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Contemporary topics in molecular materials engineering
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Contemporary topics in molecular materials engineering Editorial overview Thein Kyu Current Opinion in Chemical Engineering 2013, 2:60–62 For a complete overview see the Issue Available online 21st December 2012 2211-3398/$ – see front matter, # 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.coche.2012.11.003
Thein Kyu Department of Polymer Engineering, University of Akron, Akron, OH 44325-0301, USA e-mail: [email protected] Thein Kyu is currently the Distinguished Professor, Department of Polymer Engineering, University of Akron. His research interest encompasses thermodynamic phase equilibria and kinetics of phase separation in polymer blends, phase transitions in crystalline and liquid crystalline polymers, molecular composites, pattern formation dynamics, electro-optics of dispersed liquid crystal and photonic crystals, self-propelled crystal motion, all the way to ion-exchange membranes and flexible polymer lithium battery.
Looking back at the past few decades, the ‘Hallmark’ of the 80s and 90s has been the revolutionary advances in personal computers and ‘Internet’ communication and information technologies that empowered the world’s economy. This trend continued to evolve into the 2000s, whereby mobile phones and hand-held computers have shaped the landscape of social fabrics and social media. In the 2010s, one can witness a similar revolution taking place in the field of ‘Molecular Materials Engineering’ that encompasses flexible electro/optical devices, polymer solar cells, proton fuel cells, field responsive soft materials for biotechnology and nano-medicine, all the way to flexible and stretchable secondary lithium ion ‘polymer’ batteries, among others. This section covers only a few selected contemporary topics in this diverse field of advanced molecular materials engineering. There are ten concise original/review papers addressing recent advances in the electronic/ photonic materials for optical switching and programmable digital polymer memory, bent-core liquid crystalline materials for mechano-electrical energy conversion, supramolecular materials for energy storage and transport in proton fuel cells and inverted polymer solar cells, field responsive shape memory polymers and self-folding molecular materials, templated or directed assemblies of block copolymers and nanoparticles functionalized composites. By invitation, the experts have contributed individual chapters related to their specialized fields of molecular materials engineering with ‘Chemical Engineering’ audiences in mind. The present section begins with a review article by Chris Li and Timothy Bunning on the myriad of opportunities afforded by the photonic ‘periodic’ structures that combine holographic photolithographic polymerization and soft materials such as liquid crystals (LC), chromorphores, nanoparticles and block copolymers. Their review elaborates on possible mechanisms of how the electro-optical performance of these periodic structures may be controlled by the competition between phase separation dynamics and photopolymerization kinetics. It concludes with future directions on fabricating strategies for multi-functional and multi-field responsive materials. The advances in computer-related technologies would not have been possible without the progress in polymer and molecular materials for display designs, particularly liquid crystal displays with notable attributes such as large area flat panel design, light weight and low power consumption. Ree and co-workers review the major governing factors for controlling the LC alignment in polymer matrix and their interaction with the alignment layer that eventually determines the electro-optical performance of liquid crystal displays (LCD). Several functional polyimide derivatives have met most requirements for the LC alignment and also the overall fabrication of LCD devices. However, there is still room for improvement not only in the
Current Opinion in Chemical Engineering 2013, 2:60–62
www.sciencedirect.com
Editorial overview Kyu 61
effective LC alignment to prevent image sticking, but also in imparting multistable optically rewritable capability. Ree and co-workers further introduce electrically switchable bistable polymeric materials that have recently attracted significant attention because of their inherent advantages over conventional inorganic silicon-oxidebased and metal-oxide-based materials in memory device applications. Their review covers polymeric memory materials, device characteristics, and data storage mechanisms. Of particular interest is that the device dimension can easily be miniaturized and their properties can be easily tailored through chemical synthesis. These polymeric materials having high flexibility and high mechanical strength can be processed at low costs and good scalability. Their review concludes with the discussion on the criteria for the polymer memory materials to meet the requirements of high performance memory devices including high ON/OFF contrast ratio, long endurance and retention characteristics, and fast switching speed. In search of improving spatio resolution of periodic nanopatterns for nanolithography, block copolymers of various topologies have gained considerable attention for use as templates in nanofabrication. One major obstacle is that self-assembly of block copolymers usually have lead to poly-grain structures loaded with