Equilibration in adsorbing polymer systems can be very slow, leading to different physical properties at a given condition depending on the pathway that was used to reach this state. Here we explore this phenomenon using a diblock copolymer consisting of a cationic anchor block and a thermoresponsive block of poly(2-isopropyl-2-oxazoline), PIPOZ. We find that at a given temperature different polymer chain densities at the silica surface are achieved depending on the previous temperature history. We explore how this affects surface and friction forces between such layers using the atomic force microscope colloidal probe technique. The surface forces are purely repulsive at temperatures <40 °C. A local force minimum at short separation develops at 40 °C and a strong attraction due to capillary condensation of a polymer-rich phase is observed close to the bulk phase separation temperature. The friction forces decrease in the cooling stage due to rehydration of the PIPOZ chain. A consequence of the adsorption hysteresis is that the friction forces measured at 25 °C are significantly lower after exposure to a temperature of 40 °C than prior to heating, which is due to higher polymer chain density on the surface after heating.

We have investigated the DLVO surface forces of oxidised tungsten and cobalt surfaces using the atomic force microscope (AFM) colloidal probe technique. It was shown by X-ray Photoelectron Spectroscopy (XPS), and electrokinetic measurements that this model system is representative for industrial WC and Co powders used in the production of hard metals. We found that the attractive van der Waals forces are well described by Hamaker constants, calculated from optical data for WO3 and CoOOH. The repulsive electrostatic double layer forces between WO3 surfaces increase with increasing pH due to an increasingly negative surface potential. This surface potential decreases with increasing ionic strength at pH 7.5. The electrostatic interaction between WO3 and CoOOH is attractive at pH 10, suggesting a positively charged CoOOH surface.

The application range of man-made cellulosic fibers is limited by the absence of cost- and manufacturing-efficient strategies for anisotropic hierarchical functionalization. Overcoming these bottlenecks is therefore pivotal in the pursuit of a future bio-based economy. Here, we demonstrate that colloidal silica nanoparticles (NPs), which are cheap, biocompatible and easy to chemically modify, enable the control of the cross-sectional morphology and surface topography of ionic liquid-spun cellulose fibers. These properties are tailored by the silica NPs' surface chemistry and their entry point during the wet-spinning process (dope solution ^DSiO₂ or coagulation bath ^CSiO₂). For ^CSiO₂-modified fibers, the coagulation mitigator dimethylsulphoxide allows for controlling the surface topography and the amalgamation of the silica NPs into the fiber matrix. For dope-modified fibers, we hypothesize that cellulose chains act as seeds for directed silica NP self-assembly. This results for ^DSiO₂ in discrete micron-sized rods, homogeneously distributed throughout the fiber and for glycidoxy-surface modified ^DSiO₂@GLYEO in nano-sized surface aggregates and a cross-sectional core-shell fiber morphology. Furthermore, the dope-modified fibers display outstanding strength and toughness, which are both characteristic features of biological biocomposites.

The wetting of two different model cellulose surfaces has been studied; a regenerated cellulose (RG) surface prepared by spin-coating, and a novel multilayer film of poly(ethyleneimine) and a carboxymethylated microfibrillated cellulose (MFC). The cellulose films were characterized in detail using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM indicates smooth and continuous films on a nanometer scale and the RMS roughness of the RG cellulose and MFC surfaces was determined to be 3 and 6 nm, respectively. The cellulose films were modified by coating with various amounts of an anionic fluorosurfactant, perfluorooctadecanoic acid, or covalently modified with pentadecafluorooctanyl chloride. The fluorinated cellulose films were used to follow the spreading mechanisms of three different oil mixtures. The viscosity and surface tension of the oils were found to be essential parameters governing the spreading kinetics on these surfaces. XPS and dispersive surface energy measurements were made on the cellulose films coated with perfluorooctadecanoic acid. A strong correlation was found between the surface concentration of fluorine, the dispersive surface energy and the contact angle of castor oil on the surface. A dispersive surface energy less than 18 mN/m was required in order for the cellulose surface to be non-wetting (Ξe &gt; 90 °) by castor oil.

A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO45 MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 Å. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PEO45 MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements.

