Silica probe

Figure Bl.19.30. Height and friction images of a spin-cast polystyrene-poly(methyl methacrylate) blend obtained with (a) gold and (b) silica probes under perfluorodecalin. Note the reversal of frictional contrast and the high spatial resolution. (Taken from [142], figure 7.)...

Fig. 12 Retracting-mode force profiles of high-density PMMA brushes with and without P4VP terminal segment measured in toluene using a hydrophilic silica probe sphere...

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... 

Measurements of forces between probe particle and sessile oil drops in water were first reported by Mulvaney et al. [54] and Snyder et al. [55], with a number of studies following by Hartley et al. [56], Aston et al. [57,58], Attard and co-workers [59-61], Nespolo et al. [62] and Dagastine et al. [63]. As an example of the types of typical forces observed between an alkane droplet and a silica probe in the presence of an anionic surfactant, refer to Figure 4.4 [63]. The general shape of the force curve is similar, at first glance, to the behaviour at rigid surfaces, but as discussed below, this is a product of changes in separation and interface deformation. Also note that at low surfactant concentrations, jump-in does occur, but with an increase in surfactant concentration (which leads to a decrease in interfacial tensions) only repulsive forces are observed. 

FIGURE 4.6. The interface profile (relative to the interface position at r = 0) for an alkane drop in water with a silica probe at an axial separation distance Do of 6.5 and 4.5 nm. The dots denote the coiresponding disjoining pressure value at the marked radial distance. The inset is the disjoining pressure (electrostatic and van der Waals) for a water/aUtane/silica system with a univalent (non-surface-active) electrolyte ( " = 30 nm ijfo = 50 mV). Reprinted from Ref. [67], with permission from Elsevier. 

Continuous sampling from closed or flow systems is possible via a probe, but, ideally, neither its presence in the vessel nor its action should perturb the reaction. If these conditions are satisfied, it is possible to obtain data throughout the course of a single experiment. The products must be extracted in such a way that reaction ceases at the probe orifice. A pumping system may be used and a probe designed to quench adiabatically by a suitably large pressure drop across the probe orifice. Fine-drawn silica probes are often used in laboratory scale experiments. 

The interaction of the solutes with the membrane surface is normally characterized by the membrane hydrophilicity/hydrophobicity and a fixed charge using a contact angle measurement and a streaming potential, respectively. In this study, AFM was used to determine the force of adhesion between a HA-coated silica probe (illustrated in Figure 5.27) and the membrane surface. A typical force measurement... 

The measurement with a HA-coated silica probe showed a very good agreement with the experimental hypothesis. At a loading force of 15 nN, when the HA-coated... 

For non-polar polymers interacting with a silica probe under perfluorodecalin the Hamaker constant scales with the refractive index. This leads to the observation that the polymer with the highest refractive index shows the largest pull-off force. In fact, calculating the work of adhesion, W, from Eq. 1, and plotting the measured pull-off forces against this quantity, one sees a reasonable correlation (Figure 4), as would be expected from the appropriate contact mechanical models (25). 

Force curves measured between (A) silica (a) and polystyrene (b) substrates coated with C3M-PEO204/PAA139 and a silica probe at 10 mM NaCl, pH 7 (B) silica (a) and polysulfone (b) substrates coated with C3M-PVA445/P2MVPI228, and a silica probe at 10 mM NaCl, pH 7. Closed symbols correspond to approach and open to retraction. C3M corresponds to complex coacer-vate core micelles. (Reproduced from Brzozowska, A. M., et al.. Journal of Colloid and Interface Science, 353,380-91,2011. With permission from Elsevier.)... 

Figure 10.2 Normalized tracer rotational diffusion coefficients. (+) 113 nm silica probe spheres in a matrix suspension of 123 nm matrix spheres in dimethylformamide dimethylsulfoxide obtained using TPA(41). Colloidal 100 nm polytetrafluoroethylene-polyperfiuoromethylvinylether spheres in 18% urea 0.1 M NaCl water studied with DDLS by (x) Degiorgio, et al. (10) and by Piazza and Degiorgio(40) using (Q) DDLS and (0) FDDLS.

Beam bending 10 to 10 Rectangular beam about 10 X 0.8 X 2.5 mm Specimen supported across top of a notched holder made from silica glass tubing about 8 mm internal diameter and 10 mm deep. Short, 1 -mm-diameter silica glass rod (ground flat) as knife edge between silica probe and the beam [31]... 

With an AFM adhesion force measurement technique, Bowen et al. [42] characterized an interaction force between a colloidal silica probe and a rough membrane surface. It was found that membrane surface roughness significantly reduced electrostatic repulsion between the colloid and the surface, and the valley regions experienced a greater adhesion force. 

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