Newton Black Films Research Articles

Bubble wall confinement-driven molecular assembly toward sub-12 nm and beyond precision patterning.

Patterning is attractive for nanofabrication, electron devices, and bioengineering. However, achieving the molecular-scale patterns to meet the demands of these fields is challenging. Here, we propose a bubble-template molecular printing concept by introducing the ultrathin liquid film of bubble walls to confine the self-assembly of molecules and achieve ultrahigh-precision assembly up to 12nanometers corresponding to the critical point toward the Newton black film limit. The disjoining pressure describing the intermolecular interaction could predict the highest precision effectively. The symmetric molecules exhibit better reconfiguration capacity and smaller preaggregates than the asymmetric ones, which are helpful in stabilizing the drainage of foam films and construct high-precision patterns. Our results confirm the robustness of the bubble template to prepare molecular-scale patterns, verify the criticality of molecular symmetry to obtain the ultimate precision, and predict the application potential of high-precision organic patterns in hierarchical self-assembly and high-sensitivity sensors.

Microscopic Depictions of Vanishing Shampoo Foam Examined by Time-of-Flight Small-Angle Neutron Scattering

A novel surfactant of N–dodecanoyl–N–(2-hydroxyethyl)–β–alanine (coded as C12–EtOH–βAla) was synthesized by modifying the methyl group of N–dodecanoyl–N–methyl–β–alanine (coded as C12–Me–βAla). Amino-acid-type surfactants (C12–EtOH–βAla and C12–Me–βAla) are more healthy and environmentally friendly compared to sodium dodecyl sulfate (SDS). To investigate the microstructures of these new surfactants, we employed a method of time-of-flight small-angle neutron scattering (TOF SANS) at a pulsed neutron source, Tokai Japan (J–PARC). The advances in TOF SANS enable simultaneous multiscale observations without changing the detector positions, which is usually necessary for SANS at the reactor or small-angle X-ray scattering. We performed in situ and real-time observations of microstructures of collapsing shampoo foam covering over a wide range of length scales from 100 to 0.1 nm. After starting an air pump, we obtained time-resolved SANS from smaller wave number, small-angle scattering attributed to (1) a single bimolecular layer with a disk shape, (2) micelles in a bimolecular layer, and (3) incoherent scattering due to the hydrogen atoms of surfactants. The micelle in the foam film was the same size as the micelle found in the solution before foaming. The film thickness (~27 nm) was stable for a long time (<3600 s), and we simultaneously found a Newton black film of 6 nm thickness at a long time limit (~1000 s). The incoherent scattering obtained with different contrasts using protonated and deuterated water was crucial to determining the water content in the foam film, which was about 10~5 wt%.

When Bulk Matters: Disentanglement of the Role of Polyelectrolyte/Surfactant Complexes at Surfaces and in the Bulk of Foam Films

Foam films display exciting systems as on one hand they dictate the performance of macroscopic foams and on the other hand they allow studies of surface forces. With regard to surface forces, we attempt to disentangle the effect of the foam film surfaces and the foam film bulk. For that, we study the influence of salt (LiBr) on foam films formed by mixtures of oppositely charged polyelectrolyte and surfactant: anionic monosulfonated polyphenylene sulfone (sPSO2-220) and cationic tetradecyltrimethylammonium bromide (C14TAB). Adding a small amount of salt (≤10-3 M) decreases the foam film stability due to a weakened electrostatic net repulsion. In contrast, a large amount of salt (10-2 M) unexpectedly increases the foam film stability. Disjoining pressure isotherms reveal that the increased stability is due to an additional steric stabilization, which is attributed to sPSO2-220/C14TAB complexes in the film bulk. These bulk complexes also contribute to the measured apparent surface potential between the two air/water interfaces. We find, for the first time, the formation of Newton black films for mixtures of anionic polyelectrolytes and cationic surfactants.

Untangling effects of proteins as stabilizers for foam films

Foam film’s properties have a high impact on the properties of the macroscopic foams. This work focusses on protein stabilized foam films. The direct comparison of three different proteins with a concentration normalized to the protein surface enables to distinguish between electrostatic, steric and network stabilization effects. In order to untangle those effects, we study and compare two globular proteins (β − lactoglobulin, BLG, and bovine serum albumin, BSA) and a disordered, flexible protein (whole casein, CN) at low ionic strengths with varying solution pH. Image intensity measurement as a recently developed image analysis method in this field allows to record spatially resolved disjoining pressure isotherms in a Thin Film Pressure Balance (TFPB). This reveals insights into the structure formation in inhomogeneous protein films. As a novel method we introduce tracking inhomogeneities (features) which enables the measurement of interfacial mobility and stiffness of foam films. Around the isoelectric point (IEP), Newton Black Films (NBF) form which are stable for the globular proteins while they are unstable for the disordered flexible one. This difference in film stability is explained by different characteristics of the network structures which is supported by findings in the bulk and at the surface of the respective protein solutions.

