Aggregation States of Polymers at Hydrophobic and
Hydrophilic Solid Interfaces
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Abstract
Aggregation states of polystyrene
(PS) and poly(methyl methacrylate)
(PMMA) at hydrophobic deuterated-octadecyltrichlorosilane (OTS-<i>d</i>) and hydrophilic SiO<sub>x</sub> interfaces are discussed,
focusing on the interaction strength between polymer and substrate.
Sum-frequency generation spectroscopy revealed that PS exhibited oriented
phenyl groups along the normal direction at the interface in a spin-coated
film because of the centrifugal force generated during the film solidification
process, whereas it did not in a solvent-cast film. This result was
common for both hydrophobic and hydrophilic substrates. That is, the
aggregation states of PS depended little on which kind of substrate
was used. This is because the interaction between PS and the surfaces
is weak. In the case of a PMMA film on the hydrophobic OTS-<i>d</i> substrate, the interfacial local conformation was also
dependent on the method of film preparation. PMMA at the hydrophilic
SiO<sub>x</sub> interface, however, exhibited oriented ester methyl
groups along the direction normal to the interface, regardless of
the film preparation method. This is due to a stronger interaction
via hydrogen bonding between carbonyl groups of PMMA and the substrate
surface