Rene Crombez

Triblock Copolymer Based on Poly(propylene oxide) and Poly(1‐[11‐acryloylundecyl]‐3‐methyl‐imidazolium bromide)

The controlled atom transfer radical polymerization of an ionic liquid, 1-(11-acryloylundecyl)-3-methyl imidazolium bromide (ILBr), from both ends of a telechelic poly(propylene oxide) (PPO) macroinitiator, end-functionalized with bromoisobutyryloyl is reported. The resulting highly water-soluble triblock, poly(ILBr-b-PO-b-ILBr) is multistimuli responsive. This new class of triblocks exhibits classical surface activity in lowering surface tension at the air-water interface and in modifying wetting in waterborne coatings. It also immunizes model colloids against coagulation induced by Debye-Hückel (indifferent electrolyte) electrostatic screening. Further, sol-gel thermoreversibility is unexpectedly found as an additional form of stimuli responsiveness.

Single-wall carbon nanotube latexes.

A nanolatex copolymer (25−30 nm) of an imidalozium bromide acrylate is reported that provides stable waterborne dispersions of single-walled carbon nanotubes (SWCNT) and thermally and electrically conducting coatings that adhere to plastics. This approach to dispersing SWCNT leaps past previous reports by providing stabilization and binder functions simultaneously. Resulting films exhibit 10-fold anisotropy in both thermal and electrical conductivity and appear free of interfacial phonon scattering problems. The electrically conducting networks assembled upon film formation provide a new route to priming plastics for electrodeposition in addition to providing simple antistatic layer formulations. The efficacy of these nanolatexes is assigned to the imidazolium and bromide components shown in other studies to have an affinity for graphene surfaces.

Aqueous Graphene Dispersions–Optical Properties and Stimuli-Responsive Phase Transfer

We demonstrate essentially complete exfoliation of graphene aggregates in water at concentrations up to 5% by weight (166-fold greater than previous high concentration report) using recently developed triblock copolymers and copolymeric nanolatexes based on a reactive ionic liquid acrylate surfactant. We demonstrate that the visible absorption coefficient in aqueous dispersion, 48.9 ± 1.3 cm(2)/mg at 500 nm, is about twice that currently accepted, and we show that this value is a greatest lower bound to extant macroscopic single sheet optical studies of graphene when one considers both fine structure constant and excitonic mechanisms of visible absorption. We also show that dilute and concentrated graphene dispersions are rheo-optical fluids that exhibit an isotropic to nematic transition upon application of a shear field, and we demonstrate stimuli-responsive phase transfer.

Nanofluid acrylate composite resins—initial preparation and characterization

The introduction of solvent-free nanofluids composed of suitably surface functionalized nanoparticles (nanosilica for example) has led to some interesting new materials. Here we show that the process of surface functionalizing with both nanofluid-inducing surface groups and with reactive (acrylate) surface groups produces solvent free nanofluids that can be incorporated in reactive coatings, films, and bulk materials and composites. We demonstrate in this study some composite materials based on our new reactive acrylate-nanofluid and a commercially available tetraacrylate. While it is widely known that addition of fillers and nanoparticles to resins often produces increased storage and elastic moduli, while generally also increasing brittleness, we found in this study that increasing weight fractions of reactive nanofluid in an otherwise very brittle environment, produces materials that are tougher (softer) while maintaining or decreasing storage moduli (depending on whether the loading is small or large). Possible applications include a new class of clearcoat protective overcoats and interesting new materials where softness is a formulation variable, such as in plasticization. In addition, we demonstrate that nanocomposites at high loading may be made thermally responsive in ways the parent polymer matrix is not. AFM surface analyses show that the nanofluid particles exhibit surface activity at the air–polymer interface similar to that observed for interfacial nanoparticles in Pickering emulsions. This surface activity, along with the intrinsic softness of the nanofluid particles, may offer a simple approach to providing intrinsic lubrication for polymeric surfaces subject to frictional shear.

Mechanical and biological properties of nanoporous carbon membranes

Implantable blood glucose sensors have inadequate membrane-tissue interfaces for long term use. Biofouling and inflammation processes restrict biosensor membrane stability. An ideal biosensor membrane material must prevent protein adsorption and exhibit cell compatibility. In addition, a membrane must exhibit high porosity and low thickness in order to allow the biosensor to respond to analyte fluctuations. In this study, the structural, mechanical and biological properties of nanoporous alumina membranes coated with diamond-like carbon thin films were examined using scanning probe microscopy, nanoindentation and MTT viability assay. We anticipate that this novel membrane material could find use in immunoisolation devices, kidney dialysis membranes and other medical devices encountering biocompatibility issues that limit in vivo function.

Polymer dewetting via stimuli responsive structural relaxation-contact angle analysis

Thin films of a stimuli-responsive homopolymer dewet as a stimulus response after anion exchange of the imidazoliums counter anion. Contact angle analysis and interfacial energy considerations indicate dewetting goes counter to increasing spreading coefficient. Intrafilm stress arising from structural relaxation drives the dewetting.

Inkjet Printing of Cyanoacrylate Adhesive

In this study, we have demonstrated the use of piezoelectric inkjet printing to fabricate microscale patterns of Vetbond® n-butyl cyanoacrylate tissue adhesive. Optical microscopy, atomic force microscopy, nanoindentation, and a cell viability assay were used to examine the structural, mechanical, and biological properties of microscale cyanoacrylate patterns. The ability to rapidly fabricate microscale patterns of medical and veterinary adhesives will enable reduced bond lines between tissues, improved tissue integrity, and reduced toxicity. We envision that piezoelectric inkjet deposition of cyanoacrylates and other medical adhesives may be used to enhance wound repair in microvascular surgery.

Microscale Patterning of Two-Component Biomedical Hydrogel

In this study, piezoelectric inkjet technology was used for microscale patterning of a two-component medical hydrogel (sold under the registered trademark Coseal®). A MEMS-based piezoelectric actuator was used to control the flow of polyethylene glycol in a sodium phosphate/sodium carbonate solution through inkjet nozzles. A hydrogen chloride solution was subsequently used to cross-link the polyethylene glycol material. Optical microscopy, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and nanoindentation studies were performed to examine the structural, chemical, and mechanical properties of the inkjetted hydrogel material. Scanning electron micrographs revealed that the inkjetted material exhibited randomly oriented cross-linked networks. Fourier transform infrared spectroscopy revealed that the piezoelectric inkjet technology technique did not alter chemical bonding in the material. Piezoelectric inkjet printing of medical hydrogels may improve wound repair in next generation eye surgery, fracture fixation, and wound closure devices.