HCl Aqueous Solution Research Articles

Energy-Efficient Nitrogen Reduction to Ammonia at Low Overpotential in Aqueous Electrolyte under Ambient Conditions.

The electrochemical nitrogen reduction reaction (NRR) under ambient conditions is a promising alternative to the traditional energy-intensive Haber-Bosch process to produce NH3 . The challenge is to achieve a sufficient energy efficiency, yield rate, and selectivity to make the process practical. Here, we demonstrate that Ru nanoparticles (NPs) enable NRR in 0.01 m HCl aqueous solution at very high energy efficiency, that is, very low overpotentials. Remarkably, the NRR occurs at a potential close to or even above the H+ /H2 reversible potential, significantly enhancing the NRR selectivity versus the production of H2 . NH3 yield rates as high as ≈5.5 mg h-1 m-2 at 20 °C and 21.4 mg h-1 m-2 at 60 °C were achieved at a redox potential (E) of -100 mV versus the reversible hydrogen electrode (RHE), whereas a highest Faradaic efficiency (FE) of ≈5.4 % is achievable at E=+10 mV vs. RHE. This work demonstrates the potential use of Ru NPs as an efficient catalyst for NRR at ambient conditions. This ability to catalyze NRR at potentials near or above RHE is imperative in improving the NRR selectivity towards a practical process as well as rendering the H2 viable as byproduct. Density functional theory calculations of the mechanism suggest that the efficient NRR process occurring on these predominantly Ru (0 0 1) surfaces is catalyzed by a dissociative mechanism.

Corrosion Inhibition of Carbon Steel in Aqueous HCl Solutions by Acid Pre-Magnetization Technique: Experimental Study and Modelling

The effect of magnetization of acid before usage (pre-magnetization technique) on the corrosion inhibition of carbon steel (CS) in 7.5, 10 and 12.5 wt % (2.2, 3.0 and 3.8 M) HCl solutions were investigated by means of gravimetric weight loss method. Response Surface Methodology (Box-Behnken design) has been used to study and modelling the effects of magnetic field (MF) intensity, acid concentration, and elapsed time on inhibition efficiency. The experiments reveal that pre-magnetization is a suitable inhibitor in HCl solutions. The maximum percentage inhibition efficiency was found to be 93% for 12.5 wt % HCl. The results showed that the inhibition efficiency rises with increasing MF intensity. The surface structure of the CS was examined by SEM (scanning electron microscopy) both in the normal and magnetized HCl solutions.

Electrochemical study of a glassy carbon electrode modified by poly-4-nitroaniline-reduced/murexide and its sensitivity for metal ions

The electrochemical modification of a glassy carbon electrode using reduced poly-4 nitroaniline (P-4NA) and it's applicability for determination of metallic ions was performed in this study. The electrode modification was performed by cyclic voltammetry in the potential range between 0.9 V and 1.4 V vs Ag/Ag+ (in 10 mM AgNO3) at the scan rate of 100 mV/s by 50 cycles in non-aqueous media. The reduction of nitro groups on the P-4NA modified glassy carbon electrode surface was performed in the potential range between −0.1 V and −0.8 V vs Ag/AgCl(Sat. KCl) at a scan rate of 100 mV/s in 100 mM aqueous HCl solution. The reduced P-4NA glassy carbon surface was modified with the murexide. The affinity of the modified glassy carbon electrode with some metallic ions was investigated by electrochemical impedance spectroscopy method in phosphate buffer solution (pH = 5).

Hexamethylcucurbit[3,3]uril-Based Porous Supramolecular Assemblies and Their Adsorption Properties.

In the present work, we selected hexamethylcucurbit[3,3]uril (Me6Q[3,3]) as a building block and obtained two Me6Q[3,3]-based porous supramolecular assemblies from neutral water (A) and aqueous HCl solutions (B), respectively. Both Me6Q[3,3]-based assemblies are constructed of Me6Q[3,3] molecules through the typical outer surface interaction of cucurbit[n]urils, as well as hydrogen bonding between latticed water molecules and portal carbonyl oxygens of Me6Q[3,3]. The assemblies present different porous structure features and exhibit different adsorption properties for eight common volatile organic compounds. However, the two porous assemblies exhibit similar adsorption properties for certain fluorophore dyes, including rhodamine B (G1), fluorescein (G2), and pyrene (G3), and form solid colored fluorescent compounds, some of which exhibit responses to the selected volatile organic compounds.

