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REGISTRATION
INTRODUCTORY REMARKS and SESSION CΟ-CΗΑΙRS; M.W. Urban (Clemson University) and B.S. Sumerlin (University of Florida)
PM SESSION Dynamics and Interfaces in Soft Matter and Polymers
4:00-4:30 Olli Ikkala, “Towards Life-Inspired Soft Matter Dynamics and Functionalities,” Aalto University, Department of Applied Physics, Espoo, FINLAND.
4:30-5:00 S. Eileen Seo, “Designing Materials at the Interface of Nanotechnology and Polymer Chemistry” Arizona State University, Tempe, USA.
5:00-5:30 Santiago J. Garcia, “Quantifying the Effect of Polymer Architecture Variations on Autonomous Polymer Crack Closure and Interfacial Healing” Department of Aerospace Engineering, TUDelft, Delft, THE NETHERLANDS.
5:30-6:00 Tim Lodge, “Kinetics of Block Copolymer Micelle Fragmentation: Fission Impossible?” Department of Chemistry, University of Minnesota, USA.
WINE SOCIAL
AM SESSION Responsive Systems: From Bioinspiration to Programmable Phase Behavior; Session Chair: C. Adrian Figg
8:30-9:00 Olga Speck, “Self-sealing and Self-healing in Plants – Suitable Models for Biomimetic Solutions?” Faculty of Biology and Cluster of Excellence livMatS, University of Freiburg, Freiburg, Germany.
9:00-9:30 J. Lahann, “Stimuli-responsive Materials Based on Compartment-alization” Department of Chemical Engineering, Materials Science and Engineering, and Biomedical Engineering Biointerfaces Institute, University of Michigan, Ann Arbor, USA.
9:30-10:00 Austin M. Evans, “Thermal Electrochemical Transistors, A Thought Experiment,” University of Florida, Gainesville, USA.
10:00-10:30 Dale L. Huber, “Programming Complex Phase Behaviors with Stimuli Responsive Surfactants,” Sandia National Labs, Center for Integrated Nanotechnologies, Albuquerque, USA.
Coffee Break
AM SESSION Responsive Materials and Mechanics Under External Stimuli; Session Chair: Christopher Bates 11:00-11:30 Srinivasa R. Raghavan, “Switching on the Adhesion of Hydrogels to Tissues by an Electric Field” Department of Chemical & Biomolecular Engineering, University of Maryland, College Park, USA. 11:30-12:00 Olga Kuksenok, “Multiscale Modeling of Responsive Polymer Networks: Focus on Photo-Controlled Degradation and Patterns Restructuring,” Department of Materials Science and Eng., Clemson University, Clemson, USA. 12:00-12:30 Ryan C. Hayward, “Photomechanical Materials Based on Semicrystalline Polymers and Polymer/Crystal Composites,” University of Colorado, Boulder, USA. LUNCH BUFFET RUSSIAN RIVER; AFTERNOON OPEN AM SESSION Advanced Techniques in Polymer Synthesis and Functionalization; Session Chair: Megan Hill 8:30-9:00 Krzysztof Matyjaszewski, “Photochemical Control in ATRP,” Department of Chemistry and Center for Macromolecular Engineering, Carnegie Mellon University, Pittsburgh, USA. 9:00-9:30 C. Adrian Figg, “Precisely Placing Functional Groups in Acrylic Polymers Using Photoredox Chemistry,” Department of Chemistry and Macromolecules Innovation Institute, Virginia Tech, Blacksburg, USA. 9:30-10:00 Christopher M. Bates, “Dynamic Bottlebrush Elastomers,” Department of Materials, Materials Research Laboratory, University of California, Santa Barbara, USA. 10:00 – 10:30 COFFEE BREAK AM SESSION Toward a Circular Economy: Strategies in Polymer Recycling; Session Chair: S. Eileen Seo 10:30-11:00 Garret M. Miyake, “Chemically Recyclable Polyolefin-Like Multiblock Polymers,” Department of Chemistry, Colorado State University, Fort Collins, USA. 11:00-11:30 Thomas H. Epps, III, “Advanced Recycling – Understanding Fundamentals to Valorize Plastics Waste,” Department of Chemical & Biomolecular Engineering; Department of Materials Science & Engineering; Center for Research in Soft Matter & Polymers, University of Delaware, Newark, USA. 11:30-12:00 Ying Yang, “Entropically Driven Ring-Opening Polymerization for Circular Polymer Economy,” Department of Chemistry, University of Nevada at Reno, Reno, USA. LUNCH BUFFET RUSSIAN RIVER PM SESSION Sensing and Adaptation in Responsive Polymers and Gels; Session Chair: Ying Yang 1:30-2:00 Michael Serpe, “Sensing, Biosensing, and Drug Delivery with Responsive Microgels,” University of Alberta, Edmonton, CANADA. 2:00-2:30 Megan R. Hill, “Temperature-Responsive Poly(Lewis Pairs),” Department of Chemistry, Colorado State University, Fort Collins, USA. 2:30-3:00 D. Kuckling, “Dually Cross-linked Stimuli-sensitive Gels,” Department of Chemistry, Paderborn University, Paderborn, GERMANY. 3:00 – 3:30 COFFEE BREAK PM SESSION Scalable and Sustainable Stimuli-Responsive Electronics & Bioinspired Materials; Session Chair: Austin Evans 3:30-4:00 Jianguo Mei, “From Lab to Fab: Roll-to-roll Processed Large-area Electrochromic Windows,” Department of Chemistry, Purdue University, West Lafayette, USA. 4:00-4:30 Thomas Speck, “Plant-inspired Soft Robots and Soft Machines for Engineering, Architecture and Medicine Based on Stimuli-Responsive Materials Systems,” Garden and Cluster of Excellence Living, Adaptive and Energy-autonomous Materials Systems (livMatS), University of Freiburg, Freiburg, GERMANY. 4:30-5:00 Fabio Cicoira, “Self-Healing, Stretchable and Recyclable Electronics” of Chemical Engineering, Polytechnique Montreal, Montreal, CANADA. 5:00 Closing Remarks Marek W. Urban and Brent S. Sumerlin POSTER SESSION AND WINE SOCIAL
BEST RESEARCH POSTER AWARD PRESENTATION Co-SPONSORED BY THE ROYAL SOCIETY OF CHEMISTRY JOURNALS
PLENARY LECTURES
Olli Ikkala, Towards Life-Inspired Soft Matter Dynamics and Functionalities, Aalto University, Department of Applied Physics, Espoo, Finland.
