Diffusion Exchange Processes Research Articles

Energetically preferred Li+ ion jump processes in crystalline solids: Site-specific hopping in β-Li3VF6 as revealed by high-resolution 6Li 2D EXSY NMR

The visualization of atomic or ionic jump processes on the Ångström length scale is important to identify the preferred diffusion pathways in solid electrolytes for energy storage devices. Two-dimensional high-resolution 6Li nuclear magnetic resonance (NMR) spectroscopy is highly suited to yield unprecedented site-specific insights into local Li+ exchange processes within a single measurement. Here, the beta-modification of Li3VF6 is used as a model system for such an investigation as it provides a range of important Li+ geometric environments in one and the same crystal structure useful to elucidate qualitatively a ranking of energetic preferences of the Li+ exchange processes. In Li3VF6 the Li+ ions are subject to diffusive exchange processes among five crystallographically and magnetically inequivalent Li sites: LiFn (n = 6, 4). By using a sample with a natural concentration of the 6Li isotope, we suppressed unwanted spin-diffusion processes and visualized the various exchange processes on the ms time scale. We were able to verify the following ranking experimentally: Li+ ion jumps between face-shared polyhedra are preferred, followed by Li+ exchange between edge-shared configurations for which interstitial sites are needed to jump from site to site. Surprisingly, Li+ exchange between corner-shared polyhedra and Li+ hopping involving almost isolated LiF4 polyhedra do contribute to overall Li+ self-diffusion as well. In this sense, the current study experimentally verifies current predictions by theory but also extends our understanding of ion dynamics between corner-shared Li-bearing polyhedra.

Dilational rheological properties of 2, 5-dialkyl benzene sulfonates at air-water and decane-water interfaces

The dilational properties of two anionic surfactants 5–6–4 and 5–6-t4 (2, 5-dialkyl benzene sulfonates) at the air-water and decane-water interfaces were investigated using the drop shape analysis method. The effects of aging time, oscillating frequency, bulk concentration, and surface/interfacial pressure on the dilational elasticity and dilational viscosity were explored. The results show that the slow process and diffusion exchange process control the nature of surface/interfacial films at low and high concentrations, respectively. At low concentrations, the strong interaction between the branched long alkyl chains dominates at the surface. At high concentrations, the surface elasticity of 5–6–4 is higher because of the slower diffusion-exchange process. The insertion of oil molecules disrupts the interactions between branched long alkyl chains and simultaneously enhances the diffusion-exchange process, resulting in lower maximum interfacial dilational elasticity and viscosity for both 5–6–4 and 5–6-t4 molecules. The rigid isobutyl group endows the 5–6-t4 molecule with higher dilational elasticity and viscosity at the interface.

Effect of electrolyte on the surface dilational rheological properties of branched cationic surfactant

The studies of surface dilational rheology are important to detent the nature of adsorption film and the properties of foam. In this paper, the adsorption and dilational rheological properties of branched cationic surfactant hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride (C16G(EO)3PC) at the air-water interface in the absence and presence of electrolyte (NaCl) were investigated by drop shape analysis. The results show that the surface adsorption layer of C16G(EO)3PC behaves elastic in nature with high value up to 90 mN/m, which indicates that the slow relaxation process plays a main role because of the re-arrangement of long branched alkyl chain. The addition of NaCl will enhance diffusion-exchange process and accelerate the formation of film and decreases dilational elasticity obviously. At low NaCl concentration, the in-film slow relaxation process dominates the nature of film, dilational viscosity decreases with an increase of oscillating frequency. By adding more NaCl, diffusion-exchange process plays the crucial role and dilational viscosity increase as a function of frequency. Moreover, viscosity at high NaCl concentration shows larger value under higher oscillating frequency, indicating the contributions of fast diffusion-exchange process. The elastic adsorption film becomes to be viscoelastic by adding electrolyte.

