In recent years, single-beam optical traps have been used to manipulate individual colloids and biological objects such as cells. We have implemented a rapidly scanning laser optical trap with rates as high as 1200 Hz where a single laser beam is used to trap multiple colloids simultaneously. The optics are optimized to achieve a small laser focus size and a large scanning pattern in the sample. This approach provides great pattern flexibility and, because of the use of piezoelectrics, small particles (1 μm in diameter) in low-viscosity solvents, such as water, can be readily manipulated.

Vapor-liquid equilibrium data were obtained for dendritic polymer solutions using a classic isothermal gravimetric-sorption method; the amount of solvent absorbed by the dendrimer was measured at increasing solvent activity. The polymers were polyamidoamine (P AMAM) dendrimers of generations 1, 2, and 4 and benzyl-ether dendrimers with different end groups (aromatic rings, dodecyl chains, methyl ester groups, perfluoroalkyl chains) of generations 2 to 6, and two series of benzyl-ether linear polymers that are analogs of the dendrimers. Solvents were acetone, acetonitrile, chloroform, cyclohexane, methanol, n-pentane, npropylamine, tetrahydrofuran and toluene. The temperature range was 35 to 89 °C. The amount of solvent absorbed by the dendrimers depends, sometimes strongly, on the kind of dendrimer end groups. The relation between solvent absorption and dendrimer generation number, or molecular weight, depends on the solvent-dendrimer system and on temperature.

Optical trapping techniques have been used extensively to manipulate biological objects and micrometer-sized colloids in a wide variety of investigations. We have used an extension of this technique, scanning laser optical trapping, to simultaneously trap multiple colloids in a designed pattern and have locked-in this artificially created structure through photopolymerization of the monomer-containing solvent. This technique can be used as a means of constructing templates for lithography or as a starting point for creation of larger three-dimensional colloidal structures.

Infinite-dilution activity coefficients are measured for several polar and nonpolar solvents in hyperbranched polymers using inverse gas chromatography in the temperature range 40-160 °C. Two kinds of polymers are studied: comb polymers and dendritic polymers. The combs are poly(styrene-co-maleic anhydride) with alkyl side chains of different lengths (C12, C22). The solvents are: acetone, toluene, tetrahydrofuran (THF), and chloroform. Solvent solubility in the combs depends on the ratio between the polar backbone and the nonpolar side chain of the polymer. The dendrimers are amine-terminated poly(propylenimine) of generation 2 to 5. The solvents are: methanol, ethanol, ethyl acetate, toluene, and THF. Solvent activity coefficients change with respect to the dendrimer generation number, reaching a minimum at generation 4. Because the dendrimers are basic, the solvent quality is higher for slightly acidic solvents, such as methanol and ethanol. Flory's interaction parameters are calculated for the solvent/dendrimer systems.

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