Adsorption and catalytic oxidation of residual NH3 on coal ash after selective non-catalytic reduction in coal-fired boilers.

Selective non-catalytic reduction (SNCR) with NH3 as the reducing agent is widely used for the denitrification of flue gas in coal-fired boilers, where fly ash significantly influences the conversion of the residual NH3 that does not participate in denitrification. However, there have been few studies on the exact nature of this influence, particularly the adsorption and reaction mechanisms of NH3 on fly ash. In this study, temperature-programmed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used to study the mechanisms of NH3 adsorption and reactions over coal ash. In the absence of oxygen, in the temperature range of 50-450 °C, NH3 was adsorbed on the surface of the coal ash. The adsorption capacity of lignite ash was higher than that of anthracite ash. This difference was attributed to the large specific surface area and surface acidity of the lignite ash. However, between 450-850 °C, coal ash had a catalytic effect on NH3 decomposition and oxidation. Due to the high surface lattice oxygen content of lignite ash, its catalytic oxidative ability was superior to anthracite ash. Moreover, NH3 was first adsorbed over Lewis and Brønsted acid sites on the surface of coal ash and later underwent hydrogen abstraction to produce either the NH2 or the NH intermediate. The intermediates further reacted with the surface lattice oxygen of coal ash to produce NO and N2O. These results might be helpful for the management of NH3 residues from SNCR processes and the utilization of amino reducing agents in coal-fired boilers.

Maternal exposure to bis(2-ethylhexyl) phthalate during the thyroid hormone-dependent stage induces persistent emotional and cognitive impairment in middle-aged offspring mice.

Prenatal DEHP exposure can cause offspring neurodevelopmental toxicity, but the persistent effects of such exposure window are unclear. This study aimed to investigate the lasting neurobehavioral impact of DEHP on offspring following early exposure from GD9.5 (fetal neural tube closure) to GD16.5 (fetal thyroxin, TH, synthesis). Data showed maternal exposure to DEHP during the thyroid hormone-dependent stage induced a range of neurobehavioral phenotypic changes in adult and middle-aged mice, including anxiety, depression and cognitive impairment. Significant reductions in free TH, TH transporters, and TH metabolic enzyme deiodinase II (D2) were observed in the fetal brain, whereas D3 was elevated, indicating that TH signaling disruption was caused by in utero exposure. Gene expression analyses suggested the expression levels of the TH receptors Trα1, Trß1 and their downstream target, brain-derived neurotrophic factor, were significantly attenuated, which may partially explain the mechanisms of neurodevelopmental impairment. This study provides new evidence of the persistent effects of sex-specific neurodevelopmental impairment due to in utero DEHP exposure, possibly through damage to the fetal brain TH signaling systems that causes lifelong brain damage. These results further suggest a profound neurobehavioral toxicity of DEHP that may be programmed during early developmental stage exposure and manifested later in life.

Insights into the enhanced flux of graphene oxide composite membrane in direct contact membrane distillation: The different role at evaporation and condensation interfaces.

Graphene oxide (GO) coating has recently been reported as a novel approach to increase membrane flux of membrane distillation (MD), yet the phenomena underlying the process are still not fully understood. In this study, a mathematical model based on capillary-film assumption was developed and validated with the results (R2>0.99) from a series of MD experiments. According to the model, when GO layer was placed at the evaporation interface, the temperature difference across the membrane surface increases significantly (44.2%∼92.0%) and the temperature polarization coefficient is increased greatly from 0.29∼0.38 to around 0.55. This leads to a big increase of driving force for higher heat flow and subsequently mass flux (17.8∼45.5%). However, the vapor pressure on membrane surface was decreased due to Kelvin effect of GO capillary pores, which has a negative influence on the driving force, accounting for about 26.9% to 52.6% drop in the achieved flux. In comparison, when GO layer was placed at the condensation interface, the temperature difference across the membrane surface decreases slightly (7.2∼12.2%), but the reduced vapor pressure on GO capillary pores due to Kelvin effect become the dominant factor affecting membrane flux, resulting in an increase mass flux of 12.4∼16.4%. The model developed in this study provides a theoretical foundation for understanding the role of GO coating on flux improvement, and can be used for further development of high flux membranes.

Pseudocapacitive Charge Storage in MXene-V2O5 for Asymmetric Flexible Energy Storage Devices.