Gelation Modification of Alginate Nonwoven Fabrics

Calcium alginate nonwoven fabrics were gelation-modified by two-stage with aqueous HCl solution and then ethanolic NaOH solution. The structure and crystallinity properties of the samples were characterized by FT-IR, SEM, and XRD. The preparation conditions and modification mechanism were investigated. The results indicated that the crystal structure of calcium alginate fibers was destroyed; the crystallinity and calcium ion content decreased after HCl treatment. This resulted from the formation of ester bonds among the hydrolytic molecules after NaOH treatment. The best gel performance was obtained at the HCl concentration of 0.05-0.1 wt% with the NaOH concentration in ethanol of 2–4 mol/l. The liquid absorption of nonwoven alginate fabrics increased by 145 %. The water capability increased by 2673 % after modification, while the thickness, mass per unit area, permeability, and tensile strength of nonwoven alginate fabrics changed little.

Tuning Water Sorption in Highly Stable Zr(IV)-Metal-Organic Frameworks through Local Functionalization of Metal Clusters.

Water adsorption of metal-organic frameworks (MOFs) is attracting intense interest because of their potential applications in atmospheric water harvesting, dehumidification, and adsorption-based heating and cooling. In this work, through using a hexacarboxylate ligand, four new isostructural Zr(IV)-MOFs (BUT-46F, -46A, -46W, and -46B) with rare low-symmetric 9-connected Zr6 clusters were synthesized and structurally characterized. These MOFs are highly stable in water, HCl aqueous solution (pH = 1), and NaOH aqueous solution (pH = 10) at room temperature, as well as in boiling water. Interestingly, the rational modification of the metal clusters in these MOFs with different functional groups (HCOO-, CH3COO-, H2O/OH, and PhCOO-) enables the precise tuning of their water adsorption properties, which is quite important for given application. Furthermore, all four MOFs show excellent regenerability under mild conditions and good cyclic performance in water adsorption.

Investigation of Tm2O3 As a Gate Dielectric for Ge MOS Devices

Germanium (Ge) has been intensively investigated as a high-mobility channel material alternative to silicon (Si). A high quality Ge/dielectric interface with interface state density Dit compared to Si is required for competitive device performance. GeO2 has been identified as potential candidate for an interfacial layer (IL) due to effective Ge surface passivation with Dit in the range of 1011 cm-2eV-1 [1]. However, in order to achieve scaled effective oxide thickness (EOT) a combination of GeO2 IL and a high-k dielectric is needed. Low interface state density in the range of 1011 cm-2eV-1 has been achieved while employing Al2O3 barrier [2] as well as rare earth oxides such as Y2O3 [3]. Rare-earth thulium oxide (Tm2O3) provides high dielectric constant k~16 [4] and sufficient valence (3.05 eV) and conduction (2.05 eV) band offsets [5] for a high-k dielectric layer on Ge. In this work Ge/GeOx/Tm2O3 interface quality and the impact of post deposition anneal ambient are investigated. Metal oxide semiconductor (MOS) capacitors were fabricated to evaluate Ge/GeOx/Tm2O3 gate stacks. After n-Ge substrate clean (acetone, propanol and O2 plasma) and native germanium oxide removal with aqueous HF and HCl solutions the samples were immediately loaded into the rapid thermal anneal (RTA) chamber where oxidation was carried out at 550 °C for 5 s to 5 min. The temperature in the chamber is controlled by a pyrometer which is calibrated to a Si wafer, and oxidation is performed by placing a Ge substrate piece on a Si carrier wafer. The temperature of the Ge sample is thus lower than that of the Si wafer. After oxidation the samples were loaded to atomic layer deposition (ALD) chamber where 40 cycles (~7 nm) of Tm2O3 were deposited using TmCp3 and H2O as precursors. Then Ge/GeO2/Tm2O3 gate stacks were annealed in different ambient (O2, O3, N2 and H2/N2) and temperatures (400 - 550 °C). Reference samples without Tm2O3 deposition or without post deposition anneal (PDA) were also fabricated. Al gate metal was deposited by physical vapor deposition and patterned. MOS capacitors were electrically characterized with capacitance-voltage (CV) measurements. Interface state density in the midgap was evaluated from CV curves using a method described in [6]. X-ray photoelectron spectroscopy (XPS) was performed on some samples using Al Kα X-ray (1486.6 eV) source and PSP Vacuum Technology electron energy analyser. Electrical properties of thermally grown Ge/GeO2 interfaces were evaluated and low interface state density Dit < 5·1011 cm-2eV-1 in the midgap was extracted from CV measurements. The influence of Tm2O3 deposition on high-quality Ge/GeO2 interfaces was then determined. A degradation of the interface quality after the deposition was observed as displayed in Fig. 1. Dit is higher for thinner underlying GeOx layer and seems to saturate to ~9·1011 cm-2eV-1 for thick layers. A series of post deposition anneals in different ambient and temperatures were performed on Ge/GeOx/Tm2O3 gate stacks in order to investigate the influence on the interface state density and capacitance equivalent thickness (CET). The results are shown in Fig. 2. It can be seen that a temperature of 500 °C or higher and O2 ambient is needed to sufficiently reduce Dit, when values as low as 2·1011 cm-2eV-1 can be reached. XPS measurement was performed on Ge/GeOx/Tm2O3 gate stack with O2 PDA at 500 °C and the obtained spectrum is shown in Fig. 3. The difference between the GeOx 3d5/2 peak and Ge0 3d5/2 peak is 2.7 eV which corresponds to Ge3+ oxidation state. This result is consistent with previously reported XPS results on Ge/GeOx/Al2O3 stacks [7] and suggests that Ge3+ oxidation state provides the low Dit values of Ge/GeOx/Tm2O3 gate stacks. Tm2O3 integrated with GeO2 and O2 PDA is a viable candidate for Ge MOS devices due to low interface state density of ~2·1011 cm-2eV-1 which is correlated to Ge3+ oxidation state. A further investigation of O2 PDA time in terms of the trade-off between Dit and CET will be reported.

