica. Nonetheless, the corresponding QCM-D and  potential data on silica
clearly show reversible behaviour for the copolymer films in response to pH cycling. We have also
investigated the influence of these morphological changes on various physical properties such as
contact angle and capture/release of active molecules.8
The knowledge generated from this fundamental investigation has been used in associated research
(funded separately) to further develop and patent9 a series of tailored diblock copolymer micelles
for use as novel surface coating materials. This work has resulted in the formation of a spin-out
company, Chamelic Ltd., to commercialise this opportunity.
3. Adsorption characteristics of zwitterionic diblock copolymer micelles
Zwitterionic diblock copolymers consisting of weakly charged cationic and anionic polyelectrolyte
blocks are also pH-responsive materials. For example, poly(2-(diethylamino)ethyl methacrylate)block-poly(methacrylic acid) (PDEA-PMAA) shows pH-dependent ‘schizophrenic’ micellisation
behaviour in aqueous solution. This copolymer forms core-shell micelles at low pH, with the neutral
PMAA chains being located in the hydrophobic cores and the protonated PDEA chains forming the
cationic micelle coronas. In contrast, inverted micelles with hydrophobic PDEA cores and anionic
PMAA coronas are formed at high pH. Since such micellisation behaviour of zwitterionic diblock
copolymers in aqueous solution necessarily influences their interfacial adsorption, the pHdependent adsorption behaviour has also been of great interest.10, 11 A further impetus to this aspect
of our research was the potential opportunity of forming complex multilayer films from the
successive adsorption of cationic and anionic micellar building blocks (see below). As a result,
characterisation of these systems was a vital component of the overall research plan.
The adsorbed layer morphology was observed using in situ soft-contact AFM and suggests the
formation of a thin adsorbed layer at pH 4 as a result of unimer adsorption (i.e. individual
molecularly dissolved copolymer chains). On the other hand, the conformation of the adsorbed
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copolymer layer appears to be brush-like in alkaline solution, consisting of a PDEA anchor block
adsorbed at the silica surface and an anionic PMAA buoy block extending into the solution phase.
Interestingly, the corresponding tapping mode AFM images obtained for dried films in air show the
presence of micelle-like aggregates both from acidic and alkaline solutions. This suggests that, in
this case, the drying process is crucial when depositing copolymer micelles onto planar silica.
4. Preparation and characterisation of micellar multilayers on planar and particulate substrates
The formation of nano-structured surface coatings on planar substrates is a key challenge for the
preparation of novel functional materials. One approach involves the alternate deposition of
oppositely-charged linear polyelectrolytes in a layer-by-layer (LbL) fashion. Recently, multilayer
composite films have been constructed by replacing one or both of these polyelectrolytes with other
charged species such as proteins, DNA, dendrimers, and colloidal nanoparticles. Multilayer films
formed from micelles or vesicles via the LbL self-assembly technique have also been of great
interest in anticipation of their potential use as nano-capsules.
We prepared micellar multilayers on planar silica by sequential deposition of cationic PDMAPDEA and anionic PDEA-PMAA diblock copolymer micelles at pH 9.12, 13 Direct AFM imaging
shows that the micelle structures are retained within each level of the film for up to five layers.12
This is an exciting and entirely novel result and suggests that such micelle multilayer films have
considerably higher structural order than that achieved for traditional LbL polyelectrolyte films.
Adsorption of successive layers was also followed by surface charge and gravimetric analyses:
addition of each layer results in complete charge reversal and an increase in the adsorbed mass,
suggesting successful LbL coating by the oppositely charged diblock copolymer micelles.13 These
coatings offer a specific advantage over simple homopolyelectrolyte multilayer coatings since they
contain hydrophobic microdomains (the micelle cores) for the potential incorporation of
hydrophobic actives.