Pseudocapacitive asymmetric supercapacitors are promising candidates for achieving high energy density in flexible energy storage devices. However, seeking suitable positive electrode materials that are compatible with negative electrode materials remains a considerable challenge. In the current study, a pseudocapacitive Ti3C2Tx MXene used as negative electrodes is rationally compatible with redox-type V2O5 as positive electrodes, resulting in the assembly of an all-pseudocapacitive Ti3C2Tx MXene//V2O5 asymmetric flexible energy storage device. The solid-state asymmetric device can deliver an energy density of 8.33 mW h cm-3 at a current density of 0.5 A g-1. Moreover, it can operate in an expanded voltage window of 1.5 V, with dominant surface-capacitive charge-storage mechanisms. Additionally, the device can power a yellow light-emitting diode for up to 7 s, indicating the potential of the device for use in practical applications. This study demonstrates the possibility of using other two-dimensional transition-metal carbide nanosheets for high-energy density flexible energy storage devices.

The levels of phthalate exposure and associations with obesity in an elderly population in China.

BACKGROUND: Few epidemiological studies on the correlation between phthalate exposure and elderly obesity in China are available. The purpose of the present study is to assess phthalate exposure levels and explore the connections between exposure to phthalates and obesity using a sample of Chinese community-dwelling elderly individuals. METHODS: Data were acquired from the baseline survey of the Cohort of Health of Elderly and Controllable Factors of Environment, which was established in Lu'an, Anhui province, China, from June to September in 2016. Urine samples were obtained to analyze the concentrations of seven phthalate metabolites, utilizing a high-performance liquid chromatography-tandem mass spectrometry method. General obesity was determined based on body mass index, and abdominal obesity based on waist circumference. Binary logistic regression models were utilized to analyze the associations of creatinine-corrected phthalate metabolite concentrations (categorized into quartiles) with general and abdominal obesity in elderly people. Moreover, a stratified analysis was performed to explore the difference between genders. RESULTS: Of 942 elderly individuals, 52.9% were defined as generally obese and 75.5% as abdominally obese. The detection rates of seven phthalate metabolites ranged from 90.07% to 99.80%. The highest median concentration was 44.08 µg/l (for MBP), and the lowest was 0.55 µg/l (for MEHP). The level of exposure to LMW(low-molecular-weight) PAEs is higher than that to HMW(high-molecular-weight) PAEs. After adjustment for confounding variables, we found a significant association between urinary MEOHP (mono-2-ethyl-5-oxohexyl phthalate), MEHP (mono-2-ethylhexyl phthalate), MBP (mono-n-butyl phthalate), MEP (mono-ethyl phthalate), and MMP (mono-methyl phthalate) levels and general obesity. MBP levels were also correlated with abdominal obesity. When stratified by gender, higher urinary levels of MEOHP, MBP, MEP, and MMP were associated with general obesity in males, whereas MBP and MMP levels were eminently correlated with general obesity in females. Higher urinary MBP levels were associated with increased abdominal obesity rates in males, but not in females. CONCLUSIONS: In conclusion, higher phthalate metabolite concentrations were correlated with obesity in the elderly. Moreover, a gender difference was observed in these associations.

Characteristics, Cause, and Severity Analysis for Hazmat Transportation Risk Management.

The accidents caused by hazardous material during road transportation may result in catastrophic losses of lives and economics, as well as damages to the environment. Regarding the deficiencies in the information systems of hazmat transportation accidents, this study conducts a survey of 371 accidents with consequence Levels II to V involving road transportation in China from 2004-2018. The study proposes a comprehensive analysis framework for understanding the overall status associated with key factors of hazmat transportation in terms of characteristics, cause, and severity. By incorporating the adaptive data analysis techniques and tackling uncertainty, the preventative measures can be carried out for supporting safety management in hazmat transportation. Thus, this study firstly analyzed spatial-temporal trends to understand the major characteristics of hazmat transportation accidents. Secondly, it presents a quantitative description of the relation among the hazmat properties, accident characteristics, and the consequences of the accidents using the decision tree approach. Thirdly, an enhanced F-N curve-based analysis method that can describe the relationship between cumulative probability F and number of deaths N, was proposed under the power-law distribution and applied to several practical data sets for severity analysis. It can evaluate accident severity of hazmat material by road transportation while taking into account uncertainty in terms of data sources. Through the introduction of the as low as reasonably practicable (ALARP) principle for determining acceptable and tolerable levels, it is indicated that the F-N curves are above the tolerable line for most hazmat accident scenarios. The findings can provide an empirically supported theoretical basis for the decision-makers to take action to reduce accident frequencies and risks for effective hazmat transportation management.

