Self-diffusion, calorimetry and rheology measurements have been performed on a monodisperse associative polymer (C12E0200C12). The self-association of this polymer was found to show the same general features as non-ionic C, E, surfactants. A strongly endothermic self-association starts at 0.014 wt.%, but is a somewhat less cooperative process than micellization of surfactants, probably due to the steric constraints of the polymer backbone. Our measurements are consistent with a model in which the primary aggregates, formed at low associative polymer contents, assemble into clusters as the polymer content increases. Subsequent cluster growth gives rise to an increasing distribution of the size of the diffusing species.Surfactants were found to be solubilized primarily in the hydrophobic domains consisting of associated polymer end-groups, thereby enhancing the strength of the polymer association. These domains are easily saturated with surfactants, and by a concentration of 2 mmol kg-', sodium dodecyl sulfate (SDS) starts to associate with the ethylene oxide (EO) repeat units of the polymer backbone, in a similar way to unmodified poly(ethy1ene oxide). Since polymers of this chain length will, when saturated with SDS, on average accommodate only one SDS aggregate, it is feasible that both end-groups of a given Cl , E02, , C, , are then associated with the same SDS aggregate. As a consequence, the probability that the end-groups will act as bridges between the aggregates will then be low.

A diversity of pharmacological effects on the cardiovascular system have been reported for Camellia sinensis: antioxidative, antiproliferative and anti-angiogenic activity, and nitric oxide synthase activation. The purpose of this study was to investigate if the connection between tea and angiotensin-converting enzyme (ACE) and nitric oxide (NO) might be an explanation of the pharmacological effects of tea on the cardiovascular system. Cultured endothelial cells from human umbilical veins (HUVEC) were incubated with extracts of Japanese Sencha (green tea), Indian Assam Broken Orange Pekoe (black tea) and Rooibos tea, respectively. The main flavanols and purine alkaloids in green and black tea were examined for their effects on ACE and NO. After incubation with green tea, black tea and Rooibos tea for 10 min, a significant and dose-dependent inhibition of ACE activity in HUVEC was seen with the green tea and the black tea. No significant effect on ACE was seen with the Rooibos tea. After 10-min incubation with (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechingallate and (-)-epigallocatechingallate, a dose-dependent inhibition of ACE activity in HUVEC was seen for all four tea catechins. After 24-h incubation, a significantly increased dose-dependent effect on NO production in HUVEC was seen for the green tea, the black tea and the Rooibos tea. After 24-h incubation with (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechingallate and (-)-epigallocatechingallate, a dose-dependent increased NO production in HUVEC was seen. In conclusion, tea extracts from C. sinensis may have the potential to prevent and protect against cardiovascular disease.

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The effects of adhesion, contact area, and pressure on the lubricating properties of self-assembled monolayers on steel have been investigated with friction force microscopy. The adsorbed molecules were fatty acids with varying degrees of unsaturation (0-2 double bonds; stearic, oleic, and linoleic acid) and a rosin acid (dehydroabietic acid), adsorbed from n-hexadecane solution. The friction of these loose-packed monolayers was studied in dry N2 gas and in ethanol. Low adhesion (in ethanol) resulted in a linear increase in friction force at low loads, that is, F = muL, whereas higher adhesion (in N2 gas) gave an apparent area-dependence at low loads of the form F = S(c)A, where S(c) is the critical shear stress. A recent model for the contact mechanics of a compliant elastic film confined between stiffer substrates was applied to the data obtained in dry N2. Using this approach, we obtained interfacial energies of the compliant monolayers in good agreement with van der Waals-Lifshitz theory. With a low monolayer elastic modulus of E'(1)=0.2 GPa, we obtained a slightly higher value of Sc for stearic acid than that established for more close-packed stearic acid monolayers. An increase of mu and S(c) was found with increasing degree of unsaturation of the fatty acid.