Co-reporter:Andrea Lotierzo, Ryan M. Schofield, and Stefan A. F. Bon
ACS Macro Letters December 19, 2017 Volume 6(Issue 12) pp:1438-1438
Publication Date(Web):December 6, 2017
DOI:10.1021/acsmacrolett.7b00857
Polymerization induced self-assembly (PISA) using methacrylate-based macromonomers as RAFT agents is an unexplored, attractive route to make self-assembled colloidal objects. The use of this class of RAFT-agents in heterogeneous polymerizations is however not trivial, because of their inherent low reactivity. In this work we demonstrate that two obstacles need to be overcome, one being control of chain-growth (propagation), the other monomer partitioning. Batch dispersion polymerizations of hydroxypropyl methacrylate in the presence of poly(glycerol methacrylate) macromonomers in water showed limited control of chain-growth. Semicontinuous experiments whereby monomer was fed improved results only to some extent. Control of propagation is essential for PISA to allow for dynamic rearrangement of colloidal structures. We tackled the problem of monomer partitioning (caused by uncontrolled particle nucleation) by starting the polymerization with an amphiphilic thermoresponsive diblock copolymer, already “phase-separated” from solution. TEM analysis showed that PISA was successful and that different particle morphologies were obtained throughout the polymerization.
Co-reporter:Ross W. Jaggers
Journal of Materials Chemistry B 2017 vol. 5(Issue 44) pp:8681-8685
Publication Date(Web):2017/11/15
DOI:10.1039/C7TB02278F
In this work, we demonstrate chemical communication between millimetre-sized soft hydrogel beads in an aqueous environment. Silver cations (Ag+) and the Ag+ chelator dithiothreitol (DTT) are used as signalling molecules. By exploiting their interplay, we conduct a series of ‘conversations’ between millimetre-sized beads. The communication process is monitored by tracking the response and behaviour of a central bead. This bead is loaded with the enzyme urease and has the ability to undergo a change in colour associated with a change in pH. Competitive communication between three beads, whereby the central bead receives two competing signals from two senders, is shown. We believe that our hydrogel-based system demonstrates an advance in the communication capabilities of small soft matter objects.
Co-reporter:Ross W. Jaggers
Materials Horizons (2014-Present) 2017 vol. 4(Issue 3) pp:402-407
Publication Date(Web):2017/05/09
DOI:10.1039/C7MH00033B
In this work, we show the fabrication of soft hydrogel alginate-based objects, namely fibres and beads, that have an individually programmed time delay in their response to a shared environmental stimulus. We utilize the enzyme urease to programme a self-regulated change in pH, which in turn activates the designed response of gel fibre disintegration or a change in gel bead colour. This design allows for independent response behaviour of a collection of bodies in a single closed system, as well as inter-material communication on shorter length scales. The incorporation of responsive time control directly into soft matter objects demonstrates an advance in the field of autonomous materials.
Co-reporter:Andrea Lotierzo
Polymer Chemistry (2010-Present) 2017 vol. 8(Issue 34) pp:5100-5111
Publication Date(Web):2017/08/30
DOI:10.1039/C7PY00308K
Pickering emulsion polymerization offers a versatile way of synthetising hybrid core–shell latexes where a polymer core is surrounded by an armour of inorganic nanoparticles. A mechanistic understanding of the polymerization process is limited which restricts the use of the technique in the fabrication of more complex, multilayered colloids. In this paper clarity is provided through an in-depth investigation into the Pickering emulsion polymerization of methyl methacrylate (MMA) in the presence of nano-sized colloidal silica (Ludox TM-40). Mechanistic insights are discussed by studying both the adsorption of the stabiliser to the surface of the latex particles and polymerization kinetics. The adhesion of the Pickering nanoparticles was found not to be spontaneous, as confirmed by cryo-TEM analysis of MMA droplets in water and monomer-swollen PMMA latexes. This supports the theory that the inorganic particles are driven towards the interface as a result of a heterocoagulation event in the water phase with a growing oligoradical. The emulsion polymerizations were monitored by reaction calorimetry in order to establish accurate values for monomer conversion and the overall rate of polymerizations (Rp). Rp increased for higher initial silica concentrations and the polymerizations were found to follow pseudo-bulk kinetics.
Co-reporter:Brooke W. Longbottom;Birsen Somuncuoğlu;Jacob J. Punter;Sarah Longbottom
Soft Matter (2005-Present) 2017 vol. 13(Issue 23) pp:4285-4293
Publication Date(Web):2017/06/14
DOI:10.1039/C7SM00589J
A simple, versatile approach for the roughening of polymer microparticles surfaces via a deformation technique in the presence of an inorganic matrix is presented here. The process consists of straightforward steps: (1) preparation of a bicomposite colloidal sol, that is polymer particles and inorganic particles, dispersed in a liquid, (2) drying of the mixture onto a suitable hard substrate, (3) heating the dried film above the glass transition temperature of the polymer, and (4) re-dispersion and chemical etching of the inorganic medium. The primary driver is capillary imbibition of the polymer melt into the inorganic colloidal template. In addition, 2D particle tracking experiments of dispersed rough particles in water were performed to probe the diffusional behaviour of the roughened objects in comparison with their smooth precursors. We show that, despite large scale roughness (up to 10% asperity size with respect to particle diameter), Stokes law is obeyed and the particle motion can be modelled simply with the Stokes–Einstein–Sutherland relation.
