Web Release Date: February 16,
Buildup of Polyelectrolyte Multilayers of Polyethyleneimine and Microfibrillated Cellulose Studied by in Situ Dual-Polarization Interferometry and Quartz Crystal Microbalance with Dissipation
and
Departments of Fibre and Polymer Technology and Chemistry, School of Chemical Science and Engineering, The Royal Institute of Technology, SE-100 44 Stockholm, Sweden, BIM Kemi AB, Box 3102, SE-443 03, Stenkullen, Sweden, Institute for Surface Chemistry, YKI, P.O. Box 5607, SE-114 86, Stockholm, Sweden, and STFI-Packforsk AB, Box 5604, SE-114 86 Stockholm, Sweden
Received October 22, 2007
In Final Form: December 11, 2007
Abstract:
Polyethyleneimine (PEI) and Microfibrillated cellulose (MFC) have been used to buildup polyelectrolyte multilayers
(PEM) on silicone oxide and silicone oxynitride surfaces at different pH values and with different electrolyte and
polyelectrolyte/colloid concentrations of the components. Consecutive adsorption on these surfaces was studied by
in situ dual-polarization interferometry (DPI) and quartz crystal microbalance measurements. The adsorption data
obtained from both the techniques showed a steady buildup of multilayers. High pH and electrolyte concentration
of the PEI solution was found to be beneficial for achieving a high adsorbed amount of PEI, and hence of MFC, during
the buildup of the multilayer. On the other hand, an increase in the electrolyte concentration of the MFC dispersion
was found to inhibit the adsorption of MFC onto PEI. The adsorbed amount of MFC was independent of the bulk
MFC concentration in the investigated concentration range (15-250 mg/L). Atomic force microscopy measurements
were used to image a MFC-treated silicone oxynitride chip from DPI measurements. The surface was found to be
almost fully covered by randomly oriented microfibrils after the adsorption of only one bilayer of PEI/MFC. The
surface roughness expressed as the rms-roughness over 1 
m2 was calculated to be 4.6 nm (1 bilayer). The adsorbed
amount of PEI and MFC and the amount of water entrapped by the individual layers in the multilayer structures were
estimated by combining results from the two analytical techniques using the de Feijter formula. These results indicate
a total water content of ca. 41% in the PEM.
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