- Palestrante: Prof Jon Otto Fossum (Norwegian University of Science and Technology – NTNU);
- 5 de novembro de 2019 às 17h;
- Sala: L772
Natural materials can be divided into bio-materials (such as silk, wool, cotton, wood or cellulose,) or inorganic materials (such as soil, clay or stone including sand, glass, iron or graphite). Other materials that could be included among the natural materials are obviously petroleum and water. All these materials have in common that they have been exploited by humans for practical purposes, both before and after the industrial revolution. Currently, the interest for such materials from a technological point of view is partly driven by the need to develop new ecologically friendly sustainable materials e.g. as replacements for nano-/micro-plastic polymers.
The traditional use of natural materials is most often empirical, and only during the past couple of decades many of these materials have been considered as nano-materials, and subsequently have been included as nano-scale or meso-scale ingredients in complex structures underlying macroscopic functionalities that we seek.
Obviously, there is fundamental chemistry and physics involved in the materials science that is underlying materials technology, engineering and applications based on such natural materials. This general scientific area is enormous in volume, so in this presentation, we will focus mainly on one of these natural materials, namely clay minerals, including complex composites of clays and other natural materials, and in particular the focus will be on universal physical phenomena as they manifest themselves in clays and clayey materials. These phenomena include molecular sorption of various kinds (e.g. sorption of H2O, CO2 or more complex molecules), colloidal self-assembly (e.g. guided by gravitational or electromagnetic fields) of in water and/or oil suspensions (e.g. in Pickering emulsions), and rheology (e.g in avalanches).
Colloidal self-assembly, isotropic/nematic structures, and flow:
Wet clay minerals is macroscopically soft matter, for which the rheological properties depend on e.g. the water contents and the water salinity. This is fundamentally linked to that dry clays basically are 2D nano-layered crystalline materials (i.e. like graphene, clays are nano in one spatial direction, and macro in the other two). When exposed to e.g. water vapor, clay nano-lamellar crystalline particle grains may swell by allowing water molecules to enter their interlamellar space. The 1D crystallinity of the swollen lamellar stacked grains may remain intact for low water exposures (much like graphite intercalation compounds can do), however, if liquid water is added to such a system of clay nano-lamellar stacks, the nano-lamella themselves may exfoliate and separate from one another, and form liquid crystalline suspensions of patchy charged colloids that can serve as physical model systems for nematics based on suspended colloidal platelets. By varying water salinity and colloidal concentration, a full range of nematic related phenomena can be explored in such systems, e.g. including structural coloration from Bragg stacks.
Capture of green-house gases:
The interlamellar space in nano-lamellar clay grains contain charge-compensating cations that attract polar (such as water) or polarizable molecules (such as CO2). It has been demonstrated that in effect clay lamellar grains may capture more CO2 than any other eco-friendly material considered for this purpose. This is mainly due the enormous accessible effective surface area of clays (1 cubic meter of clay contains about 2000 square kilometers of surface area……), consisting of a huge number of capturing entities (the cations).
Gas-transport and gas/fluid-barrier properties:
Packed clay powder is basically a dual porosity system, consisting of intragrain nano-pores, and inter-grain mesoporoes. Mesoporous gas transport in such system will be influenced by the efficiency of the nano-pores (which is governed by the intercalated charge compensating cations), rendering the possibility for physically controlled anomalous diffusion in such systems. Clay-polymer nano-composites is a large research area in itself, e.g. for the purpose of gas-barrier membranes where the permeability can be controlled by nematically aligned particles embedded in a polymer matrix.
Interaction with biosystems, origin of life:
Clay minerals appeared on earth not long before (on geological time-scales) the first primitive lifeforms, and it has been suggested that clays may have played roles as instruments for the origin of spontaneous life on earth, in at least two ways: Clay interlayer surfaces are catalytic (they are used for this purpose industrially in oil refining), and thus could have helped small biomolecular building-blocks to form larger molecules such as RNA or DNA. Secondly, since clay colloids in aqueous isotropic or nematic suspensions can form salinity induced aggregates, it has been suggested that clay aggregated compartments could have been precursors to cell compartments, in the sense that such compartments can protect biochemical reactions needed for life. Clays can capture drug-molecules due to the same mechanisms that are responsible for water or CO2 capture, and captured drugs can be released controlled by temperatures or pH such as those found in human’s intestinal organs. Finally, a growing area of research within active matter science is considering interactions between complex fluids such as clays (or other natural silicates) and active swimming bacteria.
Sobre a palestrante:
Possui graduação em Licenciatura em Química pela UERJ (1969), Mestrado (1971) e Doutorado em Química (1974) pela PUC-Rio, pós doutorado na THAachen, Alemanha (1978/1979, Bolsista Humboldt Stiftung) e no Scripps I. Oceanography, USA (1988). De 1994 a 2014 foi Professora Titular da Pontifícia Universidade Católica do Rio de Janeiro, agora Profa. Emérita, pesquisadora 1A do CNPq, Cientista do Nosso Estado FAPERJ. Orientou mais de 50 teses e dissertações e possui mais de uma centena de trabalhos originais publicados. Presta consultoria cientifica a vários órgãos de fomento, instituições governamentais e ONGs nacionais e internacionais e a empresas do setor de petróleo, mineração e meio ambiente, entre outras. Foi chefe do MESL/IAEA, Professora Visitante em universidades no exterior e diretora do dept de Química na PUC. Tem experiência na área de Oceanografia Química e de Meio Ambiente relativa a poluentes orgânicos persistentes, metais traço e ciclo do carbono e elementos bioassociados. É co-coordenadora do LABMAM/PUC-Rio, que se destaca pela experiência em analises e diagnóstico ambientais e é reconhecido pela excelência na análise e avaliação do impacto do petróleo no meio ambiente. Foi membro do GEOTRACES, do Honors and Recognition Committee da American Geophysical Union, atua como revisora para vários periódicos nacionais e internacionais. Membro da Academia Brasileira de Ciências. Indice h: 24.