REGULARITIES IN ELECTRICAL CONDUCTIVITY OF AQUEOUS SOLUTIONS OF SOME INORGANIC ACIDS

The concentration and temperature dependences of the specific electric conductivity (EC) of aqueous solutions of HCl, HBr, HNO3, HClO4, H2SO4 and HBF4, H2SiF6, and H2TiF6 were analyzed. It was shown that at a temperature of 298 K maximum specific EC of solutions of acids does not exceed the value of the limit high-frequency EC of water. The analytical equation allowing on the basis of maximum EC and corresponding to it concentration to calculate the EC of acid solutions in a wide range of concentrations and temperatures was obtained.

Hydrogen storage properties of the novel crosslinked UiO-66-(OH)2

Metal organic frameworks (MOF) are a type of nanoporous materials with large specific surface area, which are especially suitable for gas separation and storage. In this work, we report a new approach of crosslinking UiO-66-(OH)2 to enhance its hydrogen storage capacity. UiO-66-(OH)2 was synthesized using hafnium tetrachloride (HfCl4) and 2, 5-dihydroxyterephthalic acid (DTPA) through a canonical modulated hydrothermal method (MHT), followed by a post-synthesis modification, which is to form a crosslinking structure inside the porous structure of UiO-66-(OH)2. During the modification process, the phenolic hydroxyl groups on the UiO-66-(OH)2 reacted with methanal, and HCl aqueous solution and triethylamine served as catalyst (the products denoted as UiO-66-H and UiO-66-T, respectively). Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), 13C nuclear magnetic resonance spectroscopy (13C NMR) proved that the crosslinking was formed. The BET specific surface area and the average adsorption pore size of UiO-66-H and UiO-66-T significantly increased after modification. The hydrogen storage capacity of UiO-66-H reached a maximum of 3.37 wt% (16.87 mmol/g) at 77 K, 2 MPa. Hydrogen adsorption enthalpy of UiO-66-T was 0.986 kJ/mol, which was higher than that of UiO-66-(OH)2 (0.695 kJ/mol). This work shows that UiO-66-(OH)2 is a promising candidate for potential application in high-performance hydrogen storage.

Fabrication of Al-Coated Mg–Li Alloy Sheet and Investigation of Its Properties

An Al-coated Mg-8 mass% Li alloy rectangular bar was fabricated by hot extrusion, and then, it was hot-rolled into a thin sheet. The Al coating was uniform in thickness and had good bonding with the substrate during all the processing. This Al-coated Mg–Li alloy exhibited a good corrosion resistance in a 0.5 mass% HCl aqueous solution. No intermetallic compound was observed at the Al/Mg–Li interface after the extrusion and the rolling. The Al-coated Mg–Li alloy sheet exhibited an elongation to fracture of 35% at room temperature at a strain rate of 0.001 s−1 without any debonding between the coating and the substrate. When tensile tested at 573 K at 0.001 s−1 in the air, the Al coating remained undamaged even until an elongation of about 150%. Further elongation generated cracks on the coating and the specimen fractured at an elongation of about 200%. In an Ar atmosphere, the specimen exhibited a fracture elongation of over 400% under the same conditions at 573 K at 0.001 s−1, although a large number of cracks generated on the Al coating.

