Paul H. Maupin

Flammability, thermal stability, and phase change characteristics of several trialkylimidazolium salts

Room temperature ionic liquids (RTILs) have emerged as tunable and potentially “greener” solvents for a multitude of applications. To investigate the solvent properties and potential use as a thermal fluid, a study was initiated to determine the effects of anion type, C-2 hydrogen substitution, and alkyl chain length on the flammability, thermal stability, and phase change characteristics of 1,2,3-trialkylimidazolium room temperature ionic liquids. A Setaflash flashpoint apparatus was used to determine the flammabilities of the RTILs. No flashpoints were detected for any of the imidazolium based RTILs below 200 °C, the maximum temperature of the instrument. The thermal stabilities of the RTILs were measured using the technique of thermogravimetric analysis. The 1,2,3-trialkylimidazolium compounds exhibit slightly higher thermal stabilities than the comparable 1,3-dialkylimidazolium compounds; RTILs with nucleophilic anions decompose about 150 °C lower than RTILs with bulky fluoride containing anions; the alkyl chain length does not have a large effect on the thermal stability of the RTILs; and the pyrolysis decomposition exhibits higher thermal stabilities via a different mechanism than the oxidative decomposition. In addition, it was found that although the calculated onset temperatures were above 350 °C, significant decomposition does occur 100 °C or more below these temperatures. The phase change behaviors of several imidazolium based RTILs were characterized by differential scanning calorimetry. The melting points of the RTILs increased with increasing alkyl chain length. Most of the salts studied exhibited significant undercooling, which decreased as the length of the alkyl chain was increased. The hexafluorophosphate and bromide RTILs exhibited polymorphic and liquid crystalline behaviors as the alkyl chain length was increased above C10. The clearing point temperatures increased more rapidly with alkyl chain length than the melting point temperatures.

Revealing the interface in polymer nanocomposites.

The morphological characterization of polymer nanocomposites over multiple length scales is a fundamental challenge. Here, we report a technique for high-throughput monitoring of interface and dispersion in polymer nanocomposites based on Förster resonance energy transfer (FRET). Nanofibrillated cellulose (NFC), fluorescently labeled with 5-(4,6-dichlorotriazinyl)-aminofluorescein (FL) and dispersed into polyethylene (PE) doped with Coumarin 30 (C30), is used as a model system to assess the ability of FRET to evaluate the effect of processing on NFC dispersion in PE. The level of energy transfer and its standard deviation, measured by fluorescence spectroscopy and laser scanning confocal microscopy (LSCM), are exploited to monitor the extent of interface formation and composite homogeneity, respectively. FRET algorithms are used to generate color-coded images for a real-space observation of energy transfer efficiency. These images reveal interface formation at a nanoscale while probing a macroscale area that is large enough to be representative of the entire sample. The unique ability of this technique to simultaneously provide orientation/spatial information at a macroscale and nanoscale features, encoded in the FRET signal, provides a new powerful tool for structure-property-processing investigation in polymer nanocomposites.

Monitoring clay exfoliation during polymer/clay compounding using fluorescence spectroscopy

A fluorescent probe molecule, Nile blue perchlorate, was used to monitor the compounding of nylon 11 with clay filler. Prior to compounding, Nile blue was incorporated into the gallery region between silicate layers of the clay by an ion-exchange process. While residing in the gallery, fluorescence from Nile blue was quenched because of fluorescence resorption in a high dye concentration environment. However, when clay is compounded with the nylon, clay exfoliation allowed the dye to escape the gallery region and to become dispersed in the resin matrix. During batch mixing, we observed that fluorescence increased with time indicating that dye molecules were migrating from the gallery. Experiments carried out using a twin-screw extruder to compound resin and clay showed that twin-screw compounding was much more efficient in producing clay exfoliation than was the batch mixer.

Formation of extended ionomeric network by bulk polymerization of l,d-lactide with layered-double-hydroxide

Abstract We report the formation of an ionomeric network in a poly( l , d -lactide) hybrid nanocomposite, (PLDLA-HYB) during in-situ melt polymerization of l , d -lactide in the presence of magnesium/aluminum layered-double-hydroxide (LDH) without added catalyst. The effect of LDH mass loading and reaction time on molecular mass and yield of soluble poly( l , d -lactide) (PLDLA-SOL) present in the hybrid was investigated for a better understanding of the conflicting roles of LDH in polymerization and degradation of PLDLA-SOL. High molecular mass PLDLA-SOL is obtained through initiation of polymerization by LDH. However an additional insoluble organic–inorganic fraction, INSOL, is also observed within the product when PLDLA-SOL is extracted using methylene chloride as solvent. It is proposed that INSOL is an ionomeric network comprising hydrogen-bonded, or otherwise co-ordinated, lactic acid monomer salts of magnesium, together with PLDLA in a 24%–76% mass ratio.