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Olsen BD, Alcazar D, Krikorian V, Toney MF, Thomas EL, Segalman RA. Crystalline Structure in Thin Films of DEH−PPV Homopolymer and PPV-b-PI Rod−Coil Block Copolymers. Macromolecules 2007. [DOI: 10.1021/ma0714971] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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127
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Kang Y, Walish JJ, Gorishnyy T, Thomas EL. Broad-wavelength-range chemically tunable block-copolymer photonic gels. NATURE MATERIALS 2007; 6:957-960. [PMID: 17952084 DOI: 10.1038/nmat2032] [Citation(s) in RCA: 342] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2007] [Accepted: 09/12/2007] [Indexed: 05/25/2023]
Abstract
Responsive photonic crystals have been developed for chemical sensing using the variation of optical properties due to interaction with their environment. Photonic crystals with tunability in the visible or near-infrared region are of interest for controlling and processing light for active components of display, sensory or telecommunication devices. Here, we report a hydrophobic block-hydrophilic polyelectrolyte block polymer that forms a simple one-dimensional periodic lamellar structure. This results in a responsive photonic crystal that can be tuned via swelling of the hydrophilic layers by contact with a fluid reservoir. The glassy hydrophobic layer forces expansion of the hydrophilic layer along the layer normal, yielding extremely large optical tunability through changes in both layer thickness and index of refraction. Polyelectrolyte polymers are known to be highly responsive to a range of stimuli. We show very large reversible optical changes due to variation of the salt concentration of a water reservoir. These one-dimensional Bragg stacks reflect incident light from the ultraviolet-visible region to the near-infrared region (lambda(peak)=350-1,600 nm) with over a 575% change in the position of the stop band. Our work demonstrates the extremely high responsivity possible for polyelectrolyte-based photonic materials.
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Lee W, Yoon J, Lee H, Thomas EL. Direct 3-D Imaging of the Evolution of Block Copolymer Microstructures Using Laser Scanning Confocal Microscopy. Macromolecules 2007. [DOI: 10.1021/ma0711341] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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129
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Xiong H, Zheng JX, Van Horn RM, Jeong KU, Quirk RP, Lotz B, Thomas EL, Brittain WJ, Cheng SZ. A new approach in the study of tethered diblock copolymer surface morphology and its tethering density dependence. POLYMER 2007. [DOI: 10.1016/j.polymer.2007.04.067] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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130
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Price FP, Gilmore PT, Thomas EL, Laurence RL. Polymer/polymer diffusion. I. Experimental technique. ACTA ACUST UNITED AC 2007. [DOI: 10.1002/polc.5070630107] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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131
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Jang JH, Ullal CK, Kooi SE, Koh C, Thomas EL. Shape control of multivalent 3D colloidal particles via interference lithography. NANO LETTERS 2007; 7:647-51. [PMID: 17295546 DOI: 10.1021/nl0626277] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We present a new route for the fabrication of highly nonspherical complex multivalent submicron particles. This technique exploits the ability of holographic interference lithography to control geometrical elements such as symmetry and volume fraction in 3D lattices on the submicron scale. Colloidal particles with prescribed complex concave shapes are obtained by cleaving low volume fraction connected structures fabricated by interference lithography. Controlling which Wyckoff sites in the space group of the parent structure are connected assures specific "valencies" of the particles. Two types of particles, 2D "4-valent" and 3D "6-valent" particles are fabricated via this technique. In addition to being able to control multivalent particle shape, this technique has the potential to provide tight control over size, yield, and dispersity.
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Shojaee-Moradie F, Baynes KCR, Pentecost C, Bell JD, Thomas EL, Jackson NC, Stolinski M, Whyte M, Lovell D, Bowes SB, Gibney J, Jones RH, Umpleby AM. Exercise training reduces fatty acid availability and improves the insulin sensitivity of glucose metabolism. Diabetologia 2007; 50:404-13. [PMID: 17149589 DOI: 10.1007/s00125-006-0498-7] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/25/2006] [Accepted: 09/06/2006] [Indexed: 12/16/2022]
Abstract
AIMS/HYPOTHESIS It is not known whether the beneficial effects of exercise training on insulin sensitivity are due to changes in hepatic and peripheral insulin sensitivity or whether the changes in insulin sensitivity can be explained by adaptive changes in fatty acid metabolism, changes in visceral fat or changes in liver and muscle triacylglycerol content. We investigated the effects of 6 weeks of supervised exercise in sedentary men on these variables. SUBJECTS AND METHODS We randomised 17 sedentary overweight male subjects (age 50 +/- 2.6 years, BMI 27.6 +/- 0.5 kg/m(2)) to a 6-week exercise programme (n = 10) or control group (n = 7). The insulin sensitivity of palmitic acid production rate (Ra), glycerol Ra, endogenous glucose Ra (EGP), glucose uptake and glucose metabolic clearance rate were measured at 0 and 6 weeks with a two-step hyperinsulinaemic-euglycaemic clamp [step 1, 0.3 (low dose); step 2, 1.5 (high dose) mU kg(-1) min(-1)]. In the exercise group subjects were studied >72 h after the last training session. Liver and skeletal muscle triacylglycerol content was measured by magnetic resonance spectroscopy and visceral adipose tissue by cross-sectional computer tomography scanning. RESULTS After 6 weeks, fasting glycerol, palmitic acid Ra (p = 0.003, p = 0.042) and NEFA concentration (p = 0.005) were decreased in the exercise group with no change in the control group. The effects of low-dose insulin on EGP and of high-dose insulin on glucose uptake and metabolic clearance rate were enhanced in the exercise group but not in the control group (p = 0.026; p = 0.007 and p = 0.04). There was no change in muscle triacylglycerol and liver fat in either group. CONCLUSIONS/INTERPRETATION Decreased availability of circulating NEFA may contribute to the observed improvement in the insulin sensitivity of EGP and glucose uptake following 6 weeks of moderate exercise.
