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 95

5.0

pH = 4

Bleached HW Kraft Fibers

pH = 5
pH = 8.5

4.5

4.0

3.5

3.0

2.5

2.0

Polymer (1% treatment level)

Figure 4.3 Effect of macromolecular composition and pH on the tensile strength of
polymer-treatedbleachedkraft fibers at 1000 µ S/cmconductivity. Polyampholytesdenoted
as 'PAmp2, 4, 8, 16' correspond topolymers of increasedchargedensity (with the ratioof
anionic-to-cationic groups kept constant) while 'Cat' and 'An' correspond to the respective
single cationicand anionicpolyelectrolytes (with samemolecularmasses). Thesepolymers
were based on cationic DMAPAA (tertiary amine), anionic itaconic acid (IA) and neutral
acrylamide (AM) (see text formore details). Reproducedwithpermission fromSong,Wang
etal.(2006).

in the context of adsorbed nanolayers with high viscoelasticity to enhance fiber bond-
ing. This phenomenon can only be explored with some of the tools described in later
sections.

4.3 Cellulose Thin Films

Studies at the nanoscale usually involve substrates that are limited to surrogates of cel-
lulose fibers. This is because the intrinsic complexity of natural fibers, which includes
chemical and topographical heterogeneities that prevents derivations of cause-effect rela-
tionships. A common approach is to use cellulose thin films as model for cellulose. There
is an abundance of literature about this topic and the reader is referred to the review
by Konturri et al . for an excellent account on the subject (Kontturi, Tammelin et al .
2006). Here we limit ourselves to spin coated films of cellulose prepared on silica or
gold substrates according to a procedure reported elsewhere (Gunnars, Wagberg et al .
2002; Falt, Wagberg et al . 2004) and modified slightly as follows (Song, Liang et al .
2009): Cellulose solution was prepared by dissolving microcrystalline Avicel cellulose
in 50%wt water/N-methylmorpholine-N-Oxide (NMMO) at 115 ◦ C. Dimethyl Sulfoxide
(DMSO) was added to adjust the concentration (0.05%) and the viscosity of the cellulose
suspension. Polyvinylamine (PVAm) was used as anchoring polymer of the cellulose
film. Silica or gold substrates were immersed in PVAm for 20 min followed by wash-
ing with water and drying with a gentle nitrogen jet. The cellulose solution was then