defects. Hirokazu Hasegawa and Mikihito Takenaka introduce the directed selfassembly approach as a viable technique either by graphoepitaxy with topographical guides or chemical registration with chemically pattered surfaces enabling control of orientation and alignment of block copolymer microdomains in thin films. This approach can further extend the resolution limit of the conventional photolithography from micrometer to nanoscale. On a related subject, Michael Hore and Russell Composto introduce novel strategies for dispersing, assembling and orienting anisotropic nanorods in polymers through the use of block copolymers having lamellar and cylindrical domains. Their review further elaborates the long-range order assembling of nanorods under mechanical shear or electrical fields during the fabrication of nanocomposites with high aspect ratios. These highly anisotropic assembled nanorods have many attractive features with potential utility in biomedical imaging, polarizing filters, and photovoltaics. Another area of interest is the shape memory polymers (SMP) by virtue of their potential in biomedical applications. SMP are functional materials made up of polymeric network with switchable segment(s), capable of undergoing controlled shape change under external stimulus. Xiaofan Luo and Patrick Mather review various strategies of designing SMP materials and associated merits of the individual approaches. David Gracias further provides a comprehensive review on novel www.sciencedirect.com
self-folding molecular materials as enabling stimuli responsive materials. Examples of the ability to manipulate include layering and patterning of thin polymer films that can bend or curve when subjected to external stimuli such as pH, chemical, thermal, electrical or optical fields. Of particular interest is that the action of folding or unfolding of molecular materials enables wire-free actuation at small length scales — a neverbefore-seen molecular device with potential applications in biomimetic actuators and microsurgical tools. Antal Ja´kli and Na´ndor E´ber introduce a new concept of physical effects involving couplings between electrical and mechanical phenomena on energy conversion of soft materials. This concept is known as piezoelectricity effect that refers to a linear coupling between electric and mechanical properties in novel non-centrosymmetric materials such as bent-core liquid crystals. Their article focuses on both direct and converse piezoelectricity and a linear coupling effect between mechanical bending and electric polarization, called ‘bending’ piezoelectricity or flexoelectricity. These phenomena are seen to exert profound influence on some functions of living organisms and have also shown to have great potential for practical applications in sensor and actuator technologies. Furthermore, the authors hypothesize that the flexoelectricity effect may prompt designing and synthesizing special functional materials with stronger coupling coefficients and ease of processability — most likely in the area of liquid crystalline elastomers and polymers. Chao Yi and Xiong Gong report a new strategy of designing inverted polymer solar cells (PSC) devices. With the deposition of conjugated interfacial layer onto the electron extraction layer, record-high power conversion efficiency (PCE) of 8.4% has been achieved for inverted PSCs. Although the PCE performance of inverted PSC is constantly improving over the years, the limited durability and service life of PSC or inverted PSC remains a challenging issue. The field of PSC or inverted PSC may still be in its infancy, newer polymer-based PSC technology with efficient device designs is anticipated to emerge in near future to rival the silicon based solar cell technology. In the laboratory of the Section Editor, considerable advances have also been witnessed in the modification of ‘Nafion’ proton fuel cell membrane for high temperature operation, that is, 115 8C possibly up to 135 8C. Their article demonstrates the successful infusion of giant supramolecules such as hyperbranched polyester or waterwheel ‘Noria’ into the ionic domains via swelling in methanol. The modified Nafion has shown to improve not only oxidative thermal, mechanical, and electrochemical stabilities, but also enhance proton conductivity at elevated temperatures in the actual fuel cell Current Opinion in Chemical Engineering 2013, 2:60–62
62 Materials engineering
environment. It is striking that the incorporated ‘Noria’ supramolecules can act like solid proton carriers for improvement of high temperature proton conductivity. Their finding opens up new opportunities for designing multi-functional supramolecules. Needless to say, there are more deserving topics to be covered — in particular, functional polymer and molecular materials for biotechnology and nano-medicine, flexible secondary lithium ion ‘polymer’ batteries for energy storage, among others. It can be anticipated that these
Current Opinion in Chemical Engineering 2013, 2:60–62
subject matters will be covered in future issues of Current Opinion in Chemical Engineering. Last but not the least, I would like to thank all the authors who graciously contributed their precious time, efforts, and high quality articles. The professional help from the editorial team of Elsevier, especially Mr. Jan ten Have and Professor Kamalesh K. Sirkar, Senior Editor of ‘Current Opinion in Chemical Engineering’ is gratefully acknowledged, without whose help, the timely completion of this section would not have been possible.