A moving eulerian-lagrangian particle method for thin film and foam simulation

We present the Moving Eulerian-Lagrangian Particles (MELP), a novel mesh-free method for simulating incompressible fluid on thin films and foams. Employing a bi-layer particle structure, MELP jointly simulates detailed, vigorous flow and large surface deformation at high stability and efficiency. In addition, we design multi-MELP: a mechanism that facilitates the physically-based interaction between multiple MELP systems, to simulate bubble clusters and foams with non-manifold topological evolution. We showcase the efficacy of our method with a broad range of challenging thin film phenomena, including the Rayleigh-Taylor instability across double-bubbles, foam fragmentation with rim surface tension, recovery of the Plateau borders, Newton black films, as well as cyclones on bubble clusters.

Chemical potential and free energy of nanoconfined water in Newton black films

In this work we investigate possible approximations to the free energy and chemical potential of water within a Newton black film as a natural nanoconfinement. As a first step we explore the different approximations in a sample of 500 water molecules (bulk water), finding that the overlapping distribution method is the more accurate. For the Newton black film we also calculate the free energy profile of the water molecules along the bilayer normal. We obtain that depending on the position of the water molecule inside the bilayer, the excess chemical potential is lower than that of bulk water, suggesting that a water molecule might be more stable inside the Newton black film than in bulk. A charged semiflexible amphiphilic model and the TIP5P model of water are used in our simulations.

Nanometer-Thick Newton Black Film for Selective Formaldehyde Gas Detection.

A fluorescence spectroscopic assay using Newton black film (NBF) for sensitive and selective detection of gaseous formaldehyde at room temperature is reported. The method relies on the Hantzsch reaction of formaldehyde with ammonium citrate and acetylacetone, plus a combination of the large surface area-to-volume ratio (5 × 108 m-1) and efficient uptake of gas by the nanometer-thick aqueous core of NBF. The assay has a limit of detection (LOD) of 4 ppb, a linear signal-to-concentration correlation up to 300 ppb of HCHO gas in the air, and a nonlinear monotonic increasing correlation in the range of 300 ppb to 1.2 ppm. It is unaffected by relevant analytes such as acetaldehyde, benzaldehyde, acetone, and propionaldehyde. We also demonstrate the sensing of formaldehyde outgassing from a plywood sample using this method and the results agree with the factory specifications.

Surface Interaction of Nanoscale Water Film with SDS from Computational Simulation and Film Thermodynamics

Foam systems have been attracting extensive attention due to their importance in a variety of applications, e.g., in the cleaning industry, and in bubble flotation. In the context of flotation chemistry, flotation performance is strongly affected by bubble coalescence, which in turn relies significantly on the surface forces upon the liquid film between bubbles. Conventionally, unusual short-range strongly repulsive surface interactions for Newton black films (NBF) between two interfaces with thickness of less than 5 nm were not able to be incorporated into the available classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. The non-DLVO interaction would increase exponentially with the decrease of film thickness, as it plays a crucial role in determining liquid film stability. However, its mechanism and origin are still unclear. In the present work, we investigate the surface interaction of free-standing sodium dodecyl-sulfate (SDS) nanoscale black films in terms of disjoining pressure using the molecular simulation method. The aqueous nanoscale film, consisting of a water coating with SDS surfactants, and with disjoining pressure and film tension of SDS-NBF as a function of film thickness, were quantitatively determined by a post-processing technique derived from film thermodynamics.

Stabilisation of dispersions using a graft copolymer of hydrophobically modified polyfructose

