Organization, manipulation and motion of brush polymers and low molecular weight amphiphiles at interfaces

The aim of this thesis was to study the organization, manipulation and motion of brush polymers on different substrates by means of scanning force microscopy.The main part of this work is concentrated on one specific type of polymer: the monodendron jacketed linear chains. This is a polymer with a methacrylate backbone in which each monomer exhibits a minidendritic unit with three dodecyl-chains at the end.A different way of adsorption was shown on different materials. On mica an unspecific adsorption of flat laying molecules was observed, whereas on highly ordered pyrolitic graphite as well as on tungsten selenide an organization of flat laying molecules with long straight segments that bend at 60 degree and 120 degree angles was observed. The straight segments are oriented parallel to the three axes defined by the crystal structure of the substrate.In parallel to these experiments the motion of single molecules and molecular clusters was studied by in-situ SFM experiments in the temperature range of 30 to 48 degree Celsius. The experiments showed motion of the clusters similar to diffusion processes. For each cluster the diffusion coefficient was calculated and the way of motion was analyzed. The main results are: The velocity increases with reduced cluster size and higher temperature. Molecules that collide with others stick together and exhibit a high shape persistence. Molecules coming into contact with defects in the substrate get caught by these and either quit moving or start a one-dimensional guided motion along the step in the graphite.Special motion modes have been identified: molecular clusters with bar shaped conformation containing parallel chains exhibit diffusion predominantly rectangular to the parallel chains. All observed motion modes are explained by a segment motion model.The external stimulation of the mobility was investigated by incorporating of photo-switchable groups. A copolymer with photo-switchable spiropyran was synthesized. The success of the synthesis and the activity of the spiropyran were confirmed. A reaction of the polymer molecules on the external stimulation with UV-light on different substrates in in-situ SFM experiments could not be established.Another way of stimulation and resulting reaction is shown for polymer brushes with butylacrylate side chains. The worm-like brush polymers have been deposited on mica substrates and exposed to ethanol vapour resulting in a collapse to dense packed spherical aggregates. Venting of the chamber to remove the ethanol vapour and exposure to humid air resulted in spreading of brush polymers on the substrate. This behaviour could be shown over several cycles. The characteristic parameter for this transition is the surface tension of the used solvents. Solvents with a smaller surface tension as the side chains push the chains aside resulting in the collapse of the polymer. In the opposite case the side chains win and the result is a spread worm-like brush polymer

Organization, manipulation and motion of brush polymers and low molecular weight amphiphiles at interfaces

The aim of this thesis was to study the organization, manipulation and motion of brush polymers on different substrates by means of scanning force microscopy.The main part of this work is concentrated on one specific type of polymer: the monodendron jacketed linear chains. This is a polymer with a methacrylate backbone in which each monomer exhibits a minidendritic unit with three dodecyl-chains at the end.A different way of adsorption was shown on different materials. On mica an unspecific adsorption of flat laying molecules was observed, whereas on highly ordered pyrolitic graphite as well as on tungsten selenide an organization of flat laying molecules with long straight segments that bend at 60 degree and 120 degree angles was observed. The straight segments are oriented parallel to the three axes defined by the crystal structure of the substrate.In parallel to these experiments the motion of single molecules and molecular clusters was studied by in-situ SFM experiments in the temperature range of 30 to 48 degree Celsius. The experiments showed motion of the clusters similar to diffusion processes. For each cluster the diffusion coefficient was calculated and the way of motion was analyzed. The main results are: The velocity increases with reduced cluster size and higher temperature. Molecules that collide with others stick together and exhibit a high shape persistence. Molecules coming into contact with defects in the substrate get caught by these and either quit moving or start a one-dimensional guided motion along the step in the graphite.Special motion modes have been identified: molecular clusters with bar shaped conformation containing parallel chains exhibit diffusion predominantly rectangular to the parallel chains. All observed motion modes are explained by a segment motion model.The external stimulation of the mobility was investigated by incorporating of photo-switchable groups. A copolymer with photo-switchable spiropyran was synthesized. The success of the synthesis and the activity of the spiropyran were confirmed. A reaction of the polymer molecules on the external stimulation with UV-light on different substrates in in-situ SFM experiments could not be established.Another way of stimulation and resulting reaction is shown for polymer brushes with butylacrylate side chains. The worm-like brush polymers have been deposited on mica substrates and exposed to ethanol vapour resulting in a collapse to dense packed spherical aggregates. Venting of the chamber to remove the ethanol vapour and exposure to humid air resulted in spreading of brush polymers on the substrate. This behaviour could be shown over several cycles. The characteristic parameter for this transition is the surface tension of the used solvents. Solvents with a smaller surface tension as the side chains push the chains aside resulting in the collapse of the polymer. In the opposite case the side chains win and the result is a spread worm-like brush polymer

Individual bottle brush molecules in dense 2D layers restoring high degree of extension after collapse-decollapse cycle: Directly measured scaling exponent

We prepared dense films of adsorbed brush-like macromolecules on mica substrate by transfer of compressed Langmuir monolayers from water subphase. The main macromolecular contours in the dense films were clearly resolved by SFM. The films were subjected to successive treatments by ethanol and water vapours. In accordance with previous results for isolated macromolecules, the films underwent collapse and subsequent decollapse morphological transformations in the changing vapour environment. Statistical analysis of the macromolecular dimensions in the films allowed us to measure the values of the scaling exponent $\nu$ determining the correlation between mean lateral and linear dimensions of the macromolecules. The analysis showed that the macromolecular conformations in the film as transferred were similar to the previously described conformations of the same macromolecules deposited directly on mica as isolated chains at much lower surface densities. The determined $\nu$ was close to the 0.75 value corresponding to the 2D SAW statistics. We assumed that the molecules retained the high degree of extension during the compression step due to suppressed reorganisation of the side chains. Differently from previous observations for isolated macromolecules, the restored conformations in the dense films after collapse-decollapse cycle were more extended with the $\nu$ of about 0.73 value. A theoretical explanation of the high degree of re-extension is proposed