Co-reporter:Ross W. Jaggers
Journal of Materials Chemistry B 2017 vol. 5(Issue 36) pp:7491-7495
Publication Date(Web):2017/09/20
DOI:10.1039/C7TB02011B
Soft composite hydrogel objects formed from the biopolymer sodium alginate, the enzyme urease, and oil droplets are formed by a simple gelation procedure to produce autonomous bodies with both time and spatial programming. These continuous objects of non-uniform dimensional composition selectively respond to an environmental stimulus of urea and change colour or disintegrate at pre-defined locations within the hydrogel structure after pre-set time intervals. The spatial and temporal responses of these hydrogels to an environmental stimulus are valuable tools in areas such as soft robotics.
Co-reporter:Ross W. Jaggers, Rong Chen and Stefan A. F. Bon
Materials Horizons 2016 vol. 3(Issue 1) pp:41-46
Publication Date(Web):20 Aug 2015
DOI:10.1039/C5MH00093A
Giant polymer vesicles which have membrane-embedded catalytically active manganese oxide particles are made using droplet-based microfluidics. It is demonstrated that these colloidal particles can regulate the membrane permeability of the polymersomes upon their exposure to, and catalytic reaction with, small amounts of dissolved hydrogen peroxide.
Co-reporter:Robert V. Bell, Christopher C. Parkins, Robert A. Young, Corinna M. Preuss, Molly M. Stevens and Stefan A. F. Bon
Journal of Materials Chemistry A 2016 vol. 4(Issue 3) pp:813-818
Publication Date(Web):08 Dec 2015
DOI:10.1039/C5TA08917D
We show that emulsion droplets stabilized by branched copolymers and Laponite clay discs can be assembled into supracolloidal fibers with control of the fiber composition and length. Upon drying they transform into a light-weight highly porous nanocomposite material. We demonstrate that the fibers made from emulsion droplets can be used to release volatile compounds in a time-controlled manner.
Co-reporter:Robert V. Bell, Luke A. Rochford, Rafael T. M. de Rosales, Molly Stevens, Jonathan V. M. Weaver and Stefan A. F. Bon
Journal of Materials Chemistry A 2015 vol. 3(Issue 27) pp:5544-5552
Publication Date(Web):09 Jun 2015
DOI:10.1039/C5TB00893J
We report on a versatile and time-efficient method to fabricate calcium phosphate (CaP) microcapsules by utilizing oil-in-water emulsion droplets stabilized with synthetic branched copolymer (BCP) as templates. The BCP was designed to provide a suitable architecture and functionality to produce stable emulsion droplets, and to permit the mineralization of CaP at the surface of the oil droplet when incubated in a solution containing calcium and phosphate ions. The CaP shells of the microcapsules were established to be calcium deficient hydroxyapatite with incorporated chlorine and carbonate species. These capsule walls were made fluorescent by decoration with a fluorescein–bisphosphonate conjugate.
Co-reporter:Nicholas Ballard, Stefan A.F. Bon
Journal of Colloid and Interface Science 2015 Volume 448() pp:533-544
Publication Date(Web):15 June 2015
DOI:10.1016/j.jcis.2015.02.069
The effective stabilization of emulsions by solid particles, a phenomenon known as Pickering stabilization, is well known to be highly dependent on the wettability and the adhesion energy of the stabilizer employed at the liquid–liquid interface. We present a user-friendly computational model that can be used to determine equilibrium orientations and the adhesion energy of colloidal particles at interfaces. The model determines the free energy profile of particle adsorption at liquid–liquid interfaces using a triangular tessellation scheme. We demonstrate the use of the model, using a variety of anisotropic particles and demonstrate its ability to predict and explain experimental observations of particle behaviour at interfaces. In particular, we show that the concept of hydrophilic lipophilic balance commonly applied to molecular surfactants is insufficient to explain the complexity of the activity of colloidal particles at interfaces. In addition, we show the importance of the knowledge of the free energy adsorption profile of single particles at interfaces and the impact on overall free energy of emulsification of packed ensembles of particles. The delicate balance between optimization of adhesion energy, adsorption dynamics and particle packing is shown to be of great importance in the formation of thermodynamically stable emulsions. In order to use the model, the code is implemented by freely available software that can be readily deployed on personal computers.
Co-reporter:Brooke W. Longbottom, Luke A. Rochford, Richard Beanland, and Stefan A. F. Bon
Langmuir 2015 Volume 31(Issue 33) pp:9017-9025
Publication Date(Web):August 8, 2015
DOI:10.1021/acs.langmuir.5b02645
We report an insight into the synthesis of silica-based “matchstick”-shaped colloidal particles, which are of interest in the area of self-propulsion on small length scales. The generation of aqueous emulsion droplets dispersed in an n-pentanol-rich continuous phase and their use as reaction centers allows for the fabrication of siliceous microparticles that exhibit anisotropy in both particle morphology, that is, a “matchstick” shape, and chemistry, that is, a transition-metal oxide-enriched head. We provide a series of kinetic studies to gain a mechanistic understanding and unravel the particle formation and growth processes. Additionally, we demonstrate the ability to select the aspect ratio of the “matchstick” particle in a straightforward manner.
Co-reporter:Adam R. Morgan, Alan B. Dawson, Holly S. Mckenzie, Thomas S. Skelhon, Richard Beanland, Henry P. W. Franks and Stefan A. F. Bon
Materials Horizons 2014 vol. 1(Issue 1) pp:65-68
Publication Date(Web):03 Sep 2013
DOI:10.1039/C3MH00003F
Particles that can undergo directed self-propulsion are desirable for colloidal cargo delivery and self-assembly. Herein we describe the synthesis of silica–manganese oxide “matchstick” colloids that undergo catalytic self-propulsion by consumption of hydrogen peroxide. Chemotaxis is observed when particles are placed in a fuel gradient. Movement opposes convective flow which is tracked by following inert polymer microspheres simultaneously.
