Model Hydrophobic Surfaces Research Articles

Solvation Forces Near Hydrophobic Surfaces: A Classical Density Functional Theory Study.

We use classical density functional theory (DFT) to model solvation interactions between hydrophobic surfaces, which we show to be characterized by depletion attraction at small surface to surface separations and a slowly decaying bipower law interaction at large separations. The solvation interaction originates from van der Waals (vdW) and Coulombic interactions between molecules in the polar solvent, e.g., water, and from the molecules thermal motion and finite volume. We investigate model hydrophobic surfaces represented by bubbles and nonpolar solids, e.g., aliphatic particles, and calculate in a DFT fashion the distribution of molecules in the interlaying solvent between two such surfaces and the hydrophobic excess force resulting from it. The interactions are largely attractive, which is well-known in measurement, albeit vdW attraction between molecules in solids and in the solvent may cause repulsion at certain interface to interface separations. We commence our analysis by suggesting an asymptotic analytical bipower law expression for the solvation interaction at large separations. Thereafter we present a full numerical solution, which is in good agreement with the analytical prediction and further explores the interaction at small surface to surface separations. Our theoretical results yield adhesion energies which agree with previous experiments.

Influence of Surface Roughness, Nanostructure, and Wetting on Bacterial Adhesion.

Bacterial fouling is a persistent problem causing the deterioration and failure of functional surfaces for industrial equipment/components; numerous human, animal, and plant infections/diseases; and energy waste due to the inefficiencies at internal and external geometries of transport systems. This work gains new insights into the effect of surface roughness on bacterial fouling by systematically studying bacterial adhesion on model hydrophobic (methyl-terminated) surfaces with roughness scales spanning from ∼2 nm to ∼390 nm. Additionally, a surface energy integration framework is developed to elucidate the role of surface roughness on the energetics of bacteria and substrate interactions. For a given bacteria type and surface chemistry; the extent of bacterial fouling was found to demonstrate up to a 75-fold variation with surface roughness. For the cases showing hydrophobic wetting behavior, both increased effective surface area with increasing roughness and decreased activation energy with increased surface roughness was concluded to enhance the extent of bacterial adhesion. For the cases of superhydrophobic surfaces, the combination of factors including (i) the surpassing of Laplace pressure force of interstitial air over bacterial adhesive force, (ii) the reduced effective substrate area for bacteria wall due to air gaps to have direct/solid contact, and (iii) the reduction of attractive van der Waals force that holds adhering bacteria on the substrate were summarized to weaken the bacterial adhesion. Overall, this study is significant in the context of designing antifouling coatings and systems as well as explaining variations in bacterial contamination and biofilm formation processes on functional surfaces.

Factors Influencing Biofilm Formation by Salmonella enterica sv. Typhimurium, E. cloacae, E. hormaechei, Pantoea spp., and Bacillus spp. Isolated from Human Milk Determined by PCA Analysis.

Bacteria enter milk during poor hygiene practices and can form a biofilm on surfaces that come into contact with human milk. The presence of a biofilm increases the risk of infections among newborns as bacteria protected by biofilm are resistant to washing and disinfection processes. The formation of the biofilm depends on the microbial species, environmental conditions, and the specific materials colonized. The aim of this study is to analyze the effects of factors such as temperature, incubation time, and initial cell concentration on biofilm formation by pathogenic bacteria isolated from human milk on model hydrophobic polystyrene surfaces. Model studies confirm that pathogenic bacteria appearing in human milk as a result of cross-contamination tend to form a biofilm. The majority of isolates formed biofilm at both 25 and 37 °C after 12 h at 1 × 103 CFU/mL inoculum count. Multivariate principal component analysis (PCA) showed that at lower temperatures, biofilm formation by bacterial isolates was the main determinant of biofilm formation, other factors were less important; however, at 37 °C, time was a factor in biofilm formation. The model research performed underlines the importance of maintaining the proper hygiene of rooms, surfaces, and devices for expressing, storing, and preparing mothers' milk and powdered infant formula (PIF) in facilities responsible for feeding newborns and premature babies.

