Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S11: Tuning Polymer Rheology for Printing, Spinning, or Coating ApplicationsFocus
|
Hide Abstracts |
Sponsoring Units: DPOLY Chair: Vivek Sharma, University of Illinois at Chicago Room: 270 |
Thursday, March 16, 2017 11:15AM - 11:51AM |
S11.00001: A new approach for high performance fiber manufacturing via simultaneous fiber spinning and UV initiated polymerization Invited Speaker: Chris Ellison Synthetic fibers have been manufactured for decades using solvents or heat to reduce the viscosity of pre-formed polymers and promote drawing. However, nature has engineered spiders and silkworms with benign ways of making silk fibers with high strength and toughness. Conceptually, their approach of chemically linking small functional units (i.e., proteins) into long chain molecules and solid fibrillar structures ``on-demand'' is fundamentally different from current synthetic fiber manufacturing methods. Drawing inspiration from nature, a method will be described that uses light to trigger a thiol-ene photopolymerization to rapidly transform reactive liquid mixtures into solid thread-like structures as they are forced out of a capillary at high speeds. Besides being manufactured without using solvents/volatile components or heat, these fibers are mechanically robust and have excellent chemical and thermal stability due to their crosslinked nature. During processing, the balance between curing kinetics, fiber flight time, and monomer mixture viscoelasticity is essential for the formation of defect free fibers. This work focuses on developing a universal operating diagram to show how the intricate interplay of gel time, flight time, and fluid relaxation time leads to the formation of uniform fibers and other undesirable fiber morphologies such as beads-on-string, fused fibers, non-uniform fibers, and droplets. This predictive capability enables adaptation of this spinning concept to all existing fiber spinning platforms, and customization of monomer formulations to target desired properties. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S11.00002: Capillary Thinning and Pinch-off Dynamics and Printability of Polyelectrolyte Solutions Vivek Sharma, Leidy N. Jimenez, Jelena Dinic, Nikila Parsi Biological macromolecules like proteins, DNA and polysaccharides, and many industrial polymers, are classified together as polyelectrolytes for in solution, the repeat units in their backbone are decorated with disassociated, charge-bearing ionic groups, surrounded by counter-ions. In diverse applications like inkjet printing, sprayable cosmetics and insecticides, paints and coatings that involve formation of fluid columns or sheets that undergo progressive thinning and pinch-off into drops, the dominant flow within the necking filament is extensional in nature. The extensional rheology response of the charged macromolecular solutions is not as well understood as that of their uncharged counterparts. Here focus on the characterization of capillary thinning and pinch-off dynamics, extensional rheology and printability of two model systems: sodium (polystyrene sulfonate) and poly(acrylic acid) by using dripping-onto-substrate (DoS) rheometry technique. Both the measured extensional relaxation times and the extensional viscosity values show salt- and polymer concentration-dependent behavior that is not expected or anticipated from the typical shear rheology response. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S11.00003: Pinch-off dynamics, dripping-onto-substrate rheometry and printability of dilute and semi-dilute polymer solutions Jelena Dinic, Leidy Nallely Jimenez, Madeleine Biagioli, Vivek Sharma Many advanced manufacturing technologies like inkjet and 3D printing, nano-fiber spinning involve complex free-surface flows, where both shear and extensional rheology affect processability. In applications that involve progressive thinning and break-up of a fluid column or sheet into drops, the dominant flow within the filament is extensional in nature. Polymeric fluids exhibit a much larger resistance to flow in an elongational flow field than Newtonian fluids with same shear viscosity. We use dripping-onto-substrate (DoS) extensional rheometry technique for examining the influence of extensibility, flexibility and concentration on pinch-off dynamics and extensional rheology response of aqueous polyethylene oxide (PEO) solutions, aqueous polyacrylamide (PAM) solutions and aqueous 2-Hydroxyethyl cellulose (HEC) solutions. Both extensional relaxation time and the transient extensional viscosity of dilute and semi-dilute solutions display concentration-dependent behavior that is strikingly different from the response observed in typical shear rheology measurements. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S11.00004: Polymer stress anisotropy leads to jetting in rectangular ducts Steven Hudson, Paul Salipante, Charles Little Polymer solutions and melts exhibit various flow instabilities. Here we report the characteristics and causes of a jetting flow instability in solutions of entangled worm-like micelles, which are living polymers, and their solutions have strongly non-Newtonian rheology. High resolution particle tracking methods are used to measure the three-dimensional flow field in rectangular microchannels of differing aspect ratios, sizes, and wall materials. The jetting flow is characterized by a localized high velocity region surrounded by much slower flow. We observe that the instability forms in high aspect ratio channels, and that the location of the high velocity jet appears to be sensitive to stress localizations. Jetting is not observed in a lower concentration solution. Simulations using the Johnson-Segalman viscoelastic model show a qualitatively similar behavior to the experimental observations and indicate that compressive normal stresses in the cross-stream directions support the development of the jetting flow. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S11.00005: Polymer Disentanglement during 3D Printing. Claire McIlroy, Peter D. Olmsted Although 3D printing has the potential to transform manufacturing processes, improving the strength of printed parts to rival that of traditionally-manufactured parts remains an underlying issue. The most common method, fused filament fabrication (FFF), involves melting a thermoplastic, followed by layer-by-layer filament extrusion to fabricate a 3D object. The key to ensuring strength at the weld between layers is successful inter-diffusion and re-entanglement of the melt across the interface. Under typical printing conditions the melt experiences high strain rates within the nozzle, which can significantly stretch and orient the polymers. Consequently, inter-diffusion does not occur from an equilibrium state. The printed layer also cools towards the glass transition, which limits inter-diffusion time. We employ a continuum polymer model (Rolie-Poly) that incorporates flow-induced changes in the entanglement density to predict how an amorphous polymer melt is deformed during FFF. The deformation is dominated by the deposition process, which involves a 90 degree turn and transformation from circular to elliptical geometry. Polymers become highly stretched and aligned with the flow direction, which significantly disentangles the melt via convective constraint release. [Preview Abstract] |
(Author Not Attending)
|
S11.00006: Rheology, thermography, and interlayer welding in polymer extrusion 3D printing Jonathan Seppala, Chelsea Davis, kalman Migler In polymer extrusion 3D printing, thermoplastic filament is extruded though a rastering nozzle onto previously deposited layers. The resulting strength of the 3D produced part is limited by the strength of the weld between each layer. During this thermal processing, the temperature of the interface between layers dictates the chain mobility, interdiffusion, entanglement, and thus weld strength. In quiescent welding experiments, it has been found that the weld strength in symmetric linear polymer systems scales with t~0.25, where t is the isothermal annealing time, before plateauing to the bulk strength. However, 3D printing is highly non isothermal and we calculated an equivalent isothermal annealing time using a combination of in situ infrared thermography and horizontal shift factors from offline rheological measurements of the neat polymer. Interlayer adhesion energy was measured directly by mode III fracture using a simplified geometry limiting the measurement to a single interlayer. Since the processing conditions are known a prioi this approach provides the data needed to estimate the final build strength at time of design. The resulting agreement between annealing time and adhesion energy for a range of printing conditions and thermoplastics are discussed. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S11.00007: Effect of Flow-Induced Molecular Alignment on Welding of Polymer Interfaces Marco Galvani, Thomas O'Connor, Mark Robbins Additive manufacturing, a process of successive deposition of layers of polymer used to synthesize objects, is quickly developing into an effective method of creating polymer-based materials. The physical properties of materials produced by additive manufacturing depend strongly on the mechanics of welded interfaces where polymer chains diffuse between contacting layers. The degree of interdiffusion and the resulting entanglement structure are the dominant factors that give rise to the interfacial strength. In this project, we use large molecular dynamics simulations to examine how flow-induced molecular alignment from the deposition process affects weld formation and strength. First the relation between alignment and entanglement loss is studied for model polymers of different entanglement lengths. Then the effect on the rate of interdiffusion is determined and the formation of interfacial entanglements is correlated to the rate of increase in interfacial strength towards the bulk value. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S11.00008: Disentangling the Role of Entanglement Density and Molecular Alignment in the Mechanical Response of Glassy Polymers Thomas O'Connor, Mark Robbins Glassy polymers are a ubiquitous part of modern life, but much about their mechanical properties remains poorly understood. Since chains in glassy states are hindered from exploring their conformational entropy, they can't be understood with common entropic network models. Additionally, glassy states are highly sensitive to material history and nonequilibrium distributions of chain alignment and entanglement can be produced during material processing. Understanding how these far-from equilibrium states impact mechanical properties is analytically challenging but essential to optimizing processing methods. We use molecular dynamics simulations to study the yield and strain hardening of glassy polymers as separate functions of the degree of molecular alignment and inter-chain entanglement. We vary chain alignment and entanglement with three different preparation protocols that mimic common processing conditions in and out of solution. We compare our results to common mechanical models of amorphous polymers and assess their applicability to different experimental processing conditions. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S11.00009: Improving the Isotropy of Parts Prepared by Fused Deposition Modeling Through the Introduction of Star Architecture Additives Neiko Levenhagen, Mark Dadmun It is well known that 3D printed parts prepared by fused deposition modeling (FDM) exhibit anisotropic characteristics in regards to their mechanical properties. More specifically, mechanical properties when printed orthogonal to the print bed (transverse) are significantly worse than those printed parallel (longitudinal). This behavior is a result of poor layer adhesion from \textit{decreased} diffusion and \quad entanglement of chains across the inter-layer interface. To improve this, our group has implemented a process in which bimodal blends comprised of a parent, high molecular weight polymer and blended with an identical but low molecular weight (LMW) polymer are utilized. These bimodal blends have led to enhancements of up to 66{\%} in the max stress, when printed in the transverse orientation. Additionally, the moduli regardless of print orientation become nearly identical; indicating a more isotropic part. Due to their beneficial flow properties, we have recently begun to study the effect of LMW additives with star architectures on improving the isotropy of 3D printed parts. PLA blends containing 3 arm and 4 arm PLA stars (M$_{w}$ of arm- \textasciitilde 11k) at loadings of 3, 10, and 15 mol{\%} were tested under the same protocol as the linear specimens. With the small addition of 3 mol{\%}, A 100{\%} i\textit{ncrease }in the max stress, in the transverse orientation, with nearly identical moduli is observed. A significant improvement in layer adhesion and a significantly more isotropic part is thus realized. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S11.00010: 3D Printing of a Thermoplastic Shape Memory Polymer using FDM Zhiyang Zhao, R.A. Weiss, Bryan Vogt Shape memory polymers (SMPs) change from a temporary shape to its permanent shape when exposed to an external stimulus. The shape memory relies on the presence of two independent networks. 3D printing provides a facile method to fabricate complex shapes with high degrees of customizability. The most common consumer 3D printing technology is fused deposition modeling (FDM), which relies on the extrusion of a thermoplastic filament to build-up the part in a layer by layer fashion. The material choices for FDM are limited, but growing. The generation of an SMP that is printable by FDM could open SMPs to many new potential applications. In this work, we demonstrate printing of thermally activated SMP using FDM. Partially neutralized poly(ethylene-co-r-methacrylic acid) ionomers (Surlyn by Dupont) was extruded into filaments and used as a model thermoplastic shape memory material. The properties of the SMP part can be readily tuned by print parameters, such as infill density or infill direction without changing the base material. We discuss the performance and characteristics of 3D printed shapes