Supplementary data S4 - Fluorescence excitation emission matrix (FEEM)
Table S4: Typical EEM peak locations of natural organic matter (Coble, 1996; Salinas-Rodriguez et al., 2009; Leenheer and Crue, 2003). Code H1 H2 Hm P1 P2
Supplementary data S5 - Force measurement using atomic force microscopy In this study, the cohesive and adhesive strengths of AOM were investigated by measuring interactions between polystyrene microspheres coated with AOM against clean and AOM-fouled membranes. The microsphere is attached to the tip of the AFM cantilever. Forces (F) were derived from the cantilever deflection using Hooke’s law while the separation distances between the microsphere and the membrane surface are measured from the scanner position and cantilever deflection. F = -k?z
Description
Humic-like primary peak Humic-like secondary peak Marine humic-like
Protein-like (tyrosine) peak
Protein-like (tryptophan) peak, phenol-like
Fluorescence range (nm) Excitation Emission 330–350 420–480 250–260 380–480 300-330 380-420 270–280 300–320 270–280 320–350
where k is the cantilever spring constant and ?z the deflection of the cantilever.
Each force measurement generates two force-distance curves: the approach force curve and the retract force curve (Figure S5-1). The approach force curve shows the force interactions of the particle probe as it approaches the membrane surface. The retract force features the adhesion force between the particle probe surface and the stationary surface. Adhesion/cohesion forces are the force needed to separate two surfaces from contact and is defined as the equivalent force at the maximum cantilever deflection in the retraction force curve. Furthermore, the total energy needed to completely separate two surfaces was calculated by integrating the measured negative forces (<0 nN) with respect to separation distance in the retract force curve.
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(+) repulsionapproach curveretract curveDetector and feedback electronics Photo-detector321LaserForce (nN)separation distance (μm)6Sample surfaceCantilever and tipattraction (-)54
Figure S5-1: Illustration of interaction force measurement using AFM and the generated force-distance curves. The arrows indicate the movement of the particle attached to the cantilever relative to the surface.
The generated approach force curves illustrate that short-range attraction forces were observed between clean PS probes and clean membrane (Figure S5-2). After the probes were coated with AOM, interaction shifted to rather long range repulsion (Figure 9a and 9b). The attraction between clean polystyrene and clean membranes may be due to van der Waals interaction, hydrogen bonding and/or hydrophobic interaction. The PS particle is hydrophobic and probably prefers contact with the membrane surface over contact with water. The electrostatic repulsion likely did not play a significant role in the surface interaction between clean or AOM-coated polysterene probe and clean membrane because the high ion concentration in the matrix (seawater) screens the charges and limits the range of electrostatic interactions to distances of less than 1 nm (Mosley et al., 2003).
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3Approach force (nN)(a)Retract force (nN)PS ? PES40Separation distance (μm)2131.5-4-8PS ? PES0123-12-1.5Separation distance (μm)(b)-16
Figure S5-2: AFM generated force-distance curves of (a) a clean PS probe approaching a clean PES membrane surface and (b) a clean PS probes retracting from clean PES membrane surface.
References
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