Solvent Penetration Research Articles

Advances in Diffusivity Measurement of Solvents in Oil Sands

Abstract This work deals with the prediction of mass transfer of solvents in bitumen in the presence and absence of sand through a unified model that uses magnetic resonance response information. Experiments were performed with pairs of solvents and bitumen in the presence of sand and without sand. Low field NMR was used to acquire spectra of the migrating solvent in bitumen or oil sand as a function of time. The experimental results of this work, along with data collected previously on similar systems in the Tomographic Imaging and Porous Media Laboratory, were fit together in a one-dimensional Fickian model. The novelty of the presented approach is not only that the new model matches all the experiments to date, but also that this matching can be done independently and without external input parameters. In previous work, matching could only be achieved if the depth of solvent penetration was provided through external measurements. The present model predicts diffusivities of solvents in bitumen in the presence of sand to be in the same order of magnitude and a bit lower than diffusivities of solvent in bulk bitumen. It is anticipated that this method would be of value when estimates of mass transfer in solvent-based heavy oil processes are attempted in the field. Introduction In solvent-based recovery processes for heavy oil and bitumen, mass transfer phenomena compete with viscous forces, gravity and capillary forces as the predominant means for oil recovery or trapping. In order to understand the relative merit of such forces, one must be able to measure mass transfer at reservoir conditions and potentially verify such measurements in the field. There is considerable literature on the measurement of recovery mechanisms and recovery efficiency through solvent-based processes for heavy oil and bitumen. The bulk of the work presented in the recent literature focuses around the VAPEX (Vapour Extraction) process, but the fundamental work presented can easily apply to any solvent displacement process. If we were to measure mass transfer phenomena in the field, it appears that a possible logging tool with significant potential is magnetic resonance. Thus, the TIPM group has embarked in a project whereby magnetic resonance is used for the determination of bitumen (or heavy oil) solvent interactions. As two miscible fluids are in contact, they will slowly diffuse into each other. This molecular transport of one substance relative to another is known as diffusion. With time, the interface between the fluids will appear as a diffused mixed zone grading from one pure fluid to the other. The mechanism of diffusion happens due to the random motion of molecules(1,2). The diffusion flux between solvent and heavy oil can be defined as the flow due to concentration gradient between solvent and heavy oil. The diffusion phenomena take place when there is no mixing in the system and the only driving force is the concentration gradient, unlike dispersion that is caused due to convective fluid mixing in the porous medium. It was observed that as solvent and heavy oil diffuse into each other, the mobility of hydrogen bearing molecules of both oil and solvent change(3).

FTIR imaging coupled with multivariate analysis for study of initial diffusion of different solvents in cellulose acetate butyrate films

Fourier transform infrared (FTIR) spectroscopic imaging was used to study the initial diffusion of different solvents in cellulose acetate butyrate (CAB) films containing different amounts of acetyl and butyryl substituents. Different solvents and solvent/non-solvent mixtures were also studied. The FTIR imaging system allowed acquisition of sequential images of the CAB films as solvent penetration proceeded without disturbing the system. The interface between the non-swollen polymer and the initial swelling front could be identified using multivariate data analysis tools. For a series of ketone solvents the initial diffusion coefficients and diffusion rates could be quantified and were found to be related to the polar and hydrogen interaction parameters in the Hansen solubility parameters of the solvents. For the solvent/non-solvent system the initial diffusion rate decreased less than linearly with the weight-percent of non-solvent present in the solution, which probably was due to the swelling characteristic of the non-solvent. For a given solvent, increasing the butyryl content of the CAB increased the initial diffusion rate. Increasing the butyryl content from 17 wt.% butyryl to 37 wt.% butyryl produced a considerably larger increase in initial diffusion rate compared to an increase in butyryl content from 37 wt.% to 50 wt.% butyryl.