compared to their compression molded analogs. [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S11.00011: 3D Printing of Ball Grid Arrays Shayandev Sinha, Daniel Hines, Abhijit Dasgupta, Siddhartha Das Ball grid arrays (BGA) are interconnects between an integrated circuit (IC) and a printed circuit board (PCB), that are used for surface mounting electronic components. Typically, lead free alloys are used to make solder balls which, after a reflow process, establish a mechanical and electrical connection between the IC and the PCB. High temperature processing is required for most of these alloys leading to thermal shock causing damage to ICs. For producing flexible circuits on a polymer substrate, there is a requirement for low temperature processing capabilities (around 150 C) and for reducing strain from mechanical stresses. Additive manufacturing techniques can provide an alternative methodology for fabricating BGAs as a direct replacement for standard solder bumped BGAs. We have developed aerosol jet (AJ) printing methods to fabricate a polymer bumped BGA. As a demonstration of the process developed, a daisy chain test chip was polymer bumped using an AJ printed ultra violet (UV) curable polymer ink that was then coated with an AJ printed silver nanoparticle laden ink as a conducting layer printed over the polymer bump. The structure for the balls were achieved by printing the polymer ink using a specific toolpath coupled with in-situ UV curing of the polymer which provided good control over the shape, resulting in well-formed spherical bumps on the order of 200 um wide by 200 um tall for this initial demonstration. A detailed discussion of the AJ printing method and results from accelerated life-time testing will be presented [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S11.00012: 3D printable highly conductive and mechanically strong thermoplastic-based nanocomposites Ilyass Tabiai, Daniel Therriault Highly conductive 3D printable inks can be used to design electrical devices with various functionalities and geometries. We use the solvent evaporation assisted 3D-printing method to create high resolution structures made of poly(lactid) acid (PLA) reinforced with multi-walled carbon nanotube (MWCNTs). We characterize fibers with diameters ranging between $100\mu m$ to $330\mu m$ and reinforced with MWCNTs from 0.5 up to 40wt\% here. Tensile test, shrinkage ratio, density and electrical conductivity measurements of the printed nanocomposite are presented. The material's electrical conductivity is strongly improved by adding MWCNTs (up to 3000S/m), this value was found to be higher than any 3D-printable carbon based material available in the literature. It is observed that MWCNTs significantly increase the material's strength and stiffness while reducing its ductility. The ink's density was also higher while still being in the range of polymers' densities. The presented nanocomposite is light weight, highly conductive, has good mechanical properties and can be printed in a freeform fashion at the micro scale. A myriad of low power consumption with less resistive heating sensors and devices can potentially be designed using it and integrated into other 3D printable products. [Preview Abstract] |
Thursday, March 16, 2017 2:03PM - 2:15PM |
S11.00013: Rheological and Thermal Properties of Bio-based Hyperbranched Polyesters Robert Bubeck, Adina Dumitrascu, Tracy Zhang, Patrick Smith Hyperbranched poly(ester)s (HBPEs) of designed molecular structures and targeted molecular weight can be prepared from a variety of multi-functional acids and alcohols. These polymers find application in the areas of coatings and rheology modifiers for coatings. These functional polymers can be synthesized in variety of architectures, possessing either hydroxyl or carboxyl reactive end-groups suitable for the attachment of active entities. The rheological characteristics as related to variation in molecular structure were determined using cone and plate or couette geometries. Viscosities of the HBPEs were found to be near Newtonian. HB polymers permit the control of Tg that is not as readily attained with linear polymers. Accordingly, Tg and viscosity are affected little as a function of Mw but vary dramatically with the nature of the end-groups, are highly dependent on hydrogen bonding of the hydroxyl end groups, and decrease dramatically with the incorporation of aliphatic end-caps. The thermal properties and the degradation characteristics of the HBPEs were determined. Thermal degradation of the hydroxyl-terminal HBPEs is initiated by dehydrative ether formation (crosslinking) while decarboxylation is the initial decomposition event for the carboxyl-terminal polymers. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700