Interfacial interactions between oleic acid and betaine molecules at decane-water interface: A study of dilational rheology

The interfacial interactions between organic acid and betaine molecules play an important role in reducing interfacial tension (IFT). To deeply detect the arrangements of organic acid and betaine molecules at the interface, the dilational rheological properties of mixed adsorption films formed by oleic acid and octadecyl carboxyl betaine (18PC) or octadecyl sulfobetaine (18PS) were investigated using drop shape analysis method at the decane-water interface. The influences of aging time, oscillation frequency and surfactants concentration were detected. The experimental results show that the properties of 18PC and 18PS adsorption film are controlled by both the fast diffusion-exchange process between the bulk and the interface and the slow re-arrangement process in the interface. 18PC film is tighter than that of 18PS because the size of carboxyl is small than sulfonyl. Oleic acid and betaine surfactants can form mixed adsorption films with less strength caused by the rapid transfer of oleic acid between the bulk and the interface, but more elastic due to the enhancement of the intermolecular interaction. In this case, the oleic acid molecules are easier to insert into the spaces between 18PS molecules on the interface, which results in a more tight mixed film than oleic acid/18PC film.

Studies on interfacial interactions between petroleum sulfonate and sulfobetaine molecules by rheological measurements

The dilational rheological properties of aqueous solutions of anionic surfactant petroleum sulfonate (KPS), zwitterionic surfactant alkyl sulfobetaine (ASB) and their mixtures have been investigated at the kerosene-water interface by the oscillating drop method. The influences of time, dilational frequency, bulk concentration and interfacial pressure on the dilational properties have been expounded. The experimental results show that the nature of film containing anionic surfactant KPS molecules is determined by the diffusion-exchange process between the bulk and the interface. On the other hand, the in-film process, such as the orientation change of hydrophilic groups, controls the properties of adsorption layers formed by betaine ASB molecules. The dilational rheological behaviors of KPS-ASB mixtures are close to those of ASB. In addition, the complex system gets the largest dilational modulus at higher bulk concentration, due to a synergistic effect between KPS and ASB caused by electrostatic attraction. The mixed adsorption of KPS and ASB may lead to more compact films and result in higher interfacial dilational modulus at optimum ratio of adsorbed KPS to ASB molecules. The mixed adsorption of KPS and ASB molecules may lead to more compact film and result in larger interfacial dilational elasticity at higher concentration.

Effect of branched chain and polyoxyethylene group on surface dilational rheology of cationic surfactants

The measurements of dynamic surface tensions and surface dilational rheological properties were carried out for four cationic surfactants aqueous solutions, hexadecanol glycidyl ether ammonium chloride (C16PC), guerbet alcohol hexadecyl glycidyl ether ammonium chloride (C16GPC), hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride(C16(EO)3PC) and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether ammonium chloride (C16G(EO)3PC), using the oscillating bubble method. The influences of surface ageing time, surface pressure, dilational frequency and bulk concentration on surface rheological properties have been expounded. It is found that diffusion-exchange process plays the crucial role for C16PC film at all experimental concentrations. On the other hand, the relaxation process in-surface dominates the properties of film at low and high bulk concentration for branched cationic surfactants and C16(EO)3PC respectively. The branched hydrophobic chain will enhanced the molecular interactions at the surface and improve the value of modulus maximum. The introducing of EO group will produce new relaxation process, such as the variation of orientation of EO group at the surface, which enhances the contributions of viscous nature of film. Moreover, the coexistence of branched chain and EO group will produce oriented variations of film structure and result in the maximum modulus at dynamic curve.

