High Polyelectrolyte Concentration Research Articles

Counterion-binding and related phenomena in sodium alginate-sodium chloride-water ternary systems: A conductometric study

Counterion-binding and related phenomena in aqueous solution of the naturally-occurring anionic polyelectrolyte sodium alginate have been explored in absence as well as in presence of sodium chloride using electrical conductivity as the probe. In particular, the variations of the counterion-binding behavior as functions of polyelectrolyte concentration, added electrolyte concentration, and temperature were investigated. A phenomenological treatment of the data which considered the additivity of salt and polyelectrolyte conductivities taking into account the Debye-Hückel interactions using Manning's theoretical expressions for self-diffusion was performed. The results indicated a marked departure from additivity. The data were, therefore, analyzed on the basis of the de Gennes scaling model for the configuration of a polyion chain in semidilute solutions. Counterion-dissociation reached its maximum in absence of the added salt, whereas counterion-binding reached its maximum in presence of the highest amount of the added salt. In moderately saline media, however, counterion-binding was initially found to increase with polyelectrolyte concentration which then gradually leveled off indicating confinement of counterions within the domains of polyion chains at higher polyelectrolyte concentrations. Results indicated the existence of alginate ions as flexible chains in aqueous solutions. A subtle balance of the influences of the effective monomer charge and the effective monomer size played a pivotal role the polyion mobility. Possible conformational changes of the polyion chains caused by dilution led to changes in hydrodynamic resistance in the investigated solutions. The results also provided important insight as to the influence of the alterations of the hydration behavior of the counterions and the relative permittivity of the media on counterion-binding in the investigated systems.

Solution properties of star polyelectrolytes having a moderate number of arms.

We investigate polyelectrolyte stars having a moderate number of arms by molecular dynamics simulations of a coarse-grained model over a range of polyelectrolyte concentrations, where both the counter-ions and solvent are treated explicitly. This class of polymeric materials is found to exhibit rather distinct static and dynamic properties from linear and highly branched star polyelectrolyte solutions emphasized in past studies. Moderately branched polymers are particle-like in many of their properties, while at the same time they exhibit large fluctuations in size and shape as in the case of linear chain polymers. Correspondingly, these fluctuations suppress crystallization at high polymer concentrations, leading apparently to an amorphous rather than crystalline solid state at high polyelectrolyte concentrations. We quantify the onset of this transition by measuring the polymer size and shape fluctuations of our model star polyelectrolytes and the static and dynamic structure factor of these solutions over a wide range of polyelectrolyte concentration. Our findings for star polyelectrolytes are similar to those of polymer-grafted nanoparticles having a moderate grafting density, which is natural given the soft and highly deformable nature of both of these "particles."

Depletion and double layer forces acting between charged particles in solutions of like-charged polyelectrolytes and monovalent salts.

Interaction forces between silica particles were measured in aqueous solutions of the sodium salt of poly(styrene sulphonate) (PSS) and NaCl using the colloidal probe technique based on an atomic force microscope (AFM). The observed forces can be rationalized through a superposition of damped oscillatory forces and double layer forces quantitatively. The double layer forces are modeled using Poisson-Boltzmann (PB) theory for a mixture of a monovalent symmetric electrolyte and a highly asymmetric electrolyte, whereby the multivalent coions represent the polyelectrolyte chains. The effective charge of the polyelectrolyte is found to be smaller than the bare number of charged groups residing on one polyelectrolyte molecule. This effect can be explained by counterion condensation. The interplay between depletion and double layer forces can be further used to predict the phase of the depletion force oscillations. However, this picture holds only at not too elevated concentrations of the polyelectrolyte and salt. At higher salt concentrations, attractive van der Waals forces become important, while at higher polyelectrolyte concentrations, the macromolecules adsorb onto the like-charged silica interface.

