Mica Surface In Water Research Articles

Development of a force measurement system with a large punctual measurement range

Atomic force microscopes (AFMs) are precise force measurement instruments that can be used to measure multiple surface properties, such as adhesion force, surface potential, and elasticity at the nanoscale. AFM is increasingly used in diverse fields, especially in industrial applications. However, most existing commercial AFMs provide a scanning range of less than a few 100 μm. Moreover, the size of the sample must usually be less than a few centimeters to fit the mechanical constraints of the device. In this paper, we propose a gantry-type force measurement system that can perform force curve measurements over a large range. The measurement range of the proposed device is 240 mm minus the sample width in air environments. In liquid environments, the measurement range is mainly limited by the size of the Petri dish. For instance, a measurement range of 41.5 mm can be achieved by using a Petri dish having a diameter of 85.5 mm. In the experiments, (a) surface adhesion measurements on the ultraviolet/ozone (UV/O3) treated glass slides in air and (b) surface potential measurements on a mica surface in water were performed. The experimental results were consistent with the values obtained by the commercial AFMs, which demonstrated the accuracy of the proposed system.

Ion Distribution and Hydration Structure in the Stern Layer on Muscovite Surface.

Based on molecular dynamics simulations of eight ions (Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, and Ba2+) on muscovite mica surfaces in water, we demonstrate that experimental data on the muscovite mica surface can be rationalized through a unified picture of adsorption structures including the hydration structure, cation heights from the muscovite surface, and state stability. These simulations enable us to categorize the inner-sphere surface complex into two different species: an inner-sphere surface complex in a ditrigonal cavity (IS1) and that on top of Al (IS2). By considering the presence of the two inner-sphere surface complexes, the experimental finding that the heights of adsorbed cations from the muscovite surface are proportional to the ionic radius for K+ and Cs+ but inversely proportional to the ionic radius for Ca2+ and Ba2+ was explained. We find that Na+, Ca2+, Sr2+, and Ba2+ can form both IS1 and IS2; K+, Rb+, and Cs+ can form only IS1; and Mg2+ can form only IS2. It is suggested that the formation of IS1 and IS2 is governed by the charge density of the ions. Among the eight ions, we also find that the hydration structure for the outer-sphere surface complexes of divalent cations differs from that of the monovalent cations by one adsorbed water molecule (i.e., a water molecule located in a ditrigonal cavity).

Modifying surface forces through control of surface potentials.

Combining direct surface force measurements with in situ regulation of surface potential provides an exceptional opportunity for investigating and manipulating interfacial phenomena. Recently, we studied the interaction between gold and mica surfaces in water with no added salt, while controlling the metal potential, and found that the surface charge at the metal may vary, and possibly even change its sign, as it progressively approaches the (constant-charge) mica surface [Langmuir, 2015, 31(47), 12845-12849]. Such a variation was found to directly affect the nature of the contact and adhesion between them due to exclusion of all mobile counterions from the intersurface gap. In this work, we extend this to examine the potential-dependent response of the adhesion and interaction between gold and mica to externally applied voltages and in electrolyte solution. Using a surface force balance (SFB) combined with a three-electrode electrochemical cell, we measured the normal interaction between gold and mica under surface potential regulation, revealing three interaction regimes - pure attraction, non-monotonic interaction from electrostatic repulsion to attraction (owing to charge inversion) and pure repulsion. Accordingly, the adhesion energy between the surfaces was found to vary both in no added salt water and, more strongly, in electrolyte solution. We justify this potential-dependent variation of adhesion energy in terms of the interplay between electrostatic energy and van der Waals (vdW) interaction at contact, and attribute the difference between the two cases to the weaker vdW interaction in electrolyte solution. Finally, we showed that through abruptly altering the gold surface potential from negative to positive and vice versa, the adhesion between gold and mica can be reversibly switched on and off. We surmise that the process of bringing the surface into contact is associated with the formation of a strong electric field O (108 V m-1) in the intersurface gap.

Accurate formula for dissipative interaction in frequency modulation atomic force microscopy

Much interest has recently focused on the viscosity of nano-confined liquids. Frequency modulation atomic force microscopy (FM-AFM) is a powerful technique that can detect variations in the conservative and dissipative forces between a nanometer-scale tip and a sample surface. We now present an accurate formula to convert the dissipation power of the cantilever measured during the experiment to damping of the tip-sample system. We demonstrated the conversion of the dissipation power versus tip-sample separation curve measured using a colloidal probe cantilever on a mica surface in water to the damping curve, which showed a good agreement with the theoretical curve. Moreover, we obtained the damping curve from the dissipation power curve measured on the hydration layers on the mica surface using a nanometer-scale tip, demonstrating that the formula allows us to quantitatively measure the viscosity of a nano-confined liquid using FM-AFM.

