Thermal-controlled frictional behaviour of nanopatterned surfaces

International audienceFriction is an important limitation of energy efficiency performances of MEMS/NEMS. However, frictional behaviourcan be accurately controlled in real-time by using thermally sensitive periodic patterned self-assembled monolayers ofn-octadecyltrichlorosilane (OTS) grafted on MEMS surfaces. Patterns have been created by micro-contact printing (μCP)using a polydimethylsiloxane (PDMS) stamp displaying a trapezoidal profile. Thus, pattern periodicity can becontinuously changed – from discontinuous to continuous – by applying a controlled normal load on the soft PDMSstamp. A multiscale tribological study has been carried out on these nano-patterns by using successively: (i) an AFMNanobruker and (ii) a multi-asperity nanotribometer CSM Instruments (NTR). As a result, Lateral Force Microscopy(LFM) extracts the individual frictional behaviour of each pattern’s component whereas NTR provides the emergingfrictional behaviour induced by the patterning according to temperature. Hence, whereas the microscale frictionalbehaviour can be accurately controlled by the pattern’s periodicity, the macroscopic one can be accurately controlled ina range of 0.12 to 0.04 by varying the contact temperature. This thermal-induced tribological behaviour is mainly due toa reversible order-disorder change within the patterned monolayers. In addition, the periodic nano-patterns stronglyincrease the lifespan of surfaces by limiting the stress level within the sub-surface

Thermal-controlled frictional behaviour of nanopatterned self-assembled monolayers as triboactive surfaces

International audienceFriction is an important limitation of energy efficiency performances of MEMS/NEMS but is, in the same time, a great opportunity for harvesting energy by designing optimized Tribo-Electric Nano-Generators (TENG). Thus, frictional behaviour can be accurately<br&gtcontrolled in real-time by using thermally sensitive periodic patterned self-assembled monolayers of n – octadecyltrichlorosilane<br&gt(OTS) grafted on MEMS surfaces. Nanopatterns are currently used in order to limit the wear rate without modifying the frictional behaviour. In<br&gtthis work, patterns have been created by micro-contact printing (μCP) using a polydimethylsiloxane (PDMS) stamp displaying a trapezoidal profile. Hence pattern periodicity can be continuously changed – and then optimized from discontinuous to pseudo-continuous – by<br&gtapplying a controlled normal load on the soft PDMS stamp. A multiscale tribological study has been carried out on these nano-patterns by using both single-asperity and multi-asperity nanotribometers. Lateral Force Microscopy (LFM) provides the individual frictional behaviour<br&gtof each pattern’s component whereas the multiasperity nanotribometer rather gives the emerging frictional behaviour induced by the patterning according to temperature. As a macroscopic crucial parameter while designing TENG’s devices, this macroscopic behavior has to be carefully optimized for each practical applications at the molecular scale. Thus, whereas the microscale frictional behaviour can be precisely optimized by the pattern’s periodicity, the macroscopic one can be accurately controlled with values of friction coefficient ranging from 0.12 to 0.04 by varying the contact temperature. In addition, any inertial effects observed in the thermal-controlled frictional behavior of nano-patterns can be drastically reduced using infra-red emission as thermal source

New Coupling Agent Structures for Preparing Filler-Polymer Hybrid Materials Under Soft Irradiation Conditions

