Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S18: Polymer and Polyelectrolyte Rheology IFocus Recordings Available
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Sponsoring Units: DPOLY Chair: Poornima Padmanabhan, RIT Room: McCormick Place W-184D |
Thursday, March 17, 2022 8:00AM - 8:36AM |
S18.00001: Polymer Dynamics, Rheology & Processing: Flexibility, Extensibility, and Charge Invited Speaker: Vivek Sharma Biological macromolecules like proteins, DNA, polysaccharides, and many industrial polymers, are classified together as polyelectrolytes. In solution, the repeat units in their backbone are decorated with dissociated, charge-bearing ionic groups, surrounded by a cloud of counter-ions. Even though a large number of polyelectrolytes are processed or used as rheology modifiers in paints, pharmaceuticals, fertilizers, pesticides, and cosmetics, the shear and extensional rheology response of the charged macromolecular solutions is not as well understood as for their uncharged counterparts, and motivate this study. We characterize the pinching dynamics as well as shear and extensional rheology of solutions of four model polyelectrolytes poly(sodium 4-styrenesulfonate) (NaPSS), poly(acrylic acid) (PAA), xanthan gum (XG), and sodium carboxymethylcellulose (NaCMC) as a function of solvent and salt concentration. We identify universalities in the shear and extensional rheology response of salt-added unentangled semi-dilute solutions and examine the influence of solvent properties on polyelectrolyte dynamics. Unlike shear relaxation time that decreases with an increase in polymer concentration in the unentangled, semidilute salt-free solutions, the measured extensional relaxation time always shows an increase with polymer concentration for the unentangled systems. We elucidate the influence of both electrostatic and hydrodynamic interactions and stretching of macromolecules on stickiness, printability, jettability, stringiness, and overall processability. |
Thursday, March 17, 2022 8:36AM - 8:48AM |
S18.00002: Determining the number-average molecular weight of polyelectrolytes Aijie Han, Veera Venkata Shravan Uppala, Daniele Parisi, Christy George, Benjamin J Dixon, Xiuli Li, Louis A Madsen, Ralph H Colby The molecular weight of polyelectrolytes can be reliably measured using terminal modulus (G) (Mn=cmRT/G) for polyelectrolytes with a high degree of polymerization, or can be measured using diffusion coefficient (D) from NMR and correlation length (ξ) from X-ray scattering (Mn=cmRTξ2/6ηsD) for polyelectrolytes with a low degree of polymerization (N < 1000) in the semidilute unentangled regime. Reliable measurement of G = (η - ηs)/τ of polyelectrolyte solutions using rheometry requires relaxation time τ > 0.01 s in order to have one full decade of shear rate with power law shear thinning. Hence, high molecular weight polyelectrolytes with high viscosity solvents (N > 1000 in ethylene glycol or N > 100 in glycerol) are preferred for evaluating τ and hence G. Measuring D, on the other hand, is more easily performed on low molecular weight polyelectrolytes with NMR diffusometry because of the decrease of the spin dephasing time (T2) with increasing molecular weight, which leads to peak broadening and poor signal strength for large N. The dispersity of polyelectrolyte samples can also be determined using signal attenuation plots from NMR diffusometry. Convenient determination of Mn and PDI of polyelectrolytes will greatly accelerate their development for real world applications. |
Thursday, March 17, 2022 8:48AM - 9:00AM |
S18.00003: Quantifying the Effect of Multivalent Ions in Polyelectrolyte Solutions Michael Jacobs, Andrey V Dobrynin, Carlos G Lopez We apply a recently developed scaling approach utilizing the concentration dependence of the specific viscosity of polymer solutions to quantify the properties of carboxymethyl cellulose and polystyrene sulfonate solutions with mono- and divalent counterions. This approach is based on the relationship between the correlation blob size ξ=lgν/B and the number of repeat units per blob, g, with projection length l. The B-parameters are acquired for each value of the exponent ν using the dependence of g on the repeat unit concentration c, g~c1/(1-3ν), and the specific viscosity in the unentangled regime, ηsp=Nw/g, where Nw is the weight-average degree of polymerization. This analysis indicates that, for polyelectrolytes with divalent counterions, the excluded volume is halved and the Kuhn length is increased by less than 10%. We also use the B-parameters to estimate the fraction f * of free counterions outside the electrostatic blobs and find that for both mono- and divalent systems, f *<12%. Combined, these effects promote a reduction in chain stretching, a larger number of repeat units per correlation blob, and a broader unentangled concentration regime in solutions with divalent ions. |
Thursday, March 17, 2022 9:00AM - 9:12AM |
