Dynamic Surface Properties Research Articles

Dynamic surface properties of DNA/surfactant solutions: Impact of DNA structure

The dynamic surface properties of mixed solutions of a cationic surfactant - cetyltrimethylammonium bromide (CTAB) - and different types of deoxyribonucleic acid in both linear (ctDNA) and plasmid (pDNA) forms were studied by surface tensiometry and dilational surface rheology. The dynamic surface elasticity and the dynamic surface tension depended strongly on the DNA type. The adsorption layers of ctDNA/CTAB solutions exhibited strong elastic behavior in a wide range of surfactant concentrations. Contrariwise, the addition of plasmid DNA altered the dynamic surface elasticity of CTAB solutions only slightly. The significant difference in the size of macromolecules, their conformation, and, thereby, their effective charge leads to the formation of DNA/CTAB complexes of different surface activity and causes drastic changes in the rheology of the adsorption layer.

Theoretical analysis of dielectric and mechanical relaxation in bulk and surface polymer structures

A theory of the dynamic properties of surface and bulk polymer structures with dipolar-type order on the level of rigid kinetic units is developed that allows us to establish the relationship between the parameters of inter- and intrachain interactions and the characteristics of orientation order on the one hand, and relaxation properties on the other.

Dynamic contact angle cycling homogenizes heterogeneous surfaces

In order to reduce restenosis, the necessity to develop the appropriate coating material of metallic stent is a challenge for biomedicine and scientific research over the past decade. Therefore, biodegradable copolymers of poly((R,S)-3,3 dimethylmalic acid) (PDMMLA) were prepared in order to develop a new coating exhibiting different custom groups in its side chain and being able to carry a drug. This material will be in direct contact with cells and blood. It consists of carboxylic acid and hexylic groups used for hydrophilic and hydrophobic character, respectively. The study of this material wettability and dynamic surface properties is of importance due to the influence of the chemistry and the potential motility of these chemical groups on cell adhesion and polymer kinetic hydrolysis. Cassie theory was used for the theoretical correction of contact angles of these chemical heterogeneous surfaces coatings. Dynamic Surface Analysis was used as practical homogenizer of chemical heterogeneous surfaces by cycling during many cycles in water. In this work, we confirmed that, unlike receding contact angle, advancing contact angle is influenced by the difference of only 10% of acidic groups (%A) in side-chain of polymers. It linearly decreases with increasing acidity percentage. Hysteresis (H) is also a sensitive parameter which is discussed in this paper. Finally, we conclude that cycling provides real information, thus avoiding theoretical Cassie correction. H10is the most sensible parameter to %A.

Adsorption kinetics of the ionic surfactant decanoic acid

The adsorption kinetics of ionic surfactant decanoic acid was examined. Dynamic and equilibrium surface tensions (ST) were measured using a video-enhanced pendant bubble tensiometer. The equilibrium ST data and the complete ST relaxation profiles were compared with theoretical profiles predicted by both non-ionic and ionic models. The quasi-equilibrium approach was used in the ionic model to describe the electric field in the electrical double layer. Both non-ionic and ionic generalized-Frumkin models predict the equilibrium and dynamic ST data very well. Using the ionic model, a comparison between the dynamic ST data and the theoretical ST profiles gave a diffusivity of 5.5×10−6cm2/s. The adsorption of decanoic acid onto the air–water interface was determined to be diffusion controlled. Dynamic surface properties (Γ and ψs), the electrical potential ψ(r, t) in the double layer, and the double layer thickness λ(C, t) were also evaluated. It was found that the surface charge density increases very quickly at the early stages (∼1s) of the surfactant adsorption process. Additionally, the electrical surface potential data implied that the surface charge density becomes significantly stronger at very dilute surfactant concentrations, where π is less than 1mN/m.

Effect of pH and electrolyte concentration on rising air bubbles in β-lactoglobulin solutions

The local velocity profile (LVP) of a rising bubble can serve as a fingerprint for the dynamic behavior of the adsorption/desorption processes going on at a solution/air interface. The LVP of bubbles in β-lactoglobulin (BLG) solutions proves to be extremely sensitive for the adsorption of BLG at low bulk concentrations. In addition, it can show the impact of pH and ionic strength on the dynamic surface properties of BLG at the solution/air interface. It is observed that the time for establishing an immobile rigid surface layer at the rising bubble surface becomes shorter with increasing pH from 3 to 7. A peculiar behavior is observed at the isoelectric point (IEP) where the LVPs show irregularities. Under dynamic conditions BLG does not exhibit highest surface active at the IEP within the range of BLG concentrations as measured by the rising bubble technique.

