Increasing Sodium Dodecyl Sulfate Concentration Research Articles

Effect of SDS Solutions on the Jamin Effect in a Capillary Tube with a Contracted Throat.

With the continuous exploitation of petroleum resources, the distribution and displacement of residual oils have become key issues in enhancing oil recovery. In a reservoir, there are various forms of residual oils caused by the capillary force, viscous force, and some other hydrodynamic effects, which lead to the Jamin effect, and they restrict the oil displacement process. In this study, the morphologies of oil droplets in a capillary tube laden with water and sodium dodecyl sulfate (SDS) solutions are experimentally investigated. The pinning behavior of the oil droplet is observed in the waterflood with a lower velocity, while depinning and rupturing behaviors occur at a higher velocity. Hereto, we build a mechanics model to analyze the evolution of the Jamin effect in a capillary tube with varying cross sections. Using this theoretical model, we obtain the two critical velocities for the depinning and rupture of the oil droplet, which agree with the experimental results. Moreover, we find that oil droplets can more easily pass through the entire capillary tube in SDS solutions compared with water. The time required for oil droplets to pass through the pore throat becomes shorter with the increase of SDS concentration. Therefore, a theoretical model is established to determine the total pressure difference and the minimum applied pressure difference. These findings are beneficial to obtain a deep insight into the detailed oil displacement and achieve a higher oil recovery rate.

CO2/H2 Separation by Synergistic Enhanced Hydrate Method with SDS and R134a.

The synergistic effect of thermodynamic promoter tetrafluoroethane (R134a) and kinetic promoter sodium dodecyl sulfate (SDS) can significantly improve the phase equilibrium conditions required for CO2 hydrate formation and promote rapid generation of CO2 hydrate. Based on this, this study investigates the influence of SDS and R134a synergy on the separation of CO2/H2 mixed gas using the hydrate method. The research reveals that without SDS addition, R134a hydrate forms first at the gas-liquid interface before CO2 hydrate induction, hindering gas-liquid exchange. The addition of SDS can inhibit the formation of the hydrate film, enhance the initiator effect of R134a in the CO2 hydrate formation process, accelerate the nucleation of CO2 hydrate, and thus synergistically strengthen the separation of CO2/H2 mixed gases. Hydrate formation can be achieved at a concentration of 100 ppm of SDS solution, and the synergistic growth effect of R134a and CO2 hydrate becomes more significant with increasing SDS concentration. Optimal separation efficiency and maximum H2 concentration are achieved at 500 ppm of SDS, with 42.29 and 54.88% separation efficiency and H2 concentration, respectively. Decreasing the initial charge temperature has little impact on separation efficiency but significantly reduces the induction time, reducing it to 3 min at 12 °C. This study improved the separation efficiency of CO2 and H2 mixed gas, providing a better reference for hydrogen purification by the hydrate method.

The investigation of sorption-desorption performance and mechanism of copper by surfactant-modified zeolite in aqueous solutions.

As the most common filler in stormwater treatment, zeolite (NZ-Y) has good cation exchange capability and stabilization potential for the removal of heavy metal from aqueous solutions. In this study, sodium dodecyl sulfate (SDS) and NZ-Y were selected to preparing new adsorbent (SDS-NZ) by using a simple hydrothermal method. The sorption-desorption performance and mechanism of Cu(II) onto SDS-NZ were investigated. The results showed that the sorption of Cu(II) on SDS-NZ was in accordance with the pseudo-second-order kinetic model with an equilibrium time of 4h. The sorption behavior fitted Langmuir isotherm with a saturation sorption capability of 9.03mg/g, which was three times higher than that of NZ-Y. The modification of SDS increases the average pore size of NZ-Y by 3.96nm, which results in a richer internal pore structure and more useful sorption sites for Cu(II) sorption. There was a positive correlation between solution pH values and sorption capability of Cu(II) in the range of 3.0-6.0. With the ionic strength increased, the sorption capability of Cu(II) onto SDS-NZ first decreased and then increased, which may be attributed to competitive sorption and compression of the electronic layer. The desorption of Cu(II) on SDS-NZ was favored by the increase in SDS concentration and ionic strength and decrease in solution pH values. The application of SDS-NZ in runoff improved the leaching risk of Cu(II). After several cycles, the ability of reused SDS-NZ to efficiently adsorb most heavy metals was verified with removal rates above 99%.