Co-reporter:Nicholas Ballard and Stefan A. F. Bon
Polymer Chemistry 2014 vol. 5(Issue 23) pp:6789-6796
Publication Date(Web):28 Aug 2014
DOI:10.1039/C4PY00726C
The synthesis of poly(methacryloyl hydrazide) microgels via dispersion polymerization for the controlled release of carbonyl containing compounds is described. The kinetics of the dynamic reaction that occurs between the hydrazide containing colloidal particles and aldehyde compounds are explored for aqueous dispersions and it is shown that the aldehyde release profiles at conditions of physiological significance indicate a dynamic balance between the reaction components providing a route to sustained release of functional molecules.
Co-reporter:Yunhua Chen;Nicholas Ballard;Oliver D. Coleman;Ian J. Hs-Portman
Journal of Polymer Science Part A: Polymer Chemistry 2014 Volume 52( Issue 12) pp:1745-1754
Publication Date(Web):
DOI:10.1002/pola.27177
ABSTRACT
We demonstrate that the volume phase transition temperature (VPTT) of copolymer microgel particles made from N-isopropylacrylamide (NIPAm) and methacryloyl hydrazide (MH) can be tailored in a reversible manner upon the reaction of the hydrazide functional groups with aldehydes. The microgels were synthesized by precipitation polymerization in water. Due to the water-soluble nature of the MH monomer, the VPTT at which the microgel particles contract shifts to higher values by increasing the incorporated amounts of methacryloyl hydrazide from 0 to 5.0 mol %. The VPTT of the copolymer microgel dispersions in water can be fine-tuned upon addition of hydrophobic/hydrophilic aldehydes, which react with the hydrazide moiety to produce the hydrazone analogue. This hydrazone formation is reversible, which allows for flexible, dynamic control of the thermo-responsive behavior of the microgels. The ability to “switch” the VPTT was demonstrated by exposing hydrophilic streptomycin sulfate salt incubated microgel particles to an excess of a hydrophobic aldehyde, that is benzaldehyde. The temperature at which these microgels contracted in size upon heating was markedly lowered in these aldehyde exchange experiments. Transformation into benzaldehyde hydrazone derivatives led to assembly of the microgel particles into small colloidal clusters at elevated temperatures. This control of supracolloidal cluster formation was also demonstrated with polystyrene particles which had a hydrazide functionalised microgel shell. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1745–1754
Co-reporter:Thomas S. Skelhon, Yunhua Chen, and Stefan A. F. Bon
Langmuir 2014 Volume 30(Issue 45) pp:13525-13532
Publication Date(Web):October 24, 2014
DOI:10.1021/la503366h
The majority of studies on Janus particles focus on those that show amphiphilicity, with distinct hydrophilic and hydrophobic domains. Here, we demonstrate the synthesis of a different class of Janus particles: “hard–soft” biphasic dumbbell- or peanut-shaped particles with distinct lobes of “soft” poly(n-butyl acrylate) and “hard” poly(styrene). The particles are made by seeded dispersion polymerization of butyl acrylate in the presence of poly(styrene) seed particles. Surface nucleation by capture of the oligoradicals onto the surface of the seed particles thereby forming a distinct new polymer phase is found to be the formation mechanism of these particles. The total available poly(styrene) seed surface area plays a significant role in the size and number of poly(butyl acrylate) lobes grown off a single particle. At particularly low values of the surface area, we observe the formation of multilobe particles. We further demonstrate that our synthesis method is versatile and can be extended to the submicrometer domains by using seed particles of 200 nm in diameter.
Co-reporter:Yunhua Chen, Nicholas Ballard and Stefan A. F. Bon
Chemical Communications 2013 vol. 49(Issue 15) pp:1524-1526
Publication Date(Web):07 Jan 2013
DOI:10.1039/C2CC38200H
High Internal Phase Emulsion hydrogels are prepared from waterborne poly(N-isopropylacrylamide) nanogel dispersions which are non-covalently crosslinked through 2-ureido-4[1H] pyrimidinone (UPy) quadruple hydrogen bond groups. The reversible UPy crosslinks allow for the HIPE-hydrogels to be molded into objects which are thermo-responsive in nature.
Co-reporter:Yunhua Chen, Nicholas Ballard and Stefan A. F. Bon
Polymer Chemistry 2013 vol. 4(Issue 2) pp:387-392
Publication Date(Web):31 Aug 2012
DOI:10.1039/C2PY20615C
Synthetic colloidal hydrogel particles of sub-micron dimensions, often referred to as microgels and/or nanogels, generally consist of water-soluble polymers held together through chemical crosslinking by covalent bonds in order to preserve the distinct colloidal particle identity. Here we demonstrate the synthesis of non-covalently crosslinked nanogel particles in which the crosslinking through covalent bonds is replaced by physical crosslinking induced by strong self-complementary quadruple hydrogen bond interactions. The multiple hydrogen bond (MHB) arrays were introduced in the form of a 2-ureido-4[1H]pyrimidinone (UPy) functionalized polyethylene glycol methacrylate (PEGMA) comonomer, which was employed in the synthesis of colloidal nanogels made from N-isopropylacrylamide (NIPAm) or a mixture of 2-(2-methoxyethoxy)ethyl methacrylate and oligo(ethylene glycol) methacrylate (MEO2MA-co-OEGMA) following conventional free radical polymerization routes. The temperature-dependent swelling properties of the non-covalently crosslinked nanogels with differences in UPy loadings were studied, clearly demonstrating that MHB arrays can work as crosslinking moieties warranting the colloidal particle identity of the prepared hydrogels.
