Aqueous Dispersions of Extraordinarily Small Polyethylene Nanoparticles (original) (raw)
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Submicron Polyethylene Particles from Catalytic Emulsion Polymerization
Journal of the American Chemical Society, 2003
General methods and materials DSC was performed on a Perkin Elmer DSC 7 instrument or on a Pyris 1 DSC at a heating and cooling rate of 10 K min-1. Samples were heated from room temperature to 140 °C, and kept at this temperature for 1 min before cooling to room temperature. Optionally the cycle was repeated several times. DSC traces of polymer dispersions were obtained on 20 to 30 mg of dispersion with ca. 5 % by weight polymer content. Optionally, stability can also be improved by addition of SDS surfactant or of ethylene glycol as a viscosity enhancer. Standard crimped sample pans proved to be reliably tight and stable up to 140 °C. T m data reported are local maxima of the second heats. 1 TEM investigations were carried out on a LEO 912 Omega apparatus using an acceleration voltage of 120 kV. Samples were prepared by applying a drop of the latex to a carbon coated grid. Samples were not stained, except for the microtome cuts (stained with RuO 4). For microtome cutting, the latex particles were embedded in nanoplast ® (a hydrophilic melamine resin). Microtome cuts of ca. 50 nm thickness were prepared with a Reichert & Jung Ultracut E microtome equipped with a 45° diamond knife supplied by Diatome. AFM experiments were performed with a Nanoscope III scanning probe microscope. The height and phase images were obtained simultaneously while operating the instrument in the tapping mode under ambient conditions. Images were taken at the fundamental resonance frequency of the Si cantilevers which was typically around 180 kHz. Typical scan speeds during recording were 0.3-1 line/s using scan heads with a maximum range of 16 × 16 µm. The phase images represent the variations of relative phase shifts (i. e. the phase angle of the interacting cantilever relative to the phase angle of the freely oscillating cantilever at the resonance frequency) and are thus able to distinguish materials by their material properties (e.g. amorphous and crystalline polymers). Polyethylene latexes were prepared according to [2]. Ethylene was polymerized in aqueous emulsion with SDS as a surfactant (0.2 % to 1 % by weight) at 30 to 70 °C (usually 50 °C) employing an in situ catalyst formed from 2,3,5,6-tetrachloroquinone, triphenylphosphine and bis(1,5cyclooctadiene)nickel. The hydrophobic catalyst was added as a solution in toluene/hexadecane droplets (2 mL) which were miniemulsified 3 in the aqueous phase (100 mL). Latexes of 5 to 20 wt-% polymer content were obtained.
Cryo-TEM and Image Analysis of Polymer Nanoparticle Dispersions
2004
The interest in aqueous-based resins for various applications such as coating or in the pharmaceutical field has recently increased due to the need for constant cost reductions and the necessity to control emissions of volatile organic compounds. As most polymers used in these applications are water insoluble, aqueous- based resins generally contain particles in suspension. The average particle size and size distribution are essential data on which the stability and properties of the dispersions depend [1]. Light scattering and cryo-transmission electron microscopy (cryo-TEM) have proved to be complementary techniques to characterise various natural [2] or synthetic [3] polymer nanoparticles dispersed in water. Light scattering is non-destructive and provides fast measurements in a wide range of particle size. However, it cannot analyse double populations, large distributions, absorbent materials, or mixtures of substances with different densities [4]. In this study, cryo-TEM and im...
Interaction of a Polymer of Intrinsic Microporosity (PIM-1) with Penetrants
American Journal of Applied Chemistry, 2015
The characterisation, solubility testing, and alcohol adsorption studies of PIM-1 are reported. Techniques used for characterisation are N 2 sorption and ATR-FTIR analysis. A number of solvents were tested for their ability to dissolve low molecular weight (~30 000 gmol-1), medium molecular weight (~60 000 gmol-1), and high molecular weight (~120 000 gmol-1) PIM-1.Results showed solubility of PIM-1 in these solvents to be dependent on molar mass. CHCl 3 , tetrahydrofuran (THF), CH 2 Cl 2 , dicholobenzene (DCB), 1,2,4-trichlorobenzene (TCB), and acetophenone were found to be good solvents at all molecular weights. Treatment of PIM-1 with nonsolvents, namely: small alcohols and water, followed by solvent removal, caused swelling, resulting in an increase in BET surface area of about 11 %, except for water, which reduced BET surface area by the same amount (11 %). Methanol (MeOH) treatment resulted in a new population of micropores around 0.6 nm. The change after ethanol (EtOH) and propanol (PrOH) treatment was not as significant. Hydrogen bonding between alcohols and PIM-1 was also investigated using shifts in the frequencies of FTIR peaks for the ether and the nitrile functional groups. Nitrile group frequencies for the alcohols were consistently blue-shifted, whereas the ether frequencies were red shifted. Both red-and blue-shifts were used as a measure of hydrogen bond strength.
