Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session A42: Polymer Thin Films: Patterning and Flow |
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Sponsoring Units: DPOLY Chair: Justin Pye, Emory University Room: 345 |
Monday, March 14, 2016 8:00AM - 8:12AM |
A42.00001: Deformation of Thin Free-standing Films with Sessile Droplets Through the Glass Transition Adam Fortais, Rafael Schulman, Kari Dalnoki-Veress Droplets on a rigid substrate will form a contact angle determined by interfacial tensions according to Young’s law. Likewise, the Laplace pressure of a droplet will deform a liquid substrate, and the contact line geometry can be determined through a Neumann construction. We explore the intermediate case of micro-droplets placed on thin, highly compliant, free-standing films. The Laplace pressure of the droplet deforms the free-standing film, creating a spherical bulge. The film’s tension is modulated by changing temperature continuously from well below the glass transition into the melt state of the film. The contact angle of the liquid droplet with the undeformed film as well as the angle of the bulge with the film is measured and compared to the contact angles predicted by a force balance at the contact line. [Preview Abstract] |
Monday, March 14, 2016 8:12AM - 8:24AM |
A42.00002: Measuring spatially distributed rheology of thin polymer films by non-contact shearing. Mithun Chowdhury, Yunlong Guo, Rodney D. Priestley For nearly two decades, a great detail of research has been devoted to understand the impact of nanoscale confinement on the glassy and viscoelastic properties of thin polymer films. Prior works in supported films mostly used indirect mechano-rhelogical means, due to the complexity associated to probe such small volume. Here we present a non-contact shearing method `blow-off', induced by the laminar flow of an inert gas through a narrow channel in order to generate a well-defined shear stress on a rectangular edge of a properly placed polymer thin film on a solid substrate. By appropriate control of temperature/ time during shearing, we explored effective viscosity and shear mobility, spatially from free surface to the material interior. In general, we found film surface has higher shear mobility and lower effective viscosity in comparison to its interior. [Preview Abstract] |
Monday, March 14, 2016 8:24AM - 8:36AM |
A42.00003: Photodirecting Marangoni Flow to Pattern Thin Polymer Films: Decoupling Viscosity and Diffusivity Chae Bin Kim, Amanda Jones, Dustin Janes, Talha Arshad, Roger Bonnecaze, Christopher Ellison The Marangoni effect causes liquids to flow towards localized regions of higher surface tension. In thin polymer films, this effect could offer a practically useful route to manufacture topographically patterned surfaces. In this presentation, we report a photochemical strategy to harness Marangoni flow as a versatile patterning method along with comparisons to a theoretical model that reveals the underlying physics of this process. The model agrees well with experiments with no adjustable parameters. It further indicates that higher aspect ratio features are favored by large surface tension gradients, low diffusivities and low viscosities. However, as described by the Rouse model, low viscosities are generally correlated with high diffusivities; diffusivity is also an important factor in the timescale by which the spatial surface tension patterns decay. This coupling between diffusivity and viscosity could critically limit feature aspect ratio for any given surface tension pattern. A potential strategy that decouples diffusivity and viscosity of the film components will be presented. [Preview Abstract] |
Monday, March 14, 2016 8:36AM - 8:48AM |
A42.00004: The Parametric Study of Focused Laser-Induced Marangoni Dewetting for Patterning Polymer Thin Films Jonathan Singer, Tianxing Ma, Steven Kooi, Edwin Thomas Highly-localized focused laser spike (FLaSk) heating of polymer thin films is a resist- and developer-free alternative to 2D laser direct write for creating patterns on the single micron or, by exploiting overlap effects, submicron scale. The massive temporal and spatial thermal gradients and resulting thermal Marangoni stresses generated by FLaSk are an effective means for the directed dewetting and patterning of such films. Here, the general applicability of this technique to glassy amorphous polymer thin film systems is investigated through systematic investigation of film thickness, glass transition temperature, and polymer mobility. The results reveal that the important parameters are the film thickness (coupled to the optical heating effects through anti-reflection coating effects) and the high-temperature polymer melt mobility, allowing for generation of single features with linewidths of down to 1 $\mu $m. Further, the introduction of spatial mobility variations by using polymer brushes, bilayers, and microphase separated block copolymers leads to additional profile manipulation effects ($i.e. $spontaneous 2D pattern generation and flattened top profiles). [Preview Abstract] |