The dynamic surface tension (DST) and the surface viscoelastic modulus of sodium oleate aqueous solutions at different concentrations were measured using an image analysis tensiometer based on the oscillating bubble technique. The diffusion coefficient of oleate moieties was calculated from DST measurements and the surface viscoelastic modulus using the Langmuir–Szyszkowski and the diffusion-controlled adsorption models. The viscoelastic moduli obtained from model calculations were compared with the corresponding experimental values. The diffusion coefficient of C12(EO)6 in water and the parameters of the Langmuir–Szyszkowski adsorption isotherm were taken from the literature and used to calculate the surface viscoelastic modulus of its aqueous solutions at different concentrations. The foaming properties of both C12(EO)6 and sodium oleate solutions, viz., the foam conductance and the water volume fraction in the foam, were measured using a commercial Foamscan device. Foaming experiments with C12(EO)6 and sodium oleate solutions were carried out either under static conditions; i.e., the foam conductance and the water volume fraction were measured as a function of time after the generation of a fixed volume of foam, or under dynamic conditions; i.e., the foam conductance and the water volume fraction were measured during foam formation. The variations in the foam permeability as a function of surfactant concentration were related to the viscoelastic properties of the air/water interface and to the presence of micelles in the foam films. With foams in which the water volume fraction was higher than 0.05, the foam electrical conduction could be described using a simple parallel resistor model and their conductance measurements were related to the foam water volume fraction. The results related to water drainage under static conditions were used to interpret water drainage under dynamic conditions. Preliminary conjectures on the influence of foam permeability and water volume fraction on the yield of the flotation deinking process were drawn from these results.

The forces between layers of a cationic polymerizable surfactant, cetyl p-vinylbenzyl dimethyl ammonium chloride (CVDAC), adsorbed onto muscovite mica have been measured with a surface force technique. The forces were measured both prior to and after partial W polymerization of the adsorbed layers, and the stability of adsorbed bilayers after dilution of the adsorption solution was studied for these two cases. Due to their large headgroup, CVDAC molecules do not pack efficiently into monolayers and bilayers. This can be observed by, for instance, the lower surface potential of adsorbed bilayers and the lower pull-off force from monolayer contact, compared to what is found for simpler surfactants like CTAB. It was also found that surface aggregates build up on top of the bilayer, due to the partly hydrophobic headgroup. When the bilayer structure, including the surface aggregates, is polymerized, it is stabilized both with respect to mechanical forces and with respect to dilution of the surrounding solution

The forces acting between negatively charged muscovite mica surfaces immersed in solutions containing sodium polyacrylate (NaPAA) have been studied. No evidence for PAA adsorption in the absence of calcium ions in the solution was found. However, at a CaCl2 concentration of about 3x10-3 M a layer of PAA adsorbed on each surface. At large separations, the forces between the PAA-coated surfaces were dominated by repulsive double-layer forces. At separations below 50-80 Å, depending on the solution conditions, an attractive force in excess of the van der Waals attraction was observed. The adhesion force between the layers was 7-8 mN/m at pH 6 and increased somewhat with increasing pH to about 9 mN/m at pH 10. We argue that both the long-range attraction and the adhesion force primarily are due to COO- - Ca2+ --OOC bridges between the opposing surfaces and possibly charge correlation effects. It was found that calcium ions bind to the PAA and to the mica surface, whereby the electrostatic repulsion between the polyelectrolyte and the surface is lowered. We suggest that this is the main re ason why Calcium ions promote the adsorption of PAA onto negatively charged minerals. However, it also seems likely that calcium ions increase the attractive interactions between the surface and the PAA segments.

Endothelial cell layers from umbilical cords were grown on methylated silica surfaces. Fluorescence microscopy showed this layer to be confluent and to consist of living cells. Initial ellipsometry measurements were performed to illustrate both the stability of the model surface in ellipsometry measurements and the Ca2+-dependent binding of lipoproteins at the cell-based substrate. The present substrate holds promise as a model substrate for in vitro investigations of lipoprotein deposition at the endothelium surface under close to in vivo conditions.