What is really driving cell-surface interactions? Layer-by-layer assembled films may help to answer questions concerning cell attachment and response to biomaterials.

Layer-by-layer (LbL) assembled multicomponent films offer the opportunity to control and to fine-tune cell attachment and behavior on solid surfaces [Layer-by-Layer Films for Biomedical Applications, edited by Picart et al. (Wiley, Weinheim, 2014) and El-Khouri et al., "Multifunctional layer-by-layer architectures for biological applications," in Functional Polymeric Ultrathin Films, edited by Advincula and Knoll (Wiley, Weinheim, 2011), Vol. 1]. At the same time, these films allow for quite detailed physicochemical characterization of static and dynamic surface properties that are typically not available in classic cell culture. In this report, the authors investigate cell adhesion and cytocompatibility of compositionally and morphologically similar thin films composed of oppositely charged synthetic or natural polyelectrolytes in which different physical parameters such as surface charge or water content are varied through chemical composition and deposition conditions. Human adult dermal fibroblasts were chosen as a model because of the need for chemically defined matrix in the field of primary cell amplification. The growth and the stability of the multilayer films in the incubation media were studied dissipation-enhanced quartz crystal micobalance (QCM-D) and ellipsometry. The QCM-D signals observed during the film deposition were analyzed qualitatively to estimate the viscoelastic properties of the films. The authors used contact angle measurements with water to study the contribution of the chemical functionalities to wetting behavior of the films. Most importantly, they also studied the interaction of the films with serum components. Our results underline that cell adhesion is a highly complex process which is not only governed by the functionality of a surface but also by its morphology, its affinity for serum components, and also by changes of surface properties brought about by adsorbing molecules. Of the many LbL-films tested, poly(4-styrenesulfonate)/poly(allyl amine) multilayers were best suited for our fibroblast cultures, which opens a way to avoid gelatin based and similar substrates whose exact chemical composition is unknown.

Rational engineering of physicochemical properties of nanomaterials for biomedical applications with nanotoxicological perspectives.

Innovative engineered nanomaterials are at the leading edge of rapidly emerging fields of nanobiotechnology and nanomedicine. Meticulous synthesis, unique physicochemical properties, manifestation of chemical or biological moieties on the surface of materials make engineered nanostructures suitable for a variety of biomedical applications. Besides, tailored nanomaterials exhibit entirely novel therapeutic applications with better functionality, sensitivity, efficiency and specificity due to their customized unique physicochemical and surface properties. Additionally, such designer made nanomaterials has potential to generate series of interactions with various biological entities including DNA, proteins, membranes, cells and organelles at nano-bio interface. These nano-bio interactions are driven by colloidal forces and predominantly depend on the dynamic physicochemical and surface properties of nanomaterials. Nevertheless, recent development and atomic scale tailoring of various physical, chemical and surface properties of nanomaterials is promising to dictate their interaction in anticipated manner with biological entities for biomedical applications. As a result, rationally designed nanomaterials are in extensive demand for bio-molecular detection and diagnostics, therapeutics, drug and gene delivery, fluorescent labelling, tissue engineering, biochemical sensing and other pharmaceuticals applications. However, toxicity and risk associated with engineered nanomaterials is rather unclear or not well understood; which is gaining considerable attention and the field of nanotoxicology is evolving promptly. Therefore, this review explores current knowledge of articulate engineering of nanomaterials for biomedical applications with special attention on potential toxicological perspectives.

Impact of a Reducing Agent on the Dynamic Surface Properties of Lysozyme Solutions.

Disulfide bond shuffling in the presence of the reducing agents dithiothreitol (DTT) or β-mercaptoethanol (BME) strongly affects the surface properties of lysozyme solutions. The addition of 0.32 mM DTT substantially alters the kinetic dependencies of the dynamic surface elasticity and surface tension relative to those of pure protein solutions. The significant increase in the dynamic surface elasticity likely relates to the cross-linking between lysozyme molecules and the formation of a dense layer of protein globules stabilized by intermolecular disulfide bonds at the liquid/gas interface. This effect differs from the previously described influence of chaotropic denaturants, such as guanidine hydrochloride (GuHCl) and urea, on the surface properties of lysozyme solutions. If both chaotropic and reducing agents are added to protein solutions simultaneously, their effects become superimposed. In the case of mixed lysozyme/GuHCl/DTT solutions, the dynamic surface elasticity near equilibrium decreases as the GuHCl concentration increases because of the gradual loosening of the cross-linked layer of protein globules but remains much higher than that of lysozyme/GuHCl solutions.