Isoelectric Point of Proteins at Hydrophobic Interfaces.

Structural and colloidal stability of proteins at different surfaces and interfaces is of great importance in many fields including medical, pharmaceutical, or material science. Due to their flexibility, proteins tend to respond to their environmental conditions and can undergo structural and conformational changes. For instance, alterations in physiological factors such as temperature, ions concentration, or pH as well as the adsorption to an interface can initiate protein aggregation. Therefore, at different surfaces and interfaces the characterization of the structural and colloidal stability of proteins, which is mainly influenced by their electrostatic and hydrophobic interactions, is of fundamental importance. In this study, we utilized sum frequency generation (SFG) spectroscopy to assess the role of solution pH on the polarity and magnitude of the electric field within the hydration shell of selected model proteins adsorbed to a hydrophobic surface. We used polystyrene (PS) as a model hydrophobic surface and determined the isoelectric point (IEP) of four structurally different model proteins. Comparing the measured IEP of proteins at the PS/solution or air/solution interface with that determined in the bulk solution via zeta potential measurement, we found significant similarities between the IEP of surface adsorbed proteins and those in the bulk aqueous phase. The pH dependence behavior of proteins was correlated to their amino acid composition and degree of hydrophobicity.

Adsorption of non-ionic surfactant and monoclonal antibody on siliconized surface studied by neutron reflectometry

The adsorption of monoclonal antibodies (mAbs) on hydrophobic surfaces is known to cause protein aggregation and degradation. Therefore, surfactants, such as Poloxamer 188, are widely used in therapeutic formulations to stabilize mAbs and protect mAbs from interacting with liquid-solid interfaces. Here, the adsorption of Poloxamer 188, one mAb and their competitive adsorption on a model hydrophobic siliconized surface is investigated with neutron scattering coupled with contrast variation to determine the molecular structure of adsorbed layers for each case. Small angle neutron scattering measurements of the affinity of Poloxamer 188 to this mAb indicate that there is negligible binding at these solution conditions. Neutron reflectometry measurements of the mAb show irreversible adsorption on the siliconized surface, which cannot be washed off with neat buffer. Poloxamer 188 can be adsorbed on the surface already occupied by mAb, which enables partial removal of some adsorbed mAb by washing with buffer. The adsorption of the surfactant introduces significant conformational changes for mAb molecules that remain on the surface. In contrast, if the siliconized surface is first saturated with the surfactant, no adsorption of mAb is observed. Competitive adsorption of mAb and Poloxamer 188 from solution leads to a surface dominantly occupied with surfactant molecules, whereas only a minor amount of mAb absorbs. These findings clearly indicate that Poloxamer 188 can protect against mAb adsorption as well as modify the adsorbed conformation of previously adsorbed mAb.

Effect of low-methoxy pectin on interfacial and emulsion stabilizing properties of heated whey protein isolate (WPI) aggregates

• QCM-D study of heated WPI and heated biopolymer complexes on hydrophobic surface. • A higher ratio of pectin to WPI increased the adsorbed mass on the surface. • A higher ratio of pectin to WPI decreased the protein load from 15.11 to 9.19 mg/m 2 . • Interfacial properties of the heated WPI-LMP affected the emulsion stability. In this study, we have investigated the interfacial and emulsion stabilizing properties of heat-induced whey protein isolate (WPI) aggregates prepared in the presence or absence of low-methoxy pectin (LMP). Sub-micron complex particles were formed by heating of oppositely charged WPI and LMP at different WPI:LMP mass ratios. The Quartz Crystal Microbalance with Dissipation (QCM-D) technique was used to better understand the adsorption properties of these biopolymeric particles at a model hydrophobic surface. Clear correlations were observed between the interfacial properties of WPI and WPI:LMP aggregates and the resulting emulsion characteristics. Compared to WPI aggregates (which led to emulsions containing larger flocculated droplets), the heated complexes (formed at a higher ratio of LMP to WPI) were highly efficient as Pickering stabilizers leading to emulsions with smaller droplets (5.5–6.8 μm). Cryo-SEM analysis clearly revealed the manipulation of the emulsions’ interfacial microstructure due to the adsorption of a WPI:LMP inter-polymeric film onto the surface of the droplets. The effectiveness of the colloidal particles in stabilizing emulsions depended largely on the formation of a sufficiently ‘dense layer’ of particles at the oil-water interface where these properties were controlled by the composition of WPI and LMP at the oil droplet surface. Moreover, the emulsion physical stability was greatly influenced by the formation of an inter-connected film at the oil droplet interface, whereby these viscoelastic films increased the steric hindrance against coalescence of emulsion droplets. This work provides the mechanism of emulsion stabilization by WPI particles formed by heating in the absence or presence of pectin.