Polyelectrolyte adsorption, interparticle forces, and colloidal aggregation

This review summarizes the current understanding of adsorption of polyelectrolytes to oppositely charged solid substrates, the resulting interaction forces between such substrates, and consequences for colloidal particle aggregation. The following conclusions can be reached based on experimental findings. Polyelectrolytes adsorb to oppositely charged solid substrates irreversibly up to saturation, whereby loose and thin monolayers are formed. The adsorbed polyelectrolytes normally carry a substantial amount of charge, which leads to a charge reversal. Frequently, the adsorbed films are laterally heterogeneous. With increasing salt levels, the adsorbed mass increases leading to thicker and more homogeneous films. Interaction forces between surfaces coated with saturated polyelectrolyte layers are governed at low salt levels by repulsive electric double layer interactions, and particle suspensions are stable under these conditions. At appropriately high salt levels, the forces become attractive, principally due to van der Waals interactions, but eventually also through other forces, and suspensions become unstable. This situation can be rationalized with the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). Due to the irreversible nature of the adsorption process, stable unsaturated layers form in colloidal particle suspensions at lower polyelectrolyte doses. An unsaturated polyelectrolyte layer can neutralize the overall particle surface charge. Away from the charge reversal point, electric double layer forces are dominant and particle suspensions are stable. As the charge reversal point is approached, attractive van der Waals forces become important, and particle suspensions become unstable. This behaviour is again in line with the DLVO theory, which may even apply quantitatively, provided the polyelectrolyte films are sufficiently laterally homogeneous. For heterogeneous films, additional attractive patch-charge interactions may become important. Depletion interactions may also lead to attractive forces and suspension destabilization, but such interactions become important only at high polyelectrolyte concentrations.

Response of Adsorbed Polyelectrolyte Monolayers to Changes in Solution Composition

Reflectometry and quartz crystal microbalance are used to study the response of adsorbed polyelectrolyte monolayers to solutions of variable composition. These techniques respectively yield the dry and wet masses of the adsorbed layer, and by combing these results, one obtains the water content and the thickness of the polyelectrolyte films. The systems investigated are films of adsorbed poly(allyl amine) (PAH) and poly-L-lysine (PLL) on silica and films of poly(styrene sulfonate) (PSS) on amino-functionalized silica. When such films are adsorbed from concentrated polyelectrolyte solutions containing high levels of salt, they are found to swell reversibly up to a factor of 2 when incubated in solutions of low salt. This swelling is attributed to the strengthening of repulsive electrostatic interactions between the adsorbed polyelectrolyte chains. PAH films may also swell upon decrease of pH, and collapse upon a pH increase. This transition shows a marked hysteresis and can be rationalized by the competition of electrostatic repulsions between the chains and their attraction to the surface. The presently observed swelling phenomena are caused by a collective process driven by the electrostatic repulsion between the densely adsorbed polyelectrolyte chains. Such responsive layers are only obtained by adsorption from high polyelectrolyte and salt concentrations. Layers absorbed at low polyelectrolyte and salt concentrations show only minor swelling effects, since the adsorbed polyelectrolytes layers are dilute and the adsorbed polyelectrolyte chains interact only weakly.

Development of novel cationic chitosan-and anionic alginate-coated poly(D,L-lactide-co-glycolide) nanoparticles for controlled release and light protection of resveratrol.

BackgroundResveratrol, like other natural polyphenols, is an extremely photosensitive compound with low chemical stability, which limits the therapeutic application of its beneficial effects. The development of innovative formulation strategies, able to overcome physicochemical and pharmacokinetic limitations of this compound, may be achieved via suitable carriers able to associate controlled release and protection. In this context, nanotechnology is proving to be a powerful strategy. In this study, we developed novel cationic chitosan (CS)- and anionic alginate (Alg)-coated poly(d,l-lactide-co-glycolide) nanoparticles (NPs) loaded with the bioactive polyphenolic trans-(E)-resveratrol (RSV) for biomedical applications.MethodsNPs were prepared by the nanoprecipitation method and characterized in terms of morphology, size and zeta potential, encapsulation efficiency, Raman spectroscopy, swelling properties, differential scanning calorimetry, and in vitro release studies. The protective effect of the nanosystems under the light-stressed RSV and long-term stability were investigated.ResultsNPs turned out to be spherical in shape, with size ranging from 135 to about 580 nm, depending on the composition and the amount of polyelectrolytes, while the encapsulation efficiencies increased from 8% of uncoated poly(d,l-lactide-co-glycolide) (PLGA) to 23% and 32% of Alg- and CS-coated PLGA NPs, respectively. All nanocarriers are characterized by a biphasic release pattern, and more effective controlled release rates are obtained for NPs formulated with higher polyelectrolyte concentrations. Stability studies revealed that encapsulation provides significant protection against light-exposure degradation, by reducing the trans–cis photoisomerization reaction. Moreover, the nanosystems are able to prevent the degradation of trans isoform and the leakage of RSV from the carrier for a period of 6 months.ConclusionOur findings indicated that the newly developed CS- and Alg-coated PLGA NPs are suitable to be used for the delivery of bioactive RSV. The encapsulation of RSV into optimized polymeric NPs provides improved drug loading, effective controlled release, and protection against light-exposure degradation, thus opening new perspectives for the delivery of bioactive related phytochemicals to be used for (nano)chemoprevention/chemotherapy.