Soft matter properties have extensively been promoted by stimulus-responsiveness, shape-memory effects, and bio-inspiration towards ever more multifunctional properties.1-3 Beyond the equilibrium and kinetically trapped static states, adaptive and dynamic dissipative feedback-controlled properties inspired by living matter would be among the next attractive functionalities, however, involving complexity.4-7 Herein, we describe soft matter approaches inspired by selected functions of living systems. Classical (Pavlovian) conditioning, habituation, and sensitization are among the simplest “learning” concepts in behaviour.8 Artificial Pavlovian condition has, not surprisingly, already been described in biosynthetic articifial systems.9 We consider light and magnetic field as feasible stimuli because they can applied remotely. We show concepts algorithmically inspired by Pavlovian conditioning in common manmade soft matter systems.10-11 We further show electrical conduction bistability, response plasticity, and adaptation based on soft ferromagnetic particle assemblies using magnetic stimulus inspired by sensitization.12 Finally, we show dynamic light-driven systems to allow feedback-controlled homeostasis and dissipative signal transduction.13 Life-inspired soft materials can provide the next generation of out-of-equilibrium dissipative platforms for embedded materials intelligence.14
References
Eileen Seo, Designing Materials at the Interface of Nanotechnology and Polymer Chemistry, Arizona State University, Tempe, USA.
Given increasing environmental issues related to plastic materials, the idea of replacing polymer networks formed via covalent bonds with non-covalent (or dynamic) bonds remains a research area of significant promise. Polymer networks formed via weak, physical interactions can be easily remolded, self-healed, and recycled on demand, but these materials typically exhibit reduced mechanical properties compared to ones that are chemically crosslinked. This makes physically crosslinked polymer networks unsuitable for many applications. Using polyvalent, cooperative binding as a key principle to establish strong, yet reversible interactions, we aim to design dynamic polymer networks by preparing nanoparticles functionalized with reconfigurable surface ligands as particle-based bonds to form stimuli-responsive, mechanically robust polymeric materials.
Santiago J. Garcia, Quantifying the Effect of Polymer Architecture Variations on Autonomous Polymer Crack Closure and Interfacial Healing, TUDelft, THE NETHERLANDS.
In this presentation, we introduce a set of uncommon but powerful characterization strategies to quantify and relate the effect of polymer architecture variations on autonomous polymer crack closure and interfacial healing. The protocols, applied to a set of well-controlled healable polyurethanes and polyetherimides, show the benefit of combining electrochemistry, (laser)optics, and rheology strategies (continuous relaxation spectra and entropy quantification) with building a clear picture of the interdependence between autonomous damage closure, interfacial sealing, and interfacial mechanical restoration.
Tim Lodge, Supriya Gupta, and Sanghee Yang, Kinetics of Block Copolymer Micelle Fragmentation: Fission Impossible? Department of Chemistry, Department of Chemical Engineering & Materials Science, University of Minnesota, USA.
Block copolymer micelles in selective solvents are of great interest across a range of technologies, including drug delivery, imaging, catalysis, lubrication, and extraction. While block copolymers generally adopt the morphologies familiar in small molecule surfactants and lipids, one key difference is that polymeric micelles are typically not at equilibrium.1 The primary reason is the large number of repeat units in the less soluble block, Ncore, which often makes the critical micelle concentration (CMC) too small to accessed experimentally; however, in the proximity of a critical micelle temperature (CMT), equilibration is possible. When micelles are significantly larger than the equilibrium size, fragmentation mechanisms become operative. We will describe measurements of fragmentation using dynamic light scattering, small-angle X-ray scattering, and liquid-phase TEM, on a series of polybutadiene-b-polyethylene oxide diblocks in ionic liquids.2 Micelles larger than the equilibrium size are prepared by a direct dissolution protocol; the distance to equilibrium can also be systematically tuned by changing the solvent after formation. The dependence of the fragmentation rate on molecular weight, interfacial tension, and distance to equilibrium, will all be described.
References
Olga Speck, Self-sealing and Self-healing in Plants – Suitable Models for Biomimetic Solutions? Faculty of Biology and Cluster of Excellence livMatS, Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Freiburg, Germany.
