Towards a responsive functional material: Modification of porosity and grafting of poly(N-isopropylacrylamide) in mesoporous silica SBA-15
(2011)- Abstract
- Mesoporous silica materials, such as SBA-15, have potential as biocompatible carriers for pharmaceutical applications
as well as mini-reactors in e.g. catalysis. This potential arises from their well-defined porous structure on the
nanometre scale accompanied by a high internal surface area (800 - 1000 m2/g).
This work addresses the following issues.
i) Surface grafted PNIPAAM was found to be located preferentially in the intrawall pores of mesoporous
silica SBA-15. Water sorption could monitor the changes in surface properties and porosity of the different
materials, obtained during the modification process. While the isotherm of original SBA-15 exhibits four regimes
of water... (More) - Mesoporous silica materials, such as SBA-15, have potential as biocompatible carriers for pharmaceutical applications
as well as mini-reactors in e.g. catalysis. This potential arises from their well-defined porous structure on the
nanometre scale accompanied by a high internal surface area (800 - 1000 m2/g).
This work addresses the following issues.
i) Surface grafted PNIPAAM was found to be located preferentially in the intrawall pores of mesoporous
silica SBA-15. Water sorption could monitor the changes in surface properties and porosity of the different
materials, obtained during the modification process. While the isotherm of original SBA-15 exhibits four regimes
of water adsorption, SBA-15 with grafted PNIPAAM lacks the second regime, which is characteristic for the presence
of intrawall pores. ii) The intrawall porosity of mesoporous silica SBA-15 was removed by addition of NaI
without altering the other characteristics of the material. The time of addition is not crucial but influences the
efficiency of the method. The method was transferred to other syntheses carried out with Pluronic as the structuredirecting
agent, such as of SBA-16, demonstrating the general applicability. Subsequently, PNIPAAM was grafted into
SBA-15 without intrawall pores. The mesoporosity of SBA-15 was modified by lowering the synthesis
temperature from 55 °C to 5 °C after 1 h of synthesis time. The micelles of the structure-directing agent Pluronic
P104 transform from an elongated shape towards a spherical shape. After 1 h of the synthesis the network of SBA-15
is still flexible, which allows adaption too the changes in the shape of the micelles and thus leading to a more
corrugated system. iii) Adsorption of γ-CD onto a cationic PNIPAAM co-polymer, which is adsorbed to a
silicon surface, in an aqueous environment at 25 °C leads to γ-CD threading onto the polymer chains,
comparable to pearls on a necklace. An increase to 40 °C leads to a collapse of the PNIPAAM part and the γ-CD
is released. γ-CD was thread onto the PNIPAAM chains grafted onto the pore walls of SBA-15, showing the function
of PNIPAAM in SBA-15. (Less) - Abstract (Swedish)
- Popular Abstract in English
Figure 1: Electron microscopy image of mesoporous material seen from above. The
left image shows a possible shape of a silica particle (scale bar: 1 μm). The
right image shows the mesopores in the particle (grey color) with the
silicon dioxide walls (black color) (scale bar: 150 nm).
Poly(N-isopropylacrylamide) (PNIPAAM) is a polymer that can provide
the active part for a drug delivery vehicle controlling the uptake and
release of drugs. Polymers are made of small repeating units forming
macromolecules like beads on a necklace, where the small repeating units
are connected to form a long chain. Examples of polymers in our... (More) - Popular Abstract in English
Figure 1: Electron microscopy image of mesoporous material seen from above. The
left image shows a possible shape of a silica particle (scale bar: 1 μm). The
right image shows the mesopores in the particle (grey color) with the
silicon dioxide walls (black color) (scale bar: 150 nm).
Poly(N-isopropylacrylamide) (PNIPAAM) is a polymer that can provide
the active part for a drug delivery vehicle controlling the uptake and
release of drugs. Polymers are made of small repeating units forming
macromolecules like beads on a necklace, where the small repeating units
are connected to form a long chain. Examples of polymers in our daily
Popular Scientific Summary in English
life are plastics, shampoo and paints. PNIPAAM is a so-called stimuliresponsive
polymer. Combining mesoporous silica with PNIPAAM can
provide a drug delivery vehicle. The hard mesoporous silica material
provides the stability, while PNIPAAM with its soft character provides
the active component. Figure 2 illustrates the mechanism of this
PNIPAAM-silica composite. The chains of PNIPAAM are attached to
the walls of the pores. When the temperature is above 32 °C (Figure 2a)
the polymer is collapsed and the pores are open, allowing molecules such
as drugs, to enter the pores. When the temperature is decreased below
32 °C (Figure 2b), the PNIPAAM chains become hydrophilic and stretch
towards the centres of the pores forming a “jungle” in which the
molecules are prevented from moving.
