Forces between cellulose beads xylan solutions

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). 

CeIluiose>cellulose interaction forces were measured in a reference solution (1 mM NaCl, pH 10) and in xylan solutions (10,50 and 100 mg xylan/1 in 1 mM NaCl, pH 10) starting from the reference and continuing with growing xylan concentration. All measurements were done at pH 10 to ensure that xylan was soluble. After changing the xylan concentration the system was allowed to stabilize for 1 h before measurements. Different loading forces were used and the time gap between consecutive force curves was varied from 0.5 to 10 min. The reproducibility of the force curves was checked by shifting the cantilever horisontally in less than 1 pm steps between measurements. Thus, the force curves were centered at slightly different spots on the lower bead, but still on the central area of the beads. 

The forces between two cellulose spheres across a solution containing xylan were measured for different xylan concentrations (10, SO, and 100 mg/1) in 1 mM NaCl, pH 10 (reference). When the compliance behaviour of the cellulose beads was taken into account and the forces were scaled by the effective radius of curvature of the immersed beads, the force measurements became very reproducible. This is illustrated in Figure 5, where approach curves in reference solution from three separate force experiments are shown. 

Figure 6. TAe forces measured on approach (a) and separation (b) between two cellulose beads across xylan solutions at different xylan concentrations (0-100 mgA). The forces after changing the solution in the chamber back to the reference solution are also shown (A). The lines are the best fit to the DLVO theory assuming constant charge using the parameters in Table L...

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