Copyright © 2020 American Chemical Society. An amphiphilic hyperbranched polymer (HBP) containing both fluoroalkyl (Rf: -C6F13) pendants and oligo(ethylene oxide) (nEO) parts was synthesized as a novel type of interfacial modifier to confer dynamic features on conventional polymer films. The HBP was always segregated at the outermost region of the polymer matrix in contact with air and water phases. The former and latter were driven by the presence of hydrophobic Rf pendants and hydrophilic nEO parts, respectively. Such a dynamic interface can be attained by changing the local conformation of HBP or segment-level segregation in the HBP molecule. In water, nEO parts formed a dissolved layer at the interface and induced excellent bioinert properties. Our strategy based on stable segregation, which could be maintained even after changing the environment, should be useful for constructing functional surfaces. ©

The local conformation of poly(styrene-co-butadiene) rubber (SBR) chains in direct contact with a quartz substrate was examined by interface-sensitive sum-frequency generation (SFG) spectroscopy. SFG signals, which could be obtained from functional groups only oriented at the interface, were clearly observed for SBR in a film at room temperature which was much higher than the bulk glass transition temperature (Tg). When the film was thermally annealed, SBR chains at the quartz interface changed their conformation to one with a lower energy state, accompanied by the randomization of both the main and side chain parts. The characteristic temperature, at which interfacial chains started to lose their orientations, was much higher than the bulk Tg. Also, the extent found to be more remarkable for the spin-coated film than for the solvent-cast one. This implies that the stress accumulated at the interface, which resulted from the centrifugal force during the spin-coating process, accelerates the mobility of chains there. Finally, the kinetics experiment well supports the slower orientation relaxation at the interface.

The rotational relaxation time (τrot) of a fluorescent molecule, coumarin 153 (C153), dispersed in different rubbery polymers is characterized by time-resolved fluorescence anisotropy measurement, and an attempt is made to quantitatively combine it with the segmental relaxation time (τseg) of the corresponding matrix polymer obtained by dielectric relaxation spectroscopy. This study here demonstrates that τseg extrapolated to higher temperatures using the Vogel–Fulcher–Tammann law can be superimposed on τrot, resulting in a single curve. This behavior is common for polymers with different glass transition temperatures such as polyisoprene and acrylonitrile/butadiene copolymer, implying that the rotational dynamics of C153 is a useful tool for the characterization of polymer dynamics.

The performance of a polymer composite material, in which inorganic fillers are dispersed, is closely related to the aggregation states and dynamics of polymer chains at the interface with the filler. In this study, the local conformation of polyisoprene (PI) at a quartz substrate interface was studied as a model system for the rubber/filler composite material. PI films were prepared from a toluene solution onto quartz substrates by a spin-coating method. Sum-frequency generation spectroscopy revealed that the local conformation of PI chains at the quartz interface depended on the spinning rate. The tilt angle of methyl groups increased with the rotational speed, probably due to the centrifugal force applied to chains and probably also the evaporation rate of the solvent during the solidification process. This result indicates that the interfacial orientation of PI chains can remain even at room temperature, which is 87 K higher than the bulk glass transition temperature (Tg b). The interfacial orientation disappeared at a temperature approximately 120 K higher than Tg b.

The kinetics of dynamic polymer brush formation, which is driven by interfacial segregation of amphiphilic block copolymers, was investigated by quartz crystal micro-balance (QCM) and neutron reflectivity (NR). High speed formation kinetics in the early stage was probed by QCM, and the later stage, where the formation kinetics became relatively slow, was investigated by NR. QCM detected fairly the fast brush formation kinetics on the order of tens of seconds for the copolymers in use. The dynamic polymer brush rapidly grows initially and hence repairs itself when the surface is damaged and the brush is partly lost. This fast dynamic polymer brush formation is driven by relatively slow diffusion of block copolymers in the matrix. The slow diffusion suggests that the diffusion mechanism is not controlled by simple Rouse or reputational diffusion but by the activation hopping mechanism of self-assembled diblock copolymers.

By means of sum-frequency generation spectroscopy, we report a depth-resolved measurement of the local conformation and chain relaxation of polystyrene (hPS) located at different distances from the quartz interface. To control the distance from the quartz interface, deuterated polystyrene (dPS) layers with thicknesses of 3.4, 7.5, and 20 nm were coated on the quartz substrates. The hPS chains in direct contact with the substrate surface predominantly orient their phenyl rings in a direction normal to the substrate. This conformation was found to be barely relaxed when the film was annealed for 24 h at 423 K, higher than the bulk glass transition temperature. In contrast, for the hPS chains supported on the dPS layer, the orientation of phenyl rings of hPS became weaker with the annealing and this trend was more significant with increasing distance from the quartz substrate. In particular, the orientation of phenyl rings of hPS after annealing vanished at a distance of 20 nm. These results might provide an important evidence of the difference in the relaxation dynamics of the PS chains located at different distances from the quartz interface. Published by AIP Publishing.

The chain dynamics of well-defined poly(2-methoxyethyl acrylate) (PMEA), which has been used in practice as a bioinert coating for heart-lung machines, was examined as a function of water content by dielectric relaxation spectroscopy (DRS). Two relaxation processes observed in both dried and hydrated films were assigned to the segmental motion (alpha-process) and the relatively smaller scale motion such as the hindered rotation of side chains (beta-process). Water molecules adsorbed on PMEA made the alpha-process faster, meaning that water molecules in PMEA played the role of a plasticizer. Combining the above knowledge with the depth dependence of water content in the PMEA film previously obtained by neutron reflectivity, the segmental dynamics of PMEA at the water interface, which should be crucial to bio-inertness, is discussed. We found that the segmental motion was markedly faster than that in the bulk and almost comparable to the side chain motion.

