Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G32: Responsive Polymers, Soft Materials, and Hybrids IIIFocus
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Sponsoring Units: DPOLY DSOFT DBIO Chair: Jinhye Bae, University of California, San Diego Room: 504 |
Tuesday, March 3, 2020 11:15AM - 11:27AM |
G32.00001: Ordering hard-sphere particle suspensions by medium crystallization: Effect of size and interaction strength Vianney Gimenez-Pinto While microstructure in soft materials is usually given by the self-assembly of their constituting building blocks, colloidal assembly can also be obtained via templating a morphology in a disordered suspension of particles by solidification of the melt. This sweep-templating process is applicable in different soft matter systems with a variety of characteristic length scales, including particle suspensions in water, liquid crystal materials, and polymer melts. Here, I numerically investigate the effect of particle-size and solvent-size in the process of solidification templating by implementing a simple coarse-grain model for the kinetics of hard-sphere particles at the melt/crystal interface. Results show that the threshold speed for solidification templating trails a power-form as size changes. Furthermore, this work analyzes and reports the effect of particle-crystal interaction strength in combination with size effects. This scaling study from a numerical perspective sets a starting point for the development of hybrid soft materials via structural templating, allowing solidification-driven particle ordering in different systems with length-scales that range from a few tens of nanometers to microns and centimeters. |
Tuesday, March 3, 2020 11:27AM - 11:39AM |
G32.00002: Exploring Solution Behavior of Fully Rigid “Block Copolymers” with Sphere-Rod Molecular Architecture JIANCHENG LUO, Tong Liu, Stephen Cheng, Tianbo Liu The rich solution behavior of block copolymers, especially self-assembly of amphiphilic block copolymers in solution, have been extensively explored in past decades. While the traditional block copolymers often involve flexible chains, some novel “copolymers” containing rigid components might also demonstrate interesting self-assembly behavior. Here, we explore solution behavior of fully rigid“block copolymers”hybrid macromolecules based on spherical polyoxometalates and rod-like oligofluorenes. We report here that rigid macromolecules can achieve continuous curvature change and consequently form unexcepted multilayer vesicular structures. The highly uniform, multilayered vesicles have complete onion-like structure from most inner to outer layers with fixed interlayer distance, and the vesicle size/layer number can be accurately controlled by solution conditions including temperature, solvent composition, and salt concentration. Additionally, reversible response of vesicle size/layer number is observed by simplify changing the solution temperature. The effects of rod length and molecular architecture will also be discussed. |
Tuesday, March 3, 2020 11:39AM - 11:51AM |
G32.00003: Stimuli-responsive phase behavior of block copolymers in ionic liquids Claire Seitzinger, Cecilia C Hall, Timothy Lodge Block copolymers microphase separate into well-defined ordered morphologies as a function of temperature and composition. However, not all applications are amenable to changes in temperature or composition, but still require transitions between disorder and order, or between different ordered symmetries. We explore the light-mediated phase behavior of a diblock copolymer, poly(methyl methacrylate)-b-poly(benzyl methacrylate-s-4-phenylazophenyl methacrylate), in a selective ionic liquid solvent, 1-alkyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide. By adjusting the length of the alkyl chain on the imidazolium group, we can control the phase transition temperatures (order-disorder and order-order transitions). In this system, the solubility of the 4-phenylazophenyl methacrylate-containing block in the ionic liquid is altered by irradiation with UV light. The phase behavior is monitored by small amplitude oscillatory shear rheology under either UV or visible light, and the ordered phases identified by small angle X-ray scattering. Understanding the phase behavior of this model system allows us to work towards inducing morphology changes in a contactless manner. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G32.00004: Exploring the Limits of Actuation Force Output of Stretch-based Deformation of Liquid Crystalline Elastomers JOSELLE MCCRACKEN, Kelsey M Lynch, Timothy J White Liquid crystal elastomer (LCE) films are amenable to surface-enforced alignment.[1] Physical limits of surface-enforced alignment constrain the thickness of LCEs aligned by this approach to a maximum of 50 µm.[2] The force output of stretch-based deformation of topologically patterned LCEs is enhanced with thickness, which we have previously accessed using a lamination approach for actuator fabrication.