Solvent Penetration and Sterical Stabilization of Reverse Aggregates based on the DIAMEX Process Extracting Molecules: Consequences for the Third Phase Formation

Studies on third phase formation during the extraction of nitric acid by malonamide extractants in various diluents are investigated. This “third phase transition” is studied from a fundamental point of view, combining vapor pressure osmometry, phase diagram, and scattering studies. The organization of the organic phases of the “malonamides/alkane/water/nitric acid” systems was studied at three “scales”: 1/at a molecular scale by determining the compositions of the extracted complexes; 2/at a macroscopic scale by determining the phase transition boundaries quantified by the limiting organic concentration (LOC) of solutes; and 3/at a supramolecular scale by analyzing the organization of the species in the organic phases (i.e. measuring the critical micellization concentration, the aggregation number, and the interactions between the aggregates). The instability (third phase apparition) has a supramolecular origin: it is a “long range” attraction between polar cores of the reverse micelles formed by the extracting agent. Water and nitric acid extraction are decoupled from these interactions. The alkyl chains of the extractant and the diluent play a symmetrical role in the physical stability of the organic phase: decreasing the diluent chain length or increasing the chain length of the complexing agent both promotes phase stability, i.e. they increase the LOC. We demonstrate here that this effect is the same as the effect observed and known for all other w/o “reverse” micelles: chains protruding from any aggregate stabilize polar solute in oil and shorts oil penetrate and swells the reverse micelles apolar layer.

Surfactant Adsorption onto Cellulose Surfaces

The adsorption of the cationic surfactant, hexadecyl trimethyl ammonium bromide, C16TAB, onto model cellulose surfaces, prepared by Langmuir-Blodgett deposition as thin films, has been investigated by neutron reflectivity. Comparison between the adsorption of C16TAB onto hydrophilic silica, a hydrophobic cellulose surface, and a regenerated (hydrophilic) cellulose surface is made. Adsorption onto the hydrophilic silica and onto the hydrophilic cellulose surfaces is similar, and is in the form of surface aggregates. In contrast, the adsorption onto the hydrophobic cellulose surface is lower and in the form of a monolayer. The impact of the surfactant adsorption and the in situ surface regeneration on the structure of the cellulose thin films and the nature of solvent penetration into the cellulose films are also investigated. For the hydrophobic cellulose surface, intermixing between the cellulose and surfactant occurs, whereas there is little penetration of surfactant into the hydrophilic cellulose surface. Measurements show that solvent exchange between the partially hydrated cellulose film and the solution is slow on the time scale of the measurements.

Monolayer-Protected Metallic Nanoparticles: Limitations of the Concentric Sphere Capacitor Model

Monolayer-protected clusters (MPC) having metallic core diameters of the order of 1 nm behave as multivalent redox molecules with small capacitances CMPC ≈ 1 aF. Theoretical estimations of this capacitance are usually based on the concentric sphere capacitor model. We have analyzed critically the predictions of this model over a broad range of experimental parameters: the metallic core radius r o , the monolayer thickness d, the charge number z of the metallic core, the dielectric constant of the monolayer e r,m , the base electrolyte concentration c s , and the dielectric constant of the solvent e r,s . To this end, we have solved the nonlinear Poisson-Boltzmann equation taking into account ion penetration. It is shown that the concentric sphere capacitance C o gives the correct order of magnitude as well as some qualitative features of the total MPC capacitance C MPC , although significant deviations are obtained for realistic values of the above parameters, especially when ion and solvent penetration are important. The results obtained are compared with recent theoretical and experimental work by Murray et al. (Anal. Chem. 2005, 77, 2662), Girault et al. (J. Phys. Chem. B 2006, 110, 21460), and Quinn et al. (J. Am. Chem. Soc. 2003, 125, 6644) and provide some extensions of these previous studies.

Development of a system for simultaneous dissolution studies and magnetic resonance imaging of water transport in hydrodynamically balanced systems: A technical note

Without disturbing the observed processes, the MRI methods combined with the dissolution studies provide insight into the phenomena occurring when the dosage form comes into contact with aqueous fluids. The MR images allow one to observe the solvent penetration into the hydrophilic matrix and the hydrogel formation. The data obtained in the MRI studies complement information obtained from the dissolution studies. The analysis of MR images may support the explanation of differences in the drug-releasing or floating properties of HBS.

