Article

Water-induced (nano) organization in poly(ethyl acrylate-co-hydroxyethyl acrylate) networks

Centro de Investigación Príncipe Felipe, Autopista del Saler 16, 46013 Valencia, Spain
European Polymer Journal (Impact Factor: 3.01). 07/2008; 44(7):1996-2004. DOI: 10.1016/j.eurpolymj.2008.04.032

ABSTRACT

The conformational changes in poly(ethyl acrylate-co-hydroxyethyl acrylate), P(EA-co-HEA) chains, which constitute a copolymer network hydrogel, induced by the presence of water are investigated by different experimental techniques and compared with the behaviour of the corresponding xerogel. The mechanical relaxation spectrum shows the presence of a new water-induced relaxation, the water content dependence of the glass transition is measured by DSC, and the dielectric relaxation assesses the effect of water for the lower concentrations. Hydrophilic and hydrophobic monomeric units in the P(EA-co-HEA) network are able to aggregate to form two separated (nano)phases in the presence of water due to hydrophobic interaction. Phase separation takes place when the water content of the sample is higher than a critical value estimated as two water molecules per –OH group in the copolymer chain. The existence of the hydrophobic domains is detected by their glass transition being nearly independent on the water content of the sample. Phase separation is also clearly revealed by phase angle measurements in AFM experiments.

Download full-text

Full-text

Available from: Roser Sabater i Serra
  • Source
    • "Such a structure favors the hydrophilic phase to behave like in the bulk phase maintaining its sorption ability [13] [14]. On the other hand, a lot of effort was attempted to combine hydrophilic and hydrophobic phase in the form of random copolymers [5] [15] [16]. Their molecular structure and homogeneity are guided from the chemical reactivity and the composition of the reacting monomers during radical polymerization. "
    [Show abstract] [Hide abstract]
    ABSTRACT: This work probes the hydration properties and molecular dynamics of hybrid poly(hydroxyethyl-co-ethyl acrylate)/silica hydrogels. Two series of hybrid copolymers were prepared by simultaneous polymerization and silica preparation by sol-gel method, the first with hydroxyethyl acrylate/ethyl acrylate (HEA/EA) composition at 100/0, 90/10, 70/30, 50/50, 30/70, 10/90 and fixed silica content at 20 wt.%, and the second with fixed HEA/EA organic composition at 70/30 and 0, 5, 10 and 20 wt.% of silica. The hydration properties of these systems were studied at 25 °C by exposure to several controlled water vapor atmospheres (water activities 0-0.98) in sealed jars and by immersion in distilled water. Finally, the molecular dynamics of the hydrated hybrids at several levels of hydration was probed with Thermally Stimulated Depolarization Currents (TSDC) in the temperature interval between -150 and 20 °C. The results indicate that a critical region of silica content between 10 and 20 wt.% exists, above which silica is able to form an inorganic network. This silica network prevents the expansion of water clusters inside the hydrogels and subsequently the total stretching of the polymer network without obstructing the water sorption at the first stages of hydration from the dry state. As concerns the copolymer composition, the presence of EA reduces water sorption and formation of water clusters affecting directly to the hydrophilic regions. The TSDC thermograms reveal the presence of a single primary main broad peak denoted as αcop relaxation process, which is closely related to the copolymer glass transition, and of a secondary relaxation process denoted as βsw relaxation, which originates from the rotational motions of the lateral hydroxyl groups with attached water molecules. The single αcop implies structural homogeneity at the nanoscale in HEA-rich samples (xHEA > 0.5), while for high EA content (xEA ≥ 0.5) phase separation is detected. Both relaxation processes show strong dependence on water content and organic phase composition. © 2009 Elsevier Ltd. All rights reserved.
    Full-text · Article · Jan 2010 · European Polymer Journal
  • Source
    • "Such a structure favors the hydrophilic phase to behave like in the bulk phase maintaining its sorption ability [13] [14]. On the other hand, a lot of effort was attempted to combine hydrophilic and hydrophobic phase in the form of random copolymers [5] [15] [16]. Their molecular structure and homogeneity are guided from the chemical reactivity and the composition of the reacting monomers during radical polymerization. "
    [Show abstract] [Hide abstract]
    ABSTRACT: This work probes the hydration properties and molecular dynamics of hybrid poly(hydroxyethyl-co-ethyl acrylate)/silica hydrogels. Two series of hybrid copolymers were prepared by simultaneous polymerization and silica preparation by sol–gel method, the first with hydroxyethyl acrylate/ethyl acrylate (HEA/EA) composition at 100/0, 90/10, 70/30, 50/50, 30/70, 10/90 and fixed silica content at 20 wt.%, and the second with fixed HEA/EA organic composition at 70/30 and 0, 5, 10 and 20 wt.% of silica. The hydration properties of these systems were studied at 25 °C by exposure to several controlled water vapor atmospheres (water activities 0–0.98) in sealed jars and by immersion in distilled water. Finally, the molecular dynamics of the hydrated hybrids at several levels of hydration was probed with Thermally Stimulated Depolarization Currents (TSDC) in the temperature interval between −150 and 20 °C. The results indicate that a critical region of silica content between 10 and 20 wt.% exists, above which silica is able to form an inorganic network. This silica network prevents the expansion of water clusters inside the hydrogels and subsequently the total stretching of the polymer network without obstructing the water sorption at the first stages of hydration from the dry state. As concerns the copolymer composition, the presence of EA reduces water sorption and formation of water clusters affecting directly to the hydrophilic regions. The TSDC thermograms reveal the presence of a single primary main broad peak denoted as αcop relaxation process, which is closely related to the copolymer glass transition, and of a secondary relaxation process denoted as βsw relaxation, which originates from the rotational motions of the lateral hydroxyl groups with attached water molecules. The single αcop implies structural homogeneity at the nanoscale in HEA-rich samples (xHEA > 0.5), while for high EA content (xEA ⩾ 0.5) phase separation is detected. Both relaxation processes show strong dependence on water content and organic phase composition.
    Full-text · Article · Jan 2010 · European Polymer Journal
  • [Show abstract] [Hide abstract]
    ABSTRACT: During system resource improvement process that based on object-oriented technology could be affect to the continuous system performance if lack appropriate management and control objects mechanism. This paper proposes a methodology to support continuous system performance and its stability. The adoption is based on Java container framework and collections framework for object collection. Also includes software engineering, object migration and multiple class loaders mechanism accommodate to construct continuous migration container (CMC). CMC is a runtime environment provides interfaces for management and control to support object equivalence checking object behavior and functional conformance method before object migration process while upgrading object. These operations are crucial for system stability and enhancement efficiency.
    No preview · Conference Paper · Dec 2004
Show more