Adsorption of thiols with cationic or anionic terminal group on gold has been studied from mixed solutions of 11-Amino-1-undecanethiol (AUT) and 3-Mercaptopropionic acid (MPA) using Quartz Crystal Microbalance with Dissipation (QCM-D), X-ray Photoelectron Spectroscopy (XPS), atomic force microscopy (AFM) and contact angles. The goal is to probe the nature of such layers, and the additivity or otherwise of the pH responsiveness, with a view to evaluate their suitability as smart materials. For each of the two pure (unmixed) cases, ordered molecular monolayers are formed with sulfur binding to gold and the alkane chain pointing out from the surface as expected. Adsorption from the thiol mixtures, however, leads to a more complex behaviour. The surface concentration of thiols from the mixtures, as determined by QCM-D, is considerably lower than for the pure cases and it reaches a minimum at a 3:1 MPA/AUT relative concentration in the solution. The XPS results confirm a reduction in adsorbed amount in mixtures with the lowest overall intensity for the 3:1 ratio. Monolayers formed from mixtures display a wettability which is much lower and less pH sensitive. Collectively these results confirm that for adsorption from mixed systems, the configuration is completely different. Complex formation in the mixed solutions leads to the adsorption of molecules parallel to the surface in an axially in-plane configuration. This parallel layer of thiols is mechanically relatively robust to nano-shaving based on AFM measurements. These results will have a significant impact on the design of biomimetic surface coatings particularly when mixtures of oppositely charged molecules are present on the surface, as is commonly the case in biological, proteinaceous surfaces (e.g. hair and skin).

Adsorption properties of bottle-brush polyelectrolytes have been investigated using dual polarization interferometry (DPI), which provides real time monitoring of adsorbed layer thickness and refractive index. The adsorption on silicon oxynitride was carried out from aqueous solution with no added inorganic salt, and the adsorbed polyelectrolyte layer was subsequently rinsed with NaCl solutions of increasing concentration. The bottle-brush polyelectrolytes investigated in this study have different ratios of permanent cationic charged segments and uncharged PEO side chains. Both the cationic groups and the PEO side chains have affinity for silica-like surfaces, and thus contribute to the adsorption process that becomes rather complex. Adsorption properties in water, responses to changes in ionic strength of the surrounding medium, adsorption kinetics and the layer structure are all strongly dependent on the ratio between backbone charges and side chains. The results are interpreted in terms of competitive adsorption of segments with different chemical nature. The adsorption kinetics is relatively fast, taking only tens to hundreds of seconds when adsorbed from dilute 100 ppm solutions. The DPI technique was found to be suitable for studying such rapid adsorption processes, including determination of the initial adsorption kinetics. We expect that the effects observed in this study are of general importance for synthetic and biological polymers carrying segments of different nature.

When two elastic surfaces carrying adsorbed layers are forced together under high loads, as in measurement with the surface forces apparatus, a bell-shaped deformation develops in the flattened contact zone. This behavior is due to the elastohydrodynamic "lubrication" of the adsorbed layer. Compression of molecules thus trapped between the surfaces may under some cicumstances, e.g., in the cases of surfaces carrying weakly adsorbed proteins, lead to irreversible changes in the adsorbed layer and consequently in the surface interaction.

The adsorption of human serum albumin (HSA) onto muscovite mica has been investigated by means of surface force and ESCA measurements. The range of protein concentration explored was 0.001-1.0 mg/ml in 10-3 M NaCl at pH 5.6. It was found that negatively charged albumin adsorbs onto negatively charged mica. Co-adsorption of small ions into the adsorbed protein layer was also inferred. Small structural changes are induced by the adsorption, and further structural changes can be induced by applying an external compressive force. The structure of the adsorbed layer depends on the surface density. As surfaces with a low adsorption density of HSA are brought together, the protein molecules are able to diffuse along the surface, facilitating the merging of the two HSA layers into one single HSA layer in the gap between the surfaces. At high surface density crowding effects impede the rearrangement of the HSA layers and two separate layers of HSA remain in the gap between the surfaces. An adhesion force is present at low packing but not at high packing densities. It was found that the short-range interaction between one HSA-coated surface and one bare mica surface was strongly attractive, demonstrating that the adhesion forces likely are induced by HSA molecules bridging between two surfaces and not by attractive interactions between the proteins themselves.

Surface characterization and foaming studies were carried out with nine industrially manufactured, colloidal silica dispersions with particles sizes from 5–40 nm. All the silica sols produced transient foams with short decay times and the dynamic foam generation (foamability) was found to vary according to the sol type with the greatest foamability occurring for the hydrophobically modified sol and the deionized hydrophilic sol. However, it was found that improved foamability of all the sols could be achieved by changing the pH to within the region of the pHpzc which corresponds to the region of lowest hydrophilicity. An increase in pH (and build-up of negative charge) enhances the surface hydrophilicity and caused a decrease in foamability. In addition, for selected hydrophilic sols, it was shown that the foamability (a) increased with decrease in particle size (within the 6–40 nm range) and (b) increased with particle concentration (within the range of 1–15 wt%). Overall, it was concluded that the foamability was primary controlled by hydrophobicity (and hence by pH) and also by the particle concentration, the particle size and the degree of agglomeration.