Residue Specific Resolution of Protein Folding Dynamics Using Isotope-Edited Infrared Temperature Jump Spectroscopy

A major difficulty in experimental studies of protein folding is the lack of nonperturbing, residue specific probes of folding. Here, we demonstrate the ability to resolve protein folding dynamics at the level of a single residue using 13C=18O isotope-edited infrared spectroscopy. A single 13C=18O isotopic label was incorporated into the backbone of the 36 residue, three-helix bundle villin headpiece subdomain (HP36). The label was placed in a solvent protected region of the second alpha-helix of the protein. The 13C=18O isotopic label shifted the carbonyl stretching frequency to 1572.1 cm-1 in the folded state, well removed from the 12C=16O band of the unlabeled protein backbone. The unique IR signature of the 13C=18O label was exploited to probe the equilibrium thermal unfolding transition using temperature-dependent FTIR spectroscopy. The folding/unfolding dynamics were monitored using temperature-jump (T-jump) IR spectroscopy. The equilibrium unfolding studies showed conformational changes suggestive of a loss of helical structure in helix 2 prior to the global unfolding of the protein. T-jump relaxation kinetics probing both the labeled site and the 12C=16O band were found to be biphasic with similar relaxation rates. The slow relaxation phase (approximately 2 x 10(5) s-1) corresponds to the global folding transition. The location of the label, a buried position in helix 2, provides an important probe of the origin of the fast relaxation phase (approximately 10(7) s-1). This phase has significant amplitude for the labeled position even though it is well protected from solvent in the folded structure. The fast phase likely represents a rapid pre-equilibrium that involves solvent penetration around the label and possible partial unfolding of helix 2 prior to the global unfolding transition. This work represents the first experimental study of ultrafast folding dynamics with residue specific resolution.

Solvent Effect of the Passivation Layer on Performance of an Organic Thin-Film Transistor

We studied the passivation of pentacene organic thin-film transistors (OTFTs) on plastic using four kinds of organic layers: photopatternable acryl (PA), polyvinylalcohol (PVA)/dichromated polyvinylalcohol (D-PVA), PVA/D-PVA/PA, and parylene-C. The initial mobility of the OTFTs was ∼ 1.0 cm 2 /V s and the on/off current ratio was ∼10 7 . The drop in the on-current and the increase in the off-currents were significant when PA was used as a passivation layer because of the damage to the pentacene active layer by the organic solvent in PA solution. On the other hand, there was little change in the performance of the OTFT when PVA/D-PVA was used as the passivation layers on the pentacene. This was done to reduce the concentration of metal ionic impurity at the interface of the pentacene and PVA. The OTFT with the passivation layers exhibited a field-effect mobility of 0.8 cm 2 /V s and on/off current ratio of 10 7 . This means that the water soluble PVA can minimize the damage to the pentacene and prevent the penetration of the organic solvent in PA solution.

Sustained-release from Layered Matrix System Comprising Chitosan and Xanthan Gum

ABSTRACTSustained-release tablets of propranolol HCl were prepared by direct compression using chitosan and xanthan gum as matrix materials. The effective prolongation of drug release in acidic environment was achieved for matrix containing chitosan together with xanthan gum which prolonged the drug release more extensive than that containing single polymer. Increasing lactose into matrix could adjust the drug release characteristic by enhancing the drug released. Component containing chitosan and xanthan gum at ratio 1:1 and lactose 75% w/w was selected for preparing the layered matrix by tabletting. Increasing the amount of matrix in barrier or in middle layer resulted in prolongation of drug release. From the investigation of drug release from one planar surface, the lag time for drug release through barrier layer was apparently longer as the amount of barrier was enhanced. Least square fitting the experimental dissolution data to the mathematical expressions (power law, first order, Higuchi's and zero order) was performed to study the drug release mechanism. Layering with polymeric matrix could prolong the drug release and could shift the release pattern approach to zero order. The drug release from chitosan-xanthan gum three-layer tablet was pH dependent due to the difference in charge density in different environmental pH. FT-IR and DSC studies exhibited the charge interaction between of NH3+ of chitosan molecule and COO− of acetate or pyruvate groups of xanthan gum molecule. The SEM images revealed the formation of the loose membranous but porous film that was due to the gel layer formed by the polymer relaxation upon absorption of dissolution medium. The decreased rate of polymer dissolution resulting from the decreased rate of solvent penetration was accompanied by a decrease in drug diffusion due to ionic interaction between chitosan and xanthan gum. This was suggested that the utilization of chitosan and xanthan gum could give rise to layered matrix tablet exhibiting sustained drug release.

