Influence of Molecular Dipole Orientations on Long-Range Exponential Interaction Forces at Hydrophobic Contacts in Aqueous Solutions

Strong and particularly long ranged (>100 nm) interaction forces between apposing hydrophobic lipid monolayers are now well understood in terms of a partial turnover of mobile lipid patches, giving rise to a correlated long-range electrostatic attraction. Here we describe similarly strong long-ranged attractive forces between self-assembled monolayers of carboranethiols, with dipole moments aligned either parallel or perpendicular to the surface, and hydrophobic lipid monolayers deposited on mica. We compare the interaction forces measured at very different length scales using atomic force microscope and surface forces apparatus measurements. Both systems gave a long-ranged exponential attraction with a decay length of 2.0 +/- 0.2 nm for dipole alignments perpendicular to the surface. The effect of dipole alignment parallel to the surface is larger than for perpendicular dipoles, likely due to greater lateral correlation of in-plane surface dipoles. The magnitudes and range of the measured interaction forces also depend on the surface area of the probe used: At extended surfaces, dipole alignment parallel to the surface leads to a stronger attraction due to electrostatic correlations of freely rotating surface dipoles and charge patches on the apposing surfaces. In contrast, perpendicular dipoles at extended surfaces, where molecular rotation cannot lead to large dipole correlations, do not depend on the scale of the probe used. Our results may be important to a range of scale-dependent interaction phenomena related to solvent/water structuring on dipolar and hydrophobic surfaces at interfaces

Synthesis of zeolite films in the surface of magnetoelastic ribbons for the detection of volatile organic compounds and the understanding of the effect of adsorption in the mechanical properties of the film

