This study investigates gelation of x-carrageenan (x-car) in water-in-water (W/W) emulsions formed by mixing two incompatible polymers. Gelation was induced by cooling in the presence of KCl. Polyethylene oxide (PEO), dextran (Dex), pullulan (Pul), and gelatin (Gel) were used to prepare the W/W emulsions and to form emulsion gels (emulgels) by adding x-car. In first instance, x-car was added to solutions of each of these polymers in order to establish the effect of the presence of these polymers on the gelation of x-car. It was found that the microstructure of the x-car network was more homogeneous with increasing viscosity of the polymer solution, but their impact on the storage modulus (G ') and gelation temperature (Tg) was very small. Subsequently, x-car was added to W/W emulsions where it partitioned between the two phases in a manner that depended on the types of polymers. Strong partitioning to the dispersed phase led to a large decrease of G ' of the emulgels, whereas in the case of weak partitioning, G' was little influenced compared to x-car in water. Strain sweeps demonstrated distinct non-linear behaviour depending on the partitioning of the x-car between the dispersed and the continuous phases. Overall, the results highlight the potential to fine-tune the mechanical properties of W/W emulgels for application in food through selection of the polymers and the phase composition.

This study investigates the stabilization of water-in-water (W/W) emulsions composed of dextran and poly(ethylene oxide) (PEO) using bis-hydrophilic diblock copolymers composed of a dextran and a POEGMA block. Confocal laser scanning microscopy (CLSM) was employed to assess the stabilization efficacy at different copolymer compositions. Macroscopic phase separation was observed in mixtures of the block copolymers with pure dextran solutions, whereas the block copolymers formed microscopic domains in pure PEO solutions. In the W/W emulsions the block copolymers formed small domains in the PEO phase that adsorbed at the interface stabilizing dispersed dextran droplets. The stability was found to depend on the concentration and composition of the copolymers, the concentration of the dextran and PEO as well as the molecular weight of the latter.

κ-Carrageenan (κ-car) is a polysaccharide extracted from red seaweed that is widely used for a range of industrial applications. The rheological and structural properties of κ-car with different degrees of acetylation (DA = 0-45 %) as well as their mixtures were investigated using light scattering, rheology, μ-DSC, and confocal microscopy. Acetylation did not significantly affect the molar mass or radius of κ-car, but it decreased its intrinsic viscosity ([η]). Gelation of κ-car was induced by cooling in the presence of KCl. The critical gelation temperature and storage modulus of the gel decreased with increasing DA and gelation did not occur above 5 °C for DA ≥ 21 %. This was caused by the increasing hindrance from the acetyl groups to form helices, which was confirmed by μ-DSC that showed a decrease of the coil-helix transition temperature and enthalpy. Rheology and μDSC showed that in mixtures of κ-car with different DA, the coil-helix and gelation temperature of each component were the same as for individual solutions. Confocal microscopy images of mixed gels with different fluorescent labels demonstrated co-aggregation of κ-car with different DA without micro-phase separation.

The gelation behaviour of κ-carrageenan (κ-car) in the presence of KCl was examined in binary mixtures with dextran (Dex) or polyethylene oxide (PEO), as well as in water-in-water (W/W) emulsions formed by these polymers. The results show that the presence of Dex or PEO has only a weak effect on κ-car gelation. However, it affects the microstructure rendering the κ-car network more homogenous with increasing viscosity of the DEX or PEO solutions. In the W/W emulsions, κ-car preferentially partitioned to the Dex-rich phase. Rheological measurements showed that the storage modulus (G') increased with the volume fraction of the PEO phase (φ) as long as the Dex phase was continuous. The transition of the DEX phase from continuous to dispersed at φ ≈ 70 % resulted in a sharp reduction of the gel stiffness. Weak gels were nevertheless formed up to φ ≈ 80 % due to aggregation of gelled Dex droplets into a system spanning network. For φ > 90 %, G' increased again sharply as an increasing fraction of the κ-car partitioned to the PEO phase. This work highlights that the rheology of W/W emulsions can be tuned by adding κ-car.