Co-reporter:Adam R. Morgan, Nicholas Ballard, Luke A. Rochford, Gabit Nurumbetov, Thomas S. Skelhon and Stefan A. F. Bon
Soft Matter 2013 vol. 9(Issue 2) pp:487-491
Publication Date(Web):26 Oct 2012
DOI:10.1039/C2SM26556G
Non-spherical particles have the potential to adopt multiple orientations once adhered to a liquid–liquid interface. In this work we combine simulations and experiments to investigate the behaviour of an isolated microscopic hematite particle of superellipsoidal shape. We show that this microparticle can adopt one of three orientations when adhered to a hexadecane–water interface. Two of the orientations, and estimates for their relative populations, could be assigned to two thermodynamic minima on the energy landscape as generated through both free-energy minimization and particle trajectory simulations. The third orientation was found to correspond to a kinetically trapped state, existing on certain particle trajectories in a region of a negligible gradient in free energy. To underpin the simulations the individual orientation of a set of 100 isolated particles was explored by means of scanning electron microscopy (SEM) using the gel trapping technique as a tool. Atomic force microscopy (AFM) was additionally used to support the experimental findings. This is the first example of such a kinetic metastable state being observed for particles at liquid–liquid interfaces.
Co-reporter:Christopher D. J. Parmenter, Rong Chen, David L. Cheung and Stefan A. F. Bon
Soft Matter 2013 vol. 9(Issue 29) pp:6890-6896
Publication Date(Web):18 Mar 2013
DOI:10.1039/C3SM50184A
We show that when unilamellar polymer vesicles dispersed in water made from a blockcopolymer, in this case poly((ethylene oxide)45-block-(methyl methacrylate)164), poly((ethylene oxide)45-block-(methyl methacrylate)170), or poly(n-butyl methacrylate)81-block-(2-(dimethylamino)ethyl methacrylate)20, are exposed to small hydrophobic molecules, here methyl methacrylate as well as n-butyl methacrylate, they can undergo morphological transitions. Upon swelling, the polymersomes lose their original simple bilayer morphology and transform into more complex coil-like and patchy colloidal structures, as investigated experimentally by cryogenic electron microscopy (cryo-EM). Dissipative particle dynamics (DPD) simulations on a model flat bilayer indeed show that transitions can occur upon bilayer swelling, which is accompanied by a change in the mechanical bilayer properties. The transition involves the formation of water pockets in the interior regions of the bilayer. Co-existence of the various morphologies in the experiments suggests an activation barrier towards morphological changes and a possibility of multiple meta-stable states. The latter indeed is supported by the existence of multiple minima in the surface tension as a function of bilayer area, as found in the simulations.
Co-reporter:Thomas S. Skelhon, Patrik K. A. Olsson, Adam R. Morgan and Stefan A. F. Bon
Food & Function 2013 vol. 4(Issue 9) pp:1314-1321
Publication Date(Web):17 Jun 2013
DOI:10.1039/C3FO60122F
Reducing the fat content of chocolate formulations is a major challenge for the confectionery industry. We report the suspension of aqueous microgel agar particles of up to 80% v/v within sunflower oil, cocoa butter, and ultimately chocolate. The optimised emulsification process involves a shear-cooling step. We demonstrate the versatility of our method when applied to white, milk, and dark chocolate formulations, whilst preserving the desired polymorph V of the cocoa butter matrix. In addition, we show that this technology can be used as a strategy to disperse alcoholic beverages into chocolate confectionery.
Co-reporter:Thomas M. Ruhland, André H. Gröschel, Nicholas Ballard, Thomas S. Skelhon, Andreas Walther, Axel H. E. Müller, and Stefan A. F. Bon
Langmuir 2013 Volume 29(Issue 5) pp:1388-1394
Publication Date(Web):January 12, 2013
DOI:10.1021/la3048642
We investigate the self-assembly behavior of Janus particles with different geometries at a liquid–liquid interface. The Janus particles we focus on are characterized by a phase separation along their major axis into two hemicylinders of different wettability. We present a combination of experimental and simulation data together with detailed studies elucidating the mechanisms governing the adsorption process of Janus spheres, Janus cylinders, and Janus discs. Using the pendant drop technique, we monitor the assembly kinetics following changes in the interfacial tension of nanoparticle adsorption. According to the evolution of the interfacial tension and simulation data, we will specify the characteristics of early to late stages of the Janus particle adsorption and discuss the effect of Janus particle shape and geometry. The adsorption is characterized by three adsorption stages which are based on the different assembly kinetics and different adsorption mechanisms depending on the particle shape.
Co-reporter:Yunhua Chen, Gabit Nurumbetov, Rong Chen, Nicholas Ballard, and Stefan A. F. Bon
Langmuir 2013 Volume 29(Issue 41) pp:12657-12662
Publication Date(Web):September 16, 2013
DOI:10.1021/la402417h
We describe a versatile and facile route for the preparation of Janus microbeads using single emulsion droplet-based microfluidics, in which water droplets that contain a mixture of branched poly(N-isopropylacrylamide)-co-(poly(ethylene glycol)diacrylate)-co-(methacrylic acid) and colloidal particles form the basis of our approach. The colloidal particles, poly(methyl methacrylate) microspheres or titanium dioxide particles, and iron oxide nanoparticles are spatially positioned within the water droplets through gravity and an externally applied magnetic force, respectively. Evaporation of water leads to gel formation of the branched copolymer matrix as a result of physical cross-linking through hydrogen bond interactions, fixing the spatial position of the colloidal particles. The thermo- and pH-responsive nature of the branched poly(N-isopropylacrylamide) (PNIPAm)-based copolymer allows for the disintegration of the polymer network of the Janus microbeads and a triggered release of the colloidal content at temperatures below the lower critical solution temperature (LCST) and at increased pH values.