[3] This contribution details our exploration of the boundaries of achieving high force actuation from these soft materials. We describe several facile approaches for accessing thick LCE actuators (>30x a standard film), including the preparation of devices with interlaid compliant electrodes that allow rapid electrothermal deformation in the multi-laminate LCEs. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G32.00005: Electro-responsive Ionic Liquid Crystal Elastomers Chenrun Feng, Chathuranga Prageeth Rajapaksha, Vikash Kaphle, Bjorn Lussem, Thein Kyu, Antal Istvan Jakli We will describe the preparation, physical properties and electric bending actuation of a new class of active materials - ionic liquid crystal elastomers (iLCEs). It is demonstrated that iLCEs can be actuated by low frequency AC or DC voltages of less than 1 V. The bending strains of the not optimized first iLCEs are already comparable to the well-developed ionic electroactive polymers (iEAPs). Additionally, iLCEs exhibit several novel and superior features, such as the alignment that increases the performance of actuation, the possibility of pre-programed actuation pattern at the level of cross-linking process, and dual (thermal and electric) actuations in hybrid samples. Since liquid crystal elastomers are also sensitive to magnetic fields, and can also be light sensitive, iLCEs have far-reaching potentials toward multi-responsive actuations that may have so far unmatched properties in soft robotics, sensing and biomedical applications. |
Tuesday, March 3, 2020 12:15PM - 12:27PM |
G32.00006: Voltage-induced deformation in soft dielectric elastomers Abhishek Ghosh, Sumit Basu Keywords: Soft dielectric, electro-elasticity, non-linear finite element, instability |
Tuesday, March 3, 2020 12:27PM - 1:03PM |
G32.00007: Tough, Responsive and Soft Biomaterials for Tissue Repair and Regeneration Invited Speaker: Jianyu Li Biomaterials find wide use in many branches of medicine and engineering. Success examples are hard biomaterials like titanium used in dentistry and prosthetics. Soft biomaterials, however, haven’t replicated these successes in repairing soft tissues. The reason is simple yet fundamental: existing soft biomaterials cannot match or integrate with soft tissues mechanically; they are often vulnerable to rupture and difficult to adhere on soft tissues, especially when interfacing with dynamic tissues such as skin and beating heart; their functionality is passive and limited. This talk will present new strategies and material systems to overcome these material constraints. A series of bioinspired hydrogel adhesives will be presented. One can be tougher than articular cartilage and achieve unprecedented adhesion performance on a variety of soft wet tissues, even under exposure of blood and dynamic movements [1]. The other can respond to the skin temperature, actively contract and heal skin wound effectively [2]. A mechanistic investigation with theoretical and computational mechanics approaches will be shown. This talk will also show how to realize spatiotemporal control of tissue adhesion on demand through controlling the surface and structure of the adhesive, and via external stimuli like ultrasound. This talk will highlight how to leverage a variety of physical, chemical and mechanical cues to finely tune the interactions between tissues and biomaterials to promote tissue repair and regeneration. |
Tuesday, March 3, 2020 1:03PM - 1:15PM |
G32.00008: Flexoionic effect of Ionic Liquid Crystal Elastomers Chathuranga Prageeth Rajapaksha, Chenrun Feng, Camilo Piedrahita, Hamad Albehaijan, Vikash Kaphle, Pushpa Paudel, Bjorn Lussem, Thein Kyu, Antal Istvan Jakli Flexoelectricity (strain gradient induced electricity) has potential of a wide variety of applications such as strain sensors and micropower generators. Our present study was motivated by the novel phenomenon of mechanoelctrical conversion (flexoionic effect) of ionic electroactive polymers [1]and a new class of active material – ionic liquid crystal elastomers (iLCEs) [2]. Here we report the flexoionic effect of iLCEs. Highly ionic conductive iLCEs are prepared using M1 (4-(6-Acryloxy-hex-1-yl-oxy) phenyl-4-(hexyloxy) benzoate), M2 (1,4-Bis-[4-(6-acryloyloxyhexyloxy) benzoyloxy]-2-methylbenzene), ionic liquid (1-Hexyl-3-methylimidazolium hexafluorophosphate) and the photo initiator. The effect of alignment (planar, homeotropic and hybrid) and ionic liquid concentration at the function of bending amplitude are studied on the mechanoelectrical conversion. |
Tuesday, March 3, 2020 1:15PM - 1:27PM |
G32.00009: Statistical field theory model for Liquid Crystal Elastomers Pratik Khandagale, Kaushik Dayal, Carmel Majidi Liquid Crystal Elastomers (LCEs) are composed of relatively stiff liquid crystal molecules connected with flexible polymeric chains. LCEs show fast reversible shape change with temperature because of nematic-isotropic phase transition of the liquid crystals. Thus, LCEs have promising applications as thermally active soft actuators, shape memory material and artificial muscles. |
