Probing the surface polarity of native celluloses using genuine solvatochromic dyes

The surface polarity of native celluloses has been investigated by the following solvatochromic dyes: dicyano-bis (1,10)-phenanthroline iron (II) Fe(phen)(2) (CN)(2) (1), bis(4-N,N-dimethylamino)-benzophenone (2), and cou-marine 153 (3). Linear Solvation Energy (LSE) relationships and the UV/Vis data have been used to characterize the surface polarity of different native cellulose batches in terms of the empirical Kamlet-Taft polarity parameters alpha (hydrogen bond acidity), beta (hydrogen bond basicity), and pi * (dipolarity/polarizability). alpha, beta, pi * and calculated Reichardt's E T (30) values are reported for various native and regenerated cellulose samples with different degrees of crystallinity. The degree of crystallinity of the cellulose samples has been determined by X-ray. The microcrystalline environment of cellulose can be exactly parameterized in terms of the alpha, beta and pi * values. It shows a fairly strong acidity alpha and a low dipolarity/polarizability. For the amorphous sections smaller alpha and larger pi * values are observed. The correspondence of the empirical polarity parameters determined has been discussed in relation to results from pyrene fluorescence and zetapotential measurements.