We have now extended this work to include the formation of multilayer micelle films on particulate
substrates for the first time.14 To further examine the nature of these surface coatings, a series of
experiments were performed using micelles pre-loaded with a hydrophobic orange dye: a
monotonic increase in the colour intensity was observed as a function of the layer number. This
provides good evidence for the formation of robust micelle multilayers that retain the hydrophobic
dye molecules. Such complex films have widespread potential applications as surface/particle
coatings and this is the subject of an on-going PhD studentship (Pavlina Mantzana) supported by
the Nanomanufacturing Institute at U. Leeds. We are also currently developing their potential
application as microcapsule walls through an EPSRC PhD CASE studentship with P&G (Timothy
Addison). One of the key tasks here is to transfer the coating technology onto emulsion droplets and
this provides a significant challenge for our on-going research.
5. Adsorption of pH-responsive microgels onto mica
A Rohm & Haas-funded PhD student (Damien Dupin) in the Armes group prepared a series of pHresponsive poly(2-vinylpyridine)-based microgels via emulsion polymerization. This student visited
the Wanless group in Australia for two months in 2006 and assisted an ARC-funded post-doc (Dr.
Paul FitzGerald) in imaging these microgel particles adsorbed at submonolayer coverage on mica.
pH-induced swelling caused some of the microgel particles to desorb from the mica surface, but the
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remaining particles proved to be quite durable: multiple pH cycles led to no further desorption, as
judged by in situ AFM imaging A joint Armes/Wanless paper describing this work has just
appeared in Soft Matter.15 Further neutron and optical reflectometry studies of these adsorbed pHresponsive microgels are on-going and Prof. Armes will visit the Wanless group for two weeks in
Jan 2008 with the aim of writing up these data.
6. Secondary Research Papers
Dr. Vo proved to be a very productive post-doc who also made contributions to a number of other
research areas within the Armes group. In particular, we published a study of surface ATRP of
various hydrophilic methacrylic monomers from (a) colloidal substrates using an anionic
polyelectrolytic macro-initiator16 and (b) carbon nanotubes.17 In addition, a detailed study of the
synthesis of branched acrylic copolymers via RAFT polymerisation has just been submitted for
publication18 and a second surface ATRP paper has been recently accepted for publication.19
Collaborations. One value-added component of this grant has been the fruitful informal
collaboration with Dr. E. J. Wanless of the University of Newcastle, Australia. A number of joint
papers with Dr. Wanless form part of this final report. A second important aspect has been the
strategic use of informal visits to the Armes group by former group members, notably Dr. V. Bütün
and Dr. M. Vamvakaki. These scientists conducted the initial GTP syntheses that provided the
Biggs and Wanless groups with multi-gram quantities of near-monodisperse diblock copolymers at
a very early stage in the grant period. This allowed the synthetic post-doc (Dr. C. D. Vo) to explore
and optimise new synthetic routes to zwitterionic block copolymers, as discussed above.
We have also developed an important collaboration with Dr. Sebastien Perrier at the University of
Leeds who is a world leader in the application of RAFT chemistry for block copolymer syntheses.
RAFT may provide a key route for the production of commercial quantities of the copolymers used
here and the scale-up manufacturing is the subject of on-going work at Leeds.
This project has also led directly to further supporting funds. To date, funding has been received for
Dr. Grant Webber (Royal Academy of Engineering, two-year fellowship); Mr. Timothy Addison
(EPSRC CASE award with P&G); Ms. Pavlina Mantzana (PhD Nanomanufacturing Institute).
Dissemination. Our results have been communicated at the following conferences [* denotes
invited keynote address]: ACS [Yale 2004]; Polyelectrolytes 2004 [U. Mass]; ESF Conference
[Toulon 2004]; ACIS 2005* [Sydney 2005]; Pott Shrigley conference* [2005]; World Congress
Chem Eng [Glasgow 2005]; EuChemS Meeting [Stockholm 2005]; ECIS Meeting [Norway 2005];
MRS Meeting* [SF 2006]; Faraday Discussions [Leeds 2004]; PSA 2005 [Stratford-on-Avon,
2005]; RSC Nanoparticles meeting [Warwick 2007]; Nanotech 2007 [SF 2007]; World Polymer
Congress [Beijing 2006]; ACS National Meeting [Chicago 2007].
