Thermoplastic Elastomers with Photo-actuating Properties

This contribution reviews elastomeric materials with photo-actuation behavior with emphasis on thermoplastic elastomers and their composites. The principles of the photo-actuation and the main factors affecting the photo-actuation phenomena of thermoplastic elastomer materials are discussed in detail. The well-performing photo-actuating systems involving both statistical and block copolymers-based thermoplastic elastomers are assessed in terms of their advantages and limitations. Methods for evaluation of photo-actuation behavior of the materials are reported as well. Finally, the utilization of the photo-actuating thermoplastic elastomers is presented

Reversible actuation ability upon light stimulation of the smart systems with controllably grafted graphene oxide with poly (glycidyl methacrylate) and PDMS elastomer: Effect of compatibility and graphene oxide reduction on the photo-actuation performance

This study is focused on the controllable reduction of the graphene oxide (GO) during the surface-initiated atom transfer radical polymerization technique of glycidyl methacrylate (GMA). The successful modification was confirmed using TGA-FTIR analysis and TEM microscopy observation of the polymer shell. The simultaneous reduction of the GO particles was confirmed indirectly via TGA and directly via Raman spectroscopy and electrical conductivity investigations. Enhanced compatibility of the GO-PGMA particles with a polydimethylsiloxane (PDMS) elastomeric matrix was proven using contact angle measurements. Prepared composites were further investigated through the dielectric spectroscopy to provide information about the polymer chain mobility through the activation energy. Dynamic mechanical properties investigation showed an excellent mechanical response on the dynamic stimulation at a broad temperature range. Thermal conductivity evaluation also confirmed the further photo-actuation capability properties at light stimulation of various intensities and proved that composite material consisting of GO-PGMA particles provide systems with a significantly enhanced capability in comparison with neat GO as well as neat PDMS matrix. © 2018 by the authors.Czech Science Foundation [16-20361Y]; Ministry of Education, Youth and Sports of the Czech Republic-program NPU I [L01504]; Operational Program Research and Development for Innovations - the European Regional Development Fund (ERDF); project CPS-strengthening research capacity [CZ.1.05/2.1.00/19.0409]; [APVV-15-0545]; [APVV-14-0891

The impact of polymer grafting from a graphene oxide surface on its compatibility with a PDMS matrix and the light-induced actuation of the composites

Poly(dimethyl siloxane) (PDMS)-based materials with improved photoactuation properties were prepared by the incorporation of polymer-grafted graphene oxide particles. The modification of the graphene oxide (GO) surface was achieved via a surface initiated atom transfer radical polymerization (SI ATRP) of methyl methacrylate and butyl methacrylate. The modification was confirmed by thermogravimetric analysis, infrared spectroscopy and electron microscopy. The GO surface reduction during the SI ATRP was investigated using Raman spectroscopy and conductivity measurements. Contact angle measurements, dielectric spectroscopy and dynamic mechanical analyses were used to investigate the compatibility of the GO filler with the PDMS matrix and the influence of the GO surface modification on its physical properties and the interactions with the matrix. Finally, the thermal conductivity and photoactuation properties of the PDMS matrix and composites were compared. The incorporation of GO with grafted polymer chains, especially poly(n-butyl methacrylate), into the PDMS matrix improved the compatibility of the GO filler with the matrix, increased the energy dissipation due to the improved flexibility of the PDMS chains, enhanced the damping behavior and increased the thermal conductivity. All the changes in the properties positively affected the photoactuation behavior of the PDMS composites containing polymer-grafted GO. © 2017 by the authors.LO1504, MOE, Ministry of EducationGrant Agency of the Czech Republic [16-20361Y]; Ministry of Education, Youth and Sports of the Czech Republic-program NPU I [LO1504]; SRDA [APVV-15-0545]; VEGA [VEGA 2/0161/17]; Slovak Academy of Sciences [SAS-MOST JRP 2014-9

Enhanced and tunable electrorheological capability using surface initiated atom transfer radical polymerization modification with simultaneous reduction of the graphene oxide by silyl-based polymer grafting

In this study, a verified process of the "grafting from" approach using surface initiated atom transfer radical polymerization was applied for the modification of a graphene oxide (GO) surface. This approach provides simultaneous grafting of poly(2-(trimethylsilyloxy)ethyl methacrylate) (PHEMATMS) chains and a controllable reduction of the GO surface. This allows the fine tuning of its electrical conductivity, which is a crucial parameter for applications of such hybrid composite particles in electrorheological (ER) suspensions. The successful coating was confirmed by transmission electron microscopy and Fourier-transform infrared spectroscopy. The molecular characteristics of PHEMATMS were characterized by gel permeation chromatography. ER performance was elucidated using a rotational rheometer under various electric field strengths and a dielectric spectroscopy to demonstrate the direct impact of both the relaxation time and dielectric relaxation strength on the ER effectivity. Enhanced compatibility between the silicone oil and polymer-modified GO particles was investigated using contact angle measurements and visual sedimentation stability determination. It was clearly proven that the modification of the GO surface improved the ER capability of the system due to the tunable conductivity during the surface-initiated atom transfer radical polymerization (SI-ATRP) process and the enhanced compatibility of the GO particles, modified by polymer containing silyl structures, with silicone oil. These unique ER properties of this system appear very promising for future applications in the design of ER suspensions.Grant Agency of the Czech Republic [16-20361Y]; Ministry of Education, Youth and Sports of the Czech Republic-program NPU I [LO1504]; European Union [CZ. 02.2.69/0.0/0.0/16_027/0008464]; Operational Program for Research, Development and Education; National Science Centre, Poland [UMO-2016/23/P/ST5/02131]; European Unions [665778]; [APVV-14-0891]; [APVV-15-0545