No Charge Reversal at Foam Film Surfaces after Addition of Oppositely Charged Polyelectrolytes?

The present work deals with control of the stability of ionic surfactant (tetradecyl trimethyl ammonium bromide) foam films by the addition of oppositely charged polyelectrolytes. In the two cases of low and high polyelectrolyte concentrations, a common black film is formed. This is due to an electrostatic repulsion (in the latter case, according to the hitherto assumption) caused by a charge reversal at film surfaces at high polyelectrolyte concentration. But what happens around the nominal isoelectric point (IEP), where the net charge of the whole film is close to zero? Is a Newton black film formed or does the film break? Disjoining pressure isotherms show a strong reduction in stability close to the IEP. The comparison between surface tension and elasticity measurements and disjoining pressure isotherms leads to a surprising conclusion: The stability of foam films seems not to be dominated by the net charge of the polyelectrolyte/surfactant complexes at the surface, which was the former hypothesis, but by the overall net charge of the film.

Real-Time Observation of Polyelectrolyte-Induced Binding of Charged Bilayers

We present real-time observations by confocal microscopy of the dynamic behavior of multilamellar vesicles (MLVs), composed of charged synthetic lipids, when put in contact with oppositely charged polyelectrolyte (PE) molecules. We find that the MLVs exhibit astonishing morphological transitions, which result from the discrete and progressive binding of the charged bilayers induced by a high PE concentration gradient. Our physical picture is confirmed by quantitative measurements of the fluorescence intensity as the bilayers bind to each other. The shape transitions lead eventually to the spontaneous formation of hollow capsules, whose thick walls are composed of lipid multilayers condensed with PE molecules. This class of objects may have some (bio)technological applications.

Grand canonical investigations of prototypical polyelectrolyte models beyond the mean field level of approximation

Understanding the chemistry and physics of polyelectrolyte systems challenges scientists from a wide spectrum of research areas, ranging from colloidal science to biology. However, despite significant progress in the past decades, the calculation of large open polyelectrolyte systems on a detailed level remains computationally expensive, due to the highly polymeric nature of the macromolecules and/or long-range character of the intermonomer interactions. To cope with these difficulties, field-theoretic methodologies based on the mean-field approximation have emerged recently and have proven to provide useful results in the regime of high polyelectrolyte concentration. In this paper we present applications of a low-cost field-theoretic calculation approach based on the method of Gaussian equivalent representation, which has recently been proven useful for delivering accurate results in case of polymer solutions beyond the mean field level of approximation. Here we demonstrate its effectiveness on the example of a Gaussian effective potential, mimicking the effective interactions between weakly charged polyelectrolyte coils, and a screened Coulomb model, describing the effective intermonomer interactions of Debye-Hückel chains. Moreover, we show that the approach opens perspectives to extend the range of applicability of the grand canonical ensemble to dense liquid and solid phases of more sophisticated polyelectrolyte models. Finally, we demonstrate that our approach is also much more reliable for determining the phase boundaries of these models than conventional mean field and grand canonical Monte Carlo approaches.

