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Preparation and Characterization of Macroporous Cryostructured Materials

Kirsebom, Harald LU (2010)
Abstract (Swedish)
Popular Abstract in Swedish

Is är något som de flesta människor i Sverige kommer i kontakt med dagligen,om det är för att kyla en dryck eller ta sig en glass, är det något som de flesta är bekanta med. Om en vattenlösning eller en vattensuspension kyls under fryspunkten för vatten ( 0 °C) så börjar iskristaller att bildas. Speciellt med denna process är att iskristallerna som bildas består endast av vattenmolekyler d.v.s. partiklar eller ämnen lösta i vattnet kommer inte att inneslutas i iskristallerna.

Istället kommer dessa ämnen att samlas runt iskristallerna, eftersom dessa ämnen nu finns i en mer begränsad volym kommer dessa att finnas i en mer koncentrerad form. Koncentrationen av dessa ämnen kommer att... (More)
Popular Abstract in Swedish

Is är något som de flesta människor i Sverige kommer i kontakt med dagligen,om det är för att kyla en dryck eller ta sig en glass, är det något som de flesta är bekanta med. Om en vattenlösning eller en vattensuspension kyls under fryspunkten för vatten ( 0 °C) så börjar iskristaller att bildas. Speciellt med denna process är att iskristallerna som bildas består endast av vattenmolekyler d.v.s. partiklar eller ämnen lösta i vattnet kommer inte att inneslutas i iskristallerna.

Istället kommer dessa ämnen att samlas runt iskristallerna, eftersom dessa ämnen nu finns i en mer begränsad volym kommer dessa att finnas i en mer koncentrerad form. Koncentrationen av dessa ämnen kommer att bestämmas av temperaturen som används för att frysa vattnet. Lägre temperatur innebär mindre volym för ämnena att rymmas i och därför en högre koncentration av dessa. Slutligen uppnås ett tillstånd med huvudsakligen iskristaller och där de övriga ämnena hamnat i en liten fas kring isen. Denna process kallas ofta kryokoncentrering. Ett sådant prov ser helt fryst ut, men i själva verket finns en andel ofryst vatten närvarande. Denna andel bestäms av hur mycket ämnen som var lösta i vattnet innan frysprocessen inledes.

När havsvatten fryser och bildar is sker detta så som beskrivet ovan, eftersom havsvatten innehåller salt som kommer att bilda en ofryst fas av koncentrerat saltvatten kring iskristallerna. På grund av att denna koncentrerade saltlösning har en hög densitet kommer den att sjunka neråt genom havsisen och slutligen kommer havsisen att bestå av rent vatten. Därför innehåller polarområdena på jorden en enorm mängd färskvatten, om än i form av is. Egenskapen av hur is bildas genom att stöta ut andra ämnen har använts för till exempel tillverkning av glass, som på samma sätt består av en viss del ofryst vatten blandat med andra ämnen samt en del is.

I denna avhandling har fenomenet med hur is skapas utnyttjats för att tillverka ihåliga och absorberande ämnen, så kallade porösa material, samt att studera hur dessa bildas. Genom att frysa diverse utspädda lösningar av monomerer (byggstenar för det slutliga materialet) har dessa oncentrerats in i ett fryst tillstånd, varvid en reaktion sker som bildar ett polymert material - en så kallad kryogel. Denna kryogel kan i sin tur binda mycket vatten på grund av hur den är skapad och är ett så kallat hydrofilt (vattenälskande) material. Iskristallerna som skapades när man frös startlösningen har bildat porerna som finns i materialet och

dessa har en diameter på ungefär 1-100 μm. På grund av dessa porer suger

materialet snabbt och effektivt upp vätskor och påminner mycket om en vanlig tvättsvamp, fast med mindre porer.

Genom att använda NMR (kärnmagnetisk resonans) var det möjligt att dels

studera hur vattnet fryser samt hur bildandet av kryogelen sker. Detta gjorde att vi kan börja förstå hur t.ex. temperatur, koncentration av olika ämnen, samt själva frysningen påverkade processen. Slutsatser från detta användes för att försöka ändra egenskaperna av kryogelerna genom att studera hur olika tillsatser av salt eller lösningsmedel påverkade den slutliga materialet.

