Browsing by Author "Meireles, Leonel Muniz"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Apparent softening of wet graphene membranes on a microfluidic platfor.
    (2018) Ferrari, Gustavo Arrighi; Oliveira, Alan Barros de; Almeida, Ive Silvestre de; Matos, Matheus Josué de Souza; Batista, Ronaldo Junio Campos; Fernandes, Thales Fernando Damasceno; Meireles, Leonel Muniz; Silva Neto, Eliel Gomes da; Chacham, Helio; Neves, Bernardo Ruegger Almeida; Lacerda, Rodrigo Gribel
    Graphene is regarded as the toughest two-dimensional material (highest in-plane elastic properties) and, as a consequence, it has been employed/proposed as an ultrathin membrane in a myriad of microfluidic devices. Yet, an experimental investigation of eventual variations on the apparent elastic properties of a suspended graphene membrane in contact with air or water is still missing. In this work, the mechanical response of suspended monolayer graphene membranes on a microfluidic platform is investigated via scanning probe microscopy experiments. A high elastic modulus is measured for the membrane when the platform is filled with air, as expected. However, a significant apparent softening of graphene is observed when water fills the microfluidic system. Through molecular dynamics simulations and a phenomenological model, we associate such softening to a water-induced uncrumpling process of the suspended graphene membrane. This result may bring substantial modifications on the design and operation of microfluidic devices which exploit pressure application on graphene membranes.
  • No Thumbnail Available
    Item
    Graphene electromechanical water sensor : the Wetristor.
    (2019) Meireles, Leonel Muniz; Silva Neto, Eliel Gomes da; Ferrari, Gustavo Arrighi; Neves, Paulo A. A.; Gadelha, Andreij de Carvalho; Almeida, Ive Silvestre de; Taniguchi, Takashi; Watanabe, Kenji; Chacham, Helio; Neves, Bernardo Ruegger Almeida; Campos, Leonardo Cristian; Lacerda, Rodrigo Gribel
    A water-induced electromechanical response in suspended graphene atop a microfluidic channel is reported. The graphene membrane resistivity rapidly decreases to ≈25% upon water injection into the channel, defining a sensi-tive “channel wetting” device—a wetristor. The physical mechanism of the wetristor operation is investigated using two graphene membrane geometries, either uncovered or covered by an inert and rigid lid (hexagonal boron nitride multilayer or poly(methyl methacrylate) film). The wetristor effect, namely the water-induced resistivity collapse, occurs in uncovered devices only. Atomic force microscopy and Raman spectroscopy indicate substantial morphology changes of graphene membranes in such devices, while covered membranes suffer no changes, upon channel water filling. The results suggest an electromechanical nature for the wetristor effect, where the resistivity reduction is caused by unwrinkling of the graphene membrane through channel filling, with an eventual direct doping caused by water being of much smaller magnitude, if any. The wetristor device should find useful sensing applications in general micro- and nanofluidics.
  • No Thumbnail Available
    Item
    Graphene nanoencapsulation action at an air/lipid interface.
    (2022) Ferrari, Gustavo Arrighi; Chacham, Helio; Oliveira, Alan Barros de; Matos, Matheus Josué de Souza; Batista, Ronaldo Junio Campos; Meireles, Leonel Muniz; Barboza, Ana Paula Moreira; Almeida, Ive Silvestre de; Neves, Bernardo Ruegger Almeida; Lacerda, Rodrigo Gribel
    In the present work, we apply a microfluidic channel platform to study mechanical and adhesion properties of suspended graphene in contact with oleic acid (a lipid). In the platform, one side of the suspended graphene, atop a window in a fluidic channel, is placed in contact with the lipid, and the mechanical response of graphene is experimentally accessed with an atomic force microscope probe. We observe a strong effect arising from the presence of oleic acid: the probe undergoes a large jump-to-contact effect, being pulled and partially encapsulated by graphene, in a phagocytosis-like phenomenon, until it penetrates 0.2 lm into graphene. In contrast, such encapsulation effect is neg- ligible in the absence of oleic acid in the channel, with probe penetration of less than 0.02 lm. The lipid-induced encapsulation effect is observed to occur concurrently with graphene delamination from the window walls. Molecular dynamics simulations and continuum mechanics analytical modeling are also performed, the latter allowing quantitative fittings to the experiments.