Surface Tensiometry Research Articles

Amphiphilic and biocompatible properties of poly (EA‐MAA)

AbstractThe amphiphilic and biocompatible behaviors of Poly (acetate‐methylacrylic acid) Poly(EA‐MAA) were investigated in this study. The aggregation behavior of Poly(EA‐MAA) in aqueous media was investigated by steady‐state fluorescence spectroscopy and surface tensiometry. The critical aggregation concentration (cac) of Poly(EA‐MAA) was determined to be ∼0.03 mg/mL. Ultraviolet spectrum (UV) and fluorescence spectrum results indicated that there are interactions form between Poly(EA‐MAA) and bovine serum albumin (BSA). And β‐sheet can be changed into α‐helix of BSA in Poly(EA‐MAA) solution effectively revealed by Circular dichroism (CD), which is driven by the H‐bond and hydrophobic interactions. The good cell‐compatibility of Poly(EA‐MAA) makes it great potential in the biomedical fields. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Mixed aggregate formation in gemini surfactant/1,2-dialkyl-sn-glycero-3-phosphoethanolamine systems

An evaluation of the physical interactions between gemini surfactants, DNA, and 1,2-dialkyl-sn-glycero-3-phosphoethanolamine helper lipid is presented in this work. Complexation between gemini surfactants and DNA was first investigated using surface tensiometry where the surface tension profiles obtained were found to be consistent with those typically observed for mixed surfactant–polymer systems; that is, there is a synergistic lowering of the surface tension, followed by a first (CAC) and second (CMC) break point in the plot. The surfactant alkyl tail length was observed to exhibit a significant effect on the CAC, thus demonstrating the importance of hydrophobic interactions during complexation between gemini surfactants and DNA. The second study presented is an investigation of the mixing interactions between gemini surfactants and DOPE using Clint’s, Rubingh’s, and Motomura’s theories for mixed micellar formation. The mixing interactions between the 16–3–16/16–7–16/16–12–16/16–7NH–16 gemini surfactants and DOPE were observed to be antagonistic, where the strength of antagonism was found to be dependent upon the gemini surfactant spacer group and the solution composition.

Interactions of Ionic Surfactants With PEO-PBO-PEO Triblock Copolymers in Aqueous Solutions

The interactions of triblock copolymers (TBP) with ionic surfactants were studied employing surface tensiometry, electrical conductivity, steady-state fluorescence (SSF), and dynamic light scattering (DLS) techniques. An increasing trend in the critical micelle concentration (CMC) of SDS/CTAB in the presence of triblock copolymers was observed especially at higher polymer to surfactant ratio. The delay in the CMC of surfactants was more pronounced in the presence of E48B10E48 possibly due to its less hydrophobic nature. The negative values of free energy of micellization (ΔGm) both in case of SDS and CTAB confirmed the spontaneity of the processes. The aggregation number (Nagg) and hydrodynamic radius (Rh) of polymer/surfactant mixed systems were determined by SSF and DLS. The suppression of the surfactant micelle size in the presence of TBP was confirmed by SSF and DLS studies.

Interaction of amphiphilic drug amitriptyline hydrochloride with β-cyclodextrin as studied by conductometry, surface tensiometry and viscometry

Cyclodextrins are very well known to form the inclusion complexes with various drugs owing to their internal cavity. In this paper we have studied the interaction of β-cyclodextrin (β-CD) with amphiphilic drug amitriptyline hydrochloride (AMT) exploiting conductometry, surface tensiometry and viscometry. It was found that addition of β-CD to the drug solution causes the shifting of micellization of amphiphilic drug toward higher concentrations. This confirms the complex formation between the drug and the host molecule as a result of the interaction between them. Surface tension isotherms suggest that the addition of β-CD results in the surface tension of the solution to decrease as compared to the pure solution of drug due to the encapsulation of surface active drug inside the hydrophobic cavity of β-CD. Similarly, viscosity of the solution decreases drastically on the addition of β-CD which further increased on increasing the drug concentration. Free energy of micellization (∆Gmic) was computed with the help of degrees of micelle ionization obtained from the specific conductivity−[AMT] plots.