Dilational rheological properites of oxyethylated fatty acid methyl esters at kerosene-water interface

Dilational rheological properties of oxyethylated fatty acid methyl esters (FMEEs) with different structure (C12E5、C14E5、C16E5 and C18=E5) at kerosene-water interface have been investigated as a function of time, frequency and bulk concentration by the oscillating drop method. The experimental results show that the dilational modulus increases with an increase in the alkyl chain length for FMEEs with saturated alkyl chains (C12E5、C14E5 and C16E5) due to the enhanced hydrophobic interaction among the molecules at interface and the slowed diffusion-exchange process. At the same time, the phase angles are relative low, which embodies characteristics of nonionic surfactants containing EO chain. As for C18=E5, the introduction of a double bone causes a decrease in the dilational modulus and a slight increase in the phase angle, as evidenced by an increase in the value of the slope of curve, because the flexible unsaturated alkyl chain enhances the diffusion-exchange process. Moreover, the modulus vs interfacial pressure curve passes through a maximum during higher interfacial pressure range for C18=E5, which indicates that the interfacial rearrangement process affects the nature of adsorption layer.

Interfacial dilational rheology of fatty acid methyl ester and alkyl benzene sulfonate mixed solutions

The dilational rheological properties of aqueous solutions of anionic surfactant sodium 3,4-diheptylbenzene sulfonate (C7C7phS), nonionic surfactant oxyethylated fatty acid methyl esters (C18=E10) and their mixtures have been investigated at the kerosene-water interface by the oscillating drop method. The influences of time, dilational frequency, bulk concentration and interfacial pressure on the dilational properties have been expounded. The experimental results show that the in-film process, such as the orientation change of EO chain, controls the properties of adsorption layers formed by nonionic surfactant C18=E10 molecules. On the other hand, the diffusion-exchange process plays the crucial roles in determining the nature of film containing anionic surfactant C7C7phS molecules. The dilational rheological behaviors of C18=E10/C7C7phS mixtures in the presence of 1 × 10−5 mol·L−1 C7C7phS are close to those of C18=E10. At the same time, mixtures at mole ratio 1:1 show similar behaviors with C7C7phS. The mixed adsorption of C18=E10 and C7C7phS may lead to more compact films and result in higher interfacial elasticity.

Effect of protein molecules and MgCl2 in the water phase on the dilational rheology of polyglycerol polyricinoleate molecules adsorbed at the soy oil-water interface

The objective of this study was to investigate the effect of inorganic salt and protein in the aqueous phase on the dilational rheology properties of interfacial film stabilized by the hydrophobic emulsifier polyglycerol polyricinoleate (PGPR). The interfacial behavior was investigated using the oscillating drop method. With increased PGPR concentration, the interfacial tension tended to decrease and reached an equilibrium value of 3.3 mN m−1, at 1.0% (w/w) PGPR. With 0.01% (w/w) PGPR in the oil phase, the presence of whey protein isolate (WPI) increased the dilational elasticity modulus of PGPR, but the addition of bovine serum albumin (BSA) decreased the elasticity modulus. This was likely due to competitive adsorption of BSA and PGPR at the soy oil/water interface, resulting in the desorption of BSA from the interface. At 1.0% (w/w) PGPR, both WPI and BSA increased the interfacial dilational elastic modulus and the reason might be that the presence of protein could suppress the diffusion-exchange process of PGPR between bulk phase and interface. The addition of MgCl2 may enhance the adsorption of PGPR molecules at the interface and therefore increased the dilational modulus.

Effect of Alkyl Chain Length on the Interfacial Dilational Properties of Hydroxy-Substituted Alkyl Benzenesulfonates

Dilational rheological behaviors of adsorption layers of three surfactants, sodium 2-hydroxy-3,5-dioctyl benzene sulfonate (C8C8), sodium 2-hydroxy-3-octyl-5-decyl benzene sulfonate (C8C10), and sodium 2-hydroxy-3-octyl-5-dodecylbenzenesulfonate (C8C12) formed at air–water and decane–water interfaces, have been investigated as a function of concentration and frequency (0.002–0.1 Hz) by the oscillating bubble/drop method. The experimental results show that the dilational moduli of hydroxy-substituted alkyl benzenesulfonates are obviously higher than those of the common surfactants, because the interfacial interactions between alkyl chains are improved drastically by the unique arrangement of C8C8 molecules at the interface. However, the moduli at the decane–water interface are much lower than those at the surfaces because decane molecules will insert into the surfactant molecules adsorbed at the interface and destroy the interactions between alkyl chains. With an increase in the number of carbon atom of 5-alkyl, the surface dilational modulus decreases because the orientation of the surfactant molecules at the surface varies from parallel to tilt. On the other hand, the diffusion-exchange process dominates the interfacial behavior and the interfacial modulus improves with the increase in the length of the alkyl chain.

