More Like this

1. Understanding Separation of Oil–Water Emulsions by High Surface Area Polymer Gels Using Experimental and Simulation Techniques

   https://doi.org/10.1021/acs.langmuir.4c03496  

   Gotad, Pratik S; Mokarizadeh, Abdol Hadi; Tsige, Mesfin; Jana, Sadhan C (November 2024, Langmuir)

   This work examines the functional dependence of the efficiency of separation of oil−water emulsions on surfactant adsorption abilities of high surface area polymer gels. The work also develops an understanding of the factors and steps that are involved in emulsion separation processes using polymer gels. The work considers four polymer gels offering different surface energy values, namely, syndiotactic polystyrene (sPS), polyimide (PI), polyurea (PUA), and silica. The data reveal that surfactant adsorption abilities directly control the emulsion separation performance. The gels of sPS and PI destabilize the emulsions due to significant surfactant adsorption. The surfactant-lean oil droplets are then absorbed in the pores of sPS and PI gels due to the preferential wettability of the oil phase. The PUA and silica gels are more hydrophilic and show a lower surfactant adsorption ability. These gels cannot effectively remove the surfactant molecules from the emulsions, leading to a poor emulsion separation performance. The study uses simulation data to understand the adsorption characteristics of two poly(ethylene oxide)- poly(propylene oxide)-poly(ethylene oxide) block copolymer surfactants. The simulation results are used for the interpretation of emulsion separation performance by the gels. 

   more » « less
2. Moduli of Mussel‐Inspired, Metal‐Coordinated Hydrogels Comprising Four‐, Six‐, and Eight‐Arm Polymers

   https://doi.org/10.1002/macp.202300102  

   Darby, Daniel R; Stephens, Lauren F; Chwatko, Malgorzata; Pham, Jonathan T (December 2023, Macromolecular Chemistry and Physics)

   Abstract Metal‐coordinated hydrogels can form a percolated network with transient bonds due to metal ions‐functional group coordination. Each metal ion can link with more than one ligand, leading to intricate speciation of bonding modes. While the mechanics of transient gels made with four‐arm polymers are often studied, less is known about how increasing the number of arms affects the modulus. Using shear rheology, the modulus of hydrogels prepared from four‐, six‐, and eight‐armed poly(ethylene glycols), functionalized with histidine ligands that complex with nickel (II) ions is measured. These gels have matched polymer wt.% and varied pH to compare their moduli. It is considered whether the modulus can be described by established polymer network models by calculating the speciation of metal‐coordinated cross‐links and then incorporating it into a phantom network prediction. This study finds that 1) increasing the number of polymer arms increases the modulus, 2) the phantom network allows reasonable modulus approximation for four‐arm and six‐arm gels, and 3) the modulus of eight‐arm gels exceeds the phantom network prediction. Since polymer cores act as chemical cross‐links and metal‐coordinated cross‐links form network strands, it is possible that increasing the number of metal‐coordinated linkages per molecule reinforces the chemical cross‐link at the polymer core. 

   more » « less
3. Structure and phase behavior of polymer-linked colloidal gels

   https://doi.org/10.1063/1.5119359  

   Howard, Michael P.; Jadrich, Ryan B.; Lindquist, Beth A.; Khabaz, Fardin; Bonnecaze, Roger T.; Milliron, Delia J.; Truskett, Thomas M. (September 2019, The Journal of Chemical Physics)

   Low-density “equilibrium” gels that consist of a percolated, kinetically arrested network of colloidal particles and are resilient to aging can be fabricated by restricting the number of effective bonds that form between the colloids. Valence-restricted patchy particles have long served as one archetypal example of such materials, but equilibrium gels can also be realized through a synthetically simpler and scalable strategy that introduces a secondary linker, such as a small ditopic molecule, to mediate the bonds between the colloids. Here, we consider the case where the ditopic linker molecules are low-molecular-weight polymers and demonstrate using a model colloid–polymer mixture how macroscopic properties such as the phase behavior as well as the microstructure of the gel can be designed through the polymer molecular weight and concentration. The low-density window for equilibrium gel formation is favorably expanded using longer linkers while necessarily increasing the spacing between all colloids. However, we show that blends of linkers with different sizes enable wider variation in microstructure for a given target phase behavior. Our computational study suggests a robust and tunable strategy for the experimental realization of equilibrium colloidal gels. 

