Surface Tension Plots Research Articles

Surface tensions and thermodynamic parameters of surface formation of aqueous salt solutions: III. Aqueous solution of KCl, KBr and KI

Surface tension of aqueous electrolyte solutions has been determined experimentally. Concentration and temperature dependence of the surface tension of three different salts has been studied. These include the chloride, bromide and iodide salts of potassium. The study was conducted at five different concentrations, i.e. 0.1, 0.5, 1.0, 1.5 and 2.0 mol dm −3, and five different temperatures ranging from 10 to 30 °C with 5 °C interval. The surface tension data were fitted into linear regression for estimation of surface excess concentration using Gibbs adsorption equation. The thermodynamic quantities of surface formation such as enthalpy and entropy were estimated from the slopes (d γ/d T) C of surface tension versus temperature plots at constant concentration. Concentration and temperature dependence of surface excess concentration and thermodynamic parameters of surface formation have been discussed.

Physicochemical Characterization and Tube-like Structure Formation of a Novel Amino Acid-Based Zwitterionic AmphiphileN-(2-Hydroxydodecyl)-l-valine in Water

Surface activity and aggregation behavior of an amino acid-based zwitterionic amphiphile N-(2-hydroxydodecyl)-L-valine were studied in aqueous solutions (pH 13). The self-assembly formation was investigated by use of a number of techniques including surface tension, conductivity, viscosity, fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The amphiphile exhibits two breaks in the surface tension vs concentration plot indicating stepwise aggregate formation and thus results in two values of critical aggregation concentration. The amphiphile was found to be very surface active compared to fatty acid soaps. The average hydrodynamic diameter and size distribution of the aggregates were obtained from DLS measurements. Conductivity measurements suggested formation of vesicles or closed tubules. TEM pictures revealed the existence of spherical vesicles, separated tubules, and tubules with multiple Y-type junctions in going from dilute to moderately concentrated solution. However, in concentrated solution, the junctions break to form separate tubular structures which upon further increase of concentration are converted to rod-like micelles. The mechanism of branched tubule formation is discussed in light of the experimental observations.

Tuning the Transport Properties of Poly(oxyethylene)bisamine−Nafion Polyelectrolyte Complexes by Dielectric Manipulation

Polyelectrolyte complexes (PECs) of Nafion-H + , a perfluorosulfonic acid ionomer, and Poly(oxyethylene)bisamine (Polyox) were synthesized, and the effect of electrostatic interactions on the physicochemical properties of the individual components was studied using a combination of spectroscopic and electrochemical techniques. More specifically, the pristine PECs were extensively characterized using viscosity, surface tension, and pH measurements and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy and their transport properties were investigated using cyclic voltammetry and electrochemical impedance spectroscopy, by employing [Fe(CN) 6 ] 3- as a redox probe. Acid-base interaction between Nafion and Polyox is evident from pH measurements of the blend solutions, which indicate salt formation at a 50:50 composition, supported further by the existence of a maximum in the plot of surface tension versus blend composition. DRIFT spectra of the PEC membranes indicate subtle changes in the ionic environment and a transition from a state of medium hydration to a partially dehydrated state of the parent ionomer, Nafion, after complexation with Polyox. Further evidence for polyelectrolyte-polyelectrolyte association is obtained from cyclic voltammetry, which shows that the interaction between the redox active chromophore, [Fe(CN) 6 ] 3- , and the pendent sulfonate groups of Nafion is minimized by complexation with the oppositely charged polyelectrolyte Polyox. The water-soluble nature of these PECs along with the tunable range of properties with blend composition could qualify them as suitable candidates for developing stimuli-responsive polymer systems for pharmaceutical and environmental applications.

