Brian C. Benicewicz’s research while affiliated with University of South Carolina and other places

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Publications (258)


FIG. 1. (a) Scheme of GNP pair indicating the core radius, R c , the effective total radius, R tot , the thickness of the dry layer, h dry , and the interpenetration layer, h inter (see text) [29]. (b) The hard sphere radius of the GNP (solid circles), R HS , obtained from the Perkus-Yevick representation of the SAXS structure factor [26], while the effective R tot is denoted by the dashed black line. The dotted blue line is simulated R HS vs N. Inset: for N < N max , the GNP radius is well represented by R HS ¼ R tot φ 1=3 (blue solid line) with φ ≃ 0.32, suggesting a hard sphere packing with interparticle contacts through adjacent dry zones (blue). The small fraction of interpenetrated chains occupies the interstitial spaces (gray). Note that only six samples (N ¼ 337, 476, 697, 930, 1163, and 1530) were used in the current study, while the previous works discussed in this figure had many more chain lengths.
FIG. 2. (a) Exemplary temperature rises on the heater ΔT h and sensor ΔT s bridged with polymethacrylate (PMA) grafted SiO 2 nanoparticle (GNP) film with a degree of polymerization, N ¼ 476 as a function of the heating power P. The solid lines are guides to the eye. Thermal resistance representing the heat transport from the heater to the sensor with (left) and without (right) sample in the upper inset. Home-built thermal bridge device consisting of two Si chips serving as heater and sensor with Au electrodes deposited on the top (lower inset). (b) Thermal conductivity, κ, of the GNP melts as a function of the PMA degree of polymerization, N. Solid line: predicted κðNÞ from Eq. (1) with κ c ¼ κ PMA ¼ 0.1 Wm −1 K −1 (dashed line) and κ SiO 2 ¼ 1.4 Wm −1 K −1 . The non-adjustable parameter representation of the experimental κðNÞ by Eq. (1) using h d and h i based on SAXS data in Fig. S1 is indicated by a red solid line. (c) The polymer contribution κ p ¼ κ dry is shown vs h d (low axis) and N dry (upper axis). The line indicates the scaling behavior of κ p with exponents 0.65 AE 0.02 (h d axis) and 0.46 AE 0.02 (N dry axis).
FIG. 3. (a) Brillouin light scattering spectrum of a GNP film with σ ≈ 0.47 chains nm −2 and N ¼ 476 at phonon wave vector q ¼ 0.0167 nm −1 . The red solid lines denote the representation of the spectrum by two Lorentzians ascribed to the longitudinal (LA) and transverse (TA) acoustic phonons. (b) The linear dispersion relation for the LA phonon obtained from the spectra in (a) recorded at different q's. (c) Average sound velocity, v PMA ¼ ðv l þ 2v t Þ=3, computed from the longitudinal v l and transverse v t sound velocities of grafted PMA in the hard sphere packing region [Fig. 1(b) inset, Ref. [29]]. The dashed line is the sound velocity of bulk PMA.
Superdiffusive Thermal Transport in Polymer-Grafted Nanoparticle Melts
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  • Full-text available

December 2024

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46 Reads

Physical Review Letters

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Mayank Jhalaria

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In contrast to normal diffusion processes, thermal conduction in one-dimensional systems is anomalous. The thermal conductivity is found to vary with the length as κ ∼ L α ( α > 0 ) , but there is a long-standing debate on the value α . Here, we present a canonical example of this behavior in polymer-grafted spherical nanoparticle (GNP) melts at fixed grafting density and nanoparticle radius. For long chains (chain length N ≥ 9 4 5 ), the experimental κ ( N ) of GNP melts decreases with N , i.e., polymer concentration. For N < 9 4 5 , however, κ ( N ) unexpectedly increases with N with a maximum near N ∼ 9 4 5 . For these systems, the extensional free energy per polymer chain is predicted to be maximized near N max ≈ 9 4 0 for σ ≈ 0.4 7 chains / nm 2 , which indicates the dominance of extended conformations at short N and Gaussian-like conformation for longer N . In the former regime, the thermal conductivity of extended polymer chains increases with N and follows κ p ∼ N dry 0.46 ± 0.02 , which provides experimental evidence of a novel class of superdiffusive thermal transport with α = 1 / 2 . Published by the American Physical Society 2024

