Wetting mechanism of a starch-stabilized alkylketene dimer emulsion: A study by atomic force microscopy

The wetting behaviour of a commercial starch-stabilized alkylketene dimer ( AKD) emulsion on glass was investigated by atomic force microscopy (AFM). T he primary objective was to elucidate whether or not the starch and surfact ant used to emulsify AKD could enhance AKD wetting an a hydrophilic surface to such a level as to allow complete spreading (theta(E) = 0); AKD wax was not previously known to spread on glass nor on cellulose. The secondary ob jective was to estimate the fraction of the furnish wetted by AKD droplets. Temperature is the primary variable affecting AKD wetting. The extent of A KD wetting increases with temperature up to 70 degrees C, after which wetti ng reaches equilibrium contact angles not differentiable by AFM. AKD wets g lass to a finite contact angle (theta(E) > 0); spreading (theta(E) = 0) was never observed with the commercial AKD suspension. The drying process also influences the extent of AKD wetting on glass. This is explained in terms of AKD hydrolysis, starch desorption from ARD and starch adsorption on the glass, which modifies the interfacial energies and thus, the equilibrium co ntact angle. The fraction of the furnish wetted by droplets (x) and the ave rage distance between two AKD droplets (L) was calculated for three example s.