Monday, March 14, 2016 8:48AM - 9:00AM |
A42.00005: Degrafting of polymer brushes from substrates enables insight about the brush structure and facilitates surface patterning. Rohan Patil, Salomon Turgman-Cohen, Jiri Srogl, Douglas Kiserow, Jan Genzer Polymers end-grafted to surfaces or interfaces, commonly referred to as polymer brushes, enable tailoring physico-chemical properties of material surfaces. Many applications of polymer brushes require information about the molecular weight (MW) and grafting density (GD) of polymer brushes. For brushes synthesized by surface initiated polymerization (SIP) determining these attributes was always a challenge. We have developed a simple method of measuring MW and GD of these systems by degrafting SIP from silica-based surfaces by using tetrabutyl ammonium fluoride (TBAF), which attacks selectively Si-O bonds and enables complete degrafting of poly(methyl methacrylate) (PMMA) brushes from silica based substrates without damaging the backbone. The rate of PMMA degrafting decreases with reaction time and depends on the concentration of TBAF, temperature, and the initial GD of the system. The molecular weight distribution of the degrafted PMMA was measured using size exclusion chromatography. The GD was calculated from known MW and dry thickness of the PMMA brush. Spatial patterns of degrafted regions on the substrate can be prepared by either localizing the TBAF to certain regions or by gradually immersing homogeneous samples into TBAF solution. [Preview Abstract] |
Monday, March 14, 2016 9:00AM - 9:12AM |
A42.00006: Fabrication of Converging and Diverging Polymeric Microlens Arrays By A Thermocapillary Replication Technique Soon Wei Daniel Lim, Kevin Fiedler, Sandra Troian Thermocapillary forces offer a powerful method for sculpting interfaces at microscale dimensions. Here we demonstrate how periodic arrays of cooled pins placed in close proximity to the surface of a molten polymer nanofilm can be used to fabricate various large area microlens arrays, which when solidified exhibit ultrasmooth surfaces and excellent focusing capability. This technique was used to fabricate both homogeneous converging and diverging microlens shapes by application of various thermal distributions. The converging arrays were incorporated into a Shack-Hartmann wavefront sensor able to image moving currents of airborne spray droplets. Feature overlap was also used to achieve hierarchical arrays comprising two superimposed patterns. By varying the width of the cooled pins, it was also possible to fabricate converging microlens structures featuring a caldera-like depression at the vertex able to focus collimated light into a sharp annulus. These demonstrations prove that with suitable microscale control over the thermal distributions projected onto molten nanofilms, a diverse set of micro-optical components can be fabricated by thermocapillary replication from a nearby mask without contact and in a single step. [Preview Abstract] |
Monday, March 14, 2016 9:12AM - 9:24AM |
A42.00007: Ultrasmooth, Polydopamine Modified Surfaces for Block Copolymer Nanopatterning on Inert and Flexible Substrates Reika Katsumata, Joon Hee Cho, Sunshine Zhou, Chae Bin Kim, Austin Dulaney, Dustin Janes, Christopher Ellison Nature has engineered universal, catechol-containing adhesives that can be synthetically mimicked in the form of polydopamine (PDA). We exploited PDA to enable block copolymer (BCP) nanopatterning on a variety of soft material surfaces in a way that can potentially be applied to flexible electrical devices. Applying BCP nanopatterning to soft substrates is challenging because soft substrates are often chemically inert and possess incompatible low surface energies. In this study, we exploited PDA to enable the formation of BCP nanopatterns on a variety of surfaces such as Teflon, poly(ethylene terephthalate) (PET), and Kapton. While previous studies produced a PDA coating layer too rough for BCP nanopatterning, we succeeded in fabricating conformal and ultra-smooth surfaces of PDA by engineering the PDA coating process and post-sonication procedure. This chemically functionalized, biomimetic thin film (3 nm thick) served as a reactive platform for subsequently grafting a surface treatment to perpendicularly orient a lamellae-forming BCP layer. Furthermore, we demonstrated that a perfectly nanopatterned PDA-PET substrate can be bent without distorting or damaging the nanopattern in conditions that far exceeds typical bending curvatures in roll-to-roll manufacturing. [Preview Abstract] |