In the course of biological evolution, plants have developed an amazing ability to cope with internal and external injuries. Since the evolutionary pressure for the development of self-repairing functions is expected to be high, independent evolution of self-repairing mechanisms can be expected in different lineages of plants. This explains the large number of different “solutions” in living organisms to deal with damage.1
In recent years, the functional principles found in nature have proven to be a treasure trove for bio-inspired and biomimetic self-repairing materials.2,3 However, it has been shown that a mere copy of the biological model does not lead to a satisfactory technical result. Rather, the abstraction process plays a central role in the development of a technical application within the framework of a step-by-step biomimetic approach.4,5
We conducted comparative morphological, anatomical and mechanical studies on succulent cylindrical plant organs of species belonging to different phylogenetic lineages and observed one or more of the following wound reactions, depending on the body plan of the plant and the duration and conditions of the tests [1]. Immediately after injury, primarily injury-induced physical responses occur that cause rapid self-sealing, including (1) tissue deformation in the injured region, resulting in wound closure, and (2) discharge of mucilage or latex, resulting in wound coating. During the subsequent self-healing phase, chemical reactions and more complex biological responses dominate (3) coagulation of the latex, (4) formation of a ligno-suberized boundary layer, and (5) development of a wound periderm, all of which contribute to at least partial restoration of anatomical structures and mechanical properties.
Since self-repair is a fundamental function of longevity, it can be assumed that it is secured by redundant mechanisms.6 In fact, our results indicate that the underlying principles complement and support each other.4,5 This is particularly interesting for transferring functional principles to technical products. The possibilities and limits of transferring self-sealing and self-healing functions from plant models to technical applications are presented and critically discussed based on several examples.
References
J. Lahann, Stimuli-responsive Materials Based on Compartmentalization, University of Michigan, USA.
Compartmentalized particles and fibers are uniquely suited to combine synergetic sets of properties. The ability to co-locate materials with orthogonal properties within close proximity enables chemical synergy and opens a broad design space for engineering multifunctional materials. Electrohydrodynamic co-jetting is a simple, scalable, yet flexible fabrication method that can lead to multicompartmental particles. Using a biomimetic approach, we have designed actively responding microparticles that sense changes in their local chemical environment or respond in the form of bending movement. A range of microactuators as well as other examples of responsive materials that are enabled by compartmentalization, will be discussed in this presentation.
Austin M. Evans, Thermal Electrochemical Transistors, A Thought Experiment, University of Florida, USA.
Thermal transport is a ubiquitous phenomenon with wide-reaching real-world relevance. Developing next-generation microelectronics, energy storage devices, and extreme-environment materials requires new multifunctional thermal insulators and conductors. A prevailing belief that polymeric materials are inherently thermally insulating (thermal conductivities of 0.1 – 0.3 W m-1 K-1) has disincentivized the exploration of these versatile synthetic materials in thermal management. I will show recently obtained evidence that challenges the paradigm that polymers are thermally insulating. The inherent stimuli responsivity of polymers also provides opportunities to create switchable thermal conductivities. I will show recent work using electrolytic reactions can drive this responsivity. I will conclude with a thought experiment on how these seemingly disparate results reveal a path forward for a thermal conductivity transistor based on electrochemistry.
Dale L. Huber, Programming Complex Phase Behaviors with Stimuli Responsive Surfactants, Sandia National Labs, Albuquerque, USA.
There is a vast literature of thermally responsive materials, particularly hydrogels and other polymeric materials. There is, however, a surprisingly limited number of reports of small-molecule thermally responsive surfactants, though these materials can be extremely easy to synthesize. This is likely due to the difficulty in designing small-molecule surfactants with useful and controllable temperature-dependent properties. The design of these surfactants to perform useful functions will be discussed and will include atomistic and mean-field simulations as well as experiments to optimize properties and ease synthesis. Tunable properties include thermal control of surface tension, liposome and vesicle stability, thermal dissolution of micelles, and related phenomena. These thermally responsive small molecules can be used themselves or paired with other non-responsive and responsive materials in applications that include separations, drug and vaccine delivery, wound care, and many others.
Srinivasa R. Raghavan, Switching on the Adhesion of Hydrogels to Tissues by an Electric Field, Department of Chemical & Biomolecular Engineering, University of Maryland, College Park, USA.
We demonstrate electroadhesion, i.e., adhesion induced by an electric field, between cationic hydrogels and animal tissues.1,2 When gel and tissue are placed under an electric field (DC, 10 V) for 20 s, the pair strongly adhere, and the adhesion persists indefinitely thereafter. Applying the DC field with reversed polarity reverses the adhesion. Electroadhesion works with tissues of many mammals (cow, pig, chicken, and mouse), and is especially strong in the case of the aorta, cornea, lung, and cartilage. Only cationic gels can be electroadhered to tissues, which suggests that the tissues have anionic character. We then show the use of electroadhesion to seal cuts or tears in tissues or model anionic gels. Electroadhered gel-patches provide a robust seal over openings in bovine aorta. Moreover, a gel sleeve is able to rejoin pieces of a severed tube (this is the equivalent of a surgery called an anastomosis). These studies raise the possibility of using electroadhesion in surgery while obviating the need for sutures or staples.1,3 Advantages include the ability to achieve adhesion on command and, moreover, the ability to reverse this adhesion in case of error.
References
Olga Kuksenok, Multiscale Modeling of Responsive Polymer Networks: Focus on Photo-Controlled Degradation and Patterns Restructuring, Department of Materials Science, Clemson University, Clemson, USA.
