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1. pH-Mediated nanoparticle dynamics in hydrogel nanocomposites

   https://doi.org/10.1039/d0sm02213f  

   Rose, Katie A. ; Lee, Daeyeon ; Composto, Russell J. ( March 2021 , Soft Matter)

   null (Ed.)

   The effect of static silica particles on the dynamics of quantum dot (QD) nanoparticles grafted with a poly(ethylene glycol) (PEG) brush in hydrogel nanocomposites is investigated using single particle tracking (SPT). At a low volume fraction of homogeneously dispersed silica ( Φ = 0.005), two distinct populations of PEG-QDs are observed, localized and mobile, whereas almost all PEG-QDs are mobile in neat hydrogel ( Φ = 0.0). Increasing the silica particle concentration ( Φ = 0.01, 0.1) results in an apparent change in the network structure, confounding the impact of silica on PEG-QD dynamics. The localized behavior of PEG-QDs is attributed to pH-mediated attraction between the PEG brush on the probe and surface silanol groups of silica. Using quartz crystal microbalance with dissipation (QCM-D), the extent of this interaction is investigated as a function of pH. At pH 5.8, the PEG brush on the probe can hydrogen bond with the silanol groups on silica, leading to adsorption of PEG-QDs. In contrast, at pH 9.2, silanol groups are deprotonated and PEG-QD is unable to hydrogen bond with silica leading to negligible adsorption. To test the effect of pH, PEG-QD dynamics are further investigated in hydrogel nanocomposites at Φ = 0.005. SPT agrees with the QCM-D results; at pH 5.8, PEG-QDs are localized whereas at pH 9.2 the PEG-QDs are mobile. This study provides insight into controlling probe transport through hydrogel nanocomposites using pH-mediated interactions, with implications for tuning transport of nanoparticles underlying drug delivery and nanofiltration. 

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2. A novel strategy to functionalize styrene butadiene rubber toward enhanced interfacial interaction with silica

   https://doi.org/10.1002/app.54476  

   Xu, Yihui ; Liu, Yudong ; Qin, Xuan ; Liu, Jun ; Zhang, Liqun ( July 2023 , Journal of Applied Polymer Science)

   Incorporation of nanofillers (such as silica) into elastomer matrix is the most common strategy to prepare high‐performance rubber products. However, the poor dispersion of nanofillers in non‐affinity rubber materials and the weak interfacial interaction significantly limit the processing and mechanical properties. To reduce the polarity difference and enhance the interfacial interaction between silica and styrene butadiene rubber (SBR), we prepared a hydroxyethyl acrylate‐grafted SBR (SBR‐g‐HEA) through the redox initiator system, and subsequently fabricated SBR‐g‐HEA/silica nanocomposites by simple mechanical blending. The effects of reaction conditions on the grafting rate were studied in detail. ATR‐FTIR and¹H‐NMR collectively confirmed the successful grafting of HEA groups on SBR molecular chains, and the grafting fraction could be regulated from 0% to 2.5%. Scanning electron microscope (SEM) and rubber processing analyzer (RPA) showed that the incorporation of HEA could significantly improve the dispersion of silica nanoparticles in SBR matrix. Notably, the resulting SBR‐g‐HEA exhibited significantly enhanced attributes when compared to their unmodified counterparts, including superior mechanical properties, improved wear resistance, and reduced heat generation. The strategy proposed here provided insights toward the fabrication of non‐affinity rubber/filler nanocomposites for high‐performance rubber products and green tire.

    

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3. Reversible assembly of silica nanoparticles at water–hydrocarbon interfaces controlled by SDS surfactant

   https://doi.org/10.1039/D1NR06807E  

   Mohammed, Sohaib ; Kuzmenko, Ivan ; Gadikota, Greeshma ( December 2021 , Nanoscale)

