RAFT (reversible addition–fragmentation chain transfer) polymerization has been widely used to synthesize different polymer architectures such as polymer brushes on nanoparticles for incorporation into polymer nanocomposites. It is believed that these polymer brushes, with the same chemistry as the matrix polymer, can be employed to improve filler dispersion by compatibilizing unfavorable enthalpic interactions between the inorganic nanoparticles and their organic host matrices. However, monomodal brush graft nanoparticles are found to aggregate into a range of isotropic and anisotropic morphologies, formed due to a delicate balance between enthalpic and entropic interfacial interactions. This coupling of enthalpy and entropy leaves only a small window of graft densities and molecular weights to obtain randomly dispersed filler morphologies. These issues can be countered by using a bimodal polymer brush that contains a small number of long homopolymer chains that can entangle, and a high density of short brushes that screens the particle/particle attraction, thereby aiding in decoupling the interfacial enthalpic and entropic interactions. In the present work, we demonstrate a robust step-by-step technique using RAFT polymerization to synthesize these bidisperse/bimodal polymer brush-anchored nanoparticles. A layer of dense brush of the first population was initially prepared using surface-initiated RAFT polymerization from colloidal silica nanoparticles. After cleavage of the chain transfer agent from the first population of chain ends, a second RAFT agent was attached onto the silica nanoparticles and then a monomer, which may be the same or different from the first brush, was polymerized. This versatile and widely applicable route enables us to independently control the molecular variables of the attached chains, such as composition, molecular weights and graft densities of the individual populations. The bimodal brush-grafted colloidal silica nanoparticles show superior dispersion and interaction with a homopolymer matrix when compared to monomodal brush-grafted particles.
Developing structure−property relationships between the filler/matrix interface chemistry and the dispersion and interface properties of polymer nanocomposites (PNC) is critical to predicting their bulk mechanical, electrical, and optical properties. In this paper we develop quantitative relationships between interfacial surface energy parameters and the dispersion and T g shifts of PNCs through systematic experiments on an array of hybrid systems spanning a wide range of interfacial interactions. We use four different matrices of surface energies varying from polar to nonpolar (poly(2-vinylpyridine) (P2VP), poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and polystyrene (PS)), filled with three monofunctional-silane modifications of colloidal silica nanospheres (octyldimethylmethoxysilane, chloropropyldimethylethoxysilane, and aminopropyldimethylethoxysilane). We hypothesize the ratio of the work of adhesion between filler and polymer to the work of adhesion of filler to filler (W PF /W FF ), in conjunction with the relative work of adhesion (ΔW a ), can be used to predict the final state of particle dispersion. Additionally, the direction and magnitude of T g deviation from the neat polymer are hypothesized to depend on the work of spreading (W s ) and the dispersion state. Our results suggest a strong and moderate dependence of dispersion on W PF /W FF and ΔW a , respectively. W s in conjunction with the dispersion parameters is shown to dictate the change in T g . Our model represents a significant step toward realizing a priori nanocomposite property prediction.
Cellulose is the most abundant renewable material in nature. In this work, ordered cellulose nanocrystals (CNCs) have been transformed into porous carbon with an increased short-range ordered lattice and percolated carbon nanofiber at a relatively low carbonization temperature of 1000 ºC. When evaluated as anode for sodium-ion batteries (SIBs), the CNC derived porous carbon shows superior performances including a high reversible capacity of 340 mAh/g at a current density of 100 mA/g, which is one of the highest capacity carbon anodes for SIBs. Moreover, the rate capability and cycling stability of the porous carbon are also excellent. The excellent electrochemical performance is attributed to the larger interlayer spacing, porous structure, and high electrical conductivity arising from the ordered carbon lattice and the percolated carbon nanofiber. The formation of nano-sized graphitic carbon from the ordered CNC at the low carbonization temperature of 1000 °C is supported by both molecular dynamic simulations and as well as in-situ TEM measurements. This study shed light on the fundamental understanding of converting hydrocarbon biopolymer from wood to high quality carbon with a large domain of ordered lattice.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.