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Secretaria:
Aptor
7encontro@sbpmat.org.br
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Fernando Galembeck
Graduado em Química pela Universidade de São Paulo (FFCL, 1964) e Doutor em
Química (Físico-Química, USP, 1970), realizou pós-doutorado nas
Universidades do Colorado (1972-3) e da Califórnia (Davis, 1974). É
Professor Titular da Universidade Estadual de Campinas, onde leciona
disciplinas de Colóides e Superfícies, Polímeros, Química Aplicada,
Físico-Química, Química Geral e Microscopia. Publicou mais de 220 artigos em
periódicos científicos especializados e cerca de duzentos trabalhos em anais
de eventos. Tem 18 capítulos de livros publicados e mais de 40 comunicações
apresentadas em congressos científicos internacionais. Orientou 35
dissertações de mestrado e 30 teses de doutorado, tendo depositado 18
patentes das quais 7 foram licenciadas. Dois produtos baseados nessas
patentes foram lançados comercialmente. Exerceu funções dirigentes na
Unicamp, MCT, CNPq, ABC, SBQ, SBPC e SBMM, de assessoria e planejamento na
Fapesp, MCT, CNPq e Capes e de consultoria em várias empresas, tendo obtido
numerosos prêmios, destacando-se o Prêmio Álvaro Alberto de Ciência e
Tecnologia de 2007.
A new model for dielectric charging and electrostatic
adhesion
Universidade Estadual de Campinas, Campinas, SP, Brazil
Electrostatic charging is widely known but it remains poorly understood, largely due to the
lack of widely accepted mechanisms for charge acquisition and dissipation and this is largely
related to the lack of consensus on the intervening species, electrons or ions.[1] This has
important practical consequences because it makes the prevention of damaging electrostatic discharges rather empirical. It is also important for nanofabrication since electrostatic forces
may largely exceed inertial forces for very small particles.
Early work from this laboratory revealed that insulator surfaces contain complex and stable
patterns of nano-sized domains that were revealed by using scanning Kelvin probe
microscopy, scanning electric potential microscopy (SEPM) or electric force microscopy
(EFM).[2] More recently, carriers of excess charges in polymer lattices were identified as ions
trapped during emulsion polymerization, by using analytical transmission electron microscopy
associated to electron energy-loss spectroscopy (ESI-TEM). However, charge carriers in
important insulators that are easily charged such as polyethylene and other thermoplastics,
rubbers, cellulose and silicate glass were not identified by using these techniques.
Progress along this line was obtained during work on calibration of SEPM instruments that
yielded two results: a procedure for electrostatic patterning of sub-micrometer domains on
silica surfaces and the verification of its dependence on the atmosphere relative humidity
(RH).[3] This led to a new model for the electrification of insulators, according to which
charge bearing species are largely dissociated water ions or ion clusters that are deposited on
the solid surfaces or removed from these, coupled to water vapor adsorption-desorption
events. Charge transfer in dielectrics is thus coupled to mass transfer across the solid-gas
interface and its rate depends largely on the atmosphere relative humidity that also contributes
to surface conductance. This new model for the formation and dissipation of electrified
domains has already been applied to many situations, especially to explain results on the
electrostatic charging of paper and polyethylene.
In another context, the identification of the presence of ions in dielectrics also led to a new
model for electrostatic adhesion [4] in nanostructured materials,6 that accounted for the
remarkable but previously unexpected adhesion between hydrophilic clay and hydrophobic
latex particles, that produces new and unmatched mechanical and swelling properties in
polymer-clay nanocomposites.
Work supported by CNPq, Fapesp and IMMC (Instituto do Milênio de Materiais Complexos).
References:
[1] Schein,L.B. Science, 2007, 316, 1572-1573.
[2] Galembeck, A.; Costa, C.A.R.; Silva, M.C.V.M.; Souza, E.F.; Galembeck, F. Polymer,
2001, 42, 4845-4851.
[3] Valadares, L.; Linares, E.; Bragança, F.C; Galembeck, F. J. Phys. Chem. C (in the press).
[4] Bragança, F.C.; Valadares, L.F.; Leite, C.A.P.; Galembeck, F., Chemistry of Materials,
2007, 19, 3334-3342.
fernagal@iqm.unicamp.br
Universidade Estadual de Campinas, Institute of Chemistry, CP 6154 Campinas SP, Brazil
13083-970
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