AFM colloidal probes

Up to date, besides the SFA, several non-interferometric techniques have been developed for direct measurements of surface forces between solid surfaces. The most popular and widespread is atomic force microscopy, AFM [14]. This technique has been refined for surface forces measurements by introducing the colloidal probe technique [15,16], The AFM colloidal probe method is, compared to the SFA, rapid and allows for considerable flexibility with respect to the used substrates, taken into account that there is no requirement for the surfaces to be neither transparent, nor atomically smooth over macroscopic areas. However, it suffers an inherent drawback as compared to the SFA It is not possible to determine the absolute distance between the surfaces, which is a serious limitation, especially in studies of soft interfaces, such as, e.g., polymer adsorption layers. Another interesting surface forces technique that deserves attention is measurement and analysis of surface and interaction forces (MASIF), developed by Parker [17]. This technique allows measurement of interaction between two macroscopic surfaces and uses a bimorph as a force sensor. In analogy to the AFM, this technique allows for rapid measurements and expands flexibility with respect to substrate choice however, it fails if the absolute distance resolution is required. 

AFM / colloidal probe adhesion under HF shear excitation... 

Gan, Y., Franks, G.V. (2006). Charging Behavior of the Gibbsite Basal (001) Surface in NaCl Solution Investigated by AFM Colloidal Probe Technique. Langmuir Vol. 22, pp. 6087-6092. 

The forces acting between preadsorbed BSM layers have been investigated using the AFM colloidal probe technique. It has been demonstrated that the electrostatic repulsion, mainly between sialic acid groups, determines the... 

Nalaskowski, J., Drehch, J., Hupka, J., and Miller, J. D. 2003. Adhesion between hydrocarbon particles and silica surfaces with different degrees of hydration as determined by the AFM colloidal probe technique. Langmuir 19 5311. 

Investigation of cellulose systems in closer detail requires the choice of representative cellulose model surfaces for the experiment. A spin-coated cellulose surface on mica was the first model surface used in studies of forces in papermaking systems (70). This work was followed by other SFA studies using Langmuir-Blodgett (LB) films of cellulose (11-14). These films are noticeably smoother and more stable than spin-coated surfaces. In studies using the atomic force microscope (AFM) colloidal probe technique (Ducker et al. (75)), interaction forces were measured either between two cellulose beads (16,17) or between cellulose beads and spin-coated cellulose surfaces (18,19). 

In this study the AFM colloidal probe technique was used to investigate the forces between cellulose beads in aqueous solutions of simple electrolyte and xylan. Particular attention was paid to the behaviour of the cellulose beads. The adsorption kinetics and characteristics of adsorbed xylan on cellulose was studied with a quartz crystal microbalance with dissipation (QCM-D). 

In this present chapter, we will describe the types of surface forces which can be expected in different types of systems (classified by conditions rather than as a description of different types of forces) and will concentrate primarily on three types of surface force measuring techniques. These are the SFA of Israelachvili (and as modified by others) (44-46), the AFM colloid probe technique (these two techniques are by far the most widely exploited), and the MASIF technique which provides high-resolution data from a purpose-built non-interferometric instrument. 

Still, other results clearly show that the attractive force starts with a discontinuity in the force curve (33, 126, 127). One such example, obtained with the AFM colloidal-probe technique using silica/glass surfaces reacted with fluorinated silanes, is illustrated in Figure 20.13. 

In this chapter we review some data on the interactions between two soUd-liquid or two air-liquid interfaces obtained with a range of surface force techniques. It is beyond the purpose of this chapter to describe the merits and drawbacks of the various methods and the interested reader is referred to the original articles describing the surface force apparatus (SFA) [10], the atomic force microscope (AFM) colloidal probe [11], the thin film balance (TFB) [12] and total internal reflection microscopy (TIRM) [13] as well as a more recent review [14]. It is, however, important to be aware that the different techniques use different interaction geometries, and the results can be compared only by using the Derjaguin approximation [15,16] ... 

Sample surfaces are atomically smooth surfaces of cleaved mica sheets for SFA, and various colloidal spheres and plates for a colloidal probe AFM. These surfaces can be modified using various chemical modification techniques, such as Langmuir-Blodged (LB) deposition [12,19] and silanization reactions [20,21]. For more detailed information, see the original papers and references texts. 

Figure 2.21. Schematic representation of colloid probe-PDMS droplet interaction during the AFM experiment. Solid line depicts the undeformed profile of the PDMS droplet and the rigid colloid probe. Dashed line shows the deformed profile of the PDMS droplet.

G. Gillies and C.A. Prestidge Interaction Forces, Deformation and Nano-Rheology of Emulsion Droplets as Determined by Colloid Probe AFM. Adv. Colloid Interface Sci. 108-109, 197 (2004). 