Electrolyte effect on mixed micelle and interfacial properties of binary mixtures of cationic and nonionic surfactants

In the present work, the adsorption behavior at the liquid–air interface and micellization characteristics of mixtures of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl) polyoxyethylene (TritonX-100) in aqueous media containing different concentrations of NaBr were investigated by surface tension and potentiometry measurements. From plots of surface tension ( γ) as a function of solution composition and total surfactant concentration, we determined the critical micelle concentration (CMC), minimum surface tension at the CMC ( γ CMC ), surface excess ( Γ max ), and mean molecular surface area ( A min ). On the basis of regular solution theory, the compositions of the adsorbed film ( Z) and micelles ( X M ) were estimated, and then the interaction parameters in the micelles ( β M ) and in the adsorbed film phase ( β σ ) were calculated. For all mole fraction ratios, the results showed synergistically enhanced ability to form mixed micelles as well as surface tension reduction. Furthermore β was calculated by considering nonrandom mixing and head group size effects. It was observed that, for both the planar air/aqueous interface and micellar systems, the nonideality decreased as the amount of electrolyte in the aqueous medium was increased. This was attributed to a decrease of the surface charge density caused by increasing the concentration of bromide ions.

Study of one-side aluminized polyimide films exposed on the Mir orbital space station

During exposure on the Mir space station, external polyimide films aluminized on one side substantially lost mass and mechanical strength and their outer surfaces became hydrophilic. The surface tension and polar plots of brightness of the exposed films acquired an anisotropic character. Spatially-oriented nano- and microsized entities, whose size and shape depend on the time of exposure, were detected by the scanning electron and atomic-force microscopy techniques on the outer surfaces of external films. The orientation axes of drops on the surface of the films, polar plots of brightness, and spatially oriented structures coincided with the direction of the station movement. It was assumed that one of the main factors of outer space responsible for mass loss and the formation of the anisotropic nano- and microsized structures is the impact of a flux of oxygen atoms onto the surface of the external film. The efficiency of the reaction of atomic oxygen with polyimides was estimated. A possible (photoelectron) mechanism of the influence of the metal on polyimide degradation is discussed.

Blending effects on adsorption and micellization of different membrane protein solubilizers: II. A thermodynamic study on a mixed system of CHAPS with a bile salt in pH 7.4 phosphate buffer solution

For a mixed system of a typical membrane protein solubilizer CHAPS (a derivative of a bile acid cholic acid) combined with a bile salt (sodium salt of glycocholic acid, NaGC), which is also a candidate as a membrane protein solubilizer, micellization and adsorbed film formation in a phosphate buffer solution of pH 7.4 at 303 K were studied paying special attention to the synergistic effect upon mixing. The collection of sufficient data based on plots of surface tension ( γ) versus logarithmic concentration ( C t or m t) in total molality at discrete mole fractions ( X 2) in the mixture of surfactants 1 and 2 (where 1 and 2 correspond to CHAPS and NaGC, respectively) allowed us to accurately determine critical micelle concentration (CMC), minimum surface tension at CMC ( γ CMC), and the slope (d γ/d ln C t) from the γ–ln C t curves in the concentration range just below CMC. These data enabled us to estimate surface excess ( Γ t), and mean molecular area ( A m) in addition to such parameters as the minimum surface Gibbs energy ( G min ( S ) ), p C 20 and CMC/ C 20 related to synergism accompanied by blending. Applying the regular solution theory (RST), the relation of compositions of the singly dispersed phase ( X 2) and the micellar phase ( Y 2) as well as the interaction parameter ( ω R) (by using the Rubingh's equations) were estimated. The relation between the composition in the adsorbed film ( Z 2) and X 2 together with the interaction parameter ( ω A) in the adsorbed film was also estimated. The partial molecular area (PMA), γ CMC, and G min ( S ) were examined as functions of X 2 and/or Z 2. The resultant CMC– X 2 and CMC– Y 2 curves and ω R and ω A values have demonstrated that mixed micelles and adsorbed film formation are attained accompanying to some extent enhanced intermolecular interaction (with negative ω R and ω A values). Comparing with previous results for mixed systems of CHAPS with n-acyl (octanoly, nonanoyl, and decanoyl)- N-methylglucamides [MEGA- n's ( n = 8, 9, and 10)] and of sodium chenodeoxycholate (NaCDC) with sodium ursodeoxycholate (NaUDC), the synergism observed for the mixed system of CHAPS with NaGC lies between both combinations. However the expected properties as a membrane protein solubilizer are judged to be sufficient.

