Predicting particle transport through an aging polymer using vacancy diffusion

Aaron W. Thornton,Anita J. Hill,Kate M. Nairn,James M. Hill 한국물리학회 2008 Current Applied Physics Vol.8 No.3,4

Understanding the process of particle transport is important for various applications such as separation, storage and blockage ofselected particles within a polymer. The diusivity of particles has been related to the fractional free volumefwithin a sample by theexpressionD(f)=A exp(. B/f A and B.Polymers are known to undergo physical aging such that the free volumedistribution changes over time towards an equilibrium. This phenomenon has been well explained by the vacancy diusion model estab-lished by Curro et al. [J.G. Curro, R.R. Lagasse, R. Simha, Macromolecules 15 (1982) 1621]. Using both the diusion expression and thevacancy diusion model, this paper models particle transport in aging, unaged and aged polymer samples.

Cross-Linked Thermally Rearranged Poly(benzoxazole-<i>co</i>-imide) Membranes for Gas Separation

Calle, Mariola,Doherty, Cara M.,Hill, Anita J.,Lee, Young Moo American Chemical Society 2013 Macromolecules Vol.46 No.20

<P>A novel strategy to tune the cavity size and free volume of thermally rearranged polybenzoxazole (TR-PBO) copolymer membranes by transesterification cross-linking reaction of <I>o</I>-hydroxy polyimide precursors with 1,4-butylene glycol in the solid state is demonstrated in this study. During the thermal rearrangement (TR) process at high temperatures, loose diester interchain cross-linkers are prone to degrade while formation of a much more rigid cross-linked structure occurs following or alongside the imide-to-benzoxazole rearrangement. As a result, a synergistic effect of high permeability and high selectivity appeared to be created in one step, and the newly synthesized cross-linked TR-PBO membranes exhibited outstanding gas separation performance, surpassing the so-called 2008 upper bound for CO<SUB>2</SUB>/CH<SUB>4</SUB> separation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2013/mamobx.2013.46.issue-20/ma4014115/production/images/medium/ma-2013-014115_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma4014115'>ACS Electronic Supporting Info</A></P>

Cross-Linked Thermally Rearranged Poly(benzoxazole-<i>co</i>-imide) Membranes Prepared from <i>ortho</i>-Hydroxycopolyimides Containing Pendant Carboxyl Groups and Gas Separation Properties

Calle, Mariola,Jo, Hye Jin,Doherty, Cara M.,Hill, Anita J.,Lee, Young Moo American Chemical Society 2015 Macromolecules Vol.48 No.8

<P>The incorporation of small amounts of 3,5-diaminobenzoic acid (DABA) comonomer (usually 5–20 mol %) into an <I>ortho</I>-hydroxypolyimide (HPI) precursor constitutes a new methodology to easily improve the gas transport performance of thermally rearranged (TR) polymer membranes. Thermogravimetric analysis (TGA) profiles of HPI with DABA copolyimides (HPID) suggests that there is an overlap between the temperature ranges of two processes: the degradation of DABA carboxyl groups and the actual thermal rearrangement process. During thermal treatment at 450 °C, carboxyl pendant groups in DABA degrade while a more rigid biphenyl cross-linked structure is formed either following or at the same time as the rearrangement of imide to benzoxazole. Mixed-gas CO<SUB>2</SUB>/CH<SUB>4</SUB> (1:1) experiments proved this new series of cross-linked TR poly(benzoxazole-<I>co</I>-imide) (XTR-PBOI) membranes as superior materials for CO<SUB>2</SUB>/CH<SUB>4</SUB> separation applications, with enhanced permeability and selectivity, as well as high resistance to plasticization up to 40 bar.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2015/mamobx.2015.48.issue-8/acs.macromol.5b00298/production/images/medium/ma-2015-00298a_0006.gif'></P>

Spatiotemporal Mapping Reveals Regional Gastrointestinal Dysfunction in mdx Dystrophic Mice Ameliorated by Oral L-arginine Supplementation

( Kristy Swiderski ),( Rebecka Bindon ),( Jennifer Trieu ),( Timur Naim ),( Shana Schokman ),( Mathusi Swaminathan ),( Anita J L Leembruggen ),( Elisa L Hill-yardin ),( Rene Koopman ),( Joel C Bornste 대한소화기 기능성질환·운동학회 2020 Journal of Neurogastroenterology and Motility (JNM Vol.26 No.1

