Water-rich Domains Research Articles

Towards understanding the mechanism of fibrous texture formation during high-moisture extrusion of meat substitutes

This paper investigates the physical mechanisms of structure formation during high-moisture extrusion of vegetable proteins. Our model starts from the observation that extrudates with fibrous, meat-like structures exhibit water-rich and protein-rich domains. The origin and structure of these domains is attributed to a spinodal phase-separation process which occurs upon cooling of the extrudate. We investigate the process using continuum-mechanics simulations, considering the combined effects of viscous flow, thermal diffusivity, and the mixing thermodynamics of water and protein. This multi-physics problem is numerically solved using an unconventional mesh-free approach, the material point method (MPM), combined with the Cahn- Hilliard model of phase separation. The method incorporates both Eulerian and Lagrangian aspects, and is well suited to model multicomponent flows of history-dependent materials. Our simulations show that fiber-like structures are obtained when the ratio of phase separation rate, heat conduction rate, and flow rate are matched within a narrow window. Our results predict that the shape of the temperature profile within the cooling channel determines the structure of the phase-separated state. These findings suggest that the physical mechanism which causes fibrous structure formation is given by spinodal phase separation under the influence of a temperature gradient.

Small-angle scattering and morphologies of ultra-flexible microemulsions.

The phase diagrams of ternary mixtures of partly miscible solvents containing a hydrotropic co-solvent exhibit a variable miscibility gap and one critical point. This work investigates the entire monophasic region far from and near to the miscibility gap in octan-1-ol/ethanol/water, for which ultra-flexible micro-emulsions (UFMEs) are observed by small-angle scattering techniques. SWAXS (combined small- and wide-angle X-ray scattering) allows the elucidation of these types of structure. Three distinct areas can be identified in the phase diagram, with scattering data resembling those from direct, bicontinuous and reverse local structures. These UFMEs are far more polydisperse than their surfactant-based counterparts. Water-rich and solvent-rich domains are only delimited by a small excess of hydrotrope, instead of a well defined surfactant layer of fixed area per molecule. It is shown that all scattering spectra obtained for the nanostructured compositions can be modelled by a simple unified analytical model composed of two uncorrelated contributions. The main one is the Ornstein-Zernike formula for composition fluctuations which gives information about the pseudo-phase domain size. The second is a Lorentzian that captures the structure of at least one of the coexisting pseudo-phases. No Porod law can be measured in the SAXS domain. The proposed expression gives access to two characteristic sizes as well as one inter-aggregate distance.

Seismic evidence for flow in the hydrated mantle wedge of the Ryukyu subduction zone.

It is widely accepted that water-rich serpentinite domains are commonly present in the mantle above shallow subducting slabs and play key roles in controlling the geochemical cycling and physical properties of subduction zones. Thermal and petrological models show the dominant serpentine mineral is antigorite. However, there is no good consensus on the amount, distribution and alignment of this mineral. Seismic velocities are commonly used to identify antigorite-rich domains, but antigorite is highly-anisotropic and depending on the seismic ray path, its properties can be very difficult to distinguish from non-hydrated olivine-rich mantle. Here, we utilize this anisotropy and show how an analysis of seismic anisotropy that incorporates measured ray path geometries in the Ryukyu arc can constrain the distribution, orientation and amount of antigorite. We find more than 54% of the wedge must consist of antigorite and the alignment must change from vertically aligned to parallel to the slab. This orientation change suggests convective flow in the hydrated forearc mantle. Shear wave splitting analysis in other subduction zones indicates large-scale serpentinization and forearc mantle convection are likely to be more widespread than generally recognized. The view that the forearc mantle of cold subduction zones is dry needs to be reassessed.

SANS study on influence of temperature on nanophase separation in epoxy-based hydrogels

