Grafted Polymer Chain Length Research Articles

A CO2-gated anodic aluminum oxide based nanocomposite membrane for de-emulsification.

A carbon-dioxide-responsive organic-inorganic nanocomposite membrane based on a through-hole anodic aluminum oxide (AAO) template was constructed. The composite was prepared via a surface-initiated reversible addition-fragmentation chain-transfer (SI-RAFT) polymerization strategy to achieve the grafting of poly(methyl methacrylate-co-2-(diethylamino)ethyl methacrylate) brushes on the AAO membrane. The grafted polymer chain length could be controlled based on the feed ratio between the free chain transfer agent (CTA) and reactive monomer, e.g., methyl methacrylate and 2-(diethylamino)ethyl methacrylate, resulting in a membrane that features adjustable water permeability. Importantly, the membrane pore size and surface wettability could be switched from hydrophobic to hydrophilic upon the introduction of carbon dioxide and nitrogen gases. This allowed for the nanocomposite membrane to be utilized for controlled water flux and oil/water emulsion separation. The simple fabrication methodology as well as sustainable gaseous stimulus will be useful for the construction of future smart membranes.

Polymer Brush Graft-Modified Starch-Based Nanoparticles as Pickering Emulsifiers.

We study biosourced core-shell particles with a starch-based core and thermo-responsive polymer brush shell using surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) as a Pickering stabilizer. The shell endows the Pickering stabilizer with reversible emulsification/demulsification of oil and water properties. The initiator attached to the starch-based nanosphere (Br-SNP) core particle was first fabricated using the precipitation method. Subsequently, dense poly( N-isopropylacrylamide) (PNIPAM) brush graft-modified starch-based nanoparticles (SNP- g-PNIPAM) were obtained via the SI-SET-LRP process. Interfacial properties of the resultant particles were analyzed by interfacial tensiometer measurements, as were the effects of the grafted polymer chain length and temperature on the interfacial activity. Pickering emulsion was obtained using SNP- g-PNIPAM particles as the stabilizer. The effect of the concentration of the Pickering stabilizer on the size of emulsion droplets was analyzed. The emulsification/demulsification process of the Pickering emulsion can be reversed and easily repeated by changing the temperature.

High-Frequency Mechanical Behavior of Pure Polymer-Grafted Nanoparticle Constructs.

Polymer-grafted nanoparticle (GNP) membranes show increased gas permeability relative to pure polymer analogs, with this effect evidently tunable through systematic variations in the grafted polymer chain length and grafting density. Additionally, these materials show less deleterious aging effects relative to the pure polymer. To better understand these issues, we explore the solid-state mechanical properties of GNP layers using quartz crystal microbalance (QCM) spectroscopy, which operates under conditions (≈5 MHz) that we believe are relevant to gas transport. The GNP's high-frequency storage moduli exhibit a characteristic increase with increasing nanoparticle (NP) core loading, consistent with past work on the reinforcement of polymers physically well mixed with bare NPs. However, these GNPs show a substantial, nonmonotonic decrease in loss as a function of chain length (at fixed grafting density), with the loss minimum corresponding to the chain length with the maximum gas permeability. We speculate that this feature corresponds to a dynamical transition, where the GNP membranes go from a jammed solid (colloid-like) to liquid-like (polymer-controlled) behavior with increasing chain length.

Assessing Pair Interaction Potentials of Nanoparticles on Liquid Interfaces.