Water-in-water (W/W) emulsions are formed by mixing incompatible aqueous polymer solutions. Their stabilization is more challenging in comparison with oil-in-water emulsions due to their extremely low interfacial tension, wide W/W interface and strong sensitivity to dilution. W/W emulsions cease to exist when diluted below the binodal curve, which significantly restricts their use in applications. This work aims to develop original double-hydrophilic grafted and diblock copolymers (DHGC and DHDC, respectively) based on dextran (Dex) and on poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA), a hydrophilic and PEO-philic polymer, to stabilize W/W emulsions made of Dex and polyethylene oxide (PEO) phases. A series of grafted and diblock copolymers (Dex-g-POEGMA and Dex-b-POEGMA) was synthesized by photo-mediated reversible addition-fragmentation chain transfer (photo-RAFT) polymerization using multifunctional and monofunctional dextran-based macromolecular chain transfer agents. Key parameters such as the molecular weight of OEGMA monomers, the lengths of Dex and POEGMA parts, and the grafting density were systematically varied. Results showed that Dex/PEO emulsion can be successfully stabilized, for at least one week, depending on the architecture and composition of the copolymers.

We have investigated the common solvent-based emulsion composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) solutions in tetrahydrofuran in the presence of PS-b-PMMA diblock copolymers. The stabilization effect of the diblock was determined visually and by confocal laser scanning microscopy at various phase volume fractions, concentrations, and compositions of the copolymer. The behavior of PS-b-PMMA in each homopolymer solution was studied with static and dynamic light scattering. The copolymer formed micelles above a critical homopolymer concentration. Light scattering measurements showed that small amounts of the other homopolymer added to the micelle solution entered the micelles spontaneously, suggesting that the observed emulsion stability is caused by the diblock copolymer laminar layer formation covering the surface of the dispersed droplets.

A range of commercial chitosan samples with different molar masses and degrees of acetylation was tested for their capacity to stabilize water in water (W/W) emulsions formed by mixing aqueous solutions of dextran and poly (ethylene oxide). To further understand the effect of the acetylation degree, commercial samples were acetylated and deacetylated to different degrees. The effect of pH and chitosan concentration on the stability was investigated. The lowest investigated degree of acetylation (6%) was sufficient to inhibit coalescence, but higher degrees that were studied (up to 50%) led to faster stabilization resulting in smaller stable dispersed droplets that did not sediment for at least one week. The effect of hydrophobic acetyl units on the stability was confirmed for κ-carrageenan that could stabilize the W/W emulsion only after acetylation. For chitosan it was shown that the molar mass should be above a critical value independent of the degree of acetylation.

Water in water (W/W) emulsions were prepared by mixing aqueous dextran and polyethylene oxide (PEO) solutions. Addition of different amounts of the polysaccharide chitosan inhibited coalescence of dispersed droplets of the dextran phase in the continuous PEO phase to different extents depending on the concentration and pH. Transmission profiles were measured during centrifugation and analysed. It is shown that the evolution of the transmission profile is determined by the relative rates of coalescence and sedimentation of the droplets. The rate of coalescence of the sedimented droplets into a continuous dextran phase depends on the resistance of the protective chitosan layer to compression by centrifugation. It is concluded that the efficacy of stabilization of W/W emulsions can rapidly be quantitatively assessed, but it is difficult to deduce the behaviour under gravity from that observed during centrifugation.

This paper reports the development in aqueous solution of mixed micelles of tunable cloud point temperature through blending in various proportions of two copolymers of different chemical natures. For that purpose, a lipid-b-poly(2-isopropyl-2-oxazoline) (lipid-b-P(iPrOx)) copolymer, self-assembling into thermosensitive micelles that phase-separate above a cloud point temperature of 38 °C, was blended in various proportions with commercial C18-b-PEOx. The latter was constituted of a hydrophobic saturated C18 chain and a hydrophilic poly(ethylene oxide) (PEO) block with varying polymerization degrees (x) and does not have any thermosensitive properties on the studied temperature range for any value of x. The different blends were thoroughly characterized by light scattering and UV-visible spectroscopy, revealing that hybridization between both copolymers always occurred, independent of the PEO block length. The resulting mixed micelles present TCP values progressively increasing with the C18-b-PEOx proportion, from 38 to 61 °C. This study demonstrates the relevance of the blending approach to tune the phase separation of micellar systems by formulation rather than by more tedious synthetic efforts. Shifting TCP through this approach extends the range of temperature where lipid-b-P(iPrOx) can find an application.