In the current thesis the development of sensors comprised of magnetoelastic ribbon(Metglas) its surface was coated with selective sensitizing layer was examined. In mostcases, zeolites were selected as sensitive layers. Different types of zeolites were synthesizedand bounded in both outer surfaces of Metglas using the hydrothermal synthesis technique.Such a sensor combines the adsorptive abilities of sensitizing layer with the inner ability ofMetglas to convert mass loadings and changes in the elastic properties in correspondingchanges of the measured resonance frequency of the ribbon. That combined ability has beenused for the detection of Volatile Organic Compounds (VOC’s). More particularly, for thesame purpose zeolite layers (FAU, MFI and LTA) and polymer (Bayhydrol-110) have beenused. The detected VOC’s are: ethyl-acetate, para-xylene, ortho-xylene, benzene, cyclohexane,n-hexane, propane and propylene. The second target of the current thesis was the calculation of mechanical properties ofzeolites. In the literature has been proved that gas adsorption upon zeolites affects not onlyits mass but also its mechanical properties through the unit cell changes. Thus, adsorption isexpected to affect applications such as zeolite membranes the performance of which isdirectly affected by their mechanical properties and possible changes. Hence, a new methodis proposed which unable the calculation the Young modulus of zeolite films, and thestresses/deformations induced in the zeolite film upon adsorption. The calculation of Youngmodulus is based on the recording of resonance frequency changes of multiple sensors withdifferent zeolite thickness each. The methodology is general and can be used for measuringYoung modulus of any microporous film as long as it can be deposited as uniform layer ona magnetoelastic ribbon.The calculation of adsorption induced stresses is succeeded with two differentmethods. The first method is applied in sensors in which zeolite coating existed on bothsurfaces of Metglas ribbon. Combined use of appropriate theory and mathematical modelfrom the literature for the magnetoelastic materials, stresses induced on FAU, LTA andsilicalite-1 zeolites upon humidity adsorption were calculated. The second method wasapplied in Metglas/MFI sensor in which uniform polycrystalline MFI layer existed onlyfrom the one side of the ribbon. The method was applied during the adsorption of VOC’sand is based on the bending and elasticity shown by the sensor during the adsorptionprocess. The differentiation of the two surfaces concerning the cohesion of the film,combined with adsorption phenomena cause remarkable bending, visible even with a nakedeye, from the magnitude of which stresses induced on zeolite film are calculated. In allcases there is a comparison of our experimental results with corresponding from theliterature.Στη παρούσα διατριβή πραγματοποιήθηκε ανάπτυξη αισθητήρων που αποτελούνταιαπό μαγνητοελαστικό έλασμα τύπου Metglas στην επιφάνεια του οποίου έγινε επικάλυψημε ευαίσθητο εκλεκτικό υμένιο. Στη μεγάλη πλειοψηφία των περιπτώσεων ως τέτοιουμένιο χρησιμοποιήθηκε ζεόλιθος. Διαφορετικοί τύποι ζεόλιθων συνετέθησαν έπειτα απόυδροθερμική σύνθεση και προσκολλήθηκαν ισχυρά στην εξωτερική επιφάνεια (και από τιςδύο πλευρές) των Metglas. Ένας τέτοιος αισθητήρας συνδυάζει τις ροφικές ικανότητες τουεκλεκτικού υμενίου με την ιδιότητα του Metglas να μετατρέπει φορτίσεις μάζας καιαλλαγές των ελαστικών ιδιοτήτων του σε μετρούμενες μεταβολές της συχνότηταςσυντονισμού του. Η συνδυασμένη αυτή ικανότητα του αισθητήρα χρησιμοποιήθηκε γιατην ανίχνευση Πτητικών Οργανικών Ουσιών (VOC’s). Πιο συγκεκριμένα για τον ίδιοσκοπό χρησιμοποιήθηκαν υμένια ζεόλιθων (FAU, MFI και LTA) και πολυμερούς(Bayhydrol-110). Τα VOC’s των οποίων η ανίχνευση εξετάστηκε με τους παραπάνωαισθητήρες είναι: αιθυλεστέρας, πάρα-ξυλόλιο, όρθο-ξυλόλιο, βενζόλιο, κυκλο-εξάνιο,κανονικό-εξάνιο, προπάνιο και προπυλένιο.Δεύτερος στόχος της διατριβής ήταν ο υπολογισμός μηχανικών ιδιοτήτων τωνζεόλιθων. Στη βιβλογραφία έχει αποδειχθεί ότι η ρόφηση αερίων επηρεάζει (εκτός από τημάζα του) και τις μηχανικές ιδιότητες των ζεόλιθων μέσω της μεταβολής του μεγέθους τηςμοναδιαίας κυψελίδας των. Επομένως η ρόφηση αναμένεται να επηρεάζει εφαρμογές τους(π.χ ζεολιθικές μεμβράνες), των οποίων η απόδοση εξαρτάται άμεσα από τις μηχανικέςτους ιδιότητες. Για το λόγο αυτό αναπτύχθηκε πειραματική μεθοδολογία με την οποίαυπολογίζονται το μέτρο ελαστικότητας Ε των ζεολιθικών φιλμ, και οιτάσεις/παραμορφώσεις που αναπτύσσονται στο ζεολιθικό υμένιο υμένιο κατά τη ρόφησηαερίων. Ο υπολογισμός για την εύρεση του μέτρου ελαστικότητας βασίζεται στηκαταγραφή των μεταβολών της συχνότητας συντονισμού fR πολλαπλών αισθητήρωνMetglas/ζεόλιθος διαφορετικού πάχους υμενίου ο καθένας. Η συγκεκριμένη μέθοδοςγενικεύεται και βρίσκει εφαρμογή για τον υπολογισμό του μέτρου ελαστικότητας E τουYoung οποιαδήποτε μικροπορώδους ομοιόμορφου και καλά προσκολλημένου στηνεπιφάνεια του Metglas υμενίου.Ο υπολογισμός των τάσεων που αναπτύσσονται στο φιλμ κατά τη ρόφησηεπιτυγχάνεται με χρήση δύο διαφορετικών μεθόδων. Η πρώτη μέθοδος, εφαρμόζεται σεαισθητήρες στους οποίους επικάλυψη με συνεχές υμένιο ζεόλιθου υπήρχε και από τις δύοπλευρές του Metglas. Με συνδυασμένη χρήση κατάλληλης θεωρίας και μαθηματικούμοντέλου της βιβλιογραφίας για τα μαγνητοελαστικά υλικά υπολογίζονται οι τάσεις πουαναπτύσσονται στους ζεόλιθους FAU, LTA και σιλικαλίτη-1 κατά τη ρόφηση υγρασίας. Ηδεύτερη μέθοδος υπολογισμού τάσεων εφαρμόστηκε σε αισθητήρα Metglas/MFI, στονοποίο επικάλυψη με συνεχές υμένιο ζεόλιθου υπήρχε μόνο από τη μία πλευρά τουελάσματος. Η μέθοδος εφαρμόζεται σε αισθητήρα Metglas/MFI κατά τη ρόφηση VOC’s,και βασίζεται στην ευκαμψία και ελαστικότητα που επιδεικνύει ο συγκεκριμένοςαισθητήρας κατά τη διεργασία αυτή. Η διαφοροποίηση των δύο επιφανειών ως προς τηνομοιομορφία του φιλμ του αισθητήρα, σε συνδυασμό με τη ρόφηση προκαλούν τη κάμψητου, ορατή ακόμα και με γυμνό μάτι, από το μέγεθος της οποίας υπολογίζονται οι τάσειςπου αναπτύσσονται στο φιλμ του ζεόλιθου. Σε όλες τις περιπτώσεις ακολουθεί σύγκρισητων πειραματικών αποτελεσμάτων μας με τη βιβλιογραφία