Personnel. We were very fortunate to recruit two hard-working post-doctoral scientists who
remained in post for the whole three-year grant period. Dr. K. Sakai has recently returned to Japan
to commence his independent academic career as an Assistant Professor at the Tokyo University of
Science, while Dr. C. D. Vo has taken up a new post-doctoral position with Prof. N. Tirelli at the
University of Manchester, UK. Both post-docs have produced impressive bodies of work during the
grant period and their high-quality publications should serve them well in their future academic
careers. We also note that Dr. Grant Webber, who worked with us on this project using the
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associated Royal Academy of Engineering funding has also moved on to an academic post as a
lecturer at the University of Newcastle (Australia). Thus we are confident that this grant has
provided excellent training and good career progression.
Follow-on Funding. As a direct result of this project, Prof. Biggs has formed a spin-out company
(Chamelic Ltd.) to further develop the baseline surface coatings technology. This company has
received £ 500 K of investment and currently employs four research staff. Prof. Biggs and Prof.
Armes continue to work together informally on colloid science/engineering projects and will submit
a new joint EPSRC grant application based on novel functional colloidosomes and microcapsules.
References
1. C. D. Vo, S. P. Armes, D. P. Randall, K. Sakai, S. Biggs, Macromolecules, 2007, 40, 157-167.
2. C. D. Vo, P. D. Iddon, S. P. Armes, Polymer, 2007, 48, 1193-1202.
3. G. B. Webber, E. J. Wanless, S. P. Armes, Y. Tang, Y. Li, S. Biggs, Adv. Mater., 2004, 16, 1794-1798.
4. K. Sakai, E. G. Smith, G. B. Webber, C. Schatz, E. J. Wanless, V. Bütün, S. P. Armes, S. Biggs, Langmuir
2006, 22, 5328-5333.
5. K. Sakai, E.G. Smith, G. B. Webber, C. Schatz, E. J. Wanless, V. Bütün, S. P. Armes, S. Biggs, J. Phys.
Chem. B 2006, 110, 14744-14753.
6. K. Sakai, E. G. Smith, G. B. Webber, M. Baker, E. J. Wanless, V. Bütün, S. P. Armes, S. Biggs, Langmuir
2006, 22, 8435-8442.
7. K. Sakai, E. G. Smith, G. B. Webber, E. J. Wanless, V. Bütün, S. P. Armes, S. Biggs, J. Colloid Interface
Sci. 2006, 303, 372-379.
8. K. Sakai, E. G. Smith, M. Baker, E. J. Wanless, V. Bütün, S. P. Armes, S. Biggs, J. Colloid Interface Sci,
in the press.
9. S. Biggs and G. Bacquey, Patent Ref: 0624729.0; filed 12/12/06
10. K. Sakai, E. J. Wanless, S. P. Armes, S. Biggs, et al. J. Colloid Interface Sci., submitted for publication.
11. K. Sakai, E. J. Wanless, S. P. Armes, S. Biggs, et al. J. Colloid Interface Sci., submitted for publication.
12. E. G. Smith, G. B. Webber, K. Sakai, S. Biggs, S. P. Armes, E. J. Wanless, J. Phys. Chem. B, in the press.
13. S. Biggs, K. Sakai, T. Addison, A. Schmid, S. P. Armes, M. Vamvakaki, V. Bütün, G. B. Webber, Adv.
Mater. 2007, 19, 247-250.
14. K. Sakai, G. B. Webber, C. D. Vo, E. J. Wanless, M. Vamvakaki, V. Bütün, S. P. Armes, S. Biggs, Soft
Matter, submitted for publication.
15. P. FitzGerald, E. J. Wanless, D. Dupin, S. P. Armes, Soft Matter, 2007, 3, 580-586.
16. C. D. Vo, A. Schmid, S. P. Armes, K. Sakai, S. Biggs, Langmuir, 2007, 23, 408-413.
17. C. Gao, C.D. Vo, Y. Z. Jin, W. W. Li, S. P. Armes, Macromolecules, 2005, 38, 8634-8648.
18. C. D. Vo, J. Rosselgong and S. P. Armes, submitted to Macromolecules, 2007.
19. S. Edmondson, C. D. Vo, S. P. Armes and G.-F. Unali, Macromolecules, in the press 2007.
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