Langmuir–Blodgett films were prepared at the air/water interface from dispersions of hydrophilic and partially, hydrophobically modified industrially manufactured silica nanoparticles. The hydrophilic particles featured expanded, fairly easily compressible, surface pressure (p)–area (A) isotherms with well defined collapse pressures which appeared to be caused by the formation of loosely structured agglomerates which exhibited elastic behavior at low surface pressure and inelastic behavior at high surface pressure. Lateral electrostatic interparticle interactions seemingly played an important role in this hydrophilic system. This contrasted with the hydrophobically modified particles which were more difficult to disperse in the ethanol/chloroform spreading solvent and appeared to be in the semi-agglomerated state at low surface pressures and exhibited a more difficult to compress compacted film. Both types of particulate films were shown to be sensitive to the spreading environment and changes in pH were found to increase particle agglomeration which drastically reduced the particulate area for the hydrophilic sol but less so, in the case of the moderately hydrophobically modified sol. In general, the LB technique proved to be a useful method to monitor changes in the state of aggregation of nanosized silica particles at the air/water interface. These results also appear to give some support of our ideas, presented in earlier publications [1,2] in which it was suggested that the major role of the hydrophobically modified hydrophilic particles in foaming was to produce an aggregated particulate film surrounding the air/water interface which provides a physical barrier preventing coalescence of bubbles.

Liquid crystalline nanoparticles (LCNPs), e.g. cubosomes and hexosomes, are receiving more and more attraction as drug delivery vehicles. Dry powder formulation that forms LCNPs upon hydration can be advantageous to make new routes of administration accessible. In this work, we investigate use of three disaccharides (lactose, trehalose and sucrose) as protective matrices for glycerol monooleate based LCNP forming powders produced by freeze-drying. Phase behavior, particle size and size distributions at the different preparation steps were monitored by small angle x-ray scattering (SAXS) and dynamic light scattering (DLS). Particle appearance was imaged by cryogenic transmission electron microscopy (cryo-TEM). Moreover, the therapeutic relevant antimicrobial peptide AP114 (plectasin derivative) was incorporated in the formulations. Peptide encapsulation and release as well as in vitro antibacterial effect were investigated. Results showed that all freeze-dried powders did form particles with liquid crystalline structure upon hydration. However, a phase transition from the bicontinuous cubic Pn3m to the reversed hexagonal was observed, as a consequence of sugar addition and the freeze-drying procedure. Data indicates that trehalose is the preferred choice of lyo-protectant in order to maintain a mono-modal particle size distribution. In addition, antimicrobial activity of AP114-containing formulations was found to be highest for the formulation containing trehalose. The release kinetics of AP114 from the nanoparticles was strongly affected by the dimensions of the hexagonal phase. Larger dimension of the hexagonal phase, significantly improved the release of AP114 and antimicrobial activity of the formulation.

A rectangular electophoresis chamber has been constructed whereby electroosmotic fluid mobility can be determined at small non-transparent sample plates. A hydrodynamic description of fluid flow in the chamber is forwarded, and verified, for accurate determination of particle mobility and electroosmosis at sample plates. Advantages of the chamber design and technique include the ability to determine electroosmotic fluid mobility at sample plates from a single particle mobility measurement within the chamber. As demonstration of the usefulness of the technique, characterization of several polymer surfaces deposited as a thin film from a cold gas plasma was performed by determining the pH dependence of electroosmotic fluid flow. The plasma polymer surfaces include those of plasma polymerized 1,2-diaminocyclohexane, acrylic acid, and hexamethyldisiloxane. Results of the characterization include quantification of ionizable surface groups with concomitant determination of pK values of these groups. The values obtained have proven useful to explain trends in protein adsorption at these surfaces.