Micelle–Vesicle Transition of Fatty Acid Based Ion‐Pair Surfactants: Interfacial Evidence and Influence of the Ammonium Counterion Structure

We describe the synthesis and the physicochemical study of new ion-pair amphiphiles from a mixture of bicyclic, cyclic, linear or branched amines and fatty acids of three chain lengths. Surface-tension measurements of bicyclic, cyclic and branched structures of ammonium/alkanoate acid ion pairs show a phase transition, with two plateaux in the plot of surface tension versus log(c) (c=concentration). Such behaviour is related to the structure of the counterion, the alkyl chain length and the temperature. Pulsed gradient spin echo NMR spectroscopy experiments were performed to demonstrate the existence of micelles on the first plateau and to confirm the phase transition. The existence of vesicles on the second plateau of the surface tension was proved by CryoTEM observation and dynamic light scattering (DLS) measurements. Mainly, according to the structure of the counterion, there is either a strong association and a positioning along the chain leading to vesicles or a less strong association leading to external positioning and the formation of micelles at low concentrations or vesicles at higher concentrations.

Adsorption and aggregation properties of amino acid-based N-alkyl cysteine monomeric and [formula omitted]-dialkyl cystine gemini surfactants

An amino acid-based gemini surfactant derived from cystine (2C n Cys, where n represents the hydrocarbon chain lengths of 8, 10, and 12) was synthesized by reacting cystine with n-alkyl bromide, and its adsorption and aggregation properties were characterized by measurements of equilibrium and dynamic surface tension and dynamic light scattering. The properties of 2C n Cys were compared with those of an amino acid-based monomeric surfactant derived from cysteine (C n Cys). For n = 8 and 10, when compared to C n Cys, 2C n Cys exhibited excellent surface activities, such as a lower critical micelle concentration (cmc), greater efficiency in lowering the surface tension of water, and smaller area occupied per molecule. Adsorption rate at air/water interface decreased with an increase in hydrocarbon chain length, chain number, and concentration of respective compounds. Further, the kinetics were discussed using the monomer diffusion coefficient obtained from short and long time scales in dynamic surface tension plots. In addition, the aggregation properties of 2C n Cys for n = 8 and 10 differed from those in the case of n = 12 . In other words, relatively larger micelles with diameters of approximately 7 nm were formed by 2C n Cys for n = 8 and 10 in comparison to those formed by C n Cys (2–3 nm). On the other hand, for a 0.832 mmol dm −3 2C 12Cys solution, the aggregation structure investigated by cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS) revealed the coexistence of small unilamellar vesicles and small rods.

The relationship between the surface activity of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers and molecular composition

A systematic investigation of surface tension, as a function of copolymer concentration, has been undertaken for a range of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers in aqueous solution. The copolymers examined form three distinct families, containing 20, 70, and 80% ethylene oxide. The focus of the study was the change in surface tension observed below the critical micelle concentration of the triblock copolymers. Thus, in general, the plots of surface tension as a function of copolymer concentration showed a low concentration break. In some cases a high concentration break—corresponding to the onset of micellisation—was also observed. Estimates of molecular area have been made for molecules adsorbed at the air–water interface either side of the low concentration break. Below the break the molecular area does not appears to show any straightforward relationship with molecular composition. However, multiple linear regression analysis of the experimentally determined molecular area data above the break indicates that there does appear to be a weak relationship (adjusted R 2 = 0.64) between molecular area and molecular composition (based upon the manufacturers’ data sheets). Estimates were also made of pC 20 values (the negative logarithm of the copolymer concentration that reduces the surface tension of pure water by 20 mN m −1). Multiple linear regression analysis of the pC 20 data indicates that pC 20 values are related to molecular composition (adjusted R 2 = 0.78). In addition, multiple linear regression analysis shows that surface tension values at a variety of aqueous copolymer concentrations are strongly correlated with molecular composition.