International audienceThe bifunctional coupling agents have become unavoidable products for preparing hybrid materials with enhanced properties. They are at the origin of the homogeneous dispersion of the filler in the polymerizable matrix and the strong chemical interactions between the composites during the thermal reticulation and vulcanization processes. However, only few structures can play this role in a photo-curable matrix, which is widely applied today in various manufactures (3D printing, cosmetic, medicine, etc.). Developing new structures capable of working under accurate irradiation conditions can extend the use of coupling agents for preparing hybrid photo-curable materials for various applications (e.g. membrane, masks, 2D- and 3D- nano/micro-objects). Recently, a new SPI (SPI-1) was proposed by our group and has revealed a high efficiency for preparing filler-polymer hybrid material. Despite its efficiency, its activity is the highest under the UV-B irradiation but lower under UV-A and inactive under visible light. In this paper, new coupling agent structures (bifunctional Silane-based Photoinitiators; SPI) are synthesized and tested under various irradiation conditions extensively used in the photocuring fields (365, 385 and 405 nm). All the new structures demonstrate higher performance than the first SPI generation (SPI-1) under the diverse light sources. More particularly, SPI-4, 5, and 6 (triphenylamine-based SPI) demonstrate a remarkable activity for preparing filler-polymer hybrid materials under visible light irradiation (LED 405 nm). The efficiency of the new structures in the photopolymerization as well as in the grafting of the silica particles (used as filler model) is elucidated. Finally, the enhancement of the mechanical properties of the hybrid composite films and the possible use of the new approach in photolithography is also demonstrated

Polyethylene Glycol-b-poly(trialkylsilyl methacrylate-co-methyl methacrylate) Hydrolyzable Block Copolymers for Eco-Friendly Self-Polishing Marine Coatings

Hydrolyzable block copolymers consisting of a polyethylene glycol (PEG) first block and a random poly(trialkylsilyl methacrylate (TRSiMA, R = butyl, isopropyl)-co-methyl methacrylate (MMA)) second block were synthesized by RAFT polymerization. Two PEGs with different molar masses (Mn = 750 g/mol (PEG1) and 2200 g/mol (PEG2)) were used as macro-chain transfer agents and the polymerization conditions were set in order to obtain copolymers with a comparable mole content of trialkylsilyl methacrylate (~30 mole%) and two different PEG mole percentages of 10 and 30 mole%. The hydrolysis rates of PEG-b-(TRSiMA-co-MMA) in a THF/basic (pH = 10) water solution were shown to drastically depend on the nature of the trialkylsilyl groups and the mole content of the PEG block. Films of selected copolymers were also found to undergo hydrolysis in artificial seawater (ASW), with tunable erosion kinetics that were modulated by varying the copolymer design. Measurements of the advancing and receding contact angles of water as a function of the immersion time in the ASW confirmed the ability of the copolymer film surfaces to respond to the water environment as a result of two different mechanisms: (i) the hydrolysis of the silylester groups that prevailed in TBSiMA-based copolymers; and (ii) a major surface exposure of hydrophilic PEG chains that was predominant for TPSiMA-based copolymers. AFM analysis revealed that the surface nano-roughness increased upon immersion in ASW. The erosion of copolymer film surfaces resulted in a self-polishing, antifouling behavior against the diatom Navicula salinicola. The amount of settled diatoms depended on the hydrolysis rate of the copolymers

Iron corrosion induced by the hyperthermophilic sulfate-reducing archaeon Archaeoglobus fulgidus at 70 °C

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New Coupling Agent Structures for Preparing Filler-Polymer Hybrid Materials Under Soft Irradiation Conditions

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Synthesis of silica-polymer core-shell hybrid materials with enhanced mechanical properties using a new bifunctional silane-based photoinitiator as coupling agent

International audienceHere, we report the use of new bifunctional silane-based type-1 photoinitiator (SPI-1) as a coupling agent for photopolymer filler and silica grafting. The SPI-1 is grafted on the surface of silica nanoparticles via interactions between the ethoxy group of the silane and the silanol groups of the silica surface. The grafted particles are then dispersed or embedded in/with acrylate polymer by a direct photopolymerization process. The materials were characterized using different techniques including UV–vis spectroscopy, FTIR, TGA, and TEM. Their mechanical properties and the surface morphology were also investigated using AFM and DMA analyses. A significant change and enhancement of the mechanical properties of the newly synthesized materials were observed with respect to that of the unmodified silica. The analysis of the morphology at the microscale level reveals interesting information on the origin of this enhancement and on the dispersion of the filler in the polymer matrix

Synthesis of silica-polymer core-shell hybrid materials with enhanced mechanical properties using a new bifunctional silane-based photoinitiator as coupling agent

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