Experimental investigation on bubble dynamic behaviors in pool boiling of surfactant solutions

In this study, pool boiling experiments on copper surfaces with different roughness levels (Ra = 0.61 μm and Ra = 0.15 μm) using sodium dodecyl sulfate (SDS) solutions at various concentrations (0.1 CMC, 1 CMC, 5 CMC, and 10 CMC) are investigated. Our study focuses on the impact of SDS concentration, wall superheat, surface roughness, and bubble behavior on boiling heat transfer. The results show that an increase in SDS concentration could improve the heat transfer. However, when the SDS concentration reaches 10 CMC, there is a deterioration in heat transfer. Additionally, rough surfaces show better heat transfer performance compared to smooth surfaces. The presence of surfactant not only promotes bubble nucleation but also reduces the bubble departure diameter and inhibits bubble coalescence. Multiple bubbles are formed from the same nucleation site in surfactant solutions with high concentrations (5 CMC, 10 CMC). Various bubble dynamic parameters, including instantaneous size, departure diameter, growth time, waiting time, and departure frequency are obtained and compared with existing empirical correlations in the literature. It is found that the bubble growth in both deionized water (DI water) and surfactant solutions is mainly influenced by the near-wall thermal conditions, aligning with the thermal diffusion mechanism. In addition, the bubble departure diameters in both DI water and surfactant solutions gradually increase with increasing Jakob number (Ja). The growth time and waiting time in the surfactant solution both decrease with increasing Ja number, leading to a significant rise in the departure frequency. In contrast, the bubble growth time in DI water increased and the waiting time decreased with increasing Ja number, resulting in a relatively stable departure frequency. A new empirical formula is proposed for fDd0.5 based on the surface tension coefficient, surface roughness, and Ja number, which demonstrates good rationality.

Wettability and evaporation of sodium dodecyl sulfate aqueous droplets on microhole-patterned polydimethylsiloxane surfaces under a direct current electric field

Wettability and evaporation of sodium dodecyl sulfate (SDS) aqueous droplets on microhole-patterned polydimethylsiloxane (PDMS) surfaces under a direct current electric field were experimentally studied. When a direct current electric field was present, the contact angle hysteresis for SDS aqueous droplets decreased with increasing applied voltage and solid fraction had an obvious influence on contact angle hysteresis. For electrowetting of SDS aqueous droplets on microhole-patterned PDMS surfaces, both actuation voltage and saturation voltage decreased with increasing SDS concentration (below ∼4.10 mM) and increasing solid fraction. For SDS aqueous droplets evaporating on these microhole-patterned PDMS surfaces with the application of a direct current electric field, the duration of constant contact radius stage was found to become shorter with increasing solid fraction, which can be attributed to the weaker adhesion between the droplet and the surface with a larger solid fraction. SDS concentration and applied voltage were also found to have an obvious influence on the evaporation characteristics.