This paper describes the use of a graft copolymer of hydrophobically modified inulin (polyfructose) (INUTEC SP1) for the stabilisation of dispersions. It starts with a section on the adsorption and conformation of the polymer at the interface. The results show a high affinity isotherm with irreversible adsorption. This is due to the multi-point attachment of the graft copolymer to the surface by several alkyl chains that are grafted to the polyyfructose backbone. The adsorbed layer thickness Δ of the graft copolymer on model polystyrene particles with radius R was determined using rheological measurements. The relative viscosity-core volume fraction π of the latex are compared with the theoretical value calculated using the Dougherty-Krieger equation allowing one to obtain the hydrodynamic thickness Δ. The latter was found to be 9.2nm indicating strong hydration of the polyfructose loops and tails by water molecules. Evidence for this strong hydration was obtained using cloud point measurements. The graft copolymer INUTEC SP1 was then used to prepare emulsions of paraffin oil or silicone oil-in-water emulsions. The latter remained stable with no coalescence for more than 1year both at room temperature and at 50°C and also in the presence of high electrolyte concentrations (2moldm−3 NaCl). This high stability of the emulsion is due to the multi-point attachment of the graft copolymer with several alkyl chains to the oil, leaving the strongly hydrated loops and tails of polyfructose dangling in solution, thus ensuring effective steric stabilisation. The high stability of the emulsion was confirmed using disjoining pressure measurements which indicated the presence of a Newton black film that showed no rupture up to a disjoining pressure of 4.5×104Pa. INUTEC SP1 was then used for the preparation of polystyrene (PS) and polymethylmethacrylate (PMMA) latex by emulsion polymerisation. The stability of the resulting latexes was determine by measuring the critical coagulation concentration (CCC) using CaCl2. By post addition of INUTEC SP1 to the latex dispersion, the CCC is significantly increased indicating effective steric stabilisation. The latter was confirmed using atomic force microscopy (AFM) whereby the interaction force between a hydrophobic glass sphere and glass plate, both coated with the graft copolymer, was measured both in water and in the presence of Na2SO4 (up to 1.5moldm−3). In all cases repulsive interaction was obtained indicating the effectiveness of INUTEC SP1 for latex stabilisation. INUTEC SP1 was also used for stabilisation of nano-dispersions (with diameters in the range 20–200nm). The high ratio of adsorbed layer thickness to particle or droplet size (d/R) results in a very shallow attractive minimum in the energy-distance curve. This indicates absence of any weak or strong flocculation. INUTEC SP1 could significantly reduce Ostwald ripening of nano-emulsions by strong adsorption at the oil/water interface and enhancement of the Gibbs elasticity.

Surface conductivity measurements in nanometric to micrometric foam films

Foam films (a liquid lamella in air covered by surfactants) are tools of choice for nanofluidic characterization as they are intrinsically nanometric. Their size is indeed fixed by a balance between external pressure and particular molecular interactions in the vicinity of interfaces. To probe the exact nature of these interfaces, different characterizations can be performed. Among them, conductivity in confined systems is a direct probe of the electrostatic environment in the vicinity of the surface. Therefore, we designed a dedicated experiment to measure this conductivity in a cylindrical bubble coupled to interferometry for film thickness characterization. We then show that this conductivity depends on the surfactant nature. These conductivity measurements have been performed in an extremely confined system, the so called Newton black foam films. Unexpectedly in this case, a conductivity close to surface conductivity is recovered.

Slow dynamics of water confined in Newton black films.

Slowdown of translational and reorientational dynamics of water confined in Newton black films (NBFs) is revealed by molecular dynamics simulations. As a film becomes thinner, both translational and reorientational dynamics become slower. The polarization of water molecules in the macroscopic electrostatic field across the NBF and the coordination of Na(+) ions and surfactant anionic groups around water molecules concertedly lead to slowdown of water dynamics. The polarization effect is obvious for water not coordinated by Na(+) ions, which exhibits reorientational dynamics depending on initial dipole orientations. Na(+) ions and surfactant anionic groups retard dynamics of surrounding water by decreasing the hydrogen bond exchange probability and increasing the viscosity of water. The dependences of translational and reorientational dynamics on coordination environments of water are similar. Dynamics of water in positions close to the interfaces of NBFs are mainly retarded by Na(+) ions and surfactant anionic groups, while the macroscopic polarization effect plays the main role in influencing water dynamics in positions far from the interfaces. This study sheds light on the improvement of knowledge about the water dynamics slowdown mechanism in similar environments like reverse micelles and lamellar structures.

Comparison of Change in Surface Structure of POPC Surfactant Bilayer on Si Substrate with MIES & UPS

Nanoparticles in the recent times have drawn more attention in the field of electronics and in particular their property of self assembly over another material surface makes them a suitable component in the development of Nanoscale materials. Self organization property of Nanoparticles has opened up whole new possibilities in the construction of 2D nanostructures through deposition of organized bilayer of surfactant called black films on a solid substrate. Newton Black Films which are much thinner than a Common Black Films attracted more interests recently with their ability to form more complex structures. In this article, Newton Black films of POPC (1-palmitoyl-2-oleoyl-phosphaticylcholine) surfactant is formed and deposited on a solid substrate after a certain amount of time and their surface structure were analyzed with time. The experiment is conducted at three different drainage states; un-dried, un-dried with a salt present, and dried; their results are compared with MIES and UPS spectrum. Where, MIES spectra being more sensitive towards surface modification show that the structure becomes more ordered with drainage time and the process gets even faster with the addition of a salt. Comparatively, in MIES the presence of new elements is more clearly observed with the variation in their energy spectra on the drained film substrate than in the un-drained substrate owing to the fact that the drained film has more patterned outermost layer comprised with the new elements.

