Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session R04: Polymers and Block Copolymers at Interfaces IFocus Live
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Sponsoring Units: DPOLY DSOFT Chair: Reza Foudazi, New Mexico State University |
Thursday, March 18, 2021 8:00AM - 8:12AM Live |
R04.00001: Rheology of lyotropic liquid crystals obtained from self-assembly of amphiphilic block copolymer at water-oil interface Sahar Qavi, Reza Foudazi At relatively high concentrations of amphiphilic block copolymer, micelles form ordered lyotropic liquid crystals (LLCs) with the length scale in the range of 2-50 nm. Block copolymers in the presence of two selective solvents provide more flexibility in designing different LLCs at a constant temperature and block copolymer composition but different solvent ratios. In this work, we study the rheological characteristics of a series of LLCs with lamellar, normal hexagonal, and reverse hexagonal structures. The flow behavior of LLCs indicates that they have yield stress. We suggest that at relatively low frequencies, defects control the rheological behavior of LLCs, while at high frequencies, the contributions in micellar scale are dominant. Applying high strains on the LLCs decreases the storage modulus in the whole frequency range and decreases the loss modulus in small-frequency regime with negligible effect at high frequencies. The decrease in moduli is reversible and the system relaxes back to its original elastic modulus at rest. The observed behavior can be attributed to the elimination of defects under high strains and their re-formation during long enough rest times. |
Thursday, March 18, 2021 8:12AM - 8:48AM Live |
R04.00002: Polymer Lung Surfactant: A Therapeutic Candidate for ARDS Developed via Polymer Physics Research Invited Speaker: You-Yeon Won Acute Respiratory Distress Syndrome (ARDS) is a life-threatening condition affecting about 200,000 patients in the United States each year. ARDS occurs when the function of native lung surfactant becomes impaired leading to a severe decrease in blood oxygenation and eventually multiple organ failures. There are currently no therapeutic surfactant formulations that have been shown to be effective in treating this condition; all prior clinical trials testing animal-derived lung surfactants in ARDS patients were unsuccessful. Our laboratory has been exploring a radically different approach, in which, instead of conventional lipid/protein-based formulations, synthetic polymers are used as the active therapeutic ingredient to control the surface tension of the alveolar epithelium. This investigation led to the development of a treatment which uses an amphiphilic block copolymer micelle formulation. This formulation has been shown to be more therapeutically effective in mouse models of acute lung injury compared to clinically available animal-derived surfactants. The polymer formulation is superior because it forms, by design, an insoluble monolayer at the alveolar air-water interface that is immune to deactivation caused by serum proteins under lung injury conditions. This talk will present accounts of our polymer physics research endeavors over the past several years that enabled the development of this first-in-class polymer lung surfactant therapy for ARDS treatment. |
Thursday, March 18, 2021 8:48AM - 9:00AM Live |
R04.00003: Inverse Design of Complex 3D Nanostructures of Block Copolymers Hejin Huang, Alfredo Alexander-Katz Directed self-assembly (DSA) of block copolymers (BCP) provides a powerful tool to fabricate complex 2D nanopatterns at small length scale. Fabrication of complex 3D nanostructures by BCP, however, remains a challenge. Here, we introduce a method based on self-directed self-assembly, that utilizes artificial intelligence tools for inverse design of aperiodic 3D nanostructures. The methods presented here encompass rapid algorithms for characterizing the internal structures of BCP morphologies from the atom coordinates generated by MD simulations to substrate optimizing algorithms for developing effective routes to propagate information from the substrate into the BCP film. We will show several examples in which this AI engine is applied. In particular, we will demonstrate how to connect multilayer films or achieve novel complex bilayer structures. Our work has uncovered new design rules for novel 3D nanostructures. |
Thursday, March 18, 2021 9:00AM - 9:12AM Live |
R04.00004: Degradation of Block Copolymer Films Confined in Elastic Media Ryan Sayko, Zilu Wang, Matthew L. Becker, Andrey Dobrynin We performed coarse-grained molecular dynamics simulations of swelling and degradation of glycine, valine, and phenylalanine-based poly(ester urea) copolymer films confined within polymer networks with different values of shear modulus. The microphase separated copolymer films are shown to degrade by surface and bulk erosion depending on the relative rates of chain breaking and water diffusion into the copolymer film. The degrees of swelling of the hydrophobic domains controlled by copolymer composition have a strong effect on degradation kinetics of the films. The competitive substitution of the solvent by hydrophilic fragments is influenced by their affinities to the network strands. The network interface dynamics are driven by the diffusion of solvent into the film which is manifested in a t1/2 scaling dependence. The evolution of the film structures is quantified by analyzing the film scattering function S(q). The peak position in the scattering function associated with interdomain spacing shifts toward smaller q values and disappears as copolymers degrade. The dispersity of the degraded fragments is found to be a universal function of the fraction of broken bonds, independent on the copolymer composition and structure. |
