@article{wilder_hall_khan_spontak_2003, title={Effects of composition and matrix polarity on network development in organogels of poly(ethylene glycol) and dibenzylidene sorbitol}, volume={19}, ISSN={["0743-7463"]}, DOI={10.1021/la027081s}, abstractNote={Dibenzylidene sorbitol (DBS) is a low-molecular-weight organic molecule that can gel a variety of organic solvents and polymers by self-organizing into a three-dimensional nanofibrillar network through hydrogen-bonding and phenyl interactions. In this work, we investigate the composition dependence of such “organogels” prepared with poly(ethylene glycol) (PEG) and two PEG derivatives differing in methoxy end- group substitution, which serves to reduce matrix polarity. Transmission electron microscopy reveals that individual DBS nanofibrils measure from about 10 to 70 nm in diameter, with a primary nanofibrillar diameter of about 10 nm. Dynamic rheological measurements indicate that the rate by which the elastic modulus increases during gelation, the temperatures corresponding to gel formation and dissolution, and the magnitude of the elastic modulus are all sensitive to the DBS mass concentration (φ) and the matrix polarity. Hydroxy-end-capped PEG/DBS systems gel more slowly, but dissolve faster, than the...}, number={15}, journal={LANGMUIR}, author={Wilder, EA and Hall, CK and Khan, SA and Spontak, RJ}, year={2003}, month={Jul}, pages={6004–6013} }
 @article{wilder_white_smith_spontak_2003, title={Gel network development inn AB, ABA, and AB/ABA block copolymer solutions inn a selective solvent}, volume={833}, DOI={10.1021/bk-2002-0833.ch017}, abstractNote={In the presence of a selective solvent, ordered block copolymers form micelles that, at sufficiently high copolymer concentrations, serve to stabilize a three-dimensional network and promote physical gelation. This study examines the steady and dynamic rheological properties of micellar solutions composed of AB diblock, ABA triblock and bidisperse mixtures of AB and ABA copolymer molecules. Of particular interest is the unexpected improvement in network development upon addition of an AB copolymer to an ABA copolymer at constant solution composition. This behavior is observed for ABA/solvent systems above and below the critical gelation concentration, and is interpreted in terms of the volume exclusion that occurs in bidisperse mixture of grafted chains.}, journal={Polymer gels: Fundamentals and applications}, publisher={Washington, D.C.: American Chemical Society}, author={Wilder, E. A. and White, S. A. and Smith, S. D. and Spontak, Richard}, editor={H. B. Bohidar, P. Dubin and Osada, Y.Editors}, year={2003}, pages={248–261} }
 @article{wilder_braunfeld_jinnai_hall_agard_spontak_2003, title={Nanofibrillar networks in poly(ethyl methacrylate) and its silica nanocomposites}, volume={107}, ISSN={["1520-6106"]}, DOI={10.1021/jp035113u}, abstractNote={Recent advances in polymer materials design seek to incorporate functionality, enhance existing properties, and reduce weight without compromising mechanical properties or processability. While much attention has been drawn to the development of organic/inorganic hybrid nanocomposites modified with discrete siliceous nanoparticles (such as fumed/colloidal silica or organoclays), other opportunities exist for comparably enlightened materials design. Dibenzylidene sorbitol (DBS) is a sugar derivative that is capable of self-organizing into a 3D nanofibrillar network at relatively low concentrations in a wide variety of organic solvents and polymers. In this work, we explore the morphological characteristics and properties of DBS in poly(ethyl methacrylate) (PEMA) and PEMA nanocomposites with colloidal silica. Transmission electron microscopy and microtomography reveal that the DBS molecules form highly connected networks, with nanofibrils measuring ca. 10 nm in diameter and ranging up to several hundred nanometers in length. Dynamic mechanical property analysis reveals that, while DBS has little effect on glassy PEMA, it serves to increase the elastic modulus in molten PEMA.}, number={42}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Wilder, EA and Braunfeld, MB and Jinnai, H and Hall, CK and Agard, DA and Spontak, RJ}, year={2003}, month={Oct}, pages={11633–11642} }