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Polybenzimidazole Membranes for Waste Stream Remediation to High Value Products

August 2024

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10 Reads

ECS Meeting Abstracts

Electrochemical remediation of industrial waste products represents an economically attractive method to continuously convert waste streams to high value products. Electrochemical remediation has been more limited for processes that are very dry, very acidic, or a combination of both, because the most widely used polymer membranes (for example, Nafion™) need external humidification to maintain conductivity. We show that para -polybenzimidazole (PBI) membranes can be used as an effective polymer membrane separator in these types of harsh environments, improving the performance of the current state-of-the-art aqueous HCl electrolyzer, enabling the first completely anhydrous gas-phase HCl electrolyzer, and pushing the electrolysis of SO 2 in the Hybrid Sulfur (HyS) cycle to the point of economic viability. The discussion will also cover how PBI membrane preparation affects electrochemical performance and the development of a Computational Fluid Dynamics (CFD) model that both provides insight into the transport phenomena of the anhydrous electrolyzer and allows us to examine operating parameters that are dangerous experimentally.


Development of an Experimentally Validated Computational Fluid Dynamics Model for a PBI Membrane-Based Anhydrous HCl Electrolyzer

May 2024

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70 Reads

We report the development of an experimentally-validated computational fluid dynamics (CFD) model for simulation of an anhydrous HCl electrolyzer. The experimental data from 3 membrane variants was used to provide kinetic and membrane parameters for the model. The model not only accurately simulates overall electrolyzer performance, but it also provides key insights into the transport phenomena within the electrolyzer. The model allows simulation of experimental parameters like high HCl flowrates and increased cell pressure that pose a high safety risk to researchers. The model shows hotspots in the temperature distribution that will need to be addressed by flow field modification when scaling up the electrolysis process. The increasing of cell pressure reduces the gradient of current distribution throughout the electrolyzer and lowers the cell voltage required for a given current density. Increasing electrolyzer temperature reduces cell voltage by decreasing losses due to kinetic overpotential and ohmic overpotential. The implications of the simulated results are discussed, including potential limitations in our experiments and how the model can be used effectively when considering important steps like industry scale-up.



Anisotropic Polybenzimidazole Ion‐Solvating Membranes Composed of Aligned Nano‐Sheets for Efficient Acid‐Alkaline Amphoteric Water Electrolysis

December 2023

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44 Reads

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6 Citations

Acid‐alkaline amphoteric water electrolysis (AAA‐WE) can produce green hydrogen under reduced voltage and energy consumption. However, its conflicting demands on ion exchange membranes to have both high ionic conductivity and barrier properties between H⁺ and OH⁻ have thwarted its own development. Here, the preparation of anisotropic polybenzimidazole (PBI) ion‐solvating membrane (ISM) made of hundreds of 28 nm thick nano‐sheets (PBI‐aNS) from gel state PBI (PBI‐Gel) membranes via 2D‐polarized/1D shrinking process, in which loosely packed multi‐layer PBI nano‐fibrous assemblies are shrunken into hundreds of layers of tight 28 nm thick nano‐sheets, is reported. The resulting PBI‐aNS membranes possess excellent dual‐ion conductivity (H⁺ and OH⁻), good acid/alkali barrier capability, and robust mechanical properties. Acid‐alkaline amphoteric water electrolysis (AAA‐WE) using PBI‐aNS separators achieves a high current density of 1 A cm⁻² at 1.4 V (with iR‐correction) under a voltage increasing rate of 6.1 mV h⁻¹. This newly designed ISM will lead to new possibilities for the development of next‐generation water electrolysis devices with improved green hydrogen production efficiencies.