För att vidga konceptet ytterligare försökte jag använda suspensioner av

partiklar i vatten istället för vattenlösningar. Dessa suspensioner var små

plastpartiklar i vatten eller suspensioner av bakterier och jästsvampar. Frysning av dessa suspensioner samtidigt som man försökte att binda samman partiklarna genom kemiska bindningar resulterade i ett material som bestod av tättpackade partiklar med stora porer mellan områden av partiklar. Det resulterande materialet var väldigt likt kryogeler som skapades av vattenlösningar, men i detta fall var kryogeler bestående av sammanbundna partiklar.

Den potentiella användningen av dessa material kan sträcka sig från

vattenrening till material för att odla celler eller vävnad för medicinska

tilllämpningar. (Less)
Abstract
Macroporous hydrogels are regarded as interesting materials both within

biotechnology and biomedicine due to their properties. These materials can be prepared from a wide range of synthetic or naturally occurring compounds using a number of different techniques for their production.

For this thesis, cryostructuring was used to prepare macroporous hydrogels,

often named cryogels. The work utilized the fact that freezing an aqueous solution or suspension results in the formation of ice crystals. As these crystals grow any solutes or particles are expelled and accumulate in a liquid non-frozen phase around the ice crystals. Gel formation takes place in this non-frozen phase resulting in a crosslinked gel-network.... (More)
Macroporous hydrogels are regarded as interesting materials both within

biotechnology and biomedicine due to their properties. These materials can be prepared from a wide range of synthetic or naturally occurring compounds using a number of different techniques for their production.

For this thesis, cryostructuring was used to prepare macroporous hydrogels,

often named cryogels. The work utilized the fact that freezing an aqueous solution or suspension results in the formation of ice crystals. As these crystals grow any solutes or particles are expelled and accumulate in a liquid non-frozen phase around the ice crystals. Gel formation takes place in this non-frozen phase resulting in a crosslinked gel-network. The properties of this non-frozen phase are determined by the freezing conditions and the composition of the sample that was frozen. The ice crystals that form act as pore-forming agents and when the sample melts after gelation a macroporous material is formed with the pores being a

replica of the ice crystals.

Nuclear magnetic resonance (NMR) was utilized in this thesis to study the

formation of cryogels produced by free radical polymerization of aqueous

solutions of monomers. This technique allowed in situ studies of both the freezing process and the polymerization reaction. It could be seen from these studies that the starting concentration of monomers influenced the size of the non-frozen phase and that the properties of this phase influenced the reaction conditions. Furthermore, studying these reactions at -10 °C made it possible to investigate the differences between polymerization in a semi-frozen state and at supercooled conditions. Polymerization of a supercooled sample generated a non-porous material similar to materials formed above the freezing point, whereas in the semifrozen sample a macroporous structure was produced. It was shown that the structure of cryogels produced from monomeric precursors could be modulated by adding different inert solutes to the monomeric mixture. Adding salts resulted in materials with thicker pore walls and smaller

pores sizes since the added solutes created a larger non-frozen phase. The addition of solvents which were poor solvents for the forming polymer resulted in cryogels with a bimodal pore size distribution. Macropores were formed due to the cryogelation process while a secondary porosity within the pore walls formed due to a polymerization-induced phase separation caused by the presence of the solvent.