Effect of Interfacial Ion Structuring on Range and Magnitude of Electric Double Layer, Hydration, and Adhesive Interactions between Mica Surfaces in 0.05–3 M Li⁺ and Cs⁺ Electrolyte Solutions

Ions and water structuring at charged–solid/electrolyte interfaces and forces arising from interfacial structuring in solutions above 100 mM concentrations dominate structure and functionality in many physiological, geological, and technological systems. In these concentrations, electrolyte structuring occurs within the range of molecular dimensions. Here, we quantitatively measure and describe electric double layer (EDL) and adhesive interactions at mica–interfaces in aqueous CsCl and LiCl solutions with concentrations ranging from 50 mM to 3 M. Complementarily, using atomic force microscopy and surface forces apparatus experiments we characterize concentration-dependent stark differences in the inner and outer EDL force profiles, and discuss differences between the used methods. From 50 mM to 1 M concentrations, interactions forces measured in CsCl-solutions exhibit strong hydration repulsions, but no diffuse EDL-repulsions beyond the Stern layer. In confinement the weakly hydrated Cs⁺ ions condensate into the mica-lattice screening the entire surface charge within the Stern layer. In contrast, strongly hydrated Li⁺ ions only partially compensate the surface charge within the Stern layer, leading to the formation of a diffuse outer double layer with DLVO behavior. Both LiCl and CsCl solutions exhibit oscillatory ion-hydration forces at surface separations from 2.2 nm to 4–8 Å. Below 4–8 Å the force profiles are dominated in both cases by forces originating from water and/or ion confinement at the solid/electrolyte/solid interface. Adhesive minima and their location vary strongly with the electrolyte and its concentration due to specific ion correlations across the interface, while dispersion forces between the surfaces are overpowered. Highly concentrated 3 M solutions exhibit solidification of the inner EDL structure and an unexpected formation of additional diffuse EDL forces with an increasing range, as recently measured in ionic liquids. Our results may have important implications for understanding and modeling of interaction forces present in static and dynamic systems under physiological and high salt conditions

Real-Time Monitoring of Aluminum Crevice Corrosion and Its Inhibition by Vanadates with Multiple Beam Interferometry in a Surface Forces Apparatus