Peptoads, a Group of Amphiphilic Long-Chain Triamides

Eleven triamides bearing long alkyl chains have been synthesized to produce a new class of amphiphilic compounds (dubbed "peptoad"). The properties of these molecules have been investigated by X-ray analysis, solubility studies, light and electron microscopy, surface tensiometry, light scattering, drug dissolution, and molecular dynamics. In the solid state, the peptoads assemble in layers with both intra- and interlayer hydrogen bonding coupled to side-by-side proximity of the hydrocarbon chains. Peptoads with a terminal primary amide and a total of three amide NH sites are water-insoluble owing presumably to attractive forces in the solid state. However, peptoads with terminal -CONMe(2) groups and two internal amide NH sites are water-soluble at room temperature. This solubility is critically dependent upon the chain length. For example, a C(7)-chained peptoad is 1600 times more soluble than its C(9) analogue. High concentrations (6-8 M) of C(7) peptoads in water are clear and do not gel. Light microscopy shows long fibers floating in an isotropic liquid. Water-soluble peptoads are highly surface-active, lowering water's surface tension as effectively as a soap with a much longer chain. Surface tension plots show a "critical aggregation concentration", but it is believed from light scattering and molecular dynamics that the aggregates grow continuously as more peptoad is added to the water. In answer to the inevitable (but valid) question, "What possible good are they?", it can be pointed out that a peptoad solubilizes a water-insoluble drug, paclitaxel (Taxol), as efficiently as does Cremophor EL, a commercial excipient widely used with paclitaxel and other nonpolar drugs. Peptoads, being small molecules and consisting of hydrolyzable amide groups, are likely biodegradable and less prone to the hypersensitivity and neurotoxicity found with Cremophor EL.

Ethyl(hydroxyethyl)cellulose–sodium dodecanoate interaction investigated by surface tension and electrical conductivity techniques

Mixtures of ethyl(hydroxyethyl)cellulose (EHEC) and sodium dodecanoate (SDoD) were investigated using surface tension, conductivity and transmittance measurements. The parameters of the surfactant to polymer association processes such as the critical aggregation concentration (cac) and saturation of the polymer by SDoD (psp) were determined from the plots of surface tension and specific conductivity versus surfactant concentration. The transmittance versus [SDoD] profiles exhibited bands that, in conjunction with conductivity and surface tension data, gave support to the explanation of the behavior of EHEC–SDoD–water solutions. Transmittance bands determined in the presence of EHEC and surfactant are sensitive to the process of surfactant to polymer binding. In this process, a discontinuity point represented by a second broader peak in the transmittance plots was identified, implying a slight inhibition of the breakdown of the network process. This is explained as a kind of intermediate re-structural network of the complexes produced by the formation of regular SDoD micelles. It was demonstrated that the second conductivity breakpoint marks the polymer saturation by surfactant clusters, and the effect of the EHEC concentration on the process of binding can be described by a linear correlation when the psp breakpoint is plotted against the polymer concentration.

Oxidation of Thioanisole by Peroxomolybdate in Assemblies of Cetylpyridinium Chloride and Methyltri-n-octylammonium Chloride

Methyltri-n-octylammonium chloride (Aliquat 336) is sparingly soluble in water but is readily soluble with a 2-fold excess of micellized cetylpyridinium chloride (CPyCl), and the mixtures show breaks in plots of surface tension or electrolytic conductance against concentration indicative of a critical micelle concentration slightly lower than that of CPyCl. Micellization markedly increases 35Cl and 14N NMR line widths of CPyCl, but addition of NaCl reduces the 35Cl line width and addition of Aliquat increases it. Mixing Aliquat and CPyCl has little effect on their 14N line widths. Ion pairing in alcohol mixtures also increases 35Cl line widths. In water these mixed assemblies behave similarly to micelles of CPyCl as regards effects on rates and equilibria of interconversion of tri- and tetraperoxomolybdate ions, and oxidation of thioanisole by the latter, although it is slightly slower than in micelles of CPyCl. Despite differences in the hydrophobic regions, and relationships between amphiphilic structures and morphologies of association colloids, assemblies of CPyCl and Aliquat behave very much like CPyCl micelles in their physical properties and effects upon reactivity. Geometrical optimization indicates that Aliquat can adopt conformations that allow intercalation with CPyCl micelles.