Effect of film properties on droplet impact on suspended films

Understanding the dynamics and underlying mechanisms of droplet impact on suspended films is crucial for controlling droplet motion. In this study, we conducted experiments to investigate droplet impact on suspended films and examined the typical phenomena and corresponding Weber number domains. We explored the effects of changing sodium dodecyl sulfate (SDS) concentration and glycerol content on the surface tension and dynamic viscosity of the films. Additionally, we elucidated the characteristics of film deformation and droplet trajectory. An energy analysis was performed, considering the droplet kinetic energy (Ek0), surface energy increment of the film (ΔEfs), and viscous dissipation (Evis). The results demonstrate that as the SDS concentration increases, the upper critical Weber number (Wecru) between bouncing and passing decreases, while the lower critical Weber number (Wecrl) between coalescence and bouncing first decreases and then increases. For droplet bouncing, increasing the SDS concentration makes the films more susceptible to deformation, whereas increasing the glycerol content enhances film rigidity. Moreover, increasing the SDS concentration and glycerol content leads to higher energy losses, resulting in a reduction in the maximum bouncing height (hbdmax). Regarding droplet passing, the passing velocity (Vpd) increases with increasing SDS concentration. For films without SDS, Vpd increases with increasing glycerol content, while for films with SDS, Vpd decreases. The different impact modes are categorized based on the dimensionless energy parameter E* = Ek0/(ΔEfs + Evis). We have successfully predicted the critical height thresholds (Hd0crl and Hd0cru) and established a relationship of We* = f (Re*, Bo*) that aligns well with experimental results.

Effects of Sodium Dodecyl Sulfate on the Enzyme Catalysis and Conformation of a Recombinant γ-Glutamyltranspeptidase from Bacillus licheniformis.

The study of interactions between proteins and surfactants is of relevance in a diverse range of applications including food, enzymatic detergent formulation, and drug delivery. In spite of sodium dodecyl sulfate(SDS)-induced unfolding has been studied in detail at the protein level, deciphering the conformation-activity relationship of a recombinant γ-glutamyltranspeptidase (BlrGGT) from Bacillus licheniformis remains important to understand how the transpeptidase activity is related to its conformation. In this study, we examined the enzyme catalysis and conformational transition of BlrGGT in the presence of SDS. Enzymatic assays showed that the transpeptidase activity of BlrGGT was greatly affected by SDS in a concentration-dependent manner with approximately 90% inactivation at 6mM. Native polyacrylamide gel electrophoresis of SDS-treated samples clearly revealed that the heterodimeric enzyme was apparently dissociated into two different subunits at concentrations above 2mM. The study of enzyme kinetics showed that SDS can act as a mixed-type inhibitor to reduce the catalytic efficiency of BlrGGT. Moreover, the t1/2 value of the enzyme at 55°C was greatly reduced from 495.1min to 7.4min in the presence of 1mM SDS. The I3/I1 ratio ofpyreneexcimerfluorescence emission changed around 3.7mMSDSin the absence ofBlrGGT and the inflection point of enzyme samples was reduced to less than 2.7mM. The Far-UV CD spectrum of the native enzyme had two negative peaks at 208 and 222nm, respectively; however, both negative peaks increased in magnitude with increasing SDS concentration and reached maximal values at above 4.0mM. Theintrinsic fluorescence spectraof tryptophan further demonstrated that the SDS-induced enzyme conformational transition occurred at approximately 5.1mM. Tween 20 significantly suppressed the interaction of BlrGGT with SDS by forming mixed micelles at a molar ratio of 1.0. Taken together, this study definitely promotes our better understanding of the relationship between the conformation and catalysis of BlrGGT.

Refinement of nanoporous copper by dealloying the Al-Cu alloy in NaOH solution containing sodium dodecyl sulfate.

