W. Richard Bowen and Nidal Hilal 4

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At pH 5.5, dissolution began to occur, but only at the step edges, not in the centre of the crystal planes. At pH values below this, as the pH decreased the dissolution rate increased, with a significant change in behaviour occurring below pH 4.0. Below this value, dissolution also began to occur at the flat crystal surfaces, although it was still most pronounced at the edges. It was suggested that this behaviour was due to the presence of oxygen in the step edges, which would be much more prone to attack by solution protons than the flat surfaces, which are positively charged at the higher pH values. A number of other studies have used AFM alongside other techniques to characterise a number of different coatings to protect metal surfaces from corrosion and wear, including TiN and ZrN thin films [24]; Sn–Ni and Sn–Cu alloy coatings [25, 26]; CrN films for enhanced wear resistance [27] and zirconia-based primers as coatings on aluminium [28]. 4.8.3 biofilms at Metal Surfaces 4.9 CONCLUsIONs 135 Yu and colleagues [29] examined the difference between nano- and microcrystallization of stainless steel surfaces and the effect on the adhesion of biofilms. Using an AFM tip coated in a synthetic peptide to simulate a biofilm, adhesion measurements were made against nanocrystalline and microcrystalline surfaces. It was found that the measured adhesion in air was significantly reduced for the nanocrystalline surface compared with the microscrystalline surface. These observations were matched by similar results from the observations of attachment of whole bacterial cells to the same surfaces in bulk solution. 4.9 COnCLUSIOnS The many benefits of AFM in investigations of membranes and membrane processes may be summarised as: 1. Atomic force microscopy can determine the key properties of synthetic membranes: pore size distribution, surface morphology and surface roughness, surface electrical properties and surface adhesion. 2. Correspondence between surface pore dimensions from AFM and MWCO is good. In addition, AFM gives surface pore size distribution. 3. Operations in liquid and colloid probe techniques are particular advantages of AFM. 4. AFM can establish the effects of changes in interactions over the surface of membranes, e.g. due to local morphology. 5. AFM allows the visualisation of solute/membrane interactions. 6. AFM is a very useful asset in assessing the properties of membranes during their development.
136 4. INvEsTIgATINg MEMbRANEs ANd MEMbRANE PROCEssEs Indeed, it is apparent that the capabilities of AFM are very closely matched to the knowledge requirements of membrane scientists and engineers. In addition, AFM is a very useful technique for investigating the interaction of process streams with the materials of construction of process equipment, including studies of particle adhesion and the effects of corrosion. ACknOWLEDgEMEnTS We thank all who have contributed to this research, especially Teodora Doneva, Daniel Johnson, Bob Lovitt, Martin Peer, Peter Williams, Chris Wright and Huabing Yin. LIST OF AbbREVIATIOnS BSA bovine serum albumin EDTA ethylenediaminetetraacetic acid MF microfiltration MT mercapto thiazoline MWCO molecular weight cut-off NF nanofiltration PSU polysulphone RO reverse osmosis SPEEK sulphonated poly (ether ether) ketone UF ultrafiltration XPS X-ray photoelectron spectroscopy Names of membranes are manufacturers’ codes. References [1] W.R. Bowen, N. Hilal, R.W. Lovitt, P.M. Williams, Atomic force microscope studies of membranes: surface pore structures of Cyclopore and Anopore membranes, J. Memb. Sci. 110 (1996) 233–238. [2] W.R. Bowen, N. Hilal, R.W. Lovitt, P.M. Williams, Visualisation of an ultrafiltration membrane by non-contact atomic force microscopy at single pore resolution, J. Memb. Sci. 110 (1996) 229–232. [3] W.R. Bowen, N. Hilal, R.W. Lovitt, C.J. Wright, A new technique for membrane characterisation: direct measurement of the force of adhesion of a single particle using an atomic force microscope, J. Memb. Sci. 139 (1998) 269–274.
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x Preface in their work. Hence, it
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xiv About thE Editors Professor Nid
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xvi List of Contributors Dr Daniel
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2 1. BAsIC PRINCIPLEs OF ATOMIC FOR
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32 2. MEASUREMENT OF PARTICLE ANd S
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82 3. QUANTIFICATION OF PARTICLE-BU
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186 6. NANOSCALE ANALySIS Of PHARMA
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196 7. MICRO/NANOENgINEERINg ANd AF
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226 8. ATOMIC FORCE MICROSCOPy ANd
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246 9. APPLICATION OF ATOMIC FORCE
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276 10. FuTuRE PRosPECTs most AFM s
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A Actin stress fiber, 197 Adhesion,
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Natural organic matter, 140 Negativ
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