10 research outputs found
Investigation on the Structure of Water/AOT/IPM/Alcohols Reverse Micelles by Conductivity, Dynamic Light Scattering, and Small Angle X-ray Scattering
We have systematically investigated the effect of alcohols (ethanol, propanol, butanol, and pentanol) on the structure of the water/AOT/IPM system using conductivity, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) techniques. The results show that no percolation phenomenon is observed in the water/AOT/IPM system, whereas the addition of ethanol (propanol and butanol) induces apparently percolation. The threshold water content (<i>W</i><sub>p</sub>) depends closely on the alcohol type and concentration. The effect of alcohols on the conductance behavior is discussed from the physical properties of alcohols, the interfacial flexibility, and the attractive interactions between droplets. The hydrodynamic diameter of droplets (<i>d</i><sub>H</sub>) obtained from DLS increases markedly with the increase in water content (<i>W</i><sub>0</sub>); however, it decreases gradually with increasing alcohol chain length and concentration. SAXS measurements display distinctly the shoulder, the low hump peaks, and the heavy tail phenomenon in the pair distance distribution function <i>p</i>(<i>r</i>) profile, which rely strongly on the alcohol species and its concentration. The gyration radius (<i>R</i><sub>g</sub>) increases with increasing <i>W</i><sub>0</sub>, and decreases with the increase of alcohol chain length and concentration. Schematic diagram of the conductance mechanism of water/AOT/IPM/alcohol systems is primarily depicted. Three different phases of the discrete droplets, the oligomers, and the isolated ellipsoidal droplets existed in the different <i>W</i><sub>0</sub> ranges correspond to three different stages in the conductivity–<i>W</i><sub>0</sub> curve. Coupling the structure characteristics of reverse micelles obtained from DLS and SAXS techniques with conductivity could be greatly helpful to deeply understand the percolation mechanism of water/AOT/IPM/alcohols systems
Pure Anisotropic Hydrogel with an Inherent Chiral Internal Structure Based on the Chiral Nematic Liquid Crystal Phase of Rodlike Viruses
Imparting
ordered structures into otherwise amorphous hydrogels
is expected to endow these popular materials with novel multiple-stimuli
responsiveness that promises many applications. The current contribution
reports a method to fabricate pure polymeric hydrogels with an inherent
chiral internal structure by templating on the chiral nematic liquid
crystal phase of a rodlike virus. A method was developed to form macroscopically
homogeneous chiral templates by confinement induced self-assembly
in the presence of monomers, cross-linkers and initiators. Polymerization
induced gelation was performed without perturbing the elegant 3D chiral
organization of the rodlike virus bearing double bonds. Furthermore,
a suitable method was found to remove the organic virus template while
keeping the desired polymeric replica intact, resulting in a pure
polymeric hydrogel with a unique internal chiral feature that originates
from the 3D chiral ordering of the cylindrical pores left by the virus.
Multiple-stimuli responsiveness has been demonstrated and can be quantified
by the change of the pitch of the chiral feature. The chiral structure
endows the otherwise featureless hydrogel with a unique material property
that might be used as a readout signal for sensing and acts as the
basis for responsive, biomimetic nanostructured materials
Pure Anisotropic Hydrogel with an Inherent Chiral Internal Structure Based on the Chiral Nematic Liquid Crystal Phase of Rodlike Viruses
Imparting
ordered structures into otherwise amorphous hydrogels
is expected to endow these popular materials with novel multiple-stimuli
responsiveness that promises many applications. The current contribution
reports a method to fabricate pure polymeric hydrogels with an inherent
chiral internal structure by templating on the chiral nematic liquid
crystal phase of a rodlike virus. A method was developed to form macroscopically
homogeneous chiral templates by confinement induced self-assembly
in the presence of monomers, cross-linkers and initiators. Polymerization
induced gelation was performed without perturbing the elegant 3D chiral
organization of the rodlike virus bearing double bonds. Furthermore,
a suitable method was found to remove the organic virus template while
keeping the desired polymeric replica intact, resulting in a pure
polymeric hydrogel with a unique internal chiral feature that originates
from the 3D chiral ordering of the cylindrical pores left by the virus.