Effect of temperature on nanophase separated structure of epoxy-based hydrogels containing polyoxyethylene (POE), polyoxypropylene (POP) and diglycidyl ether of Bisphenol A propoxylate (PDGEBA) was studied using small-angle neutron scattering (SANS). At the macroscopic level, increase of temperature causes an expulsion of water from the hydrogels. At the microscopic level, the expulsion of water is accompanied by redistribution of water and POE inside the hydrogels. Two kinds of structure have been revealed in the hydrogels by SANS. The structure with shorter characteristic length measured by Bragg’s distance (ca 70–80Å) is observed in all hydrogels and at all investigated temperatures (5–80°C). It is attributed to a distribution of water into water-rich and water-poor domains caused by nanophase separation of the crosslinked system due to differences in interaction of individual network building blocks with water. The water-rich domains consist of a part of POE blocks mixed with water. The water-poor domains consist of POP and PDGEBA blocks mixed with a small amount of water and remaining POE blocks. The domains are separated by a diffuse interface with effective thickness ca 7–10Å as estimated from deviations from Porod’s law. Formation of a new structure with longer characteristic length (ca 240Å) is observed in the highly non-stoichiometric hydrogels. Its contribution to SANS becomes more pronounced with increasing temperature. This contribution is attributed to the formation of regions of pure water (water pools) as a new hydrogel phase that is enabled by low network density and high amount of pending chains in the highly non-stoichiometric epoxy networks subject to swelling.

Oxidative degradation of norfloxacin by a lipophilic oxidant, cetyltrimethylammonium permanganate in water–acetonitrile medium: A kinetic and mechanistic study

The present study reports the oxidative metabolism of an established antibacterial drug norfloxacin (NRF) by a lipid compatible lipophilic Mn(VII) oxidant, cetyltrimethylammonium permanganate (CTAP) in acetonitrile–water binary mixture in the presence of acetic acid. The metabolized products are identified as 7-amino-1-ethyl-6-fluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid, formaldehyde, and ammonia. The kinetics of the reaction is studied in aqueous acetonitrile media in the presence of acetic acid by UV–vis spectroscopic method by monitoring the absorbance of Mn(VII) at 530nm under pseudo first-order condition. The reaction is found to be first-order with respect to CTAP and fractional order with respect to norfloxacin and acetic acid. Occurrence of Michaelis–Menten type kinetics with respect to norfloxacin confirmed the binding of oxidant and substrate to form a complex before the rate determining step. A suitable ionic mechanism is proposed based on the experimental findings. The proposed reaction mechanism is supported by the effect of solvent polarity and effect of temperature on the reaction rate. High negative entropy of activation (ΔS≠=−259 to −158JK−1mol−1) supported the existence of a forced, more ordered and extensively solvated transition state. Further, solvent polarity–reactivity relationship revealed (i) the presence of less polar transition state compared to the reactants, (ii) differential contribution from dipolar aprotic (acetonitrile) and polar protic (water) solvents toward the reaction process through specific and nonspecific solute–solvent interaction and (iii) presence of intramolecular H-bonding in oxidant–substrate complex in acetonitrile rich domain and intermolecular H-bonding between oxidant–substrate complex and water in water rich domain.

Effect of Peptide Charge Distribution on the Structure and Kinetics of DNA Complex

The complexes formed by DNA or siRNA interacting with polycations showed great potential as nonviral vectors for gene delivery. The physicochemical properties of the DNA/siRNA complexes, which could be tuned by adjusting the characteristics of polycations, were directly related to their performance in gene delivery. Using 21 bp double-stranded oligonucleotide (ds-oligo) and two icosapeptides (with the repeating units being KKGG and KGKG, respectively) of the same charge density as model molecules, we investigated the effect of charge distribution on the kinetics of complexation and the structure of the final complexes. Even though the distribution of the charged groups in peptides was only adjusted by one position, the complexes formed by (KKGG)5 and ds-oligo were larger in size and easier to precipitate than those formed by (KGKG)5. Counterintuitively, it was not the charged groups but the hydrophilic neutral spacers that determined the kinetics and the structure of the complex. We attributed such an effect to the water-mediated disproportionation process. The hydrophilic spacers next to each other were better than that in the separated pattern in holding water molecules after forming the complex. The water-rich domains in the complex functioned as a lubricant and facilitated the relaxation of the polyelectrolyte, resulting in a fast complexation process. The resulting complex was thus larger in size and lower in surface energy.

