Tools to Probe Nanoscale Surface Phenomena in Cellulose Thin Films: Applications in the Area of Adsorption and Friction - The Nanoscience and Technology of Renewable Biomaterials - page 114

80

60

In air

40

P65-1

20

P65-2

0

P65-3

− 20

P65-4

− 40

P65-5

− 60

− 80

0 1 3

Surface position ( µ m)

2 4 5

Figure 4.16 One line scanning profiles for cellulose-coated silica surfacewhile immersed
in a nonionic triblock lubricant (E19P29E19) solutions and in air. P65 is used to indicate
lubricantE19P29E19,whichisatriblockcopolymerwith19Egroupsatbothendsand29P
groups inthemiddle. P65-1

∼ P65-5represent aseriesof ethanol solutionswiththeincrease

ofethanolconcentration.

even though the surface being measured is topographically smooth. In the second case,
the cantilever may twist when it encounters a steep slope. In order to eliminate the
roughness effect caused by the second case in lubrication, two scans on the same line
(back and forth) are performed on the substrate in order to measure the net effect (Behary,
Ghenaim et al . 2000).
When a tip in lateral force microscopy is sliding on a surface, lateral force profiles can
be measured both in air (no lubricant applied) and in solution. Figure 4.16 shows lateral
force profiles for a cellulose surface imaged in air and immersed in a solution with
nonionic E-P-E triblock polymeric surfactants (commonly used as lubricant finishes).
Here E and P represent ethylene oxide and propylene oxide groups, respectively. During
these experiments, the lubricant was dissolved in ethanol aqueous solutions at various
levels of ethanol concentration (22, 38, 52, 66, and 87%). It was observed that the friction
forces measured in air were significantly larger than those in the respective solutions,
confirming the lubrication attributes of the polymer. However, the force profiles in
the five solutions were undistinguishable, making the effect of ethanol concentration
unimportant.
Studies on copolymer adsorption are usually conducted with hydrophobic surfaces
and only a few reports have addressed the case of adsorption on hydrophilic surfaces.
The adsorption behavior of E19P29E19 copolymers on hydrophilic cellulose surfaces is
hereby briefly discussed. It is expected that the self-assembly mechanism of the block
copolymer in the case of cellulose will be different from that exhibited by hydrophobic
surfaces such as propylene or polyethylene. Wu et al .(Wu,Liu et al . 2000) carried
out an AFM study involving triblock copolymer chains on hydrophilic silica surfaces.
They suggested that in the case of hydrophilic surfaces, the E blocks bind the surface