skip to main content

Search for: All records

Creators/Authors contains: "Miller, Kevin M."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Dual ionic liquid-substituted cellulosic materials were prepared by coupling a series of alkyne-terminated imidazoles with variable carbon spacer with azide-functionalized cellulose, followed by quaternization and anion exchange. All three of the [NTf2]-bearing cellulosic materials exhibited Tg values below zero and could be cast as flexible films, which exhibited stress at break values exceeding 2.3 MPa with strain at break values up to 252%. X-ray scattering analyses indicated the amorphous nature of the cellulosic materials with three scattering peaks observed, from high-to-low q, corresponding to the amorphous halo, anion-to-anion distance, and the distance between ion aggregates, respectively. The highest degree of ionic aggregation was found to exist in the CELL-C12-NTf2 material, presumably due to the longer alkyl tethers causing more uniformity in the interaggregate spacing. The conductivity of the films was found to be on the order of 10−5−10−6 S/cm at 30 °C. A slower increase in conductivity with temperature was observed for systems where ionic aggregation was the strongest. 
    more » « less
    Free, publicly-accessible full text available February 16, 2025
  2. Abstract

    In this study, poly(ethylene terephthalate)‐block‐polyethylene (PET‐PE) multiblock copolymers (MBCPs) with block molar masses of ~4 or 7 kg mol−1and either alternating or random block sequencing, and a PE‐PET‐PE triblock copolymer (TBCP) of comparable total molar mass, were synthesized. To explore the effect of molecular architecture on compatibilization, both MBCPs and TBCPs were blended into 80/20 wt/wt mixtures of PET/linear low‐density PE (LLDPE). Compatibilization was remarkably efficient for all MBCP types, with the addition of 0.2 wt% yielding blends nearly as tough as PET homopolymer. Addition of MBCP also significantly decreases LLDPE dispersed phase sizes compared to PET/LLDPE neat blends, as much as 80% in as‐mixed blends and by a factor of 10 in post‐mixing thermally annealed samples. Conversely, the TBCP was less efficient at decreasing domain sizes of the blends and improving the mechanical properties, requiring loadings of 1 wt% to produce comparably tough blends. Peel tests of PET/BCP/LLDPE trilayer films showed that both MBCPs and TBCP all improve interfacial strength over a PET‐PE bilayer film by two orders of magnitude; however, when the BCPs were preloaded into LLDPE, only the MBCP containing films showed strong adhesion highlighting their potential utility as adhesive agents in multilayer films.

    more » « less
  3. null (Ed.)
  4. Abstract

    Herein, the thiol‐yne photoclick reaction was utilized as a method for synthesizing imidazolium‐containing ionene networks whereby a bisalkynyl‐functionalized imidazolium [NTf2] ionic liquid was polymerized with the tetrafunctional thiol PTMP (pentaerythritol tetrakis(3‐mercaptopropionate)). The thiol:yne functional group ratio was varied in order to examine the breadth of thermal, mechanical, and conductive properties available from the resulting networks. The stoichiometric 1:1 thiol:yne network exhibited very high thiol and alkyne conversions by FT‐IR spectroscopy and a gel fraction greater than 95%. The highestTgvalue (3.5°C) and stress at break (1.13 MPa) were also observed for this network. As either thiol or alkyne functional group concentration was increased, the networks were noticeably lower inTgand stress at break with a modest increase in % elongation. Ionic conductivities were found to be on the order of 10−9to 10−7 S/cm at 30°C. Normalization of the ionic conductivity curves did not lead to a complete collapse meaning that the observed differences in conductivity are not solely dependent uponTg. When compared to analogous imidazolium‐containing, thiol‐ene ionene networks, the thiol‐yne networks were found to be slightly more mechanically robust, but approximately one order of magnitude lower in terms of ionic conductivity.

    more » « less
  5. null (Ed.)
  6. null (Ed.)
  7. Poly(ionic liquid) covalently adaptable networks containing thermoreversible furan–maleimide linkages were prepared and characterized for their thermal, mechanical and conductive properties. Self-healing behaviour was initially evaluated using oscillatory rheology where a G ′/ G ′′ crossover temperature of ∼110 °C was observed. Anhydrous conductivities, as determined by dielectric relaxation spectroscopy, were found to be on the order of 10 −8 S cm −1 at 30 °C. Recovery of >70% of the original stress and strain at break was found within 2 hours at 105 °C as determined from tensile testing experiments, with breakage occurring at a new point on the film. Recovery of conductivity was completed utilizing chronoamperometric cycling whereby >75% of the original current was recovered within two hours at 110 °C. 
    more » « less
  8. Abstract

    Thiol–ene photopolymerization was employed in order to prepare a series of covalently crosslinked bis(phosphonium)‐containing poly(ionic liquid) (PIL) networks. While the counteranion was held constant (NTf2), the structure of the bis(phosphonium)‐containing ‘ene’ monomer was varied in order to explore the breadth of thermal, mechanical and conductive properties available for this system. Towards this end, it was determined that more flexible spacers within the cationic monomer led to PIL networks with lowerTgvalues and higher conductivities. Most notable was a two‐ to three‐orders‐of‐magnitude increase in ionic conductivity (from 10−9to 10−6S cm−1at 30 °C, 30% relative humidity) when the R group on phosphonium was changed from phenyl to isopropyl. Changing the functional group ratio to off‐stoichiometry also led to a slight increase in conductivity. Although the thermal stability (Td5%) of the phosphonium ionic liquid monomers was found to be significantly higher (>400 °C) than that of analogous imidazolium monomers, this improvement was not observed to directly transfer over to the polymer where a two‐step decomposition pathway was observed. The first step is attributed to the thiol monomer backbone while the second step correlates well with decomposition of the phosphonium portion of the PIL. © 2019 Society of Chemical Industry

    more » « less