The viscosity (eta) of dextran (Dex), methyl cellulose (MC), hydroxypropylmethyl cellulose (HPMC), kappa-carrageenan (KC), alginate (Alg), and carboxymethyl cellulose (CMC) was measured as a function of the shear rate (gamma) over a broad range of concentrations both in salt-free water and in 0.1 M NaCl. The concentration (C) dependence of the Newtonian viscosity (eta(0)) was found to be universal for neutral polysaccharides and anionic polysaccharides in 0.1 M NaCl when C was multiplied with the intrinsic viscosity. The dependence was compared with theoretical predictions assuming dominant hydrodynamic or dominant topological interactions. The effect of electrostatic interactions was observed for anionic polysaccharides in salt-free water but not at higher concentrations. Master curves of the shear thinning behavior at different concentrations were obtained when eta/eta(0) was plotted versus tau,gamma with tau being a concentration-dependent time that characterizes the onset of shear thinning. Binary mixtures of two neutral polysaccharides (MC and HPMC), two anionic polysaccharides (Alg and CMC), and a neutral (Dex) and anionic polysaccharide (KC) were investigated as a function of the composition and the total polysaccharide concentration. The behavior of the first two mixtures was similar to that of a single polysaccharide with an intermediate intrinsic viscosity. Significant synergy was observed for the third type of mixtures in salt-free water demonstrating the important effect of electrostatic interactions between charged polysaccharides at low concentrations even in concentrated solutions of neutral polysaccharides.

The high thickening properties of pristine xanthan (PX) were combined with the interfacial stabilizing properties of hydrophobically modified xanthan (HMX) in order to obtain stable oil-in-water (O/W) emulsions. It was demonstrated that such a combination led to stable emulsions in which properties were higher than the sum of those of PX and HMX taken separately, thus indicating synergistic interactions between these two polymers. This synergy was confirmed when this PX/HMX couple was compared to a conventional thickener/molecular surfactant system, the latter being far less efficient. These results prove that PX and HMX interact in the emulsion contrary to classical thickening and interfacial stabilizing agents.

Xanthan belongs to a special class of bacterial polysaccharides by having on one hand a oligosaccharide repeating unit and on the other higher order structures resulting in an unusually large chain rigidity. It is further characterized with an ionic strength, pH, and solvent-dependent cooperative conformational (order-disorder) transition. The ordered state is predominantly double-stranded, but partially denatured, fully or aggregated forms may coexist, depending on the sample history. In this chapter, we have reviewed the literature on chemical modifications of xanthan, and the resulting physical properties resulting from the modifications. It appears that research has been carried out without fully recognizing the complex conformational issues and possible degradations (depolymerizations) accompanying the modifications of xanthan. However, in recent years this issue has been more systematically dealt with, including studies on hydrophobization in both the ordered and disordered state.

Water-in-water (W/W) emulsions show a characteristic decrease of the viscosity with increasing shear rate that is well described by equations proposed in the literature. Confocal laser scanning microscopy images showed that the decrease of the viscosity was caused by deformation and alignment of the dispersed droplets followed by string formation. W/W emulsions stabilized by the addition of polysaccharides or protein microgels still form strings when sheared with the particles remaining at the interface. After cessation of the flow, the strings break up into small droplets and the presence of stabilizing particles inhibits their coalescence. It is shown how the viscosity and the microstructure depend on the initial droplet size, the interfacial tension, the viscosity of the two phases, and the concentration of the stabilizing polymers.

The present study focuses on the chemical and physical characterization of the water-soluble fraction of the Commiphora Africana exudate. The chemical analysis proved that this fraction is mainly composed of carbohydrates and hydrophobic amino acids. Size exclusion chromatography (SEC) revealed the presence of three distinct polysaccharide populations that are all bonded to protein. In addition, both SEC and rheology demonstrated that the gum owns highly compact structure that suggests an AGP-like polymer. Commiphora Africana gum exhibits excellent surface activity at concentration 2 orders of magnitude lower than the reference, acacia gum and was attributed to the fact that the three populations contribute to the surface tension lowering. This remarkable property has been confirmed by preliminary experiments on model emulsions and suggests a very promising application in formulation. (C) 2017 Elsevier Ltd. All rights reserved.