Using the principal that growing ice crystals expel compounds, a method for

producing cryostructured materials from suspensions was described. Suspensions of synthetic particles or microorganisms were frozen and the material became closely packed between the ice crystals. In this state inter-particle covalent bonds were formed which prevented the structure from disintegrating into individual particles when the sample was thawed. The covalent bonds could be formed either through the addition of a crosslinker or through the reactions of functional groups on the surfaces of the particles. Structuring particles using this approach made it possible to incorporate activated carbon particles into the structure without blocking the internal porosity of the carbon. When a composite cryogel based on monomers was used to immobilize the carbon, blockage of the internal porosity of the carbon was observed. An evaluation of these new structures for biotechnological and biomedical applications would be interesting. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Okay, Oguz, Istanbul Technical University, Istanbul, Turkey
organization
publishing date
type
Thesis
publication status
published
subject
pages
122 pages
defense location
Lecture hall C, Center for Chemistry and Chemical Engineering, Sölvegatan 39, Lund University Faculty of Engineering
defense date
2010-09-17 10:30
ISBN
978-91-89627-66-6
language
English
LU publication?
yes
id
6c7629df-ea57-41bf-b841-a8192ea43710 (old id 1658405)
date added to LUP
2010-08-23 16:04:17
date last changed
2016-09-19 08:45:18
@misc{6c7629df-ea57-41bf-b841-a8192ea43710,
  abstract     = {Macroporous hydrogels are regarded as interesting materials both within<br/><br>
biotechnology and biomedicine due to their properties. These materials can be prepared from a wide range of synthetic or naturally occurring compounds using a number of different techniques for their production.<br/><br>
For this thesis, cryostructuring was used to prepare macroporous hydrogels,<br/><br>
often named cryogels. The work utilized the fact that freezing an aqueous solution or suspension results in the formation of ice crystals. As these crystals grow any solutes or particles are expelled and accumulate in a liquid non-frozen phase around the ice crystals. Gel formation takes place in this non-frozen phase resulting in a crosslinked gel-network. The properties of this non-frozen phase are determined by the freezing conditions and the composition of the sample that was frozen. The ice crystals that form act as pore-forming agents and when the sample melts after gelation a macroporous material is formed with the pores being a<br/><br>
replica of the ice crystals.<br/><br>
Nuclear magnetic resonance (NMR) was utilized in this thesis to study the<br/><br>
formation of cryogels produced by free radical polymerization of aqueous<br/><br>
solutions of monomers. This technique allowed in situ studies of both the freezing process and the polymerization reaction. It could be seen from these studies that the starting concentration of monomers influenced the size of the non-frozen phase and that the properties of this phase influenced the reaction conditions. Furthermore, studying these reactions at -10 °C made it possible to investigate the differences between polymerization in a semi-frozen state and at supercooled conditions. Polymerization of a supercooled sample generated a non-porous material similar to materials formed above the freezing point, whereas in the semifrozen sample a macroporous structure was produced. It was shown that the structure of cryogels produced from monomeric precursors could be modulated by adding different inert solutes to the monomeric mixture. Adding salts resulted in materials with thicker pore walls and smaller<br/><br>
pores sizes since the added solutes created a larger non-frozen phase. The addition of solvents which were poor solvents for the forming polymer resulted in cryogels with a bimodal pore size distribution. Macropores were formed due to the cryogelation process while a secondary porosity within the pore walls formed due to a polymerization-induced phase separation caused by the presence of the solvent.<br/><br>
Using the principal that growing ice crystals expel compounds, a method for<br/><br>
producing cryostructured materials from suspensions was described. Suspensions of synthetic particles or microorganisms were frozen and the material became closely packed between the ice crystals. In this state inter-particle covalent bonds were formed which prevented the structure from disintegrating into individual particles when the sample was thawed. The covalent bonds could be formed either through the addition of a crosslinker or through the reactions of functional groups on the surfaces of the particles. Structuring particles using this approach made it possible to incorporate activated carbon particles into the structure without blocking the internal porosity of the carbon. When a composite cryogel based on monomers was used to immobilize the carbon, blockage of the internal porosity of the carbon was observed. An evaluation of these new structures for biotechnological and biomedical applications would be interesting.},
  author       = {Kirsebom, Harald},
  isbn         = {978-91-89627-66-6},
  language     = {eng},
  pages        = {122},
  title        = {Preparation and Characterization of Macroporous Cryostructured Materials},
  year         = {2010},
}