NMR Diffusion Studies of Association in Surfactant Systems Inclusion Complexes, Micellar Solutions and Microemulsions

Abstract

The aim of this thesis has been to investigate self-diffusion behavior of host-guest complex,

microemulsion and polymer solution. Pulsed Field Gradient NMR (PFG-NMR) was shown to

provide detailed molecular information in all system studied. The general strategy was to measyre

the diffusivities of the species and from there get molecular insight into the aggregation and

dynamics of the system.

Guest host interaction has been studied between β-cyclodextrin (β-CD) and different

cationic surfactant. The equilibrium constant (K11) increases as a function of the number of CH2

groups in the surfactant chain. It could be concluded that the cavity of β-CD could incorporate

approximately 10-12 CH2 groups and that it is the hydrophobic interaction that mainly is

responsible for the inclusion complex formed. The interaction between the gemini surfactant and

β-CD formed a 2:1 (CD:gemini) complex in a two step mechanism with the first association

constant higher than the second one (K2:1), but both relatively small in comparison with the

analogue singled tailed surfactant. The values of the K11 and K21 increased with gemini spacer

length which indicate that the available space on the gemini molecule is important. The second

association constant shows no cooperatively and its magnitude are discussed in terms of steric

constrains. Bolaform surfactant complexation was investigated with both β-CD and α-CD with

Isothermal Titration Calorimetry (ITC). The K11, enthalpy and entropy of formation were

obtained. From ITC a molecular interpretation is made explaining the enthalpy and entropy

difference between α- and β-CD.

In a second study diblock copolymers of the type methoxy poly(ethylene oxide)-

poly(alkylene oxide) were incorporated into the nonionic bicontinuous microemulsion at 298 K.

An enhancement of the microemulsion in solubilising water and oil were observed with a

boosting factor of 9. The self-diffusion coefficients of the components in the system were

measured and provided molecular information on how the microstructure of the bicontinuous

microemulsion changed upon addition of the polymers.

The diffusion study concerning the aqueous solution of the synthetic polymers, PEO-

PPO-PEO, is focused towards analyzing the PFG-NMR decay correctly. The polydispersity has

consequences on the polymer self-assembly, which were highlighted, modeled and discussed

based on PFG-NMR data. The main conclusion is that the curved NMR decay as obtained for

self-assembly can be explained with a multi-component ideal solution.

• author: Nilsson, Markus
• supervisor: Olle Söderman Söderman
• opponent: Dr. prof. Smidth, Claudia Smidth, Department of Chemistry, Faculty of Science, university of Paderbon, Germany
• organization: Physical Chemistry
• publishing date: 2008
• type: Thesis
• publication status: published
• subject: Physical Chemistry
• keywords: host-guest complexation, gemini surfactant, cyclodextrin, bolaform surfactant, self-diffusion NMR, pluronic, bicontinuous microemulsion, polydispersity, boosting effect
• pages: 178 pages
• defense location: Chemical Center room B
• defense date: 2008-03-28 10:30:00
• language: English
• LU publication?: yes
• additional info: For erreat or disscussion cosidering the content in the thesis contact Markus Nilsson. Phone number: 0730671403
• id: c16d072f-9888-4a23-9922-8ed1ce81b7de (old id 1040142)
• date added to LUP: 2016-04-04 11:25:37
• date last changed: 2018-11-21 21:04:46