Films Stabilized Research Articles

Study of effect of dibenzoylmethane on thermal stability of PVC films stabilized with magnesium and zinc pentaerythritates

Static and dynamic thermal analysis of the destruction of PVC fi lms, as well as isothermal and non-isothermal thermogravimetric analysis (TGA) of PVC films stabilized with magnesium and zinc pentaerythritates with the addition of dibenzoylmethane as a synergistic additive were carried out.

Interfacial characteristics and foam stability: A microscopic perspective from molecular dynamics simulation

Foams play a pivotal role in diverse industrial and academic applications, yet their stability, particularly in relation to surfactants, remains inadequately understood at the microscopic level. This study undertakes a comprehensive modeling of water films stabilized by 15 surfactants, spanning 4 ion types of hydrophilic groups. We conducted a systematic comparison and correlation of key interfacial characteristics at different stages of rupture. Our findings reveal that the critical film thickness and interface tension are integral in characterizing foam stabilities near equilibrium (metastable state) and near rupture (critical state), respectively. Furthermore, we observed a positive correlation between the hydrophilicity of surfactant head groups and both the thickness of Gibbs dividing surface and the orderliness of interfacial surfactant molecules. These factors are crucial in maintaining film stability in both metastable and critical states. This work presents a quantitative framework to generalize various interfacial characteristics commonly employed in describing foam stability, which is poised to enhance the data-driven methodology for surfactant selection and design.

Polyphosphates as thermal stabilizers for poly(vinyl chloride)

Polyphosphates had been used as thermal stabilizers for polyvinylchloride (PVC). The thermal stability of PVC films stabilized with polyphosphates was verified by using weight loss method, Fourier transform infrared (FTIR) spectroscopy, thermal aging test, optical microscope and atomic force microscope. The outcomes demonstrated that mixing of polyphosphates with PVC can obviously enhance the stability time of PVC and improve the initial color of it. Furthermore, polyphosphates could considerably decrease the concentrations of forming double bonds within the PVC chemical structure and decrease weight loss. In addition, polyphosphate has an excellent ability to reduce the releasing of hydrochloric acid (HCl) molecules. Hence polyphosphates can replace the labile chlorine atoms within the chemical structure of PVC chains.

Thinning air–water films stabilized by bacterial particles

The ability of particles to stabilize liquid films has broad applications in many fields, such as drug delivery, biofuel catalysis, and crude-oil separation. The mechanism of particles to stabilize emulsions has been widely studied. However, how particles affect the stability of suspension films is still unclear. Here, the dynamics of bacterial particles on free liquid films during evaporation is obtained by direct microscopic observation. We find that the initial concentration of the bacterial solution affects the evolution of the shapes and stabilities of liquid films. The liquid film with a low bacterial concentration exhibits a drainage and rupture process similar to pure water, and bacteria would be evacuated during the evaporation of liquid film. However, when the bacterial concentration is high, bacteria form a single-layer array in the center of the film and greatly enhance the stability of the liquid film. We demonstrate that these two distinct film evaporation dynamics are caused by the difference in the lateral capillary force of the particles at different positions on the liquid film, which is not affected by the active motility of particle. Together, our research reveals the critical role of bacteria concentration in stabilizing suspension liquid film.

Studying demulsification mechanisms of water-in-crude oil emulsions using a modified thin liquid film technique

The thin liquid film (TLF) technique equipped with Scheludko-Exerowa cell has been demonstrated to be a valuable tool for studying stability of dispersed systems of soft matter such as emulsions and foams. Many industrial applications involve the addition of various chemical aids to obtain desired properties or resolve technical problems. One of the examples is the use of chemical demulsifiers to remove emulsified water from petroleum emulsions. To study the role of chemicals in this process, a TLF technique with a dosing system is required to add demulsifiers into already formed thin liquid films stabilized by interfacial layers formed from indigenous surface active molecules. Herein, we present a modified design of the Scheludko-Exerowa cell with a dosing mechanism which allows for addition of desired chemicals to the intervening organic liquid film that is already formed. The stability of the water-in-oil emulsions and the mechanisms of their chemical destabilization were studied by determining the thinning process of intervening thin oil films before and after dosing a controlled amount of demulsifiers into the film. Dosing of a biodegradable polymer demulsifier (EC300) into the intervening oil film converted a stable film formed by asphaltene-in-heptol solutions into an unstable film with lifetimes of less than 20 s. The observed change in the film drainage rate and stability is related to the disruption of asphaltene network formed at the oil-water interface by EC300 demulsifiers. The experiments with the modified TLF cell also revealed the overdosing effect of EC300 demulsifier, forming more stable films at high EC300 concentrations. A comparison of the experimental results between a dosed system and a premixed system confirmed the value of the modification in the current TLF technique to study the stabilization/destabilization processes of water-in-oil emulsions that mimic more closely the real petroleum emulsions. The modified TLF technique allows for a better understanding of the underlying demulsification mechanisms.