Co-reporter:Thomas S. Skelhon, Nadia Grossiord, Adam R. Morgan and Stefan A. F. Bon
Journal of Materials Chemistry A 2012 vol. 22(Issue 36) pp:19289-19295
Publication Date(Web):08 Aug 2012
DOI:10.1039/C2JM34233B
We demonstrate a route toward the preparation of healthier fruit juice infused chocolate candy. Up to 50 wt% of the fat content in chocolate, that is cocoa butter and milk fats, is replaced with fruit juice in the form of emulsion droplets using a quiescent Pickering emulsion fabrication strategy. Fumed silica particles are used in combination with chitosan under acidic conditions (pH 3.2–3.8) to prepare water-in-oil emulsions, the oil phase being sunflower oil, molten cocoa butter, and ultimately white, milk, and dark chocolate. Adsorption of the polycationic chitosan molecules onto the surface of the silica particles influenced the particle wettability making it an effective Pickering stabilizer, as shown by cryogenic scanning electron microscopy analysis. The formation of a colloidal gel in the continuous (molten) oil phase provided the system with a yield stress, hereby giving it a gel-like and thus quiescent behaviour under low shear conditions, as determined by rheological measurements. This warrants a homogeneous distribution of emulsion droplets as settling through gravity upon storage under molten/liquid conditions is arrested. In our low-fat chocolate formulations the cocoa butter has the desired polymorph V structure, and neither sugar nor fat bloom was observed upon storage of the fruit juice containing chocolate confectionaries.
Co-reporter:Yunhua Chen, Nicholas Ballard, Florence Gayet and Stefan A. F. Bon
Chemical Communications 2012 vol. 48(Issue 8) pp:1117-1119
Publication Date(Web):28 Nov 2011
DOI:10.1039/C2CC16670D
A convenient route to organogels templated by high internal phase emulsions has been developed. Key is the use of a waterborne polymer latex loaded with a multiple hydrogen bond (MHB) functionality that becomes disentangled and transfers across the oil–water interface forming a gel network in the oil phase viahydrogen bond interactions.
Co-reporter:Gabit Nurumbetov, Nicholas Ballard and Stefan A. F. Bon
Polymer Chemistry 2012 vol. 3(Issue 4) pp:1043-1047
Publication Date(Web):06 Feb 2012
DOI:10.1039/C2PY00605G
We demonstrate that by using a syringe needle, plastic tubing, two glass capillaries and epoxy glue a microfluidic device can be fabricated straightforwardly that allows for the production of double emulsions, or in other words the generation of droplets-in-droplets. The device in essence is a serial combination of droplet generation by co-flow and a T-junction. To reduce potential issues with channel wetting, we established that an “obstructed” T-junction outperformed a conventional T-junction. We illustrate the versatility of our device through production of a range of polymer microcapsules, including ones that contain a waterborne dispersion of colour changing pigment, and microcapsules with compartmentalized ferrofluidic segments, that is capsules that contain more than one droplet of ferrofluid.
Co-reporter:Yunhua Chen, Samuel T. Jones, Ian Hancox, Richard Beanland, Edward J. Tunnah, and Stefan A. F. Bon
ACS Macro Letters 2012 Volume 1(Issue 5) pp:603
Publication Date(Web):April 19, 2012
DOI:10.1021/mz300126u
Waterborne polymer films made from soft polymer latex dispersions generally suffer from deterioration of chemical resistance and physical barrier properties under high humidity conditions and upon solvent exposure. Here we demonstrate the fabrication of robust polyhedral cellular polymer films from poly(methyl methacrylate-co-butyl acrylate) latexes, which were made by emulsion polymerization using a 2-ureido-4-pyrimidinone (UPy) functional methacrylate comonomer. Multiple hydrogen bond (MHB) arrays provided by UPy groups arrest the film formation process thereby creating a cellular reinforcement. The cellular polymer films exhibit impressive physical and mechanical properties. Upon solvent exposure, the films show colloidal crystalline-type Bragg diffraction features and do not suffer excessive and deteriorative uptake of water and, more remarkably, can absorb high amounts of organic solvents, thereby turning into an organogel with preservation of shape, up to a 14-fold volumetric swelling ratio of the polymer films in case of chloroform.
Co-reporter:Rong Chen ; Daniel J. G. Pearce ; Sara Fortuna ; David L. Cheung
Journal of the American Chemical Society 2011 Volume 133(Issue 7) pp:2151-2153
Publication Date(Web):January 26, 2011
DOI:10.1021/ja110359f
The fabrication of polymer vesicles with a colloidal armor made from a variety of nanoparticles is demonstrated. In addition, it is shown that the armored supracolloidal structure can be postmodified through film-formation of soft polymer latex particles on the surface of the polymersome, hereby effectively wrapping the polymersome in a plastic bag, as well as through formation of a hydrogel by disintegrating an assembled polymer latex made from poly(ethyl acrylate-co-methacrylic acid) upon increasing the pH. Furthermore, ordering and packing patterns are briefly addressed with the aid of Monte Carlo simulations, including patterns observed when polymersomes are exposed to a binary mixture of colloids of different size.
Co-reporter:Nicholas Ballard and Stefan A. F. Bon
Polymer Chemistry 2011 vol. 2(Issue 4) pp:823-827
Publication Date(Web):02 Dec 2010
DOI:10.1039/C0PY00335B
We describe a new method for the decoration of the intricate morphology of spore particles with polymer nanoparticles and investigate their behaviour at liquid–liquid interfaces. We found a large difference in the interfacial activity between spherical microspheres and the anisotropic particles synthesized here and describe this in terms of particle wettability.