This work reports the refinement of nanoporous copper (NPC) ligaments by introducing the sodium dodecyl sulfate (SDS) surfactant in the dealloying process. The Al80Cu20 (at%) alloy precursor is chemically dealloyed in a mixed solution of NaOH and SDS surfactant, producing NPC with a hierarchical microstructure. Micron-scaled skeletons that build up higher level networks consist of geometrically similar nano-scaled bi-continuous ligament-pore networks at the lower level. It has been found that the size of the ligaments in the lower level networks reduces from ∼32 nm to ∼24 nm with increasing SDS concentration to 1 mM. Further increasing the SDS concentration to 5 mM only leads to a slight ligament size decrease to ∼21 nm. Remarkably, nano-sized cones are formed on the lower level network surface in the dealloying solution containing 1 mM SDS, and the cone number greatly rises when the SDS concentration increases to 5 mM. The surface diffusivity of Cu adatoms is evaluated based on the experimental data, and the refinement of the ligament as well as the formation of cones are associated with the decreased surface diffusivity and the retarded Cu adatom motions with the addition of SDS. Quantum chemical calculations and molecular dynamics simulations are performed to model the adsorption behavior of SDS. It has been found that the SDS-substrate interaction increases with the number of SDS molecules before SDS reaches saturation.

Thixotropy and slip of kaolinite hybrid suspensions in the presence of surfactants

In this paper, the behavior of Kaolinite suspensions is explored in the presence of two ionic surfactants, namely, cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The steady-shear behavior of these suspensions is explored above and below the critical micelle concentration. The yield stress was found to increase monotonically with CTAB concentration, which can be explained by improved network strength. On the other hand, the yield stress was initially decreased with an increase in SDS concentration up to 10 mM with subsequent relatively small increase at higher concentrations. Both kaolinite and kaolinite-CTAB systems were found to exhibit thixotropic and anti-thixotropic behavior at short and long timescales, respectively.

Experimental investigation of hydrate formation kinetics and microscopic properties by a synthesized ternary gas mixture with combination additives

Given the recycling, environmental friendliness and other advantages, hydrate-based gas separation (HBGS) technology has recently gained considerable attention. This work examined synthesized ternary gas mixture (CH4/CO2/N2) hydrate formation kinetics with both cyclopentane (CP) and sodium dodecyl sulfate (SDS) as additives under 7.0 MPa at different temperatures (275.1, 280.1, 295.1 and 290.1 K). Two volume ratios of CP and SDS aqueous solution were used. Hydrate samples were analyzed by powder X-ray diffraction (PXRD), Raman spectroscopy, and cryo-scanning electron microscopy (Cryo-SEM) to reveal the microscopic influence mechanism of additives on hydrates. It was found that the use of mixed additives clearly promotes the hydrate formation kinetics, while enhancing gas separation under some special conditions. Ternary mixed gas with CP and SDS can form a hydrate, in which structure I and II coexisted. CO2 molecules can be encaged in both small and large cages in hydrate. However, CH4 molecules occupied only the small cage of structure I hydrate except with 0.01% SDS with volume ratio of CP and solution at 0.308 and 0.03% SDS with the volume ratio of CP and solution at 0.154. The increasing SDS concentration can smoothen the hydrate crystal surface, thereby inducing more complete crystallization.

A novel strain of Stenotrophomonas acidaminiphila produces thermostable alkaline peptidase on agro-industrial wastes: process optimization, kinetic modeling and scale-up.

Bacterial alkaline peptidases, especially from Bacillus species, occupy the frontline in global enzyme market, albeit with poor production economics. Here, we report the deployment of response surface methodology approximations to optimize fermentation parameters for enhanced yield of alkaline peptidase by the non-Bacillus bacterium; Stenotrophomonas acidaminiphila. Shake flask production under optimized conditions was scaled up in a 5-L bench-scale bioreactor. Logistic and modified Gompertz models revealed significant fits for biomass formation, total protein, and substrate consumption models. Maximum specific growth rate (µmax = 0.362h-1) of the bacterium in the optimized medium did not differ significantly from those in Luria-Bertani and trypticase soy broths. The aqueous two-phase system-purified 45.7kDa alkaline protease retained 83% activity which improved with increasing sodium dodecyl sulfate concentration thus highlighting potential laundry application. Maximum enzyme activity occurred at 75ºC and pH 10.5 but was inhibited by 5mM phenyl-methyl-sulfonyl fluoride suggesting a serine-protease nature.