Thursday, March 18, 2021 9:12AM - 9:24AM Live |
R04.00005: Free and Grafted Polymer in Polymer Grafted Nanoparticle Solutions by Small Angle Neutron Scattering Ashraful Haque, Sara Triana Hamilton, Tony Feric, Ah-Hyung (Alissa) Park, Mark Dadmun Liquid-like polymer grafted nanoparticles have shown great promise in applications such as electrochemistry, gas separation, and redox flow batteries due to their enhanced conductivity, tunability, and negligible vapor pressure. However, to employ these nanoparticle assemblies in these applications, it is important to understand the conformation and structure of the polymer in these assemblies in the electrochemical milieu. Here, we report the use of small-angle neutron scattering to probe the structure and dispersion of polymer grafted to SiO2 nanoparticle in an aqueous solution with and without supporting electrolyte. Our results indicate that in aqueous solution, there exists a large amount of free polymer that is not grafted to the functionalized nanoparticles, which may also strongly interact with the grafted polymer layer. The presence of supporting electrolyte dramatically alters the structure of these solutions, as it not only alters the structure of the free polymer but also hinders the interaction of the polymer with the functionalized nanoparticles. These results also correlate well to changes in the viscosity of the solutions, providing valuable insight into the importance of the polymer-nanoparticle interface in these promising functional constructs. |
Thursday, March 18, 2021 9:24AM - 9:36AM Live |
R04.00006: Microgels at interfaces behave as 2D elastic particles featuring reentrant melting Fabrizio Camerin, Nicoletta Gnan, José Ruiz Franco, Andrea Ninarello, Lorenzo Rovigatti, Emanuela Zaccarelli The structural and dynamical properties of colloidal assemblies are determined by the way particles interact with each other. The collective behavior of microgels, which present a characteristic fried-egg shape when adsorbed at an interface [1], remains largely unexplored and limited to indirect experimental feedback. Nonetheless, the development of novel assembly and patterning strategies on surfaces and the design of novel materials with desired interfacial behavior depend on this knowledge [2]. |
Thursday, March 18, 2021 9:36AM - 9:48AM Live |
R04.00007: Adsorption of block-copolymers on the surface of carbon nanotubes in organic solvent Irena Levin, Yachin Cohen Carbon nanotubes (CNTs), find attractive applications due to their unique properties. In some cases, such as polymer nanocomposites, the processing method requires their dispersion in an organic solvent. The dispersion quality strongly impacts the properties of the final nanocomposite. This research characterizes the adsorption of block copolymers of the styrene-b-4-vinylpyridine family (S4VP) onto multi-walld CNTs (MWCNT) in N,N-dimethyl formamide (DMF), using cryogenic transmission electron microscopy (cryo-TEM) and small angle neutron scattering (SANS) measurements with contrast variation. The results show that the block copolymer adsorbs onto the MWCNT surface as a continuous coverage. PS blocks adsorb more tightly (forming a 20 Å layer containing about 6% PS), whereas P4VP blocks emanate into the solvent forming a thick (110 Å) but dilute (<1%) layer, indicating chain extension. Finally, some comparison will be made with adsorption of S4VP from DMF onto the surface of dispersed single-walled CNTs and graphene nanoplatelets, indicating the effect of surface curvature. |
Thursday, March 18, 2021 9:48AM - 10:00AM Live |
R04.00008: Effect of polymer topology on the structure and dynamics of homo and block copolymers in bulk solution and at Liquid/Liquid Interfaces kun qian, Mesfin Tsige The behavior of molecules such as polymers in bulk solution and at liquid/liquid interfaces are both scientifically and technologically important and has been the focus of much attention in recent years given the various types of materials that have been successfully assembled in bulk solution and at liquid/liquid interfaces. Polymers do assemble in various ordered aggregates at liquid/liquid interfaces and understanding the effect of polymer topology on the overall behavior of a given polymer at surface and interfaces and especially at liquid/liquid interfaces is very important. Molecular dynamics simulations using a bead-spring model on representative block copolymer architectures in bulk and at liquid/liquid interfaces have been carried out. The results of our detailed investigation on the structure and dynamics of the block copolymers at the interface will be presented and discussed. |
Thursday, March 18, 2021 10:00AM - 10:12AM Live |
R04.00009: Shape-Specified Model Polymer Nanoparticles via Copolymer Sequence Control Davindra Tulsi, David Simmons Nature employs molecular sequence to control macromolecular shape in order to realize exquisite control over biological nanostructures such as protein assemblies, membranes and DNA complexes. Over the last decade, significant strides have been made in synthesizing artificial sequence-controlled polymers, potentially paving the way for synthetic materials mimicking biological nanostructures. Further advances are hindered by the fact that the relationship between sequence and molecular shape remains poorly understood. Here we employ molecular dynamics simulations to probe the relationship between sequence and molecular shape in model synthetic polymers. Results point to a conformation diagram that provides fundamental physical insights towards design of molecular building blocks for hierarchical assembly. As a first step in this direction, we show how the creation of diblock motif copolymers – consisting of two different molecular building blocks, can yield nanoparticulate shapes that are inaccessible via multimolecular assembly. |