Plasma polymerization of 1,2-diaminocyclohexane (DACH) results in an amino functional surface which is not stable under ambient conditions. The aging process has previously been assumed to be an oxidation initiated by residual polymer radicals. We here propose that the surface process is not an oxidation but a carboxylation. Primary amino groups react with atmospheric carbon dioxide to give carbamate groups which are stabilized by salt formation with adjacent ammonium groups. We have used a novel electrokinetic technique to measure electroosmosis and monitor the aging process. While the total number of ionizable surface groups was constant, a gradual change in the ratio of basic to acid sites at the surface was found. After 64 days the ratio of was almost 1:1. This amphoteric surface which spontaneously changed its ratio of basic to acid sites was used as substrate to investigate effect of surface charge on adsorption of two proteins, human serum albumin (HSA) and lysozyme. It was found that lysozyme adsorbs in much higher amounts than HSA irrespective of the charge at the surface. Whereas adsorption of HSA was not dependent on the change in surface charge, adsorption of lysozyme decreased with aging, i.e. as the ratio of acid to base sites at the surface approached unity. An interesting finding was that more lysozyme was adsorbed the more positively charged the surface, even at pH values where the protein carried a strong net positive charge.

he interaction between the local anaesthetic agents prilocaine and lidocaine, on one hand, and poly(N-isopropyl acrylamide) (pNIPAM), on the other, is investigated through studies of the polymer phase behavior and through surface tension and adsorption measurements. In particular, the cloud points (CP) for pNIPAM in the presence of lidocaine and prilocaine under different conditions were compared to the effects of electrolytes and alcohols. It was found that the electrolytes affect the CP of pNIPAM in a lyotropic manner, whereas alcohols depress the CP of pNIPAM in an alkyl chain length dependent way; i.e., the longer the chain, the larger the decrease in CP. Lidocaine and prilocaine affect the CP of pNIPAM in a pH-dependent manner. Below the p Ka of lidocaine and prilocaine, these cosolutes do not substantially affect the CP in the concentration range investigated, but rather behave analogous to simpler electrolytes. Above the p Ka, on the other hand, they strongly depress the CP already at low concentrations. In parallel, at low pH, the surface tension reduction due to lidocaine or prilocaine is marginal, whereas at high pH the surface tension is reduced considerably. Thus, the poor solubility of prilocaine and lidocaine at high pH causes these to become more surface active and simultaneously interact in a more pronounced way with pNIPAM. Furthermore, it was found from ellipsometry that an adsorbed pNIPAM layer contracts when lidocaine is added, presumably due to a lidocaine-pNIPAM interaction similar to that causing pNIPAM to phase separate. Analogous to this, it was demonstrated that an adsorbed pNIPAM layer shrinks and swells reversibly when the temperature is cycled above and beneath the CP.

The interaction between solid fluorocarbon surfaces immersed in aqueous solutions of a poly(ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide) block copolymer (Proxanol 268) has been determined after different adsorption times. It was found that the compressed layer thickness is independent of the adsorption time, whereas the range of the repulsive force decreases during the first hours. This is interpreted as evidence for a decreasing fraction of polymer tails in the adsorbed polymer layer. A weak attractive force is observed when Proxanol coated surfaces are separated from contact. The presence of this attraction on separation only indicates structural changes in the block copolymer layer when two such layers on opposing surfaces are in contact for a prolonged time. Most of the Proxanol layer is easily desorbed by dilution with water. These results are discussed in connection with the known properties of perfluorocarbon emulsions coated with the same block copolymer.

The forces acting between muscovite mica surfaces across solutions containing either uncharged carbohydrates (cyclodextrin and sucrose) or a weakly charged hemicellulose (xylan) were measured using a surface force apparatus. Both the uncharged carbohydrates and xylan adsorb onto the mica basal plane. The adsorption of the uncharged carbohydrates results in a decrease in the longrange electrostatic double-layer force, thereby indicating a reduction in surface charge density. At a low ionic strength (1 x 10-3 M KBr) the adsorption of xylan is very limited, and the resulting adsorbed layer has a thickness similiar to that observed for cyclodextrin and sucrose. When the ionic strength of the solution is increased, a slow buildup of the adsorbed xylan layer takes place. The functional form of the interactions between these thicker layers is consistent with the forces expected for anchored polymer brushes in an good solvent.