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Huang P, Zheng JX, Leng S, Van Horn RM, Jeong KU, Guo Y, Quirk RP, Cheng SZD, Lotz B, Thomas EL, Hsiao BS. Poly(ethylene oxide) Crystal Orientation Changes in an Inverse Hexagonal Cylindrical Phase Morphology Constructed by a Poly(ethylene oxide)-block-polystyrene Diblock Copolymer. Macromolecules 2007. [DOI: 10.1021/ma061871h] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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134
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Ma M, Krikorian V, Yu JH, Thomas EL, Rutledge GC. Electrospun polymer nanofibers with internal periodic structure obtained by microphase separation of cylindrically confined block copolymers. NANO LETTERS 2006; 6:2969-72. [PMID: 17163741 DOI: 10.1021/nl062311z] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Continuous fibers are described having concentric layer or aligned sphere microphase-separated, styrene-isoprene block copolymer morphologies. The fibers are obtained by a two-fluid coaxial electrospinning technique in which the desired block copolymer is encapsulated as the core component within a polymer shell having a high glass transition temperature (Tg). The fibers range in diameter from 300 to 800 nm, and the block copolymer core ranges from 50 to 500 nm. Subsequent annealing of the fibers above the upper Tg of the block copolymer but below the Tg of the shell polymer results in microphase separation of the block copolymer under cylindrical confinement. The resulting fibers exhibit improved long-range order. This two-step strategy creates the opportunity to fabricate continuous nanofibers with periodic internal structure.
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Thomas EL, Groishnyy T, Maldovan M. Phononics: colloidal crystals go hypersonic. NATURE MATERIALS 2006; 5:773-4. [PMID: 17013407 DOI: 10.1038/nmat1744] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
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136
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Yoon J, Lee W, Thomas EL. Optically pumped surface-emitting lasing using self-assembled block-copolymer-distributed Bragg reflectors. NANO LETTERS 2006; 6:2211-4. [PMID: 17034085 DOI: 10.1021/nl061490h] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
A thin-film organic laser cavity using a block-copolymer-based one-dimensional (1D) photonic crystal was fabricated. Polymeric distributed Bragg reflectors (DBRs) were prepared through the self-assembly of a lamellar-forming poly(styrene-b-isoprene) (PS-b-PI) diblock copolymer having a 1D photonic stop band overlapping with the fluorescence spectrum of a gain medium. Optically pumped surface-emitting lasing was obtained using poly(methyl methacrylate) (PMMA) doped with 1,4-di-(2-methylstyryl)benzene (Bis-MSB) as an organic gain medium and the polymeric self-assembled DBR as a spectral-band selective feedback element.
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Ding DK, Thomas EL. Structures of Point Integer Disclinations and Their Annihilation Behavior in Thermotropic Liquid Crystal Polyesters. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259408029748] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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138
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Briber RM, Thomas EL. Investigation of two crystal forms in MDI/BDO-based polyurethanes. J MACROMOL SCI B 2006. [DOI: 10.1080/00222348308224773] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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139
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140
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Hand JW, Li Y, Thomas EL, Rutherford MA, Hajnal JV. Prediction of specific absorption rate in mother and fetus associated with MRI examinations during pregnancy. Magn Reson Med 2006; 55:883-93. [PMID: 16508913 DOI: 10.1002/mrm.20824] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
There is uncertainty regarding the risk posed by magnetic resonance imaging (MRI) examinations to pregnant patients. The most frequently used methods, such as single-shot fast spin echo (ssFSE), often require operation at the specific absorption rate (SAR) limits imposed by safety guidelines. With the introduction of higher-field systems, such limits will be even more significant for fetal imaging. An electromagnetic solver based on the time domain finite integration technique (FIT) was used to predict SAR in an anatomically realistic model of a pregnant patient (28 weeks' gestation) associated with the radiofrequency (RF) fields from birdcage body coils typical of 1.5 T and 3 T MRI systems (i.e., operating at approximately 64 and 127 MHz, respectively). The results suggest that 1) the highest local SAR is in the mother, with the fetus being exposed to a peak of approximately 40-60% of that value at 64 MHz, increasing to approximately 50-70% at 127 MHz; 2) compliance with U.S. Food and Drug Administration (FDA) and International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines requires control of SAR values averaged over 1 g or 10 g of tissue, respectively; and 3) compliance with Medical Device Agency (MDA) guidelines requires control of the maximum SAR(10g) within the fetus.