Water Penetration into Protein Secondary Structure Revealed by Hydrogen−Deuterium Exchange Two-Dimensional Infrared Spectroscopy

Two-dimensional infrared spectroscopy in conjunction with hydrogen-deuterium exchange experiments provides detailed information about solvent penetration into protein structure. Correlating the secondary-structure sensitivity of the amide I vibration and the solvent-exposure sensitivity of amide II provides a direct probe of solvent-inaccessible residues of proteins embedded in the hydrophobic core or those involved in strong hydrogen bonds in secondary structures. Distinct spectral signatures of the cross-peak region arising from the coupling of the amide I and II modes imply a significant degree of structural stability of hydrogen-bonded contacts in alpha-helices and beta-sheets in a series of proteins. Ubiquitin, an alpha/beta-protein, exhibits strong alpha-helical signatures and lacks those of the beta-sheet in the cross-peak region, demonstrating that ubiquitin's beta-sheet exchanges protons with the surrounding solvent and is conformationally unstable.

In‐situ neutron reflectometry probing competitive swelling and de‐swelling of thin polystyrene films

AbstractThe competitive penetration of toluene with respect to oxygen, nitrogen and carbon dioxide into a thin and initially dry film of deuterated polystyrene (dPS) is compared to the reverse process of de‐swelling. In‐situ neutron reflectometry is used to follow the swelling and de‐swelling kinetics, allowing the determination of the total dPS thickness, roughness and solvent penetration. Swelling cannot be described in terms of case II diffusion due to the small film thickness and undersaturation results in a small swelling rate of 0.03 nm s–1. De‐swelling is slower by more than two orders in magnitude, thereby underlining the difficulty to remove once incorporated solvent molecules. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)magnified image

Charged Extracellular Residues, Conserved throughout a G-protein-coupled Receptor Family, Are Required for Ligand Binding, Receptor Activation, and Cell-surface Expression

For G-protein-coupled receptors (GPCRs) in general, the roles of extracellular residues are not well defined compared with residues in transmembrane helices (TMs). Nevertheless, extracellular residues are important for various functions in both peptide-GPCRs and amine-GPCRs. In this study, the V(1a) vasopressin receptor was used to systematically investigate the role of extracellular charged residues that are highly conserved throughout a subfamily of peptide-GPCRs, using a combination of mutagenesis and molecular modeling. Of the 13 conserved charged residues identified in the extracellular loops (ECLs), Arg(116) (ECL1), Arg(125) (top of TMIII), and Asp(204) (ECL2) are important for agonist binding and/or receptor activation. Molecular modeling revealed that Arg(125) (and Lys(125)) stabilizes TMIII by interacting with lipid head groups. Charge reversal (Asp(125)) caused re-ordering of the lipids, altered helical packing, and increased solvent penetration of the TM bundle. Interestingly, a negative charge is excluded at this locus in peptide-GPCRs, whereas a positive charge is excluded in amine-GPCRs. This contrasting conserved charge may reflect differences in GPCR binding modes between peptides and amines, with amines needing to access a binding site crevice within the receptor TM bundle, whereas the binding site of peptide-GPCRs includes more extracellular domains. A conserved negative charge at residue 204 (ECL2), juxtaposed to the highly conserved disulfide bond, was essential for agonist binding and signaling. Asp(204) (and Glu(204)) establishes TMIII contacts required for maintaining the beta-hairpin fold of ECL2, which if broken (Ala(204) or Arg(204)) resulted in ECL2 unfolding and receptor dysfunction. This study provides mechanistic insight into the roles of conserved extracellular residues.