Novel carboxymethyl cellulose-polyvinyl alcohol blend films stabilized by Pickering emulsion incorporation method

The aim of this study was to investigate the possibility of increasing the antimicrobial and antioxidant properties of biodegradable active films stabilized via Pickering emulsions. The blend films were prepared from carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA), emulsified with oleic acid (OL) and incorporated with rosemary essential oil (REO). Formation of Pickering emulsion was confirmed by scanning electron microscopy (SEM), optical microscopy, mean droplet size and emulsion stability. Morphological, optical, physical, mechanical, thermal, antifungal and antioxidant properties of the films incorporated with different concentrations of REO (0.5, 1.5 and 3%) were determined. The results showed an increase in UV absorbance and elongation at break but, a decrease in tensile strength and thermal stability of the films. Interestingly, films containing REO exhibited considerable antioxidant and antimicrobial properties. In vitro microbial tests exhibited 100% fungal inhibition against Penicillium digitatum in the films containing 3% REO. In addition, no fungal growth were observed after 60days of storage at 25°C in bread slices were stored with active films incorporated with 3% REO, could attributed to the slow and regular release of REO caused by Pickering emulsions. The results of this study suggest that Pickering emulsion is a very promising method, which significantly affects antioxidant and antimicrobial activities of the films.

Interfacial properties, thin film stability and foam stability of casein micelle dispersions

Foam stability of casein micelle dispersions (CMDs) strongly depends on aggregate size. To elucidate the underlying mechanism, the role of interfacial and thin film properties was investigated. CMDs were prepared at 4°C and 20°C, designated as CMD4°C and CMD20°C. At equal protein concentrations, foam stability of CMD4°C (with casein micelle aggregates) was markedly higher than CMD20°C (without aggregates). Although the elastic modulus of CMD4°C was twice as that of CMD20°C at 0.005Hz, the protein adsorbed amount was slightly higher for CMD20°C than for CMD4°C, which indicated a slight difference in interfacial composition of the air/water interface. Non-linear surface dilatational rheology showed minor differences between mechanical properties of air/water interfaces stabilized by two CMDs. These differences in interfacial properties could not explain the large difference in foam stability between two CMDs. Thin film analysis showed that films made with CMD20°C drained to a more homogeneous film compared to films stabilized by CMD4°C. Large casein micelle aggregates trapped in the thin film of CMD4°C made the film more heterogeneous. The rupture time of thin films was significantly longer for CMD4°C (>1h) than for CMD20°C (<600s) at equal protein concentration. After homogenization, which broke down the aggregates, the thin films of CMD4°C became much more homogeneous, and both the rupture time of thin films and foam stability decreased significantly. In conclusion, the increased stability of foam prepared with CMD4°C appears to be the result of entrapment of casein micelle aggregates in the liquid films of the foam.

Role of Asphaltenes in Stabilizing Thin Liquid Emulsion Films

Drainage kinetics, thickness, and stability of water-in-oil thin liquid emulsion films obtained from asphaltenes, heavy oil (bitumen), and deasphalted heavy oil (maltenes) diluted in toluene are studied. The results show that asphaltenes stabilize thin organic liquid films at much lower concentrations than maltenes and bitumen. The drainage of thin organic liquid films containing asphaltenes is significantly slower than the drainage of the films containing maltenes and bitumen. The films stabilized by asphaltenes are much thicker (40-90 nm) than those stabilized by maltenes (∼10 nm). Such significant variation in the film properties points to different stabilization mechanisms of thin organic liquid films. Apparent aging effects, including gradual increase of film thickness, rigidity of oil/water interface, and formation of submicrometer size aggregates, were observed for thin organic liquid films containing asphaltenes. No aging effects were observed for films containing maltenes and bitumen in toluene. The increasing stability and lower drainage dynamics of asphaltene-containing thin liquid films are attributed to specific ability of asphaltenes to self-assemble and form 3D network in the film. The characteristic length of stable films is well beyond the size of single asphaltene molecules, nanoaggregates, or even clusters of nanoaggregates reported in the literature. Buildup of such 3D structure modifies the rheological properties of the liquid film to be non-Newtonian with yield stress (gel like). Formation of such network structure appears to be responsible for the slower drainage of thin asphaltenes in toluene liquid films. The yield stress of liquid film as small as ∼10(-2) Pa is sufficient to stop the drainage before the film reaches the critical thickness at which film rupture occurs.