Multiple-stimuli responsiveness has been demonstrated and can be quantified
by the change of the pitch of the chiral feature. The chiral structure
endows the otherwise featureless hydrogel with a unique material property
that might be used as a readout signal for sensing and acts as the
basis for responsive, biomimetic nanostructured materials
Air–Seawater Exchange of Organochlorine Pesticides along the Sediment Plume of a Large Contaminated River
Gaseous
exchange fluxes of organochlorine pesticides (OCPs) across
the air–water interface of the coastal East China Sea were
determined in order to assess whether the contaminated plume of the
Yangtze River could be an important regional source of OCPs to the
atmosphere. HexaÂchloroÂcycloÂhexanes (HCHs), chlordane
compounds (CHLs), and dichloroÂdiphenylÂtrichloroÂethanes
(DDTs) were the most frequently detected OCPs in air and water. Air–water
exchange was mainly characterized by net volatilization for all measured
OCPs. The net gaseous exchange flux ranged 10–240 ng/(m<sup>2</sup>·day) for γ-HCH, 60–370 ng/(m<sup>2</sup>·day) for <i>trans</i>-CHL, 97–410 ng/(m<sup>2</sup>·day) for <i>cis</i>-CHL, and ∼0 (e.g.,
equilibrium) to 490 ng/(m<sup>2</sup>·day) for <i>p</i>,<i>p</i>′-DDE. We found that the plume of the large
contaminated river can serve as a significant regional secondary atmospheric
source of legacy contaminants released in the catchment. In particular,
the sediment plume represented the relevant source of DDT compounds
(especially <i>p</i>,<i>p</i>′-DDE) sustaining
net degassing when clean air masses from the open ocean reached the
plume area. In contrast, a mass balance showed that, for HCHs, contaminated
river discharge (water and sediment) plumes were capable of sustaining
volatilization throughout
the year. These results demonstrate the inconsistencies in the fate
of HCHs and DDTs in this large estuarine system with declining primary
sources
Assessing and Forecasting Atmospheric Outflow of α-HCH from China on Intra-, Inter-, and Decadal Time Scales
Atmospheric outflow of α-HCH from China from 1952
to 2009
was investigated using Chinese Gridded Pesticide Emission and Residue
Model (ChnGPERM). The model results show that the outflows via the
northeast boundary (NEB, longitude 115–135 °E along 55
°N and latitude 37–55 °N along 135 °E) and the
mid-south boundary (MSB, longitude 100–120 °E along 17
°N) of China account for 47% and 35% of the total outflow, respectively.
Two climate indices based on the statistical association between the
time series of modeled α-HCH outflow and atmospheric sea-level
pressure were developed to predict the outflow on different time scales.
The first index explains 70/83% and 10/46% of the intra-annual variability
of the outflow via the NEB and MSB during the periods of 1952–1984
and 1985–2009, respectively. The second index explains 16%
and 19% of the interannual and longer time scale variability in the
outflow through the NEB during June–August and via the MSB
during October–December for 1991–2009, respectively.
Results also revealed that climate warming may potentially result
in stronger outflow via the NEB than the MSB. The linkage between
the outflow with large scale atmospheric circulation patterns and
climate warming trend over China was also discussed
Assessing Cancer Risk in China from γ‑Hexachlorocyclohexane Emitted from Chinese and Indian Sources
Three models, including an atmospheric
transport model, a multimedia
exposure model, and a risk assessment model, were used to assess cancer
risk in China caused by γ-HCH (gamma-hexachlorocyclohexane)
emitted from Chinese and Indian sources. Extensive model investigations
revealed the contribution of different sources to the cancer risk
in China. Cancer risk in Eastern China was primarily attributable
to γ-HCH contamination from Chinese sources, whereas cancer
risk in Western China was caused mostly by Indian emissions. The contribution
of fresh use of lindane in India to the cancer risk in China was almost
1 order of magnitude higher than that of the reemission of γ-HCH
from Indian soils. Of total population, 58% (about 0.79 billion) residents
in China were found to live in the environment with high levels of
cancer risk exceeding the acceptable cancer risk of 10<sup>–6</sup>, recommended by the United States Environmental Protection Agency
(U.S. EPA). The cancer risk in China was mostly induced by the local
contamination of γ-HCH emitted from Chinese sources, whereas
fresh use of lindane in India will become a significant source of
the cancer risk in China if Indian emissions maintain their current
levels
Assessing Environmental Fate of β‑HCH in Asian Soil and Association with Environmental Factors
Chinese Gridded Pesticide Emission and Residue Model
was applied
to simulate long-term environmental fate of β-HCH in Asia spanning
1948–2009. The model captured well the spatiotemporal variation
of β-HCH soil concentrations across the model domain. β-HCH
use in different areas within the model domain was simulated respectively
to assess the influence of the different sources of β-HCH on
its environment fate. A mass center of soil residue (MCSR) was introduced