Crevice corrosion (CC) of metals remains a serious concern for structural materials. Yet a real-time in situ visualization of corrosion, and its inhibition within a confined geometry, remains challenging. Here, we present how multiple-beam interferometry in a Surface Forces Apparatus can be utilized to directly visualize corrosion processes in real-time and with Angstrom resolution within welldefined confinement geometries. We use atomically smooth muscovite mica surfaces to form round-shaped ∼1000 μm2 crevices on aluminum. After exposure to NaCl solutions we can detect and track active sites of aluminum corrosion within this confined geometry. CC of aluminum randomly initiates in the confined crevice mouth, where the distance between apposing surfaces is between 20-300 nm. We can directly track oxide dissolution/formation, and corrosion-rates as well as their retardation due to sodium vanadate inhibitors present in solution. Formation of a compacted oxide layer effectively inhibits CC in 5 mM NaCl solutions with 2.5 mM of added NaVO3, while inhibition rapidly breaks down at chloride concentrations above 50 mM. Breakdown of the inhibition-layers is initiated by rapid dissolution of the protective oxide within the confined zone. Our technique may be adapted for monitoring CC, corrosion inside of crack-tips, and evaluation of inhibitor efficiencies in a variety of metals

Angstrom-Resolved Real-Time Dissection of Electrochemically Active Noble Metal Interfaces

Electrochemical solid|liquid interfaces are critically important for technological applications and materials for energy storage, harvesting, and conversion. Yet, a real-time Angstrom-resolved visualization of dynamic processes at electrified solid|liquid interfaces has not been feasible. Here we report a unique real-time atomistic view into dynamic processes at electrochemically active metal interfaces using white light interferometry in an electrochemical surface forces apparatus. This method allows simultaneous deciphering of both sides of an electrochemical interfacethe solution and the metal sidewith microsecond resolution under dynamically evolving reactive conditions that are inherent to technological systems <i>in operando.</i> Quantitative <i>in situ</i> analysis of the potentio­dynamic electrochemical oxidation/reduction of noble metal surfaces shows that Angstrom thick oxides formed on Au and Pt are high-<i>ik</i> materials; that is, they are metallic or highly defect-rich semiconductors, while Pd forms a low-<i>ik</i> oxide. In contrast, under potentiostatic growth conditions, all noble metal oxides exhibit a low-<i>ik</i> behavior. On the solution side, we reveal hitherto unknown strong electrochemical reaction forces, which are due to temporary charge imbalance in the electric double layer caused by depletion/generation of charged species. The real-time capability of our approach reveals significant time lags between electron transfer, oxide reduction/oxidation, and solution side reaction during a progressing electrode process. Comparing the kinetics of solution and metal side responses provides evidence that noble metal oxide reduction proceeds <i>via</i> a hydrogen adsorption and subsequent dissolution/redeposition mechanism. The presented approach may have important implications for designing emerging materials utilizing electrified interfaces and may apply to bioelectro­chemical processes and signal transmission

Influence of molecular dipole orientations on long-range exponential interaction forces at hydrophobic contacts in aqueous solutions.

Strong and particularly long ranged (&gt;100 nm) interaction forces between apposing hydrophobic lipid monolayers are now well understood in terms of a partial turnover of mobile lipid patches, giving rise to a correlated long-range electrostatic attraction. Here we describe similarly strong long-ranged attractive forces between self-assembled monolayers of carboranethiols, with dipole moments aligned either parallel or perpendicular to the surface, and hydrophobic lipid monolayers deposited on mica. We compare the interaction forces measured at very different length scales using atomic force microscope and surface forces apparatus measurements. Both systems gave a long-ranged exponential attraction with a decay length of 2.0 ± 0.2 nm for dipole alignments perpendicular to the surface. The effect of dipole alignment parallel to the surface is larger than for perpendicular dipoles, likely due to greater lateral correlation of in-plane surface dipoles. The magnitudes and range of the measured interaction forces also depend on the surface area of the probe used: At extended surfaces, dipole alignment parallel to the surface leads to a stronger attraction due to electrostatic correlations of freely rotating surface dipoles and charge patches on the apposing surfaces. In contrast, perpendicular dipoles at extended surfaces, where molecular rotation cannot lead to large dipole correlations, do not depend on the scale of the probe used. Our results may be important to a range of scale-dependent interaction phenomena related to solvent/water structuring on dipolar and hydrophobic surfaces at interfaces