Thursday, March 18, 2021 10:12AM - 10:24AM Live |
R04.00010: In-situ hydrolysis of block copolymers at the water-oil interface Zhan Chen, Mingqiu Hu, Darren Smith, Xindi Li, Javid Rzayev, Thomas Russell Understanding the behavior of polymer chains at interfaces and the effects of polymer composition and architecture on interfacial behavior is critical in designing novel polymer emulsifiers. In this work, a series of linear and bottlebrush block copolymers of poly(styrene-b-solketal methacrylate) (PS-b-PSM) have been used to investigate and in-situ hydrolysis, where the hydrophobic PSM block is converted into a hydrophilic glycerol monomethacrylate (PGM) block. The In-situ interfacial tension was measured to monitor the evolution of the conversion brought about by the interfacial reaction. PS-b-PSM adopts a Janus-type behavior at the interface activity even before conversion, due to preferential affinity of PSM to aqueous water phase. As interfacial hydrolysis proceeds, the PSM block becomes more polar, significantly increasing the amphiphilicity of the block copolymer, along with a corresponding reduction in the interfacial tension. The Janus character of PS-b-PSM were also changed by varying the molecular weight, volume fraction, end groups and architecture to investigate the influence of these parameters on the interfacial evolution behavior through the in-situ hydrolysis. |
Thursday, March 18, 2021 10:24AM - 10:36AM Live |
R04.00011: Exploring the influence of polymer structure on adsorption onto metal surfaces Christopher O'Bryan, Daeyeon Lee, Russell John Composto In mineral processing, the separation of a desired mineral ore from the gangue material is often achieved through the froth flotation process. By leveraging hydrophobic interactions, air bubbles passing through a slurry of the raw materials collect hydrophobic particles and drag them to the surface to form a froth for harvesting. Water-soluble molecules are commonly added to the mineral slurry to alter the surface wettability of select mineral to achieve the desired flotation or the suppression of unwanted material. The effectiveness of these additives depends on the surface coverage, layer thickness, and rigidity of the adsorbed polymer layer. However, particularly in the case of polymeric additives, how their structure relates to their adsorption behavior is far from understood. Unravelling the relationship between polymeric structure and the resulting adsorption kinetics and polymer conformation would enable the development of more efficient polymeric additives. Here, we investigate the role of polymer structure on their adsorption behavior onto metal surfaces. Through a combination of QCM-D and ellipsometry measurements, we explore the effects of the polymer blockiness on the kinetics of the polymer adsorption and the polymer conformation at the interface. |
Thursday, March 18, 2021 10:36AM - 10:48AM On Demand |
R04.00012: Effect of silicone surfactant on the CO2 bubble nucleation in polyol Sriteja Mantha, Huikuan Chao, Andrew Ylitalo, Thomas Fitzgibbons, Weijun Zhou, Valeriy Ginzburg, Zhen-Gang Wang Polyol based foams are widely sought-after materials for manufacturing thermal insulators, high resilience foam seating, adhesives, hard plastics for electronic instruments, etc. The polyol foams are produced by the reaction of di-isocyanate with polyol to form polyurethane and water. Some amount of isocyanate reacts with water to produce CO2. The generated CO2 nucleates into bubbles within the polymer matrix, forming a foam. Silicone surfactants, made of poly dimethyl-siloxane backbone and polyether branches, are commonly used to stabilize the foam formulation. The silicone surfactants reduce interfacial tension between polyol-CO2 interface, promotes bubble generation and impacts the foam cell size. It is also known that the composition of silicone surfactant significantly influences its role in stabilizing the foam formulation as well. However, the physical mechanism of how these silicone surfactants affect the nucleation and stability of the bubbles is not well understood. In this talk, using classical density functional theory models, we propose design principles for silicone surfactants and elucidate the mechanism through which they lead to foams with improved physical properties. |
Thursday, March 18, 2021 10:48AM - 11:00AM On Demand |
R04.00013: 3-Dimensional Confined Assembly of Bottlebrush Block Copolymer in Emulsion Droplet Eun Ji Kim, Jaeman Joseph Shin, Taeyang Do, Gue Seon Lee, Jeung Gon Kim, Bumjoon Kim Self-assembly of bottlebrush block copolymers (BBCP) under three-dimensional confinement is a relatively unprecedented area with great potential for affording diverse structured polymer particles. Here, we report a confined self-assembly of BBCPs in evaporative emulsions, where each block consisted of polystyrene (PS) and polylactide (PLA). The molecular weight of BBCP (i.e. backbone degree of polymerization) was found to be critical in the morphological transition of the particles from onions to ellipsoids. The formation mechanism of onion and ellipsoid particles of BBCP was investigated by monitoring the evaporation time-dependent morphological evolution. In particular, the ellipsoid BBCP particles exhibited interesting features that were not observed in the linear diBCP particles. The sequential lamellae stack formation on the surface with anisotropic nucleation and growth was observed in ellipsoid, while this was suppressed in onion formation due to skin layer generation over the particle surface. Finally, the analysis on the shape-anisotropy (in terms of aspect ratio (AR) of the ellipsoid particles) of BBCP was performed to investigate the origin of the large value of the AR. |
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