Figure 2: Schematic illustration of a mesopore with grafted PNIPAAM: a) above
32 °C allowing drug molecules to be loaded into the pores, and b) below
32 °C showing the drug molecules trapped inside the pore by the
PNIPAAM chains.
The first part of this work deals with the functionalization of the
mesoporous silica material with PNIPAAM. This procedure is carried out
in three steps starting with the original mesoporous silica material and
resulting in a PNIPAAM-silica composite, in which the PNIPAAM
chains are linked to the inner surface of the pores in the mesoporous
silica. The materials were characterized using several different techniques.
The aim was to understand where the polymer is located inside the
mesoporous silica matrix, and to obtain information about the chemical
properties of the materials.
The second part concerned the mesoporous silica material itself.
Different applications require different porous properties. The porosity
of a common mesoporous silica material, SBA-15, which consists of two
different types of pores, was studied. The primary mesopores, which have
a cylindrical shape, are connected by small irregular pores called intrawall
SiO2 (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/2171895
- author
- Reichhardt, Nina LU
- supervisor
- opponent
-
- Schmidt, Wolfgang N., Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany
- organization
- publishing date
- 2011
- type
- Thesis
- publication status
- published
- subject
- keywords
- mesoporous silica, SBA-15, intrawall pores, PNIPAAM, lower critical solution temperature, water sorption calorimetry, gas sorption
- pages
- 200 pages
- publisher
- Department of Chemistry, Lund University
- defense location
- Center of Chemistry and Chemical Engineering, Lund, Lecture Hall B
- defense date
- 2011-11-03 10:30:00
- ISBN
- 978-91-7422-281-4
- language
- English
- LU publication?
- yes
- id
- 8b15b736-0e18-4a0d-ac47-7bf11b9fa3f9 (old id 2171895)
- date added to LUP
- 2016-04-04 10:32:27
- date last changed
- 2018-11-21 20:59:21
@phdthesis{8b15b736-0e18-4a0d-ac47-7bf11b9fa3f9, abstract = {{Mesoporous silica materials, such as SBA-15, have potential as biocompatible carriers for pharmaceutical applications<br/><br> as well as mini-reactors in e.g. catalysis. This potential arises from their well-defined porous structure on the<br/><br> nanometre scale accompanied by a high internal surface area (800 - 1000 m2/g).<br/><br> This work addresses the following issues.<br/><br> i) Surface grafted PNIPAAM was found to be located preferentially in the intrawall pores of mesoporous<br/><br> silica SBA-15. Water sorption could monitor the changes in surface properties and porosity of the different<br/><br> materials, obtained during the modification process. While the isotherm of original SBA-15 exhibits four regimes<br/><br> of water adsorption, SBA-15 with grafted PNIPAAM lacks the second regime, which is characteristic for the presence<br/><br> of intrawall pores. ii) The intrawall porosity of mesoporous silica SBA-15 was removed by addition of NaI<br/><br> without altering the other characteristics of the material. The time of addition is not crucial but influences the<br/><br> efficiency of the method. The method was transferred to other syntheses carried out with Pluronic as the structuredirecting<br/><br> agent, such as of SBA-16, demonstrating the general applicability. Subsequently, PNIPAAM was grafted into<br/><br> SBA-15 without intrawall pores. The mesoporosity of SBA-15 was modified by lowering the synthesis<br/><br> temperature from 55 °C to 5 °C after 1 h of synthesis time. The micelles of the structure-directing agent Pluronic<br/><br> P104 transform from an elongated shape towards a spherical shape. After 1 h of the synthesis the network of SBA-15<br/><br> is still flexible, which allows adaption too the changes in the shape of the micelles and thus leading to a more<br/><br> corrugated system. iii) Adsorption of γ-CD onto a cationic PNIPAAM co-polymer, which is adsorbed to a<br/><br> silicon surface, in an aqueous environment at 25 °C leads to γ-CD threading onto the polymer chains,<br/><br> comparable to pearls on a necklace. An increase to 40 °C leads to a collapse of the PNIPAAM part and the γ-CD<br/><br> is released. γ-CD was thread onto the PNIPAAM chains grafted onto the pore walls of SBA-15, showing the function<br/><br> of PNIPAAM in SBA-15.}}, author = {{Reichhardt, Nina}}, isbn = {{978-91-7422-281-4}}, keywords = {{mesoporous silica; SBA-15; intrawall pores; PNIPAAM; lower critical solution temperature; water sorption calorimetry; gas sorption}}, language = {{eng}}, publisher = {{Department of Chemistry, Lund University}}, school = {{Lund University}}, title = {{Towards a responsive functional material: Modification of porosity and grafting of poly(N-isopropylacrylamide) in mesoporous silica SBA-15}}, year = {{2011}}, }