Understanding and controlling degradation of polymer networks is critical for a broad range of applications. Degradation that can be controlled by external stimuli, for example photo-controlled degradation, permits spatially-resolved dynamic control of material properties, in particular mechanical properties of hydrogel-based materials. In the first part of my talk, I will introduce our recently developed dissipative particle dynamics (DPD) approach that captures degradation and erosion of polymer networks on the mesoscale. To overcome topological crossings of bonded polymer chains, we utilize a modified Segmental Repulsive Potential (mSRP) formulation. We focus on hydrogels formed by the end-linking of multi-arm polyethylene glycol precursors. We track the degradation via measuring the fraction of degradable bonds intact and spatial distributions of network fragments. Peak in reduced weight average degree of polymerization allows us to identify the reverse gel point. We demonstrate that the dispersity and the fraction of broken-off fragments scales with the relative extent of degradation, which in turn identifies proximity to the reverse gel point. We also characterize dynamical heterogeneity during degradation and variations in network elasticity as degradation proceeds. Our results allow one to predict mechanical properties of degrading networks. In addition, we recently extended the above mesoscale framework to model random scission in polyolefin melts.
In the second part of my talk, I will focus on dynamic control of pattern formation and restructuring in hydrogels with host-guest interactions. Pattern formation under external stresses plays an important role in defining functionality of a broad range of soft confined systems. We recently extended the three-dimensional gel Lattice Spring Model (gLSM) to capture the dynamics of the PNIPAAm hydrogels with pendant azobenzene moieties immersed into alpha-cyclodextrins (alpha-CD) solutions in the continuum limit. While trans-azobenzene moieties are recognized and accommodated by the alpha-CD cavities to form inclusion complexes, an exposure to UV light drives the trans-to-cis photoisomerization and dissociation of the complexes. We use spaciotemporal variations in UV irradiation to control pattern formation in thin hydrogel films under the rigid and soft confinements and to control hysteresis loops. The above examples of modeling stimuli-responsive networks could provide guidelines for the future design of materials with dynamically controlled properties and functionalities.
Ryan C. Hayward, Photomechanical Materials Based on Semicrystalline Polymers and Polymer/Crystal Composites, University of Colorado, Boulder, USA.
Materials capable of directly converting photon energy into mechanical deformation offer promise in a wide variety of contexts including adaptive optics, remotely operated swimmers, and actuators controlled via lightweight optical cables that resist corrosion and electromagnetic interference. Organic photoswitches offer significant potential in this regard, thanks to their ability to undergo large changes in molecular geometry following photochemical reactions, and their highly tailorable absorption spectra. To date, efforts have largely involved either crystalline lattices of small photomechanical molecules, which offer the possibility for greater work output due to their high density and well-organized nature, or on polymer matrices containing a modest concentration of photochromes, which generally have superior processability and mechanical properties. We have recently focused on developing hybrid materials that combine the advantages of these disparate approaches. In one case, we focus on semicrystalline polymers built from photoisomerizable units. While initial efforts suffered from both inefficient switching at ambient temperature and limited penetration of light, we have recently studied higher mobility chain extenders and modified photochromes that enable efficient room-temperature switching and deep penetration. In a second, we have studied the growth of micrometer-scale photomechanical diarylethene crystals within the pores of polymer membranes. By nearly matching the mechanical stiffness of the crystals, and biaxially controlling their orientation in a desirable way, such materials exhibit photomechanical work outputs surpassing the best previously reported systems, while enabling facile processing into mechanically robust samples with cm-scale lateral dimensions.
Krzysztof Matyjaszewski, Photochemical Control in ATRP, Carnegie Mellon University, Center for Macromolecular Engineering, Pittsburgh, USA.
Atom transfer radical polymerization (ATRP) was successfully controlled and fine-tuned by various stimuli. Air-tolerant ATRP systems were developed in the presence of green, red and NIR light. It was applied to preparation of new (bio)hybrid materials.
C. Adrian Figg, Jared G. Baker, Richard Zhang, Precisely Placing Functional Groups in Acrylic Polymers Using Photoredox Chemistry, Department of Chemistry and Macromolecules Innovation Institute, Virginia Tech, Blacksburg, USA.
Light-mediated redox reactions provide access to distinct initiation mechanisms of thiocarbonylthio-mediated reversible addition-fragmentation chain transfer (RAFT) polymerizations. This activation-deactivation mechanism enables conventional monomer limitations of RAFT polymerization to be overcome. Herein, the precise placement of a single monomer will be discussed where the photoinduced electron/energy transfer (PET) reaction is critical to achieving insertion of exactly one vinyl ether. These copolymers will be used as responsive materials where that single vinyl ether functionality elicits a macromolecular change upon introduction of a stimulus.
Christopher M. Bates, Dynamic Bottlebrush Elastomers, Materials Department, Materials Research Laboratory, University of California, Santa Barbara, USA.
Bottlebrush elastomers have attracted considerable attention as a class of super-soft and solvent-free materials. This talk will discuss the synthesis and characterization of dynamic bottlebrush elastomers with tunable stimuli-responsive properties for applications ranging from flexible electronics to 3D printing.
Garret M. Miyake, Chemically Recyclable Polyolefin-Like Multiblock Polymers, Department of Chemistry, Colorado State University, Fort Collins, USA.
Polyolefins are the most important and largest volume plastics produced. Unfortunately, the enormous use of plastics and lack of effective disposal or recycling options have created a plastic waste catastrophe. Here, we report an approach to create chemically recyclable polyolefin-like materials with diverse mechanical properties through the construction of multiblock polymers from hard and soft oligomeric building blocks synthesized using ruthenium-mediated ring-opening metathesis polymerization of cyclooctenes. The multiblock polymers exhibit broad mechanical properties, spanning elastomers to plastomers to thermoplastics, while integrating a high melting transition temperature (Tm) and low glass transition temperature (Tg) making them suitable for use across diverse applications (Tm as high as 128 °C and Tg as low as -60 °C). After use, the different plastics can be combined and efficiently deconstructed back to the fundamental hard and soft building blocks for separation and repolymerization to realize a closed-loop recycling process.