We report the peculiar time evolution of the contact angle of water on reconstructive polymer surface. Surface reconstruction is driven by segregation of amphiphilic diblock copolymer to the water interface of the elastomer, in which amphiphilic diblock copolymer is mixed. In other words, the brush of hydrophilic block is spontaneously formed at the elastomer/water interface and can be called dynamic polymer brush. The contact angle measurement of water droplet was carried out as a function of time after a droplet was placed on the surface. The contact angles stay the same value for certain induction period before decrease monotonically with time. We also proposed a simple model to explain the experimental results quantitatively. The model is based on two hypotheses: water droplet starts to spread only after a depletion layer of the hydrophilic block at the air interface is dissolved, and segregated block copolymer brush begins to repel one another.

series of amphiphilic polydimethylsiloxane-b-poly[tri(ethylene glycol) methyl ether methacrylate] (PDMS-b-PM3) diblock copolymers were prepared with varying PM3 compositions. The well-defined PDMS-b-PM3 was synthesized by using a coupling reaction between the living PM3 and omega-benzyl bromide-functionalized PDMS. The obtained polymers had narrow molecular weight distributions (M-w/M-n <= 1.08) and predictable molecular weights. The bulk-state self-assembly of the polymers was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) measurements. The microphase separated morphologies in these amphiphilic block copolymers varied from the PDMS-cylinder to lamellar, even if the molecular fraction of the PM3 was progressively reduced from 70 wt% to 17 wt%. We also performed the detailed surface structural characterization of the amphiphilic PDMS-b-PM3 thin-films by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and static water contact angle measurement. Based on these structural analyses, we proposed that the block copolymer self-assembled into a cylinder-like nanostructure at the top of thin film surface without any tedious annealing method in the case of the block copolymer possessing high PM3 content (>= 70 wt%).

The density profile in a thin cross-linked polyisoprene (PI) film spin-coated on a quartz substrate in n-hexane was examined by specular neutron reflectivity. We found two layers with different PI densities at the substrate interface. The characteristics of the layers are discussed in terms of bound rubber typically associated with the field of rubber materials and adsorbed layers typically associated with the field of glassy materials. (C) 2016 Elsevier Ltd. All rights reserved.

The thin film stabilities of omega-N-(3-(dimethylamino) propyl)propylamide-terminated polystyrene (PS-N) and its blends with conventional polystyrene (PS-H) supported on silicon wafers with a native oxide layer were examined. Whereas a 20-nm-thick film of PS-H with a number-average molecular weight of similar to 50k decomposed at 423 K, a comparable PS-N film and blended films containing a PS-N fraction of 440 wt% were stable. Although the local conformation of chains at the substrate interface was not the same for PS with and without the functional end group, the glass transition temperature at the interface was identical for both PS-H and PS-N. The residual adsorbed layer on the substrate after washing the films with a good solvent was thicker for PS-N than for PS-H. This implies that end functionalization, rather than segmental dynamics, affects chain movement on a large scale.

The objective of this study is to carry out nanoscale characterization of the epoxy resin interface on silica by determining the glass-transition temperature (T-g) and molecular conformation at the interface by means of a novel nondestructive method. The T-g was determined by fluorescence lifetime measurements using evanescent wave excitation. It was revealed that the T-g of epoxy resin at a distance of 30 nm from the interface was 10 K higher than that at a distance of 80 nm. The chemical composition and molecular conformation were analysed by X-ray photoelectron spectroscopy and sum-frequency generation (SFG) spectroscopy, respectively. The SFG data revealed that unreacted epoxy group remained at the interface. The T-g of epoxy resin increased in the regions near the interface, and the epoxy group remained unreacted at a distance of ca. 10 nm or less from the interface.

Aggregation states of polystyrene (PS) and poly(methyl methacrylate) (PMMA) at hydrophobic deuterate-doctadecyltrichlorosilane (OTS-d) and hydrophilic SiOx 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 SiOx 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.

A series of highly dielectric polyrotaxane derivatives consisting of axle polyethylene glycol (PEG) and threated alpha-cyclodextrins (CDs) were synthesized by Modifying the hydroxyl groups of CDs with cyanoethyl or dicyanobutyl groups. We found that the introduction of poly(2-hydroxyethyl methacrylate) (PHEMA) side chain with a number of hydroxyl groups and subsequent cyanoethylation give particularly high dielectric constant (23.4), which is comparable to those of commercially available highly dielectric polymeric materials. We also succeeded in preparing a highly dielectric (epsilon' similar to 16 at 10 kHz) and flexible (Young's modulus similar to 3.4 MPa) elastomer film without any inorganic filler, which is a desirable material for insulator of dielectric elastomer actuators. (C) 2014 Elsevier Ltd. All rights reserved.

A self-repairable high density polymer brush of poly(ethylene glycol) (PEG) is formed at the interface between cross-linked poly(dimethyl siloxane) (PDMS) and water by spontaneous surface segregation of an amphiphilic diblock copolymer consisting of PEG and PDMS. The surface reconstruction by the formation of the brush was observed as the large hysteresis of the contact angle of the water droplet. Neutron reflectivity measurement revealed that the grafting density of the polymer brush is 2.8 chain/nm(2), which is comparable to those of polymer brushes by the surface-initiated polymerization method. The formation of such a remarkably dense polymer brush by segregation can be well supported by the balance between the mixing enthalpy of PEG and water and the stretching energy of PEG.