At the outermost surface, aggregation states of polymers generally tend to alter to their most stable ones in response to their surrounding environment. We here apply a time-resolved contact angle measurement to study the rate of the surface reorganization of poly(methyl methacrylate) (PMMA) in water. By doing these measurements at various temperatures, it is possible to determine the apparent activation energy of the surface dynamics based on the relation of the surface relaxation time and temperature. Also, the sum-frequency generation spectroscopy revealed that the surface reorganization involves the conformational changes in the main chain part as well as the side chains. Hence, the dynamics observed here may reflect the segmental motion at the outermost region of the PMMA film, in which water plays as a plasticizer.

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...

The nature of the polymer-water interface in the poly(methyl 2-propenyl ether) (PMPE)-water model system is investigated by sum-frequency generation spectroscopy, which at the moment gives the best depth resolution among available techniques. PMPE, synthesized via living cationic polymerization, is structurally similar to poly(methyl methacrylate) (PMMA) except for lacking a carbonyl group. We here probe the polymer local conformation as well as the aggregation states of water at the interface. Comparing the results of our measurements to the PMMA-water system, the effect of a carbonyl group on the water structure at the interface is discussed. This knowledge should be crucial to the design and construction of highly functionalized polymer interfaces for bioapplications.

The aggregation states of polystyrene (PS) thin films at interfaces with nonsolvents such as water, methanol, and hexane were examined by specular neutron reflectivity and sum-frequency generation vibrational spectroscopy. The density profiles of the PS thin films along the direction normal to the interface with water and methanol were comparable to that in air. However, this was not the case for the film in hexane exhibiting a diffuse interfacial layer due to swelling. Also, the local conformation of PS in the outermost region of the films was quite sensitive to the surrounding environment and consequently responded to a change in its environment. This was the case for typical nonsolvents such as water and methanol. The extent of the conformational change might be explained in terms of the interfacial energy.

An effect of stereoregularity on the structure of poly(methyl methacrylate) at air and water interfaces