Electrorheological performance of graphene oxide particles grafted with poly(alpha-methylstyrene) using SI-ATRP approach

Electrorheological (ER) suspension are special class of systems, those physical properties, such as viscosity can be tuned using external electric field strength. Generally, they are two-phase systems consisting of solid polarizable particles and liquid insulating medium. After application of the external electric field, the particles are polarized and create the chain-like structures in the direction of the electric field streamlines. Such internal structure development resulting in the significant increase in viscosity usually in four orders of magnitude and more. This phenomenon is reversible, repeatable and once the electric field is switched-off the suspension become to its initial state. However, due to the usually various nature of dispersed phase and liquid medium, the sedimentation stability of the suspensions is the main issue. In addition, the ER performance of various systems based on conducting polymers is not sufficient, thus the development of the novel dispersed phases are still attractive. Moreover, graphene oxide (GO) particles and their hybrids were recently recognized as suitable materials for ER suspensions. Hence, we were performed the SI-ATRP from GO surface as a novel approach how to provide GO-polymer particles with tunable conductivity and polymer layer in single step and thus solve the main drawbacks such as sedimentation stability as well as proper ER performance. © 2018 TANGER Ltd. All Rights Reserved.Grant Agency of the Czech Republic [16-20361Y]; Ministry of Education, Youth and Sports of the Czech Republic - program NPU I [LO1504]; [APVV-15-0545

Preparation and characterization of graphene oxide sheets controllably grafted with PMMA brushes via surface-initiated ATRP

Recently, graphene oxide (GO) has gained significant attention in many applications, such as touch displays, electronic devices or electrorheological fluids. However, neat GO is hydrophilic, which limits its efficiency in hydrophobic media, e.g. polymer matrices, oil carriers. Therefore, the utilization of GO-coated core-shell structures was proven to be advantageous. In this study, GO sheets were prepared by chemical exfoliation of graphite using modified Hummers method. The specific ATRP initiator, bromoisobutyryl bromide, was covalently immobilized onto as-prepared GO through oxygen-functional hydrophilic groups. Initiator-treated GO sheets were further grafted with poly(methyl methacrylate) (PMMA) via surface-initiated ATRP technique. The monomer conversion, molar mass and polydispersity of PMMA chains were investigated using nuclear magnetic resonance and gel permeation chromatography, respectively. The successful grafting process was confirmed by Fourier transform infrared spectroscopy. Raman spectroscopy and electric conductivity measurements revealed significant chemical reduction of GO during surface-initiated ATRP. Synthesized GO/PMMA structures exhibited considerably enhanced wettability in hydrophobic media, which was proved via contact angle measurements. Therefore, the synthesized GO/PMMA hybrids may found utilization in many aforementioned practical applications providing well-dispersed composite systems.Grant Agency of the Czech Republic [16-20361Y]; Ministry of Education, Youth and Sports of the Czech Republic -program NPU I [LO1504]; Slovak grand agency [APVV-14-0891

Electrorheological fluids containing graphene oxide sheets grafted with poly(methyl methacrylate)

Electrorheological (ER) fluids are fascinating materials with a wide range of potential applications. However, low performance in electric field and poor sedimentation stability are the most serious limitations for these applications. To reduce the mentioned drawbacks various materials such as graphene were explored. Recent efforts to improve performance of the ER fluids led to the modification of the graphene with polymer substances. Herein, the proposed ER structures are based on the graphene oxide (GO) sheets controllably grafted with poly(methyl methacrylate) (PMMA). The oxygen-containing functional groups introduced by modified Hummers method enabled the immobilization of 2-Bromoisobutyryl bromide onto the GO. The controlled PMMA chain growth was performed by atom transfer radical polymerization resulting in the GO-g-PMMA entities. The reaction process was monitored via nuclear magnetic resonance spectroscopy and gel permeation chromatography. The successful grafting process was confirmed via infrared spectroscopy. Conductivity of the neat GO as well as the fabricated GO-g-PMMA structures was investigated using four-point method, while their reduction was examined via Raman spectroscopy. Such particles were further thoroughly dispersed in silicone oil (SO) and the ER performance of as-prepared ER fluids was investigated. The system containing the GO-g-PMMA exhibited superior dynamic yield stress and higher ER effects as the modified particles were able to develop more rigid field-induced internal structures, due to the enhanced particle conductivity and thus better response to external electric field. The results also showed that the presence of PMMA grafts enhanced the compatibility with SO, which was reflected in substantially improved stability against sedimentation. © 2018 TANGER Ltd. All Rights Reserved.Grant Agency of the Czech Republic [GJ16-20361Y]; Internal Grant Agency of Tomas Bata University in Zlin [IGA/CPS/2017/004]; Ministry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504]; [APVV-15-0545