Bouncing Droplets: A Hands-On Activity To Demonstrate the Properties and Applications of Superhydrophobic Surface Coatings

Here we report a hands-on activity addressed to master’s students in Physical Chemistry and Materials Science courses on the properties and applications of superhydrophobic surfaces. This simple and intuitive experience can also be used to teach undergraduate and high school students, thanks to its application-oriented approach and tangible results. Superhydrophobicity was achieved by the functionalization of oxide powders with alkylsilanes and their subsequent deposition on a glass substrate. The film’s superhydrophobicity was assessed by different application tests and compared with the behaviors of model hydrophobic, hydrophilic, and superhydrophilic surfaces. Its antistain properties were tested with both model dye solutions and everyday liquids. Films were fouled with graphite and dye powders to compare the self-cleaning capabilities of the different surfaces, and single droplet transport was achieved by adding magnetic particles. This engaging and adaptable experience introduces students to basic concepts of surface science in an intuitive and tangible way.

Extracellular DNA Provides Structural Integrity to a Micrococcus luteus Biofilm.

Force spectroscopy was used to show that extracellular DNA (eDNA) has a pre-eminent structural role in a biofilm. The adhesive behavior of extracellular polymeric substances to poly(ethylene terephthalate), a model hydrophobic surface, was measured in response to their degradation by hydrolytic enzymes known for their biofilm dispersion potential: DNaseI, protease, cellulase, and mannanase. Only treatment with DNaseI significantly decreased the adhesive force of the model bacterium Micrococcus luteus with the surface, and furthermore this treatment almost completely eliminated any components of the biofilm maintaining the adhesion, establishing a key structural role for eDNA.

Surface Water as a Mediator and Reporter of Adhesion at Aqueous Interfaces.

Understanding the adsorption of molecules onto surfaces is integral to a wide variety of fields with scientific, engineering, and industrial applications. The surface-adsorbed structure is governed by the nature of the molecule, surface characteristics, and solution environment. There are therefore three critical interactions that govern adhesion: solvent-analyte, substrate-analyte, and substrate-solvent. The last two interactions require a surface-specific probe restricted to a few nanometers or less. This is particularly true of efforts to probe polymer surface structure without being overwhelmed by bulk polymer signal or interfacial water structure in the presence of bulk water. Second-order nonlinear optical techniques are ideal probes of such interactions, as their reporting depth is determined by the polar arrangement of molecules (a break in the macroscopic inversion symmetry) rather than the penetration of the optical fields. This Account begins with an introduction of surface water structure from the perspective of a nonlinear probe. Details about the unique view of the water orientation distribution are discussed and contrasted with information obtained from conventional vibrational techniques. The salient features of water next to model hydrophobic and hydrophilic surfaces are discussed, in preparation for a discussion of solute interactions that follows. We then present three examples using a combination of linear and nonlinear vibrational spectroscopy and molecular dynamics simulations to illustrate how water is both a mediator and a marker of adhesion. The first is a study of amphipathic peptide adhesion onto hydrophobic and hydrophilic surfaces, characterizing the adsorbed structure in relation to the water surrounding the molecule and trapped near the surface. Water is found to be especially important in mediating adhesion to hydrophilic surfaces, where it aids in solvating the peptide as well as facilitating interactions with the surface. In the second example, we look at adhesion of a multicomponent polymer adhesive using surface-bulk heterospectral correlation analysis, in which surface vibrational spectroscopy is combined with bulk infrared absorption to determine interfacial structure development during the evaporation of water. When acrylic acid is added to the polymer, there is a change in orientation of the polymer before an increase in population. This is opposite to what is observed when no additive is present. In our third example, we show how interfacial water provides a unique window into the surface microenvironment during bacterial adhesion, highlighting the role of solution conditions at the surface in cell attachment and biofilm growth. Changes in the nonlinear vibrational response of interfacial water reflect changes occurring in the pH and ionic strength only at the surface, due to the presence of polymeric adhesives secreted by the bacteria. These studies underline the importance of surface water in governing the structure of adhered molecules and in mediating changes in the interfacial environment as a result of adhesion and provide insight into a nanoscale region that is otherwise difficult to query. They also illustrate the importance of combining surface-sensitive and bulk spectroscopic probes with computer modeling to gain a better understanding of the interplay between water and adsorbate structure.

