Aggregation States of Polymers at Hydrophobic and Hydrophilic Solid Interfaces

Abstract

Aggregation states of polystyrene (PS) and poly-(methyl methacrylate) (PMMA) at hydrophobic deuteratedoctadecyltrichlorosilane (OTS-d) and hydrophilic SiO x 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-d substrate, the interfacial local conformation was also dependent on the method of film preparation. PMMA at the hydrophilic SiO x 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.T he remarkable physical properties of polymers at surfaces and interfaces, which generally substantially deviate from those in the bulk, have been studied intensively. 1−29 One of the most striking and fascinating properties is the segmental dynamics. We have, using time-and space-selective fluorescence spectroscopy, reported that the glass transition temperature (T g ) for a typical glassy polymer, polystyrene (PS), increases in close proximity to the substrate interface and that the extent is dependent on the distance from the substrate and on the interaction with the substrate surface. 30,31 The experimental results were well supported by molecular dynamics simulation, 31 and this is not inconsistent with a recent finding of a dead layer that existed at the substrate interface. 32,33 The T g elevation at the substrate interface indicates that there is a significant effect on the aggregation states of glassy polymers at a solid substrate interface. Recently, we have applied sum-frequency generation (SFG) spectroscopy 34−36 to study the local conformation of PS chains at the solid interface in a film. 37 When a PS film was prepared on a quartz substrate by a spin-coating method, the chains were aligned in the plane at the substrate interface, resulting in the orientation of side chain phenyl groups of PS along the direction normal to the interface. 37 A dissipative particle dynamics simulation revealed that the spinning torque induced the chain orientation during the film preparation process and that the extent of the orientation was a function of the distance from the interface. This interfacial orientation of chains was not observed for a PS film prepared by a solvent-casting method. In this case, chain ends were rather oriented at the interface in a solvent-cast film because the polymer chains could reach a more stable sta...

Unswollen layer of cross-linked polyisoprene at the solid interface

“…[24][25][26][27][28] This is mainly because the dynamics of the chains is faster in the surface region than in bulk. [29][30][31][32][33][34][35] At the same time, it is also accepted that chains form an adsorbed layer on the silicon surface [36][37][38][39][40][41][42][43][44][45][46][47] and exhibit slower dynamics. [48][49][50] These properties are similar to those of bound rubber, meaning that we should be able to explain how rubber and glassy polymers attach to solid surfaces in the same way.…”

Effect of Molecular Architecture on Conformational Relaxation of Polymer Chains at Interfaces

“…[ 50,51 ] This scenario was also supported by a recent result evidencing an elevated glass transition temperature for polymer chains grafted onto silica nanoparticles though in this case, the depressed chain mobility was explained in terms of the stretching conformation of tethered chains in addition to the interfacial effect. [ 52,53 ] Postulating that the interaction between chains and the interface alters the chain dynamics at the interface, [ 10,54,55 ] the slower conformational relaxation for sPS could be understood. Also, if that is the case, the adsorption behavior of chains onto the substrate surface should be dependent on the architecture.…”

Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

“…35 Triangular prism and hemi-cylinder prism are also frequently used to enhance the reflectivity of SFG signal at buried polymer interfaces (Figure 5b and 5c). [36][37][38][39][40][41] However, for the study of polymer surface in air, the prism geometry could also detect strong signal from the buried polymer/prism interface. 42 A trapezoid Dove prism has been used to achieve a multi-reflection geometry surfaces (Figure 5d).…”

“…123 Inutsuka et al further compared the effect of the two deposition methods in preparing the PS and PMMA films on hydrophobic deuterated octadecyltrichlorosilane and hydrophilic SiO x surfaces. 40 For the PS film, the interaction between polymer and the substrate was weak, resulting in discrepant orientation behaviors of phenyl groups in different polymer aggregation states when prepared using different methods. Similar difference was also observed for the PMMA film at the hydrophobic interface.…”

“…However, strong hydrogen bonding between carbonyl groups in PMMA and the hydrophilic SiO x surface gave similarly orientated ester methyl groups along interface normal at the PMMA/SiO x interface. 40 These papers revealed that the centrifugal force could affect the interfacial structures when the polymer/substrate interaction force was low. In an SFG-VS measurement of a polymer thin film, the detected signal can come from multiple interfaces, such as the polymer/substrate and polymer/air interfaces.…”