Suppressed XIAP and cIAP expressions in human brain cancer stem cells using BV6- and GDC0152-encapsulated nanoparticles

BackgroundSmac mimetics functioned against inhibitors of apoptosis proteins (IAP) often fail to achieve sufficient ability in glioblastoma multiforme (GBM) treatment due to the obstruction of the blood-brain barrier (BBB). MethodsBV6- and GDC0152-encapsulated solid lipid nanoparticles (SLNs) with surface transferrin (Tf) and folic acid (FA) (BV6-GDC0152-Tf-FA-SLNs) were developed to downregulate IAP in U87MG cells and human brain cancer stem cells (HBCSCs) for GBM treatment. Significant findingsAn increase in stearic acid (SA) level enlarged SLNs with improved entrapment of BV6 and GDC0152. 1H NMR study revealed hydrogen bonding between SA and the two IAP antagonists, supporting controlled release of BV6 and GDC0152 from SLNs. Increasing sodium dodecyl sulfate concentration reduced the size of SLNs, and raised the particle stability. Conjugated Tf and FA on SLNs favored permeating the BBB as corroborated from decreased transendothelial electrical resistance, and raised BBB permeability of propidium iodide, BV6 and GDC0152. The ability of BV6-GDC0152-Tf-FA-SLNs to target IAP in U87MG cells and HBCSCs was validated from the downregulated XIAP and cIAP-1 expressions and upregulated caspase-3 expression in immunofluorescence staining, flow cytometry and western blot analysis. Hence, Tf- and FA-grafted SLNs can be an effective colloidal delivery system to deliver BV6 and GDC0152 across the BBB, facilitate IAP targeting, and enhanced drug bioavailability of the two Smac mimetics in GBM cells for potential clinical trials.

EFFECTS OF SYNTHESIS CONDITIONS ON STRUCTURE OF TIN NANORODS PREPARED BY SURFACTANT-ASSISTED CHEMICAL REDUCTION METHOD

Metallic nanorods/nanowires have recently become the focus of intensive research due to their unique properties and have been used to fabricate electronic, energy devices and sensors in nanoscale. In this study, tin nanorods were synthesized through a surfactant assisted chemical reduction method in aqueous solutions at low temperature (~ 0 oC). Sodium dodecyl sulfate (SDS) and sodium borohydride (NaBH4) were used as the surfactant and reductant, respectively. Parameters such as pH, surfactant concentration, and temperature were studied to control the diameter and length of the nanorods formed. The structure, composition and surface morphology of the obtained products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the morphology as well as the aspect ratio of tin nanorods could be effectively controlled by adjusting the parameters of the synthesis process. It was found that tin nanoparticles were formed at 30 oC while nanorods appeared at lower temperatures (0, 5 oC). A low SDS concentration of 4 mM helped to form Sn nanoparticles but higher SDS concentrations of 8, 12 mM facilitated the growth of nanorods. The increase of SDS concentration reduced the length of nanorods. pH values less than 4.5 were found to be favorable to the formation of nanorods.

Reversible assembly of silica nanoparticles at water-hydrocarbon interfaces controlled by SDS surfactant.

Achieving reversible and tunable assembly of silica nanoparticles at liquid-liquid interfaces is vital for a wide range of scientific and technological applications including sustainable subsurface energy applications, catalysis, drug delivery and material synthesis. In this study, we report the mechanisms controlling the assembly of silica nanoparticles (dia. 50 nm and 100 nm) at water-heptane and water-toluene interfaces using sodium dodecyl sulfate (SDS) surfactant with concentrations ranging from 0.001-0.1 wt% using operando ultrasmall/small-angle X-ray scattering, cryogenic scanning electron microscopy imaging and classical molecular dynamics simulations. The results show that the assembly of silica nanoparticles at water-hydrocarbon interfaces can be tuned by controlling the concentrations of SDS. Silica nanoparticles are found to: (a) dominate the interfaces in the absence of interfacial SDS molecules, (b) coexist with SDS at the interfaces at low surfactant concentration of 0.001 wt% and (c) migrate toward the aqueous phase at a high SDS concentration of 0.1 wt%. Energetic analyses suggest that the van der Waals and electrostatic interactions between silica nanoparticles and SDS surfactants increase with SDS concentration. However, the favorable van der Waals and electrostatic interactions between the silica nanoparticles and toluene or heptane decrease with increasing SDS concentration. As a result, the silica nanoparticles migrate away from the water-hydrocarbon interface and towards bulk water at higher SDS concentrations. These calibrated investigations reveal the mechanistic basis for tuning silica nanoparticle assembly at complex interfaces.