Toward a Molecular Dynamics Force Field for Simulations of 40% Trifluoroethanol–Water

Various computational models of trifluoroethanol (TFE) and water have been explored with the goal of finding a system for molecular dynamics (MD) simulations that reliably predict properties of 40% TFE-water (v/v) and can be used in studies of peptide-solvent nuclear cross-relaxation. Models derived by modification of TFE parameters developed by Fioroni et al. (J. Phys. Chem. B 2000, 104, 12347), in combination with either TIP4P-Ew or TIP5P-E water, were most successful. Simulations of 40% TFE-TIP4P-Ew water evidenced separation of the system into large TFE-rich and water-rich domains. With TIP5P-E water, simulations showed aggregation of each solvent component into small clusters. Nuclear spin dipolar interactions between solvent fluorines and the methyl hydrogens of acetate ion dissolved in 40% TFE-water were calculated. The cross-relaxation parameter σHF reckoned for the TFE-TIP5P-E system agreed with experiment while the value calculated using the TFE-TIP4P-Ew system was too low. While the TFE-TIP5P-E model of 40% TFE-water leads to good predictions of the system density, translational diffusion coefficients, and a solvent-solute cross-relaxation parameter, this model performs poorly in predicting the enthalpy of mixing. Preliminary studies of 20% TFE-water and 50% TFE-water suggest that the model will perform with the same characteristics for mixtures that have compositions near 40% TFE-water.

Octanol-rich and water-rich domains in dynamic equilibrium in the pre-ouzo region of ternary systems containing a hydrotrope

Ternary mixtures of medium-chain fatty alcohols, water and a hydrotrope (such as ethanol), near the immiscibility gap, make stable single phases at constant temperature. Interestingly, in this `pre-ouzo region' these single phases consist of two distinct nanoscopic pseudo-phases, one octanol-rich and one water-rich. This domain of composition, which is known to produce strong light scattering and to separate under ultracentrifugation into two phases, has been studied using contrast variation in small-angle neutron scattering (SANS) combined with small- and wide-angle X-ray scattering (SWAXS). The existence of fatty alcohol-rich domains of well defined size of the order of 2 nm radius is proven. The scattering can be approximated by an Ornstein–Zernike function, which is close to the general expression of Choi, Chen, Sottmann & Strey [Physica B, (1998),241–243, 976–978] with vanishing quadratic Porod term. Exploitation of the relative intensities at the vanishing scattering angle in SANS demonstrates that the distribution coefficient of ethanol between the octanol-rich and the water-rich domains is close to one. WAXS of the two coexisting pseudo-phases is compared with the corresponding binary water–ethanol and octanol–ethanol samples.

Finger-like pattern formation in dilute surfactant pentaethylene glycol monododecyl ether solutions

We report here peculiar finger-like patterns observed during the phase separation process of dilute micellar pentaethylene glycol monododecyl ether solutions. The patterns were composed of parallel and periodic threads of micelle-rich domains. Prior to this pattern formation, the phase separation always started with the appearance of water-rich domains rimmed by the micelle-rich domains. It was found that these rims played a significant role in the pattern formation. We explain this pattern formation using a simple simulation model with disconnectable springs. The simulation results suggested that the spatially inhomogeneous elasticity or connectivity of a transient gel of worm-like micelles was responsible for the rim formation. The rims thus formed lead rim-induced nucleation, growth, and elongation of the domains owing to their small mobility and the elastic frustration around them. These rim-induced processes eventually produce the observed finger-like patterns.

Molecular Simulations of Hydrated Proton Exchange Membranes: the Structure

The structure of two hydrated proton exchange membranes for fuel cells (PEMFC), Nafion® (Dupont) and Hyflon® (Solvay), is studied by all-atom molecular dynamics (MD) computer simulations. Since the characteristic times of these systems are long compared to the times for which they can be simulated, several different, but equivalent, initial configurations with a large degree of randomness are generated for different water contents and then equilibrated and simulated in parallel. A more constrained structure, analog to the newest model proposed in the literature based on scattering experiments, is investigated in the same way. One might speculate that a limited degree of entanglement of the polymer chains is a key feature of the structures showing the best agreement with experiment. Nevertheless, the overall conclusion remains that the scattering experiments cannot distinguish between the several, in our view equally plausible, structural models. We thus find that the characteristic features of experimental scattering curves are, after equilibration, fairly well reproduced by all systems prepared with our method. We thus study in more detail some structural details. We attempt to characterize the spatial and size distribution of the water rich domains, which is where the proton diffusion mostly takes place, using several clustering algorithms.

