Photoinduced Polar Transition of Substrate Surfaces by Photodegradable Cationic Adsorbate Monolayers

We describe a novel method to prepare adsorption templates for colloidal particle partterning on silica and poly(ethylene terephthalate) (PET) plates using environment-friendly water media by convenient photolithography of an adsorbed monolayer formed from a new photodegradable multivalent cationic adsorbate. The photodegradable decaphenylcyclopentasilane derivative possessing quaternary pyridinium groups was adsorbed by a negatively charged silica or PET surface from the aqueous solutions to form a photodegradable cationic adsorbed monolayer exhibiting desorption resistance toward deionized water. Exposure to UV light emitting from a widely used low-pressure mercury lamp resulted in photodegradation of the photoreactive cyclopentasilane skeleton in the adsorbate molecule and reduced markedly the desorption resistance of the photodegraded adsorbate toward deionized water because of a photochemical decrease in adsorption sites per molecule. The photodegraded adsorbate desorption from the substrate surface was confirmed by UV-visible absorption spectroscopy and contact-angle and zeta-potential measurements. As a result, it was found that the photodegradable cationic adsorbed monolayer exhibiting a positive zetapotential value was capable of inducing a polar transition to a negative zeta-potential value near the initial substrate surface by UV exposure. Taking into account the overall facts, we successfully prepared a photopatterned cationic adsorbed monolayer of the quaternized cyclopentasilane derivative on a silica or PET plate by imagewise UV exposure and multiple rinses with deionized water. The substrate surface possessing a photopatterned surface-charge heterogeneity was available to adhesive templates for the site-selective surface adsorption of carboxy- and amino-modified polystyrene spheres charged with negative and positive signs, respectively. Furthermore, a new approach to fabricate binary particle arrays consisting of both the carboxy- and amino-modified spheres on the substrate surface was demonstrated by controlling the electrostatic interaction among the particles, the UV-exposed surface, and the unexposed surface as a function of pH values.