The effect of prolonged exposure on sodium dodecyl sulfate penetration into human skin

The purpose of this study was to examine the effect of prolonged surfactant exposure on mechanisms of anionic surfactant penetration into human skin. A radiolabeled probe (14-carbon sodium dodecyl sulfate (14C-SDS)) was used to trace the penetration of a model anionic surfactant, sodium dodecyl sulfate (SDS), into excised human skin and into an inert membrane composite in vitro. SDS dose varied from 0.03 to 15 mg/cm2, mimicking the exposure of a rinse-off cleanser on skin. Two surfactant exposure lengths were tested, 2 min and 5 h. SDS penetration into excised human skin was constant from 50 to 600 mM for skin samples exposed to SDS for 2 min. For skin samples exposed to SDS for 5 h, SDS penetration into skin increased log-linearly with increasing SDS concentration. SDS penetration into the inert membrane composite was constant from 50 to 600 mM SDS regardless of length of surfactant exposure. Penetration of the radiolabeled probe into skin and into the inert membrane correlated well with the monomeric concentration of the radiolabeled probe in the applied surfactant solution. These results support that monomer concentration is the driving force for initial SDS penetration into upper layers of the stratum corneum over a wide range of concentrations. With prolonged exposure, SDS penetrates the skin in a dose-dependent manner due to surfactant-induced damage to the skin.

New Insights into the Kinetics and Morphology of CO2 Hydrate Formation in the Presence of Sodium Dodecyl Sulfate

This work reports an experimental investigation on the morphology and kinetics of CO2 hydrate formation in the presence of sodium dodecyl sulfate (SDS). The experiments were conducted at 277.15 K and 3.5 MPa, and the quantity of SDS varies from 0 to 3000 ppm. The “wall climbing” phenomenon of CO2 hydrate formation in the presence of SDS was observed, and the growth of CO2 hydrate above the gas–liquid interface was found to become stronger as the SDS concentration was increased from 300 to 3000 ppm. This indicates that the promoting effect of SDS on CO2 hydrate formation was enhanced with the increase of SDS concentration. The largest gas consumption for CO2 hydrate formation in SDS solutions was obtained at 1500 ppm of SDS among the four SDS concentrations tested in this work, which increased by 85% compared to that obtained in pure water under the same temperature and pressure conditions. When CO2 hydrate formation was conducted for a considerably long period, two rapid jumps in the gas consumption could be observed as the SDS concentration increased above 300 ppm, and the plateau between the two jumps was shortened with the increase of SDS concentration. As a result, a high efficiency for CO2 hydrate formation was obtained at 1500 and 3000 ppm of SDS. This will provide an implication to the improvement of the hydrate-based CO2 capture technology in the future.