Effects of elctrolytes on the stability of wetting films: Implications on seawater flotation

Surface force measurements were conducted using the force apparatus for deformable surfaces (FADS) to better understand the stability of the wetting films formed on hydrophobic surfaces in the presence of KCl and MgCl2. The measurements were conducted using thiol-coated gold surfaces as robust model hydrophobic surfaces. The results obtained in pure water show that the wetting films of water on weakly hydrophobic surfaces are metastable due to the presence of a repulsive double-layer force in the films. At high concentrations of KCl, the wetting films become unstable due to double-layer compression, causing them to rupture. In the presence of MgCl2, both contact angles and hydrophobic forces decrease due to the adsorption of the hydrolysis products such as MgOH+ ions and Mg(OH)2 precipitates on the surface. The FADS data obtained in the present work were analyzed using the Frumkin-Derjaguin isotherm to determine the roles of the short- and long-range hydrophobic forces in determining the stability of the wetting films formed on hydrophobic surfaces. The results of the present study are discussed in view of the roles of electrolytes in seawater flotation.

Underwater Adhesion of a Stimuli-Responsive Polymer on Highly Oriented Pyrolytic Graphite: A Single-Molecule Force Study

Exploration aiming to understand how a single polymer chain interacts with interested solid–water interface and its dependence on the environmental stimulus is critical, as it is important for a variety of scientific research and practical applications, such as underwater adhesives or smart systems for controlled attachment/detachment. Here, by single molecule force spectroscopy (SMFS), results on underwater adhesion of a single stimuli-responsive polymer chain on a model hydrophobic surface are reported. Salt concentration was used as an effective stimulus for the transition of the stimuli-responsive polymer from hydrophilic (solvophilic) hydrated state to hydrophobic (solvophobic) state in SMFS experiment. The probed equilibrium single-molecule adhesion force that changed from 45 to 76 pN with increasing salt concentration were free of other interactions that are responsible for cohesions, indicating that solvent quality is critical in determining the strength of single-molecule interfacial adhesion. Moreover, the derived simple quantitative thermodynamic model by combining single-molecule detachment mechanics with hydration free energy illustrated that higher single-molecule adhesion force was resulted from higher solvation/hydration free energy. The experimental study and theoretical analysis presented in this work quantitatively revealed the role of hydrophobic and more general solvophobic interactions in single-molecule level and shed light on the molecular structure optimization for desired applications, such as underwater adhesives or smart interfaces.