Monolayers of a cationic, double-chained fluorocarbon surfactant (N-(α-trimethylammonioacetyl)-O-O'-bis (1H, 1H, 2H, 2H-perfluorodecyl)-L-glutamate chloride) were studied at the air-water interface and adsorbed on the muscovite mica basal plane. The stability of the monolayer at the air-water interface was considerably higher on a 10-2 M KBr subphase than on pure water. Fluorocarbon surfactant-coated mica surfaces were obtained either by Langmuir-Blodgett (LB) deposition or by adsorption from a polar solvent. The adsorbed layer was characterized by means of ESCA, transfer ratio and contact angle measurements. A more densely packed layer could be obtained by LB deposition than by adsorption from solution. For this surfactant the preferential conformation of the molecule in layers adsorbed from solution is different from that in LB layers. At low adsorption denseties the advancing contact angle increases rapidly with the adsorbed amount. The receding angle is hardly affected until the area per molecule is less than about 140 Å2. At higher adsorption densities, the receding contact angle is more sensetive to the adsorbed amount than the advancing angle. The reason for the low salt stability, the low adhesion force in water, and the numerous cavities forming around the contact region when surfaces coated by this fluorocarbon surfactant are brought together in water is proposed to be due to (molecular size) heterogeneities in the surfactant layer.

A simple method is described for determining of the contribution of hydrodynamically coupled solvent to the adsorbed film mass determined in a quartz crystal microbalance (QCM) when operated in liquid. The method requires no additional apparatus and utilizes the change in QCM resonant frequency response between measurements made in nondeuterated and deuterated solvents. The mass of coupled water in a polymer film has been determined and is found to agree with that determined by XPS analysis of the dried polymer film

In this article are presented results form direct measurements of interactions between one polyelectrolyte covered mics surface and one bare mica surface. There is a strong and long ranged attraction between the bare mica surface and the mica surface neutralized by adsorbed polyelectrolyte. The attraction is stronger and more long ranged in this asymmetric system than in a corresponding symmetric system. This attraction is of the same magnitude in strength in both 0.1 mM KBr and 10 mM KBr solution. The results support the findings from Monte Carlo simulations and mean field calculations presented in the preceeding article by Sjöström and Åkesson.

The surface force apparatus was used to study the effects of polyelectrolyte concentration on the interaction between mica sheets immersed in aqueous polyelectrolyte solution. We have found that at low polyelectrolyte concentration, adsorption of cationic polyelectrolyte to negatively charged mica leads to extremely flat adsorbed layers in solution of low ionic strength. There is a repulsion between the surfaces at separations between about 100 and 10 nm. This force is of electrostatic origin when the polyelectrolyte concentration is lower than that needed to neutralize the surface charge. When increasing the polyelectrolyte concentration above the charge neutralization point, cnp, only a slight additional adsorption takes place in low ionic strength solution. In these systems, a steric component in the interaction force appears. The adsorption at the cnp is approximately 20 % below that at the plateau level in the adsorption isotherm, which is found by ESCA measurements.

Poly(acrylic acid) was grown from substrates by photopolymerization, and the grafting process was monitored in situ by Quartz Crystal Microbalance with Dissipation (QCM-D) measurements in a 1:1 v/v mixture of water/ethanol. The polymerization process was monitored into the thick film region, where the change in frequency and dissipation with increasing film mass changes sign as predicted by the Voigt viscoelastic model. Our experimental data are compared with predictions of this model, and satisfactory agreement is found for low overtone numbers. The Voigt model was applied to analyze the measured changes in frequency, Δf, and dissipation, ΔD, in order to extract information on layer thickness, shear elasticity, μ, and shear viscosity, η, of the growing film. The increasing rate of changes in Δf and ΔD observed after about 150 s of polymerization was found to correlate with an increasing growth rate of the film thickness. For longer polymerization times a close to linear increase in thickness with time was observed. The sensitivity, defined as the derivatives of Δf and ΔD with respect to thickness, depends on overtone number and is different for the frequency and dissipation signals - facts that should be considered when investigating small changes in thick films used in e.g. sensor applications.

Amine functionalities have been introduced on glassy carbon surfaces through electrografting of 4-(2-aminoethyl)benzenediazonium tetrafluoroborate. The grafted layers were characterized by ellipsometry and by nanomechanical mapping in air and aqueous solutions using the atomic force microscopy PeakForce QNM mode. The layer was found to be 2.5. nm thick with low roughness, comparable to that of the glassy carbon substrate. However, small semi-spherical features were observed in the topographical image, indicating a clustering of the grafted amine compound. The nanomechanical mapping also demonstrated some swelling of the layer in water and pointed toward an important contribution of electrostatic interactions for the tip-surface adhesion. The forces between an aminated glassy carbon surface and a μm-sized silica particle in aqueous solutions were measured at different ionic strength and pH-values. The results demonstrate that an attractive double-layer force predominates at large separations, and that the surface charge densities increase as the separation between the surfaces decreases. The degree of charge regulation on the aminated glassy carbon is significant. The relatively low surface charge density of the aminated glassy carbon is attributed to significant incorporation of counterions in the water-rich grafted layer.