Co-reporter:Roberto F. A. Teixeira, Holly S. McKenzie, Ashton A. Boyd, and Stefan A. F. Bon
Macromolecules 2011 Volume 44(Issue 18) pp:7415-7422
Publication Date(Web):August 30, 2011
DOI:10.1021/ma201691u
The fabrication of “soft” nanocomposite clay armored polymer latexes is described. Laponite clay XLS is used as stabilizer in the Pickering emulsion polymerization of a variety of monomer mixtures, that is, methyl methacrylate and n-butyl acrylate, styrene and n-butyl acrylate, and styrene and 2-ethylhexyl acrylate. Overall solids contents of the hybrid latexes in complete absence of coagulation of up to 24 wt % are reported under batch conditions. Key mechanistic aspects of the Pickering emulsion polymerization process are discussed. The use of monomers that have high water solubility and are prone to hydrolyze under basic conditions, for example methyl methacrylate, should be restricted. The use of small amounts of methacrylic acid as auxiliary monomer promotes clay adhesion to the surface of the particles in the Pickering emulsion (co)polymerization of hydrophobic monomers. Detailed kinetic studies at both 60 and 80 °C of the Pickering emulsion copolymerization of styrene and n-butyl acrylate (Sty:BA = 0.67 w/w) are reported, with varying amounts of Pickering stabilizer. The Laponite clay discs play a crucial role in the particle formation (nucleation) stage of the Pickering emulsion polymerization process. Use of increasing amounts leads to smaller average particle sizes but inflicts longer nucleation periods, thereby broadening the particle size distributions. We report the occurrence of a catastrophic coagulation phenomenon for Pickering emulsion polymerizations carried out at a low initiator (ammonium persulfate) flux at 60 °C, for a small window of concentrations of Laponite clay discs.
Co-reporter:Catheline A. L. Colard, Roberto F. A. Teixeira and Stefan A. F. Bon
Langmuir 2010 Volume 26(Issue 11) pp:7915-7921
Publication Date(Web):February 19, 2010
DOI:10.1021/la904817f
The fate of nanoparticles used as stabilizers in solids-stabilized, or Pickering, emulsion polymerization for the formation of armored hybrid polymer latexes was studied. We showed that disk centrifugation can be used as a powerful quantitative tool to analyze and determine the concentration of nanoparticles in the water phase throughout solids-stabilized emulsion polymerizations. We performed a series of emulsion polymerizations using vinyl acetate, vinyl pivalate, methyl methacrylate, or butyl acrylate in presence of silica nanoparticles (Ludox TM-40, ca. 25 nm in diameter). The developed method to quantify the number of silica nanoparticles in the water phase proved to be an invaluable tool for determining key features of the polymerization process. The obtained concentration profiles versus monomer conversion explained the existence of limited coalescence of armored particles in the later stages of the solids-stabilized emulsion polymerization process of vinyl acetate, leading to nonspherical structures. Moreover, we demonstrated that the correlation of the measured number of silica nanoparticles present in the water phase with the average particle sizes of the latex particles provided excellent predictions for the coverage of the armored layer of nanoparticles on the surfaces of the polymer particles, corresponding to observed packing patterns.
Co-reporter:Catheline A. L. Colard;Richard A. Cave;Nadia Grossiord;James A. Covington
Advanced Materials 2009 Volume 21( Issue 28) pp:
Publication Date(Web):
DOI:10.1002/adma.200990106
Co-reporter:Catheline A. L. Colard;Richard A. Cave;Nadia Grossiord;James A. Covington
Advanced Materials 2009 Volume 21( Issue 28) pp:2894-2898
Publication Date(Web):
DOI:10.1002/adma.200803007
Co-reporter:David L. Cheung and Stefan A. F. Bon
Soft Matter 2009 vol. 5(Issue 20) pp:3969-3976
Publication Date(Web):03 Aug 2009
DOI:10.1039/B908462B
Using Monte Carlo simulations the interaction of a nanometre-sized, spherical Janus particle (a particle with two distinct surface regions of different functionality, in this case showing amphiphilic behaviour) with an ideal fluid interface is studied. In common with previous simulations of spherical, isotropic particles, the range of the nanoparticle-interface interaction is significantly larger than the nanoparticle radius due to the broadening of the interface due to capillary waves. For a uniform particle (an isotropic particle with one surface characteristic) the stability of the particle at a liquid interface is decreased as the affinity for one liquid phase is increased relative to the other; for large affinity differences the detachment energies calculated from continuum theory become increasingly accurate. For a symmetric Janus particle (where the two different surface regions are of equal area), the presence of the particle at the interface becomes more stable upon increasing the difference in affinity between the two faces, with each face having a high affinity for the respective liquid phase. In the case studied here, where surface tension between the A-region of the particle with the A-component is identical to the surface tension between the B-region and B-component, the interaction is symmetric with respect to the nanoparticle interface separation. The particle is found to have a large degree of orientational freedom, in sharp contrast to micrometre-sized colloidal particles. Comparison with continuum theory shows that this significantly overestimates the detachment energy, due to its neglect of nanoparticle rotation; simulations of nanoparticles with fixed orientations show a considerably larger detachment energy. As the areas of the surface regions become asymmetric the stability of the Janus nanoparticle is decreased and, in the case of large differences in affinities of the two faces, the difference between detachment energies from simulation and continuum theory diminishes.