Application of magnetic resonance techniques in investigation of hydrocarbons interaction with composite polymers

AbstractComposite polymers such as high impact poly stirene (HIPS) or acrylonitrile–butadiene–styrene (ABS) are widely used in manufacturing industry. In special applications, such as refrigerator liners, a good resistance to fluids aggression is required. In this study we have applied NMR and ESR techniques to investigate the effect of diffusion of fluids (light hydrocarbons) used as blowing agents for polyurethanes (thermal insulators) inside selected HIPS materials. The application of NMR relaxation analysis on materials exposed to deuterated hydrocarbons (C6D12) allowed selective observation of rubber phase modification. Both longitudinal (T1) and transversal (T2) relaxation provided information on polymer chain dynamics effects, determined by solvent interactions. In fact, a consistent increase in relaxation times of polybutadiene rubber phase after solvent exposition was observed. Similar results were obtained by using hexachlorobutadiene as solvent. Another confirmation was also obtained by spin‐probe ESR technique. This technique could give useful insight into the molecular mobility of the two phases of HIPS. This experimental investigation provided a clear demonstration of consistent solvent penetration inside the rubbery phase of such composite polymers. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2810–2817, 2006

Preparation of zinc gluconate nanostructures with different shapes by lamellar liquid crystal template

Due to the penetration of solvent into the amphiphile bilayer of lamellar liquid crystal and the limitation of the thickness of the solvent layer of the lamellar liquid crystal, the zinc gluconate nanoparticles were synthesized by a direct template route in the lamellar liquid crystal formed by Triton X-100/ n-C 10H 21OH/H 2O system. The particles obtained were characterized by the transmission electron microscopy technique. Furthermore, the effects of the composition of lamellar liquid crystal, the zinc gluconate concentration and the temperature on the shape of particles were also studied. The studies show that monodisperse zinc gluconate particles can be produced by the lamellar liquid crystal template, and the shape and size are nearly independent of the composition of lamellar liquid crystal. However, the shape of particles evolves from spheres to nanowires with the increasing zinc gluconate concentration, and from spheres to nanorods as the temperature increases. The formation of one-dimensional zinc gluconate nanostructures can be attributed to an ideal microenvironment in the lamellar liquid crystal.

NMR Imaging of Coatings on Porous Substrates

Coatings are often applied on porous substrates, for example, wood, stone, or gypsum layers. The type and porosity of the substrate influences the coating performance. Until recently, no techniques were available to monitor the drying process in-depth as a function of time with a high spatial resolution (about 5 μm) in nontransparent coating systems. In the study presented in this paper, we show that with high resolution NMR imaging the drying process, consisting of penetration and evaporation of solvent and subsequent curing (chemical cross-linking) on and inside the substrate (wood and gypsum), can be monitored. The drying of a waterborne alkyd emulsion on a gypsum substrate was investigated. The curing of the emulsion was studied for both glass and gypsum substrates as a function of catalyst concentration, in this case cobalt based. Curing was not only observed at the coating surface, but also, in the case of gypsum, it was observed at the coating/substrate interface. On both substrates a concentration...

Adsorption of Pure and Mixed Solvent Solutions of Spin Probes onto Stationary Phases

Water, methanol (MeOH), acetonitrile (ACN), and binary MeOH-water and ACN-water solutions of different spin probes (nitroxides), selected to mimic the behavior of different pollutants, were adsorbed onto stationary phases usually used in reversed-phase high-performance liquid chromatography (RP-HPLC). These stationary phases are constituted by porous silica and differ from each other regarding the surface area, the pore size, the particle size, the surface functions (NH2, C8, and C18), and the percentage of functionalization. The electron paramagnetic resonance (EPR) spectra of the probe solutions adsorbed into the pores were analyzed by computer-aided computation of the spectral line shape, which provided structural and dynamical parameters of the probes and their environments. These parameters provided information on the surface properties of the stationary phases, such as alkyl chain density, solvent penetration, stationary-phase ordering, and residual silanol effects, which modify the retention times in HPLC. A different availability of polar surface groups in the pure and mixed solvents was found for the different stationary phases depending on (1) the different functionalization degree, (2) the surface-chain length, (3) the particle size, and (4) the polarity of both the probe and the solvent. The C8 functionalization rendered the surface more hydrophobic with respect to C18. The endcapping process of the residual silanols strongly enhanced the surface hydrophobicity tested by the probes. At the highest water content, the adsorption of the polar or charged probes onto the hydrophobic surface is the lowest and self-aggregation occurs. When the probes bear both hydrophilic and hydrophobic moieties, the adsorption is enhanced by a synergy between hydrophilic and hydrophobic bonds with the surface. A balance between the hydrophilic and hydrophobic forces leads to high adsorption and partial insertion of the surfactant probes in an ordered C18 chain layer at the solid surface which forms in the binary mixtures; this layer is ascertained between 40% and 70% of the less hydrophilic solvent, depending on the type of both the solid and the probe. This insertion and the response on the formation of the ordered layer were favored in ACN-water with respect to MeOH-water.