Supramolecular Interactions between Inorganic and Organic Blocks of Pentacyanoferrate/Poly(4-vinylpyridine) Hybrid Metallopolymer

The combination of organic and inorganic molecular building blocks gives rise to hybrid supramolecular materials showing properties from both chemical domains. This work presents the synthesis of metallopolymers made from poly(4-vinylpyridine) (P4VP) and pentacyanoferrate(II) at various polymer repeating unit/[Fe(CN)(5)](3-) ratios (py/Fe) and focuses on the influence of each block on the properties of the other. The solvatochromic shift of the [Fe(CN)(5)](3-) moiety was investigated as a function of the py/Fe ratio and the water molar fraction (X(H(2)O)) of the ethanol/water medium. Asymmetric solvation favoring ethanol was enhanced as the py/Fe ratio increased. The results lead to a modification of the well-established thermodynamical model for asymmetrical solvation and suggest the formation of water-rich domains within the polymer coils with a large number of [Fe(CN)(5)](3-) units. From the macromolecular perspective, the increase of [Fe(CN)(5)](3-) units resulted in higher values of intrinsic viscosity, which is rationalized by the increase of the polymer coil charge density and therefore the increase in hydrodynamic volume due to repulsive electrical forces. Evaluating the intrinsic viscosity of a sample with py/Fe = 25 in solvent mixtures with different water molar fractions, it was found that the hydrodynamic volume is maximized at intermediate X(H(2)O) values, where both the ethanol-soluble uncomplexed polymer block and the water-soluble [Fe(CN)(5)](3-)-pendant units can be suitably solvated, preventing coil shrinkage.

Electrochemical and PM-IRRAS studies of floating lipid bilayers assembled at the Au(111) electrode pre-modified with a hydrophilic monolayer

A floating bilayer lipid membrane (fBLM) assembled on a 1-thio-β-D-glucose (β-Tg)-modified Au(111) surface was engineered to mimic the environment of a biological cell membrane. This bilayer consists of a mixture of the phospholipid (DMPC), polyethylene glycol lipid (DMPE-PEG350) and cholesterol. Prior to membrane adsorption, a monolayer of β-Tg was first self-assembled at the Au(111) surface to increase the hydrophilicity of the electrode surface. The asymmetric bilayer was then deposited onto the hydrophilic support using a combination of Langmuir–Blodgett and Langmuir–Schaefer techniques. The inner leaflet of the bilayer was composed of DMPC, DMPE-PEG350 and cholesterol, while the outer leaflet consisted of DMPC and cholesterol. The hydrophilic PEG spacer subunit of the DMPE-PEG350 molecule promotes the formation of a water-rich domain, which separates the bilayer from the β-Tg modified surface. The Langmuir compression isotherms were recorded to examine the miscibility of these mixed monolayers at the air-solution interface of the Langmuir trough. Differential capacitance measurements showed that this fBLM was remained stable on the surface of the modified-gold electrode for potentials ranging from −0.40 to 0.45V versus Ag/AgCl and achieved a minimum capacitance of ∼3.0μFcm−2. Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was used to obtain information regarding the conformation and orientation of the acyl chains and measure the degree of hydration of the phospholipid polar head groups within the film. These spectra demonstrated that the acyl chains of the lipids assume a small angle with respect to surface normal and that the phospho-glycerol groups are well-hydrated. The IR spectra of the PEG subunits demonstrated that the spacer unit adopts an amorphous, disordered conformation, which favors the hydration of the inner layer. This work demonstrates that the fBLM, composed of DMPE-PEG350 molecules, forms a water-rich region that separates the bilayer from the metal surface and that these new biomimetic systems are promising for future investigations involving transmembrane proteins.

Adsorption of Ethanol Vapor on Mica Surface under Different Relative Humidities: A Molecular Simulation Study

The adsorption of ethanol vapor on a mica surface at 298 K and different relative humidities (RHs) are studied using grand canonical Monte Carlo and molecular dynamics simulations. The simulations show that the adsorbed ethanol molecules form a monolayer on the mica surface, sharply contrasting the behavior of water, which forms multiple adsorption layers on the mica surface. Simulations of an ethanol and water mixture reveal that the adsorbed molecules are segregated into a water-rich domain near the mica surface and an ethanol-rich domain on top of the water-rich domain. The water-rich domain exhibits multilayers unless the RH is extremely low (<1%), whereas the ethanol-rich domain exhibits a monolayer. These findings are supported by calculations of the isosteric heats of adsorption and analyses of configurations, concentrations, and diffusivities of molecules in different layers.