Monday, March 14, 2016 9:24AM - 9:36AM |
A42.00008: Adsorption and Pattern Recognition of Polymer at Complex Heterogeneous Surfaces Leila Rajabibonab, Shaun Hendy The statistical mechanics of polymer adsorption on a substrate has been well studied. However, there has been recent interest in the conformational behaviour of polymer chains on patterned heterogeneous surfaces, where absorption strength varies. Here we report on Monte Carlo simulations of the adsorption of homo-polymer chains on patterned surfaces. One difficulty in studying polymer self-assembly on a patterned surface is the fluctuation of polymer conformations, which can make calculating the free energy a challenge. To overcome this we apply an expanded ensemble method to compute free energy differences. Applying this approach enables us to identify different adsorbed phases at a range of temperatures. The simplest case of heterogeneous surface is striped pattern, but we consider heterogeneous surfaces with four other that are structured on different length scales. At low temperatures we find that the polymer chain will recognise the pattern, by conformationally adapting as it adsorbs before eventually becoming fully relaxed on the surface. Polymers are found to adsorb on simple patterns at higher temperatures than on complex patterns. [Preview Abstract] |
Monday, March 14, 2016 9:36AM - 9:48AM |
A42.00009: Wake and wave resistance on viscous thin films Rene Ledesma-Alonso, Michael Benzaquen, Thomas Salez, Elie Raphael The effect of an external pressure disturbance, which is displaced with constant speed along the free surface of a viscous thin film, is studied theoretically in the lubrication approximation in one- and two-dimensional geometries. In the comoving frame, the imposed pressure field creates a stationary deformation of the interface - a wake - that spatially vanishes in the far region. The shape of the wake and the way it vanishes depend on both the speed $v$ and size $a$ of the external source and the properties of the film: density $\rho$, air-liquid surface tension $\gamma$, shear viscosity $\mu$, and film thickness $h_0$. The wave resistance, namely the force that has to be externally furnished in order to maintain the disturbance speed and the stationary wake, is analyzed in detail. For finite-size pressure disturbances, it increases with the speed, up to a certain transition value above which a monotonic decrease occurs. The role of the horizontal extent of the pressure field is studied as well, revealing that for a smaller disturbance the latter transition occurs at a higher speed. Eventually, for a Dirac pressure source, the wave resistance either saturates for a 1D geometry, or diverges for a 2D geometry. [Preview Abstract] |
Monday, March 14, 2016 9:48AM - 10:00AM |
A42.00010: Plug flow in a viscous freely-suspended film Kari Dalnoki-Veress, Mark Ilton, Miles Couchman, Thomas Salez, Michael Benzaquen, Paul Fowler, Elie Raphael The flow of viscous polymer liquids supported by a solid substrate has been well characterized by a variety of experimental techniques. Previous studies found that the velocity profile within a flowing liquid film depends strongly on the friction at the liquid-substrate interface. For the case of low interfacial friction, liquid molecules can slide along the solid substrate. This is the ``slip'' boundary condition. Here we probe flow in a system with no interfacial friction: a viscous polymer film suspended at its edges. Using AFM, we measure the capillary-driven relaxation of freestanding polymer films with an initially stepped film thickness profile. The time evolution of the profile is consistent with plug flow. A freely-suspended viscous polymer film provides a physical realization of an idealized infinite slip boundary condition. Interestingly, in such a context, the profile evolution satisfies a diffusion-like equation, thus allowing for the use of a broad mathematical and physical toolbox by analogy. [Preview Abstract] |
Monday, March 14, 2016 10:00AM - 10:12AM |
