Tailored modification of quartz surfaces by covalent immobilization of small molecules (gamma-aminopropyltriethoxysilane), monodisperse macromolecules (dendrimers), and poly(styrene/acrolein/divinylbenzene) microspheres withnarrow diameter distribution

Quartz plates were modified by consecutive immobilization of gamma-aminopro pyltriethoxysilane (APTS), phosphorus containing dendrimers with aldehyde g roups (generation 5 - G5), Starburst PAMAM dendrimers generation 4 (G4-PAMA M), and poly(styrene/acrolein/divinylbenzene) microspheres [P(SAD)]. In thi s way surfaces with heterogeneity on molecular, macromolecular, and microsc opic levels, and which were equipped with functional amino or aldehyde grou ps were obtained. Surface layers were characterized by X-ray photoelectron spectroscopy (XPS) and by contact-angle measurements. Analysis of XPS spect ra revealed that the thickness of the layer of G5 on the SiO2-APTS substrat e was 3.7 nm, i.e., the thickness was typical for macromolecular dimensions . The average thickness of the layer of PAMAM dendrimers on SiO2-APTS-G5 wa s found to be 0.35 and 0.29 nm, depending on whether calculations were base d on attenuation of the intensity of the Si2p or the P2p signal respectivel y. This thickness was unreasonably low for a monolayer of PAMAM dendrimers and indicated that the surface of the SiO2-APTS-G5 substrate was incomplete ly covered with these macromolecules. The XPS method was also used for the determination of the degree of coverage of the surface of a SiO2-APTS-G5-PA MAM plate with P(SAD) microspheres. The degree of coverage was found to be 0.60 and approaches the maximum theoretically possible value (0.62) for mic rospheres attached chaotically and irreversibly to the surface in an arrang ement one microsphere thick. Subsequent coverage of the SiO2-APTS-G5-PAMAM- P(SAD) substrate with PAMAM dendrimers resulted in the formation of a PAMAM adlayer 3.2 nm thick, close to the molecular dimensions of these dendrimer s. Contact-angle measurements revealed considerable differences in the hydr ophobicity of the surfaces of the quartz plates, depending on their modific ation. Hydrophobicity increased in the order SiO2 < SiO2-APTS-G5-PAMAM < Si O2-APTS less than or equal to SiO2-APTS-G5 < SiO2-APTS-G5-PAMAM-P(SAD).