www.sciencedirect.com
Contemporary topics in molecular materials engineering Editorial overview Thein Kyu Current Opinion in Chemical Engineering 2013, 2:60–62 For a complete overview see the Issue Available online 21st December 2012 2211-3398/$ – see front matter, # 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.coche.2012.11.003
Thein Kyu Department of Polymer Engineering, University of Akron, Akron, OH 44325-0301, USA e-mail: [email protected] Thein Kyu is currently the Distinguished Professor, Department of Polymer Engineering, University of Akron. His research interest encompasses thermodynamic phase equilibria and kinetics of phase separation in polymer blends, phase transitions in crystalline and liquid crystalline polymers, molecular composites, pattern formation dynamics, electro-optics of dispersed liquid crystal and photonic crystals, self-propelled crystal motion, all the way to ion-exchange membranes and flexible polymer lithium battery.
Looking back at the past few decades, the ‘Hallmark’ of the 80s and 90s has been the revolutionary advances in personal computers and ‘Internet’ communication and information technologies that empowered the world’s economy. This trend continued to evolve into the 2000s, whereby mobile phones and hand-held computers have shaped the landscape of social fabrics and social media. In the 2010s, one can witness a similar revolution taking place in the field of ‘Molecular Materials Engineering’ that encompasses flexible electro/optical devices, polymer solar cells, proton fuel cells, field responsive soft materials for biotechnology and nano-medicine, all the way to flexible and stretchable secondary lithium ion ‘polymer’ batteries, among others. This section covers only a few selected contemporary topics in this diverse field of advanced molecular materials engineering. There are ten concise original/review papers addressing recent advances in the electronic/ photonic materials for optical switching and programmable digital polymer memory, bent-core liquid crystalline materials for mechano-electrical energy conversion, supramolecular materials for energy storage and transport in proton fuel cells and inverted polymer solar cells, field responsive shape memory polymers and self-folding molecular materials, templated or directed assemblies of block copolymers and nanoparticles functionalized composites. By invitation, the experts have contributed individual chapters related to their specialized fields of molecular materials engineering with ‘Chemical Engineering’ audiences in mind. The present section begins with a review article by Chris Li and Timothy Bunning on the myriad of opportunities afforded by the photonic ‘periodic’ structures that combine holographic photolithographic polymerization and soft materials such as liquid crystals (LC), chromorphores, nanoparticles and block copolymers. Their review elaborates on possible mechanisms of how the electro-optical performance of these periodic structures may be controlled by the competition between phase separation dynamics and photopolymerization kinetics. It concludes with future directions on fabricating strategies for multi-functional and multi-field responsive materials. The advances in computer-related technologies would not have been possible without the progress in polymer and molecular materials for display designs, particularly liquid crystal displays with notable attributes such as large area flat panel design, light weight and low power consumption. Ree and co-workers review the major governing factors for controlling the LC alignment in polymer matrix and their interaction with the alignment layer that eventually determines the electro-optical performance of liquid crystal displays (LCD). Several functional polyimide derivatives have met most requirements for the LC alignment and also the overall fabrication of LCD devices. However, there is still room for improvement not only in the
Current Opinion in Chemical Engineering 2013, 2:60–62
www.sciencedirect.com
Editorial overview Kyu 61
effective LC alignment to prevent image sticking, but also in imparting multistable optically rewritable capability. Ree and co-workers further introduce electrically switchable bistable polymeric materials that have recently attracted significant attention because of their inherent advantages over conventional inorganic silicon-oxidebased and metal-oxide-based materials in memory device applications. Their review covers polymeric memory materials, device characteristics, and data storage mechanisms. Of particular interest is that the device dimension can easily be miniaturized and their properties can be easily tailored through chemical synthesis. These polymeric materials having high flexibility and high mechanical strength can be processed at low costs and good scalability. Their review concludes with the discussion on the criteria for the polymer memory materials to meet the requirements of high performance memory devices including high ON/OFF contrast ratio, long endurance and retention characteristics, and fast switching speed. In search of improving spatio resolution of periodic nanopatterns for nanolithography, block copolymers of various topologies have gained considerable attention for use as templates in nanofabrication. One major obstacle is that self-assembly of block copolymers usually have lead to poly-grain structures loaded with defects. Hirokazu Hasegawa and Mikihito Takenaka introduce the directed selfassembly