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Huang P, Guo Y, Quirk RP, Ruan J, Lotz B, Thomas EL, Hsiao BS, Avila-Orta CA, Sics I, Cheng SZ. Comparison of poly(ethylene oxide) crystal orientations and crystallization behaviors in nano-confined cylinders constructed by a poly(ethylene oxide)-b-polystyrene diblock copolymer and a blend of poly(ethylene oxide)-b-polystyrene and polystyrene. POLYMER 2006. [DOI: 10.1016/j.polymer.2005.06.129] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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142
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Park JW, Thomas EL. Frustrated Crystallization of a Rod−Coil Block Copolymer from Its Liquid Crystalline State. Macromolecules 2006. [DOI: 10.1021/ma060336e] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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143
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Osuji CO, Chao CY, Ober CK, Thomas EL. Supramolecular Microphase Separation in a Hydrogen-Bonded Liquid Crystalline Comb Copolymer in the Melt State. Macromolecules 2006. [DOI: 10.1021/ma052547+] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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144
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Korley LTJ, Pate BD, Thomas EL, Hammond PT. Effect of the degree of soft and hard segment ordering on the morphology and mechanical behavior of semicrystalline segmented polyurethanes. POLYMER 2006. [DOI: 10.1016/j.polymer.2006.02.093] [Citation(s) in RCA: 275] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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145
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Jang JH, Ullal CK, Gorishnyy T, Tsukruk VV, Thomas EL. Mechanically tunable three-dimensional elastomeric network/air structures via interference lithography. NANO LETTERS 2006; 6:740-3. [PMID: 16608275 DOI: 10.1021/nl052577q] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We show how to employ an interference lithographic template (ILT) as a facile mold for fabricating three-dimensional bicontinuous PDMS (poly(dimethylsiloxane)) elastomeric structures and demonstrate the use of such a structure as a mechanically tunable PDMS/air phononic crystal. A positive photoresist was used to make the ILT, and after infiltration with PDMS, the resist was removed in a water-based basic solution which avoided PDMS swelling or pattern collapse occurring during the ILT removal process. Since the period of the structure is approximately 1 microm, the density of states of gigahertz phonons are altered by the phononic PDMS/air crystal. Brillouin light scattering (BLS) was employed to measure phononic modes of the structure as a function of mechanical strain. The results demonstrate that the phononic band diagram of such structures can be tuned mechanically.
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Tsui NT, Paraskos AJ, Torun L, Swager TM, Thomas EL. Minimization of Internal Molecular Free Volume: A Mechanism for the Simultaneous Enhancement of Polymer Stiffness, Strength, and Ductility. Macromolecules 2006. [DOI: 10.1021/ma060047q] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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147
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Yoon J, Mathers RT, Coates GW, Thomas EL. Optically Transparent and High Molecular Weight Polyolefin Block Copolymers toward Self-Assembled Photonic Band Gap Materials. Macromolecules 2006. [DOI: 10.1021/ma0516642] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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148
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Zheng JX, Xiong H, Chen WY, Lee K, Van Horn RM, Quirk RP, Lotz B, Thomas EL, Shi AC, Cheng SZD. Onsets of Tethered Chain Overcrowding and Highly Stretched Brush Regime via Crystalline−Amorphous Diblock Copolymers. Macromolecules 2005. [DOI: 10.1021/ma052166w] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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149
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Thomas SW, Long TM, Pate BD, Kline SR, Thomas EL, Swager TM. Perpendicular Organization of Macromolecules: Synthesis and Alignment Studies of a Soluble Poly(iptycene). J Am Chem Soc 2005; 127:17976-7. [PMID: 16366528 DOI: 10.1021/ja056241u] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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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Deng T, Breen C, Breiner T, Swager TM, Thomas EL. A block copolymer nanotemplate for mechanically tunable polarized emission from a conjugated polymer. POLYMER 2005. [DOI: 10.1016/j.polymer.2005.08.060] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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