Anisotropic Polymer Blend and Gel Nanocomposites Using External Electric or Magnetic Fields
Abstract
Morphology control in polymeric materials is essential to optimize the properties of polymeric materials for the desired application. Often, the desired enhancement of properties is highly directional, such as those in energy conversion and storage devices. For example, in a proton-exchange membrane in fuel-cell applications, the main property to enhance is ion conductivity in the direction normal to the film plane, which is not easily achieved by conventional material-composition design or processing methods. In this dissertation, new ways for controlling the internal structures of a system of polymer composites, polymer blends, and hydrogel composites by means of external electric or magnetic fields are presented. The first part of this study addresses the development of an anisotropic phaseseparated morphology in polymer blends by using electrically pre-oriented clay particles. It was observed that electrically pre-oriented montmorillonite clay particles in a homogenous singlephase blend lead to anisotropic phase-separated morphology of the blends, undergoing demixing upon temperature shift to a two-phase regime. The initial co-continuous microstructure developed into a coarsened and directionally organized phase-separated morphology parallel to the direction of oriented clay particles (applied AC electric field direction) over the annealing time. It was also found that the degree of clay orientation under AC electric field was linearly proportional to the degree of polymer-phase orientation. The temporal morphological evolution was thoroughly analyzed by electron microscopy and X-ray diffraction studies. The second part of the study covers anisotropic hydrogel nanocomposites developed by orienting magnetically sensitive nontronite clay minerals under the strong magnetic fields. Anisotropic hydrogel nanocomposites were formed by magnetic-field assisted orientation of nontronite clays suspended in a hydrogel precursor solution followed by a gelation process. The degree of orientation of nontronite minerals was quantitively characterized by birefringence and small-angle X-ray scattering. The resultant hydrogels exhibited anisotropic optical, mechanical, and swelling properties along the direction of oriented clay minerals. Anisotropic water swelling behaviors can be particularly applied in medical dressing materials, where vertical wicking of fluid into the wound dressing is sought after for minimizing periwound maceration damage.
Degree
Ph.D.
Advisors
Cakmak, Purdue University.
Subject Area
Nanotechnology|Electromagnetics|Materials science|Mathematics|Mechanics|Physics|Polymer chemistry
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