Cultural and demic diffusion of first farmers, herders,and their innovations across Eurasia

Was the spread of agro-pastoralism from the Eurasian founder regions dominated by demic or by cultural diffusion? This study employs simulations that unfold a complex inter-regional and time varying pattern of demic and diffusive exchange processes during the Neolithisation, and thus supports from a modelling perspective the hypothesis that there is no simple or exclusive demic or cultural diffusion, but that in most regions of Eurasia a combination of demic and cultural processes were important.

Dynamic surface dilational properties of anionic Gemini surfactants with polyoxyethylene spacers

Abstract The dynamic interfacial dilational properties of anionic Gemini surfactants (oligooxa)-α,ω-bis( m -octylbenzene sulfonate) (C 8 E 4 C 8 and C 8 E 8 C 8 ) with polyoxyethylene spacers at the water–air interface were investigated by means of oscillating the drop profile method. The influences of temperature and salt on dilational properties were explored. The experimental results show that the special structure of surfactant C 8 E 8 C 8 is a principal factor to control the nature of interfacial adsorption film. The distinct two peak values appear in dilational modulus vs. time curves for surfactant C 8 E 8 C 8 , which is different from that of traditional surfactants with low molecular weight. The first peak is believed to be related to the molecular diffusion-exchange process between the bulk and interface, and the second peak may be due to the formation and collapse of interfacial sublayer by ethylene oxide groups. In addition, the temperature has obviously effect on the second peak value of dilatioanl modulus. However, there is nearly no effect on the value of the second peak by addition of NaCl. The mechanisms responsible for unique interfacial behaviors mentioned above have been provided schematically.

Effect of Glyphosate Isopropylamine on the Surface Tension and Surface Dilational Rheology Properties of Polyoxyethylene Tallow Amine Surfactant

In order to develop the substitutes for polyoxyethylene tallow amine (POEA), the understanding the interaction of glyphosate isopropylamine and POEA is essential. The surface behaviors of POEA and POEA in the presence of 1 wt% glyphosate isopropylamine have been investigated at the air-water interface by the drop shape analysis method. The influences of surface tension, dilational frequency, and bulk concentration on the surface properties were expounded. The experiment results show that the adsorption films of POEA behave elastic in nature at low bulk concentration. With increasing in bulk concentration, the dilational modulus, dilational elasticity, and dilational viscosity pass through a maximum value, the phase angle increase monotonically. These phenomena can be attributed to the diffusion-exchange process between the bulk and the interface. The addition of 1 wt% glyphosate isopropylamine significantly influences on the POEA surface tension and dilational properties. The dilational modulus, dilational elasticity, and dilational viscosity obvious decrease in general, and the values of phase angle significant change after the addition of 1 wt% glyphosate isopropylamine. Glyphosate isopropylamine and POEA form a new complex in the solution and the surface activity and surface dilational properties of complex is different from POEA.

Dilational Rheological Properties of P-(n-alkyl)-benzyl Polyoxyethylene Ether Carboxybetaine at Water–Decane Interface

The dilational rheological behaviors of absorbed films of p-(n-alkyl)-benzyl polyoxyethylene ether carboxybetaine CxBE2CB (x = 8, 10, 12) at the water–decane interface have been investigated by the drop-shape analysis method. The influences of time, oscillation frequency, and bulk concentration on dilational modulus and phase angle have been expounded. The experimental results show that the phase angle of CxBE2CB (x = 10, 12) decreases with the increase of time, the slope of the log ϵ − log ω curve and phase angle of CxBE2CB (x = 10, 12) decrease in a wide concentration range. These phenomena become more and more apparent with the increase of hydrocarbon chain length and it cannot be attributed to the diffusion-exchange process between the bulk and the interface. It is reasonable to consider that ethylene oxide groups are flexible and can be compressed and expanded, just like a spring. Therefore, the compression and expansion of the ethylene oxide groups in the interfacial layer and the exchange between interface and sublayer play a more important role for CxBE2CB (x = 10, 12) adsorption film. The dependence of dilational modulus on interfacial pressure can support our provided mechanism strongly.