Theoretical simulation of noncontact atomic force microscopy in liquids

Methods of theoretical simulations of noncontact atomic force microscopy in liquids have been developed. Though there are several difficult issues for the theoretical simulations in liquids, the authors introduce here the simulation methods for the cantilever oscillation in liquids and the tip-sample interaction force mediated by water molecules. As for the cantilever motion, a very efficient numerical method is proposed which solves the oscillation of the elastic beam cantilever and fluid dynamics simultaneously. The results reproduce fairly well the resonant curve and related properties of the Si beam cantilever. As for the simulation of the tip-sample interaction force in water, classical molecular dynamics (MD) method is adopted in the present work. The case study by MD for the mica surface in water revealed new features that appeared in the three-dimensional force map.

AFM investigation of the surface properties of silica particles dispersed by bead milling

In the present study, atomic force microscopy (AFM) was used to determine the mechanism by which bead milling enhances particle surface potential. The force curves between silica particles and a mica surface were measured in water, and AFM was used to examine the surfaces of the particles. AFM was performed in contact mode with a colloid probe and was used to measure the interaction forces between silica particles and a mica surface in water and to investigate the influence of friction between the silica particles and the glass beads on the zeta potential of the silica particles. The zeta potential was enhanced by an increasing number of friction cycles. Friction between the tested silica particles and the glass beads during bead milling contributed to the enhanced zeta potential of the tested silica particles. AFM performed in imaging mode was employed to investigate the influence of friction between the tested silica particles and the glass beads on particle surface morphology. The surface roughness of both the tested silica particles and the glass beads was decreased slightly by friction. It is possible that friction between particles by the loading force of 10 nN slightly abrades the particle surface, thereby removing contaminations and impurities from the surface, increasing the hydrophilicity enhancing the surface potential.

Evidence of the No-Slip Boundary Condition of Water Flow between Hydrophilic Surfaces Using Atomic Force Microscopy

In this study we present measurements of the hydrodynamic force exerted on a glass sphere glued to an atomic force microscopy (AFM) cantilever approaching a mica surface in water. A large sphere was used to reduce the impact of the cantilever beam on the measurement. An AFM cantilever with large stiffness was used to accurately determine the actual contact position between the sphere and the sample surface. The measured hydrodynamic force with different approach velocities is in good agreement with the Taylor force calculated in the lubrication theory with the no-slip boundary conditions, which verifies that there is no boundary slip on the glass and mica surfaces. Moreover, a detailed procedure of how to subtract the electrostatic double-layer force is presented.

Photothermal excitation and laser Doppler velocimetry of higher cantilever vibration modes for dynamic atomic force microscopy in liquid

The authors present an optically based method combining photothermal excitation and laser Doppler velocimetry of higher cantilever vibration modes for dynamic atomic force microscopy in liquid. The frequency spectrum of a silicon cantilever measured in water over frequencies ranging up to 10 MHz shows that the method allows us to excite and detect higher modes, from fundamental to fifth flexural, without enhancing spurious resonances. By reducing the tip oscillation amplitude using higher modes, the average tip-sample force gradient due to chemical bonds is effectively increased to achieve high-spatial-resolution imaging in liquid. The method's performance is demonstrated by atomic resolution imaging of a mica surface in water obtained using the second flexural mode with a small tip amplitude of 99 pm; individual atoms on the surface with small height differences of up to 60 pm are clearly resolved.

Hydration force and dynamic squeeze-out of hydration water under subnanometerconfinement

We have performed molecular dynamics simulations to study the normal forces betweentwo mica surfaces in water and the consequent dynamic squeeze-out process. Aliquid–vapor molecular ensemble has been designed for this purpose. We find, however, thatonly the two-layer hydration water can support a repulsive hydration force, and beyondthis thickness the overall forces are attractive. From the hydrodynamic pressure developedduring a normal approach and dynamic squeeze-out, we estimate that the viscosity ofconfined hydration water in the thickness of 0.7–1.35 nm is about 5–16 times the bulk value.A steered diffusion model has been proposed, which directly predicts the critical velocitybelow which hydrodynamic effects can be eliminated in hydration force measurements.