Co-reporter:Sara Fortuna, Catheline A. L. Colard, Alessandro Troisi and Stefan A. F. Bon
Langmuir 2009 Volume 25(Issue 21) pp:12399-12403
Publication Date(Web):May 13, 2009
DOI:10.1021/la9010289
Fascinating packing patterns of identical spherical and discotic objects on curved surfaces occur readily in nature and science. Examples include C60 fullerenes,(1, 2)13-atom cuboctahedral metal clusters,(3) and S-layer proteins on outer cell membranes.(4) Numerous situations with surface-arranged objects of variable size also exist, such as the lenses on insect eyes, biomineralized shells on coccolithophorids,(5) and solid-stabilized emulsion droplets(6) and bubbles.(7) The influence of size variations on these packing patterns, however, is studied sparsely. Here we investigate the packing of nanosized silica particles on the surface of polystyrene latex particles fabricated by Pickering miniemulsion polymerization of submicrometer-sized armored monomer droplets. We are able to rationalize the experimental morphology and the nearest-neighbor distribution with the help of Monte Carlo simulations. We show that broadening of the nanoparticle size distribution has pronounced effects on the self-assembled equilibrium packing structures, with original 12-point dislocations or grain-boundary scars gradually fading out.
Co-reporter:T. Chen;P. J. Colver;S. A. F. Bon
Advanced Materials 2007 Volume 19(Issue 17) pp:2286-2289
Publication Date(Web):24 JUL 2007
DOI:10.1002/adma.200602447
Organic–inorganic hybrid hollow spheres are prepared by using a TiO2-stabilized Pickering emulsion polymerization method (see figure). By self-organization of TiO2 nanoparticles at the interface of oil (monomer and solvent) and water, colloidosomes are formed and used as polymerization vessels to obtain the hybrid hollow spheres. The diameter and mechanical stability can be tailored by varying the relative amount of oil phase and the relative amount of divinylbenzene (DVB) in the monomer, respectively.
Co-reporter:Stefan A. F. Bon, Séverine Cauvin and Patrick J. Colver
Soft Matter 2007 vol. 3(Issue 2) pp:194-199
Publication Date(Web):02 Nov 2006
DOI:10.1039/B612066K
Supracolloidal interpenetrating polymer network reinforced capsules are prepared by using micron-sized colloidosomes of poly(methyl methacrylate-co-divinylbenzene) microgels as reaction vessels. An interpenetrating polymer network as scaffold is generated via radical polymerisation of the interior phase to produce hollow supracolloidal structures with a raspberry core–shell morphology. Their flexibility is tailored by variation of the monomer feed composition.
Co-reporter:Stefan A.F. Bon, Steven D. Mookhoek, Patrick J. Colver, Hartmut R. Fischer, Sybrand van der Zwaag
European Polymer Journal 2007 Volume 43(Issue 11) pp:4839-4842
Publication Date(Web):November 2007
DOI:10.1016/j.eurpolymj.2007.09.001
A route to the production of stable non-spherical emulsion droplets has been developed by pushing millimeter-sized liquid droplets stabilized by an excess amount of solid Pickering particles through a narrow capillary. This excess amount allows for the full coverage of the newly created droplets’ interface during deformation. Upon exiting the capillary the adhered particles wedge, or “jam”, on the surface preserving the non-spherical shape. Stable millimeter-sized non-spherical liquid droplets with aspect ratios exceeding 10 and cross-sections in line with capillary dimensions are easily obtained. Post-modification can be performed in conventional reactors. The ability to fabricate non-spherical droplets creates exciting opportunities in areas such as self-healing polymer composites.
Co-reporter:Patrick J. Colver;Tao Chen
Macromolecular Symposia 2006 Volume 245-246(Issue 1) pp:34-41
Publication Date(Web):7 FEB 2007
DOI:10.1002/masy.200651306
Solid particles can adhere to liquid-liquid interfaces. When emulsion droplets are stabilized in such a way one speaks of a Pickering emulsion. The supracolloidal structures formed by this interface driven assembly process can be referred to as colloidosomes. Herein we explain the concept of colloidosome formation, their deformation behavior upon evaporation of their inner phase. Moreover, we describe Pickering miniemulsion and suspension polymerization processes, both yielding armored raspberry-type core-shell composite polymer particles.
Co-reporter:Stefan A.F. Bon;Jennifer Waterson;David R. Morsley;David M. Haddleton;Martin R. Lees;Tim Horne
Macromolecular Symposia 2001 Volume 165(Issue 1) pp:29-42
Publication Date(Web):9 APR 2001
DOI:10.1002/1521-3900(200103)165:1<29::AID-MASY29>3.0.CO;2-5
Catalytic chain transfer copolymerisation of MMA and HEMA (70:30) has been carried out under semi-continuous emulsion polymerisation conditions, using CoBF as catalyst. It has been shown that macromonomers of low molar mass can be synthesised with an apparent chain transfer constant, CSE, of ca. 1300 down to a threshold value of ca. 20 ppm of CoBF. Below this value an initial 20% shot of monomer/catalyst mixture was necessary to prevent events involved in the catalytic chain transfer process becoming diffusion controlled and to prevent the reaction to proceed under monomer starved conditions. Analysis of the Co(II) species by SQUID has been carried out. CoBF shows a value for its effective magnetic susceptibility of 1.77μB. It was found that a correction for the response of the sample container is essential for reliable data to be achieved. Diffusion ordered 2D-NMR spectroscopy (DOSY) has been used as a method to study the catalyst diffusion dependence for the rate coefficient of chain transfer. However, the apparent values of the found diffusion coefficients are an order of magnitude above the natural limit for center of mass diffusion.