Thomas H. Epps, III, Advanced Recycling – Understanding Fundamentals to Valorize Plastics Waste, Department of Chemical & Biomolecular Engineering; Department of Materials Science & Engineering; Center for Research in Soft Matter & Polymers, University of Delaware, Newark, USA.
Approaches that valorize plastics waste have continued to emerge over recent years. One common strategy is deconstruction/depolymerization, whereby polymers are degraded into smaller molecules by various reaction pathways. The dynamics of these complex systems of molecules, with evolving molecular weights and molecular weight distributions that span the range from monomer up to commodity polymer, are a strong function of process technology. Hence, efficient development of plastics deconstruction technologies will benefit from simple and descriptive models that link process parameters to physical properties and product distributions. We have applied these models and learnings to both biobased and petroleum-based macromolecules. For example, we have recently achieved the chemical recycling and upcycling of two higher-glass-transition temperature (> 100 °C), lignin-derivable polymethacrylates, poly(syringyl methacrylate) (PSM) and poly(guaiacyl methacrylate) (PGM). Neat PSM and PGM were thermally depolymerized to quantitative conversions, producing their constituent monomers at high yields and purity in both N2 and air. We were able to scale these analytical insights to the bulk depolymerization of free-radically polymerized PGM and PSM under dynamic vacuum without solvent or catalyst to high polymer conversions (89-90 wt.%) and monomer yields (86-90 mol%) without byproduct formation. The resultant monomers were then upcycled without further purification to narrow-dispersity polymers and phase-separated block polymers via controlled polymerization. Additionally, we have made similar progress in heteroatom-containing, petroleum-based feedstocks demonstrating the ability to chemically depolymerize both thermoplastics and thermosets back to monomers that can be repolymerized to generate upgraded polymeric materials. Overall, these studies offer new pathways to ‘closing the loop’ on the life cycle for higher-performance polymer systems.
Ying Yang, Entropically Driven Ring-Opening Polymerization for Circular Polymer Economy, Department of Chemistry, University of Nevada at Reno, Reno, USA.
The world is drowning in plastics. A viable solution is to design polymers that can be depolymerized into their monomers, which can then be repolymerized to produce the same polymer products, creating a circular economy. The polymer system needs to be near its thermodynamic equilibrium to achieve the depolymerizability. A commonly used approach is reversible ring-opening polymerization (ROP). Cyclic monomers and their corresponding polymers have the same types of bonding so that thermodynamics can be tuned by the ring-strain energy. This presentation will highlight our recent findings on polydithioacetals that are capable of reversible entropy-driven ring-opening polymerization (ED-ROP) and ring-closing depolymerization (RCD) as a versatile platform for the development of recyclable polymers, as well as dynamic covalent systems. The dynamics are enabled by acid-catalyzed dithioacetal exchanges. A range of thermal and mechanical properties can be obtained via copolymerization. The syntheses of polydithioacetals, thermodynamics and kinetics of the ROP and RCD reactions, as well as the advantages and challenges of ED-ROP for the development of sustainable polymers will be discussed.
Michael Serpe, Sensing, Biosensing, and Drug Delivery with Responsive Microgels, University of Alberta, Edmonton, Canada.
Utilizing poly (N-isopropylacrylamide) (pNIPAm)-based microgels, our group has developed novel technologies for solving environmental and health-related problems. PNIPAm-based microgels are fully water soluble and swellable at T < 32 °C. Additionally, pNIPAm-based microgels are well known to be responsive to temperature, shrinking in diameter (and expelling water) at T >32 °C; the temperature triggered response is fully reversible over many cycles. While our group has exploited these properties for numerous applications, today’s talk will highlight recent work on the development of these devices for sensing, biosensing, and controlled/triggered drug delivery.
Megan R. Hill, Temperature-Responsive Poly(Lewis Pairs), Colorado State University, USA.
The functionalization of polymers with Lewis acidic boron sites has led to materials with diverse applications from polymer catalysts to sensors due to the favorable interactions between nucleophiles and the Lewis acidic sites. This seminar describes the synthesis of polyboranes through hydroboration reactions and their temperature-responsive behaviors. We demonstrate how modifying dative bond interactions between the polyboranes and nucleophiles enables tuning of our resulting material properties. Furthermore, we demonstrate that hydroboration/retrohydroboration reactions can be used to transform unsaturated polymers into electronically-conductive polymers through isomerization of the backbone double bonds. The future directions and interests of the Hill group will lastly be presented.
Dirk Kuckling, Dually Cross-linked Stimuli-sensitive Gels, Department of Chemistry, Paderborn University, Paderborn, Germany.
In the last few years, particular attention has been focused on stimuli-responsive polymers. This group of materials is of interest due to their ability to respond to internal and/or external chemico-physical stimuli that is often manifested by large macroscopic responses. To increase the scope of such hydrogels a novel dual cross-linking system combining photo cross-linkable covalent bonding with special molecular recognitions sites was introduced. When the noncovalent bond is broken or formed, the polymer gel’s swelling ratio will change significantly. A new dually cross-linked supramolecular hydrogel (DCSH) was developed by introducing a photo cross-linker for permanent crosslinking and β-cyclodextrin (β-CD) and ferrocene (Fc) as host-guest recognition pair. The DCSH showed responsive behaviors e.g. towards the target small molecule adamantane amine (Ada). Ada can break the non-covalent bonding between β-CD and Fc through competitive molecular guest interaction with β-CD. A reversible sensor was developed for specific small molecule detection of Ada by using a combination of surface plasmon resonance and optical waveguide spectroscopy. The DCSH is further used as a SPR biosensor for cancer biomarker detection.