Enhanced efficiency of water desalination in nanostructured thin-film membranes with polymer grafted nanoparticles

June 2023

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29 Reads

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2 Citations

Nanoscale

Polyamide composite (PA-TFC) membranes are the state-of-the-art ubiquitous platforms to desalinate water at scale. We have developed a novel, transformative platform where the performance of such membranes is significantly and controllably improved by depositing thin films of polymethylacrylate [PMA] grafted silica nanoparticles (PGNPs) through the venerable Langmuir-Blodgett method. Our key practically important finding is that these constructs can have unprecedented selectivity values (i.e., ∼250-3000 bar-1, >99.0% salt rejection) at reduced feed water pressure (i.e., reduced cost) while maintaining acceptable water permeance A (= 2-5 L m-2 h-1 Bar-1) with as little as 5-7 PGNP layers. We also observe that the transport of solvent and solute are governed by different mechanisms, unlike gas transport, leading to independent control of A and selectivity. Since these membranes can be formulated using simple and low cost self-assembly methods, our work opens a new direction towards development of affordable, scalable water desalination methods.




Polymer Molecular Weights via DOSY NMR

May 2023

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498 Reads

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26 Citations

Analytical Chemistry

Diffusion-ordered spectroscopy (DOSY) 1H nuclear magnetic resonance (1H NMR) has become a powerful tool to characterize the molecular weights of polymers. Compared to common characterization techniques, such as size exclusion chromatography (SEC), DOSY is faster, uses less solvent, and does not require a purified polymer sample. Poly(methyl methacrylate) (PMMA), polystyrene (PS), and polybutadiene (PB) molecular weights were determined by the linear correlation between the logarithm of their diffusion coefficients (D) and the logarithm of their molecular weights based on SEC molecular weights. Here, we emphasize the importance of the preparation needed to generate the calibration curves, which includes choosing the correct pulse sequence, optimizing parameters, and sample preparation. The limitation of the PMMA calibration curve was investigated by increasing the dispersity of PMMA. Additionally, by accounting for viscosity in the Stokes-Einstein equation, a variety of solvents were used to produce a "universal" calibration curve for PMMA to determine molecular weight. Furthermore, we place a spotlight on the increasing importance of DOSY NMR being incorporated into the polymer chemist's toolbox.


Citations (71)


... This indicated reduced polymer chain mobility and greater activation energy to move the chain. The dynamic mechanical response of polymer composites to changing temperature conditions is better understood in these findings 127 . ...

Reference:

The Rubberized Mechanical Features: Hardness, Modulus, Tensile Strength, Elongation at Break and Aging for Manufacturing Automotive Tires-An Overview
Mechanical Properties of Polyisoprene-Based Elastomer Composites
  • Citing Article
  • February 2024

Macromolecules

... The para-PBI that was used in our previous work exhibits relatively high mechanical creep over a long (2+ years) period of time. 29 To solve the issue of creeping, Murdock et al. 30 developed a method to densify the para-PBI membrane, providing better mechanical properties while maintaining the high proton conductivity. ...

Teaching an Old Dog New Tricks: Synthesis, Processing, and Application of Polybenzimidazole (PBI) Membranes
  • Citing Article
  • December 2023

ACS Applied Energy Materials

... The polymers are generated using a self-avoiding random walk algorithm and grafted directly onto the surface beads of nanoparticles. The grafting density is kept constant at 0.5 ch/nm 2 , which falls under the range of experimental studies 6,41 and can be considered an intermediate grafting density. The polymer graft length (N) is varied from short 20 monomers to 200, above the entanglement weight of PMMA. ...

Activated Gas Transport in Polymer-Grafted Nanoparticle Membranes

Macromolecules

... [9] Numerous determinations of average molar masses or MMDs on high-field NMR spectrometers have been reported. [10][11][12][13][14][15][16][17] PFG NMR is a non-invasive method, without special sample preparation and with low solvent consumption (<1 mL). Furthermore, the simultaneous study of NMR chemical shifts and J-couplings is possible which provides more information about the sample and allows assigning and differentiating molecules with the same molar mass but different chemical structures. ...