Enhanced permeation, leaf retention, and plant protease inhibitor activity with bicontinuous microemulsions

Bicontinuous microemulsions (BCMEs) have excellent solubulizing properties along with low interfacial tension and aqueous content that can be controlled. In this work, water soluble plant protease inhibitor (PI), well characterized for its activity against insect pests, was incorporated into a BCME system and explored for permeation on hydrophobic leaf surfaces and protease inhibition activity. The bicontinuous nature of the microemulsion containing water:2-propanol:1-butanol (55:35:10w/w) was characterized using conductivity and self-diffusion coefficient measurements. The PI was soluble in the water-rich bicontinuous domains, stable in the microemulsions, and protease inhibition activity was retained for a prolonged duration. The microemulsions ensured greater wettability and a wider spread of the PI on hydrophobic leaf surfaces as revealed by contact angle measurements. Significantly, trypsin inhibition activity assays of the PI recovered from the leaves after delivery from the microemulsion indicated a significant increase in the PI retention on the leaf. This BCME enabled greater leaf permeation and retention of the PI can be attributed to a temporary disruption of the waxy leaf surface followed by self-repair without causing any long term damage to the plant.

SANS and DSC study of water distribution in epoxy-based hydrogels

Distribution of water in stoichiometric hydrophilic epoxy network swollen in heavy water to different degrees (epoxy-based hydrogels) at 25 °C has been investigated by small-angle neutron scattering (SANS) and differential scanning calorimetry (DSC). Nanophase separated structure of the hydrogels consisting of water-rich and water-poor domains was revealed by SANS. Two regimes for hydrogel structure were found: (a) at low water content hydrogel consists of isolated water-rich domains dispersed in continuous water-poor phase and (b) at high water content the water-rich domains form another continuous phase. Isosbestic point of scattering curves was found by SANS in the latter region and attributed to conservation of Porod’s length of the nanophase separated structure. Thermal properties of the system are qualitatively different in the two regions: in the former one the glass transition temperature decreases with growing water content while in the latter one it remains constant. Percolation threshold separating both regimes is reflected in a jump of glass transition temperature and inversion of the dependence of the specific heat difference at glass transition.

Photopolymerized Thermosensitive Poly(HPMAlactate)-PEG-Based Hydrogels: Effect of Network Design on Mechanical Properties, Degradation, and Release Behavior

Photopolymerized thermosensitive A-B-A triblock copolymer hydrogels composed of poly(N-(2-hydroxypropyl)methacrylamide lactate) A-blocks, partly derivatized with methacrylate groups to different extents (10, 20, and 30%) and hydrophilic poly(ethylene glycol) B-blocks of different molecular weights (4, 10, and 20 kDa) were synthesized. The aim of the present study was to correlate the polymer architecture with the hydrogel properties, particularly rheological, swelling, degradation properties and release behavior. It was found that an increasing methacrylation extent and a decreasing PEG molecular weight resulted in increasing gel strength and cross-link density, which tailored the degradation profiles from 25 to more than 300 days. Polymers having small PEG blocks showed a remarkable phase separation into polymer- and water-rich domains, as demonstrated by confocal microscopy. Depending on the hydrophobic domain density, the loaded protein resides in the hydrophilic pores or is partitioned into hydrophilic and hydrophobic domains, and its release from these compartments is tailored by the extent of methacrylation and by PEG length, respectively. As the mechanical properties, degradation, and release profiles can be fully controlled by polymer design and concentration, these hydrogels are suitable for controlled protein release.

Macromolecular Diffusion in Self-Assembling Biodegradable Thermosensitive Hydrogels.

Hydrogel formation triggered by a change in temperature is an attractive mechanism for in situ gelling biomaterials for pharmaceutical applications such as the delivery of therapeutic proteins. In this study, hydrogels were prepared from ABA triblock polymers having thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) flanking A-blocks and hydrophilic poly(ethylene glycol) B-blocks. Polymers with fixed length A blocks (~22 kDA) but differing PEG-midblock lengths (2, 4 and 10 kDa) were synthesized and dissolved in water with dilute fluorescein isothiocyanate (FITC)-labeled dextrans (70 and 500 kDA). Hydrogels encapsulating the dextrans were formed by raising the temperature. Fluorescence recovery after photobleaching (FRAP) studies showed that diffusion coefficients and mobile fractions of the dextran dyes decreased upon elevating temperatures above 25 °C. Confocal laser scanning microscopy and cryo-SEM demonstrated that hydrogel structure depended on PEG block length. Phase separation into polymer-rich and water-rich domains occurred to a larger extent for polymers with small PEG blocks compared to polymers with a larger PEG block. By changing the PEG block length and thereby the hydrogel structure, mobility of FITC-dextran could be tailored. At physiological pH the hydrogels degraded over time by ester hydrolysis, resulting in increased mobility of the encapsulated dye. Since diffusion can be controlled according to polymer design and concentration, plus temperature, these biocompatible hydrogels are attractive as potential in situ gelling biodegradable materials for macromolecular drug delivery.