Copper-phospholipid interaction at cell membrane model hydrophobic surfaces

Detailed investigation of Cu (II) binding with natural lipid phosphatidylglycerol (PG) in aqueous solution was carried out by voltammetric measurements at the mercury drop electrode, complemented by monolayer studies in a Langmuir trough and electrophoretic measurements, all used as models for hydrophobic cell membranes. Penetration of copper ions into the PG layer was facilitated by the formation of hydrophilic Cu-Phenanthroline (Phen) complex in the subphase, followed by the mixed ligand Cu-Phen-PG complex formation at the hydrophobic interface. Electrophoretic measurements indicated a comparatively low abundance of the formed mixed ligand complex within the PG vesicles, resulting it the zeta potential change of +0.83mV, while monolayer studies confirmed their co-existence at the interface. The Cu-Phen-PG complex was identified in the pH range from 6 to 9. The stoichiometry of the complex ([PhenCuOHPG]), as well as its stability and kinetics of formation, were determined at the mercury drop electrode. Cu-Phen-PG reduces quasireversibly at about −0.7V vs. Ag/AgCl including reactant adsorption, followed by irreversible mixed complex dissociation, indicating a two-electron transfer - chemical reaction (EC mechanism). Consequently, the surface concentration (γ) of the adsorbed [PhenCuOHPG] complex at the hydrophobic electrode surface was calculated to be (3.35±0.67)×10−11molcm−2. Information on the mechanism of Cu (II) - lipid complex formation is a significant contribution to the understanding of complex processes at natural cell membranes.

Surface chemistry effects on heterogeneous clathrate hydrate nucleation: A molecular dynamics study

We report results from a molecular dynamics study of clathrate hydrate nucleation near model hydrophilic and hydrophobic surfaces. –CH3 and –OH terminated self-assembled monolayers (SAMs) are used as model surfaces. We study the nucleation of a soluble, structure II forming guest molecule with a coarse-grained model compatible with monatomic water. Despite the presence of SAMs, we show that nucleation occurs through a homogeneous mechanism in OHSAM and CH3SAM systems. Formation of ice-like or intermediate water structure is not observed near either surface prior to nucleation. Nucleation occurs more quickly in OHSAM systems than CH3SAM systems. However, the faster nucleation is driven by a partitioning of guest molecules which results in higher bulk guest concentration in OHSAM systems compared with CH3SAM systems. Despite significant aggregation of guest molecules near CH3SAM, no nucleation is observed near the surface. The formation of guest contact pairs, facilitated by the presence of CH3SAM, may prevent nucleation in this region. Our results highlight the numerous routes by which surfaces can affect hydrate nucleation due to the multicomponent nature of the phenomena.

Interfacial structures of whey protein isolate (WPI) and lactoferrin on hydrophobic surfaces in a model system monitored by quartz crystal microbalance with dissipation (QCM-D) and their formation on nanoemulsions

In this work, the interactions between two oppositely charged proteins in solution, namely whey protein isolate (WPI) and lactoferrin, were investigated for uses in nanoemulsions. ζ-potential and turbidity measurements indicated that these two proteins interact strongly via electrostatic attraction at pH 6. Quartz crystal microbalance with dissipation (QCM-D) was employed to study the adsorption behaviour and the formation of different interfacial structures of the two proteins onto a model hydrophobic surface that mimics the interface of an oil droplet in emulsions. Sequential addition of WPI and lactoferrin (or vice versa) formed thin and rigid protein bi-layers (8–10 nm). However, a viscous and thick surface layer (101 nm) was formed by the protein complex using a mixture of WPI and lactoferrin. High pressure homogenization and solvent evaporation were then used to replicate the QCM-D results on real nanoemulsion systems. Sequential adsorption of WPI and lactoferrin created bi-layered nanoemulsions with stable and relatively small droplets (90 nm in diameter). In contrast, the sequential adsorption of lactoferrin and WPI as well as the use of a mixture of WPI and lactoferrin (mixed layer) resulted in large aggregates with poor stability. This study provided insights into the stability of nanoemulsions influenced by structural features of interfacial layers based on two oppositely charged protein molecules.