Design principles for supercritical CO2 viscosifiers

This work reveals new principles for designing new self-assembling additives as viscosity enhancers for supercritical fluid CO2. Employing the approaches outlined in this work a maximum increase in CO2 viscosity of 100% has been achieved, the highest ever reported for surfactant CO2 viscosifiers. A series of semi-fluorinated F–H hybrid surfactants were synthesised based on the pentadecafluoro-5-dodecyl (F7H4) sulfate anion, but featuring different metallic counterions: Li-F7H4, K-F7H4, Na-F7H4 and Rb-F7H4 (denoted M-F7H4). These M-F7H4 variants were designed to reveal the effects of hydrated cation radius (rhyd) on packing self-assembly in supercritical CO2 (scCO2). The CO2-philic M-F7H4 surfactants were investigated at the air–water interface by surface tensiometry, and in the bulk by small-angle neutron scattering (SANS), in both aqueous solutions and scCO2. Surface tensiometry of aqueous solutions showed that interfacial packing density and limiting head group area at the critical micelle concentration (Acmc), depends implicitly on the identity of M+, suggesting that micelles in water or scCO2 should have different geometric packing parameters (PlimC) as a function of M+. SANS measurements on M-F7H4 aqueous micellar solutions confirmed sphere → ellipsoid → vesicle transitions as a function of M+ with decreasing rhyd. Using high pressure SANS (HP-SANS), and changing solvent from water to scCO2 showed that all the M-F7H4 variants stabilise water-in-CO2 (w/c) microemulsion droplets on addition of water. In scCO2 Li-F7H4 forms prolate ellipsoidal droplets, Na-F7H4 forms long cylindrical droplets, K-F7H4 forms ellipsoidal droplets, whereas Rb-F7H4 stabilises spherical microemulsion droplets. The ability of M-F7H4 additives to enhance the viscosity of scCO2 was shown by high pressure falling cylinder viscometry. The HP-SANS and viscometry experiments were shown to be quantitatively consistent, in that aggregate aspect ratios (X) determined in structural studies account for the enhanced relative viscosities (ηmic/ηCO2).

Surface Composition of Mixtures of Ethylammonium Nitrate, Ethanolammonium Nitrate, and Water

Surface tensiometry of binary mixtures of ethylammonium nitrate (EAN), ethanolammonium nitrate (EtAN), and water reveals distinctive amphiphilic character for the ethylammonium cation, but not for ethanolammonium. Results also show that the surface film incorporates nitrate counterions, and that electrostatic and H-bonding interactions, rather than alkyl chain packing, determines the saturated adsorbed film structure and limiting molecular area.

Hydrogen-Bonded Order in Mercury-Supported Monolayers of End-Functionalized Alkanes

The order formed by hydrogen bonding in mercury-supported Langmuir films (LFs) of end-functionalized, surface-parallel, alkane molecules was studied by surface-specific X-ray methods and surface tensiometry. Hexadecane derivatives, substituted at one or both ends by mercapto, carboxy, or hydroxy moieties were studied. The dimensionality of the monolayer's surface-parallel order was found to correspond to the number of molecular carboxyl groups, with the zero-, one-, or two-carboxyl molecules exhibiting no, one-, or two-dimensional order, respectively. The observed structural motifs are rationalized based on the molecular conformations and bonding synthons. Similarities, or otherwise, with the corresponding structure of three-dimensional (3D) crystals and graphite-supported LFs are also discussed.

INTERFACIAL CHARACTERIZATION OF COFFEE MIX USING DYNAMIC SURFACE TENSIOMETER

ABSTRACTInstant coffee with different blends and various trades is available all over the world. The brands vary in their composition because of the concentration of basic ingredients, i.e., coffee, sugar and cream. Coffee and other beverages are explained on the basis of three basic properties: taste, foaming and wetting. By using dynamic surface tensiometric analysis, the effects of the basic ingredients are examined by experiments. Different brands and instant coffee sticks were experimented and results were compared.PRACTICAL APPLICATIONSDynamic surface tensiometry is an important technology to evaluate the changes in the surface of liquid solutions: stagnant and flowing fluids. This technique is also applied to characterize the biological liquids, waste water treatment and beverages with large and complex molecular weight components.

Micellar evolution in mixed nonionic/anionic surfactant systems

Surfactant mixtures are widely used in industrial applications due to their favorable synergistic interactions. For instance, anionic and nonionic mixtures are often employed in detergent, personal care, and enhanced oil recovery. It is useful to understand micellization behaviors of such mixtures, as they are important for formulation optimizations. A range of techniques including surface tensiometry, fluorescence spectroscopy, ultrafiltration, and analytical ultracentrifugation (AUC), were employed in this work to obtain information on the micellization behaviors of the mixed n-dodecyl-β-d-maltoside (DM)/sodium dodecyl sulfonate (SDSN) system. The interaction parameter, monomer concentration, and micellar size and shape distribution were obtained for this mixed surfactant system as a function of total surfactant concentration as well as mixing ratio to achieve a full understanding of their aggregation behaviors. The coexistence of two types of micelles was identified in this mixed anionic/nonionic surfactant system for the first time. A model is proposed to explain such coexistence based on the surface activities and the interactions between the two types of surfactants. These findings are useful for optimizing the composition of mixed surfactant systems and enhancing the synergetic efficiency of the system to achieve more effective and economical formulations.

