Intermediate states in bivalent ion induced shrinking of polyacrylate coils on surfaces and in solution [Elektronische Ressource] / von Prashant Sinha

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• Publié par: technische_universitat_dresden
• Publié le: 01 janvier 2009
• Nombre de lectures: 40
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

Intermediate states in bivalent ion induced shrinking of
polyacrylate coils on surfaces and in solution


D I S S E R T A T I O N

zur Erlangung des akademischen Grades
Doktor rerum naturalium
(Dr. rer. nat.)


vorgelegt
am Fachbereich Chemie
der Fakultät Mathematik und Naturwissenschaften
der Technischen Universität Dresden

von

Prashant Sinha
geboren am 14.09.1978 in Lucknow, Indien

Gutachter: Prof. Dr. M. Stamm
Prof. Dr. K.-F. Arndt


Eingereicht am: 20.05.2009
Tag der Verteidigung: 09.07.2009 Acknowledgements
Acknowledgements
I would like to express my deepest gratitude to Prof. Dr. Manfred Stamm for accepting to
guide me during the course of this work. His vast experience and knowledge was
something I always banked upon. His invaluable suggestions gave my work a direction
which has reached fruition with this thesis report.
It is difficult to overstate my gratefulness to my thesis advisor, Dr. Anton Kiriy. I will
always remember our adjacent offices separated by a single door which was never closed.
Many a new ideas came up here and were diligently followed up.
I have been lucky to be a part of a collaborative effort involving working groups from
Dresden, Paderborn and Düsseldorf. All my meetings, email exchanges and telephonic
conversations with Prof. Dr. Klaus Huber (Paderborn), Prof. Dr. Hartmut Löwen
(Düsseldorf) and Dr. Rene Messina (Düsseldorf) were very helpful in both professional
and personal ways. I also would like to thank Prof. Dr. Peter Müller-Buschbaum
(München) for his ideas regarding a new image processing protocol I was trying to
develop.
I met Sebastian during scattering experiments at Paderborn and on a number of other
occasions. He was my expert when it came to scattering techniques. We remain excellent
friends. I also thank Dr. Ralf Schweins (Grenoble), whom I met through Sebastian, for
sharing with me his expertise in the field of scattering. I remember vividly the week when
me and Sebastian were joined by Dr. Ralf Schweins and Dr. Günter Goerigk (Hamburg)
to help us conduct (A)SAXS experiments at HASYLAB/DESY, Hamburg. The long
beam times gave us an opportunity to come up with really fruitful discussions which
helped me improve my understanding of scattering techniques.
i Acknowledgements
I am grateful to Prof. Dr. Peter Lindner (Grenoble), Prof. Dr. Otto Glatter (Graz) and
thProf. Dr. Tony Ryan (Sheffield) whom I met during the “9 European Summer School on
Scattering Methods applied to Soft Condensed Matter” in Bombannes. I sincerely
appreciate their personal interest in my work, suggesting me the way forward and for
almost always paying for my beers (despite my polite resistance). I met Martin-I,
Angelica, Klaus, Michael and Oscar in Bombannes and informal discussions with them
were very helpful.
During my stay at the Leibniz-Institut für Polymerforschung Dresden e.V., I made some
excellent friends. It has been a pleasure to be a part of the same office floor where Vera
and Constantin also sat. I got all possible help from them in my endeavors and I wish
them all the very best in their lives. Vera has since moved to Michigan but my first
lessons in Atomic Force Microscopy go very much to her credit.
I was also a proud member of a group which should rightfully be called the coffee group
because of the tons of coffee we drank together during lunch time. Everything under the
sun came up for discussion, from our laboratory experiments to our personal lives.
Surprisingly, these discussions always helped me, both in the laboratory and outside it.
Saija is one person who deserves a separate mention. She has been and will remain a
special friend. I thank her and the coffee group for helping me get through the difficult
times, and for all the emotional support, camaraderie, entertainment and caring they
provided. Thank you Saija, Martin-II, Martin-III, Marco, Sina, Nadine, Monica, Sofia,
Eva, Mattheiu and Dimitris (order of names is not intentional).
Dresden has a small Indian community which provided me with a home away from
home. Kamlesh, Nitesh and Pradyumn remain in Dresden while Mukesh, Sahil, Rohini
ii Acknowledgements
and Jagdeep have since shifted to Michigan, München, Leipzig and Zurich respectively. I
will always treasure the time I spent with them.
Most importantly, I wish to thank my parents. They bore me, raised me, supported me,