Properties of emulsions and free emulsion (Aqueous) films stabilized with hexylamine-modified silica

The type and stability of emulsions, as well as the stability and thickness of free aqueous emulsion films stabilized with Aerosil-hexylamine mixtures, have been studied. The rheological characteristics (dynamic yield stress, elasticity modulae, and viscosity) have been measured for suspensions from which emulsions and films have been prepared. It has been shown that the properties of the films depend on the rheological properties of the suspensions.

Drainage and critical thickness of foam films stabilized by n-dodecyl-β-D-maltoside

The kinetic stability of foam films stabilized with n-dodecyl-β-D-maltoside (C12G2) in the presence of electrolyte (NaCl) has been investigated. The surface charge, type of the film and its electrostatic stabilisation were controlled by changing of the surfactant (from 0.01 to 1CMC) and electrolyte (0.1 and 0.001M) concentration. The drainage coefficient, critical thickness and life time to the critical state of films with different radii (0.05, 0.1 and 0.15mm) were measured interferometrically using a new procedure suggested by us for determination of the reflected light intensity from a video recording of the film evolution. It was found that the films from solutions of C12G2 up to CMC (even at CMC) with 0.001M NaCl are ``common (CF) electrostatically stabilized films'', while at the same C12G2 concentrations they were unstable films (UF) or stable Newtonian black films (NBF), when the added electrolyte was 0.1M. The values of film critical thickness obtained at a high electrolyte concentration were similar even when the concentration of C12G2 was varied from 0.1 to 1CMC. It means that in a wide surfactant concentration range the electrostatic disjoining pressure is screened and the experimental data of critical thickness are appropriate for theoretical analysis. The disjoining pressure acting at different steps of the film evolution was evaluated based on experimental data of the film drainage. A non-DLVO attractive force for films with non covered surfaces and Πel=0 was detected. It was expressed by a power law in the same form as the van-der-Waals force, which makes it possible to directly compare these two forces by means of the force constant K232 and the Hamaker constant. The non-DLVO force was found to be considerably stronger than the Lifshitz – van-der-Waals forces.The obtained new experimental data for critical thickness were compared with those calculated by us with different equations (Radoev–Sheludko–Manev, Vrij, and Coons). In some of these cases we used the experimentally obtained value of the drainage coefficient instead of the velocity of the film thinning, calculated theoretically. It was found that the calculated hcr are noticeably lower than experimentally measured ones. Good agreement between measured and calculated hcr was achieved with a non-DLVO attraction force taken into account, when the films were obtained from solutions with low (C12G2) and high (NaCl) concentrations.

Effect of aqueous phase structuring on the properties of model emulsion films stabilized with solid microsized particles

The thickness and stability of emulsion films stabilized with microsized silica particles are studied. The stabilization mechanism is shown to be realized via the formation of a thixotropic gel in a dispersion medium.

A Model for the Stability of Films Stabilized by Randomly Packed Spherical Particles

Particle stabilized thin films occur in a range of industrial applications where their properties affect the efficiency of the process concerned. However, due to their dynamic and unstable nature they are difficult to observe experimentally. As such, a tractable way of gaining insight into the fundamental aspects of this complicated system is to use computer simulations of particles at interfaces. This paper presents modeling results of the effect of nonuniform packing of spherical particles on the stability of thin liquid films. Surface Evolver was used to model cells containing up to 20 particles, randomly packed in a thin liquid film. The capillary pressure required to rupture the film for a specific combination of particle arrangement, packing density, and contact angle was identified. The data from the periodic, randomly packed models has been used to find a relationship between particle packing density, contact angle, and critical capillary pressure which is refined to a simple equation that depends on the film loading and contact angle of the particles it contains. The critical capillary pressure for film rupture obeys the same trends observed for particles in regular 2D and 3D packing arrangements. The absolute values of P*(crit), however, are consistently lower than those for regular packing. This is due to the irregular arrangement of the particles, which allows for larger areas of free film to exist, lowering the critical capillary pressure required to rupture the film.