Study of drug concentration effects on in vitro lipolysis kinetics in medium-chain triglycerides by considering oil viscosity and surface tension

Simple oil formulations are widely used in oral drug delivery and the fate of these systems is governed mainly by the dispersion and digestion process. The current work aimed to study concentration effects of six poorly water-soluble drugs on the in vitro lipolysis rate of medium-chain triglycerides. The results were compared with drug effects on oil viscosity and surface tension. First the different drugs were characterized by molecular modeling and their influence on physical oil properties was assessed. Herein capillary viscosimetry was employed as well as dynamic surface tensiometry. Subsequently, an apparent in vitro lipolysis rate was determined in biorelevant medium using an automated pH stat titrator linked to a thermo-controlled vessel. The different drugs exhibited varying effects on oil viscosity and surface tension. However, all drugs significantly lowered the apparent lipolysis rate of the oil. This effect was very similar among the different compounds with exception of orlistat, which practically blocked lipolysis because of a potent direct inhibition. The other drugs affected lipolysis kinetics most likely by different mechanism(s). In light of the obtained results, a drug effect on oil viscosity or surface tension appeared to play a minor role in reducing the lipolysis rate. The lipolysis kinetics was further not affected by the drug load, which was deemed advantageous from a pharmaceutical viewpoint. Different dose strengths are therefore not assumed to alter lipolysis kinetics, which is beneficial for limiting the variability of in vivo drug release. Further studies of drug solubility kinetics in the evolving digestion phases are, however, needed to finally assess potential effects of dosage strength in simple oil formulations.

Measurement of Aggregate Cohesion by Tissue Surface Tensiometry

Rigorous measurement of intercellular binding energy can only be made using methods grounded in thermodynamic principles in systems at equilibrium. We have developed tissue surface tensiometry (TST) specifically to measure the surface free energy of interaction between cells. The biophysical concepts underlying TST have been previously described in detail. The method is based on the observation that mutually cohesive cells, if maintained in shaking culture, will spontaneously assemble into clusters. Over time, these clusters will round up to form spheres. This rounding-up behavior mimics the behavior characteristic of liquid systems. Intercellular binding energy is measured by compressing spherical aggregates between parallel plates in a custom-designed tissue surface tensiometer. The same mathematical equation used to measure the surface tension of a liquid droplet is used to measure surface tension of 3D tissue-like spherical aggregates. The cellular equivalent of liquid surface tension is intercellular binding energy, or more generally, tissue cohesivity. Previous studies from our laboratory have shown that tissue surface tension (1) predicts how two groups of embryonic cells will interact with one another, (2) can strongly influence the ability of tissues to interact with biomaterials, (3) can be altered not only through direct manipulation of cadherin-based intercellular cohesion, but also by manipulation of key ECM molecules such as FN and 4) correlates with invasive potential of lung cancer, fibrosarcoma, brain tumor and prostate tumor cell lines. In this article we will describe the apparatus, detail the steps required to generate spheroids, to load the spheroids into the tensiometer chamber, to initiate aggregate compression, and to analyze and validate the tissue surface tension measurements generated.

Measurement of Aggregate Cohesion by Tissue Surface Tensiometry

Measurement of Aggregate Cohesion by Tissue Surface Tensiometry

Synthesis and evaluation of new imidazolium‐based aromatic ether functionalized cationic mono and gemini surfactants

Synthesis of a novel series of imidazolium-based surfactants, [(ROArCH2MIm)Br] with aromatic ether functionalized hydrophobic tail of varying chain lengths and also their gemini counterparts were conducted in the present work. Synthesis involves initial conversion of 4-hydroxy benzoic acid to its methyl ester followed by its O-alkylation with long chain fatty alcohols, which was subsequently reduced and brominated to get 4-alkyloxy benzyl bromide. For the synthesis of monocationic surfactant, 4-alkyloxy benzyl bromide is quaternized with N-methylimidazole. Gemini surfactants are synthesized by initial coupling of imidazole to 4-alkyloxy benzyl bromide followed by its quaternization with dibromoalkane. The surface properties of all the synthesized surfactants were determined using surface tensiometry. Within the same homologous series, expected decrease in critical micelle concentration (cmc) with the increase in hydrophobicity was observed for shorter chain homologs. However, the deviation in cmc value from regularity was observed when the number of carbon atoms in the hydrophobic chain exceeded a certain number. The cmc values of the geminis were found to be remarkably low compared to their monomeric counterparts.

