IPST Members Meeting Design of Pickering Emulsion Templated Colloidosomes and Fundamentals of Emulsification with Nanoparticles Hongzhi Wang Sven Research Group April 10,2012
Research Overview Dual research Design microcapsules Fundamentals of Pickering emulsions Design ph responsive composite microcapsules for controlled release of antimicrobial cargoes Investigate effects of particle charge on Pickering emulsions that are neglected in conventional theory
Design colloidosomes: motivation and objective Colloidosomes are semipermeable microcapsules whose external shell is formed by colloid particles. Colloidosomes represent a promising encapsulation technology with good controllable permeability, mechanical properties and bio-compatibility. Aim to design composite ph responsive colloidosomes for controlled release R. Aveyard, B. P. Binks, J. H. Clint, Advances in Colloid and Interface Science 2003, 100-102, 503-546.
Pickering emulsions Phase I Phase II G A OW OW θ<90º hydrophilic o/w θ>90º hydrophobic w/o VS Oil Water Adsorption energy E>> kt Irreversible θ<90º θ=90º adsorption θ>90º B.P. Binks, Current Opinion in Colloid and interface Science, 7, 21 (2002) R. Aveyard, B. P. Binks, J. H. Clint, Advances in Colloid and Interface Science 2003, 100-102, 503-546.
Design Protocol Explore double Pickering emulsion as template
Experimental observation The water phase is labeled with FITC-dextran (10 kda) encapsulated (green zone), while the oil phase is not labeled.(black zone) By rational design of the shell composition, we are able to generate colloidosome capsules with different release properties.
ph responsive colloidosomes FITC-dextran (10KDa) was encapsulated inside Fast release : ~3s My research focus: Composite colloidosomes with a sustainable release fashion Stepwise release : ~30s
Composite ph responsive colloidosomes Hybrid ph responsive colloidosomes with a long-lasting release profile are generated by the inclusion of inorganic particles and polymeric particles The shell permeability can be controlled by adjusting the shell thickness and adding polymer matrix. Thin shell Thick shell Incorporate polymer matrix The size range of colloidosomes is 20 60 mm
f(t)/arbitry units Permeability Evaluation The permeability of hybrid colloidosomes for 10 kda FITC-dextran is evaluated by fluorescence recovery after photo bleaching (FRAP). 1.4 1.2 Frap cruve for 10kDa FITC-labeled dextran Increase ph 1 0.8 0.6 0.4 0.2 before release triggerred After release triggered 0 0 100 200 300 400 500 600 700 800 900 1000 time/s http://en.wikipedia.org/wiki/fluorescence_recovery_after_photobleaching
Envisioned applications Antimicrobial colloidosomes Encapsulate antimicrobial inside Stimulus trigger Sustainable antimicrobial protection
Fundamentals of emulsification with polymeric nanoparticles
Motivation and objective Motivation: Current fundamental understanding is far from satisfactory, which limits the applications! Objective: Explore the important factors affecting Pickering emulsions that are neglected in conventional theory by investigating emulsification with charged latex particles Carboxyl -COOH ph -COO - + H + Amidine -C(=NH)NH ph 2 + H + -C(=NH 2 )NH 2 +
ph increased charge density increased interfacial charge ph increased charge density increased interfacial charge Our experimental findings No emulsions form when polymer particles are highly charged under low salt concentration Particles with macroscopic contact angle greater than 90º should stabilize w/o emulsions 13 12 11 10 9 8 7 6 5 4 3 2 No emulsion w/o o/w 1 Increased screening 0 10-4 10-3 10-2 10-1 10 0 10 1 Electrolyte concentration/m 1 2 3 4 5 6 7 8 9 10 11 No emulsion w Increased screening o/w 12 10-4 10-3 10-2 10-1 10 0 10 1 Electrolyte concentration/m
Hypothesis and supporting evidence Electrical repulsive force including double layer force and image force can impede adsorption of particle to the interface to stabilize emulsions Repulsion! The repulsive force are expected to cause a deformation when the interface is very close to the particle
Hypothesis and supporting evidence Self energy of particle counter-ion dipole causes shift in equilibrium particle position and leads to a different contact angle in the interface from macroscopic contact angle θ<90º 3D
Conclusions We explore double Pickering emulsions as precursors for composite ph-responsive colloidosome for customizable release control We propose the electrostatic interaction between the particle and interface, including electrical double layer force and image force, can impede the particle adsorption and therefore affect the emulsion formation. The self-energy of the particle-counterion dipole can shift the particle s equilibrium position toward the water phase and yield a modified contact angle and emulsion type not predicted from macroscopic contact angle measurements.
Acknowledgements Funding from IPST through a PSE fellowship and from the National Science Foundation Professors Toan Nguyen, Professors Jennifer Curtis Dr. Jan Scrimgeour, Dan Kovari
Thank you!