and used to explore environmental factors contributing to the spatiotemporal
variation of β-HCH soil residue. Results demonstrate that the
primary emission dominates β-HCH soil residues during the use
of this pesticide. After phase-out of the pesticide in 1999, the change
in β-HCH soil residues has been associated with the Asian summer
monsoon, featured by northward displacement of the MCSR. The displacement
from several major sources in China and northeastern Asia shows a
downward trend at a 95% confidence level, largely caused by environmental
degradation and northward delivery of β-HCH under cold condition
in northern area. The MCSRs away from the India and southern and southeastern
Asia sources show a rapid northward displacement at a 99% confidence
level, featuring the cold trapping effect of the Tibetan Plateau
First Assessment of NO<sub><i>x</i></sub> Sources at a Regional Background Site in North China Using Isotopic Analysis Linked with Modeling
Nitrogen
oxides (NO<sub><i>x</i></sub>, including NO
and NO<sub>2</sub>) play an important role in the formation of atmospheric
particles. Thus, NO<sub><i>x</i></sub> emission reduction
is critical for improving air quality, especially in severely air-polluted
regions (e.g., North China). In this study, the source of NO<sub><i>x</i></sub> was investigated by the isotopic composition (δ<sup>15</sup>N) of particulate nitrate (p-NO<sub>3</sub><sup>–</sup>) at Beihuangcheng Island (BH), a regional background site in North
China. It was found that the δ<sup>15</sup>N-NO<sub>3</sub><sup>–</sup> (<i>n</i> = 120) values varied between −1.7‰
and +24.0‰ and the δ<sup>18</sup>O-NO<sub>3</sub><sup>–</sup> values ranged from 49.4‰ to 103.9‰.
On the basis of the Bayesian mixing model, 27.78 ± 8.89%, 36.53
± 6.66%, 22.01 ± 6.92%, and 13.68 ± 3.16% of annual
NO<sub><i>x</i></sub> could be attributed to biomass burning,
coal combustion, mobile sources, and biogenic soil emissions, respectively.
Seasonally, the four sources were similar in spring and fall. Biogenic
soil emissions were augmented in summer in association with the hot
and rainy weather. Coal combustion increased significantly in winter
with other sources showing an obvious decline. This study confirmed
that isotope-modeling by δ<sup>15</sup>N-NO<sub>3</sub><sup>–</sup> is a promising tool for partitioning NO<sub><i>x</i></sub> sources and provides guidance to policymakers with
regard to options for NO<sub><i>x</i></sub> reduction in
North China
High Time- and Size-Resolved Measurements of PM and Chemical Composition from Coal Combustion: Implications for the EC Formation Process
Inefficient
coal combustion is a significant source of elemental
carbon (EC) air pollution in China, but there is a limited understanding
of EC’s formation processes. In this study, high time-resolved
particle number size distributions (PNSDs) and size-resolved chemical
compositions were obtained from the combustion of four bituminous
coals burned in a quartz tube furnace at 500 and 800 °C. Based
on the distinct characteristics of PNSD, the flaming stage was divided
into the first-flaming stage (with a PNSD peak at 0.3–0.4 μm)
and the second-flaming stage (with a PNSD peak at 0.1–0.15
μm). For the size-segregated EC and OC measurements, more soot-EC
was observed in particles larger than 0.3 μm, whereas the smaller
ones possessed more char-EC. The results indicated that gas-phase
and direct-conversion EC generation mechanisms dominate different
burning stages. The analysis of 16 parent PAHs showed more high-molecular-weight
PAHs in the second-flaming stage particles, which supports the idea
of different formation processes for char-EC and soot-EC. For all
four coals, the PNSD and chemical compositions shared a similar trend,
confirming that the different formation processes of EC in different
flaming stages were common. This study provides novel information
concerning EC formation
Residential Coal Combustion as a Source of Levoglucosan in China
Levoglucosan
(LG) has been widely identified as a specific marker
for biomass burning (BB) sources and frequently utilized in estimating
the BB contribution to atmospheric fine particles all over the world.
However, this study provides direct evidence to show that coal combustion
(CC) is also a source of LG, especially in the wintertime in Northern
China, based on both source testing and ambient measurement. Our results
show that low-temperature residential CC could emit LG with emission
factors (EF) ranging from 0.3 to 15.9 mg kg<sup>–1</sup>. Ratios
of LG to its isomers, mannosan and galactosan, differ between CC and
BB emissions, and the wintertime ratios in Beijing ambient PM<sub>2.5</sub> and source-specific tracers including carbon isotopic signatures
all indicated a significant contribution from CC to ambient levoglucosan
in winter in Beijing. The results suggest that LG cannot be used as
a distinct source marker for biomass burning in special cases such
as some cities in the northern China, where coal is still widely used
in the residential and industrial sectors. Biomass burning sources
could be overestimated, although such an over-estimation could vary
spatially and temporally