The chemical stability and cytotoxicity of carbonyl iron particles grafted with poly(glycidyl methacrylate) and the magnetorheological activity of their suspensions

Carbonyl iron (CI) particles were grafted with poly(glycidyl methacrylate) (PGMA) using atom transfer radical polymerization. Compact coating of PGMA largely improved the chemical stability of the particles in an acid environment and thus reduced the common drawback of bare CI particles. Furthermore, due to possible medical applications of CI-polymer systems for magnetic drug targeting, an in vitro cytotoxicity test was performed using an NIH/3T3 cell line. The cell viability was evaluated by spectrometric assay (MTT). The results show that the prepared particles are not cytotoxic. Moreover, bare CI particles as well as synthesized core-shell particles were suspended in silicone oil, and the rheological behavior of MR suspensions was investigated in controlled shear rate mode under various magnetic field strengths. Dynamic yield stress as a measure of the rigidity of the created internal structures of the suspensions was determined using the Herschel-Bulkley model, which provided a reasonably good fit for rheological data. MR suspensions of PGMA-coated particles exhibited only slightly decreased yield stresses due to their negligibly-affected magnetic performance. This journal is © The Royal Society of Chemistry.Operational Program Research and Development for Innovations - European Regional Development Fund (ERDF); National Budget of the Czech Republic [CZ.1.05/2.1.00/03.0111]; TBU in Zlin [IGA/CPS/2015/007]; Centre of Excellence FUN-MAT; Czech Science Foundation [13-08944S

Controllable reduction of graphene oxide/poly(Butyl acrylate) hybrids under ATRP conditions

This study is aimed on the controllable reduction of the graphene oxide (GO) sheets during surface initiated atom transfer radical polymerization (SI-ATRP). GO sheets were successfully synthesized using Hummers method and properly characterized by Fourier transform infrared spectroscopy (FTIR). SI-ATRP approach was used to simultaneously modify the GO surface by poly(butyl acrylate) (PBA) brushes and its chemical reduction in the single-step synthesis. The presence of the polymer brushes on the GO sheets was investigated by gel permeation chromatography, nuclear magnetic resonance and FTIR. Simultaneous GO reduction during polymerization was confirmed using Raman spectroscopy and finally by conductivity measurement. Compatibility of the GO and GO-PBA sheets was investigated via contact angle measurements of sessile drop between GO substrates and poly(dimethyl siloxane). From the potential applicability point of view, the modification of graphene-based hybrids by polymers is highly important especially when the compatibility as well as conductivity of GO-PBA sheets with surroundings plays a crucial role i.e. the light-stimulated sensors based on silicon or other elastomers.Grant Agency of the Czech Republic [16-20361Y]; Ministry of Education, Youth and Sports of the Czech Republic -program NPU I [LO1504]; [APVV-14-0891

Grafting of magnetic particles with poly(2-isopropenyl-2-oxazoline)

Magnetic particles play an important role in modern biomedical applications including targeted drug delivery, local embolization of blood veins, hyperthermia etc. Therefore, the development of more effective systems with high biocompatibility is of interest for many researchers. Nevertheless, these magnetic systems have to meet certain criteria necessary for in vivo applications. We have considered key requirements desired from such materials, and we have prepared a promising system based on core-shell particles via surface-initiated atom transfer radical polymerization (ATRP). The finest grade of the carbonyl iron particles was used as a suitable core and the treatment of its surface in acidic environment ensured the presence of hydroxyl groups, which were further coupled with ethoxy groups of (3-Aminopropyl)triethoxysilane. After the functionalization, the immobilization of 2-Bromoisobutyryl bromide, which served as an initiator, was performed. Finally, the initiator-treated particles were grafted with poly(2-isopropenyl-2-oxazoline) (PIPOx) under ATRP conditions as the PIPOx has recently shown a great potential in biomedical applications. The cleaning and washing procedures ensured high purity of the product. The reaction conversion, molar mass and dispersity of PIPOx grafts were investigated using nuclear magnetic resonance and gel permeation chromatography, respectively. The presence of grafted PIPOx was confirmed using Fourier-transform infrared, and energy-dispersive X-ray spectroscopies. The grafted PIPOx layer had negligible effect on particle magnetization as revealed via vibration-sample magnetometry. Synthesized core-shell structures may find utilization as a promising material for local embolization or may serve as a drug delivery system due to the presence of PIPOx bearing the active sites allowing the drug bonding. © 2018 TANGER Ltd. All Rights Reserved.Grant Agency of the Czech Republic [17-24730S]; Internal Grant Agency of Tomas Bata University in Zlin [IGA/CPS/2017/004]; Ministry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504]; [APVV-15-0545