Direct visualization of cationic surfactant aggregates at a cellulose-water interface

The structure of adsorbed aggregates of the cationic surfactant cetyltrimethylammonium bromide (C₁₆TAB) at the cellulose-water interface was determined using soft-contact atomic force microscopy imaging. C₁₆TAB was adsorbed to the surface from a solution with a concentration above the critical micelle concentration. Imaging of the surfactant aggregate layer showed predominantly spherical micellar structures at the cellulose-water interface with some areas of short rodlike aggregates. These structures are similar to those previously observed for C₁₆TAB adsorbed to other hydrophilic surfaces such as silica; hence, a similar mechanism for the arrangement of C₁₆TAB on cellulose is suggested, in agreement with previous neutron reflectivity data. The buildup of the surfactant layer proceeds via direct micelle adsorption to the uncharged cellulose surface. This occurs through polar interactions between the C ₁₆TAB headgroup and the hydrophilic substrate to form the observed admicelle structures.