A42.00011: Understanding and Improving the Quality of Inter-Layer Interfaces in FDM 3-D Printing Edward Duranty, Brandon Spradlin, Madeline Stark, Mark Dadmun We have studied the effect of thermal history and material diffusion on inter-filament bonding in FDM 3D printed parts and developed methods to improve interlayer adhesion in 3D printed samples. The available thermal energy during the FDM print environment was determined quantitatively by tracking the temperature of the bottom most printed layer using a thermocouple attached to the print bed. The role of the thermal history of the filaments during the deposition process on the quality of inter-layer bonding in an FDM ABS part was monitored using a T-peel test and an innovative sample design. Additionally, the interfacial adhesion between 3D printed layers was improved by the addition of a chemical cross-linking agent 4,4$\prime $-diaminodiphenylmethane (DADPM). These studies have increased our understanding of the importance of the complex thermal history of a filament in the 3D printing process and its impact on the interfaces that form during the fused deposition modeling print process. Furthermore, the chemical crosslinking process demonstrates a potential method to covalently link layers in FDM printed parts, improving the bulk strength of the part. The insight provided in this work may aid in the development of techniques that can produce FDM parts that could be used as replacement parts in structural applications, or as completely standalone products. [Preview Abstract] |
Monday, March 14, 2016 10:12AM - 10:24AM |
A42.00012: Modelling Polymer Deformation during 3D Printing Claire McIlroy, Peter Olmsted Three-dimensional printing has the potential to transform manufacturing processes, yet improving the strength of printed parts, to equal that of traditionally-manufactured parts, remains an underlying issue. The fused deposition modelling technique involves melting a thermoplastic, followed by layer-by-layer extrusion to fabricate an object. The key to ensuring strength at the weld between layers is successful inter-diffusion. However, prior to welding, both the extrusion process and the cooling temperature profile can significantly deform the polymer micro-structure and, consequently, how well the polymers are able to ``re-entangle'' across the weld. In particular, polymer alignment in the flow can cause de-bonding of the layers and create defects. We have developed a simple model of the non-isothermal extrusion process to explore the effects that typical printing conditions and material rheology have on the conformation of a polymer melt. In particular, we incorporate both stretch and orientation using the Rolie-Poly constitutive equation to examine the melt structure as it flows through the nozzle, the subsequent alignment with the build plate and the resulting deformation due to the fixed nozzle height, which is typically less than the nozzle radius. [Preview Abstract] |
Monday, March 14, 2016 10:24AM - 10:36AM |
A42.00013: Fundamental characterization of soft matter 3D printing processes Kalman Migler, Jonathan Seppala, Chelsea Davis, Kaitlyn Hillgartner In fused filament fabrication (FFF), a material extrusion 3D printing method, thermoplastic filament is extruded though a rastering nozzle on the previous layer. The resulting strength of the FFF produced part is limited by the strength of the weld between each layer. While numerous factors can affect the weld strength, the temperature of the extrudate and the previous layer dictate the amount of interdiffusion and thus the weld strength. Temperature measurements were performed using forward looking infrared imaging. Interdiffusion estimates were calculated from temperature profiles, normalized using horizontal shift factors from offline rheological measurements of the neat polymer. Weld strength was measured directly by Mode III Fracture using a simplified geometry limiting the measurement to a single weld. Since the processing conditions are known aprioi this approach provides the data needed to estimate the final build strength at time of design. The resulting agreement between interdiffusion estimates and weld strength for a range of printing conditions are discussed. [Preview Abstract] |
Monday, March 14, 2016 10:36AM - 10:48AM |
A42.00014: Pinch-off dynamics, extensional viscosity and relaxation time of dilute and ultradilute aqueous polymer solutions Madeleine Biagioli, Jelena Dinic, Leidy Nallely Jimenez, Vivek Sharma Free surface flows and drop formation processes present in printing, jetting, spraying, and coating involve the development of columnar necks that undergo spontaneous surface-tension driven instability, thinning, and pinch-off. Stream-wise velocity gradients that arise within the thinning neck create and extensional flow field, which induces micro-structural changes within complex fluids that contribute elastic stresses, changing the thinning and pinch-off dynamics. In this contribution, we use dripping-onto-substrate (DoS) extensional rheometry technique for visualization and analysis of the pinch-off dynamics of dilute and ultra-dilute aqueous polyethylene oxide (PEO) solutions. Using a range of molecular weights, we study the effect of both elasticity and finite extensibility. Both effective relaxation time and the transient extensional viscosity are found to be strongly concentration-dependent even for highly dilute solutions. [Preview Abstract] |
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