Real-Time Multiple Beam Interferometry Reveals Complex Deformations of Metal–Organic-Framework Crystals upon Humidity Adsorption/Desorption

Gas adsorption in metal–organic-frameworks (MOFs) can dramatically affect the size of the crystals (expansion and/or shrinkage) or lead to distortion of their porous structure/framework. This can strongly affect mechanical properties of MOFs potentially leading to loss or improvement of the performance of applications such as membranes, filters, or sensors. Here, we utilize white light multiple-beam-interferometry (MBI) in a surface forces apparatus (SFA) to measure in real-time the deformations taking place in HKUST-1 crystals during humidity adsorption/desorption cycles. MBI provides a real-time measurement of crystal deformations during guest molecule uptake with msecs time and Å distance resolution. We find unusual and unexpected dynamic and nonmonotonic deformation behavior upon humidity loading in HKUST-1 crystals, which we attributed to the gradual filling of the different adsorption sites in the MOF crystal framework. Also, the effect of the external mechanical pressure applied to hydrated/dehydrated crystals strongly affects the flexibility of HKUST-1 crystals and hence their deformation characteristics during guest molecule loading. Our results may have important implications for better understanding/modeling of the effect of gas adsorption on the mechanical properties of MOFs. MBI may be extended not only to other MOFs but also to any other guest–molecule systems in which adsorbate/adsorbent interactions affect structure–property relationships

Real-Time Multiple Beam Interferometry Reveals Complex Deformations of Metal–Organic-Framework Crystals upon Humidity Adsorption/Desorption

Gas adsorption in metal–organic-frameworks (MOFs) can dramatically affect the size of the crystals (expansion and/or shrinkage) or lead to distortion of their porous structure/framework. This can strongly affect mechanical properties of MOFs potentially leading to loss or improvement of the performance of applications such as membranes, filters, or sensors. Here, we utilize white light multiple-beam-interferometry (MBI) in a surface forces apparatus (SFA) to measure in real-time the deformations taking place in HKUST-1 crystals during humidity adsorption/desorption cycles. MBI provides a real-time measurement of crystal deformations during guest molecule uptake with msecs time and Å distance resolution. We find unusual and unexpected dynamic and nonmonotonic deformation behavior upon humidity loading in HKUST-1 crystals, which we attributed to the gradual filling of the different adsorption sites in the MOF crystal framework. Also, the effect of the external mechanical pressure applied to hydrated/dehydrated crystals strongly affects the flexibility of HKUST-1 crystals and hence their deformation characteristics during guest molecule loading. Our results may have important implications for better understanding/modeling of the effect of gas adsorption on the mechanical properties of MOFs. MBI may be extended not only to other MOFs but also to any other guest–molecule systems in which adsorbate/adsorbent interactions affect structure–property relationships

Selective sensor utilizing a thin monolayer of b-oriented silicalite-1 crystals– magneto-elastic ribbon assembly

This report presents the development of new selective gas sensors utilizing a b-oriented silicalite-1 layer–magneto-elastic ribbon assembly. The key principle for the operation of these sensors is monitoring the changes in the resonance frequency of the Metglas® strip in relation to the concentration of a component in the gas phase. This technique provides a simple way for monitoring the effects of the amount of adsorbed gases in the silicalite-1 coating. The thickness of the zeolite layer is that of a single crystal. The silicalite-1 crystals are oriented in the b-direction, meaning that the straight channels are perpendicular to the sensor surface, which is confirmed by X-ray diffraction (XRD) analysis. The sensor was able to repeatedly sense carbon dioxide in air and could discriminate between linear and branched hydrocarbons. The sensor was able to detect n-butane, while it did not respond to the presence of iso-butane, indicating sensing selectivity