Sol-Gel Transition of a Thermo-Responsive Polymer at the Closest Solid Interface.

Thermo-responsive polymers are applied as surface modifications for the temperature switching of hydrophilic and hydrophobic properties through adsorption and grafting on solid substrates. The current understanding of the influence of polymer chains bound to the solid surface on the transition behavior of thermo-responsive polymers is rather restricted. In this study, we aim to elucidate the effect of the bound polymer chains at the interface on the thermo-responsive sol-gel transition behavior of aqueous methylcellulose (MC) solutions by employing a quartz crystal microbalance (QCM) to evaluate the shear modulus near the solid interface.

Interfacial Selective Study on the Gelation Behavior of Aqueous Methylcellulose Solution via a Quartz Crystal Microbalance.

It is important to understand the interfacial structure and physical properties of a polymer material to improve its function. In this study, we used a quartz crystal microbalance (QCM) and neutron reflectivity (NR) measurements to evaluate the viscoelasticity and structure of an aqueous methylcellulose solution near the gold interface. The apparent shear modulus, which was calculated from the complex frequency, was used to assess gelation behavior.

Detailed Structural Study on the Poly(vinyl alcohol) Adsorption Layers on a Si Substrate with Solvent Vapor-Induced Swelling.

We investigated in detail the structures in the poly(vinyl alcohol) (PVA) adsorption layers on a Si substrate, which remained on the substrate after immersing the relatively thick 30-50 nm films in hot water, by neutron reflectometry under humid conditions. For the PVA with a degree of saponification exceeding 98 mol %, the adsorption layer exhibits a three-layered structure in the thickness direction. The bottom layer is considered to be the so-called inner adsorption layer that is not fully swollen with water vapor.

Elucidation of a Heterogeneous Layered Structure in the Thickness Direction of Poly(vinyl alcohol) Films with Solvent Vapor-Induced Swelling.

We investigated the swelling behaviors of poly(vinyl alcohol) (PVA) films deposited on Si wafers with water vapor, which is a good solvent for PVA for elucidating structural and dynamical heterogeneities in the film thickness direction. Using deuterated water vapor, structural and dynamical differences in the thickness direction can be detected easily as different degrees of swelling in the thickness direction by neutron reflectivity. Consequently, the PVA film with a degree of saponification exceeding 98 mol % exhibits a three-layered structure in the thickness direction.

Nanopore formation on unilamellar vesicles of long- and short-chain lipids.

The structure of unilamellar vesicles (ULVs), comprising long- and short-chain lipids, was investigated, and the formation of nanopores on the surface of the ULVs was confirmed under the condition of long- and short-chain lipids being separated. It was also revealed that the behavior of the structural phase transition from ULVs to bilayered micelles (bicelles) depends on the number of nanopores formed on the surface of the ULVs. Because both the rim structures of nanopores and bicelles are considered to be microdomains of short-chain lipids, this phase behavior was explained by considering the kinetic pathway of the growth of the rim domain.

X-ray reflectivity study of a transcription-activating factor-derived peptide penetration into the model phospholipid monolayers.

The penetration of a transcription-activating factor (TAT)-derived, cell-penetration peptide onto 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dipalmitoyl-sn-glycero-3-[phospho-L-serine] (DPPS) monolayer on phosphate-buffered saline subphase was characterized. The surface area at the target pressure increased noticeably by the peptide penetration from the subphase to the phospholipid monolayer, which might suggest a direct penetration of the peptide across the pure phospholipid bilayer membrane. Interestingly, the more significant area increase at 35 mN/m was monitored from DPPC monolayer, contrary to the simple charge interaction: the net neutral DPPC, the net-negative DPPS, and the positive TAT-derived peptides (TDP).

Friction behavior of high-density poly(2-methacryloyloxyethyl phosphorylcholine) brush in aqueous media.

Super-hydrophilic polymer brushes were prepared by surface-initiated atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) on initiator-immobilized silicon wafers. The graft density was estimated to be 0.22 chains nm based on the linear relationship between and the layer thickness.

Surface and interfacial segregation in blends of polystyrene with functional end groups and deuterated polystyrene.

The effect of chain-end chemistry on surface and interfacial segregation in symmetric blends of polystyrene (hPS)/deuterated polystyrene (dPS) has been investigated by X-ray photoelectron and secondary ion mass spectroscopy in conjunction with neutron reflectivity measurements. Alpha,omega-fluoroalkyl- and alpha,omega-carboxy-terminated polystyrenes (alpha,omega-hPS(Rf)2 and alpha,omega-hPS(COOH)2) were used as end-functionalized polymers; the former possesses chain ends with lower surface energies, and the latter possesses higher surface energies compared with that of the main chain. In the case of an alpha,omega-hPS(Rf)2/dPS blend film, alpha,omega-hPS(Rf)2 was enriched at the surface owing to the surface localization of the Rf groups, although the surface energy of the hPS segments was slightly higher than that of the dPS ones.

