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Water diffusion and free volume in hydrophilic polymers

Trotzig, Charlotte LU (2006)
Abstract (Swedish)
Popular Abstract in Swedish

Vid vattenabsorption i en polymer antas vattenmolekylerna röra sig genom polymeren via små kaviteter, som inte upptas av polymermolekylerna och dess termiska vibrationer. Den ej upptagna volymen, som de små kaviteterna representerar kallas fri volym. Storleken på kaviteterna liksom andra egenskaper hos polymeren såsom andelen kristallin fas ändras kontinuerligt i takt med att vatten absorberas in i polymeren. Den här avhandlingen handlar om hur förändringen av polymerens egenskaper ändrar förutsättningarna för vattendiffusion.



En studie av relationen mellan självdiffusionskoefficienten av vatten i homogena polymer-vatten system och storleken på kaviteter bestående av fri volym... (More)
Popular Abstract in Swedish

Vid vattenabsorption i en polymer antas vattenmolekylerna röra sig genom polymeren via små kaviteter, som inte upptas av polymermolekylerna och dess termiska vibrationer. Den ej upptagna volymen, som de små kaviteterna representerar kallas fri volym. Storleken på kaviteterna liksom andra egenskaper hos polymeren såsom andelen kristallin fas ändras kontinuerligt i takt med att vatten absorberas in i polymeren. Den här avhandlingen handlar om hur förändringen av polymerens egenskaper ändrar förutsättningarna för vattendiffusion.



En studie av relationen mellan självdiffusionskoefficienten av vatten i homogena polymer-vatten system och storleken på kaviteter bestående av fri volym har utförts med hjälp av kärnmagnetisk resonans (NMR) och positronannihilerings livstidsspektroskopi (PALS) i system baserade på polymererna polyetylenoxid (PEO) och hydroxypropylmetylcellulosa (HPMC). Vidare har förändringen av drag-lagringsmodulen vid tillsats av både vatten och ett modelläkemedel i HPMC samt förändringen av kristallinitetsgraden och glasövergångstemperaturen vid tillsats av vatten till både ren PEO och en blandning av PEO och lera (med nanometer dimensioner) studerats med dynamisk-mekanisk analys (DMA) och differentiell skanningskalorimetri (DSC).



I HPMC-vatten systemet verkade en ökning av storleken på fri volym kaviteterna vara kopplad till en ökning av självdiffusionskoefficienten av vatten. I PEO-vatten systemet, däremot, föreföll vattendiffusionen inte styras av storleken på kaviteterna, åtminstone inte när mer än 50 % av PEO-vatten systemet var kristallint. Minskningen av kristallin fas i PEO när vattenhalten ökade resulterade troligen i en relaxation av amorfa delar med spända konfigurationer. Vattnet tenderade a formera sig i kluster i HPMC-vatten systemet, men inte i PEO-vatten systemet i de studerade vattenhaltsområdena. Tillsats av triacetin till HPMC resulterade i en reduktion av mängden absorberat vatten. Under tillsats av lika substansmängd triacetin och vatten sjönk drag-lagringsmodulen mer vid inkorporering av triacetin än vid inkorporering av vatten. Tillsats av triacetin vid konstant viktsfraktion vatten ledde till en ökning av självdiffusionskoefficienten av vatten och storleken på kaviteterna bestående av fri volym. Självdiffusionskoefficienten påverkades mer av en ökad mängd vatten i systemet än av en ökad mängd triacetin, medan en motsatt effekt observerades för storleken på kaviteterna bestående av fri volym. Närvaron av lera i PEO resulterade i att mindre vatten absorberades och verkade leda till att vattnets inverkan på glasövergångstemperaturen och storleken på fri volym kaviteterna i PEO ökade något. (Less)
Abstract
During moisture uptake in polymers, the diffusion of the water molecules is believed to occur via unoccupied voids. These voids are called free volume cavities and their sizes are continuously altered when the moisture content in the polymer is enhanced. Not only the free volume cavity sizes, but also other polymer properties such as the degree of crystallinity, are changed as a consequence of moisture uptake. By modifying the polymer properties, the conditions for water diffusion are altered, which is the issue at stake in this thesis.



A study of the coupling between the self-diffusion coefficients of water and the free volume hole sizes in polymer-water systems based on poly(ethylene oxide) (PEO) and hydroxypropyl... (More)
During moisture uptake in polymers, the diffusion of the water molecules is believed to occur via unoccupied voids. These voids are called free volume cavities and their sizes are continuously altered when the moisture content in the polymer is enhanced. Not only the free volume cavity sizes, but also other polymer properties such as the degree of crystallinity, are changed as a consequence of moisture uptake. By modifying the polymer properties, the conditions for water diffusion are altered, which is the issue at stake in this thesis.



A study of the coupling between the self-diffusion coefficients of water and the free volume hole sizes in polymer-water systems based on poly(ethylene oxide) (PEO) and hydroxypropyl methylcellulose (HPMC) has been performed by means of nuclear magnetic resonance (NMR) and positron annihilation lifetime spectroscopy (PALS). Moreover, the change in the tensile storage modulus upon adding water and a model drug to HPMC as well as the change in the degree of crystallinity and the glass transition temperature upon adding water and a nano-sized clay filler to PEO was studied by means of dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC).