Jianguo Mei, From Lab to Fab: Roll-to-roll Processed Large-area Electrochromic Windows, Department of Chemistry, Purdue University, West Lafayette, USA.
The concept of organic electronics emerged in the late 1980s. The promise of solution-processing, mechanical flexibility, lightweight, and low cost has driven the development of organic semiconductors and electronics. Three decades of continuous efforts from the community have nurtured the technological maturity of a number of organic electronics. Part of my research group has been actively pursuing the development of polymer-based electrochromic technology. In this talk, I will share our journey of moving electrochromic technology from lab to fab. In particular, I will introduce our latest development on highly conductive transparent organic conductors (TOCs), ultra-high contrast transparent-to-colored electrochromic polymers and chiroptical electrochromic polymers.
Thomas Speck, Plant-inspired Soft Robots and Soft Machines for Engineering, Architecture and Medicine Based on Stimuli-Responsive Materials Systems, Botanic Garden and Cluster of Excellence Living, Adaptive and Energy-autonomous Materials Systems (livMatS), University of Freiburg, Freiburg, Germany.
Today, biomimetics is attracting increasing attention in basic and applied research, as well as in various fields of industry and construction. Biomimetics has a high innovation potential and offers opportunities for developing sustainable technical products and production chains. Novel, sophisticated methods for analyzing and simulating the form-structure-function relationship on different hierarchical levels allow fascinating new insights into the multiscale mechanics and other functions of biological material systems. In addition, for the first time, new production methods allow many of the outstanding properties of biological models to be transferred into innovative biomimetic products at a reasonable cost.
In recent decades, plants have been recognized as valuable concept generators for biomimetic research and development in many application areas of engineering, architecture and medicine, including static and moving structures and systems. Plant-inspired developments in the field of soft machines and soft robotics are demonstrated by research projects currently being carried out in the livMatS Cluster of Excellence and the Plant Biomechanics Group Freiburg. Examples include liana-inspired soft robots, façade shading systems inspired by leaves and flowers, demonstrators for self-adaptive building shells inspired by pine cones, and artificial Venus fly traps. As an example of a medical application, a prototype of an adaptive wrist-forearm splint is presented. This and all examples of architectural applications have been developed in collaboration with the ICD Cluster of Excellence at the University of Stuttgart. A particular focus of current research is the embodied energy and physical intelligence found in moving plant organs, which offer huge potential for a new generation of material systems for soft robots, bio-inspired architecture and engineering applications in general.
References
T. Speck, T. Cheng, F. Klimm, A. Menges, S. Poppinga, O. Speck, Y. Tahouni, F. Tauber, M. Thielen, MRS Bulletin, 2023, 48, 1-16.
M. Farhan, F. Klimm, M. Thielen, A. Rešetič, A. Bastola, M. Behl, T. Speck, A. Lendlein, Adv. Mat., 2023, 35, 2211902
F. Klimm, T. Speck, M. Thielen, Adv. Sci., 2023, 26, 2301496.
F.J. Tauber, F. Scheckenbach, M. Walter, T. Pretsch, T. Speck, In Biomimetic and Biohybrid Systems, 12th International Conference, Living Machines 2023, Proceedings, Part I, 91–108. Lecture Notes in Artificial Intelligence LNAI/LNSC 14157. Springer Nature, Cham.
C.J. Eger, M. Horstmann, S. Poppinga, R. Sachse, R. Thierer, N. Nestle, B. Bruchmann, T. Speck, M. Bischoff, J. Rühe, Adv. Sci., 2022, 9(22), 2200458.
B. Mazzolai, A. Mondini, E. Del Dottore, L. Margheri, F. Carpi, K. Suzumori, M. Cianchetti, T. Speck …… , F.C. Simmel, A. Lendlein, Multifunct. Mater., 2022, 5(3), 032001
T. Cheng, Y. Tahouni, D. Wood, M. Thielen, S. Poppinga, L. Buchholz, T. Steinberg, A. Menges, T. Speck, Adv. Sci., 2021, 8(13): 2100411.
Y. Tahouni, F. Krüger, S. Poppinga, D. Wood, M. Pfaff, J. Rühe, T. Speck, A. Menges, Bioinspir. Biomim., 2021, 16: 055002.
F.J. Esser, P. Auth, T. Speck, Front. Robot. AI, 2020, 7, 75.
J. Knippers, U. Schmid, T. Speck (eds.), Biomimetics for Architecture: Learning from Nature, 208 pp. Birkhäuser Verlag, 2019, Basel.
S. Poppinga, C. Zollfrank, O. Prucker, J. Rühe, A. Menges, T. Cheng, T. Speck, Adv. Mat., 2018, 30 (19), 1703653.
Fabio Cicoira, Self-Healing, Stretchable and Recyclable Electronics, Department of Chemical Engineering, Polytechnique Montreal, Montreal, Canada.
The ability of certain materials to regenerate after damage has attracted a great deal of attention since the ancient times. For instance, self-healing concretes, able to resist earthquakes, aging, weather, and seawater have been known since the times of ancient Rome and are still the object of research.
