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

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

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

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

Superabsorbent hydrogels made from bio-sourced butyrolactone monomer in aqueous solution

A new water-soluble monomer, sodium 4-hydroxy-4-methyl-2-methylene butanoate (SHMeMB), formed by saponification of the bio-derived monomer γ-methyl-α-methylene-γ-butyrolactone (MeMBL), was copolymerized with acrylamide (AM) in aqueous solution to make superabsorbent hydrogels with equilibrium degree of swelling in the range of 6700–59 000%, depending on monomer ratio and crosslink density. Mechanical strength and storage and loss moduli of the hydrogels were tunable over a wide range through adjustment of the comonomer composition and the crosslinker content. Monomer reactivity ratios of rSHMeMB = 0.12–0.17 and rAM = 0.95–1.10 were determined using copolymer compositions measured at low monomer conversion as well as by applying the integrated form of the Mayo-Lewis equation to fit the drift in comonomer composition with conversion. The reactivity of the SHMeMB : AM system was lower than that of the previously-studied SHMB : AM system, with sodium 4-hydroxy-2-methylene butanoate (SHMB) derived from a similar renewable monomer, α-methylene-γ-butyrolactone (MBL). The differences in reactivity were studied by pulsed laser polymerization coupled with size exclusion chromatography; the comonomer-averaged propagation rate coefficient of the SHMB : AM system was found to be more than double that of SHMeMB : AM, with first estimates for the SHMeMB and SHMB homopropagation rate coefficients of 25 and 165 L mol−1 s−1, respectively, at 60 °C. Despite its lower reactivity, SHMeMB offers advantages over SHMB due to its availability and as superior overall properties of the final hydrogels were achieved.European Regional Development Fund through project POLYFRIEND, within Hungary-Slovakia Cross-border Co-operation Programme [HUSK 1101/1.2.1/0209]; Slovak Academic Information Agency (SAIA) [VEGA 2/0158/17]; Natural Sciences and Engineering Research Council of Canada (NSERC

Preparation and characterization of fibrous non-woven textile decorated by silver nanoparticles for water filtration

The environmentally friendly preparation of silver nanoparticles was proposed for the production of antibacterial non-woven textile used in water filtration. The silver nanoparticles were prepared by chemical reduction of silver nitrate using two environmentally friendly reducing agents, such as fructose or ascorbic acid. For comparison also commonly used reducing agent-sodium borohydride was used. The silver nanoparticles in various size and yield were produced by immersion of the plasma pre-treated polypropylene (PP) nonwoven textile in the colloidal solutions for different periods (35, 45 and 135 min). The morphology of the silver nanoparticles was characterized by SEM and EDX analysis. Additionally, the antibacterial activity of the silver decorated PP non-woven textile was evaluated by an agar diffusion test using both Gram-positive Staphylococcus Aureus and Gram-negative Escherichia coli. The results suggest that the type of the reducing agent has major effect both on the morphology of silver nanoparticles and the antibacterial activity. © NANOCON 2018 - Conference Proceedings, 10th Anniversary International Conference on Nanomaterials - Research and Application. All rights reserved.Institutional Research Project [RVO 67985874]; Ministry of Education, Youth and Sports of the Czech Republic - Programme NPU I [LO1504