Atomic force microscopy colloidal probe

Colloid Probe Atomic Force Microscopy. Colloid probe atomic force microscopy (AFM) uses a microsphere as a probe for the quantitative measurement of surface forces.The main advantage of using a microsphere instead of a sharp tip is the improved definition of the contact geometry and thus the ability to perform quantitative comparisons with theoretical models of interfacial forces. 

Surfaces can be characterized using scaiming probe microscopies (see section B1.19). In addition, by attaching a colloidal particle to tire tip of an atomic force microscope, colloidal interactions can be probed as well [27]. Interactions between surfaces can be studied using tire surface force apparatus (see section B1.20). This also helps one to understand tire interactions between colloidal particles. 

Typical forces profdes measmed between glass surfaces in ethanol-cyclohexane mixtures are shown in Fig. 2. Colloidal probe atomic force microscopy has been employed. In pure cyclohexane, the observed force agrees well with the conventional van der Waals attraction calculated with the nometarded Hamaker constant for glass/cyclohexane/glass. 

G. Gillies, C.A. Prestidge, and P. Attard Determination of the Separation in Colloid Probe Atomic Force Microscopy of Deformable Bodies. Langmuir 17, 7955 (2001). 

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. 

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. 

An experimental trial for finding foe freezing point elevation phenomena was conducted, employing foe so-called colloidal-probe Atomic Force Microscopy. A carbonaceous nanospace with slit geometry was successfully made up by this technique. 

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. 

Application of Scanning Probe Microscopy (Scanning Tunneling Microscopy and Atomic Force Microscopy) in Colloid and Surface Chemistry K.S. Birdi and D.T. Vu... 

Pasche, S., Textor, M., Meagher, L., Spencer, N.D., Griesser, H.J. Relationship between interfacial forces measured by colloid-probe atomic force microscopy and protein resistance of poly/ethylen glycol)-grafted poly(L-lysine) adlayers on niobia surfaces. Langmuir 21, 6508-6520 (2005). doi 10.1021/la050386x... 

Relationship between Interfacial Forces Measured by Colloid-Probe Atomic Force Microscopy and Protein Resistance of Poly(ethylene glycoD-Grafted Poly(L-lysine) Adlayers on Niobia Surfaces... 

Measurement of interfacial forces thus offers the potential to study the factors involved in protein repellence or adsorption. Force measurements on adsorbed and grafted PEG layers have been reported, using both the surface forces apparatus (SFA) and the colloid-probe atomic force microscopy (AFM) technique. - Adsorbed PEG layers show responses due to relaxation processes,... 

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