Effect of the degree of grafting in hydrophobically modified inulin polymeric surfactants on the steric forces in foam and oil-in-water emulsion films

The interaction forces in foam and oil-in-water emulsion films stabilized by four inulin based graft copolymers with different degree of grafting of the dodecyl chains onto the inulin backbone were investigated. The adsorbing copolymers were found to form inulin-loops at the oil (air)/water interface, as the inulin-loop size decreased with increasing degree of grafting. Disjoining pressure isotherms (disjoining pressure, Π vs. equivalent film thickness, h w) were measured for the foam and emulsion films at sufficiently high NaCl concentration, whereby there is no electrostatic interaction in the films. Under these conditions, the stabilization of the films is due to interaction between the two layers of inulin-loops at oil (air)/water film interfaces. Transition to a stable Newton black film in the disjoining pressure isotherm for the emulsion films was observed for all the copolymers and the transition pressure significantly decreased for the films from the copolymer with the smallest inulin-loops. The stability against rupture of the foam films decreased with reducing inulin-loop size. The de Gennes’ scaling theory for interaction between polymer ‘brushes’ was fitted to the experimental data for the foam films with the inulin-loops layer thickness as a fitting parameter. The results were interpreted on the basis of inulin-loop size induced changes of the steric forces in the foam and emulsion films.

About mechanism of foam stabilization by solid particles

The main objective of the research was to study the properties of the foam and foam films stabilized by solid particles. The properties of the foam films were compared with the analogous ones of the emulsion films. The experiment provided the rheological characteristics of the dispersion medium. The research provided the study of the correlation of the contact angle, the shear stress, the surface tension and the radii of aggregates by the solid particles and the modifier concentration. The effect of the foam film stabilization by the solid particles is significant.

Unique Properties of Bubbles and Foam Films Stabilized by HFBII Hydrophobin

The HFBII hydrophobin is an amphiphilic protein that can irreversibly adsorb at the air/water interface. The formed protein monolayers can reach a state of two-dimensional elastic solid that exhibits a high mechanical strength as compared to adsorption layers of typical amphiphilic proteins. Bubbles formed in HFBII solutions preserve the nonspherical shape they had at the moment of solidification of their surfaces. The stirring of HFBII solutions leads to the formation of many bubbles of micrometer size. Measuring the electrophoretic mobility of such bubbles, the ζ-potential was determined. Upon compression, the HFBII monolayers form periodic wrinkles of wavelength 11.5 μm, which corresponds to bending elasticity k(c) = 1.1 × 10(-19) J. The wrinkled hydrophobin monolayers are close to a tension-free state, which prevents the Ostwald ripening and provides bubble longevity in HFBII stabilized foams. Films formed between two bubbles are studied by experiments in a capillary cell. In the absence of added electrolyte, the films are electrostatically stabilized. The appearance of protein aggregates is enhanced with the increase of the HFBII and electrolyte concentrations and at pH close to the isoelectric point. When the aggregate concentration is not too high (to block the film thinning), the films reach a state with 12 nm uniform thickness, which corresponds to two surface monolayers plus HFBII tetramers sandwiched between them. In water, the HFBII molecules can stick to each other not only by their hydrophobic moieties but also by their hydrophilic parts. The latter leads to the attachment of HFBII aggregates such as dimers, tetramers, and bigger ones to the interfacial adsorption monolayers, which provides additional stabilization of the liquid films.

Effects of Counterions and Co-ions on Foam Films Stabilized by Anionic Dodecyl Sulfate

The influence of counterions and co-ions on the stability and thickness of foam films stabilized by anionic dodecyl sulfate (DS(-)) has been studied in a thin film pressure balance. Particularly, the effect on the properties of foam films of (i) the counterions Li(+), Na(+), and Cs(+) of DS(-) and (ii) monovalent inorganic salts added to sodium dodecyl sulfate solutions is considered. Generally, addition of salt improved the stability of the foam films. As a second order, an increasing ionic size led to an increased adsorption, which in the case of cations gave thinner and less stable films and in the case of anions led to thicker and more stable films. Hence, an effect of anions was observed though the film surfaces were already negatively charged by the anionic DS(-), leading to the conclusion that adsorption of anions to the film surface is governed by ion specific rather than electrostatic interactions. At a fixed surfactant and varying salt concentration, a maximum in film thickness could be identified at a salt concentration well below the surfactant concentration. We anticipate that (i) at low salt concentration salt mainly affects the charging of a film interface, whereas (ii) at high salt concentration salt mainly affects the screening of the electrostatic repulsion between the two interfaces of the film.