Modification of deeply buried hydrophobic interfaces by ionic surfactants.

Hydrophobicity, the spontaneous segregation of oil and water, can be modified by surfactants. The way this modification occurs is studied at the oil-water interface for a range of alkanes and two ionic surfactants. A liquid interfacial monolayer, consisting of a mixture of alkane molecules and surfactant tails, is found. Upon cooling, it freezes at T(s), well above the alkane's bulk freezing temperature, T(b). The monolayer's phase diagram, derived by surface tensiometry, is accounted for by a mixtures-based theory. The monolayer's structure is measured by high-energy X-ray reflectivity above and below T(s). A solid-solid transition in the frozen monolayer, occurring approximately 3 °C below T(s), is discovered and tentatively suggested to be a rotator-to-crystal transition.

Analysis of Thiol-sensitive Core-cross-linked Polymeric Micelles Carrying Nucleoside Pendant Groups using 'On-line' Methods: Effect of Hydrophobicity on Cross-linking and Degradation

Amphiphilic block copolymers were prepared via reversible–addition fragmentation chain transfer (RAFT) polymerization and their synthesis, cross-linking, and degradation were studied using on-line monitoring. The focus of this work is the systematic alteration of the hydrophobic block using copolymers based on 5′-O-methacryloyluridine (MAU) and styrene at different compositions to determine the effect of the copolymer composition on the properties of the micelle. A poly(poly(ethylene glycol) methyl ether methacrylate) (PEGMA) macroRAFT agent was chain extended with a mixture of styrene and MAU. In both systems, an increasing fraction of styrene was found to reduce the rate of polymerization, but the functionality of the RAFT system was always maintained. The amphiphilic block copolymers were dialyzed against water to generate micelles with sizes between 17 and 25 nm according to dynamic light scattering (DLS). Increasing styrene content lead to smaller micelles (determined by DLS and transmission electron microscopy) and to lower critical micelle concentrations, which was measured using surface tensiometry. The micelles were further stabilized via core-cross-linking using bis(2-methacroyloxyethyl) disulfide as crosslinker. NMR analysis revealed a faster consumption of crosslinker with higher styrene content. These stable cross-linked micelles were investigated regarding their ability to degrade in the presence of dithiothreitol as a model reductant. Increasing the styrene content resulted in a faster degradation of the cross-linked micelles into unimers.

Catanionic Mixtures Forming Gemini-like Amphiphiles

The properties of aqueous mixtures of cationic species with alkyl dicarboxylic acid compounds have been studied. The cationic compounds used in this study were tertiary amine-type N-methyl-N-(2,3-dioxypropyl)hexadecylamine (C16amine) and quaternary ammonium-type N,N-dimethyl-N-(2,3-dioxypropyl)hexadecylammonium chloride (C16Q). The alkyl dicarboxylic acid compounds used were HOOC(CH(2))(10)COOH (C12H) and its sodium salt (C12Na). Three aqueous mixtures were examined in this study: (System I) C16amine + C12H, (System II) C16Q + C12Na, and (System III) C16Q + C12H. The solution pH was set at 12 for System III. The combination of (1)H-NMR and mass spectroscopy data has suggested that a stoichiometric complex is formed in the aqueous solutions at a mole fraction of C12H (or C12Na) = 0.33. Here, the C12H (or C12Na) molecule added to the system bridges two cationic molecules, like a spacer of gemini surfactants. In fact, the static surface tensiometry has demonstrated that the stoichiometric complex behaves as gemini-like amphiphiles in aqueous solutions. Our current study offers a possible way for easily preparing gemini surfactant systems.