Stability of Newton Black Films Under Mechanical Stretch – A Molecular Dynamics Study

The stability of Newton black films (NBFs) under lateral mechanical stretch was investigated by nonequilibrium molecular dynamics (NEMD) simulations using force field parameters validated by accurate prediction of surface tensions. The applied strains accelerated film ruptures, enabling efficient measurements of the critical thicknesses of the films. Two representative surfactants, sodium dodecyl sulfate (SDS) for ionic surfactant and pentaethylene glycol monododecyl ether (C12EO5H) for nonionic surfactant, were investigated and compared. The predicted critical thickness of C12EO5H-coated film is smaller than that of the SDS-coated film, which is consistent with previously reported experimental observations. Our simulation results show that while the two surfactant-coated films exhibit similar dynamic properties attributed to the Marangoni-Gibbs effect, their surface structural characteristics are quite different. Consequently the two films demonstrate distinct rupture mechanisms in which rupture starts at uncovered water domains in the SDS-coated film, but at lateral surfactant/water interfaces in the C12EO5H-coated film. Our findings provide new insights into the stabilization mechanisms of NBFs and will facilitate the design and development of new films with improved properties.

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.

Thin–Thick Transition of Foam Film Driven by Phase Transition of Surfactant–Alkane Mixed Adsorbed Film

Abstract This paper reports the influence of surface phase transitions of a surfactant–alkane mixed adsorbed film on the foam film thickness. The DLVO free-energy between the adsorbed films is estimated using total-reflection XAFS. The foam film thickness shows discontinuous changes at the surface phase transition. In addition, the foam film thicknesses on either side of the thickness transition were in the range for common black films (CBFs), which shows a striking difference from existing thin–thick transitions between CBF and Newton black films (NBFs).

Molecular Dynamics Simulation of the Effects of NaCl on Electrostatic Properties of Newton Black Films

The effects of NaCl on electrostatic properties of Newton black films (NBF) coated with two monolayers of sodium dodecyl sulfate were investigated by using molecular dynamics simulations. Film systems without salt and with 1.0 mol/L NaCl were studied separately. Charge density profiles of salt ions are calculated and fitted using a function we proposed. Fitting results show that adding NaCl leads to more positive charge adsorbed to the surface and less diffusing in the middle of the film. More positive charge adsorbed to the surface leads to the destruction of solvation shells around amphiphilic groups, so that water molecules arrange less regularly. Adding NaCl leads to a decrease of both ions and water contributions to the electrostatic field, which are controlled by ionic charge distributions and water orientations. The relative decrements of ions and water contributions determine the difference in electrostatic potential. On the basis of the investigation of electrostatic potential and species distrib...

Newton black films as wetting systems

Financial support for this work was provided by The Royal Society project “Intrinsic Structure of Aqueous Interfaces” and the Direccion General de Investigacion, Ministerio de Ciencia y Tecnologia of Spain, under Grant No. FIS2010-22047-C05, and by the Comunidad Autonoma de Madrid under the R&D Program of activities MODELICOCM/ S2009ESP-1691. H.M. would like to thank the Universidad Autonoma de Madrid for the award of a FPU-UAM doctoral grant. F.B. would like to thank the EPSRC for the award of a Leadership Fellowship (EP/J003859/1)

Thermodynamic studies on thin liquid films IV. Foam film stabilized by sodium dodecyl sulfate

Thermodynamic treatment of thin liquid films in Part III of this series was applied to foam films stabilized by sodium dodecyl sulfate. Miscibility of sodium chloride and sodium dodecyl sulfate in the adsorbed films at the film surfaces and transition between the black films were studied by measuring film thickness and contact angle. A discontinuous change in the thickness and a break on the contact angle vs. concentration curve appeared at the transition. Judging from the phase diagram of adsorption, sodium chloride and sodium dodecyl sulfate are a little miscible in the adsorbed films. The miscibility was ascribed to specific interaction between sodium ion and dodecyl sulfate ion in the adsorbed films. The miscibility in an adsorbed film was compared between the film surface and meniscus and between the common black and Newton black films.

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.

Adhesive transitions in Newton black films: A computer simulation study

We report molecular dynamics simulations of Newton black films (NBFs), ultra thin films of aqueous solutions stabilized with two monolayers of ionic surfactants, sodium dodecyl sulfate. We show that at low water content conditions and areas per surfactant corresponding to experimental estimates in NBFs, homogeneous films undergo an adhesion "transition," which results in a very thin adhesive film coexisting with a thicker film. We identify the adhesive film with the equilibrium structure of the Newton black film. We provide here a direct microscopic view of the formation of these important structures, which have been observed in experimental studies of emulsions and foams. We also report a detailed investigation of the structural properties and interfacial fluctuation spectrum of the adhesive film. Our analysis relies on the definition of an "intrinsic surface," which is used to remove the averaging effect that the capillary waves have on the film properties.