Hydrophilic behavior of graphene and graphene-based materials

Graphene and the graphene-based materials like graphite, carbon nanotubes, and fullerenes are not only usually regarded as hydrophobic but also have been widely employed as paradigms for the investigation of the behavior of water under nonpolar confinement, a question of major concern for fields ranging from biology to materials design. However, some experimental and theoretical insights seem to contradict, at least partially, such a picture. In this work, we will provide firm evidence for a neat hydrophilic nature of graphene surfaces. Our molecular dynamics studies will demonstrate that parallel graphene sheets present a strong tendency to remain fully hydrated for moderately long times (even when the equilibrium state is indeed the collapse of the plates), and thus, they are less prone to self-assembly than model hydrophobic surfaces we shall employ as control which readily undergo a hydrophobic collapse. Potential of mean force calculations will indeed make evident that the solvent exerts a repulsive contribution on the self-assembly of graphene surfaces. Moreover, we shall also quantify graphene hydrophilicity by means of the calculation of water density at two pressures and water density fluctuations. This latter study has never been performed on graphene and represents a means both to confirm and to quantify its neat hydrophilic behavior. We shall also make evident the relevance of the mildly attractive water-carbon interactions, since their artificial weakening will be shown to revert from typically hydrophilic to typically hydrophobic behavior.

Two types of Cassie-to-Wenzel wetting transitions on superhydrophobic surfaces during drop impact.

Despite the fact that superhydrophobic surfaces possess useful and unique properties, their practical application has remained limited by durability issues. Among those, the wetting transition, whereby a surface gets impregnated by the liquid and permanently loses its superhydrophobicity, certainly constitutes the most limiting aspect under many realistic conditions. In this study, we revisit this so-called Cassie-to-Wenzel transition (CWT) under the broadly encountered situation of liquid drop impact. Using model hydrophobic micropillar surfaces of various geometrical characteristics and high speed imaging, we identify that CWT can occur through different mechanisms, and at different impact stages. At early impact stages, right after contact, CWT occurs through the well established dynamic pressure scenario of which we provide here a fully quantitative description. Comparing the critical wetting pressure of surfaces and the theoretical pressure distribution inside the liquid drop, we provide not only the CWT threshold but also the hardly reported wetted area which directly affects the surface spoiling. At a later stage, we report for the first time to our knowledge, a new CWT which occurs during the drop recoil toward bouncing. With the help of numerical simulations, we discuss the mechanism underlying this new transition and provide a simple model based on impulse conservation which successfully captures the transition threshold. By shedding light on the complex interaction between impacting water drops and surface structures, the present study will facilitate designing superhydrophobic surfaces with a desirable wetting state during drop impact.

Assessing the Gold Standard: The Complex Vibrational Nonlinear Susceptibility of Metals

Sum-frequency generation techniques can offer molecular-level, structural details of surfaces and interfaces. The incorporation of a metallic layer, either exposed or buried, is frequently used to provide a nonvibrationally resonant reference to which the phase of the resonant responses may be compared. This in turn provides further structural information, such as the polarity of interfacial groups. Because the phase of the metal depends strongly on factors that alter the electronic structure of the interface, such as the wavelength of the visible beam, chemical bonding, and surface coverage, it is beneficial to characterize the phase of the nonresonant response. A direct measurement of the absolute phase of a commonly prepared model hydrophobic surface, 1-octadecanethiol bound to gold, is presented and compared with relative phase measurements. Assignment of the phase of metallic samples requires careful consideration of the effects of the local field upon phase in both the near and far fields. We have outlined an approach that is suitable for the characterization of any dielectric or metal surface.

Molecular dynamics simulations of peptides at the air-water interface: influencing factors on peptide-templated mineralization.

