Velocity distributions in a gas-gun microparticle accelerator.

Here, we build and characterize a single-stage gas-gun microparticle accelerator, where a pressurized gas expands and launches particles on a target. The microparticles in the range of 60-250 µm are accelerated by the expansion of pressurized nitrogen. By using a high-speed camera, we study how the velocity distribution of accelerated particles is modified by particle size, pressure in the gas reservoir, valve's opening time, and diaphragm's thickness and composition. We employ this microparticle accelerator to study the impact of glass particles with diameters of (69 ± 6) µm accelerated at moderate velocities ∼ (10-25) m/s, using films of poly-dimethylsiloxane as targets.

Tunable temperature responsive liquid chromatography through thiolactone-based immobilization of poly(N-isopropylacrylamide).

A straightforward and efficient functionalization of aminopropylsilica with polymeric structures is described for the development of temperature responsive stationary phases applicable in purely aqueous liquid chromatography. The immobilization of the thermoresponsive polymers involves a thiolactone-based ring opening using the primary amines in aminopropylsilica, with a simultaneous one-pot, thiol-ene functionalization with an acrylate of choice. This mild, straightforward and modular grafting process results in high polymer coupling yields. By variation of the acrylate for the thiol-ene reaction, different stationary phases can be readily obtained. Two stationary phases as a result of the modular modification of aminopropylsilica were evaluated with test mixtures of hydrophobic analytes and a mixture of di- and tripeptides. Analyses using the 5µm material packed in 10cm×4.6mm columns revealed high hydrophobic retention, which proved adaptable as a function of the temperature in aqueous mobile phases. High versus low retention were obtained at temperatures above and below the lower critical solution temperature of the polymer, respectively. Moreover, the columns depict potential for diastereoisomeric peptide separation. Finally, the lower retention, observed when using PEGylated silica, illustrates the potential of the approach for modular stationary phase tuning.

Structure of micelles formed by highly asymmetric polystyrene-b-polydimethylsiloxane and polystyrene-b-poly[5-(N,N-diethylamino)isoprene] diblock copolymers.

The internal structure of polystyrene(PS)-shell micelles having core-forming blocks consisting of polydimethylsiloxane (PDMS) or poly[5-(N,N-diethylamino)isoprene] (PAI) was determined in detail by accessing the multilevel structural organization using static and dynamic light scattering and small-angle X-ray scattering techniques. Well-defined PS-b-PDMS and PS-b-PAI diblock copolymers with molar masses in the range of 12.0k-18.2k g/mol were dispersed in cyclohexane, dimethylacetamide, or dimethylformamide. Colloidal nanoparticles exhibiting either swollen core with a large surface area per corona chain that enables the PS chains to assume a random coil conformation with gaussian statistics, or compact core and slightly stretched PS chains in the corona were obtained. Therefore, the results of this study provide an interesting alternative allowing for precise control of the core and corona properties of PS-b-PDMS and PS-b-PAI micelles in selective solvents. Admittedly, such differences in terms of micellar properties can dictate the potential of block copolymer micelles for generating thin films from preformed nano-objects, as well as the capability to function as nanoreactors in organic medium.