Coatings of polyethylene glycol for suppressing adhesion between solid microspheres and flat surfaces

This article describes the development and the examination of surface coatings that suppress the adhesion between glass surfaces and polymer microspheres. Superparamagnetic doping allowed for exerting magnetic forces on the microbeads. The carboxyl functionalization of the polymer provided the means for coating the beads with polyethylene glycol (PEG) with different molecular weight. Under gravitational force, the microbeads settled on glass surfaces with similar polymer coatings. We examined the efficacy of removing the beads from the glass surfaces by applying a pulling force of ~1.2 pN. The percent beads remaining on the surface after applying the pulling force for approximately 5 s served as an indication of the adhesion propensity. Coating of PEG with molecular weight ranging between 3 and 10 kDa was essential for suppressing the adhesion. For the particular substrates, surface chemistry and aqueous media we used, coatings of 5 kDa manifested optimal suppression of adhesion: that is, only 3% of the microbeads remained on the surface after applying the pulling magnetic force. When either the glass or the beads were not PEGylated, the adhesion between them was substantial. Addition of a noncharged surfactant, TWEEN, above its critical micelle concentrations (CMCs) suppressed the adhesion between noncoated substrates. The extent of this surfactant-induced improvement of the adhesion suppression, however, did not exceed the quality of preventing the adhesion that we attained by PEGylating both substrates. In addition, the use of surfactants did not significantly improve the suppression of bead-surface adhesion when both substrates were PEGylated. These findings suggest that such surfactant additives tend to be redundant and that covalently grafted coatings of PEGs with selected chain lengths provide sufficient suppression of nonspecific interfacial interactions.     

Simulating the vapour–liquid equilibria of large cyclic alkanes

Self-adapting fixed endpoint configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out to determine the vapour–liquid coexistence curves of cyclic alkanes from c-pentane to c-octadecane. In general, the critical temperatures and densities of the cyclic alkanes are substantially higher than those of their linear counterparts. Furthermore, the simulation data point to a maximum in the critical density for cyclic alkanes with about eight carbon atoms as also observed for the linear alkanes.     

Further studies on the utility of sodium hypochlorite in organic synthesis. Selective oxidation of diols and direct conversion of aldehydes to esters

Sodium hypochlorite in acetic acid solution selectively oxidizes secondary alcohols to ketones in the presence of primary alcohols and converts aldehydes to methyl esters in the added presence of methanol.     

Generating Convex Polynomial Inequalities for Mixed 0–1 Programs

We develop a method for generating valid convex quadratic inequalities for mixed0–1 convex programs. We also show how these inequalities can be generated in the linear case by defining cut generation problems using a projection cone. The basic results for quadratic inequalities are extended to generate convex polynomial inequalities.     

One-step multifunctionalization of random copolymers via self-assembly

A novel methodology for random copolymer functionalization based on a noncovalent, one-step, multifunctionalization strategy has been developed. Random copolymers possessing both palladated-pincer complexes and diaminopyridine moieties (hydrogen-bonding entities) have been synthesized using ring-opening metathesis polymerization. Noncovalent functionalization of the resultant copolymers is accomplished via (1) directed self-assembly, (2) multistep self-assembly, and (3) one-step orthogonal self-assembly. This system shows complete specificity of each recognition motif for its complementary unit, with no observable changes in the association constants regardless of the degree of functionalization.     

Microencapsulation of oil with poly(styrene-N,N-dimethylaminoethyl methacrylate) by SPG emulsification technique: effects of conversion and composition of oil phase

Microcapsules with narrow size distribution, in which hexadecane (HD) was used as a oily core and poly(styrene-co-N,N-dimethylaminoethyl methacrylate) [P(St-DMAEMA)] as a wall, were prepared by a Shirasu porous glass (SPG) emulsification technique and a subsequent suspension polymerization process. That is, a mixture of St monomer, DMAEMA monomer, HD, and N,N'-azobis(2,4-dimethylvaleronitrile) initiator was permeated through the uniform pores of an SPG membrane into a continuous phase containing a poly(vinylpyrrolidone), sodium lauryl sulfate, and sodium nitrite water-soluble inhibitor by applying a pressure, to form uniform droplets. Then, the droplets were polymerized at 70 degrees C. It was found that HD was encapsulated completely only when conversion was quite high, irrespective of whether a DMAEMA hydrophilic monomer was incorporated into the polymer. As the amount of HD increased, HD was more easily encapsulated by the polymer. In order to clarify the reason for such unique behavior, a simulation was carried out, taking the St monomer partition in the HD phase and PSt wall phase into the consideration. It was found that the main reason HD could not be encapsulated completely by PSt when conversion was lower was that the interfacial tension of the HD phase with water and the PSt phase with water got closer. As a result, both HD and PSt can come in contact with the water phase.