In the HPMC-water system, an increase in the free volume hole size seemed to be associated with an increase in the self-diffusion coefficient. In contrast, the water self-diffusion in PEO seemed not to be controlled by the free volume hole size, at least not in the water weight fraction range where more than 50 % of the sample still was crystalline. The reduction of the crystalline phase in the PEO as a function of water weight fraction seemed to result in a relaxation of a strained amorphous phase. Strong indications of water clustering in the measured water weight fraction region were observed in the HPMC, but not in the PEO. Addition of triacetin to the HPMC resulted in a reduction of the amount of water absorbed by the HPMC. On a molar basis, the triacetin decreased the tensile storage modulus to a higher extent than water did. At constant water weight fractions, the self-diffusion coefficient of water and the free volume hole size increased upon addition of triacetin. The self-diffusion coefficient of water in the HPMC-water system was more influenced by an increasing amount of water than by an increasing amount of triacetin, whereas the opposite effect was observed for the free volume hole size. The presence of a nano-sized clay filler in PEO resulted in less water absorbed by the PEO and seemed to slightly increase the influence of water on the glass transition temperature and the free volume hole size. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Gedde, Ulf W, Dept of Fiber and Polymer Technology, Royal Institute of Technology, Stockholm
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Physical chemistry, free volume, self-diffusion, degree of crystallinity, glass transition temperature, tensile storage modulus, surface tension, isotherm, HPMC, PEO, water, triacetin, clay, Macromolecular chemistry, dynamic mechanical analysis, Fysikalisk kemi, differential scanning calorimetry, nuclear magnetic resonance, positron annihilation, Makromolekylär kemi
publisher
Department of Polymer & Materials Chemistry
defense location
Center for Chemistry and Chemical Engineering, Lecture Hall B
defense date
2006-11-23 10:15
ISBN
978-91-628-6968-7
language
English
LU publication?
yes
id
58491ca4-46ef-481e-bd71-c5f6b63d62ec (old id 547494)
date added to LUP
2007-10-13 11:36:55
date last changed
2016-09-19 08:45:01
@misc{58491ca4-46ef-481e-bd71-c5f6b63d62ec,
  abstract     = {During moisture uptake in polymers, the diffusion of the water molecules is believed to occur via unoccupied voids. These voids are called free volume cavities and their sizes are continuously altered when the moisture content in the polymer is enhanced. Not only the free volume cavity sizes, but also other polymer properties such as the degree of crystallinity, are changed as a consequence of moisture uptake. By modifying the polymer properties, the conditions for water diffusion are altered, which is the issue at stake in this thesis.<br/><br>
<br/><br>
A study of the coupling between the self-diffusion coefficients of water and the free volume hole sizes in polymer-water systems based on poly(ethylene oxide) (PEO) and hydroxypropyl methylcellulose (HPMC) has been performed by means of nuclear magnetic resonance (NMR) and positron annihilation lifetime spectroscopy (PALS). Moreover, the change in the tensile storage modulus upon adding water and a model drug to HPMC as well as the change in the degree of crystallinity and the glass transition temperature upon adding water and a nano-sized clay filler to PEO was studied by means of dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC).<br/><br>
<br/><br>
In the HPMC-water system, an increase in the free volume hole size seemed to be associated with an increase in the self-diffusion coefficient. In contrast, the water self-diffusion in PEO seemed not to be controlled by the free volume hole size, at least not in the water weight fraction range where more than 50 % of the sample still was crystalline. The reduction of the crystalline phase in the PEO as a function of water weight fraction seemed to result in a relaxation of a strained amorphous phase. Strong indications of water clustering in the measured water weight fraction region were observed in the HPMC, but not in the PEO. Addition of triacetin to the HPMC resulted in a reduction of the amount of water absorbed by the HPMC. On a molar basis, the triacetin decreased the tensile storage modulus to a higher extent than water did. At constant water weight fractions, the self-diffusion coefficient of water and the free volume hole size increased upon addition of triacetin. The self-diffusion coefficient of water in the HPMC-water system was more influenced by an increasing amount of water than by an increasing amount of triacetin, whereas the opposite effect was observed for the free volume hole size. The presence of a nano-sized clay filler in PEO resulted in less water absorbed by the PEO and seemed to slightly increase the influence of water on the glass transition temperature and the free volume hole size.},
  author       = {Trotzig, Charlotte},
  isbn         = {978-91-628-6968-7},
  keyword      = {Physical chemistry,free volume,self-diffusion,degree of crystallinity,glass transition temperature,tensile storage modulus,surface tension,isotherm,HPMC,PEO,water,triacetin,clay,Macromolecular chemistry,dynamic mechanical analysis,Fysikalisk kemi,differential scanning calorimetry,nuclear magnetic resonance,positron annihilation,Makromolekylär kemi},
  language     = {eng},
  publisher    = {ARRAY(0x96f0b20)},
  title        = {Water diffusion and free volume in hydrophilic polymers},
  year         = {2006},
}