We report a simple strategy to produce single and multipatch particles via the conventional dip-coating process. In this method, a close-packed monolayer of micron-sized silica particles is first formed at air-polymer solution interface, followed by dip coating of particles on a glass substrate. The simultaneous deposition of both polymer and particles on the substrate gives rise to a thin polymer layer and a monolayer of silica particles. Sonication of the substrate leads to the formation of a polymeric patch on one side of the particles. The patch shape depends on the aging of the polymer film prior to sonication. With aging time the patch evolves from ring-like to disk-like. This technique allows easy control of patch width by varying the concentration of polymer in the solution. We further show that the number of patches on the particle can be increased by controlling the concentration of silica particles at the interface such that surface coverage is less than that required for the formation of a close-packed monolayer. The single and multipatch particles are characterized by scanning electron and optical microscopy for the patch size, shape, and number distribution. The as-synthesized particles are used as a model to study self-assembly of colloids with electrostatic repulsion and patchy hydrophobic attractions due to polymeric patches. We find the formation of doublets and finite-sized clusters due to patchy interactions. Dip coating can be automated to produce large quantities of patchy particles, which is one of the major limitations of other methods of producing patchy particles.

A binary mixture of oppositely charged colloids can be used to stabilize water-in-oil or oil-in-water emulsions. A Monte Carlo simulation study to address the effect of charge ratio of colloids on the stability of Pickering emulsions is presented. The colloidal particles at the interface are modeled as aligned dipolar hard spheres, with attractive interaction between unlike-charged and repulsive interaction between like-charged particles. The optimum composition (fraction of positively charged particles) required for the stabilization corresponds to a minimum in the interaction energy per particle. In addition, for each charge ratio, there is a range of compositions where emulsions can be stabilized. The structural arrangement of particles or the pattern formation at the emulsion interface is strongly influenced by the charge ratio. We find well-mixed isotropic, square, and hexagonal arrangements of particles on the emulsion surface for different compositions at a given charge ratio. The distribution of coordination numbers is calculated to characterize structural features. The simulation study is useful for the rational design of Pickering emulsifications wherein oppositely charged colloids are used, and for the control of pattern formation that can be useful for the synthesis of colloidosomes and porous shells derived thereof.

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The photophysical properties of 1, in the absence and presence of titanium dioxide (TiO 2 ) nanoparticles have been studied using UV-visible absorption spectro scopy and steady-state fl uorescence spectroscopy. The fl uorescence intensity of the DHDMAQ decreases as the concentration of TiO 2 nanoparticles increases. The quenching is characterized by a Stern-Volmer plot, which dis plays a positive deviation from linearity. This could be explained by static quenching models. The Stern-Volmer quenching constant, association constant, and binding constant have been calculated. The distance between DHDMAQ and TiO 2 nanoparticles has also been evaluated using Forster's theory of non-radiative energy transfer. Introduction.Anthraquinone is an aromatic organic compound and an important quinone derivative of anthracence. Anthraquinone is chemically stable under normal condition. Anthraquinone naturally occurs in some plants like aloe, cascara, senna, buckthorn etc. They are used principally in photographic dye chemicals, in the paper industry as a catalyst, in the textile industry for coloring textile materials, and in medicine as an antioxidant. The hydroxyanthraquinone chromophore is the biologically active site in several antitumor anthracyclines. The stacking interaction between the chromophore of the drug and the base pair of DNA has been studied by means of several spectroscopic studies. Hydroxyanthraquinone glycosides are found in the leaves and fl ower of Cassia fi stula Linn [1]. It is also found in the leaves and bark of cassia podocarpa. Its commercialization is enhanced as a laxative due to its antimicrobial effect [2].The chemistry of anthraquinones [3] is based mainly on the concept of their exclusively 9,10-anthraquinoid structures. However, a growing amount of facts indicates a considerably greater role of tautomeric anthraquinones in chemical [4] and photochemical [5] processes. Since the majority of the applications of anthraquinones concern their color, spectrophotometry held a special position among the physicochemical methods used in their investigation. The information on absorption spectra [6] is very important for establishing the relation between the structure and properties. Titanium dioxide (TiO 2 ) is a material with applications in solar energy transfer and photocatalysis of poisonous compounds in the environment [7]. Further, the strong oxidizing power of the photogenerated holes, the chemical inertness, and the nontoxity of TiO 2 NPs has also made it a superior photocatalyst [8]. The use of TiO 2 NPs as a pigment in paints and the global oil crisis have inspired scientifi c and renewed interest in this material and the problem of using TiO 2 NPs for splitting of water, based on the principles of photoelectrochemistry [9]. This material is known to exist in several forms, among the most abundant being anatase, rutile, and brookite [10]. TiO 2 NPs are generally considered to be toxicologically inert, is manufactured in large quantities, and is extensively applied in consumer products such as s...