Neutron and X-ray scattering on the monolayer structure of a lecithin fullerene-derivative.

Using neutron reflectivity with contrast variation, X-ray reflectivity, and grazing incident small-angle X-ray scattering (GISAXS), we have characterized the in-depth and in-plane structural characteristics of the Langmuir and Langmuir-Blodgett (LB) films formed by a novel lecithin C60-derivative, FPTL, of three phospholipids jointly bonded on one single olefinic moiety of a C60 cage. Based on the neutron reflectivity measured, we have proposed a monolayer structure, with the C60 cages of FPTL lifted into the air and hydrophilic phospholipid heads immersed in water, for the FPTL Langmuir layer formed on water. On the other hand, the LB film of FPTL prepared on mica exhibits clear Kiessig fringes in the X-ray reflectivity profile, indicating a 27 angstroms monolayer film with less molecular orientation.

Structure and dewetting behavior of polyhedral oligomeric silsesquioxane-filled polystyrene thin films.

Polyhedral oligomeric silsesquioxane (POSS) meets increasing interest as a building unit for inorganic-organic hybrid materials. The incorporation of cyclopentyl-substituted POSS (CpPOSS) into polystyrene (PS) thin films led to an inhibition of dewetting. In this paper, the dispersion state of CpPOSS in the CpPOSS/PS hybrid films and, furthermore, the relationships between the structure and dewetting inhibition effect are discussed.

Fabrication of metal nanoparticle monolayers on amphiphilic poly(amido amine) dendrimer Langmuir films.

A newly designed 1.5th generation poly(amido amine) dendrimer with an azacrown core, hexylene spacers, and octyl terminals was spread on gold nanoparticle (Au-NP) suspension. The surface pressure-area isothermal curves indicated that the molecular area of dendrimer on Au-NP suspension was significantly smaller than that on water, indicating the formation of dendrimer/Au-NP composites.

Structural and morphological changes of monolayers of a block copolymer with dendron and perfluoroalkyl side chains by mixing a perfluorooctadecanoic acid.

Hybrid Langmuir and Langmuir-Blodgett monolayers of a perfluorooctadecanoic acid mixed with a rigid block copolymer, poly(3,5-bis(3,5-bis(benzyloxy)benzyloxy)benzyl methacrylate-randommethacrylic acid)-block-poly(2-perfluorooctylethyl acrylate), which is composed of benzyloxy dendron side chains and perfluorinated side chains, were prepared and characterized by surface pressure-surface area isotherms, atomic force microscopic images and neutron and X-ray reflectometries. The two-dimensionally phase-separated structures of monolayer films and their morphologies with plateau and terrace were confirmed. The monolayers were separated into a dendron layer, a perfluorinated layer, and a carboxyl layer.

Nanostructure of a "carpet"-like dense layer/polyelectrolyte brush layer in a block copolymer monolayer at the air-water interface.

The "carpet"/brush double layer structure in the polyelectrolyte layer in the amphiphilic diblock copolymer monolayer at the air-water interface was quantitatively studied by in situ neutron reflectometry in addition to X-ray reflectivity measurements. As a result of the higher contrast between polyelectrolyte [poly(methacrylic acid)] and solvent (D(2)O) for the neutron, the brush structure could be estimated more accurately as a function of surface pressure, that is, brush density. The thickness of the carpet layer, which is thought to be formed to reduce the interfacial free energy between water and the hydrophobic layer, was almost constant at 10-20 A at any surface pressure studied.

Effect of salt concentration on the nanostructure of weak polyacid brush in the amphiphilic polymer monolayer at the air/water interface.

The effect of salt concentration on the nanostructure of a spread monolayer of ionic amphiphilic diblock copolymer, (diethylsilacyclobutane)m-b-(methacrylic acid)n, at the air-water interface was directly investigated by in situ X-ray reflectivity and neutron reflectivity techniques. Previously, we had found that a poly(methacrylic acid) (PMAA) hydrophilic layer under the water was not in the form of a simple polyelectrolyte brush but consisted of a dense carpet upper layer and a diffuse brush lower layer when the hydrophilic chain was long enough. Here we observed this double layer formation in the monolayer in aqueous NaCl solution at a constant surface pressure.