Dilational rheological properties of sulphobetaines at the water–decane interface: Effect of hydrophobic group

The interfacial tensions and dilational properties of adsorbed films of two zwitterionic surfactants with different hydrophobic groups, alkyl sulphobetaine (ASB) and benzyl substituted alkyl sulphobetaine (BSB), at the decane–water interface have been investigated by the drop shape analysis method. The influences of dilational frequency and bulk concentration on the interfacial dilational modulus and phase angle were expounded. The effects of electrolyte NaCl on the interfacial tensions and dilational properties have also been researched. The experimental results show that the similar CMC and IFTCMC values for ASB and BSB indicate their similar interfacial activity. The Amin value of BSB is larger than that of ASB, which is due to the steric effect of benzene ring in BSB molecule. The dilational data show that betaines can form compact adsorption films due to their electric neutrality in experimental condition, which results in the higher maximum values of dilational moduli for both BSB and ASB than those of common surfactants. Moreover, the whole hydrophilic part, sulfonic group, hydroxyl and ammonium group, can response to the area variations by change the orientation between parallel to the interface and introduce to the aqueous instead of diffusion-exchange process, which can enhance the elasticity of the film. The electrolyte NaCl has a function of accelerating the diffusion-exchange process of surfactant molecules. As a result, the dynamic interfacial properties such as dilational properties show obvious variations, while the static interfacial property such as interfacial tension has little change after the addition of 1% NaCl.

Dilational rheological properties of novel zwitterionic surfactants containing benzene ring and polyoxyethylene group at water–decane interface

The interfacial dilational rheological behaviors of four zwitterionic surfactants with benzene ring and polyoxyethylene group, p-(n-lauryl)-benzyl polyoxyethylene ether carboxybetaine C12BExCB (x=0, 1, 2, 3), were investigated via the drop shape analysis method. The influences of time, oscillating frequency and bulk concentration on dilational properties were explored. The experimental results show that the number of ethylene oxide groups is one of the principal factors to control the interfacial film. The dilational properties of C12BExCB are quite different from those of common surfactants: the phase angle decreases with aging time, the slope of the logε−logω curve and phase angle of C12BExCB decrease in a wide concentration range, and the dilational modulus of C12BExCB passes through a plateau value with the increasing concentration for surfactant with more ethylene oxide groups. These phenomena become more and more apparent with increasing ethylene oxide groups and it cannot be attributed to the diffusion-exchange process between the bulk and the interface. It is reasonable to consider that ethylene oxide groups are flexible and can be compressed and expanded, just like a spring. The compression and expansion of the ethylene oxide groups in the interfacial layer and the exchange between interface and sub-layer play a crucial role for C12BExCB. Possible schematic diagrams of adsorbed molecules with time and concentration at the water–decane interface are proposed. The results of static modulus measurements and dynamic interfacial viscoelasticity for CyBE2CB (y=8, 10, 12) with different length of hydrophobic chain can support our provided mechanism strongly.