While the field of mechanically healable materials is relatively established, self-healing conductors are still rare, and are nowadays attracting enormous interest for applications in electronic skin for health monitoring, wearable and stretchable sensors, actuators, transistors, energy harvesting, and storage devices, such as batteries and supercapacitors. Self-healing can significantly enhance the lifetime of conducting materials, leading to the improved environmental sustainability and reduced costs.
Conducting polymers exhibit attractive properties, such as mixed ionic-electronic conductivity, leading to low interfacial impedance, tunability by chemical synthesis, ease of process via solution process and printing, and biomechanical compatibility with living tissues, which makes them ideal materials for bioelectronics and stretchable electronics. However, they show typically poor mechanical properties and are therefore not suitable as self-healing materials. Self-healing conductors can be achieved upon mixing with other polymers, such as poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG) and polyurethane (PU), which provide the mechanical characteristics leading to self-healing.
Self-healable and recyclable conducting materials are central in the field of electronics due to their potential to address two major challenges: sustainability and durability. Electronic waste is a growing concern worldwide, as the rapid pace of technological innovation has led to a high turnover rate of electronic devices, accumulating a significant amount of electronic waste. Self-healable and recyclable conducting composites have the potential to reduce electronic waste by enabling the repair and reuse of electronic components, which can extend the lifespan of electronic devices. Furthermore, electronic devices are often subject to mechanical stress, which can cause damage to their components, including conducting materials.
My talk will deal with self-healing materials obtained blending PEDOT:PSS with other materials, such as polyethylene glycol (PEG), tannic acid and polyurethane. Various self-healing modes will be presented and correlated with the electrical and mechanical properties of the materials. The use of the self-healing gels and films as epidermal electrodes will be also presented.1-8 We will finally discuss rechyclable conducting composites based on PEDOT:PSS-PU blends.
References
Shape memory polymers (SMPs) have shown great potential in areas such as wearable electronics, implantable biomedical devices, and soft robotics, but most SMPs suffer from low energy densities, which limits the load that can be overcome during actuation. Recent work has shown that incorporating periodic dynamic bonds can enable high energy density SMPs by forming stable supramolecular structures under strain. In this work, we show that modifying the polymer molecular design by incorporating weaker H-bonding units allows one to tune the SMP actuation temperature (from 60 to 25 °C) while maintaining high energy density (almost 80% of the original polymer). We comprehensively characterize the SMPs’ performance under various actuation loads and temperatures, highlighting the differences between experimentally measured and ideal behavior. In addition, we show that the modified polymers can be self-healed at accessible temperatures. By combining this high energy density shape memory behavior with traditional self-healing properties, we realize rapid and complete healing of large, macroscopic damages (e.g., knife punctures), which are unable to heal in samples without shape memory behavior. We demonstrate the practical applications of our SMP by fabricating a force sensor that exhibits self-healing ability, high cyclability, and high sensitivity. Our work highlights the high energy density and tunability of SMPs with periodic dynamic bonds and opens up new possibilities for fabricating smart wearable devices with superior performance and durability.
102. Fluorescent molecular rotors (FMRs) of organoboron derived from Schiff bases and their multi-stimuli responsive, Marisol Ibarra-Rodríguez, Blanca M. Muñoz-Flores, and Víctor M. Jiménez-Pérez.* Universidad Autónoma de Nuevo León, Facultad de Ciencias Químicas, Ciudad Universitaria, 66451 Nuevo León, México; corresponding author: victor.jimenezpr@uanl.edu.mx
A short series of binuclear fluorescent Boron Schiff bases (BOSCHIBAs), namely bis(1-B)Ph (5), bis(2-B)Ph (6), bis(3-B)Ph (7), and bis(4-B)Ph (8), has been synthesized, and the effects of temperature, pH, viscosity, and pressure on their fluorescence have been investigated. Compound 6 presents a high response to various stimuli: it shows an 18-fold increase in fluorescence quantum yield with the increase in viscosity of the medium due to the restricted rotation at 90% glycerol. Under basic conditions of pH, the boron compound 6 exhibits poor emission intensities, but when the pH value is adjusted slightly below neutral pH, the fluorescence peak experiences a hypsochromic shift from 421 to 400 nm.
In the solid state, the compound was exposed to compression at 8t (t: metric tons), resulting in a change in colour from yellow to dark yellow, and a gradual loss of its fluorescence property. This binuclear compound exhibits the property of reversible thermochromism. Compounds 5-8 have also been investigated using DFT (Density Functional Theory). Computational work shows that the compound 6 has free rotation about the carbon-boron bond.
The growing interest in virtual and augmented reality has raised the importance of haptic devices to provide realistic sensations to the users. Dielectric elastomer actuators (DEA) are one of the promising candidates for haptics due to their lightweight, stretchability and conformability to human skin. To achieve a large actuation strain, DEA requires a compliant electrode with low modulus and high electrical conductivity. While carbon grease has been commonly used as a compliant electrode, there has been a lack of extensive research in the development of a compliant solid electrode that can attain a similar actuation as its non-solid counterpart. In this study, we developed transparent and patternable solid electrode that can achieve a comparable actuation performance to a non-solid counterpart (e.g. carbon grease) by incorporating PEDOT:PSS and diacrylate surfactant. Mixing different ratios of PEDOT:PSS and diacrylate surfactant, its electrical and mechanical properties can be optimized to achieve a complaint solid electrode. Moreover, the PEDOT:PSS based solid electrode showed excellent transmittance over 95%. We also investigated the morphologies of electrodes with different ratios to understand how the ratio of PEDOT:PSS and diacrylate surfactant affects the fiber formation and their corresponding electrical and mechanical properties. This work highlights the importance of tunning electrical and mechanical properties of solid electrodes to achieve the transparent, patternable, compliant solid electrodes for applications in haptics and soft robotics.