S18.00004: Effect of charge density and sequence on physical properties of salt-free polyelectrolyte solutions Mohammad Hossein Khalili Samani, Taniya M Pathiranage, Amanda B Marciel Polyelectrolytes are polymers with ionizable monomers. Due to the electrostatic interactions, polyelectrolytes exhibit weaker scalings compared to neutral polymers for viscosity, diffusion coefficient, and frequency responses, showing potential in viscosity modifiers and small ion transport applications. However, we still lack a full understanding on the role of charge fraction and charge sequence on salt-free solution behavior. At concentrated regime, the mechanism by which entanglements happen in polyelectrolytes is of importance as strong electrostatic interactions dominate and delay the entanglement compared to neutral polymers of the same length, suggesting polyelectrolytes as potential candidates for soft materials. Aided by random and block copolymers with varying charge fractions (20-80%) and types, we will enrich our understanding of the electrostatic interactions and the resulting conformational changes. PDMAEA and PAA are utilized as cationic and anionic monomers, respectively, and PBA consists the neutral part. The effect of each interaction will be explored by steady shear viscosity and frequency sweep measurements, and resulting changes in relaxation time, critical overlap concentration c*, entanglement concentration Ce and modulus Ge, will be further discussed. |
Thursday, March 17, 2022 9:12AM - 9:24AM |
S18.00005: How to Quantify Properties of Polysaccharide Solutions Ryan Sayko, Michael Jacobs, Andrey V Dobrynin The structural diversity of polysaccharides contributes to a complexity in finding universal frameworks to describe their solution properties. To resolve this issue, we utilize a scaling theory of semidilute polymer solutions based on the relationship between solution correlation length ξ=Mgν/BNA1/3 (NA being Avogadro’s number) and the molar mass of the chain segment inside a correlation blob Mg as a function of concentration c, parameter B, and exponent n. The interaction parameter B and exponent n are determined by the solvent quality for the polysaccharide backbone on the length scale of the correlation length. The values of the B parameters are extracted from the plateaus of the normalized specific viscosity ηsp(c)/Mwc1/(3ν-1), where Mw is the weight-average molecular weight of the polymer chain. We expand the scaling approach to the entangled solution regime and calculate the chain packing parameter Pe. The set {B,Pe} uniquely expresses the properties of polysaccharides/solvent pairs in different concentration regimes. This information is used to construct a universal diagram of states for this class of polymers. |
Thursday, March 17, 2022 9:24AM - 9:36AM |
S18.00006: Early Onset of Non-Linear Response in Entangled Monodisperse DNA Solutions Gregory B McKenna, Sourya Banik, Dejie Kong, Michael J San Francisco It is generally observed that entangled polymer melts and solutions exhibit linear rheological response for the dynamic moduli [G'(ω) and G''(ω)] to shear strains of the order of 50 to 100%. We recently[1] discovered that λ-phage DNA, a double-stranded linear DNA having a molecular weight of 48.5 kbp (3.1x107 g/mol), that this ideally monodisperse system did not behave in the same way as do synthetic polymers. Rather the onset of non-linear rheological behavior is seen at strains of approximately 2% or less depending on frequency of the oscillatory shear. Furthermore, unlike the synthetic polymers, the λ-DNA solutions exhibit an onset of non-linearity that occurs at decreasing strains as the frequency of test decreases. Importantly, non-monodisperse DNA solutions, such as calf-thymus DNA have been reported to exhibit behavior similar to linear polymers[2]. The reasons for this are not currently understood and lead to fundamental questions about the rheology of entangled systems. Is DNA fundamentally different from the linear synthetic counterpart? or does polydispersity lead to a different behavior? |
Thursday, March 17, 2022 9:36AM - 9:48AM |
S18.00007: Probing Conformation Effects on Structure and Dynamics of Unentangled Polyelectrolyte Solutions using Neutron Scattering Ali H Slim, Ryan Poling-Skutvik, Antonio Faraone, Jacinta C Conrad Polyelectrolytes are essential components of many biological systems as they form interpenetrating networks that make muscle tissues and influence mechanical properties. Understanding the structure and dynamics of polyelectrolyte chains under various conditions is key to decouple their complex transport phenomena. Here, we examine the effects of chain conformation, varied through ionic strength, on the structure and dynamics of sodium polystyrene sulfonate in aqueous solutions. The solution viscosities follow the predicted scaling with concentration η~c1/2 and η~c5/4 in the low and high salt limits, respectively. The dynamics of chains with similar structural properties behave similarly, and we observe two scaling regimes of the relaxation rate as a function of wavevector that reflect segmental and collective chain dynamics at small and large length scales, respectively. We compare our data across the existing predictions of Rouse (weak hydrodynamic interactions, > ξ) and Zimm (strong hydrodynamics, < ξ). The Rouse-Zimm scaling predictions, however, are not capable of quantitatively describing our relaxation rates or collapsing our scattering data, suggesting that the electrostatic interactions on polyelectrolyte chains influence the underlying assumptions of traditional models. |
Thursday, March 17, 2022 9:48AM - 10:00AM |
S18.00008: Behaviour of Sodium polystyrene sulfonate (NaPSS) in aqueous NaCl solutions Anish Gulati, Carlos G Lopez For a polyelectrolyte system as heavily probed as NaPSS in water, the screening interactions in this system are relatively less well understood. In this study, we investigate the rheological behaviour of NaPSS with different molar masses (Mw ~ 30 - 2000 kg/mol) in aqueous salt solutions under a broad range of polymer and added salt concentrations and examine the applicability of the scaling theory for polyelectrolyte solutions to these measurements. |
Thursday, March 17, 2022 10:00AM - 10:12AM |