Structural and Mechanical Properties of UV-Photo-Cross-Linked Poly(N-vinyl-2-pyrrolidone) Hydrogels

Biocompatible poly( N-vinyl-2-pyrrolidone) (PVP) hydrogels have been produced by UV irradiation of aqueous polymer mixtures, using a high-pressure mercury lamp. The resulting materials have been characterized by a combination of experimental techniques, including rheology, small-angle neutron scattering (SANS), electron paramagnetic resonance (EPR), and pulsed gradient spin-echo nuclear magnetic resonance (PGSE-NMR), to put in evidence the relationship between the microstructural properties and the macrofunctional behavior of the gels. Viscoelastic measurements showed that UV photo-cross-linked PVP hydrogels present a strong gel mechanical behavior and viscoelastic moduli values similar to those of biological gels. The average distance between the cross-linking points of the polymer network was estimated from the hydrogels elastic modulus. However, SANS measurements showed that the network microstructure is highly inhomogeneous, presenting polymer-rich regions more densely cross-linked, surrounded by a water-rich environment. EPR and PGSE-NMR data further support the existence of these water-rich domains. Inclusion of a third component, such as glycerol, in the PVP aqueous mixture to be irradiated has been also investigated. A small amount of glycerol (<3% w/w) can be added keeping satisfactory properties of the hydrogel, while higher amounts significantly affect the cross-linking process.

Double-Chain Cationic Surfactant and n-Pentanol: An L3 Phase in the Rich-Water Domain?

A ternary system containing water, pentanol and a quaternary cationic surfactant, dioctadecyldimethylammonium bromide (DODAB) was investigated. We present the phase diagram and ESR studies that demonstrate the existence of the well-known L3 or sponge phase in the water-rich domain of the diagram. The remarkable fact is the existence of some kind of order in such diluted conditions.

FTIR study on the nature of water sorbed in polypropylene (PP)/ethylene alcohol vinyl (EVOH) films

FTIR transmission spectroscopy, along with gravimetric analysis and scanning electron microscopy (SEM), have been used to investigate the structure of water sorbed in PP/EVOH films. Aims of this investigation were to determine water content spectroscopically, to elucidate the different types of interaction that water molecules form with the macromolecular network and their change as a function of blend composition, morphology and the state (gaseous or liquid) of the water contacting with the PP/EVOH system at equilibrium. The extinction coefficients ( ε) of the water sensitive bands ( ν OH, δ OH, 2150 and 700 cm −1) are proportional to the EVOH content. These results are explained by the phase separation between PP and EVOH and the increasing size of the dispersed EVOH spheres with the EVOH content. Moreover, the ε values suggest that when the films are in contact with water vapor, most of the water sorbed locates around the hydrogen bonding sites of the polymer although the effective hydration region around the EVOH residues should be much larger than the primary hydration region. Besides, “bulk water”, generally categorized as “free water”, is lacking in the polymer blends under our experimental conditions. When they contact with liquid water both the water uptake and the ε values are changed, but these variations are not large enough to assume the formation of “bulk water”. Band decomposition of the O–H stretching vibration ( ν OH) on the basis of the four-state model supports the assumption of the absence of “water-rich domains”, regardless of the blend composition or whether the PP/EVOH film contacts with liquid water or water vapor. Besides, either in contact with water vapor or liquid water, the more hydrophobic mixtures (90/10) show the greatest effect of perturbation with respect to pure water for the “weaker hydrogen bonded” water. Conversely, the interactions between the “strongly bound” water and OH groups in the EVOH chains become stronger with increasing hydrophilicity of the blends and this type of water has a greater plasticising efficiency. Furthermore, these structural changes are greater for liquid water than for water vapor and this trend is equally observed for mixtures of different hydrophilicity.