approach as a viable technique either by graphoepitaxy with topographical guides or chemical registration with chemically pattered surfaces enabling control of orientation and alignment of block copolymer microdomains in thin films. This approach can further extend the resolution limit of the conventional photolithography from micrometer to nanoscale. On a related subject, Michael Hore and Russell Composto introduce novel strategies for dispersing, assembling and orienting anisotropic nanorods in polymers through the use of block copolymers having lamellar and cylindrical domains. Their review further elaborates the long-range order assembling of nanorods under mechanical shear or electrical fields during the fabrication of nanocomposites with high aspect ratios. These highly anisotropic assembled nanorods have many attractive features with potential utility in biomedical imaging, polarizing filters, and photovoltaics. Another area of interest is the shape memory polymers (SMP) by virtue of their potential in biomedical applications. SMP are functional materials made up of polymeric network with switchable segment(s), capable of undergoing controlled shape change under external stimulus. Xiaofan Luo and Patrick Mather review various strategies of designing SMP materials and associated merits of the individual approaches. David Gracias further provides a comprehensive review on novel www.sciencedirect.com
self-folding molecular materials as enabling stimuli responsive materials. Examples of the ability to manipulate include layering and patterning of thin polymer films that can bend or curve when subjected to external stimuli such as pH, chemical, thermal, electrical or optical fields. Of particular interest is that the action of folding or unfolding of molecular materials enables wire-free actuation at small length scales — a neverbefore-seen molecular device with potential applications in biomimetic actuators and microsurgical tools. Antal Ja´kli and Na´ndor E´ber introduce a new concept of physical effects involving couplings between electrical and mechanical phenomena on energy conversion of soft materials. This concept is known as piezoelectricity effect that refers to a linear coupling between electric and mechanical properties in novel non-centrosymmetric materials such as bent-core liquid crystals. Their article focuses on both direct and converse piezoelectricity and a linear coupling effect between mechanical bending and electric polarization, called ‘bending’ piezoelectricity or flexoelectricity. These phenomena are seen to exert profound influence on some functions of living organisms and have also shown to have great potential for practical applications in sensor and actuator technologies. Furthermore, the authors hypothesize that the flexoelectricity effect may prompt designing and synthesizing special functional materials with stronger coupling coefficients and ease of processability — most likely in the area of liquid crystalline elastomers and polymers. Chao Yi and Xiong Gong report a new strategy of designing inverted polymer solar cells (PSC) devices. With the deposition of conjugated interfacial layer onto the electron extraction layer, record-high power conversion efficiency (PCE) of 8.4% has been achieved for inverted PSCs. Although the PCE performance of inverted PSC is constantly improving over the years, the limited durability and service life of PSC or inverted PSC remains a challenging issue. The field of PSC or inverted PSC may still be in its infancy, newer polymer-based PSC technology with efficient device designs is anticipated to emerge in near future to rival the silicon based solar cell technology. In the laboratory of the Section Editor, considerable advances have also been witnessed in the modification of ‘Nafion’ proton fuel cell membrane for high temperature operation, that is, 115 8C possibly up to 135 8C. Their article demonstrates the successful infusion of giant supramolecules such as hyperbranched polyester or waterwheel ‘Noria’ into the ionic domains via swelling in methanol. The modified Nafion has shown to improve not only oxidative thermal, mechanical, and electrochemical stabilities, but also enhance proton conductivity at elevated temperatures in the actual fuel cell Current Opinion in Chemical Engineering 2013, 2:60–62
62 Materials engineering
environment. It is striking that the incorporated ‘Noria’ supramolecules can act like solid proton carriers for improvement of high temperature proton conductivity. Their finding opens up new opportunities for designing multi-functional supramolecules. Needless to say, there are more deserving topics to be covered — in particular, functional polymer and molecular materials for biotechnology and nano-medicine, flexible secondary lithium ion ‘polymer’ batteries for energy storage, among others. It can be anticipated that these
Current Opinion in Chemical Engineering 2013, 2:60–62
subject matters will be covered in future issues of Current Opinion in Chemical Engineering. Last but not the least, I would like to thank all the authors who graciously contributed their precious time, efforts, and high quality articles. The professional help from the editorial team of Elsevier, especially Mr. Jan ten Have and Professor Kamalesh K. Sirkar, Senior Editor of ‘Current Opinion in Chemical Engineering’ is gratefully acknowledged, without whose help, the timely completion of this section would not have been possible.
www.sciencedirect.com