The behaviour of self-assembled monolayers of thiohexadecanoic acid adsorbed onto gold interacting in assymmetric 2:1 electrolytes has been studied with direct force measurements. The effects of two divalent cations (Mg2+ and Ca2+) were studied at concentrations ranging from 1 µM to 10 mM. As compared to interactions in the presence of Na+, the divalent ions adsorb strongly to the surfaces, with the effect of lowering the surface potential, and decreasing the double-layer repulsion. At concentrations above 10 µM, the Ca2+ ions were found to adsorb stronger than Mg2+, causing charge reversal at higher concentrations, and the net interactions at 10 mM were attractive over the measurable range.

Long-range interactions between self-assembled monolayers (SAMs) of semifluorinated alkanethiols have been studied by direct force measurements in water and aqueous NaCl solutions. SAMs prepared from three different thiols, with identical fluorinated headgroups but varying hydrocarbon spacer lengths, were investigated: CF3(CF2)9(CH2)xSH, where x = 2, 11, or 17. Force measurements show that the interactions in water and electrolyte solutions are composed of both double-layer interactions emerging from what appears to be charges adsorbed onto the surfaces, and long-range "hydrophobic" attractions, in excess of the expected van der Waals forces. The three investigated thiols produce similar results in force measurements, though the contact angles with water are slightly different. The "hydrophobic" attraction has the form of step-like attractive discontinuities in the force profiles at separations ranging from 20 to 40 nm, caused by bridging of microscopic bubbles residing at the surfaces. The shape or range of these discontinuities are not significantly affected by replacement of the water with either 1 mM or 1 M NaCl solutions. The origin of the charges causing the electrostatic double-layer interaction is unclear, but some possible causes are discussed.

Corrosion is of considerable concern whenever metal is used as construction material. In this study we address whether superhydrophobic coatings could be used as part of an environmentally friendly corrosion-protective system, and specific focus is put on how the wetting regime of a superhydrophobic coating affects corrosion inhibition. Superhydrophobic alkyl ketene dimer (AKD) wax coatings were produced, using different methods resulting in hierarchical structures, where the coatings exhibit the same surface chemistry but different wetting regimes. Contact angle measurements, ESEM, confocal Raman microscopy, open circuit potential and electrochemical impedance spectroscopy were used to evaluate the surfaces. Remarkably high impedance values of 1010Ωcm2 (at 10-2Hz) were reached for the sample showing superhydrophobic lotus-like wetting. Simultaneous open circuit potential measurements suggest that the circuit is broken, most likely due to the formation of a thin air layer at the coating-water interface that inhibits ion transport from the electrolyte to the metal substrate. The remaining samples, showing superhydrophobic wetting in the rose state and hydrophobic Wenzel-like wetting, showed less promising corrosion-protective properties. Due to the absence of air films on these surfaces the coatings were penetrated by the electrolyte, which allowed the corrosion reaction to proceed.

The adsorption of extracted and purified samples of asphaltenes and resins onto gold surfaces has been studied as a function of bulk concentration using a quarts crystal microbalance with dissipation measurements (QCM-D). With this device, which works equally well in transparent, opaque, and nontransparent samples, the adsorbed amount is measured through a change in resonant frequency of the quartz oscillator. The measured change in dissipation reports on changes in layer viscoelasticity and slip of the solvent at the surface. The results show that the adsorbed amount for resins from heptane corresponds to a rigidly attached monolayer. The adsorbed amount decreases with increasing amount of toluene in the solvent and is virtually zero in pure toluene. Asphaltenes, on the other hand, adsorb in large quantities and the mass and dissipation data demonstrate the presence of aggregates on the surface. The aggregates are firmly attached and cannot be removed by addition of resins. On the other hand, resins and asphaltenes associate in bulk liquid and the adsorption from mixtures containing both resins and asphaltenes is markedly different from that obtained from the pure components. Hence, we conclude that preformed resin aggregates adsorb to the surface. These results are compared and discussed in relation to adsorption from crude oil diluted in heptane/toluene mixtures