Background/Aims Patients with Duchenne muscular dystrophy exhibit significant, ongoing impairments in gastrointestinal (GI) function likely resulting from dysregulated nitric oxide production. Compounds increasing neuronal nitric oxide synthase expression and/or activity could improve GI dysfunction and enhance quality of life for dystrophic patients. We used video imaging and spatiotemporal mapping to identify GI dysfunction in mdx dystrophic mice and determine whether dietary intervention to enhance nitric oxide could alleviate aberrant colonic activity in muscular dystrophy. Methods Four-week-old male C57BL/10 and mdx mice received a specialized diet either with no supplementation (control) or supplemented (1 g/kg/day) with L-alanine, L-arginine, or L-citrulline for 8 weeks. At the conclusion of treatment, mice were sacrificed by cervical dislocation and colon motility examined by spatiotemporal (ST) mapping ex vivo. Results ST mapping identified increased contraction number in the mid and distal colon of mdx mice on control and L-alanine supplemented diets relative to C57BL/10 mice (P < 0.05). Administration of either L-arginine or L-citrulline attenuated contraction number in distal colons of mdx mice relative to C57BL/10 mice. Conclusions GI dysfunction in Duchenne muscular dystrophy has been sadly neglected as an issue affecting quality of life. ST mapping identified regional GI dysfunction in the mdx dystrophic mouse. Dietary interventions to increase nitric oxide signaling in the GI tract reduced the number of colonic contractions and alleviated colonic constriction at rest. These findings in mdx mice reveal that L-arginine can improve colonic motility and has potential therapeutic relevance for alleviating GI discomfort, improving clinical care, and enhancing quality of life in Duchenne muscular dystrophy.

Architecturing Nanospace via Thermal Rearrangement for Highly Efficient Gas Separations

Thornton, Aaron W.,Doherty, Cara M.,Falcaro, Paolo,Buso, Dario,Amenitsch, Heinz,Han, Sang Hoon,Lee, Young Moo,Hill, Anita J. American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.46

<P>The ability to monitor free volume formation during space-making treatments is critical for the ultrafine tuning of nanospace for efficient gas separation. Here, investigating the polymer thermal rearrangement using synchrotron in situ small-angle X-ray scattering for the first time and combining this information with transport theory, we elucidate the evolution of nanospace features in polymer-based gas separation membranes. The proposed nanospace monitoring technique encompasses the structure–property relationships, therefore offering a powerful tool for tuning the polymer properties for particular gas-related clean energy applications. These results demonstrate that the fine control of the nanospace dimension and magnitude leads to a drastic improvement in gas separation performance above any material to date.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-46/jp410025b/production/images/medium/jp-2013-10025b_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp410025b'>ACS Electronic Supporting Info</A></P>

Nanocrack-regulated self-humidifying membranes

Park, Chi Hoon,Lee, So Young,Hwang, Doo Sung,Shin, Dong Won,Cho, Doo Hee,Lee, Kang Hyuck,Kim, Tae-Woo,Kim, Tae-Wuk,Lee, Mokwon,Kim, Deok-Soo,Doherty, Cara M.,Thornton, Aaron W.,Hill, Anita J.,Guiver, Nature Publishing Group, a division of Macmillan P 2016 Nature Vol.532 No.7600

<P>The regulation of water content in polymeric membranes is important in a number of applications, such as reverse electrodialysis and proton-exchange fuel-cell membranes. External thermal and water management systems add both mass and size to systems, and so intrinsic mechanisms of retaining water and maintaining ionic transport(1-3) in such membranes are particularly important for applications where small system size is important. For example, in proton-exchange membrane fuel cells, where water retention in the membrane is crucial for efficient transport of hydrated ions(1,4-7), by operating the cells at higher temperatures without external humidification, the membrane is self-humidified with water generated by electrochemical reactions(5,8). Here we report an alternative solution that does not rely on external regulation of water supply or high temperatures. Water content in hydrocarbon polymer membranes is regulated through nanometre-scale cracks ('nanocracks') in a hydrophobic surface coating. These cracks work as nanoscale valves to retard water desorption and to maintain ion conductivity in the membrane on dehumidification. Hydrocarbon fuel-cell membranes with surface nanocrack coatings operated at intermediate temperatures show improved electrochemical performance, and coated reverse-electrodialysis membranes show enhanced ionic selectivity with low bulk resistance.</P>