The role of protein "Stability patches" in molecular recognition: A case study of the human growth hormone-receptor complex.

Dynamic characteristics of protein surfaces are among the factors determining their functional properties, including their potential participation in protein-protein interactions. The presence of clusters of static residues-"stability patches" (SPs)-is a characteristic of protein surfaces involved in intermolecular recognition. The mechanism, by with SPs facilitate molecular recognition, however, remains unclear. Analyzing the surface dynamic properties of the growth hormone and of its high-affinity variant we demonstrated that reshaping of the SPs landscape may be among the factors accountable for the improved affinity of this variant to the receptor. We hypothesized that SPs facilitate molecular recognition by moderating the conformational entropy of the unbound state, diminishing enthalpy-entropy compensation upon binding, and by augmenting the favorable entropy of desolvation. SPs mapping emerges as a valuable tool for investigating the structural basis of the stability of protein complexes and for rationalizing experimental approaches, such as affinity maturation, aimed at improving it.

Graphene on Ni(111): Electronic Corrugation and Dynamics from Helium Atom Scattering.

Using helium atom scattering, we have studied the structure and dynamics of a graphene layer prepared in situ on a Ni(111) surface. Graphene/Ni(111) exhibits a helium reflectivity of ∼20% for a thermal helium atom beam and a particularly small surface electron density corrugation ((0.06 ± 0.02) Å peak to peak height). The Debye–Waller attenuation of the elastic diffraction peaks of graphene/Ni(111) and Ni(111) was measured at surface temperatures between 150 and 740 K. A surface Debye temperature of θD = (784 ± 14) K is determined for the graphene/Ni(111) system and θD = (388 ± 7) K for Ni(111), suggesting that the interlayer interaction between graphene and the Ni substrate is intermediary between those for strongly interacting systems like graphene/Ru(0001) and weakly interacting systems like graphene/Pt(111). In addition we present measurements of low frequency surface phonon modes on graphene/Ni(111) where the phonon modes of the Ni(111) substrate can be clearly observed. The similarity of these findings with the graphene/Ru(0001) system indicates that the bonding of graphene to a metal substrate alters the dynamic properties of the graphene surface strongly and is responsible for the high helium reflectivity of these systems.

Influence of guanidine hydrochloride and urea on the dynamic surface properties of lysozyme solutions

Guanidine hydrochloride and urea have different effects on the surface properties of lysozyme solutions due to different interaction mechanisms between the protein and denaturants: an increase in the guanidine hydrochloride concentration leads to noticeable changes in the dynamic surface elasticity, while the main effect of urea consists in a significant drop of the static surface tension.

Rapid Movement of Water Droplets on the Hydrophobic Surface of ZnO Nanorod Array Impregnated by Lubricant

In this paper, it is described that the motion of water droplets on the hydrophobic surface of ZnO nanorod array impregnated lubricant, is called slippery liquid-infused porous surface (SLIPS). The energy gradient required to induce the motion of the droplets is created on the boundary of superhydrophobic ZnO nanorod array and SLIPS. Because of the lower viscous force of SLIPS, the water droplet can rapidly move for longer distance on the surface. In view of changing the release distance of water droplet, the mechanism for the rapid movement is discussed. The results indicate that the movement distance of water droplet markedly increases with the increasing of the release distance. Because the potential energy of the height is converted into kinetic energy, the water droplet intensively collides the interface between ZnO nanorod array and SLIPS. This impact makes the water droplet distort, which enhances the driving force. These new findings will not only deepen our understanding of the relationship between surface structure and dynamic wetting properties, but also afford the new notion and beneficial reference for designing liquid droplet transportation devices in micro-fluidic systems.

Dynamic surface properties of lysozyme solutions. Impact of urea and guanidine hydrochloride

Urea and guanidine hydrochloride (GuHCl) have different influence on surface properties of lysozyme solutions. The increase of GuHCl concentration leads to noticeable changes of kinetic dependencies of the dynamic surface elasticity and ellipsometric angles while the main effect of urea reduces to a strong drop of the static surface tension. The difference between the effects of these two denaturants on the surface properties of other investigated globular proteins is significantly weaker and is mainly a consequence of a different extent of the globule unfolding in the surface layer at equal concentrations of the denaturants. The obtained results for lysozyme solutions are connected with the strongly different denaturation mechanisms under the influence of urea and GuHCl. In the former case the protein preserves its globular structure in the adsorption layer at high urea concentrations (up to 9M) but without tightly packed interior of the globule and with a dynamic tertiary structure (molten globule state). On the contrary, the increase of GuHCl concentration leads to partial destruction of the protein tertiary structure in the surface layer, although this effect is not as strong as in the case of previously studied bovine serum albumin and β-lactoglobulin.

