Competitive Adsorption between a Polymer and Solvents onto Silica.

In polymer nanocomposites, particle-polymer interactions play a key role both in the processing and in the final properties of the obtained materials. Specifically, for silica, because of the surface polarity, surface modification is commonly used to improve the compatibility with apolar polymer matrices in order to prevent agglomeration. In this work, a new way to investigate the polymer-silica affinity and determine dispersibility parameters (HDP) of silica particles in the 3D Hansen space using a solvent approach is proposed. These parameters are estimated from the assessment of the stability of suspensions in a set of organic solvents. Based on the respective locations of the solvent, polymer, and silica representative points in the 3D Hansen space, the adsorption of a given polymer in solution in a given solvent can be predicted. This is shown with the industrial precipitated silica Zeosil 1165MP in combination with polystyrene and polybutadiene. It is shown that silanization of the silica particles decreases the adsorption of polystyrene, even though because of this surface treatment, silica comes closer to polystyrene in the Hansen space. This counter-intuitive effect is rationalized based on the consideration of an adsorption parameter χS computed from the relative locations of the solvent, polymer, and particles in the 3D Hansen space. Basically, this parameter is related to the respective distances of the solvent and polymer representative points to that of the particle in the Hansen space.

Aortic atherosclerosis is a key modulator of the prognostic value of postural blood pressure changes.

BACKGROUND AND AIMS: Orthostatic blood pressure decrease or increase has been related to cardiovascular events in hypertensive patients. Large blood pressure changes after orthostatic stress are associated with autonomic and neurohormonal abnormalities; aortic atherosclerosis (ATS) may also play a role. METHODS: We investigated the interaction of ATS on the prognostic value of postural blood pressure changes. In a cohort of 958 hypertensive patients with an aortography (mean ± standard deviation age 44 ± 11 years, 61% men, mean blood pressure 182/110 mmHg), blood pressure was measured after 10 min of rest in the supine position. Systolic blood pressure (SBP) was also measured in standing position, 1 min after the supine position. Blood pressure changes were calculated as supine SBP minus standing SBP and analyzed as absolute or arithmetic means. ATS was assessed using an aortography score. RESULTS: After 15 years of follow-up, 280 all-cause and 167 cardiovascular deaths occurred. In a multivariable Cox regression analysis adjusted for major cardiovascular risk factors and stratified according to ATS status, SBP changes were statistically associated with all-cause and cardiovascular mortality only in the presence of ATS: tertile 3 versus 1, 2.99 (1.37-6.49) and 4.08 (1.55-10.72) respectively, tertile 3 versus 2, 2.89 (1.29-6.46) and 4.82 (1.79-12.98), respectively (p for interaction: 0.003 for all-cause and 0.003 for cardiovascular mortality) for absolute changes. The hazard associated with the magnitude of SBP changes was more important than that associated with its direction. CONCLUSIONS: The prognostic significance of postural SBP changes is markedly influenced by ATS in hypertensive patients.

Polymorphism of natural fatty acid liquid crystalline phases.

We study the phase behavior in water of a mixture of natural long chain fatty acids (FAM) in association with ethylenediamine (EDA) and report a rich polymorphism depending on the composition. At a fixed EDA/FAM molar ratio, we observe upon dilution a succession of organized phases going from a lamellar phase to a hexagonal phase and, finally, to cylindrical micelles. The phase structure is established using polarizing microscopy, SAXS, and SANS. Interestingly, in the lamellar phase domain, we observe the presence of defects upon dilution, which SAXS shows to correspond to intrabilayer correlations. NMR and FF-TEM techniques suggest that these defects are related to an increase in the spontaneous curvature of the molecule monolayers in the lamellae. ATR-FTIR spectroscopy was also used to investigate the degree of ionization within these assemblies. The successive morphological transitions are discussed with regards to possible molecular mechanisms, in which the interaction between the acid surfactant and the amine counterion plays the leading role.