Silica colloid probe

Table 7.2. Normalized adhesion forcefor a polystyrene and silica colloid probe at the membrane [42]...

It was mentioned in Section 6.1 that an atomic force microscope can also quantify the other key properties controlling membrane performance. The crucial innovation in the determination of such properties is the development of colhid probes. Such probes are formed by attaching particles of dimensions of the order of 1 pm to the end of tipless cantilevers. Such attachment may be carried out using the manipulation properties of an atomic force microscope, but greater success is achieved with the use of specially designed micromanipulation equipment. An example of a colloid probe is shown in the electron microscopy image of Figure 6.6. The silica colloid probed shown is at about the lower size limit for successfitl micromanipulation and subsequent measurement. 

Table 6.3 Effective experimental decay lengths for approach curves between silica colloid probe and AFC99 membrane and...

Figure 6.18 Adhesion of a silica colloid probe at a peak and a valley on an AFC99 membrane in 10 M NaCI solution (pull-off force).

Table 6.4 Normalized adhesion forces for silica colloid probes and AFC99 membrane.

The figure shows how a 0.75 pm silica colloid probe sees the pores in a 1.0 pm Cyclopore membrane in solutions of two ionic strengths when imaged in each... 

The colloid probe technique was first applied to the investigation of surfactant adsorption by Rutland and Senden [83]. They investigated the effect of a nonionic surfactant petakis(oxyethylene) dodecyl ether at various concentrations for a silica-silica system. In the absence of surfactant they observed a repulsive interaction at small separation, which inhibited adhesive contact. For a concentration of 2 X 10 M they found a normalized adhesive force of 19 mN/m, which is small compared to similar measurements with SEA and is probably caused by sufactant adsorption s disrupting the hydration force. The adhesive force decreased with time, suggesting that the hydrophobic attraction was being screened by further surfactant adsorption. Thus the authors concluded that adsorption occurs through... 

Special probes were introduced to measure surface forces in colloidal systems as a function of the ionic strength and the concentration of surfactant molecules [214]. A so-called colloid probe can be prepared by gluing a silica sphere onto a conventional Si3N4 tip [179]. 

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 aptamer described above was attached to the surface of the silica colloidal crystal comprising 290 nm silica spheres (resulting in 22.5 nm radius nanopores) via maleimide-activated support. The transport rate of a redox-active probe molecule (ferrocene dimethanol) through the resulting nanoporous films was measured as a function of cocaine concentration using cyclic voltammetry. A neutral redox probe, Fc(CH20H)2, was used to exclude the possibility that the observed changes in the molecular transport would result from electrostatic effects [26,27]. 

Table 1. Average Values ( Standard Deviation) for PLL(20)-g[3.5]-PEG(5), Adsorbed on a Silica Substrate Surface, of the Wet Mass Density, wei, the Dry Mass Density, mdry, the Solvation, W, the Number of Solvent Molecules per EG Monomer Averaged over the Cross Section of the PEG Brush, A mig, and the Coefficient of Friction for Symmetric (Silicon Wafer and Colloidal Probe Coated with PLL-g-PEG), and Asymmetric (Silicon Wafer Coated with PLL-g-PEG,...

The experiments with adsorbed mucin layers were conducted in the following manner The fused silica liquid cell was cleaned with Deconex 11 Universal solution (Borer Chemie, Switzerland) and rinsed with plenty of purified water, flushed with ethanol, and dried under a flow of nitrogen gas. A mercaptohexadecane-modifiedQCM crystal and a cantilever with the colloidal probe were washed with ethanol and dried in a flow of filtered nitrogen gas and mounted into the AFM. Next, the probe was brought close to the flat surface and 30 mM NaN03 solution was injected into the liquid cell and allowed to equilibrate for 10 min before measuring ten force displacement curves. 

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. 

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. 

The first part of the chapter focuses on the ordering of silica nanoparticles (diameter 9-26 nm) in an aqueous suspension confined between a colloidal probe (about 7 p.m in diameter) and a planar Silicon wafer. The colloidal probe is glued... 

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