ChemInform Abstract: Nanocatalysis II: In Situ Surface Probes of Nano‐Catalysts and Correlative Structure‐Reactivity Studies

AbstractReview: 120 refs.

Dynamic Structural/Amphiphilic “Portrait” of Biomembranes as their Fundamental Property Relevant to Function: Results of Atomistic Simulations

Analysis of local dynamic heterogeneities and hydrophobic surface properties of lipid bilayers is an important step toward understanding of the physical processes underlying formation of lipid domains and molecular mechanisms of the so-called “membrane response” observed upon binding of external molecules to cell membranes. Here, we used atomistic molecular dynamics simulations to address these problems and study structural/amphiphilic “portrait” of a large series of model bilayer membranes (1,2). Rearrangements of membranes upon binding of antimicrobial peptides and association of transmembrane helices were investigated as well (3,4).It was shown that the water-lipid interface of biomembranes represents a highly dynamic and “mosaic” picture, whose parameters depend on the bilayer composition. Formation of such heterogeneities is caused by various intermolecular interactions between lipids, water and ions. Because clustering of the components is determined by a thin balance of differently directed factors, even their minor changes can induce serious rearrangements on the membrane surface. These issues still resist easy experimental characterization.Probably, these phenomena are indispensable for fast mass/energy transfer near the water/membrane boundary, thus regulating diffusion of molecules in this functionally important area: e.g., approaching of ligands to membrane receptors, delivery of proteins to their sites of insertion into membrane, and so on. Putative role of local heterogeneities and collective phenomena in lipid/water systems is discussed.

Surface Composition and Morphology of Particles Dried Individually and by Spray Drying

This study investigates how the morphology of spray-dried particles is related to the formulation and properties of the components in the formulation. Further, the scale effects in comparisons of levitation-dried single particles and spray-dried particles in a lab-scale spray dryer have been addressed. The Drying Kinetics AnalyzerTM generates single particles from a levitated drop under simulated spray-drying conditions. A set of surface-active polymers (bovine serum albumin, hydroxypropyl methyl cellulose, and triblock co-polymer Poloxamer), in combination with lactose, were analyzed for their dynamic surface properties in solution, and their effect on particle morphology and surface composition were determined by low-vacuum SEM and XPS analyses. The morphology obtained in spray drying was reproduced in the single-particle drying. The surface compositions were also similar, but higher levels of surface-active materials were found at the surface of the single particles as compared to the spray-dried particles. Further, the adsorption rate of surface-active compounds at the drop surface estimated by dynamic surface tension was found to be an important parameter to estimate the surface composition at different drying scales. The particle morphology was primarily determined by the surface rheological properties of the feed solution and, to a lesser extent, by the surface composition.

Nanocatalysis II: In Situ Surface Probes of Nano-Catalysts and Correlative Structure–Reactivity Studies

Model nano-catalysts with monodisperse particle sizes and architectures are essential for a fundamental understanding of surface property dynamics during catalytic reactions. Surface tools and techniques, when conducted under catalytically relevant temperature and pressure conditions, render possible measurements of dynamic surface properties such as oxidation state, composition, coordination, and bonding. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy with purposely built in situ reaction cells and ambient pressure X-ray photoelectron spectroscopy (APXPS) provide (near) surface sensitive and chemical specific information on the oxidation states of metal and oxide (co-)catalysts as well as adsorbent functional elements such C, O and N under reactive gas atmospheres and even liquid environments. Likewise, sum frequency generation (SFG) vibrational spectroscopy with in situ reaction cells helps uncover the bonding geometry and configuration of the topmost surface again under conditions pertinent to catalysis. Furthermore, the local dynamics in the nanoscale and on the single particle level are revealed by environmental transmission electron microscopy (ETEM) and the spectro-microscopy techniques equipped within. A correlative approach, where an array of these in situ tools and techniques were conducted in parallel with catalytic measurements, was employed to gain molecular insight into some of the modern scientific challenges in heterogeneous catalysis. Several case examples of this correlative approach are presented here. The CO oxidation reaction over hybrid nano-catalysts of Pt nanoparticles (NPs) with various mesoporous metal oxides such as Co3O4, MnO2 and CeO2 was explored in relation to bifunctional catalysis and interfacial charge transfer chemistry by using in situ NEXAFS spectroscopy. Likewise, bimetallic CoPt and PtSn nanoparticle catalysts supported on silica were investigated by using a combination of in situ NEXAFS spectroscopy and APXPS. Next, CO2 hydrogenation was carried out over bimetallic CoPt/SiO2 and Co/TiO2 hybrid nano-catalysts. In this case, in situ NEXAFS spectroscopy, APXPS, and ETEM indicated severe, yet reversible, surface restructuring that involved hydrogen atom spillover. Finally, ~2 nm Pt NPs were investigated using in situ SFG to study hydrogenation and hydrogenative isomerization reactions. Specifically, SFG indicated that the hydrogenation of furfural and crotonaldehyde proceed by interfacial hydrogen atom spillover from TiO2, while the hydrogenative isomerization of methylcyclopentane (MCP) proceeds by spillover and surface diffusion of cyclohexene over mesoporous zeolites. These studies unequivocally indicated the presence of a particular reaction channel that involved one way flow of charged (i.e. electrons or protons) or neutral species (i.e. reactants) at a broadly defined interface between metals and oxides. In addition to these case studies, experimental approaches employing capillary flow micro-reactors are discussed in relation toward the goal of short time resolutions that could help isolate such charged or neutral intermediates in the future.