Tuesday, March 3, 2020 1:27PM - 1:39PM |
G32.00010: Branching out and back: Reconfigurable nematic drops driven by molecular heterogeneity Wei-Shao Wei, Yu Xia, Sophie A Ettinger, Yuchen Wang, Shu Yang, Arjun G Yodh Traditionally, polydispersity in matter is often avoided, since it tends to impede self-assembly and state transformation. Here we report reconfigurable nematic liquid crystal oligomer drops, which reveal, surprisingly, that molecular heterogeneity facilitates equilibrium transitions among dramatically different morphological structures, via spatial segregation. Specifically, fine-tuning the temperature and oligomer chain length distribution alters the balance between interfacial tension and liquid crystal elasticity, driving spontaneous formation of roughened spheres, flowers, and highly branched filamentous networks with uniform and controllable diameters. This feature provides potential connections to surface patterning in biological world, such as pollen grains. Further, we employ the achieved structures to template assembly of plasmonic nanoparticles, as well as helical coils with chiral dopant. With the capabilities of being produced reversibly and permanently locked into liquid crystal elastomers, the demonstrated simple rules thus offer new routes for programmed spatio-temporal networks. |
Tuesday, March 3, 2020 1:39PM - 1:51PM |
G32.00011: Imaging crack propagation in tough model gels by ultrasound elastography Heiva Le Blay, Thomas Deffieux, Mickael Tanter, Alba Marcellan Assessing biomechanical properties of soft tissues by ultrasound imaging is still a challenge to help physicians to characterize pathologies. Benefiting from the recent progress in the field, the idea is to develop a novel, non-invasive tool with a high time-resolution to understand crack propagation processes in synthetic model gels. This approach offers new insights into soft matter fracture. |
Tuesday, March 3, 2020 1:51PM - 2:03PM |
G32.00012: Photoisomerization in a Glassy Matrix: Predicting a Broad Distribution of Dynamics with Machine Learning Kenneth Salerno, Timothy W Sirk, Juan De Pablo The response of azo-containing molecules undergoing a trans → cis photoisomerization transition has been primarily studied through simulation and experiment in solution or vacuum. The response of these photoactive molecules in glassy solids, where barriers to motion are significantly higher, is poorly characterized. Results from molecular dynamics simulations show that the dynamics of photoactivated molecules in glassy solids depends critically on local density features. A characteristic power-law wait time for photoisomerization occurs in samples for densities that vary with photoactive molecule and glass-matrix material. Dynamic behavior is driven by difficult-to-identify local density features, which suggests an opportunity for a machine-learning approach. We apply methods from structural analysis of an ideal disordered solid [1] to an all-atom molecular system for the first time, predicting a propensity to isomerize as an analog to “softness.” Our results not only demonstrate that simple machine learning methods can be applied to complex, all-atom molecular systems, but also highlight predictive features of local environments far beyond simple scalar quantities or visually identified features. |
Tuesday, March 3, 2020 2:03PM - 2:15PM |
G32.00013: Response of Polymer Conformations to Crowded Environments Kurt VanDonselaar, Matthew Kurtti, Alan Denton Quantifying the effects of macromolecular crowding on conformations of polymers is important for understanding the structure and function of macromolecules in cellular environments, e.g., biochemical reactions between biopolymers. To efficiently study conformations of crowded polymers in good solvents, we adopt a coarse-grained model of a polymer as a penetrable ellipsoid whose size and shape fluctuate according to the statistics of a self-avoiding walk [1]. We model the crowders as spherical particles that interact via Lennard-Jones or Yukawa pair potentials with hard cores that can penetrate the polymer at a cost in entropy predicted by polymer field theory. To compute the polymer shape distribution, radius of gyration, and asphericity, we perform Monte Carlo simulations, including trial displacements and trial changes in polymer conformation. By varying interactions between crowders, we find that with increasing strength of attraction, the polymer geometric properties settle towards their uncrowded limits as a result of clustering of the crowders. These results may offer insight into reaction rates and functions of folded proteins within cells. |
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