Tethered chains in theta solvent conditions: An experimental study involving Langmuir diblock copolymer monolayers

Journal Article · Wed Apr 01 00:00:00 EST 1998 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.475952· OSTI ID:597196

Kent, M S ^[1]; Majewski, J; Smith, G S ^[2]; Lee, L T ^[3]; Satija, S ^[4]

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1. Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
2. Los Alamos National Laboratories, Los Alamos, New Mexico 87545 (United States)
3. Lab. Leon Brillouin, CEN-Saclay, 91191 Gif-sur-Yvette Cedex (France)
4. Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

Langmuir monolayers of polydimethylsiloxane-polystyrene (PDMS-PS) diblock copolymers on dioctyl phthalate (DOP) at 22{degree}C are employed as a model tethered chain system in theta solvent conditions. The segmental concentration profile of the tethered PS block is obtained over an order of magnitude in both surface density ({sigma}) and molecular weight (M) by neutron reflection. A depletion layer of PS segments is observed at the air{endash}liquid interface which increases with M and is independent of {sigma}. The variation of the tethered layer height with {sigma} and M is consistent with h{approximately}{sigma}{sup 0.18}M{sup 0.74} over the range of reduced surface density ({sigma}{pi}R{sub g}{sup 2}) from 1 to 11. These dependencies, along with the form of the profile, indicate that the asymptotic limit is not achieved for {sigma}{pi}R{sub g}{sup 2}{le}11 in theta solvent conditions. The upper limit of surface density is limited by the interaction of the submerged blocks, which leads to a sharp rise in surface pressure ({Pi}). The increase of {Pi} with {sigma} far exceeds theoretical predictions, even in the asymptotic limit, and is attributed to distortion of chain configurations arising from limited lateral interpenetration. Anchoring energies compare well with differential chain energies at the desorption transition when the surface PDMS blocks are noninteracting. Comparisons are made with results obtained previously in good solvent conditions. {copyright} {ital 1998 American Institute of Physics.}

• OSTI ID: 597196
• Journal Information: Journal of Chemical Physics, Vol. 108, Issue 13; Other Information: PBD: Apr 1998
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
40 CHEMISTRY
COPOLYMERS
CHAINS
LAYERS
POLYSTYRENE
INTERFACES
ANCHORS
DESORPTION
SURFACE PROPERTIES
SOLUTIONS
MOLECULAR WEIGHT