   Achieving reversible and tunable assembly of silica nanoparticles at liquid–liquid interfaces is vital for a wide range of scientific and technological applications including sustainable subsurface energy applications, catalysis, drug delivery and material synthesis. In this study, we report the mechanisms controlling the assembly of silica nanoparticles (dia. 50 nm and 100 nm) at water–heptane and water–toluene interfaces using sodium dodecyl sulfate (SDS) surfactant with concentrations ranging from 0.001–0.1 wt% using operando ultrasmall/small-angle X-ray scattering, cryogenic scanning electron microscopy imaging and classical molecular dynamics simulations. The results show that the assembly of silica nanoparticles at water–hydrocarbon interfaces can be tuned by controlling the concentrations of SDS. Silica nanoparticles are found to: (a) dominate the interfaces in the absence of interfacial SDS molecules, (b) coexist with SDS at the interfaces at low surfactant concentration of 0.001 wt% and (c) migrate toward the aqueous phase at a high SDS concentration of 0.1 wt%. Energetic analyses suggest that the van der Waals and electrostatic interactions between silica nanoparticles and SDS surfactants increase with SDS concentration. However, the favorable van der Waals and electrostatic interactions between the silica nanoparticles and toluene or heptane decrease with increasing SDS concentration. As a result, the silica nanoparticles migrate away from the water–hydrocarbon interface and towards bulk water at higher SDS concentrations. These calibrated investigations reveal the mechanistic basis for tuning silica nanoparticle assembly at complex interfaces. 

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4. Mechanical and Optical Properties of Stretchable Silicon Nanocrystal/Polydimethylsiloxane Nanocomposites

   https://doi.org/10.1002/pssa.202000015  

   Izadi, Alborz ; Toback, Branton ; Sinha, Mayank ; Millar, Andrew ; Bigelow, Michael ; Roccabianca, Sara ; Anthony, Rebecca ( June 2020 , physica status solidi (a))

   Nanoparticle‐infused polymer composites have long been an area of interest due to the typically stabilizing effects they have on the mechanical behavior of the composites, as well as added functionalities such as reduced surface resistance. Newer applications of these nanocomposites include dispersing optoelectronically functional nanoparticles in polymer matrices, for example, including luminescent nanocrystals in rigid slabs for luminescent solar concentrating photovoltaics and electrochromic panels. Dispersion of luminescent nanocrystals in stretchable polymers adds novel possibilities for applications, such as wearable health monitoring systems, flexible communications devices, and more. To leverage the exciting combined properties that these nanocomposites promise, there is a pressing need to evaluate and understand the interconnections between the optical effects, mechanical behavior, and the properties of the constituents. Herein, the optical and mechanical behavior of brightly emissive silicon nanocrystal/polydimethylsiloxane (PDMS) nanocomposites are investigated as a function of nanocrystal concentration and nanocrystal surface functionality. Mechanically, incorporating the nanocrystals at higher concentration leads to a dramatic reduction in the mechanical properties of the nanocomposite. The results suggest that the nanocrystal inclusions interfere with polymer cross‐linking, changing the mechanical behavior of the host PDMS as compared to the control.

    

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5. 2D‐Nanofiller‐Based Polymer Nanocomposites for Capacitive Energy Storage Applications

   https://doi.org/10.1002/smsc.202300016  

   Bera, Sumit ; Singh, Maninderjeet ; Thantirige, Rukshan ; Tiwary, Saurabh Kr ; Shook, Brian T. ; Nieves, Elianie ; Raghavan, Dharmaraj ; Karim, Alamgir ; Pradhan, Nihar R. ( April 2023 , Small Science)

   High‐energy‐density storage devices play a major role in modern electronics from traditional lithium‐ion batteries to supercapacitors for a variety of applications from rechargeable devices to advanced military equipment. Despite the mass adoption of polymer capacitors, their application is limited by their low energy densities and low‐temperature tolerance. Polymer nanocomposites based on 2D nanomaterials have superior capacitive energy densities, higher thermal stabilities, and higher mechanical strength as compared to the pristine polymers and nanocomposites based on 0D or 1D nanomaterials, thus making them ideal for high‐energy‐density dielectric energy storage applications. Here, the recent advances in 2D‐nanomaterial‐based nanocomposites and their implications for energy storage applications are reviewed. Nanocomposites based on conducting 2D nanofillers such as graphene, reduced graphene oxide, MXenes, semiconducting 2D nanofillers including transition metal dichalcogenides such as MoS₂, dielectric 2D nanofillers including hBN, Mica, Al₂O₃, TiO₂, Ca₂Nb₃O₁₀and MMT, and their effects on permittivity, dielectric strength, capacitive energy density, efficiency, thermal stability, and the mechanical strength, are discussed. Also, the theory and machine‐learning‐guided design of polymer 2D nanomaterial composites is learnt and the challenges and opportunities for developing ultrahigh‐capacitive‐energy‐density devices based on these nanofiller polymer composites are presented.

    

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