Nonionic Surfactant Mixtures in an Imidazolium-Type Room-Temperature Ionic Liquid

The physicochemical properties of nonionic surfactant mixtures in an aprotic, imidazolium-type room-temperature ionic liquid (RT-IL) have been studied using a combination of static surface tensiometry, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM). The surfactants used in this study are phytosterol ethoxylates (BPS-n, where n is an oxyethylene chain length of either 5 or 30) and the selected RT-IL is 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)). The shorter chain oxyethylene surfactant (BPS-5) exhibits greater surface activity in BmimPF(6) than BPS-30; hence, BPS-5 is a major component in driving the interfacial adsorption and molecular aggregation of the mixed system. The surface tension data demonstrate that an increased mole fraction of BPS-5 results in a decreased critical aggregation concentration (cac) and negatively increased Gibbs free energies estimated for molecular aggregation (ΔG(0)(agg)) and interfacial adsorption (ΔG(0)(ads)). Indeed, the compositions of the monolayer adsorbed at the air/solution interface and the molecular aggregate formed in the bulk solution are enriched with BPS-5. The combination of the DLS and cryo-TEM results demonstrates the spontaneous formation of multi-lamellar vesicles resulting from the BPS-5-rich composition of the molecular aggregates.

Characterization of wormlike micellar systems using DLS, rheometry and tensiometry

Alkyl polyethoxylates are surfactants widely used in vastly different fields, from oil exploitation to pharmaceutical applications. One of the most interesting characteristics of these surfactants is their ability to form micellar systems with specific geometry, the so-called wormlike micelle. In this study, dynamic light scattering (DLS), capillary viscometry, torque rheometry and surface tensiometry experiments were carried out in systems based on xylene, water, butanol (cosurfactant), and nona-ethyleneglycol-monododecyl ether (surfactant), with fixed surfactant:cosurfactant:oil composition (with and without oil phase) and varying overall concentration. The results showed that a transition from wormlike micelles to nanodrops was characterized by maximum relative viscosity (depending on how relative viscosity was defined), which was connected to maximum effective diameter, determined by DLS. Surface tension suggested that adsorption at the air–water interface had a Langmuir character and that the limiting value of the surfactant surface excess was independent of the presence of cosurfactant and xylene.

Complexation behavior of gelatin with amphiphilic drug imipramine hydrochloride as studied by conductimetry, surface tensiometry and circular dichroism studies

Herein we report our studies carried out on the interaction between IMP and gelatin in aqueous medium at 25 °C using conductimetry, surface tensiometry and circular dichroism (CD) techniques. Both surface tensiometry and conductimetry results indicate that the drug interacts with the gelatin in a surfactant-like manner, i.e., both critical aggregation (cac) and polymer saturation points (psp) were observed. The interaction starts with the formation of a highly surface-active complex as revealed by the lowering of surface tension on the addition of drug to the macromolecule. The decrease in cac on increasing gelatin concentration is an indication of the strong interaction between gelatin and IMP. However, at low concentration of gelatin the interaction was not much strong as exposed by surface tension study, i.e., the cac was not very clear (as with higher gelatin concentrations). As usual, the psp increased on increasing the gelatin concentration and was always higher than the critical micelle concentration of the drug in pure aqueous medium. Using CD measurements the influence of IMP on the secondary structure of gelatin in aqueous solutions was also investigated. CD studies (performed at very low drug concentrations) illustrated that the random coil content of gelatin increases with increasing drug concentration. Free energies of aggregation (Δ G agg) and micellization (Δ G mic) were computed with the help of degrees of micelle ionization obtained from the specific conductivity – [IMP] plots.

Kinetic analysis of the interaction between poly(amidoamine) dendrimers and model lipid membranes

We used fluorescence spectroscopy and surface tensiometry to study the interaction between low-generation (G1 and G4) poly(amidoamine) (PAMAM) dendrimers, potential vehicles for intracellular drug delivery, and model lipid bilayers. Membrane association of fluorescently labeled dendrimers, measured by fluorescence anisotropy, increased with increasing size of the dendrimer and with increasing negative charge density in the membrane, indicating the electrostatic nature of the interaction. When the membrane was doped with pyrene-labeled phosphatidyl glycerol (pyrene-PG), pyrene excimer fluorescence demonstrated a dendrimer-induced selective aggregation of negatively charged lipids when the membrane was in the liquid crystalline state. A nonlinear Stern–Volmer quenching of dendrimer fluorescence with cobalt bromide suggested a dendrimer-induced aggregation of lipid vesicles, which increased with the dendrimer's generation number. Surface tensiometry measurements showed that dendrimers penetrated into the lipid monolayer only at subphysiologic surface pressures (<30mN/m). We conclude that the low-generation PAMAM dendrimers associate with lipid membranes predominantly electrostatically, without significantly compromising the bilayer integrity. They bind stronger to membranes with higher fluidity and lower surface pressure, which are characteristic of rapidly dividing cells.