Preparation of Polyimide Ablator Coatings Using an Improved Solvent Vapor Smoothing Process

We completed the development of a method for preparing smooth vapor-deposited polyimide ablators up to 160 m thick for NIF target capsules. The process consists of two steps. The first step is vacuum chemical vapor deposition of monomer species, pyromellitic dianhydride and 4,4′-oxidianiline, onto the surface of a spherical shell mandrel where they may react to form polyamic acid. In the second step dimethyl sulfoxide (DMSO) vapor exposure in a gas-levitation smoothing apparatus swells and fluidizes the outer surface. Roughness in the outer fluid layer is reduced by surface-tension-driven flow. The shells are cured in the final smoothing step by heating to 300°C, converting the polyamic acid to polyimide. Recent experiments using X-ray radiography have allowed us to determine the depth of solvent penetration and the solvent concentration over a range of solvent exposure conditions. We found that the rate of penetration is a function of the solvent partial pressure in the flowing vapor stream. The concentration of solvent in the swollen layer is ∼0.43 g/cm3 and is independent of exposure conditions. Using the penetration information we were able to improve the smoothing process by increasing the solvent partial pressure. The optimized vapor smoothing process allowed us to consistently meet the surface smoothness specifications of NIF capsules.

Nuclear Magnetic Resonance Imaging Characterization of Resistance Properties of Polymers to Solvent Diffusion

Nuclear magnetic resonance (NMR) imaging (MRI) was applied to study the penetration of aggressive fluids, used as blowing agents for thermal insulators (polyurethane). The penetration profiles of cyclopentane and fluorotrichloromethane (Freon 11©) were obtained through a series of NMR images taken dynamically during saturation of polymer rods. The applied technique allowed efficient observation of radial diffusion of the solvents. The method provides quantitative measurements of the solvent penetration rate by determining the translational diffusion coefficients DTRL. These parameters were applied in evaluating materials with different compositions, and they were useful in understanding the resistance properties to solvent aggression. Significant chemical and physical parameters influencing diffusion were identified.

Chemical shift imaging (CSI) by precise object displacement

A mechanical device (NMR lift) has been built to displace vertically an object (typically an NMR sample tube) inside the NMR probe with an accuracy of 1 microm. A series of single pulse experiments are performed for incremented vertical positions of the sample. With a sufficiently spatially selective radio-frequency (r.f.) field, one obtains chemical shift information along the displacement direction (one-dimensional chemical shift imaging (CSI)). Knowing the vertical r.f. field profile (the amplitude of the r.f. field along the vertical direction), one can reconstruct the spectrum associated with all the slices corresponding to consecutive sample positions and improve the spatial resolution, which is simply related to the accuracy of the displacement device. Beside tests performed on phantoms, the method has been applied to solvent penetration in polymers and to benzene diffusion in a heterogeneous zeolite medium.

Molecular Dynamics Studies of the Size, Shape, and Internal Structure of 0% and 90% Acetylated Fifth-Generation Polyamidoamine Dendrimers in Water and Methanol

We have performed molecular dynamics simulations of 0% and 90% acetylated fifth-generation (G5) polyamidoamine (PAMAM) dendrimers in water and methanol and obtained radii of gyration of 2.51-2.57 and 2.11-2.33 nm, respectively, similar to those measured experimentally in methanol by Prosa et al. (J. Polym. Sci. 1997, 35, 2913-2924) and in water by Choi et al. (Nano Lett. 2004, 4, 391-397). Calculation of the moments of inertia and the relative shape anisotropy show that both 0% and 90% acetylated G5 are modestly ellipsoidal. The distribution of branch points relative to the center of the dendrimer and penetration of solvent show that the core and surface of the dendrimer are more exposed to water than is the region between the core and the surface due to the interactions between monomers, including hydrogen bonds that rapidly break and re-form as solvent molecules compete for hydrogen-bonding sites on the monomers. The water and methanol solvents seem to produce similar numbers of hydrogen bond interactions between monomers.