Polymer Molecular Weights via DOSY NMR

Analytical Chemistry

... 17,18 PBI membranes have been used as cation exchange membranes for multiple electrochemical devices, including fuel cells, hydrogen separation pumps, redox flow batteries, hybrid sulfur electrolyzers, and both aqueous and anhydrous HCl electrolyzers. [19][20][21][22][23] In our previous work, a gel para-PBI membrane showed outstanding performance in both anhydrous and aqueous (ODC) HCl electrolyzers. 23 The anhydrous HCl electrolyzer, which used the gel para-PBI membrane, had an estimated HCl conversion per single pass over 90% with no evidence of corrosion in the system. ...

Polybenzimidazole Membranes as Nafion Replacement in Aqueous HCl Electrolyzers
  • Citing Article
  • May 2023

ACS Applied Energy Materials

... In principle, wrinkles can be avoided by wrapping large membranes around a plate and clamping the edges, [35] or by shrinking membranes between tightly clamped porous plates. [36] Unfortunately, both methods change the direction of the shrinking from lateral to vertical, and thus affect the membrane properties. Therefore, for practical reasons in addition to the higher verdazyl absorption, mPBI-85P1S membranes were not further considered in this work. ...

Preparation of Dense Polybenzimidazole Films without Organic Solvents
  • Citing Article
  • March 2023

Macromolecules

... This process disrupts the weak Van der Waals bonds within the crystals, allowing polymer chains to intercalate and form a well-defined interphase that substantially impacts the material's mechanical, thermal, and electrical properties [14]. Among the most critical properties influenced by the interphase are polarization and electrical conductivity [15]. According to the Lewis model, free charges on the surface of filler particles attract negative polymer charges, forming a dipole-like structure characterized J Mater Sci by a dense Stern layer near the surface and a more flexible diffusion layer further away [16,17]. ...

Dielectric Properties of Polymer Nanocomposite Interphases Using Electrostatic Force Microscopy and Machine Learning

ACS Applied Electronic Materials

... Our results showed that maximum mechanical reinforcement occurs for the sample with intermediate grafting density NPs, which formed a connected network, where NP percolation mediated by the graft chains allows for stress propagation. 44 Here, we expand on this study and investigate an array of morphologies, but this time in the cross-linked state. Importantly, our earlier melt state mechanical measurements were conducted in shear mode, while the current solid-state experiments use tensile deformation. ...

Melt State Reinforcement of Polyisoprene by Silica Nanoparticles Grafted with Polyisoprene

ACS Macro Letters

... 23 The anhydrous HCl electrolyzer, which used the gel para-PBI membrane, had an estimated HCl conversion per single pass over 90% with no evidence of corrosion in the system. 24 However, the gel para-PBI membrane has a mechanical creep problem. 25 To solve this problem, a densified para-PBI was developed, which has better mechanical properties and maintains high proton conductivity. ...

Fully anhydrous HCl electrolysis using polybenzimidazole membranes
  • Citing Article
  • July 2022

International Journal of Hydrogen Energy

... Molecular dynamics (MD) simulation, especially the coarsegrained (CG) MD simulations, offers a promising avenue to complement experimental work and comprehensively address these challenges. Previous studies have extensively explored the dynamics, 29 structure, 30,31 dispersion, 32−34 mechanical, 35 viscoelastic, 36 percolation 37 of nanofiller reinforced polymer nanocomposites based on many design parameters, like graft and matrix polymer chemistry, 32 shape, size, and aspect ratio of the fillers, 37,38 grafted chain length, 39 grafting density, 40 polymer/nanofiller interaction strength, 36,41 and so on. However, existing studies have predominantly focused on nanoparticles or nanorod fillers using a generic bead−spring CG model, which lacks chemistry specificity. ...

Local Structure of Polymer-Grafted Nanoparticle Melts
  • Citing Article
  • July 2022

ACS Nano