   more » « less
4. Antifouling Activity of Bottlebrush Network Hydrogels

   https://doi.org/10.1021/acsabm.5c00291  

   Chiang, Meng-Chen; Clarke, Brandon R; Tew, Gregory N; Schiffman, Jessica D (April 2025, ACS Applied Bio Materials)

   Mitigating the attachment of microorganisms to polymer biomaterials is critical for preventing hospital-acquired infections. Two chemical strategies to mitigate fouling include fabricating fouling-resistant surfaces, which typically present hydrophilic polymers, such as polyethylene glycol (PEG), or creating fouling-release surfaces, which are generally hydrophobic featuring polydimethylsiloxane (PDMS). Despite the demonstrated promise of employing PEG or PDMS, amphiphilic PEG/PDMS copolymer materials remain understudied. Here, for the first time, we investigated if phase-separated amphiphilic copolymers confounded microbial adhesion. We used bottlebrush amphiphilic PEG/PDMS co-networks and homopolymer networks to study bacterial adhesion across a library of gels (ϕPEG = 0.00, 0.21, 0.40, 0.55, 0.80, and 1.00). Hydrated atomic force microscopy measurements revealed that most of the gels had low surface roughness, less than 5 nm, and an elastic modulus of ∼80 kPa. Interestingly, the surface roughness and elastic modulus of the ϕPEG = 0.40 gel were twice as high as those of the other gels due to the presence of crystalline domains, as confirmed using polarized optical microscopy on the hydrated gel. The interactions of these six well-characterized gels with bacteria were determined using Escherichia coli K12 MG1655 and Staphylococcus aureus SH1000. The attachment of both microbes decreased by at least 60% on all polymer gels versus the glass controls. S. aureus adhesion peaked on the ϕPEG = 0.40, likely due to its increased elastic modulus, consistent with previous literature demonstrating that modulus impacts microbial adhesion. These findings suggest that hydrophilic, hydrophobic, and amphiphilic biomaterials effectively resist the early attachment of Gram-negative and Gram-positive microorganisms, providing guidance for the design of next-generation antifouling surfaces. 

   more » « less
5. Decoupling of Mechanical and Transport Properties in Organogels via Solvent Variation

   https://doi.org/https://doi.org/10.3390/gels7020061  

   Mineart, Kenneth P.; Hong, Cameron; Rankin, Lucas A. (May 2021, Gels)

   Di Chenna, Pablo H. (Ed.)

   Organogels have recently been considered as materials for transdermal drug delivery media, wherein their transport and mechanical properties are among the most important considerations. Transport through organogels has only recently been investigated and findings highlight an inextricable link between gels’ transport and mechanical properties based upon the formulated polymer concentration. Here, organogels composed of styrenic triblock copolymer and different aliphatic mineral oils, each with a unique dynamic viscosity, are characterized in terms of their quasi-static uniaxial mechanical behavior and the internal diffusion of two unique solute penetrants. Mechanical testing results indicate that variation of mineral oil viscosity does not affect gel mechanical behavior. This likely stems from negligible changes in the interactions between mineral oils and the block copolymer, which leads to consistent crosslinked network structure and chain entanglement (at a fixed polymer concentration). Conversely, results from diffusion experiments highlight that two penetrants—oleic acid (OA) and aggregated aerosol-OT (AOT)—diffuse through gels at a rate inversely proportional to mineral oil viscosity. The inverse dependence is theoretically supported by the hydrodynamic model of solute diffusion through gels. Collectively, our results show that organogel solvent variation can be used as a design parameter to tailor solute transport through gels while maintaining fixed mechanical properties. 

   more » « less