A new dual hydrophilic–hydrophobic acrylic resin containing pyridine and 1,3,4-oxadiaxole moieties for removal of Co(II)ions

The present study reports the synthesis and characterization of a new acrylamide-based monomer containing pyridine and 1,3,4-oxadiazole moieties, N-(4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-l)phenyl) acrylamide (POPA). The adsorbent resin was obtained by free radical copolymerization of POPA and acrylamide with a ratio of 9:91 mol% in the presence of N,N′-methylenebisacrylamide (MBA) as cross-linking agent. Thermal properties of poly(POPA), poly(acrylamide) and the cross-linked resin were assessed by thermogravimetric analysis and differential thermal analysis. The capability of cross-linked resin to remove Co(II) cations was shown under optimal adsorption time, pH and adsorbent mass. The adsorption kinetics obeyed the pseudo-second-order kinetic equation, and the Langmuir model described the adsorption isotherm with a maximum adsorption capacity of 24.10 mg g−1. In addition, the resin was regenerated by simply washing with 0.1 M aqueous solution of HCl, and no significant decrease was observed in the extraction efficiency following the test of up to eight cycles. The current findings suggest that the obtained resin is a stable and reusable adsorbent that can be potentially applied to water treatments for the efficient removal of Co(II) cations.

Fabrication and characterization of robust hydrophobic lotus leaf-like surface on Si3N4 porous membrane via polymer-derived SiNCO inorganic nanoparticle modification

Robust hydrophobic surface was produced by modifying the surface of porous Si3N4 membrane, via aminolysis and pyrolysis process, with organosilane-derived inorganic SiNCO nanoparticles, which are tightly adhered to the Si3N4 grains. The resultant material had a high water contact angle of 142°, attributed to -Si-CH3 surface terminal groups and a lotus leaf-like hierarchical structure of the nanoparticles, which had a frame structure with Si-N and Si-O covalent bonds in their bulk. The hydrophobic behavior remained practically unchanged after exposure of the produced membranes to aqueous solutions of humic acid, HCl and NaOH, to benzene, as well as to stirring abrasive slurry with SiC particles, and after exposure at high temperatures, up to 500 °C, to air. The inorganic membrane can be considered for use in a broad range of applications which require robust hydrophobic surfaces.

PREPARASI DAN KARAKTERISASI MIKROKRISTALIN SELULOSA (MCC) BERBAHAN BAKU TANDAN KOSONG KELAPA SAWIT (TKKS)

[PREPARATION AND CHARACTERIZATION OF MICROCRYSTALLINE CELLULOSE (MCC) MADE FROM EMPTY PALM OIL BUNCHES (TKKS)] Empty Palm bunches (TKKS) is solid waste from industrial processing of oil palm (Elaeis guineensis Jacq) that have a high cellulose content. This research aims to synthesize Microcrystalline Cellulose (MCC) from TKKS and determine the characteristics of the MCC produced. The manufacturing process begins with the MCC delignifikasi multistage pulping TKKS using mixed of 3.5% HNO3 and NaNO2 in temperatures of 90 ?C for 2 hours, followed by heating of a mixture of 2% NaOH and Na2SO3 2 % at temperature 50?C for 2 hours. The second stage of the lignification process is done using NaOH 17.5 %, followed by hydrolysis towards ?-Cellulose lignification results with heating in the aqueous solution of HCl at concentrations of 3, 3.5 and 4 M for 30, 45 and 60 minutes. From the results obtained from the hydrolysis of the optimum yield of 80.73 %, i.e., MCC that use concentration of HCl 3 M for 30 minutes. MCC produced then analyzed using FTIR, XRD, and PSA. FTIR absorption for MCC results showed an of waves number on a 3375.43 cm-1 and 2899,01cm-1, indicating the presence of hydroxyl OH and CH.The results of the analysis with the PSA suggests that MCC has generated a measure of particle diameter 0.5281 µm. Using XRD analysis results that MCC has a degree of crystallinity of 86,79 %. And the results of testing the content of carbohydrates in MCC produced shows levels of carbohydrates of 88.36 %.

