Silvio Prause

Empirical Polarity Parameters of Celluloses and Related Materials

Kamlet–Tafts α (hydrogen-bond donating (HBD) ability), β (hydrogen-bond accepting (HBA) ability), and π* (dipolarity/polarizability) parameters of native cellulose batches, carboxymethyl celluloses (CMCs), cellulose tosylates (CTs), and other derivatives with different degree of substitution (DS), chitine, amylose, amylopectine, and cellobiose are presented. Fe(phen)2(CN)2 [cis-dicyano-bis-(1,10)-phenanthroline-iron(II), (1)], Michlers ketone [bis-4,4′-(N,N-dimethylamino)benzophenone, (2)], 4-aminobenzophenone (3), coumarine 153 (4), and Reichardts dye (5) were used as solvatochromic surface polarity indicators. The UV/Vis reflectance spectra of the five surface polarity indicators 1, 2, 3, 4, and 5, adsorbed on the samples from the organic solvents, were measured and the absorption maxima were used to calculate the α, β, π*, and ET(30) values of the polysaccharides surface. α, β, and π* depending on degree of crystallinity of the cellulose samples have been determined. α depends on both amount and strength of accessible acidic surface groups on the cellulose surface. It is significantly larger for crystalline sections than for amorphous parts. The π* scale is suitable for the classification of different cellulose batches, because it seems to be independent of inhomogeneities of the cellulose surface. The α-values of CMCs and CTs significantly decrease with increasing DS inasmuch the number of cellulosic-OH groups (Cell-OH) decreases. A slight increase of π* with DS is observed for CTs.

Electrokinetic and solvatochromic studies of functionalized silica particles

Zeta potential plots, Kamlet-Tafts α (hydrogen bond-donating, HBD), β (hydrogen bond-accepting, HBA), and π* (dipolarity/polarizability) parameters as well as Gutmanns DN (donor numbers) are presented for 12 differently functionalized (i.e. alkyl, cyanoalkyl, aminoalkyl, and imidazolidine) silica particles. The pH-dependent zeta potential plots were measured in aqueous solution, whereas the solvatochromic studies were performed in 1,2-dichloroethane and cyclohexane as solvents using a special UV/visible spectroscopic technique. For the determination of the solvatochromic polarity parameters, a set of carefully characterized polarity indicators was employed: Cu(tmen)(acac)+B(C6H5)4 - for β and DN; dicyano-bis(1,10-phenanthroline)iron(II) for α; 4,4′-bis(N,N-dimethylamino)benzophenone for π*; and an aminobenzofuranone derivative {3-(4-amino-3-methylphenyl)-7-phenyl-benzo[1,2b : 4,5b′]difuran-2,6-dione} (ABF) for α, β, and π*. The calculation of the polarity parameters was carried out via linear solvation energy (LSE) correlation equations using the Kamlet-Taft solvent parameters as a reference system. A linear correlation between the electrokinetically determined value of the isoelectric point and the β parameter of the functionalized silicas is demonstrated.

Comparison of polarity parameters for glass fibers obtained by inverse gas chromatography and solvatochromism

Glass fibers with different surface properties (differently sized and unsized) have been investigated by means of inverse gas chromatography (IGC) at infinite dilution as well as by UV/Vis spectroscopy of solvatochromic probe dye molecules. Surface acid–base parameters obtained from the specific energies of adsorption of polar probes using IGC were compared with empirical polarity parameters obtained from shifts in the UV/Vis absorption maxima of adsorbed solvatochromic probe dyes. Both methods give useful information on surface characteristics. Solvatochromism seems to be suitable for a quick sizing characterization and, therefore, this method may become a significant surface analytical tool in the field of adhesion compared with the established IGC methodology.

Plasma modification of diamond surfaces

Because of its extreme hardness, diamond is a very interesting material for many industrial applications. One way to extend the field of diamond application and optimize the process conditions in diamond tool production is to enhance its surface reactivity. Low-pressure oxygen-plasma treatments were applied to equip the diamond surfaces with chemically reactive groups to improve their adhesion properties. XPS and DRIFT spectroscopy investigations showed that oxygen plasmas were suitable to oxidize the diamond surface. Combining derivatization reactions and solvatochromic dye adsorption studies, the introduction of alcoholic groups was confirmed. Besides the surface oxidation, the plasma treatment initiates decomposition of the diamond lattice which is followed by a re-arrangement of the carbon atoms in a graphite-like structure. The planar graphite structure supports the formation of carbonyl groups.

The Solvent-Like Nature of Silica Particles in Organic Solvents

Kamlet-Taft’s α (hydrogen bond donor acidity) and π* (dipolarity/polarizability) values of various silica batches measured in various solvents are presented. The α and π* parameters for the various solid acids are analyzed by means of Fe(phen)2(CN)2 (cis-dicyano-bis-(1,10)-phenanthroline-iron(II), 1), Michler’s ketone (4,4′-bis-(dimethylamino)-benzophenone, 2), and two hydrophilic derivatives of 2, (4-(dimethylamino)-4′-(di-2-hydroxyethyl)-amino-benzophenone (3a) and 4,4′-bis-(di-(2-hydroxyethyl)-amino)-benzophenone (3b) as well as coumarin 153 (4) as solvatochromic surface polarity indicators. Apparent β (hydrogen bond acceptor basicity) parameters for bare silica have been evaluated by means of an aminobenzodifuranone dye (5) as solvatochromic probe.