Shear and squeeze rheometry of suspensions of magnetic polymerized chains

We present the first experimental results on the magnetorheology of suspensions of non-Brownian magnetic ellipsoidal particles. These particles are made of spherical iron particles linked by polymers and are called polymerized chains. Steady shear, oscillatory shear, and oscillatory squeeze rheological tests have been performed. The rheological properties of the suspension of polymerized chains have been compared with those of the suspension of spherical iron particles. In shear flow, both suspensions develop nearly the same yield stress, while in squeeze flow, the yield stress is several times higher for the suspension of polymerized chains. We show that the squeezing force of a suspension of spherical particles is an increasing function of the magnetic field intensity at low magnetic fields but decreases dramatically at higher fields. Surprisingly, this phenomenon, attributed to cavitation or air entrainment, does not occur in the suspension of polymerized chains.     

Optical techniques for in situ dynamical investigation of plastic damage

We follow the damage process of high-density polyethylene during tensile tests. We simultaneously track changes in the density and average orientation of cavities using incoherent light transport. At the same time, we measure the true strain with a video-extensometer and the heat with an infrared imager. We see that the damage process has two major separate steps. First, a globally isotropic nucleation and growth of cavities occurs up to a deformation of about 1.1. Then, at higher deformations, cavities stop growing. Instead, they progressively orient and elongate along the tensile axis. The transition between these two damage processes seems to be related to strong physical and geometrical constraints, also probed through a typical thermal signature.     

An application of Curie’s principle to elastoplastic dynamics

This paper deals with the stability and the dynamics of a harmonically excited elastic–perfectly plastic unsymmetrical oscillator. Stability of the periodic orbits is analytically investigated with a perturbation approach. The occurrence of ratcheting effect is discussed for this system, and is related to the loss of symmetry of the periodic orbit in the phase space. Curie’s principle of symmetry is numerically verified for the symmetrical system with positive damping. Therefore, the observation of ratcheting phenomenon is necessarily associated to a breaking of symmetry in the constitutive behaviour, or in the forcing term. However, the generalized version of Curie’s principle has to be considered when a negative damping is introduced.     

Synthetic approaches to 4,8‐dimethyl‐5′‐(N‐pyridiniummethyl)‐ 4′,5′‐dihydropsoralens and 4,8‐dimethyl‐5′‐ (N‐aminomethyl)‐ 4′,5′‐dihydropsoralens

New synthetic approaches to 4,8‐dimethyl‐5′‐(N‐pyridiniummethyl)‐4′,5′‐dihydropsoralens and 4,8‐dimemyl‐5′‐(N‐aminomethyl)‐4′,5′‐dihydropsoralens are described. The 5′‐halomethyl‐4′,5′‐dihydro‐psoralen precursors are formed by electrophilic ring closures of 4,8‐dimethyl‐6‐allyl‐7‐hydroxycoumarin. The ring‐closure reactions may also be applied to the synthesis of 5′‐halomethyl‐4‐methyl‐4′,5′‐dihydroangelicins. The compounds are potential therapeutic agents for improved psoralen ultraviolet A radiation treatment.     

New Functional Polyolefins: Towards a Bridge Between Catalytic and RAFT Polymerizations?

Summary: Di‐polyethylenyl magnesium compounds, obtained by a transition metal catalyzed chain growth reaction on butyloctyl magnesium, are reacted with a range of disulfides of thiocarbonylated compounds (RC(S)SSC(S)R). Xanthate, dithiocarbamate, dithioester, and trithiocarbonate‐functionalized polyethylenes are thus obtained and characterized by ¹H NMR and IR spectroscopy, and MALDI TOF mass spectrometry. These macroRAFT agents may serve as building blocks for the synthesis of block copolymers based on polyolefins and polar segments.

Thio thiocarbonylate‐terminated polyethylene chains are easily prepared in high yield by a two step reaction and analyzed by MALDI‐TOF mass spectrometry.     

Preparation of Well‐Defined PVOH/C60 Nanohybrids by Cobalt‐Mediated Radical Polymerization of Vinyl Acetate

Summary: Poly(vinyl acetate) chains end‐capped by a Co(acac)₂ complex [PVAc‐Co(acac)₂] were prepared by bulk cobalt‐mediated radical polymerization (CMRP) of vinyl acetate and used for grafting fullerene (C60) with four PVAc arms at low temperature (30 °C). A photoactive water‐soluble poly(vinyl alcohol)/C60 nanohybrid was then prepared by hydrolysis of the PVAc arms of the nanohybrid. Because of photoactivity and very low cytotoxicity, this type of water‐soluble nanohybrid is very promising for the photodynamic cancer therapy.

Strategy for the preparation of PVAc/C60 nanohybrid and hydrolysis of PVAc/C60 nanohybrid into PVOH/C60 nanohybrid.     

Influence of Morphology on PTC in Conducting Polypropylene-Silver Composites

Blends of polypropylene with silver particles of controlled morphology are performed to elaborate polymer-metal conductive composites which can present a PTC effect to be used for a specific current limited function. The samples present quite low percolation threshold around 22% in volume of Ag and a resistivity at room temperature around 100 ohm.cm. Looking at the results of the analysis of the PTC effect, it can be observed that the electrical behaviour of the samples is depending of the crystalline morphology of the systems which is governed by the specific nucleation effect of the silver filler on the polypropylene matrix.     

Syntheses of 2,4‐diaryl‐2,3‐dihydro‐1,5‐benzothiazepines

The condensation of α,β‐unsaturated ketones with substituted o‐aminothiophenols, obtained by reductive cleavage of the corresponding disulfides in the presence of triphenylphosphine, is an effective method for the synthesis of 2,4‐diaryl‐2,3‐dihydro‐1,5‐benzothiazepines under neutral conditions.     

Poly(ethylene glycol) Surface Coated Magnetic Particles

Summary: A methacrylate‐functionalized poly(ethylene glycol) macromonomer was copolymerized at the surface of methacrylate‐derivatized maghemite nanoparticles. After silylation of the magnetic core with methacryloxypropyltrimethoxysilane, two grafting procedures based on either a direct copolymerization reaction in water or an inverse emulsion polymerization were compared. A direct copolymerization led to low polymer surface amounts, whereas an inverse emulsion process allowed nanocomposite particles containing up to 90 wt.‐% polymer to be obtained.

TEM picture of maghemite‐PEG hybrid particles.