The issue addressed here is whether kappa carrageenan (kappa-car) and iota carrageenan (iota-car) mixed in aqueous solution microphase separate during gelation as has been claimed in the literature. Rheological properties and microstructure of individual kappa-car and iota-car solutions as well as their mixtures were studied at different concentrations (5, 10, 20 g/L) in the presence of CaCl2(0-100 mM). Mixtures showed a two-step gelation process at gelation temperatures (T-c) that coincided with those of corresponding individual kappa-car and iota-car solutions. However, the stiffness of the mixed gels was much higher than the sum of the corresponding individual gels. Confocal laser scanning microscopy (CLSM) and turbidity measurements showed that the kappa-car gel was always more heterogeneous than the iota-car gel, but less in the mixture than in the individual systems. The results show that microphase separation of iota-car and kappa-car in mixed gels is highly unlikely. It is suggested that the increased stiffness of the mixed gels is caused by co-aggregation of kappa-car and iota-car or a different structure of the kappa-car formed in the mixture.

The present study focuses on the chemical and physical characterization of the water-soluble fraction of the Commiphora Africana exudate. The chemical analysis proved that this fraction is mainly composed of carbohydrates and hydrophobic amino acids. Size exclusion chromatography (SEC) revealed the presence of three distinct polysaccharide populations that are all bonded to protein. In addition, both SEC and rheology demonstrated that the gum owns highly compact structure that suggests an AGP-like polymer. Commiphora Africana gum exhibits excellent surface activity at concentration 2 orders of magnitude lower than the reference, acacia gum and was attributed to the fact that the three populations contribute to the surface tension lowering. This remarkable property has been confirmed by preliminary experiments on model emulsions and suggests a very promising application in formulation.

The impact of xanthan chemical modification under both ordered and disordered conformations on oil-in-water (O/W) emulsion stabilization was investigated. While both hydrophobically modified xanthan (HMX) are able to stabilize the O/W interface, a dramatic difference was observed macroscopically. When HMXord (ordered conformation) could produce stable emulsions at concentrations down to 0.2% w/w, HMXdis (disordered conformation) led to unstable systems mostly by creaming whatever the concentration studied. Moreover, in the case of HMXdis, the role of the grafted chain length was investigated and two different behaviors were observed depending on the grafting unit. It was demonstrated that the cornerstone of these emulsion stability was the rheological properties of the continuous phase which was governed by two main factors: the partitioning of HMXdis between the interface and the continuous phase and the viscosifying ability of the polymer, the latter being directly linked to the backbone stiffness.

The effect of adding a small quantity of linear polymers on the stability of water-in-water (W/W) emulsions was studied for emulsions of dextran-rich droplets in a continuous poly(ethylene oxide) (PEO) phase (D/P) and vice versa (P/D). It was found that out of 16 different polymers that were tested, three had a significant effect: chitosan (Chit), diethyl aminoethyl dextran (DEAED), and propylene glycol alginate (PGA). In the presence of Chit or PGA, P/D emulsions were much less stable than D/P emulsions, but DEAED stabilized both types of emulsion. Interactions of these polymers with PEO or dextran were investigated with light scattering, and the microstructure of the emulsions was studied with confocal laser scanning microscopy. The effect of pH, polymer concentration, interfacial tension, and ionic strength on the stability was investigated and was found to be different for the three polymer types. The results suggest that stabilization of W/W emulsions by linear polymers requires that they contain both charged and hydrophobic units.

The effect was studied of adding both KCl and CaCl2 on gelation of solutions of ι-carrageenan, κ-carrageenan and mixtures of both types. The gel temperature (Tg) of ι-car was found to be determined by the CaCl2 concentration and Tg of κ-car by the KCl concentration. At a given salt concentration, ι-car was stiffest with pure CaCl2, but κ-car gels and mixed carrageenan gels were stiffer when both KCl and CaCl2 were present. Gelation of κ-car increased the turbidity of mixed carrageenan gels in the presence of KCl or CaCl2, but when both salts were present it led to a drop of the turbidity. In mixed salt, K+ induces formation of a homogeneous κ-car network that causes the mixed network to become more homogeneous. Rheological and structural properties of carrageenan gels can be tuned for a given polymer and salt concentration by adding both KCl and CaCl2 to κ-car/ι-car mixtures.