Co-metabolism for enhanced phenol degradation and bioelectricity generation in microbial fuel cell.

Co-metabolism is one of the effective approaches to increase the removal of refractory pollutants in microbial fuel cells (MFCs), but studies on the links between the co-substrates and biodegradation remain limited. In this study, four external carbon resources were used as co-substrates for phenol removal and power generation in MFC. The result demonstrated that acetate was the most efficient co-substrate with an initial phenol degradation of 78.8% and the voltage output of 389.0 mV. Polarization curves and cyclic voltammogram analysis indicated that acetate significantly increased the activity of extracellular electron transfer (EET) enzyme of the anodic microorganism, such as cytochrome c OmcA. GC-MS and LC-MS results suggested that phenol was biodegraded via catechol, 2-hydroxymuconic semialdehyde, and pyruvic acid, and these intermediates were reduced apparently in acetate feeding MFC. The microbial community analysis by high-throughput sequencing showed that Acidovorax, Geobacter, and Thauera were predominant species when using acetate as co-substrate. It can be concluded that the efficient removal of phenol was contributed to the positive interactions between electrochemically active bacteria and phenolic degradation bacteria. This study might provide new insight into the positive role of the co-substrate during the treatment of phenolic wastewater by MFC.

Di-(2-ethylhexyl) phthalate inhibits expression and internalization of transthyretin in human placental trophoblastic cells.

During pregnancy, fetal thyroid hormones (THs) are dependent on maternal placental transport and their physiological level is crucial for normal fetal neurodevelopment. Earlier research has shown that Di-(2-ethylhexyl) phthalate (DEHP) disrupts thyroid function and THs homeostasis in pregnant women and fetuses, and affects placental THs transport. However, the underlying mechanisms are poorly understood. The present study, therefore, aimed to systematically investigate the potential mechanisms of DEHP-induced disruption in the placental THs transport using two human placental trophoblastic cells, HTR-8/SVneo cells and JEG-3 cells. While the exposure of DEHP at the doses of 0-400 µM for 24 h did not affect cell viability, we found reduced consumption of T3 and T4 in the culture medium of HTR-8/Svneo cells treated with DEHP at 400 µM. DEHP treatment did not affect T3 uptake and the expression of monocarboxylate transporters 8 (MCT8) and organic anion transporters 1C1 (OATP1C1). However, DEHP significantly inhibited transthyretin (TTR) internalization, down-regulated TTR, deiodinase 2 (DIO2), and thyroid hormone receptors mRNA expression and protein levels, and up-regulated deiodinase 3 (DIO3) protein levels in a dose-dependent manner. These results indicate that DEHP acts on placental trophoblast cells, inhibits its TTR internalization, down-regulates TTR expression and affects the expression of DIO2, DIO3, and thyroid hormone receptor. These may be the mechanisms by which PAEs affects THs transport through placental.

Fabrication of a highly dispersed/active Pd nanoparticle supported catalyst: a cation-assisted reduction method in ethylene glycol-water solution at mild temperature.

Development of sustainable routes to synthesize precious metal supported catalysts is of great importance because of their wide applications in the catalysis field. This paper reported a controllable and recyclable cation-assisted reduction route to fabricate a palladium nanoparticle supported catalyst. At 323 K, highly dispersed Pd/Al2O3-CARM was prepared through introducing M2+ (M = Mn, Zn or Cu) ions to promote the reduction of H2PdCl4 in ethylene glycol-water solution, and the residual filtrate after preparation could be recycled to prepare Pd/Al2O3 catalysts. A turnover frequency of 300 × 102 h-1 was obtained for Pd/Al2O3-CARMn in solvent-free aerobic oxidation of benzyl alcohol to benzaldehyde.

Effect of impure components in flue gas desulfurization (FGD) gypsum on the generation of polymorph CaCO3 during carbonation reaction.