taught me and loved me. They even flew to Europe all the way from India to see for
themselves that their son was really happy !!
I have no words to thank my wife, Anjali. She is my best friend and without her, this
work could not have been accomplished. Together, we helped each other throughout our
stay in Dresden. While I was writing this manuscript, she told me that she was pregnant
with our first child. I thank her for never complaining despite the fact that I was not able
to give her much time. I am indebted to her for being patient with me and for
understanding me, as always. To her and our would be child, I dedicate this thesis.
iii Abstract
Abstract
Specifically binding ions induce the transition of anionic polyacrylate coils from
extended conformation to collapsed globules passing through a cascade of intermediate
states when solution conditions approach the L-type precipitation threshold. It is the
conformation of these intermediate states on surfaces and in solution which is at the focus
of this thesis. In comparing the surface and solution conformations of intermediate states,
we were able to qualitatively and quantitatively underline the effects of sample history.
Two types of quantitative comparisons have been emphasized. In real space, the radius of
gyration values of adsorbed molecules have been evaluated incorporating fully the x, y
and z axes. These values have been compared with radius of gyration values of the very
same sample solution obtained using SLS. In reciprocal space, a novel image processing
protocol has been used to generate the 2D form factor curve wherein the correlation
maxima have been compared with corresponding maxima obtained for the very same
sample solution using small angle scattering techniques like the SANS.
The influence of bivalent ions, respectively, Strontium, Lead and Calcium, on the shape
of polyacrylate coils is studied. In the last case, temperature has been introduced as a
secondary parameter to shed further light on the mechanism by which polyelectrolyte-
bivalent ion complexation takes place. Both scattering and AFM experiments reveal
2+formation of necklace-like structures as intermediates for NaPA-Sr system. Since the
mol. wt. of the NaPA coils used was relatively large in this case, adsorption on mica
surfaces was strong. Under such conditions, the molecules undergo a z collapse upon flux
drying but do not get altered in x and y directions. The ratio R (AFM)/R (SLS) was g g
found to be in the range 0.7-0.9. The remaining (insignificant) differences in the R g
iv Abstract
values arise due to the fact that AFM gives the square root of number averaged mean
squared radius of gyration while SLS gives the square root of z-averaged mean squared
radius of gyration. The differences in radius of gyration values observed in solution and
2+on surfaces were more prominent for NaPA-Pb system. Again, although both scattering
and AFM reveal necklace-like structures as intermediates, the ratio R (AFM)/R (SLS) g g
was now found to be nearly 0.6. The fact that R (AFM) is the square root of number g
averaged and R (SLS) is the square root of z-averaged mean squared radius of gyration, g
alone cannot explain this low value. Since the mol. wt. of NaPA coils used in this case
was quite low, adsorption on mica surfaces was weak. Under such conditions, the
molecule does not only undergo a z collapse upon flux drying, but also shrinks in the x
2+and y directions due to capillary forces. Finally, with NaPA-Ca system, the picture did
not show a one-to-one correspondence between solution and surface conformations at all.
In fact, it showed a one-step-ahead correspondence. As already stated, the coil to globule
transition was induced by increasing the equilibration temperature from 15°C to 30°C in
this case. SANS could not identify any necklace-like intermediates in solution at the
equilibration temperature of 15°C while AFM scans at this temperature showed the
beginning of formation of pearls. Likewise, at the equilibration temperature of 30°C,
SANS could identify necklace-like intermediates in solution with a large majority of
dumbbells while AFM scans at this temperature showed a mix of dumbbells, sausage-like
structures and globules. Indeed, we were witnessing an accelerated coil to globule
transition on surfaces as compared to the situation in solution resulting in a pre-emption
in the formation of intermediate states on surfaces. Since the ratio R (AFM)/R (SLS) g g
(given the square root of number averaged and the square root of z-averaged mean
v Abstract
squared values respectively) at the equilibration temperature of 30°C showed a range of
0.7-0.9 indicating strong ads