Tuning of micelle adsorption on nanoparticles by combination of surfactants

The interaction of anionic silica nanoparticles with nonionic decaethylene glycol mono-dodecyl ether (C12E10) and ionic surfactants [both anionic sodium dodecyl sulfate (SDS) and cationic dodecyl trimethyl ammonium bromide (DTAB)] has been studied by small-angle neutron scattering and dynamic light scattering. The nonionic and cationic surfactant micelles are adsorbed on nanoparticles, whereas no adsorption of SDS surfactant micelles on nanoparticles is observed. The adsorption of C12E10 micelles provides additional steric stability to nanoparticles. However, the adsorption of cationic micelles leads to micelles-mediated fractal aggregation of nanoparticles. In the case of SDS surfactant, nanoparticles and micelles coexist in the solution. Furthermore, the adsorption behavior of surfactant micelles on nanoparticles has been tuned using a combination of nonionic and ionic surfactants. The combination of nonionic C12E10 with anionic SDS makes surfactant micelles to desorb from nanoparticles, whereas the combination of nonionic C12E10 with cationic DTAB leads to fractal aggregation of nanoparticles. The systematic transitions of micelle adsorption to desorption on nanoparticles with a C12E10–SDS mixed surfactant system and the aggregation of nanoparticles in a C12E10–DTAB mixed surfactant system as a function of ionic surfactant (SDS or DTAB) concentration have been examined. The micelles desorption from nanoparticles follows an exponential decay behavior with an increase in SDS concentration in C12E10–SDS, whereas the aggregate size shows an exponential growth with DTAB in C12E10–DTAB. The electrostatic interactions between nanoparticles and surfactant micelles are found to be dominating for tuning these transitions.

The degradation of xanthan gum in ionic and non-ionic denaturants studied by rheology and molecular dynamics simulation

The use of xanthan gum (XG) as a thickener increases solution viscosity, and therefore, the cost of subsequent processes such as fluid transportation and purification. Herein, we investigate the degradation of XG by urea, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). The results showed that CTAB degraded the XG more than SDS or urea. Interestingly, the degree of CTAB-induced degradation varied with the concentration regime. Thus, increasing CTAB concentration from 0.01 to 0.1 M decreased the complex viscosity (|η*|), whereas from 0.2 to 0.5 M the |η*| increased. For XG/SDS, the |η*| was unchanged with increasing SDS concentration from 0.01 to 0.1 M, whereas it decreased from 0.2 to 0.5 M. For XG/urea, the |η*| was stable in all concentrations. At the atomic-scale, computer simulations revealed that the degrading effect of CTAB was due to preferential interaction with the XG sidechain. These findings can enhance industrial applications of XG.

Influence of particle size on the thermoresponsive and rheological properties of aqueous poly(N-isopropylacrylamide) colloidal suspensions

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) particles of different sizes are synthesized by varying the concentration of sodium dodecyl sulphate (SDS) in a one-pot method. The sizes, size polydispersities and the thermoresponsivity of the PNIPAM particles are characterized by using dynamic light scattering and scanning electron microscopy. It is observed that the sizes of these particles decrease with increase in SDS concentration. Swelling ratios of PNIPAM particles measured from the thermoresponsive curves are observed to increase with decrease in particle size. This observation is understood by minimizing the Helmholtz free energy of the system with respect to the swelling ratio of the particles. Finally, the dynamics of these particles in jammed aqueous suspensions are investigated by performing rheological measurements.

Effect of additives on the growth of HKUST-1 crystals synthesized by microfluidic chips with concentration gradient.

Metal-organic frameworks (MOFs) have attracted considerable attention as novel nanoporous materials that combine the properties of organic and inorganic porous materials. HKUST-1 is one of the most well-developed and representative MOFs with wide applications in gas storage and separation, adsorption, and capture. In this study, we used microfluidics, an advanced technique of manipulation of small fluid volumes in microscale or even nanoscale channels, to investigate the effect of sodium dodecyl sulfate (SDS) on the growth of HKUST-1 crystals. We directly observed the morphological evolution of HKUST-1 crystals through droplet arrays with the SDS concentration gradient. The morphology of HKUST-1 evolved from cubic to cuboctahedron and finally to octahedron with increasing SDS concentration. The study results demonstrated the important role played by anions in solution in the structural regulation of HKUST-1.