The reactivity of ethyl esters of 2-(benzoylamino) (1-R-2-oxoindoline-3-ylidene) acetic acids

The studies in a series of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids and their derivatives have shown that compounds of the isostructural series exhibit the nootropic, antihypoxic, anabolic activity. Aim. To study the reactivity of esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids. Materials and methods. The concentration of NaOH in the solution was determined by potentiometric titration on an EV-74 ionomer using the standard aqueous HCl solution. The reaction kinetics was performed in triplicates, the experiments contained 6-8 measurements (the depth of the change was not less than 80 %). The accuracy of the results obtained was assessed by the methods of mathematical statistics of small samples with statistical significance of 0.95. Results and discussion. The reaction rate constants of alkaline hydrolysis of esters of 2-(benzoylamino)(1-R-2-oxoindoline-3-ylidene) acetic acids depend on the structure and the length of the hydrocarbon chain at the heterocyclic nitrogen atom. Introduction of hydrocarbon radicals to the structure of the heterocycle slows down the reaction, while the chain extension accelerates it. The effect of the electronic nature of the substituents on the reactivity of ethyl esters was quantitatively assessed by Hammett equation. The data obtained suggest that the values of the reaction parameter ρ are positive in the temperature range studied; it is additionally confirmed by the BAC2 mechanism of this reaction. Conclusions. The reaction kinetics of alkaline hydrolysis of biologically active ethyl esters of 2-(benzoylamino) (1-R-2-oxoindoline-3-ylidene) acetic acids has been studied in a wide temperature range; its BAC2 mechanism has been proven with formation of highly symmetrical intermediate. The effect of the substituents at the heterocyclic nitrogen atom on the numerous kinetic and activation parameters of the reaction has been analyzed; isokineticity and synchronicity of the reaction have been proven using independent tests.

Fused Silica Microcapillaries Used for a Simple Miniaturization of the Electrified Liquid-Liquid Interface.

Short pieces of fused silica capillary tubing were used to support an electrified liquid–liquid interface. A methyl deactivated silica capillary having a diameter of 25 μm was filled with 1,2-dichloroethane solution and served as the organic part of the liquid–liquid interface. A nondeactivated fused silica capillary having a diameter of 5, 10, or 25 μm was filled with an aqueous HCl solution and served as the aqueous part of the electrochemical cell. For the latter, silanization of the capillary interior with chlorotrimethylsilane allowed for a successful phase reversal. All capillaries were characterized by ion transfer voltammetry using tetramethylammonium cation as a model ion. This simple, fast, and low-cost miniaturization technique was successfully applied for detection of the antibiotic ofloxacin.

Influence of hydrophobic nanosilica and hydrophobic medium on water bound in hydrophilic components of complex systems

The temperature behavior of water bound to compacted nanosilica cA-300 alone or in mixture with hydrophobic nanosilica AM1 alone or with addition of human serum albumin (HSA) or tannin was compared for different dispersion media (air, CDCl3 alone or with addition of HCl or trifluoroacetic acid, TFAA) using low-temperature 1H NMR spectroscopy and cryoporometry. There is overlapping of the confined space effects for water bound in voids between silica nanoparticles with the effects caused by the colligative properties of aqueous solutions of TFAA or HCl. These phenomena determine the temperature behavior of bound water unfrozen at T <273 K upon changes of the dispersion media. Typically, the contact area between unfrozen water and a surface of nanosilicas is smaller than the specific surface area of the solids due incomplete filling of voids between nanoparticles by bound water. Bound water tends to be in a clustered state upon the adsorption. In composites with cA-300/AM1, there is a tendency of diminution of the contact area of water with hydrophobic nanosilica AM1 and hydrophobic liquid CDCl3 immiscible with water. This effect changes the temperature behavior of water bound to hydrophilic silica or polar biomolecules. The observed effects can be of importance upon practical applications of nanosilica based composites.

Zr(IV)-Based Metal-Organic Framework with T-Shaped Ligand: Unique Structure, High Stability, Selective Detection, and Rapid Adsorption of Cr2O72- in Water.