As one of the typical solid-wastes, FGD gypsum usually occupies land and causes resource waste and environmental pollution. Its high content of CaSO4·2H2O shows highly potential in synthesizing CaCO3 by incorporating CO2. Nevertheless, the impurities in FGD gypsum have significant effects on polymorph of CaCO3 and the formation mechanism of CaCO3 polymorph during FGD gypsum carbonation was still unclear. Here, we selected CaSO4·2H2O as model to explore the effects of impurities of muscovite and dolomite in FGD gypsum on polymorph of CaCO3 during carbonation. Results showed that the carbonation products of FGD gypsum are a mixture of vaterite (˜60%) and calcite (˜40%), while only pure vaterite was obtained in CaSO4·2H2O carbonation reaction. Muscovite has negligible effects on obtaining pure vaterite during CaSO4·2H2O carbonation. Interestingly, the content of calcite increases to the maximum value (˜27%) at 1.0 wt% dolomite and then decreases with the increment of dolomite in CaSO4·2H2O carbonation reaction. Correspondingly, vaterite declines first and then increases. Mechanism study shows that hydrophilicity and negative surface charge of dolomite might be the key factors to selectively form calcite during the carbonation of FGD gypsum. These findings might contribute to further utilization of FGD gypsum.

Facile Preparation of Ag-Coated Superhydrophobic/Superoleophilic Mesh for Efficient Oil/Water Separation with Excellent Corrosion Resistance.

We present the facile preparation of a superhydrophobic-oleophilic stainless steel mesh with excellent oil/water separation efficiency and resistance to corrosion through hydrofluoric (HF) acid etching, Ag nanoparticle coating, and stearic acid modification, to construct a superhydrophobic micro/nanohierarchical structure. The surface of the treated mesh exhibits superhydrophobicity, with a water contact angle of 152°, and superoleophilicity, with an oil contact angle of 0°. The effects of variation in the HF etching time and Ag nanoparticle coating on surface wettability were explored. The treated mesh demonstrated a very high separation efficiency, as high as 98% for the optimal preparation, on a series of oil/water mixtures. The durability of the treated mesh was tested by repeated separation of kerosene/water mixtures, with the separation efficiency remaining higher than 97% after 40 cycles. In addition, the mesh exhibited an excellent chemical resistance to both acidic and alkaline conditions, with good wearing in hot water. The improved superhydrophobic-oleophilic mesh represents a feasible and realistic oil/water separation methodology even under harsh conditions, and it could have wide application in industrial processes.

Synthesis of pH-Responsive Inorganic Janus Nanoparticles and Experimental Investigation of the Stability of Their Pickering Emulsions.

Pickering emulsions exhibit outstanding stability, especially those prepared with Janus particles, whose desorption energy is expected to be up to 3-fold greater than emulsions of homogeneous particles from theoretical calculations. To the best of our knowledge, however, there remains no experimental proof of this behavior in practice. In this study, inorganic Janus nanoparticles were fabricated by regioselective modification of the separate side of SiO2 nanoparticles with a judiciously selected mixture of trimethoxysilylpropyldiethylenetriamine and n-octyltrimethoxysilane. Janus nanoparticles demonstrated excellent interfacial activity, forming Pickering emulsions with oil phases at oil-water interfacial tensions ranging from 6.6-52.8 mN m-1. Furthermore, as the interface of the Janus nanoparticles was regionally functionalized with -NH2 groups, phase inversion could be realized by tuning pH. This is the first example for the Pickering emulsions stabilized with inorganic Janus particles. Importantly, based on the results of centrifugation experiment, the desorption energy of Janus nanoparticles at the interface was 3.2 times larger than that of homogeneous nanoparticles, which is in accordance with the result from theoretical calculations. These experimental results will substantially enrich our understanding of Janus nanoparticle Pickering emulsions and their interfacial assembly behavior.

Compartmentalized Droplets for Continuous Flow Liquid-Liquid Interface Catalysis.

To address the limitations of batch organic-aqueous biphasic catalysis, we develop a conceptually novel method termed Flow Pickering Emulsion, or FPE, to process biphasic reactions in a continuous flow fashion. This method involves the compartmentalization of bulk water into micron-sized droplets based on a water-in-oil Pickering emulsion, which are packed into a column reactor. The compartmentalized water droplets can confine water-soluble catalysts, thus "immobilizing" the catalyst in the column reactor, while the interstices between the droplets allow the organic (oil) phase to flow. Key fundamental principles underpinning this method such as the oil phase flow behavior, the stability of compartmentalized droplets and the confinement capability of these droplets toward water-soluble catalysts are experimentally and theoretically investigated. As a proof of this concept, case studies including a sulfuric acid-catalyzed addition reaction, a heteropolyacid-catalyzed ring opening reaction and an enzyme-catalyzed chiral reaction demonstrate the generality and versatility of the FPE method. Impressively, in addition to the excellent durability, the developed FPE reactions exhibit up to 10-fold reaction efficiency enhancement in comparison to the existing batch reactions, indicating a unique flow interface catalysis effect. This study opens up a new avenue to allow conventional biphasic catalysis reactions to access more sustainable and efficient flow chemistry using an innovative liquid-liquid interface protocol.

