Biomedical subjects

Steven R Kline

Publications and source records attributed to Steven R Kline.

6 recordsLinked to original sources

PubMed2006

Polymerized rodlike nanoparticles with controlled surface charge density.

Stable rodlike nanoparticles with highly controlled surface charge density have been developed by the free radical polymerization of the mixture of polymerizable cationic surfactant, cetyltrimethylammonium 4-vinylbenzoate (CTVB), and hydrotropic salt sodium 4-styrenesulfonate (NaSS) in aqueous solution. The surface charge of the polymerized CTVB/NaSS rodlike nanoparticles was controlled by varying the NaSS concentration during the polymerization process, and the charge variation was interpreted in terms of the overcharging effect in colloidal systems. The SANS measurements show that the diameter of the polymerized CTVB/NaSS rodlike nanoparticles is constant at 4 nm and the particle length ranges from 24 to 85 nm, depending on the NaSS concentration. The polymerized particles are longest when the NaSS concentration is 5 mol % which corresponds to the charge inversion or neutral point. The SANS and zeta potential measurements show that the Coulomb interactions between the particles are strongly dependent on the NaSS concentration and the zeta potential of the polymerized CTVB/NaSS nanoparticles changes from positive to negative (+12.8 approximately -44.2 mV) as the concentration of NaSS increases from 0 to 40 mol %. As the NaSS concentration is further increased, the zeta potential is saturated at approximately -50 mV.

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PubMed2005

perpendicular organization of macromolecules: synthesis and alignment studies of a soluble poly(iptycene).

We describe herein a polymeric material that prefers to align perpendicular to a stretch-aligned polymer host in the solid state. Poly(iptycene) poly-1 was synthesized from monomer 1 under hyperbaric techniques via a Diels-Alder polymerization. Polarized excitation spectra of the anthracene end groups in this material in a stretch-aligned, solution-cast poly(vinyl chloride) (PVC) film showed that the poly(iptycene) prefers to align normal (counter aspect ratio) to the stretching direction of the PVC. This is explained by a "threading" mechanism, whereby the PVC intercalates through the internal free volume presented by poly-1, similar to effects observed in small molecule iptycenes under similar conditions.

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PubMed2005

Metathesis depolymerization for removable surfactant templates.

Current methodologies for the production of meso- and nanoporous materials include the use of a surfactant to produce a self-assembled template around which the material is formed. However, post-production surfactant removal often requires centrifugation, calcination, and/or solvent washing which can damage the initially formed material architecture(s). Surfactants that can be disassembled into easily removable fragments following material preparation would minimize processing damage to the material structure, facilitating formation of templated hybrid architectures. Herein, we describe the design and synthesis of novel cationic and anionic surfactants with regularly spaced unsaturation in their hydrophobic hydrocarbon tails and the first application of ring closing metathesis depolymerization to surfactant degradation resulting in the mild, facile decomposition of these new compounds to produce relatively volatile nonsurface active remnants.

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PubMed2005

Thermally cleavable surfactants based on furan-maleimide Diels-Alder adducts.

Two new surfactant molecules are reported that contain thermally labile Diels-Alder adducts connecting the hydrophilic and hydrophobic sections of each molecule. The two surfactants possess identical hydrophobic dodecyl tail segments but have phenol and carboxylic acid hydrophilic headgroups, respectively. Deprotonation with potassium hydroxide affords the formation of water-soluble surfactants. Room temperature aqueous solutions of both surfactants exhibit classical surface-active agent behavior similar to common analagous alkylaryl surfactant molecules. Critical micelle concentrations have been determined for each surfactant through dynamic surface tension and dye solubilization techniques. Small-angle neutron scattering measurements of the aqueous surfactant solutions indicate the presence of spherical micelles with radii of 16.5 angstroms for the carboxylate and 18.8 angstroms for the phenolate. When these surfactants are exposed to elevated temperatures (>50 degrees C), the retro Diels-Alder reaction occurs, yielding hydrophilic and hydrophobic fragments. Aqueous solutions of each surfactant subsequently exhibit a loss of all surface-active behavior and the micellar aggregates are no longer detectable.

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PubMed2004

Characterization of rodlike aggregates generated from a cationic surfactant and a polymerizable counterion.

The polymerization of elongated micellar structures offers a novel approach to the production of high-aspect-ratio, water-soluble amphiphilic nanorods. A cationic surfactant with a vinyl-containing counterion, cetyltrimethylammonium 4-vinylbenzoate, has been synthesized and polymerized to produce high-aspect-ratio nanoparticles which are insensitive to changes in solution conditions. Aggregates are polymerized over a range of initiator concentrations allowing for control of the product length. Small-angle neutron scattering and light scattering are used to characterize the dimensions of the polymerized aggregates, showing them to have a fixed radius of 2 nm and contour lengths varying from 96 to 340 nm. Proton NMR verifies the chemical structure and provides insight into the mobility of the aggregate components. Finally, gel permeation chromatography of the polymer extracted from the aggregates indicates that the polymerization reaction controls the aggregate dimensions.

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PubMed2004

The adsorption of polymerized rodlike micelles at the solid-liquid interface.

Solutions of rodlike polymeric micellar aggregates, formed from the polymerization of cetyltrimethyl-ammonium 4-vinylbenzoate (CTVB), adsorb at the solid-liquid interface. The poly-CTVB aggregates are imaged in situ using soft contact atomic force microscopy. The aggregates form self-organized two-dimensional films that show a high degree of order on nanometer to micrometer length scales. Unlike their simple surfactant analogues, the adsorbed layer structures are permanently adsorbed and the structure is resilient to washing with pure solvent. In the case of poly-CTVB, the adsorbed aggregates appear to be rigid cylindrical structures of between 30 and 60 nm in length. At the interface, the center to center spacing of the aligned aggregates is 8+/-1 nm. Images of a second series ofpolymerized aggregates formed by the copolymerization of CTVB with sodium vinyltosylate revealed a change in the aggregate structure to a set of linked spherical aggregates. These polymerized aggregates also spontaneously form a permanent adsorbed layer at the solid-liquid interface.

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