TRANSPORT OF MATTER PHENOMENA IN POLYMERS

 

Research Objectives/Activities

    Micromolecular sorption and transport in polymeric materials by a combination of theoretical and experimental approaches. The aim of this work is to help create the basic scientific background for the optimization of the design of polymeric materials for important applications.

Research activities include

•    Controlled release systems
•    Mechanisms of non-Fickian transport kinetics in glassy polymers
•    Permeability properties of composites
•   Chemical sensors (collaboration with the laboratory of Polymer-based Chemical Sensors, INN ,Demokritos)

Controlled release systems
    Development of controlled release devices aims at the regulated, prolonged delivery of drugs, agrochemicals or other bioactive agents. Matrix-type controlled release (MCR) devices consist of a polymer matrix incorporating the bioactive solute and are activated by the ingress of water when placed in aqueous biological environment. In comparison with other types of controlled release systems (e.g. reservoir systems or osmotic pumps), MCR devices are very attractive commercially, due to their structural simplicity and low cost of manufacture. Examples of marketed MCR medical devices include subdermal and ocular implants, transdermal “patches” and drug-eluting stents.

Our work includes

Modeling of MCR performance
    We have developed advanced, realistic models, simulating the release performance of single-layer as well as multilayered MCR devices. These models can serve as a tool for the (i) elucidation of the effect of individual MCR design factors on the rate of release and (ii) predictive evaluation of the performance of proposed specific CR devices.
   The model takes account for the effect of each diffusing species (solvent-solute) on the diffusivity and/or solubility of the other and can simulate the release performance of devices functioning under various experimental conditions.

Experimental work

  • Validation of the developed models against experiment in model, as well as pharmaceutical, systems
  • Study of complex release mechanisms involving (i) osmotic effects induced by a hydrophilic drug or additive in a hydrophobic elastomeric matrix and (ii) increased sorption capacity of a slowly relaxing glassy hydrogel
  • Modification of release kinetics from hydrogels or elastomers by varying the swelling capacity of the matrix, through chemical (crosslinking, grafting ) or physical (heat treatment, blending) methods

Single-layer matrix devices, of uniform permeability properties and uniform drug load, operating by diffusion-controlled release kinetics (t1/2 kinetics) are characterized by a continuously declining dose rate. One method to stabilize the rate of release is the construction of multilayer devices with layers of different polymeric materials and/or different concentration of the embedded drug. The figure presents validation of our MCR model against experimental release rates of theophylline from single-, and from three-layer, poly(dimethylsiloxane) devices

 

Mechanisms of non-Fickian transport kinetics in glassy polymers

    Sorption kinetics in glassy polymer systems exhibits a variety of deviations from normal Fickian behavior, attributable to either (i) slow viscous relaxations of the swelling polymer, or (ii) differential swelling stresses generated by the constraints imposed on local swelling during sorption. Our group develops models based on both mechanisms, capable of simulating all basic features of observed non-Fickian kinetic behavior, including Case II kinetics. Experimental work includes sorption from the vapor or the liquid phase.

Water sorption kinetics in a poly(vinyl alcohol) hydrogel. Non-Fickian (deviating form t1/2 law) kinetics results from slow molecular relaxations of the swelling glassy polymer matrix that occur on time scales comparable to those of water diffusion. The line represents fitting of the experimental data to our relevant model, with output the diffusion coefficient of water.

 

Permeability properties of composites

   The proper theoretical description of the permeability or analogous properties (thermal and electrical conductivity, electrical or magnetic permittivity, elastic modulus, etc.) of composite polymeric materials is of great interest, particularly in view of the growing technological importance of these materials and the significant improvement of their properties when the dispersed particle phase is of the nanoscale. The polymer-particle interface modifies the polymer structure and should be taken into account in modeling, especially in the case of nanocomposites, due to the high surface to volume ratio of the nanoparticles. The use of cubic rather than spherical particles leads to a much simpler and fully consistent idealized treatment of a three-phase medium.

Schematic representation of a 3-phase composite medium consisting of particles A, with their surrounding zones B1, dispersed in the bulk matrix B. Note the effect of increasing pseudo particle (A+B1) fractional volume.

Application of our 3-phase modeling approach (broken lines) to experimental gas permeability data (points) through a PES-Zeolite composite medium. The unusual phenomenon of permeability P passing through a minimum with increasing volume fraction vA is successfully simulated (Chem Eng Sci, 131, 2015, 360).

 

Chemical sensors (collaboration with the laboratory of Polymer-based Chemical Sensors, INN, Demokritos)

    The quantitative detection and monitoring of VOCs and moisture by chemical sensors is based on changes of a physicochemical property of the polymeric sensing layer due to absorption of the target vapor analyte. The operation of the low cost, low energy consumption capacitive- type sensors, is based on changes in the dielectric properties of the polymer layer due to sorption of the vapor analyte. For a particular geometrical design of a capacitive sensor, sorption properties determine not only the sensitivity of the sensor to a particular VOC but also its selectivity for the target VOC in real complex environments.

    Our collaboration with the laboratory of Polymer- based Chemical sensors, includes development and evaluation of (i) optical methodologies for fast screening the sorption properties of polymeric materials for gas sensor applications (ii) simulation methodologies for the prediction of chemocapacitors performance and (iii) sensor arrays, developed at the laboratory of Polymer based Chemical sensors, for specific applications concerning the detection and continuous monitoring of VOCs and/or moisture in complex vapor environments (e.g. industrial installations using solvents)

 


Research Collaborator

Dr. Petropoulos John H.

Funded Projects (2005-  )

1.    “Autonomous and integrated system for in-situ and continuous contaminant gases monitoring in industrial environments- ALEPOU” – General Secretariat for Research & Technology, 2012-2015

2.    “Development of innovative bio-active magnetic nanomaterials for diagnosis and monitoring of pathogenic conditions by magnetic tomography”, PEP Attikis, 2006-2008.

3.    “Morphological control of polymer blend nanofilms for organic (opto-) electronics” Joint research and technology programmes, Greece -Poland, 2006 – 2008.

4.    “Computer aided molecular design of multifunctional materials with controlled permeability properties-Multimatdesign”, FP6-NMP-STREP, 2005-2008.

5.    “Facing pathogenic conditions by combined use of bio-medical methods and nanotechnology” Infrastructure, Measure 4.5, Action «Consortia of research and technological development in sectors of National priorities», 2050-4/2, 2005-2008.

Lab Services

Thermal Analysis Lab