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Coad B.R.,University of South Australia | Bilgic T.,Institute des Materiaux | Klok H.-A.,Institute des Materiaux
Langmuir | Year: 2014

A new method for generating a surface density gradient of polymer chains is presented. A substrate-independent polymer deposition technique was used to coat materials with a chemical gradient based on plasma copolymerization of 1,7-octadiene and allylamine. This provided a uniform chemical gradient to which initiators for atom transfer radical polymerization (ATRP) were immobilized. After surface-initiated atom transfer radical polymerization (SI-ATRP), poly(2-hydroxyethyl methacrylate) (PHEMA) chains were grafted from the surface and the measured thickness profiles provided direct evidence for how surface crowding provides an entropic driving force resulting in chain extension away from the surface. Film thicknesses were found to increase with the position along the gradient surface, reflecting the gradual transition from collapsed to more extended surface-tethered polymer chains as the grafting density increased. The method described is novel in that the approach provides covalent linkages from the polymer coating to the substrate and is not limited to a particular surface chemistry of the starting material. © 2014 American Chemical Society.

Deng C.,Soochow University of China | Wu J.,Soochow University of China | Cheng R.,Soochow University of China | Meng F.,Soochow University of China | And 3 more authors.
Progress in Polymer Science | Year: 2014

Polypeptides derived from naturally occurring α-amino acids have emerged as a unique and versatile family of bio-inspired biomaterials that can be tailor-made for varying biomedical applications such as controlled drug release, gene delivery, tissue engineering and regenerative medicine. In contrast to traditional biodegradable polymers such as aliphatic polyesters and polycarbonates, polypeptides are inherently functional, allow precise control over polarity and charges, show excellent stability against hydrolysis, and are prone to rapid biodegradation in vivo by specific enzymes. Ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) is the most straightforward and practical approach for large-scale production of high molecular weight polypeptides. In the past decade, a remarkable progress has been made in controlled NCA polymerization, which offers an unprecedented access to precision polypeptide and hybrid materials by combining with living radical polymerization, click chemistry, and/or post-polymerization modification. Notably, several micellar anti-cancer drugs based on poly(ethylene glycol)-polypeptides have been already advanced to the clinical evaluation. In this review paper, we give an overview on de novo design, controlled synthesis and emerging biomedical applications of functional polypeptide and hybrid materials. © 2013 Elsevier Ltd. All rights reserved.

Maziz A.,Institute des Materiaux | Plesse C.,Institute des Materiaux | Soyer C.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Chevrot C.,Institute des Materiaux | And 3 more authors.
Advanced Functional Materials | Year: 2014

This paper reports results on ionic EAP micromuscles converting electrical into micromechanical response in open-air. Translation of small ion motion into large deformation in bending microactuator and its amplification by fundamental resonant frequency are used as tools to demonstrate that small ion vibrations can still occur at frequency as high as 1000 Hz in electrochemical devices. These results are achieved through the microfabrication of ultrathin conducting polymer microactuators. First, the synthesis of robust interpenetrating polymer networks (IPNs) is combined with a spincoating technique in order to tune and drastically reduce the thickness of conducting IPN microactuators using a so-called "trilayer" configuration. Patterning of electroactive materials as thin as 6 μm is demonstrated with existing technologies, such as standard photolithography and dry etching. Electrochemomechanical characterizations of the micrometer sized beams are presented and compared to existing model. Moreover, thanks to downscaling, large displacements under low voltage stimulation (±4 V) are reported at a frequency as high as 930 Hz corresponding to the fundamental eigenfrequency of the microbeam. Finally, conducting IPN microactuators are then presenting unprecedented combination of softness, low driving voltage, large displacement, and fast response speed, which are the keys for further development to develop new MEMS. Ultrathin conducting polymer microactuators are designed and operated in open-air in the kHz frequency range. These materials are fabricated through processes compatibles with standard microsystems techniques leading to the thinnest air-operating conducting polymer microactuators ever described. These electroactive materials combine softness, low driving voltage, downscaling ability, large displacement and speed, opening new perspectives for next generation MEMS. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Maziz A.,Institute des Materiaux | Plesse C.,Institute des Materiaux | Soyer C.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Cattan E.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Vidal F.,Institute des Materiaux
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

This paper presents the synthesis and characterization of thin and ultra-fast conducting polymer microactuators which can operate in the open air. Compared to all previous existing electronic conducting polymer based microactuators, this approach deals with the synthesis of robust interpenetrating polymer networks (IPNs) combined with a spincoating technique in order to tune and drastically reduce the thickness of conducting IPN microactuators using a so-called "trilayer" configuration. Patterning of electroactive materials has been performed with existing technologies, such as standard photolithography and dry etching. The smallest air-operating microbeam actuator based on conducting polymer is then described with dimensions as low as 160x30x6 μm3. Under electrical stimulation the translations of small ion motion into bending deformations are used as tools to demonstrate that small ion vibrations can still occur at frequency as several hundreds of Hz. Conducting IPN microactuators are then promising candidates to develop new MEMS combining downscaling, softness, low driving voltage, and fast response speed. © 2015 SPIE.

