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1. Polymer-Infiltrated Nanoparticle Films Using Capillarity-Based Techniques: Toward Multifunctional Coatings and Membranes

   https://doi.org/10.1146/annurev-chembioeng-101220-093836  

   Venkatesh, R. Bharath; Manohar, Neha; Qiang, Yiwei; Wang, Haonan; Tran, Hong Huy; Kim, Baekmin Q.; Neuman, Anastasia; Ren, Tian; Fakhraai, Zahra; Riggleman, Robert A.; et al (June 2021, Annual Review of Chemical and Biomolecular Engineering)

   null (Ed.)

   Polymer-infiltrated nanoparticle films (PINFs) are a new class of nanocomposites that offer synergistic properties and functionality derived from unusually high fractions of nanomaterials. Recently, two versatile techniques,capillary rise infiltration (CaRI) and solvent-driven infiltration of polymer (SIP), have been introduced that exploit capillary forces in films of densely packed nanoparticles. In CaRI, a highly loaded PINF is produced by thermally induced wicking of polymer melt into the nanoparticle packing pores. In SIP, exposure of a polymer–nanoparticle bilayer to solvent vapor atmosphere induces capillary condensation of solvent in the pores of nanoparticle packing, leading to infiltration of polymer into the solvent-filled pores. CaRI/SIP PINFs show superior properties compared with polymer nanocomposite films made using traditional methods, including superb mechanical properties, thermal stability, heat transfer, and optical properties. This review discusses fundamental aspects of the infiltration process and highlights potential applications in separations, structural coatings, and polymer upcycling—a process to convert polymer wastes into useful chemicals. 

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2. Freeze‐cast honeycomb structures via gravity‐enhanced convection

   https://doi.org/10.1111/jace.17871  

   Arai, Noriaki; Faber, Katherine T. (May 2021, Journal of the American Ceramic Society)

   Abstract The effect of gravity on directional solidification was investigated in solution‐based freeze casting. A preceramic siloxane‐based polymer was freeze‐cast with a cyclohexene solvent from two different directions: that against the direction of the gravitational force and that in concert with the gravitational force. Because the density of preceramic polymer is higher than the solvent, the segregated polymer creates a denser solution ahead of the freezing front than the underlying solution when the freezing direction is the same as the gravity direction. This results in convective flow in the liquid phase. This convective flow influences constitutional supercooling, which changes not only the pore size of freeze‐cast structure but also the pore morphology from dendritic to cellular pores. 

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3. Elucidations of Chain-Level Structure of Semicrystalline Polymer Freeze-Dried from a Dilute Solution by Solid-State NMR spectroscopy

   Hosseini, Leilasadat; Sun, Chenxuan; Miyoshi, Toshikazu (March 2025, APS)

   Chain entanglements play a crucial role in polymer crystallization, yet their effects on crystallization remain not fully understood. Freeze-drying is one way to potentially preserve disentangled states of long polymer chains. In fact, it is known that freeze-drying (FD) significantly accelerates the crystallization kinetics of semicrystalline polymers. However, the chain-level structure of the FD polymer chains without a long-range order (glass) has been a debatable matter. In this study, we investigate the effect of freeze-drying on single chain-level structures of 13CH3 enriched poly(L-lactic Acid) and 13CH enriched poly(D-lactic acid) racemate by using 1H-1H spin diffusion via 13C detection solid-state NMR spectroscopy. Spatial distributions of PLLA and PDLA glassy chains in the range of a few Å – 30 nm are evaluated via 1H-1H spin diffusion. This analysis provides core-shell morphology of single chains where the outer shell layers include both PDLA and PLLA mixture and the inner core possess a single component. 

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4. Dynamics of meniscus-bound particle clusters in extensional flow

   https://doi.org/10.1122/8.0000805  

   Chaudhary, Sagar; Velankar, Sachin S; Schroeder, Charles M (May 2024, Journal of Rheology)

   Capillary suspensions are three-phase mixtures containing a solid particulate phase, a continuous liquid phase, and a second immiscible liquid forming capillary bridges between particles. Capillary suspensions are encountered in a wide array of applications including 3D printing, porous materials, and food formulations, but despite recent progress, the micromechanics of particle clusters in flow is not fully understood. In this work, we study the dynamics of meniscus-bound particle clusters in planar extensional flow using a Stokes trap, which is an automated flow control technique that allows for precise manipulation of freely suspended particles or particle clusters in flow. Focusing on the case of a two-particle doublet, we use a combination of experiments and analytical modeling to understand how particle clusters rearrange, deform, and ultimately break up in extensional flow. The time required for cluster breakup is quantified as a function of capillary number Ca and meniscus volume V. Importantly, a critical capillary number Cacrit for cluster breakup is determined using a combination of experiments and modeling. Cluster relaxation experiments are also performed by deforming particle clusters in flow, followed by flow cessation prior to breakup and observing cluster relaxation dynamics under zero-flow conditions. In all cases, experiments are complemented by an analytical model that accounts for capillary forces, lubrication forces, hydrodynamic drag forces, and hydrodynamic interactions acting on the particles. Results from the analytical models are found to be in good agreement with experiments. Overall, this work provides a new quantitative understanding of the deformation dynamics of capillary clusters in extensional flow. 

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5. Effects of polymer–nanoparticle interactions on the viscosity of unentangled polymers under extreme nanoconfinement during capillary rise infiltration

   https://doi.org/10.1039/c7sm02465g  

   Hor, Jyo Lyn; Wang, Haonan; Fakhraai, Zahra; Lee, Daeyeon (January 2018, Soft Matter)

   We explore the effect of confinement and polymer–nanoparticle interactions on the viscosity of unentangled polymers undergoing capillary rise infiltration (CaRI) in dense packings of nanoparticles. In CaRI, a polymer is thermally induced to wick into the dense packings of nanoparticles, leading to the formation of polymer-infiltrated nanoparticle films, a new class of thin film nanocomposites with extremely high concentrations of nanoparticles. To understand the effect of this extreme nanoconfinement, as well as polymer–nanoparticle interactions on the polymer viscosity in CaRI films, we use two polymers that are known to have very different interactions with SiO 2 nanoparticles. Using in situ spectroscopic ellipsometry, we monitor the polymer infiltration process, from which we infer the polymer viscosity based on the Lucas–Washburn model. Our results suggest that physical confinement increases the viscosity by approximately two orders of magnitude. Furthermore, confinement also increases the glass transition temperature of both polymers. Thus, under extreme nanoconfinement, the physical confinement has a more significant impact than the polymer–nanoparticle interactions on the viscosity of unentangled polymers, measured through infiltration dynamics, as well as the glass transition temperature. These findings will provide fundamental frameworks for designing processes to enable the fabrication of CaRI nanocomposite films with a wide range of nanoparticles and polymers. 

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