- Novo procedimento para a aquisição de bens para pesquisa - que entra em vigor a partir de 02/01/2017, passa a ser obrigatório para todas as aquisições de bens para pesquisa (sejam elas permanentes ou de consumo) pelos Pesquisadores, que os documentos fiscais sejam emitidos em nome da FAPESP, com o respectivo CNPJ.
- Cartão BB Pesquisa - Em breve todas as contas pesquisa deveram migrar para Cartão BB Pesquisa
Horário: 19:00 h
Docente responsável: Leandro Wang Hantao
Date: December 07 (tuesday), at 10:00
Abstract: Adsorption and assembly of colloidal particles (such as clay particles) at the surface of liquid droplets are at the base of particle-stabilized emulsions and templating.
Colloidal clay in water suspensions are known to exhibit a multitude of bulk phases depending on initial colloidal concentration and ionic strength, and examples of this include repulsive Wigner colloidal glasses at low ionic strength and attractive gels at higher ionic strength due to screened electrostatic forces by the electrolyte. From confocal Raman microscopy combined with elasticity measurements, we infer that clay trapped at quasi two-dimensional interfaces between oil and water also exhibit confined self-assembled glass-like or gel-like states . Furthermore we have demonstrated that the results are important for the preparation of particles stabilized colloidal emulsions .
For oil drops in oil suspension (immiscible oils), the situation is different. In this case. it has been demonstrated that electro-hydrodynamic and dielectrophoretic effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces , suggesting new routes for Janus or patchy colloidosome self-assembly, including jammed colloidal shells(Pickering drops) with designed heterogeneous surfaces that combine the functionalities offered by Janus or patchy particles, and those given by permeable shells such as colloidosomes . Further it has been demonstrated that the stress induced by uniform electric-fields in colloidal jammed Pickering drops, is absorbed by plastic deformation or surface crumpling, at electric fields above a yield stress. At stronger electric fields, simultaneous deformation and spontaneous electro-hydrodynamic rotation of Pickering drops has been observed, followed by a transition from a solid to a liquid state and tank-treading dynamics of the Pickering particle layer .
Beyond control of self-assembly of colloids at single drop interfaces or emulsion interfaces, one goal is to use such self-assembly for processing of colloidal based functional structures from the nano- to the macro- scale. Functionalities that one wish to design and control include porous structures for the purpose of structural coloring (such as on finds in the natural world), for scaffolds as templates for cell growth for tissue engineering, and other applications.
1. Gholamipour-Shirazi A., Carvalho M.S., Huila M., Araki K., Dommersnes P., Fossum J.O. (2016). Transition from glass- to gel-like states in clay at a liquid interface. SCIENTIFIC REPORTS by NATURE 6, 37239.
2. Gholamipour-Shirazi A., Carvalho M.S., Fossum J.O. (2016). Controlled microfluidic emulsification of oil in a clay nanofluid: Role of salt for Pickering stabilization. EUROPEAN PHYSICAL JOURNAL SPECIAL TOPICS 225, 757-765.
3. Dommersnes P., Rozynek Z., Mikkelsen M., Castberg R. , Kjerstad, K., Hersvik K., Fossum J.O. (2013) Active structuring of colloidal armour on liquid drops, NATURE COMMUNICATIONS 4:2066
4. Rozynek Z., Mikkelsen A., Dommersnes P., Fossum J.O. (2014), Electroformation of Janus and patchy capsules, NATURE COMMUNICATIONS, 5:3945
5. A. Mikkelsen, P. Dommersnes, Z. Rozynek, A. Gholamipour-Shirazi, M. S. Carvalho and J.O. Fossum (2017) Mechanics of Pickering Drops Probed by Electric Field–Induced Stress, Materials 10, 436 doi:10.3390/ma10040436 (2017)
6. A. Mikkelsen, P. Dommersnes, Z. Rozynek and J.O. Fossum (2017) Folding, wrinkling and solid-fluid transitions of and in quasi 2-dimensional granular colloidal Pickering layers, work in progress to be submitted
Responsible: Prof. Watson Loh