Adsorption of cationic polyelectrolyte at the solid/liquid interface and dispersion of nanosized silica in water

Adsorption of cationic polyelectrolyte, a homopolymer of maleimide propyl trimethylammonium chloride (MPTMAC), on silica nanoparticles from aqueous solution was studied. The adsorbed amount of MPTMAC and the adsorption layer thickness from solutions of different pH, polyelectrolyte concentration, salt type, and salt concentration were measured. The adsorbed amount exhibited a maximum as a function of the electrolyte concentration. The onset of the decline in the adsorbed amount depended on the type of counterions. The thickness of the adsorption layer increased gradually with increased of electrolyte concentration and leveled off at high electrolyte concentration. The enhanced adsorption in the presence of Na 2SO 4 can be explained by the bivalent SO 2− 4 causing a better shielding effect. With increasing pH the adsorbed amount of MPTMAC increased, whereas the thickness of an adsorbed layer of MPTMAC decreased. At low polyelectrolyte concentrations unstable silica suspensions were observed from a stability test. At high polyelectrolyte concentrations the higher particle coverage caused electrosteric stabilization of the dispersion. However, further increase in MPTMAC concentration after saturated adsorption would flocculate the dispersed system. At low pH, MPTMAC tending to create a loops or tails conformation stabilized the suspension.

Adhesive forces between adsorbed anionic polyelectrolyte layers in high ionic strength solutions

Direct interaction forces between a hematite surface and a silica sphere in the presence of high-molecular weight anionic polyelectrolytes, sodium polyacrylate (NaPAA), an acrylamide/acrylate copolymer, an hydroxamate copolymer and starch have been measured using the atomic force microscope (AFM). In aqueous solution at high pH, the interaction between the bare oxide surfaces is well described by DLVO theory and is dominated by a repulsive electrostatic force. Addition of a high-molecular weight polyelectrolyte did not significantly alter the forces on approach. There was no sign of steric repulsion prior to the distance of closest approach. Therefore, it appears that these molecules are adsorbed to the surface in a flat conformation. On separation, the adhesive force between the surfaces was observed to change in magnitude as a function of polyelectrolyte type and concentration. Elastic minima that were found to extend to large surface separations were observed to occur on separation of the surfaces for all polyelectrolytes studied. At high-polyelectrolyte concentration, the interaction on both approach and separation of the surfaces was repulsive. Specific interaction of the functional groups with the metal ion of the oxide surface appears to be responsible for the differences in the adhesive force. Hydroxamate and starch molecules were found to produce the strongest and most extended adhesive forces.

Wetting Films of the Aqueous Cationic Polyelectrolyte Solutions on Quartz

It was shown that the stability of the wetting films of aqueous cationic polyelectrolyte solutions on the flat quartz surface depends on solution concentration. At a low concentration, the films are stable owing to the electrostatic repulsive forces. At a high polyelectrolyte concentration, the films are unstable due to the hydrophobization of quartz and the appearance of the hydrophobic attractive forces in the films. In the intermediate concentration range, the films are metastable and their lifetime depends upon the competition between the electrostatic repulsive and hydrophobic attractive forces. Thus, the concentration of cationic polyelectrolyte substantially affects the wetting conditions of the quartz surface. This conclusion can also be extended to other solid surfaces negatively charged in aqueous solutions, which is inherent to the majority of natural materials.

Dynamics, Site Binding, and Distribution of Counterions in Polyelectrolyte Solutions Studied by Electron Paramagnetic Resonance Spectroscopy

A microscopic picture of counterion condensation in liquid and glassy frozen solutions of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) is derived from data obtained by a combination of continuous-wave and pulse electron paramagnetic resonance techniques. The condensation of such divalent anions to the polyelectrolyte chain in the presence of a large excess of polyelectrolyte and monovalent counterions can be described by a dynamic equilibrium between specifically site-bound and nonspecifically territorially bound counterions with exchange between the two states proceeding on time scales significantly shorter than 1 ns. No free divalent counterions are detected. The dynamic electrostatic attachment is manifest in an axially symmetric rotational diffusion tensor, with the unique axis of fast rotation corresponding to the electrostatic bond between one sulfonate group of Fremy's salt and the quaternary ammonium group of the PDADMAC repeat unit. A distance of 0.43 nm between the electron spin and the 14N nucleus of the ammonium group is found by electron spin−echo envelope modulation spectroscopy, suggesting that the site-bound state corresponds to contact ion pairs. The same experiment provides an estimate of 20% site-bound and 80% territorially bound divalent counterions in glycerol/water glassy frozen solution. Pulse electron−electron double resonance measurements show that on nanometer length scales the counterions are virtually homogeneously distributed in three dimensions for high polyelectrolyte concentration but linearly distributed along stretched chains at low polyelectrolyte concentrations where no overlap of chains is expected.