Dichromate is known for severe health impairments to organisms. New and valid strategies have been developed to rapidly detect and efficiently remove this pollutant. Constructing stable luminescent metal-organic frameworks (MOFs) for dichromate recognition and removal from aqueous solution could provide a feasible resolution to this problem. Herein, a new luminescent Zr(IV)-MOF, Zr6O4(OH)7(H2O)3(BTBA)3 (BUT-39, BUT = Beijing University of Technology) was constructed through the reaction of a newly designed functionalized T-shaped ligand 4,4',4″-(1 H-benzo[ d]imidazole-2,4,7-triyl)tribenzoic acid (H3BTBA) with zirconium salt. BUT-39 has a unique porous framework structure, in which Zr6 cluster acts as a rare low-symmetric 9-connected node and BTBA3- as a T-shaped 3-connected linker. As far as we know, this represents the first case of a (3,9)-connected Zr(IV)-MOF. BUT-39 could retain its framework integrity in boiling water, 2 M HCl aqueous solution, and pH 12 NaOH aqueous solution. Due to its good water stability and strong fluorescent emission, BUT-39 is then employed in fluorescence sensing for various ions in aqueous solution and shows good performance toward Cr2O72- selectively, at a low concentration and a short response time (<1 min). Simultaneously, it also exhibits excellent capacity to rapidly capture Cr2O72- (within 1 min) with a high uptake up to 1 mmol g-1. Taking advantage of its excellent stability, sensitive and selective sensing, as well as rapid and high adsorption, BUT-39 is expected to be useful in Cr2O72- detection in and removal from water.

Solubility of MoO3 in Aqueous Acid Chloride-Bearing Solutions at 573 K

This study reports the measurements of the solubility of crystalline molybdenum trioxide, MoO3, in aqueous solutions of the mixture HCl–HClO4–NaCl (up to 1 m of chloride ion) at 573.2 K and pressures close to the saturation water vapor pressure by the autoclave method with the chemical analysis of quenched solutions. In total, there are 75 data points. The data treatment shows that the most probable chloride species of Mo(VI) in the studied solutions is MoO2(OH)2Cl– (the coordinated water is omitted), which agrees with the literature extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra studies of speciation of Mo(VI) in chloride solutions at elevated temperatures. For the solubility reaction MoO3(cr) + H2O(l) + Cl– = MoO2(OH)2Cl–, log10 K° = −(0.87 ± 0.2).

Wavelet Transform Modulus Maxima and Holder Exponents Combined with Transient Detection for the Differentiation of Pitting Corrosion Using Electrochemical Noise

A potentially powerful tool to detect and classify corrosion mechanisms is the analysis of electrochemical noise (EN). Data analysis in the time-frequency domain using, e.g., continuous wavelet transform (CWT) allows the extraction of localized frequency information, providing information on the type of corrosion, i.e., uniform or localized corrosion, from the EN signal. The CWT provides the opportunity to analyze changes in frequency behavior of EN signals over time. In the presence of transients generated by pitting corrosion that occur only during short instants of time, this is an important property. This paper introduces the combination of automated transient detection with wavelet transform modulus maxima (WTMM) and the Holder exponent. WTMM enhances the determination of transient frequencies by indicating the ridges of a CWT spectrum. The Holder exponent, a measure of singularity of an EN signal, provides a single parameter discrimination tool based on WTMM and serves to differentiate between general corrosion and two types of pitting corrosion of stainless steel Type 304 exposed to aqueous HCl solutions of different concentrations and as such at different pH values.

PH-switchable and CO2-switchable viscoelastic fluids based on a pseudo-hydrophobically associating water-soluble polymer

The non-hydrophobically associating water-soluble polymer (DPAM) of acrylamide (AM) and dimethylamino propyl methacrylamide (DMAPMA) was synthesized. Then pH-switchable and CO2‑switchable viscoelastic liquids based on DPAM and anionic surfactant sodium dodecyl sulfate (SDS)(referred to as DPAM-SDS) were developed. When minor HCl aqueous solution was added into the DPAM and SDS aqueous mixture or CO2 was bubbled into it, the tertiary amine groups of DPAM were protonated to form quaternary ammonium groups, some of which in the same quaternary ammonium groups of DPAM “bridged” some SDS through noncovalent electrostatic attraction, behaving like a pseudo-hydrophobically associating water-soluble polymer and forming viscoelastic fluids as checked through environmental scanning electron microscope(ESEM) and rheology. Upon removing of CO2 or back of pH by minor NaOH aqueous solution, the quaternary ammonium species of DPAM were deprotonated back to tertiary amine groups, separating the pseudo-hydrophobically associating water-soluble polymer back to DPAM and SDS molecules, which resulted in forming low-viscosity water solution. The switchable viscoelastic conversion can be repeated.