MR myocardial perfusion analysis of first-pass enhancement kinetics with a lagrangian approach

Background Observation of the kinetics of tissue enhancement after the injection of a bolus of tracer has been used for the analysis of perfusion and related variables. In general, a gradient of concentration in the exchanging vascular compartment between the ar terial and venous ends is represented in models via focus on maintaining the detailed balance between the advective and diffusive exchange processes. Conventionally, this is by considering the exchange in an Eulerian framework, based on considering the exchange within each compartment as a separate unit (e.g., tissue homogeneity (TH) model [1]). Herein, we present a Lagrangian approach to the exchange modeling, such that the blood flowing between compartments is considered as the primary unit, and, thereby, allowing for coarser discretization and more efficient calculations (Figure 1a). Methods

Surface Dilational Properties of Sodium 4-(1-methyl)-Alkyl Benzene Sulfonates: Effect of Alkyl Chain Length

AbstractThe dilational properties of absorbed film of three sodium 4-(1-methyl)-alkyl benzene sulfonates at the air-water interface have been investigated by drop shape analysis method. The influences of time, dilational frequency and surfactant bulk concentration on surface dilational modulus and phase angle have been expounded. The nature of interfacial film depends on the molecular structure of surfactants. For 2Φ-14 and 2Φ-16, the diffusion-exchange process controls the dilational properties and the film shows viscoelastic character. As an increase of the hydrophobic chain, the dilational modulus of 2Φ-18 is independent on applied frequency in the studied bulk concentration except for 1 × 105mol/L, which indicates the adsorbed layer behaves nearly purely elastic. Furthermore, the phase angle of 2Φ-14 and 2Φ-16 are remarkably higher than those of 2Φ-18, confirming that the presence of strong interactions between hydrophobic chains of 2Φ-18. Best agreements with the experimental data have been obtained from the curves of dilational modulusvs.surface pressure.

Dilational Properties of Novel Amphiphilic Dendrimers at Water–Air and Water–Heptane Interfaces

In this work, a series of novel amphiphilic dendrimers taking polyamidoamine dendrimer as the core with different hydrophobic tails QPAMC(m) were synthesized and the dilational properties were studied as monolayers by dilational rheological measurements at the water-air and water-n-heptane interfaces to explore the nature of adsorption behaviors. The results showed that the maximum values of the dilational modulus seemed to have no obvious variation in a wide change of hydrophobic chain length at the surface. However, there was considerable variability in the tendency of the influence of bulk concentration on the dilational modulus at the two different interfaces. It was interestingly found that the diffusion-exchange process slowed down with the increase of alkyl chain length leading to more elastic nature of adsorption film, which was contrary to the tendencies of conventional single chain and gemini surfactants. It is reasonable to consider that, in the case of the molecule having short chain length such as QPAMC(8), the alkyl chains are too short to overlap across the headgroup, enable the intermolecular hydrophobic interaction to be predominant with increasing of surface concentration, which enhances the elasticity and shows the slowest diffusion-exchange process. Whereas, when the chain length increases to 12 or 16, the alkyl chains are long enough to act intramolecularly to form intracohesion conformation, which results in enhancing the diffusion-exchange process. In conclusion, the interfacial behaviors are dictated by the size ratio between the tail and headgroup. A reasonable model with respect to the molecular interaction was proposed on the basis of experimental data. The results of interfacial tension relaxation and dynamic light scattering (DLS) experiments, in accord with the proposed mechanism, also present the unusual tendency comparing to the traditional single or gemini surfactants.

Surface dilational rheological and lamella properties of branched alkyl benzene sulfonate solutions

The dilational properties of adsorbed film of three branched-alkyl benzene sulfonates at the air–water interface have been investigated by drop shape analysis method. The influences of time, dilational frequency and bulk concentration on surface dilational elasticity and dilational viscous component were expounded. The experimental results show that the change of surface dilational properties with time is accordant to the variation of surface tension with surface aging. At low concentration, the dilational properties are independent of frequency and the film behaves elastic in nature. As concentration increases, the surface film shows remarkable viscoelasticity, which means the diffusion-exchange process controls the dilational properties. Moreover, the position of the phenyl in the alkyl chains is one of the principal factors to control the nature of interfacial film: as the phenyl is moved from a terminal position to a more central position, the dilational elasticity increases. The surface elasticity was compared with the stability of lamella stability made with these surfactants. The results suggest that surface dilational elasticity is crucial for the ability of a surfactant solution to form a stable lamella.