In vitro mineralization of gelatin-polyacrylic acid complex matrices

Gelatin-polyacrylic acid (gel-PAA) matrices were obtained by slow diffusion of polyacrylic acid into gelatin gels. The matrices were submitted to uniaxial stretching, which induces a preferential orientation of the collagen molecules, and used as biomimetic substrates for the nucleation of hydroxyapatite from simulated body fluid (SBF). The relative amount of hydroxyapatite deposited from 1.5SBF increases as a function of polyelectrolyte content in the matrices, up to about 30 wt%. In the absence of PAA, the inorganic phase is laid down on the surface of the gelatin matrices as hemispherical aggregates. At variance, hydroxyapatite deposition in the gel-PAA composite matrices at relatively low PAA content occurs preferentially in the spaces between the layers on the surface of the matrices and displays a tablet-like morphology. At high polyelectrolyte concentration, an almost uniform layer of hydroxyapatite covers the whole surface of the matrices. The preferential orientation of the (002) hydroxyapatite reflection indicates a close relationship between the inorganic crystals and the collagen molecules.

Polyelectrolyte adsorption at the solid/liquid interface: Interaction forces and stability

The forces between negatively charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2(methacryloyloxy)ethyltrimethylammonium chloride have been investigated using an atomic force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering experiments. The adsorbed amount of polyelectrolyte and adsorbed layer conformation at the solid/liquid interface were found to be strongly dependent on the polymer concentration from which initial adsorption takes place. At low polyelectrolyte concentrations unstable silica suspensions were observed from stability tests; light scattering experiments indicate a large aggregate size under equivalent conditions. The adsorbed amount was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a flat conformation. At high polyelectrolyte concentrations, an increase in the adsorbed amount was observed which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.

Light Scattering on Semidilute Polyelectrolyte Solutions: Ionic Strength and Polyelectrolyte Concentration Dependence

Semidilute solutions of the flexible highly charged polyelectrolyte sodium poly(styrenesulfonate) have been studied with dynamic light scattering over a wide polyelectrolyte concentration range. To perform a systematic study of the slow mode filters with a relatively large pore size of 0.65 μm were used. Double-exponential correlation functions were measured. At the lowest polyelectrolyte concentrations the correlation functions became single exponential. The apparent fast and slow diffusion coefficients were determined for three ionic strengths and one molar mass. The fast diffusion coefficient depends on the polyelectrolyte concentration and on the ionic strength but becomes polyelectrolyte concentration independent at a certain high polyelectrolyte concentration. This transition concentration depends on the ionic strength. In the semidilute regime the fast diffusion coefficient follows a power law, with a power law exponent that depends on the ionic strength. The slow diffusion coefficient depends on t...

Dynamics of polyelectrolyte solutions

We have derived a theory of dynamics of dilute and semidilute polyelectrolyte solutions by explicitly considering triple screening associated with electrostatic, excluded volume, and hydrodynamic interactions. The three screening lengths corresponding to these interactions are coupled among themselves differently at different polyelectrolyte (c) and salt (cs) concentrations. We have derived expressions for the self-translational diffusion coefficient D, electrophoretic mobility μ, coupled diffusion coefficient Df, and the viscosity η of the solution by accounting for the coupling between electrostatics and hydrodynamics. In infinitely dilute solutions, we show that Zimm dynamics is applicable and D∼1/Rg, μ∼M0, and η−η0∼cRg3/M for all values of cs, where Rg and M, respectively, are the radius of gyration and molecular weight of the polyelectrolyte and η0 is the solvent viscosity. Df is derived to be M0 at low cs and to approach D at higher cs. As the polyelectrolyte concentration is increased to semidilute conditions, excluded volume and hydrodynamic interactions get progressively screened. In the Rouse regime, where hydrodynamic interaction is screened and entanglement effects are weak, we have derived expressions for the various transport coefficients. In this regime, at low cs, D∼c0M−1, Df∼c0M0, μ∼c0M0, and η−η0∼cM; at high cs, D∼c−1/2M−1, Df∼c/(c+2cs), μ∼c−1/2M0, and η−η0∼c5/4M. The crossover formulas between these asymptotic laws with numerical prefactors are derived. We have demonstrated that the Rouse law applicable to semidilute unentangled polyelectrolyte solutions at low cs is the empirical Fuoss law. The slow diffusion coefficient observed in light scattering studies of polyelectrolyte solutions is attributed to the emergence of an effective attractive interaction between similarly charged segments of topologically correlated objects such as polyelectrolytes at sufficiently high c and low cs. The consequences of entanglements at very high polyelectrolyte concentrations are briefly mentioned. The theoretical formulas derived here are in qualitative agreement with all known phenomenological results of polyelectrolyte dynamics, and some fresh predictions are made.