The effect of washing water on bonding to etched enamel.

There is current concern about bacterial contamination of dental unit waterlines. This research hypothesized that the presence of increasing concentrations of bacteria in water used to wash etched enamel would result in a corresponding decrease in both shear bond strength (SBS) and critical surface tension (gammaC) of enamel. A further hypothesis was made that there is a correlation between SBS and gammaC. The effect of 3.5 ppm iodine in the water as a bacteriostatic agent was also assessed. Five groups of 10 samples of bovine enamel were etched, washed, and a resin composite bonded to them. The control group was washed with distilled water. Another group was washed with the dilute iodine solution. The remaining three groups used a different concentration of Escherichia coli DH5alpha as follows (in cfu mL(-1)): group 1: 10(2); group 2: 10(4); group 3: 10(6). Shear bond strength data were measured on an Instron testing machine at a crosshead speed of 1 mm min(-1). Adhesion data were (MPa): control: 24.6 +/- 6.0; with iodine: 20.8 +/- 2.7; group 1: 19.8 +/- 2.7; group 2: 13.5 +/- 3.0; group 3: 13.9 +/- 3.6. The F-test yielded a highly significant difference between control group, iodine group and group 1, compared with groups 2 and 3 (P < 0.0001). Tukey's Studentized Range Test was used for pairwise comparison testing between groups. Using a Cahn dynamic contact angle analyzer and linear regression analysis, the plots of surface tension versus costheta were extrapolated to costheta = 1 to give gammaC data for the control group and groups 1-3. In all cases reasonable linearity was observed (r2 > or = 0.87). Data (mN m(-1)) were: control group: 50.8; group 1: 45.1; group 2: 43.2; group 3: 39.5. The SBS and gammaC were then plotted against each other and linear regression analysis performed. It was concluded that increasing concentrations of bacteria in wash water decreased both SBS and gammaC and that a linear correlation (R2 = 0.84) was found between the values of these two parameters.

Adsorption of Oppositely Charged Polyelectrolyte/Surfactant Mixtures. Neutron Reflection from Alkyl Trimethylammonium Bromides and Sodium Poly(styrenesulfonate) at the Air/Water Interface: The Effect of Surfactant Chain Length

The interactions between a series of cationic surfactants (alkyltrimethylammonium bromides) (CnTAB) and the anionic polymer sodium poly(styrenesulfonate) (NaPSS) have been studied using surface tension and neutron reflectivity. The effect of surfactant chain length on surfactant/polymer adsorption has been studied using chain lengths from 10 to 16 carbon atoms (i.e. C10TAB to C16TAB). The surface tension plots (γ against ln c) have two types of shape. The C10TAB and C12TAB with NaPSS systems have plots with plateaus, while the longer chain C 14TAB and C16TAB systems have a pronounced hump in the surface tension at surfactant concentrations just below the critical micelle concentration (cmc) of the free surfactant. Neutron reflection shows that there is a surfactant monolayer (thickness 20−22 A) adsorbed at dilute surfactant concentrations for the C10TAB, C12TAB, and C14TAB systems, but this changes to a thick layer (60−100 A) at concentrations closer to the cmc. The corresponding areas per adsorbed surfac...