Foam Films from Thermosensitive PNIPAM and SDS Solutions

Thin liquid foam films stabilized with the addition of a temperature-sensitive neutral polymer, poly(N-isopropylacrylamide) (PNIPAM), in the presence of varying amounts of an anionic surfactant, SDS, were investigated using the thin-film balance. Data were analyzed in light of new and previously reported neutron reflectivity data describing the adsorption behavior of PNIPAM/SDS mixtures at the single air-water interface. In the case of thin films prepared from pure polymer solutions, unexpectedly thick and stable films were observed, and increases in solution temperature or polymer molecular weight induce corresponding increases in the thin-film thickness. This behavior is attributed to a stabilization of the films by repulsive entropic forces between long dangling polymer tails adsorbed at the interfaces. The addition of SDS causes a striking decrease in the thin-film thickness that is very well correlated with the desorption of polymer chains from the interface resulting from polymer-surfactant interactions in the bulk. Upon SDS introduction, repulsive forces stabilizing the films vary from purely entropic forces for small amounts of surfactant to supramolecular oscillatory forces at high SDS concentrations, whereas a combination of electrostatic and entropic forces is expected in intermediate concentration regions. Properties of thin films made from PNIPAM and SDS are thus highly sensitive to parameters such as the polymer-surfactant ratio, temperature, and molecular weight, offering precise control of the thin-film thickness that could be used to tailor foam characteristics.

Black foam films stabilized with the mixtures of bovine serum albumin and nonionic surfactant Tween 80

Stable black films are prepared for the first time from aqueous solutions of Tween 80-bovine serum albumin mixtures. Conditions for their formation and stabilization factors are studied in a Scheludko-Exerowa cell by microinterferometry. It is found that such films are formed when saturated surface layers consist of surfactant-protein 1: 1 complexes, Tween 80 molecules, or their mixtures. A possible mechanism for the thinning of liquid layers and the stabilization of black films is discussed.

Interaction Forces in Thin Liquid Films Stabilized by Hydrophobically Modified Inulin Polymeric Surfactant. 2. Emulsion Films

The interaction forces in emulsion films stabilized using hydrophobically modified inulin (INUTEC SP1) were investigated by measuring the disjoining pressure of a microscopic horizontal film between two macroscopic emulsion drops of isoparaffinic oil (Isopar M). A special measuring cell was used for this purpose whereby the disjoining pressure Pi was measured as a function of the equivalent film thickness hw. The latter was determined using an interferometric method. In this way Pi-hw curves were established at a constant INUTEC SP1 concentration of 2x10(-5) mol.dm-3 and at various NaCl concentrations. At a constant disjoining pressure of 36 Pa, a constant temperature of 22 degrees C, and a film radius of 100 microm, hw decreased with an increase in the NaCl concentration, Cel, and reached a constant value of 11 nm at Cel=5x10(-2) mol.dm-3. This reduction in film thickness is due to the compression of the electrical double layer, and at the above critical NaCl concentration any electrostatic repulsion is removed and only steric interaction remains. This critical electrolyte concentration represents the transition from electrostatic to steric interaction. At a NaCl concentration of 2x10(-4) mol.dm-3 the Pi-hw isotherms showed a gradual decrease in hw with an increase in capillary pressure, after which there was a jump in hw from approximately 30 to approximately 7.2 nm when Pi reached a high value of 2-5.5 kPa. This jump is due to the formation of a Newton black film (NBF), giving a layer thickness of the polyfructose loops of approximately 3.6 nm. The film thickness did not change further when the pressure reached 45 kPa, indicating the high stability of the film. Pi-hw isotherms were obtained at various NaCl concentrations, namely, 5x10(-2), 5x10(-1), 1.0, and 2.0 mol.dm-3. The initial thicknesses are within the range 9-11 nm, after which a transition zone starts, corresponding to a pressure of about 0.5 kPa. In this zone all films transform to an NBF with a jump, after which the thickness remains constant with a further increase in the disjoining pressure up to 45 kPa, with no film rupture. This indicates the very high stability of the NBF in the presence of high electrolyte concentrations. The high emulsion film stability (due to strong steric repulsions between the strongly hydrated loops of polyfructose) is correlated with the bulk emulsion stability.

Foam Films Stabilized with Dodecyl Maltoside. 2. Film Stability and Gas Permeability

The gas permeability and stability of foam films stabilized by n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) were determined. The permeability coefficient (K, cm/s) and the mean film lifetime were measured as a function of the surfactant concentration. The films are less permeable than those stabilized by other surfactants at comparable conditions. The permeability coefficient decreases with increasing surfactant concentration. It does not show a remarkable dependence on the salt concentration. Stable Newton black foam films (NBFs) are formed above a surfactant concentration of 3.9 x 10(-)(6) M beta-C(12)G(2) in the presence of 0.2 M NaCl. The theory of nucleation hole formation in NBFs was applied to describe the observed dependencies of the permeability and film stability on the surfactant concentration. The theory gave satisfactory relation to the experiment.