Biomineralization is the intricate, biomedically highly relevant process by which living organisms deposit minerals on biological matrices to stiffen tissues and build skeletal structures and shells. Rapaport and coworkers ( J. Am. Chem. Soc. 2000 , 122 , 12523 ; Adv. Funct. Mater. 2008 , 18 , 2889 ; Acta Biomater. 2012 , 8 , 2466 ) have designed a class of self-assembling amphiphilic peptides that are capable of forming hydrogels and attracting ions from the environment, generating structures akin to the extracellular matrix and promoting bone regeneration. The air-water interface serves both in experiment and in simulations as a model hydrophobic surface to mimic the cell's organic-aqueous interface and to investigate the organization of the peptide matrix into ordered β-pleated monolayers and the subsequent onset of biomineral formation. To obtain insight into the underlying molecular mechanism, we have used molecular dynamics simulations to study the effect of peptide sequence on aggregate stability and ion-peptide interactions. We find-in excellent agreement with experimental observations-that the nature of the peptide termini (proline vs phenylalanine) affect the aggregate order, while the nature of the acidic side chains (aspartic vs glutamic acid) affect the aggregate's stability in the presence of ions. These simulations provide valuable microscopic insight into the way ions and peptide templates mutually affect each other during the early stages of biomineralization preceding nucleation.

Influence of non-ionic and ionic surfactants on kinetics of the bubble attachment to hydrophilic and hydrophobic solids

Abstract The paper is devoted to kinetics and mechanism of the three-phase contact (TPC) formation by the colliding bubble at model hydrophobic (polytetrafluoroethylene – Teflon) and hydrophilic (muscovite mica) solid surfaces. To determine influence of type of the surfactant polar group the experiments were carried out in solutions of non-ionic (n-hexanol and n-octanol), cationic (n-octyl-(OTABr), n-dodecyl-(DDTABr) and n-hexadecyl-trimethylammonium (CTABr) bromides, and anionic (sodium hexadecyl sulfate (SHS)) surface active substances (SAS). The time of the TPC formation (tTPC) and timescale of rupture of the thin liquid film separating the colliding bubble and a solid surface was determined using high-speed video registrations. The tTPC was defined as the time span from the moment of the bubble first collision up to the liquid film rupture and formation of the TPC (dewetted) hole. It was shown that the influence of SAS on the kinetics of the TPC formation could be completely different depending on the hydrophilic/hydrophobic properties of the solid surface. At the Teflon surface the TPC was formed always, both in distilled water and in SAS solutions of various composition and concentration. Moreover, the tTPC was significantly prolonged at higher SAS concentrations, independently on the SAS type (ionic, non-ionic). At the mica surface the wetting film was stable and the TPC was never registered in distilled water as well as in solutions of non-ionic and anionic surfactants. However, the TPC was formed at the mica surface in solutions of cationic surfactants, but the tTPC values were decreasing with increasing cationic surfactants concentration. Mechanism of the TPC formation is presented and reasons of the completely different influence of SAS on kinetics of the TPC formation at the hydrophilic and hydrophobic solid surfaces are explained.

Effect of Chemical Oxidation on the Sorption Tendency of Dissolved Organic Matter to a Model Hydrophobic Surface

The application of chemical oxidants may alter the sorption properties of dissolved organic matter (DOM), such as humic and fulvic acids, proteins, polysaccharides, and lipids, affecting their fate in water treatment processes, including attachment to other organic components, activated carbon, and membranes (e.g., organic fouling). Similar reactions with chlorine (HOCl) and bromine (HOBr) produced at inflammatory sites in vivo affect the fate of biomolecules (e.g., protein aggregation). In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to evaluate changes in the noncovalent interactions of proteins, polysaccharides, fatty acids, and humic and fulvic acids with a model hydrophobic surface as a function of increasing doses of HOCl, HOBr, and ozone (O3). All three oxidants enhanced the sorption tendency of proteins to the hydrophobic surface at low doses but reduced their sorption tendency at high doses. All three oxidants reduced the sorption tendency of polysaccharides and fatty acids to the hydrophobic surface. HOCl and HOBr increased the sorption tendency of humic and fulvic acids to the hydrophobic surface with maxima at moderate doses, while O3 decreased their sorption tendency. The behavior observed with two water samples was similar to that observed with humic and fulvic acids, pointing to the importance of these constituents. For chlorination, the highest sorption tendency to the hydrophobic surface was observed within the range of doses typically applied during water treatment. These results suggest that ozone pretreatment would minimize membrane fouling by DOM, while chlorine pretreatment would promote DOM removal by activated carbon.