Computer simulation of semi-dilute polyelectrolyte solutions

We use Monte Carlo simulation methods to study the conformational properties of flexible partially ionized polyelectrolyte chains and the ordering of the polyelectrolyte chains, for polyelectrolyte concentrations where chain—chain interactions start to become important. In this model the ionic and solvent degrees of freedom are frozen and the charges on the polyelectrolyte chains interact via a screened Coulomb interaction of Debye—Hückel form. Our simulations are restricted to polyelectrolyte ionizations and added-salt concentrations where we know that the screening model is not an unreasonable approximation. For semi-dilute polyelectrolyte concentrations we observe some local anisotropy with some alignment between the nearest polyion chains. This alignment only exists for small polyion separations and generally the chains are isotropically distributed and oriented with respect to one another. The observed interchain correlation at small separation distances disappears for dilute polyelectrolyte concentrations below the overlap threshold concentration c*, and also for high polyelectrolyte concentration where interactions between polyions beyond the nearest neighbours begin to become important. For polyelectrolyte concentrations above this value the results for the two added salt concentrations of 0.1 and 0.01 mol dm −3 are almost identical.

Phase separation of polyelectrolyte/nonionic polymer systems in aqueous solution: effects of salt and charge density

Aqueous systems of two soluble polymers often phase separate. The phase separation and the composition of each phase strongly depend on the nature of polymers and the existence of specific interactions between them. In this work we study the phase separation of poly(sodium acrylate)/nonionic polymer systems in aqueous solution. It is found that the phase diagrams are very asymmetrical, phase separation occurs mainly for mixtures of high polyelectrolyte concentration. The asymmetry and the position of the cloud point curve in the ternary diagram highly depends on the salt concentration (NaCl) in the mixture. This behaviour is ascribed to the presence of polyelectrolyte counterions. The phase diagram also depends on the neutralization degree (α) of poly(sodium acrylate). The compatibility of the mixture increases when the neutralization degree decreases and for values of α < 20% complex coacervation occurs.

An Investigation into Capillary Hydrodynamic Chromatography

AbstractNow fifteen years ago, Small and co‐workers [1, 2], introduced Hydrodynamic Chromatography (HDC) as a simple method for the sizing of submicron particles. The particles are fractionated when flowing through a packed column of uniform impermeable beads and emerge in order of decreasing diameter. Noel et al. [4] and Mullins and Orr [3] reported a variant of the technique using a long open capillary tube which has been called Capillary Hydrodynamic Chromatography (CHDC).Recently Brough et al. [5] were able to expand the size range of CHDC down to particle diameters of 0.07 μm and showed that the technique is also able to achieve fractionation in organic solvents.In an attempt to obtain the same particle size analysis range with CHDC as with the recently commercialised HDC (Micromeritics), we investigated the CHDC performance in very small capillaries (0.1 and 0.15 mm). The emphasis of the study has been led on the nature and the concentration of the eluent composition. Indeed an effective reduction in capillary diameter can be obtained if one uses a commercial block copolymer as eluent material. Adsorption of the block copolymer both on the capillary wall and the particles gives rise to a sterical barrier which reduces further the effective capillary diameter and enhances the resolution of the column towards smaller particle sizes.In our view CHDC represents more possibilities in analysing real particle systems, i. e. dispersions with relatively high polymer or polyelectrolyte concentrations. For such systems classical HDC results mostly in the clogging of the column. A series of dispersions and emulsions in concentrated gelatine have been analysed and the P. S. are compared with the results obtained by LCS.