Large Area, Molecularly Smooth (0.2 nm rms) Gold Films for Surface Forces and Other Studies

Using large-area (cm2) single-crystal mica sheets as the templating substrate, we have created correspondingly large template-stripped (TS) gold films (thickness 82 +/- 2 nm) that appear smooth to within 0.2 nm rms roughness over their entire area. These gold films, created without the use of any releasing solvent, are characterized using AFM, X-ray diffraction, multiple beam interferometric fringes of equal chromatic order (FECO), and contact angle measurements. Being molecularly smooth over large areas and (adjustably) semitransparent, these films are especially suitable for use in the surface force balance (SFB), as shown by measurements of the normal force (F) versus distance (D) profiles between such a flat gold surface and a bare mica surface in water. The F(D) profiles are in good agreement with DLVO theory down to molecular contact and indicate that the gold surface is negatively charged under water.

In situ observation of single polymers adsorbed onto mica surfaces in water

The morphology of a cationic polymer of high molecular weight, poly[2-(acryloyloxy)ethyl(trimethyl)ammoniumchloride], adsorbed on to a mica surface in water was observed in situ using the tapping mode of an atomic force microscope with a high-resolution probe. It was found that the morphology of adsorbed polymers changes with time to be lumplike, floclike, and then fibril-like and that it takes surprisingly a long time for the polymers to relax completely in water, even though they are highly charged. Detailed structures of extended polymers are also discussed.

High speed tapping mode atomic force microscopy in liquid using an insulated piezoelectric cantilever

Quicker imaging times for tapping mode atomic force microscopy in liquid could provide a real-time imaging tool for studying dynamic phenomena in physiological conditions. We demonstrate faster imaging speed using microcantilevers with integrated piezoelectric actuators. The exposed electric components of the cantilever necessitate an insulation scheme for use in liquid; three coating schemes have been tested. Preliminary tapping mode images have been taken using the insulated microactuator to simultaneously vibrate and actuate the cantilever over topographical features in liquid, including a high speed image of steps on a mica surface in water and an image of two e coli bacteria taken in saline solution at 75.5 μm/s, a threefold improvement in bandwidth versus conventional piezotube actuators.

Time dependence of forces between mica surfaces in water and its relation to the release of surface ions

A surface force balance has been used to investigate the time-dependent behavior of the normal forces between two smooth mica surfaces immersed in salt-free (conductivity) water. A long-ranged repulsion on initial approach to adhesive contact indicates an equilibrium surface-charge density σ=σ0 due to the loss of K+ ions from the mica surface into the water. Subsequent force measurements at times τ following separation of the surfaces reveal that σ drops markedly following contact and separation, but then relaxes back to σ0 with a characteristic time τr=11±2 min. This behavior is attributed to condensation of the counterions into the surfaces when they come into contact, and to their subsequent slow release into the water. The energy barrier associated with the counterion release was estimated from the value of τr to be 33±4 kBT.

Adhesion between Silica Particle and Mica Surfaces in Water and Electrolyte Solutions

An atomic force microscope (AFM) is used to study the adhesion between a silica sphere and a mica plate in pure water and solutions of monovalent cations (LiCl, NaCl, KCl, and CsCl). It is found that the adhesive force depends not only on the electrolyte concentration but also on the hydration enthalpy of cations and the contact time of the particle on the surface. Possible mechanisms by which the observed phenomena can be explained consistently are discussed extensively. It is suggested that the adhesive force is closely related to the structure of the layer of cations and water molecules adsorbed on the surfaces: the strong adhesive force is obtained when highly hydrated cations (Li+, Na+) are adsorbed to form a thick but weakly adsorbed layer, while the weak adhesive force is observed when poorly hydrated cations (Cs+, K+) are adsorbed to form a thin but strongly adsorbed layer.

Direct Observation of Water Layers on Mica Surface in Water by Atomic Force Microscope

Abstract Water film on mica surface immersed in water is directly detected and imaged by atomic force microscope. The depressions and islands indicate the existence of water layer, which preserve some solid characters of mica lattice. The observation is attributed to the inhomogeneity and disruption of water layers adjacent to mica.

Adhesion of two solid surfaces in water: Effect of rotational mismatch of surface lattices

The adhesion force needed to separate two molecularly smooth mica surfaces in water has been directly measured as a function of the rotational angle θ between the two surface lattices (relative crystallographic orientation). The results give the variation of the surface energy with θ, which shows sharp peaks (adhesion maxima) at θ=0 and 180°. Preliminary results also indicate effects at other angles, and that the whole interaction potential (oscillatory potential of mean force) between the surfaces in liquids may depend on the relative orientation of their surface lattices.

Measurements of the Effect of Angular Lattice Mismatch on the Adhesion Energy Between two Mica Surfaces in Water

Measurements of the Effect of Angular Lattice Mismatch on the Adhesion Energy Between two Mica Surfaces in Water