Macromolecules, 2006
Introduction. Controlled ordering of nanoparticles in block polymer matrices has been exploited to synthesize novel composites for a variety of applications such as catalysis, semiconductors, photonic materials, electricity, and biological and medical fields. 1-3 Recently, a novel strategy 4-7 has been developed to organize nanoparticles in polymer matrices with controlled patterns by exploiting microphase separation of block copolymers, and it is observed that the confinement of nanoparticles in organized patterns improves the optical 8,9 and mechanical properties 10 of the nanocomposites. To gain better insight into the physical properties of these functional materials, significant effort is being devoted to understanding the morphologies of nanocomposites both theoretically and experimentally. Since solvent selectivity is an important parameter that determines the phase behavior of block copolymer solutions, its role has to be considered in solution-based synthetic routes for tailoring morphologies of nanocomposites. It has been found that order-disorder (ODT) and order-order (OOT) transition temperatures are correlated to the polymer concentration in solution, and the composition profiles and dimensions of microdomains vary with dilution. In a selective solvent, the solvent expands only the favorable block, causing shifts along both temperature and composition directions in the phase diagram. Effects similar to this can also be obtained by sequestering nanoparticles in the favorable domain. By using solvents with different selectivity and concentration of polymer and nanoparticles, it would be possible to tune the morphologies in the microdomains and consequently the nanocomposites.
Probing Polymer Material Properties on the Nanometer Scale
Microscopy Today, 2010
Polymers play an essential role in modern materials science. Because of the wide variety of mechanical and chemical properties of polymers, they are used in nearly every industry. Knowledge about their physical and chemical properties on the nanometer scale is often required. However, some details about the phase-separation process in polymers are difficult to study with conventional characterization techniques because these methods cannot chemically differentiate phases with good spatial resolution without damage, staining, or preferential solvent washing.
Journal of Colloid and Interface Science, 2003
Solubilization environment afforded by several of the novel allyl glycidyl ether-modified methylhydrosiloxane polymers are investigated using a common polycyclic aromatic hydrocarbon fluorescence probe, pyrene. The backbone of the polymer has been modified by the addition of an alkyl chain of varying length (either C 8 , C 12 , or C 18 ) and to differing degrees of substitution. The nomenclature adopted for the purposes of these studies is as follows: "AGENT" represents the backbone polymer with no alkyl substitution, and "OAGENT," "DAGENT," and "SAGENT" are substituted with n-octyl, n-dodecyl, and n-octadecyl, respectively. The percentage of alkyl substitution is designated as 10, 15, and 20%. The pyrene polarity scale (defined as the ratio of the intensity of peak I to peak III) was used to determine the relative dipolarity of the cybotactic region provided by ∼1 w/w% aqueous polymer solutions compared to 10 mM sodium dodecylsulfate (SDS) micellar solution. Results indicate that 10-15% DAGENT afforded the most hydrophobic solubilization site, followed by 15% OAGENT and 15% SAGENT. In addition, as the degree of alkyl substitution of DAGENT increased from 10 to 20%, the cybotactic region appeared to become more hydrophobic. Furthermore, a deeper investigation into the relative size of the solubilization site revealed that all alkyl-substituted polymers promoted excimer formation at relatively low pyrene concentrations, indicating the possibility of localized concentration enhancement within the solvation pockets and/or compartmentalization of the solute molecules. The pyrene fluorescence excitation data strongly indicates ground-state heterogeneity that is most prominent in AGENT and decreases as the alkyl chain length is increased. This provides a relative sense of the size and shape of the solvation pockets afforded by each polymer solution. An overall analysis of the collected data indicated that these alkyl-substituted polymers may provide a more selective and efficient pseudostationary phase in electrokinetic chromatography with better solvation capacity for hydrophobic compounds compared to SDS. (C.P. Palmer).