Friedli J.,Institute des Materiaux | Fife J.L.,Institute des Materiaux | Fife J.L.,Paul Scherrer Institute | Di Napoli P.,Institute des Materiaux | Rappaz M.,Institute des Materiaux
IOP Conference Series: Materials Science and Engineering | Year: 2012

Recently, Gonzales and Rappaz [Met. Mat. Trans. A37:2797, 2006] showed the influence of an increasing zinc content on the growth directions of aluminum dendrites. 100 and 110 dendrites were observed below 25wt.% and above 55wt.% zinc, respectively, whereas textured seaweeds and 320 dendrites were observed at intermediate compositions. Considering the complexity of these structures, it is necessary to first characterize them in further details and second, to model them using the phase field method. The so-called Dendrite Orientation Transition (DOT) was thus reinvestigated in quenched Bridgman solidification samples. The combination of X-ray tomographic microscopy and electron backscattered diffraction (EBSD) analysis on a whole range of compositions, from 5 to 90wt.% Zn, allowed insights with unprecedented details about texture, growth directions and mechanisms of the aforementioned structures. We show that seaweeds rather than dendrites are found at all intermediate compositions. Their growth was confirmed to be constrained within a (100) symmetry plane. However, new findings indicate that the observed macroscopic texture does not necessarily correspond to the actual growth directions of the microstructure. Further, it seems to operate by an alternating growth direction mechanism and could be linked to the competition between the 100 and 110 characters of regular dendrites observed at the limits of the DOT. These characters, as well as 3D seaweeds, are observed in phase-field simulations of equiaxed growth and directional solidification, respectively. This study emphasizes the importance of accurate experimental data to validate numerical models and details the progress that such combinations provide for the understanding of growth mechanisms. © Published under licence by IOP Publishing Ltd.

Paripovic D.,Institute des Materiaux | Klok H.-A.,Institute des Materiaux
Macromolecular Chemistry and Physics | Year: 2011

Hydrophilic polymer brushes grown via surface-initiated ATRP from silicon oxide surfaces are susceptible to detachment via hydrolytic cleavage of the anchoring siloxane bond. This paper investigates the influence of the structure of the ATRP initiator on the stability of these brushes and seeks for strategies to further enhance their stability. It is found that increasing the hydrophobicity of the organosilane modified ATRP initiator reduces the susceptibility of the brushes toward cleavage. Robust, hydrophilic polymer brushes are prepared, which are obtained by introducing a short, hydrophobic PMMA or PEHMA block between the silicon oxide substrate and the hydrophilic polymer brush. Hydrolytic cleavage of the anchoring siloxane bond limits the stability and durability of hydrophilic polymer brushes grown from silicon oxide surfaces functionalized with dimethylchlorosilane modified ATRP initiators. The stability of the brushes can be enhanced by increasing the hydrophobicity of the surface-tethered ATRP initiator, or, more effectively, by introducing a short hydrophobic block between the silicon oxide substrate and the polymer brush. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Friedli J.,Institute des Materiaux | Di Napoli P.,Institute des Materiaux | Rappaz M.,Institute des Materiaux | Dantzig J.A.,Institute des Materiaux
IOP Conference Series: Materials Science and Engineering | Year: 2012

With a few exceptions, phase-field simulations of dendritic growth in cubic materials have been modeled using simple expressions for the interfacial energy anisotropy and with strong anisotropy. However, recent experimental results show that the Dendrite Orientation Transition (DOT) observed in Al-Zn alloys by Gonzales and Rappaz [Met. Mat. Trans. A37 (2006) 2797] occurs at weak anisotropy, and modeling these results requires at least two anisotropy parameters. In the present work, we solve the corresponding phase-field model on an adaptive grid, after measuring and compensating for the grid anisotropy. A systematic scan of equiaxed growth simulations was performed in the range of the anisotropy parameter space where the transition is expected. We find separate domains of existence of 100 and 110 dendrites, similar to those previously reported by Haxhimali et al. [Nat. Mat. 5 (2006) 660] for pure materials. In the so-called hyperbranched regime, lying between the 100 and 110 regions, we observe a competition between 100 and 110 growth directions, but no seaweed structures. Directional solidification simulations showed the stabilizing effect of the thermal gradient on the twofold splitting of 110 dendrites, and the importance of the choice of anisotropy parameters. We also found a strong dependence between the orientation of the crystal axes with respect to the thermal gradient and the actual growth direction. Finally, 3-dimensional seaweed microstructures were modeled for the first time, demonstrating that this pattern is a result of not only the values of anisotropy parameters, but also a consequence of directional solidification. © Published under licence by IOP Publishing Ltd.