 @article{wilder_hall_spontak_2003, title={Physical organogels composed of amphiphilic block copolymers and 1,3 : 2,4-dibenzylidene-D-sorbitol}, volume={267}, ISSN={["0021-9797"]}, DOI={10.1016/S0021-9797(03)00619-2}, abstractNote={The 1,3:2,4-dibenzylidene-D-sorbitol (DBS) molecule is capable of self-organizing into nanoscale fibrils through intermolecular forces such as hydrogen bonding and π interactions. At sufficiently high concentrations (typically less than ∼2 wt%), the nanofibrils can form a network that promotes physical gelation of the matrix medium. Previous studies have investigated the mechanism of DBS-induced gelation and the features of DBS-containing gels in poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). In this work, we examine the effect of adding DBS to a series of amphiphilic PPG-b-PEG-b-PPG triblock copolymers differing in composition and molecular weight. Dynamic rheological measurements reveal that the resultant gels are thermoreversible (i.e., they exhibit comparable mechanical properties before dissolution and after reformation under quiescent conditions), exhibiting a maximum in the elastic modulus (G′) at temperatures near the gel dissolution (Td) and formation (Tf) temperatures. Both Td and Tf tend to increase with increasing DBS concentration and PPG content, and their difference decreases with increasing PPG fraction in the copolymer. The magnitude of G′ is sensitive to copolymer composition and polymer identity at low DBS concentrations, but becomes polymer-independent as the DBS network saturates at concentrations in excess of ∼1 wt%.}, number={2}, journal={JOURNAL OF COLLOID AND INTERFACE SCIENCE}, author={Wilder, EA and Hall, CK and Spontak, RJ}, year={2003}, month={Nov}, pages={509–518} }
 @article{spontak_wilder_smith_2001, title={Improved network development in bidisperse AB/ABA block copolymer gels}, volume={17}, ISSN={["0743-7463"]}, DOI={10.1021/la0015819}, abstractNote={Blending a B-selective solvent and an ordered ABA triblock copolymer can, at sufficiently high solvent concentrations, produce a physical gel composed of a network of B midblocks stabilized by A-rich micelles. We demonstrate here that addition of short AB diblock copolymer molecules to such a gel at constant copolymer composition can enhance the solid-like character of the gel, as indicated by an increase in the magnitude of the dynamic elastic modulus. Similarly, addition of AB molecules to a nongelled ABA/solvent system can induce gelation. In light of recent theoretical predictions and related experimental evidence, these results are consistent with a scenario in which tail-induced volume exclusion (due to the presence of AB molecules) within the micellar coronas improves network development through an increase in the population of bridged B midblocks.}, number={8}, journal={LANGMUIR}, author={Spontak, RJ and Wilder, EA and Smith, SD}, year={2001}, month={Apr}, pages={2294–2297} }
 @article{sidorov_volkov_davankov_tsyurupa_valetsky_bronstein_karlinsey_zwanziger_matveeva_sulman_et al._2001, title={Platinum-containing hyper-cross-linked polystyrene as a modifier-free selective catalyst for L-sorbose oxidation}, volume={123}, ISSN={["0002-7863"]}, DOI={10.1021/ja0107834}, abstractNote={Impregnation of hyper-cross-linked polystyrene (HPS) with tetrahydrofuran (THF) or methanol (ML) solutions containing platinic acid results in the formation of Pt(II) complexes within the nanocavities of HPS. Subsequent reduction of the complexes by H2 yields stable Pt nanoparticles with a mean diameter of 1.3 nm in THF and 1.4 nm in ML. The highest selectivity (98% at 100% conversion) measured during the catalytic oxidation of L-sorbose in water is obtained with the HPS-Pt-THF complex prior to H2 reduction. During an induction period of about 100 min, L-sorbose conversion is negligible while catalytic species develop in situ. The structure of the catalyst isolated after the induction period is analyzed by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electron micrographs reveal a broad distribution of Pt nanoparticles, 71% of which measure less than or equal to 2.0 nm in diameter. These nanoparticles are most likely responsible for the high catalytic activity and selectivity observed. The formation of nanoparticles measuring up to 5.9 nm in diameter is attributed to the facilitated intercavity transport and aggregation of smaller nanoparticles in swollen HPS. The catalytic properties of these novel Pt nanoparticles are highly robust, remaining stable even after 15 repeated uses.}, number={43}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Sidorov, SN and Volkov, IV and Davankov, VA and Tsyurupa, MP and Valetsky, PM and Bronstein, LM and Karlinsey, R and Zwanziger, JW and Matveeva, VG and Sulman, EM and et al.}, year={2001}, month={Oct}, pages={10502–10510} }