Co-reporter:Andrew G. Steward;David M. Haddleton
Journal of Polymer Science Part A: Polymer Chemistry 2000 Volume 38(Issue 15) pp:2678-2686
Publication Date(Web):12 JUN 2000
DOI:10.1002/1099-0518(20000801)38:15<2678::AID-POLA70>3.0.CO;2-P
Four different approaches to introduce a specific functional group at the ω terminus of poly(methacrylate)s (PMMAs) prepared via copper(I)bromide/pyridinalimine-mediated atom transfer polymerization, under polymerization conditions, are reported. Method 1 involves the homolysis of the ω-CBr bond with a subsequent reaction, via coupling or disproportionation, with an external radical species. The reaction with 2,2,6,6-tetramethylpiperidin-N-oxyl shows a high conversion (>78%) of the ω-bromo PMMA chains into their corresponding macromonomer analogues. Method 2 utilizes monomers that are able to undergo radical addition followed by subsequent fragmentation. Reactions with trimethyl[1-(trimethylsiloxy)phenylethenyloxy]silane and allyl bromide show quantitative and 57% transformation, respectively. Method 3 is the reaction of a monomer that yields a relatively more stable secondary, or primary, carbon–halogen bond. Reactions with divinylbenzene, n-butylacrylate, and ethylene showed quantitative, 62%, and quantitative additions, respectively. Method 4 is the addition of nonhomopropagating monomers, that is, maleic anhydride. This reaction proceeds quantitatively. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2678–2686, 2000
Co-reporter:Yunhua Chen, Nicholas Ballard, Florence Gayet and Stefan A. F. Bon
Chemical Communications 2012 - vol. 48(Issue 8) pp:NaN1119-1119
Publication Date(Web):2011/11/28
DOI:10.1039/C2CC16670D
A convenient route to organogels templated by high internal phase emulsions has been developed. Key is the use of a waterborne polymer latex loaded with a multiple hydrogen bond (MHB) functionality that becomes disentangled and transfers across the oil–water interface forming a gel network in the oil phase viahydrogen bond interactions.
Co-reporter:Yunhua Chen, Nicholas Ballard and Stefan A. F. Bon
Chemical Communications 2013 - vol. 49(Issue 15) pp:NaN1526-1526
Publication Date(Web):2013/01/07
DOI:10.1039/C2CC38200H
High Internal Phase Emulsion hydrogels are prepared from waterborne poly(N-isopropylacrylamide) nanogel dispersions which are non-covalently crosslinked through 2-ureido-4[1H] pyrimidinone (UPy) quadruple hydrogen bond groups. The reversible UPy crosslinks allow for the HIPE-hydrogels to be molded into objects which are thermo-responsive in nature.
Co-reporter:Robert V. Bell, Christopher C. Parkins, Robert A. Young, Corinna M. Preuss, Molly M. Stevens and Stefan A. F. Bon
Journal of Materials Chemistry A 2016 - vol. 4(Issue 3) pp:NaN818-818
Publication Date(Web):2015/12/08
DOI:10.1039/C5TA08917D
We show that emulsion droplets stabilized by branched copolymers and Laponite clay discs can be assembled into supracolloidal fibers with control of the fiber composition and length. Upon drying they transform into a light-weight highly porous nanocomposite material. We demonstrate that the fibers made from emulsion droplets can be used to release volatile compounds in a time-controlled manner.
Co-reporter:Thomas S. Skelhon, Nadia Grossiord, Adam R. Morgan and Stefan A. F. Bon
Journal of Materials Chemistry A 2012 - vol. 22(Issue 36) pp:NaN19295-19295
Publication Date(Web):2012/08/08
DOI:10.1039/C2JM34233B
We demonstrate a route toward the preparation of healthier fruit juice infused chocolate candy. Up to 50 wt% of the fat content in chocolate, that is cocoa butter and milk fats, is replaced with fruit juice in the form of emulsion droplets using a quiescent Pickering emulsion fabrication strategy. Fumed silica particles are used in combination with chitosan under acidic conditions (pH 3.2–3.8) to prepare water-in-oil emulsions, the oil phase being sunflower oil, molten cocoa butter, and ultimately white, milk, and dark chocolate. Adsorption of the polycationic chitosan molecules onto the surface of the silica particles influenced the particle wettability making it an effective Pickering stabilizer, as shown by cryogenic scanning electron microscopy analysis. The formation of a colloidal gel in the continuous (molten) oil phase provided the system with a yield stress, hereby giving it a gel-like and thus quiescent behaviour under low shear conditions, as determined by rheological measurements. This warrants a homogeneous distribution of emulsion droplets as settling through gravity upon storage under molten/liquid conditions is arrested. In our low-fat chocolate formulations the cocoa butter has the desired polymorph V structure, and neither sugar nor fat bloom was observed upon storage of the fruit juice containing chocolate confectionaries.
Co-reporter:Robert V. Bell, Luke A. Rochford, Rafael T. M. de Rosales, Molly Stevens, Jonathan V. M. Weaver and Stefan A. F. Bon
Journal of Materials Chemistry A 2015 - vol. 3(Issue 27) pp:NaN5552-5552
Publication Date(Web):2015/06/09
DOI:10.1039/C5TB00893J
We report on a versatile and time-efficient method to fabricate calcium phosphate (CaP) microcapsules by utilizing oil-in-water emulsion droplets stabilized with synthetic branched copolymer (BCP) as templates. The BCP was designed to provide a suitable architecture and functionality to produce stable emulsion droplets, and to permit the mineralization of CaP at the surface of the oil droplet when incubated in a solution containing calcium and phosphate ions. The CaP shells of the microcapsules were established to be calcium deficient hydroxyapatite with incorporated chlorine and carbonate species. These capsule walls were made fluorescent by decoration with a fluorescein–bisphosphonate conjugate.
![SILANE, TRIMETHYL[4-[1-[(TRIMETHYLSILYL)OXY]ETHENYL]PHENOXY]-](http://img.cochemist.com/ccimg/60100/60068-18-0.png)
![SILANE, TRIMETHYL[4-[1-[(TRIMETHYLSILYL)OXY]ETHENYL]PHENOXY]-](http://img.cochemist.com/ccimg/60100/60068-18-0_b.png)