Sugnaux C.,Institute des Materiaux | Lavanant L.,Institute des Materiaux | Klok H.-A.,Institute des Materiaux
Langmuir | Year: 2013

In this Article, we studied the surface immobilization of five organic-acid-modified atom-transfer radical polymerization (ATRP) initiators based on salicylic acid, catechol, phthalic acid, and m- and p-benzoic acid on alumina, and we also investigated the growth of hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(poly(ethylene glycol)methycrylate) (PPEGMA 6) brushes from the resulting initiator-modified substrates. Whereas the surface immobilization of phthalic acid- and benzoic acid-based initiators results in only very thin brushes or no brush growth at all, SI-ATRP of HEMA and PEGMA6 from alumina surfaces modified with salicylate or catechol generates brushes with thicknesses comparable to those obtained using organosilane-based initiators. Most interestingly, the surface immobilization of the catechol- and salicylate based-initiators was found to be pH-dependent, which allowed facile variation of the ATRP initiator surface concentration and, concomitantly, the polymer brush grafting density by adjusting the pH of the aqueous solution that was used to immobilize the initiator. This is in contrast to organosilane-based initiators, where the variation of the grafting density is usually accomplished using mixtures of the ATRP initiator and an ATRP inactive "dummy". Another difference between the organosilane-based initiators and the organic acid analogues is the stability of hydrophilic brushes grown from alumina. After a certain threshold thickness was exceeded, organosilane-tethered PPEGMA6 brushes were observed to detach from the substrate, in contrast to brushes grown from catechol or salicylate initiators, which did not show signs of degradation. Finally, as a first proof-of-concept, the salicylate-based initiator was used to develop an all-aqueous protocol for the modification of alumina membranes with hydrophilic PHEMA and succinic anhydride post-modified polymer brushes. The water permeation properties of these hybrid membranes can be controlled by adjusting the brush thickness in the case of the neutral PHEMA brush coating or can be pH-gated after post-polymerization modification to introduce carboxylic acid groups. © 2013 American Chemical Society.

Kerr-Phillips T.E.,University of Auckland | Woehling V.,Institute des Materiaux | Agniel R.,Institute des Materiaux | Nguyen G.T.M.,Institute des Materiaux | And 4 more authors.
Journal of Materials Chemistry B | Year: 2015

Electroactive, elastomeric, microfiber mats that show controllable pore size variation upon electrochemical stimulation are produced from semi-interpenetrating polymer networks (s-IPNs). This type of porous, elastomeric scaffolds that are mechanically dynamic under electrochemical stimuli could find new applications in stretchable electronics, (bio)filtration, soft robotics and stimulation of biological cells. These microfiber mats are prepared in two simple steps. Firstly, a mixture of high molecular weight nitrile butadiene rubber (NBR) and cross-linking agent, poly(ethylene glycol)dimethylacrylate are electrospun with in situ cross-linking. Secondly, a conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is embedded into the electrospun fibres by oxidative chemical polymerization of EDOT-swollen microfiber mats. This two-step process affords robust, highly flexible and conductive s-IPN microfiber mats. The microfiber mat undergoes a controllable pore size variation upon applying an electrochemical stimulus in the form of a reduction-oxidation cycle to the mats in an electrolyte. The maximum average pore size variation, measured in situ using confocal microscopy, is 25%, achieved in 1 M lithium bis-trifluoromethanesulfonimide (LiTFSI) in propylene carbonate (PC) for a potential step between +0.6 V and -0.5 V (vs. Ag wire). These mats also show pore size variation in a biologically compatible solution, phosphate buffered saline. © The Royal Society of Chemistry 2015.

Drezet J.-M.,Institute des Materiaux | Sistaninia M.,Institute des Materiaux | Rappaz M.,Institute des Materiaux
Materiaux et Techniques | Year: 2010

Hot tearing or solidification cracking is a flaw that appears during casting and welding of metals and alloys. Hot tearing initiates during solidification i.e. when the liquid phase is still present and under tensile deformations acting upon the remaining liquid films. The cracks are always intergranular except in single crystals, and its fracture surfaces appear as dendritic. The present paper aims at giving a state of the art in the understanding and modelling of hot tearing. The key challenge lies in coupling microscopic phenomena such as grain coalescence, solid phase percolation and strain localisation with macroscopic phenomena such as heat transfer and strain build up at the scale of the work piece. Mesoscopic granular models appear to be suitable to capture such coupling. © EDP Sciences, 2010.

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