 @misc{bronstein_chernyshov_valetsky_wilder_spontak_2000, title={Metal nanoparticles grown in the nanostructured matrix of poly(octadecylsiloxane)}, volume={16}, ISSN={["0743-7463"]}, DOI={10.1021/la0009341}, abstractNote={Metal nanoparticles grown within the nanostructured matrix of the amphiphilic polymer poly(octadecylsiloxane) (PODS) are investigated here by transmission electron microscopy. Due to its silanol groups and alkyl chain, PODS forms a bilayered nanostructure containing an intercalated layer of water within an aqueous environment. Replacement of water molecules with metal ions within the siloxy bilayers, followed by reduction, results in the formation of metal nanoparticles. The increase in electron density upon nanoparticle formation permits direct visualization of these bilayers, as well as the individual nanoparticles residing within them. These nanoparticles measure about 1−2 nm in diameter and possess a relatively narrow size distribution due presumably to volume availability within the ordered bilayers of PODS.}, number={22}, journal={LANGMUIR}, author={Bronstein, LM and Chernyshov, DM and Valetsky, PM and Wilder, EA and Spontak, RJ}, year={2000}, month={Oct}, pages={8221–8225} }
 @article{sidorov_bronstein_davankov_tsyurupa_solodovnikov_valetsky_wilder_spontak_1999, title={Cobalt nanoparticle formation in the pores of hyper-cross-linked polystyrene: Control of nanoparticle growth and morphology}, volume={11}, ISSN={["0897-4756"]}, DOI={10.1021/cm990274p}, abstractNote={Impregnation of hyper-cross-linked polystyrene (HPS) by either Co2(CO)8 in 2-propanol or the [Co(DMF)6]2+[Co(CO)4]-2 complex in dimethylformamide (DMF), followed by thermolysis at 200 °C, results in the formation of discrete Co nanoparticles. The concentration and characteristics of such nanoparticles were investigated by X-ray fluorescence (XRF) spectroscopy, ferromagnetic resonance (FMR) spectroscopy, and transmission electron microscopy (TEM). The FMR data here confirm the formation of spherical nanoparticles. At relatively low concentrations of Co, the magnitude of the FMR line width reveals that the mean Co nanoparticle diameter is about 2 nm, which agrees closely with the mean particle diameter discerned by TEM. An increase in Co content higher than 8 wt % is accompanied by an increase in mean particle diameter due to an increase in the population of large Co nanoparticles up to 15 nm across. Regulated nanoparticle growth over a wide range of Co concentrations is attributed to nanoscale HPS cavities...}, number={11}, journal={CHEMISTRY OF MATERIALS}, author={Sidorov, SN and Bronstein, LM and Davankov, VA and Tsyurupa, MP and Solodovnikov, SP and Valetsky, PM and Wilder, EA and Spontak, RJ}, year={1999}, month={Nov}, pages={3210–3215} }
 @article{jackson_wilder_white_bukovnik_spontak_1999, title={Modification of a thermoplastic elastomer gel through the addition of an endblock-selective homopolymer}, volume={37}, ISSN={["1099-0488"]}, DOI={10.1002/(SICI)1099-0488(19990801)37:15<1863::AID-POLB10>3.0.CO;2-X}, abstractNote={Addition of a midblock-selective oil to an ABA triblock copolymer with a rubbery B-midblock and thermoplastic A-endblocks yields a thermoplastic elastomer gel (TPEG) if the oil constitutes the majority blend constituent and a physically crosslinked network, responsible for solid-like mechanical properties, is retained. These blends typically exhibit a micellar morphology in which the micellar cores are composed of the oil-incompatible A-endblocks. Since the micelles serve as crosslink sites, the properties of TPEGs depend on (i) the intrinsic characteristics of the solid-state endblocks, and (ii) the degree to which the micelles interact through bridged and looped midblocks. In this work, a poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and an aliphatic oil are used to prepare TPEGs into which poly(2,6-dimethylphenylene oxide) (PPO), a styrene-compatible homopolymer, is added. The morphologies and bulk properties of these ternary systems are examined by electron microscopy, viscometry, and dynamic rheology. A slight increase in the PPO content in these TPEGs promotes increases in micelle size, confirming that the PPO primarily resides within the micelles, and disordering temperature, signified by an abrupt change in rheological properties. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1863–1872, 1999}, number={15}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Jackson, NR and Wilder, EA and White, SA and Bukovnik, R and Spontak, RJ}, year={1999}, month={Aug}, pages={1863–1872} }