No abstract

We show that noncovalently bound dye molecules can be used as labels in single-molecule fluorescence experiments for the determination of aggregate formation in standard surfactant systems. Aqueous solutions of sulfosuccinic acid bis(2-ethylhexyl) ester sodium salt, hexadecyltrimethylammonium chloride, and pentaethylene glycol monododecyl ether have been studied by fluorescence correlation spectroscopy using commercially available dyes. The translational diffusion coefficient and the critical micelle concentrations have been determined and compare well to values reported in the literature. The respective charges of the surfactant and of the dye molecule are crucial for the effectiveness of the presented method.

Calorimetric studies of the crystallization behavior of physically and chemically crosslinked semicrystalline polymer, polydimethylsiloxane (PDMS) are presented. Physical crosslinks are introduced either via entanglements in high-molecular-weight PDMS, or by anchoring chain ends to rigid polyethylene oxide (PEO) endblocks in a PEO-b-PDMS-b-PEO triblock copolymer. Chemical end-linking of di-vinyl PDMS chains results in the formation of a crosslinked network. Comparison of the thermograms obtained for each of these systems at constant cooling/heating rates with their noncrosslinked analogues indicates that, contrary to conventional wisdom, the different types of crosslinks result in an increased crystallization tendency. We suggest that this effect is a manifestation of the enhancement of local ordering together with reduced dynamics as compared to the non-crosslinked melt.