Swelling of Thin Graphene Oxide Films Studied by in Situ Neutron Reflectivity

Permeation of multilayered graphene oxide (GO) membranes by polar solvents is known to correlate with their swelling properties and amount of sorbed solvent. However, quantitative estimation of sorption using standard (e.g., gravimetric) methods is technically challenging for few nanometers thick GO membranes/films exposed to solvent vapors. Neutron reflectivity (NR) was used here to evaluate the amount of solvents intercalated into the film which consists of only ∼31.5 layers of GO. Analysis of NR data recorded from the GO film exposed to vapors of polar solvents provides information about change of film thickness due to swelling, amount of intercalated solvent, and selectivity in sorption of solvents from binary mixtures. A quantitative study of GO film sorption was performed for D₂O, <i>d</i>-methanol, ethanol, dimethyl sulfoxide (DMSO), acetonitrile, dimethylformamide (DMF), and acetone. Using isotopic contrast, we estimated selectivity in sorption of ethanol/<i>d</i>-methanol mixtures by the GO film. Estimation of sorption selectivity was also performed for D₂O/DMF, D₂O/DMSO, and D₂O/acetonitrile binary mixtures. Sorption of polar solvents was compared for the thin GO film, micrometer thick free standing GO membranes, and graphite oxide powders

Nucleotide sequences of the primers applied^*.

<p>*PPO degenerate primer (R = A/G, Y = C/T, M = A/C, K = G/T, S = C/G, W = A/T, H = A/C/T, B = C/G/T, V = A/C/G, D = A/G/T, N = A/C/G/T).</p

Expression of <i>LcPPO</i> in different litchi tissues of Feizixiao.

<p>The different letter above the column indicated that there were significantly different among the samples (<i>P</i><0.05). The highest expression was found in the flower and leaf, and the lowest expression was in the pulp.</p

Phylogenetic tree of <i>LcPPO</i> with other PPOs from different species.

<p>All of PPO sequences except <i>LcPPO</i> (JF926153 Litchi chinensis) were from NCBI database. The polygenetic tree was drawn based on the NJ methods, which were described in Mega 5. Numbers at the branches represent percentage bootstrap support with 1000 replicates.</p

Changes in pericarp-browning index, PPO activity, and <i>LcPPO</i> expression of Feizixiao fruit after stored at the low temperature.

<p>A. Pericarp-browning index: B. PPO activity, and C. <i>LcPPO</i> expression Pericarp browning was delayed while stored the fruit at 4°C. The low temperature also can cause the reduction of the PPO activity and <i>LcPPO</i> expression level in pericarp during the first 2 days after harvest.</p

Changes in pericarp-browning index, pericarp water loss, PPO activity, and <i>LcPPO</i> expression of Feizixiao fruit under packaging treatment.

<p>A. Pericarp-browning index: B. Pericarp water loss; C. PPO activity; and D. <i>LcPPO</i> expression. Fruit bagging reduced the water loss in pericarp of Fizixiao, and slowed down the pericarp-browning. During the first three days of storage, both the PPO activity and the <i>LcPPO</i> expression were decreased in bagged fruit.</p

Changes in pericarp-browning index, PPO activity, and <i>LcPPO</i> expression of postharvest litchi fruits of different cultivars.

<p>Pericarp-browning index (A) of Nandaowuhe increased fast compared with Feizixiao and Ziniangxi. PPO activity (B) for Nandaowuhe was higher than Feizixiao and Ziniangxi, but <i>LcPPO</i> expression (C) level increased fast than others on the first day after harvest, and then both Nandaowuhe and Feizixiao reached highest level on day 2.</p

Southern blotting analysis of <i>LcPPO</i>.

<p>Numbers on the top of the lane represent that Genomic DNA from Feizixizo leaves was digested by <i>EcoR</i> I (1), and <i>Xho</i> I and <i>EcoR</i> I (2) at first, and then was hybridized with the <i>LcPPO</i>-specific probe. A clear band was visible in lane 1 and lane 2.</p

<i>LcPPO</i> expression in litchi pericarp at different developmental stages.

<p>Fruits of Feizixiao were harvested on May 14^th, 2010; Ziniangxi and Nandaowuhe were harvested on July 7^th, 2010. Expression of <i>LcPPO</i> in pericarp increased sharply after harvested. Similar changes were observed with Feizixiao, Ziniangxi and Nandaowuhe.</p

Gene families of <i>P</i>. <i>litchii</i> potentially implicated in plant pathogenesis.

<p>Gene families of <i>P</i>. <i>litchii</i> potentially implicated in plant pathogenesis.</p