Adsorption and Micelle Formation of Mixed Surfactant Systems in Water. III. A Comparison between Cationic Gemini / Cationic and Cationic Gemini / Nonionic Combinations

A surface tension study (drop volume method) was performed at 30°C on micellization and adsorbed film formation of a mixed system of a cationic Gemini-type surfactant with a cationic surfactant in comparison with another mixed system of the same Gemini-type surfactant with a nonionic surfactant. The systems studied were Bis-ammonium Gemini derived from tartaric acid dibromide salt [BAGTB, 1,4-Bis(trimethylammonio)-2,3-dodecyloxy butane dibromide] with hexadecyltrimethylammonium bromide (HTAB): BAGTB / HTAB mixed system and with n-decanoyl-N-methylglucamide (MEGA-10): BAGTB / MEGA-10 mixed system. The data of surface tension (γ ) vs logarithmic molality plots as a function of mole fraction of surfactant 2 (2 corresponds to HTAB or MEGA-10), X 2, enabled us to determine the critical micellization concentration (CMC), the surface tension at CMC (γCMC), surface excess concentration (Γt ), the mean molecular surface area (A m), the partial molecular area (PMA), and the measures of efficiency of adsorption (pC20 = -log C20) and CMC / C20 which is available for evaluating the facilitating balance between adsorption and micellization. In addition, a newly defined measure of synergism in surface activity, i.e., the minimum surface Gibbs energy (G (S)min) was employed. Based on these data, the examination of synergism in micelle formation and in surface tension reduction elucidated that the Gemini-type surfactant does not exhibit any positive synergism for either BAGTB / HTAB or BAGTB / MEGA-10 mixed systems. Most of these parameters are found to depend conspicuously on the mixing ratio for both mixtures; indicating that the state of adsorbed film is divided into three ranges of X 2; the lower, the middle and the higher. The compositions of micelles formed at CMC (Y 2) and of adsorbed film (Z 2) equilibinated with bulk solution at a fixed surface tension were estimated.

Behavior of Nonionic Water Soluble Homopolymers at the Air/Water Interface: Neutron Reflectivity and Surface Tension Results for Poly(vinyl methyl ether)

The composition and structure of layers of poly(vinylmethyl ether) (PVME) adsorbed at the air/water interface have been determined by neutron reflection and surface tension. For temperatures above and below the cloud point and over most of the range of concentration, neutron reflection gives results in agreement with the Gibbs equation. However, an upturn in the surface tension at low concentrations, which has been observed in several related systems, is attributed to two possible contributions. One is depletion, which has been previously identified by others. The other is polydispersity. At higher concentrations, larger molecular weight species dominate the surface activity and lead to a shallow slope in the surface tension (γ) versus ln(concentration) plot, but at low concentrations smaller molecular weight species increasingly occupy the surface and they give rise to steeper slopes in the γ−ln c plot. The segment density profile of PVME normal to the surface is unsymmetrical with a tail extending into the solution. A new method of analyzing reflectivity data that is better able to handle such unsymmetrical distributions is introduced. As the temperature is increased above the cloud point, the adsorbed polymer layer tends to collapse with expulsion of water.

Micellar Structure of Silicone Surfactants in Water from Surface Activity, SANS and Viscosity Studies

The aqueous solutions of two nonionic silicone surfactants based on polyether modified poly(dimethylsiloxane)s have been analyzed by cloud point, surface tension, small angle neutron scattering (SANS), and viscosity measurements. These surfactants have a comb-like structure with a linear poly(dimethylsiloxane) backbone chain and a grid containing block oligomers of ethylene oxide and/or propylene oxide as branches. The critical micelle concentrations (CMCs) were obtained from break points in surface tension vs log concentration plots and, as expected, decreased systematically with the increase in the hydrophobicity. Small angle neutron scattering (SANS) measurements have been made in aqueous solutions of silicone surfactants at different concentrations (1, 2, and 5 % w/v) and temperatures (30, 45, and 60 °C) to elucidate the structural information on micelles. The analysis of the SANS curves revealed the presence of oblate ellipsoidal micelles in three selected concentrations and temperatures. The size of micelles has strikingly showed a nonvariance in the concentration range of 1−5 % w/v, whereas an increase of 30−60% in the seminor major axis b values was noted when the temperature was raised from 30 to 60 °C. Under the same temperature interval, an increase in the aggregation number and a decrease in the number density of micelles were noted. Viscosity measurements also support the presence of aggregates of nonspherical shape. The shape factor for the aggregates calculated from intrinsic viscosities has been found to be in close agreement with the values for the same obtained independently from the SANS measured axial ratios. The micellization of silicone surfactants has been found to be described adequately by closed association process, which was used to obtain the thermodynamic parameters viz. standard free energies (ΔG°Mic), enthalpies (ΔH°Mic), and entropies (ΔS°Mic) of micellization. The micellization process has always been characterized by endothermic enthalpies and thus is driven mainly by entropy factor. The stretching of the core part at elevated temperatures has been attributed to the dehydration phenomenon, as a result of which the water is expelled from the interior of the micelles facilitating the addition of more surfactant molecules into aggregates.