G. Gillies and C.A. Prestidge Colloid Probe AFM Investigation of the Influence of Cross-Linking on the Interaction Behavior and Nano-Rheology of Colloidal Droplets. Langmuir 21, 12342 (2005). 

The second device with which surface forces can be measured directly and relatively universally is the atomic force microscope (AFM) sometimes also called the scanning force microscope (Fig. 6.8) [143,144], In the atomic force microscope we measure the force between a sample surface and a microfabricated tip, placed at the end of an about 100 //,m long and 0.4-10 //,m thick cantilever. Alternatively, colloidal particles are fixed on the cantilever. This technique is called the colloidal probe technique . With the atomic force microscope the forces between surfaces and colloidal particles can be directly measured in a liquid [145,146], The practical advantage is that measurements are quick and simple. Even better, the interacting surfaces are substantially smaller than in the surface forces apparatus. Thus the problem of surface roughness, deformation, and contamination, is reduced. This again allows us to examine surfaces of different materials. 

Example 11.4. McGuiggan et al. [492] measured the friction on mica surfaces coated with thin films of either perfluoropolyether (PFPE) or polydimethylsiloxane (PDMS) using three different methods The surface forces apparatus (radius of curvature of the contacting bodies R 1 cm) friction force microscopy with a sharp AFM tip (R 20 nm) and friction force microscopy with a colloidal probe (R 15 nm). In the surface force apparatus, friction coefficients of the two materials differed by a factor of 100 whereas for the AFM silicon nitride tip, the friction coefficient for both materials was the same. When the colloidal probe technique was used, the friction coefficients differed by a factor of 4. This can be explained by the fact that, in friction force experiments, the contact pressures are much higher. This leads to a complete penetration of the AFM tip through the lubrication layer, rendering the lubricants ineffective. In the case of the colloidal probe the contact pressure is reduced and the lubrication layer cannot be displaced completely. 

The development of novel methods that allow probing the mechanics of colloidal scale shells is a prerequisite for gaining understanding of the physico-chemical mechanisms that govern shell mechanics. This however requires also an in depth treatment of the shell deformation problem under the specific circumstances of the experiment. Both aims are subject of this paper for the particular case of polyelectrolyte multilayer shells investigated with the colloidal probe AFM technique. While the experimental... 

Membranes are very finely porous structures and like all such porous structures used in an industrial context are susceptible to fouling caused by adhesion of components of the materials being processed. This fouling can be minimised or avoided if suitable polymers are used in membrane manufacture. However, the selection of membrane polymers suited to particular separations has until now been a matter of experience (and failure) rather than science. However, an AFM used with the colloid probe technique [23] can provide a rapid means of assessing the adhesion of solutes to membrane materials and is hence a powerful tool for the membrane technologist. 

The first reported uses of an AFM to study EDL interactions using the colloid probe technique were the studies by Ducker et al. [29,301 and by Butt [311... 

The work of Larson et al. (62) represented the first detailed study to show agreement between AFM-derived diffuse layer potentials and ((-potentials obtained from traditional electrokinetic techniques. The AFM experimental data was satisfactorily fitted to the theory of McCormack et al. (46). The fitting parameters used, silica and alumina zeta-potentials, were independently determined for the same surfaces used in the AFM study using electrophoretic and streaming-potential measurements, respectively. This same system was later used by another research group (63). Hartley and coworkers 63 also compared dissimilar surface interactions with electrokinetic measurements, namely between a silica probe interacting with a polylysine coated mica flat (see Section III.B.). It is also possible to conduct measurements between a colloid probe and a metal or semiconductor surface whose electrochemical properties are controlled by the experimenter 164-66). In Ref. 64 Raiteri et al. studied the interactions between... 

The employed technique for this purpose was the so-called colloidal-probe AFM (Atomic Force Microscopy). A carbon microparticle with high degree of carbonization was attached to the top of the cantilever tip, forming the colloidal probe, and its interaction force with cleaved graphite was measured within a liquid cell filled with organic liquid, controlled at a desired temperature above the bulk freezing point of the liquid. The two surfaces will form a slit-shaped nanospace because the radius of the particle is far larger than the separation distance concerned here. 

A slit-like nanospace can be made up by applying so-called the colloidal probe AFM technique, which was in its origin developed to measure the force between a solid surface and a particle of micrometer size. The particle was glued on the cantilever tip, and this colloidal probe is to be used instead of the usual cantilever. The vertical scanning of the cantilever controls the distance between the particle surface and a solid surface, and the usual manner of detecting the bending of cantilever gives the... 

Alternatively, one may employ colloidal probe atomic force microscopy (AFM) to measure force distance curves such as the ones plotted in Fig. 5.1 [162]. The important difference between SFA and colloidal probe AFM experiments is that in the latter the entire force distance curve is accessible rather than only that portion satisfying Eq. (5.66) [163, 164]. In Ref. 164 a comparison is presented between theoretical and experimental data for confined poly-electrolyt.e systems. 

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