Synthesis, Surface Activities, and Aggregation Behaviors of Butynediol-ethoxylate Modified Polysiloxanes.

Five different butynediol-ethoxylate modified polysiloxanes (PSi-EO) were designed and synthesized via two-step reactions: the preparation of low-hydrogen containing silicone oil (LPMHS) by acid-catalyzed polymerization and the following hydrosilylation reaction with 1,4-bis(2-hydroxyethoxy)-2-butyne. The chemical composition of each product was confirmed by FT-IR, (1)H NMR, and (29)Si NMR. The surface activities and aggregation behaviors of PSi-EO surfactants in aqueous solution were studied systematically using surface tension, dynamic light scattering (DLS), transmission electron microscopy (TEM), and contact-angle methodologies. Relatively low critical aggregation concentration (15-34 mg·L(-1)) and surface tension (∼25 mN·m(-1)) were measured for PSi-EO aqueous solution. The rate of surface tension reduction increased both with increasing PSi-EO concentration and with increases in the proportion of hydrophilic moieties within the synthesized compounds. Furthermore, DLS and TEM studies revealed that PSi-EO self-assembled in aqueous solution to form spherical aggregates. Contact-angle measurements conducted upon low-energy paraffin film surfaces demonstrated that PSi-EO exhibited efficient spreading at concentrations above the critical aggregation concentration.

Surface Activity and Aggregation Behavior of Siloxane-Based Ionic Liquids in Aqueous Solution.

Six novel siloxane-based surface-active ionic liquids (SAILs)--siloxane ammonium carboxylate [Si(n)N(2)-CA(1), (n = 3, 4)]--were designed and synthesized. Their melting points, surface activities, and self-aggregation behavior in aqueous solution were studied. The results showed that because of the bulky hydrophobic siloxane chains at the end of the tail, all six siloxane-based SAILs are room-temperature ionic liquids (RT-SAILs). The introduction of the siloxane group can reduce the melting point of ionic liquids to below room temperature and can promote the micellization and aggregation behavior more efficiently. These siloxane-based SAILs can greatly reduce the surface tension of water, as shown by the critical aggregation concentration (γCAC) values of 20 mN·m(-1); all six siloxane RT-SAILs can form a vesicle spontaneously in aqueous solution, indicating potential uses as model systems for biomembranes and vehicles for drug delivery.

Recycling nanoparticle catalysts without separation based on a pickering emulsion/organic biphasic system.

A conceptually novel methodology is explored for in situ recycling of nanoparticle catalysts based on transforming a conventional organic/aqueous biphasic system into a Pickering emulsion/organic biphasic system (PEOBS). The suggested PEOBS exists as two phases, with the nanoparticle catalyst "anchored" in the Pickering emulsion phase, but is "continuous" between the organic phase and the continuous phase of the Pickering emulsion. Aqueous hydrogenations are used to evaluate the reaction performances of PEOBS, and the underlying principles of PEOBS are preliminarily elaborated. The unique properties of PEOBS lead to many intriguing findings, which are unlikely to be achieved in the reported biphasic systems. PEOBS exhibits more than a fourfold enhancement in catalysis efficiency in comparison with a conventional biphasic system. Impressively, PEOBS enables the organic product to be facilely isolated through simple decantation and the nanoparticle catalyst can be recycled in situ without the need for "separation". Its recycling effectiveness is justified by ten reaction cycles without significant catalyst loss. The simple protocol, in conjunction with the stability to simultaneously achieve high catalysis efficiency and excellent catalyst recyclability, makes PEOBS a promising methodology to develop more sustainable nanocatalysis.

Synthesis and aggregation behavior of grafted maleic acid copolymers.