Superspreading of Trisiloxane Surfactant Mixtures on Hydrophobic Surfaces. 1. Interfacial Adsorption of Aqueous Trisiloxane Surfactant−N-Alkyl Pyrrolidinone Mixtures on Polyethylene

Interfacial adsorptions of aqueous solutions of trisiloxane surfactant (SILWET L77), N-alkyl pyrrolidinones [N-butyl-(C4P), N-cyclohexyl-(CHP), N-hexyl-(C6P), N-2-ethyhexyl-(C2,6P), N-octyl-(C8P), and N-decyl-(C10P)], and their mixtures have been measured. The adsorptions at the air/aqueous solution interface were obtained from the plots of surface tension versus log(C) by use of the Gibbs equation. The adsorptions onto the powdered polyethylene surface were determined by the use of UV spectroscopy for pyrrolidinones and two-phase titration for SILWET L77, respectively. The adsorptions at the solid/air interface were evaluated by the use of an equation derived from the Gibbs and Young equations. It was found that the addition of the N-alkyl pyrrolidinones to the solution produces little or no enhancement of the total surfactant adsorption at the air/aqueous solution interface. At the solid/aqueous solution interface, the enhancement effectiveness of the pyrrolidinones decreases in the order C2,6P > C8P > ...

Rational solvent selection strategies to combat striation formation during spin coating of thin films

Striation defects in spin-coated thin films are a result of unfavorable capillary forces that develop due to the physical processes commonly involved in the spin-coating technique. Solvent evaporation during spinning causes depletion at the surface of the more volatile solution components while simultaneous viscous out-flow occurs providing the main source of solution thickness reduction during any typical spinning run. The composition changes in the surface layer can either stabilize or destabilize the surface with respect to convective motions within the coating solution. Destabilization (and therefore possible striation formation) happens when the surface composition changes so that a larger surface tension will develop. Thus, a careful cross-referencing of solvent volatility with surface tension effects can help establish solution conditions that will prevent this instability from arising. A plot of solvent vapor pressure (Pv) versus solvent surface tension (σ) is introduced and utilized to help discuss the impact of solvent choice when making coatings via spin coating. One important result is that when desiring to deposit a coating having a surface tension of σsolid, then it is favorable to use a fully miscible solvent that has a higher surface tension (i.e., σliquid&gt; σsolid). More complicated solution mixtures were also examined, including dual-solvent systems and water-containing systems.

The cross-sectional headgroup area of nonionic surfactants; the influence of polydispersity

In this work, we have measured surface tension as a function of concentration of pure and technical nonionic ethoxylated surfactants. Critical micelle concentration(CMC) values, surface tension at the CMC and the cross-sectional headgroup areas are compared. It is shown that the CMC does not depend significantly on the polydispersity of the polyoxyethylene chain. However, the surfactant headgroup area, as determined from the surface tension plots, is much smaller for polydisperse surfactants than for homologue pure surfactants. This is proposed to be due to selective adsorption of the shorter polyoxyethylene species at the surface. For the same reason, the surface tension at the CMC is lower for technical surfactants than for homologue pure species.