We report reprocessable and shape-memory bio-based vitrimers with controlled architecture to develop more sustainable polymers with enhanced creep resistance. Three different prepolymers of vanillin methacrylate (VMA), and a mixture of methacrylic esters with an average alkyl side chain length of 13 units (C13MA) were synthesized: 1) poly(C13MA-co-VMA), 2) poly(C13MA-b-VMA), 3) poly(C13MA-co-VMA-co-GMA) with ~74% bio-based carbon. RAFT polymerization allowed control over backbone architectures of statistical or block copolymers with similar Mn of ~35,000 g/mol and molar composition (FVMA = 17%). Vitrification occurred by the reaction of aldehyde (from VMA) and isophorone diamine (IPDA) to form dynamic imine (Schiff base) cross-linking bonds. The epoxy-based precursor (FGMA = 2%) exhibited a hybrid static-dynamic cross-linking network confirmed by FTIR. Statistical vitrimers showed excellent retention of thermomechanical and chemical properties after 4x cycles of reprocessing. Microphase separation was confirmed in block copolymer based vitrimers using AFM, DSC (via identification of 2 Tgs of -44˚C and +186˚C) and DMTA. Interestingly, while statistical vitrimers had comparable tensile properties, with 3.5 MPa and 40% stress and elongation at break, the block vitrimer had poor tensile strength, with stress and strain at break of 0.99 MPa and 5.3 %, respectively. Compared to the statistical vitrimers made with prepolymer (1), hybrid cross-linking and block copolymer vitrimer could effectively suppress creep, up to 84%. Shape memory was successfully incorporated in to the statistical vitrimer via prepolymer (1). Reprocessed vitrimers were used and at least 2 programming cycles of shape fixing, deformation and recovery were shown. We illustrate that C13MA/VMA copolymers can be used as a platform for more sustainable thermosets with high tunability of properties and stimuli-responsive functionalities.
The fluorescence imaging technologies are becoming the most powerful and noninvasive diagnostic tools in cellular biology and the modern medicine where abnormal cell arrangements are associated with diseases. Thus, these techniques require new fluorescent dyes with excellent chemical, physical and photophysical properties. A new series of four boron Schiff bases has been prepared by condensation between phenylboronic acid with the corresponding ligand. The organoboron complexes were characterized by NMR (1H, 13C, and 11B), UV/vis, fluorescence spectroscopy, and high-resolution mass spectrometry. The crystal structures of three compounds showed tetracoordinated boron atoms with semiplanar skeleton ligands. Interesting organoboron response to viscosity on their fluorescence. Additionally, boron compounds 1 and 2 were found to serve as a fluorescent dye for cell imaging (B16F10, CaCo, and A-431 cells) since it has the capability to rapidly accumulate within the cells and gave bright green fluorescence, it showed low cytotoxicity activity and high photostability. Additionally, the boron compounds have also been investigated using DFT.
The emerging chemistry of dynamic polymer networks is enabling a new generation of soft, smart and re-processable materials for various applications. These dynamic systems are characterized by their ability to adapt and reconfigure network topology in response to external stimuli, which is important for designing materials and processes for targeted applications in soft electronics, robotics, and biomedical devices. To fully realize their potential, it is important to understand how these dynamic interactions at the molecular scale give rise to bulk properties like viscoelasticity, toughness, and self-healing behavior. In recent years, the Bao group has investigated the impact of various periodic non-covalent bonding mechanisms (e.g., metal-ligand coordination (ML) and hydrogen bonding (HB)), primarily using poly(dimethylsiloxane) (PDMS)-based flexible polymer backbones. For ML coordination chemistry, the overall group findings have demonstrated that (1) the kinetic lability of Zn(II) metal leads to reversable octahedral and tetrahedral conformations, (2) embedding multi-metal salt mixtures into polymer matrix results in improved stretchability and self-healing efficacy, (3) decreasing coordination strength and mixing various types of counter anions also exhibited an increase in toughness and dynamicity of polymer matrix. Nevertheless, this chemistry presents several challenges related to reversibility rate, the trade-off between toughness and stretchability, biocompatibility, and dependence on external stimuli. In contrast, HB moieties embedded within elastomers show promise in addressing these challenges. An important discovery within the group showed that introducing HB interactions of mixed strength into PDMS-based elastomers results in materials with enhanced stretchability, toughness, notch-insensitivity, biocompatibility, and even the ability to heal from damage underwater. This approach offers a promising alternative to address the limitations associated with ML coordination. Current research efforts focus on integrating these periodic dynamic moieties into other polymer backbones and investigating their bulk and interfacial properties. The latest breakthrough within the group demonstrates the design of a pair of polymers with immiscible backbones but the same periodic dynamic bonding motif and similar viscoelastic behavior, leading to excellent adhesion between the immiscible phases, and also autonomous alignment and self-healing capabilities within a multilayered system. In conclusion, the increasing complexity of medical and energy devices has driven the demand for adaptable and multifunctional materials. Periodic dynamic polymers, with their chemical tuneability, offer a solution that enables self-healing elastomers with useful properties and the seamless integration of multiple layers with distinct functionality.