S18.00009: Solution rheology of polyelectrolytes with monovalent and divalent counterions Carlos G Lopez, Ferenc Horkay, Walter Richtering We report solution rheology data for the sodium, magnesium and calcium salts of polystyrene sulfonate (PSS) and carboxymethyl cellulose (CMC) in salt-free aqueous solutions as a function of polymer concentration and molar mass. Below the overlap concentration, both polymers are found to exhibit rod-like conformations for high degrees of polymerization. The chain dimensions for the divalent salts are significantly smaller than for the monovalent ones, suggesting larger electrostatic blobs. This is consistent with the stronger binding of divalent ions to the chains inferred from conductivity data. In the semidilute regime, the correlation length for NaCMC and the various salts PSS follows the scaling prediction of ξ ∼ c−1/2. The divalent salts of CMC do not exhibit a peak in their scattering function and therefore extracting the correlation length is challenging. |
Thursday, March 17, 2022 10:12AM - 10:24AM Withdrawn |
S18.00010: Shear-Induced Counterion Release of a Polyelectrolyte Jiang Zhao, Kaikai Zheng, Kuo Chen, Weibin Ren, Jingfa Yang The shear-induced changes in counterion distribution of a model polyelectrolyte, sodium polystyrene sulfonate (NaPSS), is investigated at single molecular level. Fluorescence resonance energy transfer (FRET) between the fluorescence donor attached at the PSS− chain end and the cationic acceptor serving as the counterion probes in solution shows the increase of average counterion-chain distance. The emission spectra of the pH-responsive fluorophore labeled at PSS− chain end show the dilution of hydronium ions near the chain by shear. The results indicate that the shear applied to the NaPSS solution makes the counterions released from the PSS− chain. The mechanism of counterions' redistribution is attributed to the shear-induced transient overlap of electric fields of multiple PSS− chains. The results indicate that the effective charge of a polyelectrolyte molecule increases with shear, in contrast to the conventional assumption of the invariable charges. |
Thursday, March 17, 2022 10:24AM - 10:36AM |
S18.00011: Probing Shear Thinning of Liquids at High Strain Rates using Simulations and Machine Learning Vikram Jadhao, JCS Kadupitiya The extraction of accurate rheological properties using nonequilibrium molecular dynamics simulations has improved our understanding of liquid flows under high shear strain rate conditions. However, the high dimensionality of the simulation output data makes a deeper interrogation of the link between molecular-scale features and rheological properties challenging. We demonstrate that dimension reduction methods can expedite the analysis of data generated by nonequilibrium molecular dynamics simulations of small-molecular liquids such as squalane. Dimension reduction of the orientation tensors of all atom pairs associated with squalane molecules enabled a clear visualization of the transition from Newtonian to non-Newtonian shear thinning with increasing shear rate. The end-to-end atom pairs dominate the largest variations in tensor components at low pressures, and provide the clearest separation of the orientation tensors with rate. However, the side atom pairs dominate the largest variations in tensor components at high pressures (>400 MPa). Dimension reduction shows that the decrease in viscosity with rate for low pressures is strongly correlated with changes in molecular alignment. However, for high pressures, shear thinning occurs at saturated orientational order. |
Thursday, March 17, 2022 10:36AM - 10:48AM |
S18.00012: Characterization of As-Prepared Polymeric Films by Simultaneously Measuring the Glass Transition, Crystallinity, and Order-Disorder Transition through the Restitution Jinwon Park, Seongsoo Han, Hyeonjung Park, Jaehong Lee, Suchan Cho, Myungeun Seo, Bumjoon J Kim, Siyoung Q Choi The glass transition temperature (Tg) and degree of crystallinity (Xc) are important properties of polymers, and the order-disorder transition temperature (TODT) is another important property to characterize block copolymers (BCPs). However, conventional techniques have some inconveniences in measuring these properties at the same cycle of measurement. Thus, we developed a new intuitive technique to simultaneously measure the Tg, Xc, and TODT by measuring the restitution of a ball on intact polymeric films based on the Hertz contact theory and rheology. With various types of polymers, including BCPs and conjugated polymers, we showed that Tg can be determined by the onset of the decrease in restitution, Xc is the normalized minimum restitution for Xc up to 50%, and TODT is related to another dramatic restitution decreasing point at higher temperatures. All the measured Tgs and Xcs by the ball collision method matched well with the theoretical and/or well-known values measured by the conventional techniques (differential scanning calorimetry, X-ray diffraction), and measured TODTs were also compared with the values from dynamic mechanical analysis and/or X-ray scattering. Furthermore, an approach to measuring the sub-micrometer-thick films will be discussed. |
Thursday, March 17, 2022 10:48AM - 11:00AM |
S18.00013: Eight Decades In One Rheometer: Exploring the dynamics of complex polymers, measuring from millihertz to a hundred kilohertz in a single device Mathias Mikkelsen, Jorge Lacayo-Pineda, Tina Hecksher, Tage E Christensen We present an investigation of the shear mechanical dynamics of filled and unfilled rubbers across eight decades in frequency. |
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