W. Richard Bowen and Nidal Hilal 4

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236 8. ATOMIC FORCE MICROSCOPy ANd POLyMERS ON SURFACES point (D � 0) and the minimum of each attractive force. We have assumed that the Kuhn statistical segment is b � 0.6 nm. In Figure 8.9(b), we zoom on an attractive peak (dashed rectangular in Figure 8.9a). For this plot, the variables have been reversed (y � D and x � F) and the absolute value of the force has been used. The theoretical formula of the stretching by ⎡ its ends of a freely jointed chain is ⎛ Fb⎞ kT ⎤ R � Lc ⋅ ⎢coth ⎜ � ⎝⎜ kT ⎠⎟ ⎥ , where R is ⎣⎢ Fb ⎦⎥ the end-to-end chain distance when a restoring force F is exerted, Lc is the contour length (full length of the stretched polymer chain), k is the Boltzmann constant and T is the absolute temperature [32]. As we can see in Figure 8.8, it fits the AFM data well. 8.4 DIBLoCk CoPoLymErS ADSorBED on SurFACES Amphiphilic diblock copolymers have great potential in a variety of applications, ranging from their use as responsive layers for the fabrication of smart surfaces to supramolecular responsive carriers for drug/ gene delivery. We have recently studied the adsorption of poly(isopreneb-ethylene oxide) block copolymer (PI-PEO) on mica [33]. The polymer consists of a short and very flexible hydrophobic block (PI) (in melt state at room temperature) and a long hydrophilic block (PEO). Tapping mode AFM imaging was employed in dry state. The deposition of a droplet of deionised water polymer solutions onto freshly cleaved mica, followed by gentle rinsing and finally drying, resulted in the initial formation of ultraflat polymeric islands (Figure 8.10a). It is well known that mica is hydrophilic and an adsorbed water layer in the form of semi-continuous water islands forms on its fresh surface upon cleavage under normal ambient conditions [34, 35]. The polymer molecules organised in polymer brush-like flat nanometre-thick islands with the PEO within the ultrathin water layer and the PI block collapsed at the water/air interface (Figure 8.11a). As mica became gradually less hydrophilic with time, most of the water evaporated and the polymeric monolayer islands were laterally compressed and increased in height (Figure 8.10b). Ultimately, parts of the PEO blocks remained adsorbed on to mica (some strongly adsorbed water molecules still remain on the mica surface) and other parts aggregated owing to the monomer-monomer attractive interactions in the dry state and dewetted the mica surface. The dewetting behaviour was aided further by the aggregation and fusion of the flexible PI blocks; they came together to create a hydrophobic core. The height of the polymer islands was increased by a factor of about 5 as mica became less hydrophilic with time. The final structure has the organisation of a surface micelle with
1000.0 950.0 900.0 850.0 800.0 750.0 700.0 650.0 Y [nm] –2300.0 –2200.0 –2100.0 –2000.0 –1900.0 –1800.0 X [nm] 8.5 STAR-SHAPEd POLyMERS AdSORBEd ON SURFACES 237 5.0 2.0 0.0 (a) (b) Y [nm] (c) 2600.0 2500.0 Z [nm] Y [nm] 600.0 500.0 400.0 a hydrophobic core at the top and a stretched hydrophilic layer partially in close contact with the mica surface (Figures 8.10c and 8.11b). 8.5 StAr-ShAPED PoLymErS ADSorBED on SurFACES Star-shaped polymers consist of several linear polymer chains (arms) covalently attached to a low–molecular weight core. They are of particular interest in soft condensed matter since the number of arms (also called functionality) controls their interactions and consequently many physical properties. It is expected that as the number of arms increases, their polymer- like behaviour will change and become more colloidal-like. We adsorbed polybutadiene (PB) star-shaped polymers of three different functionalities (number of arms: 18, 32 and 59) onto freshly cleaved mica surfaces from dilute polymer solutions in toluene. We investigated the structural regimes of the submonolayers and monolayers of adsorbed PB star polymers, which were formed on the mica surfaces by using AFM tapping mode imaging in dry state [36]. We attained various adsorbed 300.0 –2000.0 –1900.0 –1800.0 –1700.0 –1600.0 –1500.0 –1400.0 X [nm] 2400.0 15.0 12.5 2300.0 10.0 7.5 2200.0 5.0 2.5 0.0 –1800.0 –1700.0 –1600.0 –1500.0 –1400.0 –1300.0 –1200.0 X [nm] 17.5 20.0 Z [nm] 10.0 7.5 5.5 2.5 0.0 FIgurE 8.10 AFM 3D-graph topography of a polymer island (a) 133 min, (b) 745 min and (c) 2980 min after sample preparation. Z [nm]
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Butterworth-Heinemann is an imprint
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x Preface in their work. Hence, it
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xii Preface them from hostile condi
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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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20 1. BAsIC PRINCIPLEs OF ATOMIC FO
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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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100 3. QUANTIFICATION OF PARTICLE-B
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C H A P T E R 4 Investigating Membr
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4.2 THE RANgE OF POssIbILITIEs FOR
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4.2 THE RANgE OF POssIbILITIEs FOR
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4.3 CORREsPONdENCE bETwEEN sURFACE
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4.3 CORREsPONdENCE bETwEEN sURFACE
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4.4 IMAgINg IN LIqUId ANd THE dETER
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4.4 IMAgINg IN LIqUId ANd THE dETER
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4.5 EFFECTs OF sURFACE ROUgHNEss ON
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4.6 ‘vIsUALIsATION’ OF THE REjE
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4.7 THE UsE OF AFM IN MEMbRANE dEvE
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Dfractional 0.18 0.16 0.14 0.12 0.1
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4.8 CHARACTERIsATION OF METAL sURFA
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At pH 5.5, dissolution began to occ
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REFERENCEs 137 [4] W.R. Bowen, N. H
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C H A P T E R 5 AFM and Development
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5.2 MEAsUREMENT OF ADHEsION OF COLL
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5.2 MEAsUREMENT OF ADHEsION OF COLL
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The antibacterial activity of initi
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5.3 MODIFICATION OF MEMBRANEs 147 t
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5.3 MODIFICATION OF MEMBRANEs 149 B
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Force (nN m -1 ) Loading force (mN
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5.3 MODIFICATION OF MEMBRANEs 153 p
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Adhesion force (mN m -1 ) 10 8 6 4
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Adhesion force (mN m -1 ) 20 15 10
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Adhesion force (mN m -1 ) 10 8 6 4
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5.3 MODIFICATION OF MEMBRANEs 161 F
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5.4 MODIFICATION OF MEMBRANEs wITH
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5.4 MODIFICATION OF MEMBRANEs wITH
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Å 200 100 0 5.4 MODIFICATION OF ME
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AbbrEvIAtIonS And SyMbolS NOM Natur
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REFERENCEs 171 [29] W.R. Bowen, T.A
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174 6. NANOSCALE ANALySIS Of PHARMA
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W. Richard Bowen and Nidal Hilal 4

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