Micro- and nano-scale phenomena effect on bubble size in mechanical flotation cell

The micro/nano-scale phenomena affecting the bubble size observed in a mechanical flotation cell were investigated using an extensive dynamic surface property study with commercial laboratory instruments. The results highlighted two distinct dynamic surface properties: a rapid adsorption/desorption rate leading to undetectable dilatation surface elasticity, and a slow adsorption/desorption process taking place within minutes and leading to a significant increase in the dilatation elasticity of the interface. The latter is observed in highly surface-active reagent grade Polypropylene Glycol and in commercial Dowfroth 250 frothers while the rapid adsorption/desorption rate is a characteristic of weakly surface-active reagent grade 1-Pentanol and commercial Dowfroth 200.The bubble size distribution and therefore the Sauter mean diameter results also highlighted the unambiguous similarity in the effect of frother on bubble size between the I-Pentanol and the Dowfroth 200 and indeed between the Polypropylene Glycol and the Dowfroth 250. The present paper examines the similarity between the two groups in order to gain understanding on how the dynamic surface properties affect the bubble size in two-phase systems.

Synthesis and Performance of Novel Fluorinated Acrylate Polymers: Preparation and Reactivity of Short Perfluoroalkyl Group Containing Monomers

Developing novel fluorinated monomers and polymer materials with a short perfluoroalkyl group is attracting the attention of researchers. The synthesis of fluorinated monomers, [N-methyl-perfluorobutane-1-sulfonamide]ethyl acrylate (C4SA) and methacrylate (C4SMA), [N-methyl-perfluorohexane-1-sulfonamide]ethyl acrylate (C6SA), and methacrylate (C6SMA) were presented from a three-step procedure, which combined the reaction of perfluorobutanesulfonyl fluoride or perfluorohexanesulfonyl fluoride with an excess of methylamine, alkylation reaction with 2-bromoethanol, and esterification reaction with acryloyl chloride or methacryloyl chloride. The outcome compounds structures of each step were confirmed by 1H NMR, 19F NMR, FT-IR, and elemental analysis. Free radical copolymerizations of fluorinated acrylates and butyl methacrylate (BMA) in butyl acetate (BuOAc) were performed to determine the comonomers reactivity ratios and Q-e values. The surface wetting properties of fluorinated homopolymers were investigated by surface tension and dynamic contact angles. As a result, the target polymers showed extreme low surface energies and dynamic surface properties.

Tuning the Magnetization Dynamics in Sputtered ${\hbox{Co}}_{2}{\hbox{FeAl}}_{0.5}{\hbox{Si}}_{0.5}$ Heusler Alloy Thin Film by Gas Pressure

The influences of sputtering gas pressure on the high frequency magnetization dynamics properties of sputtered Co2FeAl0.5Si0.5 (CFAS) Heusler alloy thin films have been systematic studied. Results show that the surface roughness, grain size, anisotropy field and dynamic magnetic properties can be tailored by changing sputtering gas pressures. The inhomogeneous linewidth broadening of the sputtered CFAS Heusler thin films is monotonously enhanced with the pressure increasing, similar as with the anisotropy field. A low value intrinsic damping parameter is extracted as 0.0073 with a low sputtering pressure, 1.58 ×10-4 mbar. The intrinsic damping parameter increases monotonously up to 0.0122 with the pressure increasing. The high tunability of the damping constant indicates that controlling the sputtering gas pressure could be an effective method to tune the magnetization dynamics in sputtered CFAS thin film.