Reversible strain alignment and reshuffling of nanoplatelet stacks confined in a lamellar block copolymer matrix

We designed a nanocomposite consisting of CdSe nanoplatelets dispersed in the form of short stacks in the polybutadiene domains of a polystyrene-polybutadiene-polystyrene (SBS) thermoplastic elastomer matrix. Under strain, the material displays reversible, macroscopic anisotropic properties, e.g. the fluorescence signal. We present here a structural study of the composite under stretching, by in situ high-resolution X-ray scattering using synchrotron radiation. Modelling the scattering signal allows us to monitor the evolution of both the matrix and the platelets under strain. In particular, we show that the strain "reshuffles" the platelet stacks, which tilt their long axis from parallel to the plane of the microstructure lamellae at rest to perpendicular to this plane at high strain, at the same time breaking into smaller pieces, more easily accommodated in the soft butadiene domains. This reshuffling is fully reversed after strain relaxation. Moreover, it can be prevented by adding free oleic acid, which reinforces the interactions between the platelets in the stacks.

Hypertension: What are the self-care and health-care-seeking behaviours in women over time?

The aim of this study was to estimate the prevalence and incidence of hypertension in women, and describe their self-care and health-seeking behaviours. This research was conducted as part of the Australian Longitudinal Study on Women's Health, a study comprising a nationally representative sample of Australian women in three age groups. The focus of this research is 14 099 women born in 1946-1951, who have been surveyed six times (1996-2010). Student t-tests were used to compare women who did or did not have hypertension by their health-care utilization. Longitudinal analyses were conducted using a Poisson generalized estimating equation model. The incidence of hypertension among this cohort during 1996 to 2010 ranged from 400 to 597 participants per survey, resulting in an increase in prevalence of hypertension from 20.9% in 1996 to 41.3% in 2010. For all survey periods, women with hypertension had a significantly higher average number of visits to doctors and allied health practitioners compared with women without hypertension (P<0.005). The use of complementary medicine (practitioners and self-prescribed treatments) by women with hypertension was significantly lower compared to women without hypertension (P<0.005). Over time, conventional health-care utilization was higher for women with hypertension compared with women without hypertension (adjusted RR=1.18; 95% CI: 1.14, 1.22; P<0.0001). Our findings show that women with hypertension are using a range of conventional and complementary and alternative medicine: with hypertensive women using more conventional medicine and less complementary and alternative medicine than non-hypertensive women. As such, health-care providers should communicate with their patients regarding their use of complementary and alternative medicine in their efforts to provide safe, effective and coordinate care.

Light-induced Soret effect and adsorption of nanocrystals in organic solvents

A light-induced Soret effect accompanied by photoinduced adsorption of pigment nanoparticles is described in organic solvents. We report an unexpected inversion of the nanoparticle flux which is directed along the temperarture gradient at short exposures to the light and switches against the gradient at longer exposures. This change of flux direction is due to light-induced adsorption of the nanocrystals onto the substrates of the cell.

Stable Freestanding Thin Films of Copolymer Melts Far from the Glass Transition

Thin polymer films have attracted attention because of both their broad range of applications and of the fundamental questions they raise regarding the dynamic response of confined polymers. These films are unstable if the temperature is above their glass transition temperature T_g. Here, we describe freestanding thin films of centimetric dimensions made of a comb copolymer melt far from its glass transition that are stable for more than a day. These long lifetimes allowed us to characterize the drainage dynamics and the thickness profile of the films. Stratified regions appear as the film drains. We have evidence that the stability, thinning dynamics, and thickness profile of the films result from structural forces in the melt. Understanding the key mechanisms behind our observations may lead to new developments in polymeric thin films, foams, and emulsions without the use of stabilizing agents.

Strain-controlled fluorescence polarization in a CdSe nanoplatelet–block copolymer composite

Composite materials obtained by doping a SBS thermoplastic elastomer matrix with CdSe nanoplatelets show reversible platelets alignment upon stretching.

Effect of interfaces on the melting of PEO confined in triblock PS-b-PEO-b-PS copolymers

Block copolymers form nanostructures that have interesting physical properties because they combine, for a single compound, the complementary features brought by each block. However, in order to fully exploit these properties, the physical state of each kind of domain must be precisely controlled. In this work, triblock PS-b-PEO-b-PS copolymers consisting of a central poly(ethylene oxide) (PEO) block covalently bonded to polystyrene (PS) blocks were synthesized by Atom Transfer Radical Polymerization. Their morphology was investigated by X-ray scattering and TEM experiments whereas their thermodynamic behavior was characterized by DSC. A strong decrease of both the melting temperature and the degree of crystallinity of PEO, due to its confinement between the PS domains, was observed and analyzed with a modified Gibbs-Thomson equation, following the approaches used for fluids confined in porous media. The existence of an amorphous bound layer, a few nanometers thick, at the PEO/PS interface, that does not undergo any phase transition in the temperature range investigated, accounts for both the melting temperature depression and the decrease of crystallinity upon confinement. This interfacial layer may significantly affect the mechanical and transport properties of these block copolymers that find applications as solid polymer electrolytes in batteries for example. Moreover, the value obtained for the solid PEO/liquid PEO surface tension is lower than those previously published but is thermodynamically consistent with the surface tensions of polymers at the solid/vapor and liquid/vapor interfaces.