Grafted SMA containing poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether) (SMA-PEG) and its hydrophobically modified products poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether & dodecyl) (SMA-PEG+C(12)) and poly(styrene-co-maleic anhydride)-g-(dodecyl) (SMA-C(12)) were prepared using a single batch method. Their adsorption and rheology behavior was investigated using equilibrium surface tension and rheological techniques. The adsorption parameters, saturation surface excess concentration (Γ(max)), and the minimum area (A(min)) of these copolymers were evaluated. The results show that Γ(max) increased and A(min) correspondingly decreased with increasing hydrophobicity. Aggregation standard free energy of SMA-PEG+C(12) and SMA-C(12) suggested that increased hydrophobicity enhanced the tendency for aggregation to occur. The distinctive differences in the macroscopic appearance were shown by aqueous samples of the copolymers. The samples of SMA-M behaved as Newtonian fluids at all concentrations (from 1.0 wt% to 20.0 wt%), indicating that there were no macromolecular chain entanglements or interactions between aggregates in solution. For SMA-PEG+C(12), at concentrations above 10.0 wt%, the presence of cross-links between aggregates is presumed to be the reason for the viscoelastic behavior. Solid-like elastic behavior could occur at low concentration (5.0 wt%) of SMA-C(12), suggesting the formation of networks by inter-chain aggregation of the hydrophobic dodecyl chains.

Adsorption and aggregation behavior of tetrasiloxane-tailed surfactants containing oligo(ethylene oxide) methyl ether and a sugar moiety.

Three novel amphiphilic dicephalic (double-headed) surfactants containing oligo(ethylene-oxide)methyl-ether and a sugar moiety TGA-m (m = 1, 2, and 3) that incorporate a tetrasiloxane at the terminus of a hydrocarbon chain were designed and synthesized. Their surface activity and aggregation behavior in aqueous solution were systematically investigated by surface tension, dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques at 298 K. The surface tension measurements provided the critical aggregation concentration (CAC) and the surface tension at the CAC (γ(cac)). In addition, with application of the Gibbs adsorption isotherm, the maximum surface excess concentration (Γ(max)) and the minimum surface area/molecule (A(min)) at the air-water interface were estimated. The effect of EO chain length on the surface activity and aggregation behavior was also investigated. It was found that both the γ(cac) and the CAC were lower than those for reported traditional hydrocarbon surfactants. Aggregates of three surfactants, TGA-m (m = 1, 2, and 3), formed in aqueous solutions could be assigned as spherical vesicles as suggested by analysis using DLS and TEM. Moreover the formation of vesicles can be confirmed by the encapsulation of bromophenol blue. These results indicate that these three surfactants have excellent efficiencies of vesicle formation and surface tension reduction in the aqueous phase.

Carbohydrate-modified siloxane surfactants and their adsorption and aggregation behavior in aqueous solution.

Four carbohydrate-modified siloxane surfactants, Si(n)N-GA and Si(n)N-LA (n = 3, 4), were designed and synthesized. Their surface activities, adsorption, and aggregation behavior in aqueous solution were investigated by surface tension measurements, dynamic light scattering (DLS) and transmission electron microscopy (TEM). Due to the bulky siloxane moiety at the end of hydrophobic chains, the surfactant solutions displayed low critical aggregation concentration (cac) and low surface tension. Surface tension measurement for all three surfactants are under 22 mN x m(-1), much lower than those of ordinary hydrocarbon surfactants. Due to its poor solubility in water, surface tension of Si(4)N-GA could not be measured. DLS and TEM analysis of Si(3)N-GA, Si(3)N-LA, and Si(4)N-LA aqueous solutions revealed self-assembled spherical vesicles, indicating potential applications as microsphere drug delivery systems and as models of biomembranes.

Preparation and properties of comb-like surfactants containing poly(ethylene oxide) methyl ether grafts.

The comb-like surfactants, poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether), poly(St-co-MA)-g-(MPEG), have been prepared using a macromonomer approach to get controlled molecular structures. The macromonomer (MAMPEG) was obtained by esterification of poly(ethylene glycol) monomethyl ether with maleic anhydride. Poly(St-co-MA)-g-(MPEG) with various molar ratios of St to MAMPEG (R) were then constructed by radical copolymerization. The comb-like structures of the surfactants were confirmed by infrared and (1)H nuclear magnetic resonance spectroscopy. It is found from gel permeation chromatography characterization that the molecular weight of the surfactants increases as R increases. The polydispersity index was in the range between 1.4 and 2.0 in all the cases. The surfactants with a higher St percentage are less soluble in water due to aggregation. The value of critical aggregation concentration (CAC) and the surface tension at the CAC (gamma(CAC)) decrease as R increases. The steady-shear measurements show that the surfactant solutions at 50 g/L are dilatant fluids. In addition, it appears that there are two break points in the viscosity-shear rate curve. Both break points increase with increasing R. It can therefore be concluded that the properties of comb-like surfactants poly(St-co-MA)-g-(MPEG) are related to molecular structure. The results demonstrate that the properties of these comb-like surfactants can be tailored through appropriate molecular design.