The pair interaction potentials of polymer-grafted silica nanoparticles (NPs) at liquid surfaces were determined by scanning electron microscopy, exploiting the nonvolatility of ionic liquids to stabilize the specimens against microscope vacuum. Even at near contact, individual, two-dimensionally well-dispersed NPs were resolved. The potential of mean force, reduced to the pair interaction potential for dilute NPs, was extracted with good accuracy from the radial distribution function, as both NP diameter and grafted polymer chain length were varied. While NP polydispersity somewhat broadened the core repulsion, the pair potential well-approximated a hard sphere interaction, making these systems suitable for model studies of interfacially bound NPs. For short (5 kDa) poly(ethylene glycol) ligands, a weak (< kB T) long-range attraction was discerned, and for ligands of identical length, pair potentials overlapped for NPs of different diameter; the attraction is suggested to arise from ligand-induced menisci. To understand better the interactions underlying the pair potential, NP surface-binding energies were measured by interfacial tensiometry, and NP contact angles were assessed by atomic force microscopy and transmission electron microscopy.

Identifying the Ideal Characteristics of the Grafted Polymer Chain Length Distribution for Maximizing Dispersion of Polymer Grafted Nanoparticles in a Polymer Matrix

We investigate, using theory and simulations, the role of the short and long grafted chains in polydisperse polymer grafted nanoparticles in stabilizing particle dispersion in a chemically similar polymer matrix in the presence of particle–particle attractions. The effect of the short and long chains in a polydisperse or bidisperse graft length distribution on the potential of mean force between the polymer grafted nanoparticles is coupled and distinct from their role in the corresponding deconstructed short and long monodisperse distributions. At high grafting density, the increased monomer crowding near the particle surface from both short and long chains maximizes shielding of particle–particle attraction, while the length and crowding of long chains away from the particle surface determine the location, range, and strength of the steric repulsion and midrange attraction. We find that to maximize grafted nanoparticle dispersion, it is best to synthesize grafted particles at high grafting density with p...

Adhesive cell cultivation on polymer particle having grafted epoxy polymer chain

In this study, we synthesized a new cell immobilization support having poly(glycidyl methacrylate) as a graft polymer chain and used this support for cell cultivation. Base polymer particle was synthesized by suspension polymerization and epoxy polymer chain was extended from particle surface on graft polymerization. Produced polymer particles had broad particle size distribution ranging from 20 to 1000μm and the degree of polymerization of grafted polymer chain was ranged from 500 to 1000. The effects of various factors, such as grafted polymer chain length and its surface density, composition of base polymer network and graft polymer chain, on the cell growth of murine fibroblast cell line (MS-5 cell) on polymer particle were studied. This polymer particle could cultivate not only fibroblast cell line but also epidermal cell line (HeLa cell), osteoblast cell line (MC3T3E1 cell), and chondrocyte cell line (ch-8 cell) on its surface. Growth rate is almost the same as that of cells using poly(styrene) tissue culture dish. To apply this cell cultivation system for examination of cell co-culture, HeLa cell immobilized on 100μm of polymer particle was successfully co-cultured with MS-5 cell immobilized on 300μm of polymer particle for four weeks.

Protein‐resistant polyurethane via surface‐initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate

Protein-resistant polyurethane (PU) surfaces were prepared by surface-initiated simultaneous normal and reverse atom transfer radical polymerization (s-ATRP) of poly(oligo(ethylene glycol) methacrylate) (poly (OEGMA)). Oxygen plasma treatment was employed for initial activation of the PU surface. The grafted polymer chain length was adjusted by varying the molar ratio of monomer to sacrificial initiator in solution from 5:1 to 200:1. The modified PU surfaces were characterized by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Protein adsorption experiments from tris-buffered saline (TBS) and plasma were carried out to evaluate the protein-resistance of the surfaces. Adsorption from single and binary protein solutions as well as from plasma was significantly reduced after modification. Adsorption decreased with increasing poly(OEGMA) chain length. Fibrinogen (Fg) adsorption on the 200:1 monomer/initiator surface was in the range of 3-33 ng/cm(2) representing 96-99% reduction compared with the unmodified PU. Fg adsorption from 0.01-10% plasma was as low as 1-5 ng/cm(2). Moreover, binary protein adsorption experiments using Fg and lysozyme (Lys) showed that protein size is a factor in the protein resistance of these surfaces.