Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Graphene oxide membranes: on the absence of "graphene capillaries",
  "ultrafast flow" rate and "ultraprecise sieving"   The data by Q.Yang et al suggest absence of "ultrafast flow" of solvent
across graphene oxide (GO) membranes. The "ultrafast flow" is result of using
unrealistic geometrical model with close packed hole-free micrometer sized GO
flakes providing only 0.1 % of area in each layer available for permeation. The
data by Q.Yang et all demonstrate that at least 3-5 % of total layer area are
available for permeation in real GO membranes due to holes between irregularly
shaped flakes. At least 2-3 percent of area also needs to be added to the
permeation cross section due to holes and cracks in GO flakes, especially
abundant due to prolonged sonication of dispersions. Permeation of solutions
mostly through pinholes penetrating tens of GO layers suggests that "graphene
capillaries" are not required to explain water flow across the membrane. Taking
into account realistic packing of GO flakes with holes between the flakes and
across the flakes, 2-3 orders of magnitude shorter permeation path should be
formed. Considering shorter zigzag permeation path between GO sheets and 5-10 %
of area in each layer available for permeation due to holes across and between
GO flakes, permeation rates across GO membranes can be explained by trivial
diffusion. In absence of "graphene capillaries", the "ultra-precise sieving"
related to "cutoff" value of 4.5 \AA{} (hydration diameter) provided by
"graphene capillaries" has little meaning. As it is well known from earlier
studies and now demonstrated by Q.Yang et al using their own samples the
swelling of GO membranes is different for different solutions, depends on
concentration of solutes and results in delamination in many solutions. Q.Yang
et al provide controversial data for stability of their GO membranes in water
citing use of surfactant to prevent dissolving. Oxidation state of GO membranes
remains to be unknown due to incorrect analysis of XPS spectra.

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The categories of this paper are: nlin
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
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The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga