Tisato Kajiyama

Bovine serum albumin adsorption onto immobilized organotrichlorosilane surface: Influence of the phase separation on protein adsorption patterns

Octadecyltrichlorosilane (OTS) and [2-(perfluorooctyl)ethyl]trichlorosilane (FOETS) monolayers and their mixed monolayer were polymerized on a water subphase and subsequently immobilized onto a silicon wafer surface by covalent bonding. Atomic force microscopic (AFM) observation of the mixed (OTS/FOETS) monolayer revealed the formation of a phase-separated structure. Protein-adsorption behavior onto the monolayers was investigated in situ on the basis of an attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopic flow cell method and the morphology of the monolayer surface-adsorbed bovine serum albumin (BSA) was observed by AFM. Protein adsorption behavior observed by ATR-FT-IR flow cell method revealed that the amount of BSA adsorption onto the OTS and FOETS monolayers increased remarkably at an initial experimental stage and attained a steady state within a few minutes at pH 7.5. The amount of steady state adsorption was c. 0.18-0.2 microgcm(-2). AFM observation of the monolayer after exposure to BSA solution suggested that BSA adsorbed in the end-on adsorption state on OTS monolayer and side-on one in the FOETS monolayer, respectively. However, in the case of the mixed (OTS/FOETS) monolayer, ATR-FT-IR flow cell experiment revealed that the amount of steady state adsorption of BSA was suppressed. Also, AFM observation revealed that at pH 7.5, BSA preferentially adsorbed onto the FOETS phase of the mixed (OTS/FOETS) monolayer, which had a higher interfacial free energy against water. On the other hand, BSA adsorbed homogeneously onto the OTS and FOETS phases at the isoelectric point of BSA (pH 4.7). These results indicate that the preferential adsorption of BSA onto the FOETS phase in the mixed (OTS/FOETS) monolayer system is due to: (1) the minimization of the interfacial free energy between a monolayer surface and an aqueous solution; and (2) the electrostatic repulsion between BSA molecules bearing negative charges.

Surface glass transition temperatures of monodisperse polystyrene films by scanning force microscopy

Abstract Surface molecular motion of monodisperse polystyrene (PS) films was examined by scanning viscoelasticity microscopy (SVM) in conjunction with lateral force microscopy (LFM). The dynamic storage modulus, ƴ, and loss tangent, tan d , at a PS film surface with a smaller number-average molecular weight, Mn, than 40k were found to be smaller and larger than those for the bulk sample even at room temperature, meaning that the PS surface is in a glass–rubber transition state or a fully rubbery one at this temperature if the Mn, is small. In order to elucidate quantitatively how vigorous the molecular motion at the PS surface is, SVM and LFM measurements were made at various temperatures. The glass transition temperature, Tg, at the surface wasdiscerned to be markedly lower than its bulk Tg, and the discrepancy of Tg between surface and bulk becomes larger with the decreasing Mn. Such an intensive activation of thermal molecular motion at the PS surfaces can be explained in terms of an excess free volume in the vicinit of the film surfaceinduced by the preferential segregation of chain end groups.

Formation mechanism of n-octadecyltrichlorosilane monolayer prepared at the air/water interface

Abstract The n-octadecyltrichlorosilane (OTS) monolayer was prepared by the Langmuir–Blodgett method. The formation mechanism of the OTS monolayer on the water subphase was investigated on the basis of electron diffraction (ED) study, Fourier transform infrared external reflection spectroscopic (FT-IR/ERS) measurement and high-resolution atomic force microscopic (AFM) observation. Morphological changes in the monolayer in a compression process were observed by AFM. FT-IR/ERS measurement was performed for the monolayer at the air/water interface, and that the ED and AFM observations were done for the monolayer transferred onto substrate. ED study and high-resolution AFM observation revealed that the OTS monolayer was in a crystalline state at 293 K. Also, FT-IR/ERS measurement and AFM observation showed that the OTS molecules crystallize and polymerize spontaneously right after spreading a toluene solution of OTS on the water subphase. Then, during a monolayer compression, the crystalline OTS monolayer domain did not form the larger ones by sintering at the crystalline domain interface at 293 K. Also, AFM and ED observations revealed that the defect-diminished OTS monolayer could be successfully prepared by using the multi-step creep method.

In situ atomic force microscopic observation of albumin adsorption onto phase-separated organosilane monolayer surface

A mixed (n-octadecyltrichlorosilane (OTS)/[2-(perfluorooctyl)ethyl]trichlorosilane (FOETS)) monolayer was prepared on the water subphase and was subsequently immobilized onto the silicon wafer surface by chemical bonds. Atomic force microscopic (AFM) observation of the mixed (OTS/FOETS) monolayer revealed the formation of a phase-separated structure. In situ AFM observation of the adsorption behavior of bovine serum albumin (BSA) onto the mixed (OTS/FOETS) monolayers, successfully showed the adsorption behavior of BSA onto the phase-separated surface. It also revealed that in the case of pH 7.5, BSA was preferentially adsorbed onto the lower surface free energy FOETS phase of the mixed (OTS/FOETS) monolayer. On the other hand, BSA was adsorbed homogeneously onto the OTS and FOETS phases at the isoelectric point of BSA (pI 4.7). These results indicate that the preferential adsorption of BSA onto the FOETS phase in the mixed (OTS/FOETS) monolayer system may be due to: (1) the minimization of interfacial free energy between a monolayer surface and an aqueous solution; and (2) the electrostatic repulsion among BSA molecules bearing negative charges.

Scanning force microscopic study of surface structure and properties of (alkylsilane/ fluoroalkylsilane) mixed monolayers

(Alkylsilane/fluoroalkylsilane) mixed monolayers were immobilized covalently on a silicon wafer surface with stable surface structure. Atomic force microscopic observation of the n-octadecyltrichlorosilane (OTS)/[2-(perfluorooctyl)ethyl]trichlorosilane (FOETS) mixed monolayer revealed that the crystalline OTS circular domains of ca. 1–2μm in diameter were surrounded by a sealike amorphous FOETS matrix, even though the molar fraction of OTS was above 75%. Also, the phaseseparated monolayer can be prepared from FOETS, and a non-polymerizable and crystallizable amphiphile such as lignoceric acid (LA). The phase separation of the (alkylsilane/fluoroalkylsilane) mixed monolayer might be attributed to both faster spreading of FOETS molecules on the water surface and the crystallizable characteristics of alkylsilane molecules. The mixed monolayer of crystalline alkylsilane (OTS) and amorphous alkylsilane (n-dodecyltrichlorosilane, DDTS) formed a phase-separated structure on the water surface because of the crystallizable characteristics of OTS. Lateral force microscopic (LFM) observation revealed that the order of the magnitude of lateral force generated against the silicon nitride tip was: n-triacontyltrichlorosilane (TATS) domain with longer alkyl chain > amorphous FOETS matrix > crystalline OTS domain. On the other hand, scanning viscoelasticity microscopic observation revealed that the order of the magnitude of modulus was: Si substrate > crystalline OTS domain > amorphous FOETS matrix.

Effect of aggregation state on nanotribological behaviors of organosilane monolayers

Nanotribological behaviors of organosilane monolayers prepared by the Langmuir-Blodgett (LB) and chemisorption methods are discussed in terms of their aggregation states. Aggregation structure of the LB n-octadecyltrichlorosilane (OTS-C18) monolayers changed from a rectangular to an amorphous phase via a hexagonal phase with increasing temperature. A distinct lateral force decrease accompanies the phase transition. The LB alkyltrichlorosilane monolayers with longer alkyl chains were in a crystalline state at 293 K. The lateral force of the LB alkyltrichlorosilane monolayers at 293 K increased with increasing chain length. The n-triacontyltrichlorosilane LB monolayer (TATS-C30) in a rectangular phase showed higher lateral force than that of the alkyltrichlorosilane with shorter alkyl chains in a hexagonal phase. The lateral force of the OTS-C18 monolayer prepared by the LB method was higher than that of the chemisorbed one because of the higher packing density of alkyl chain for the LB monolayer, though both monolayers are in a hexagonal phase at 293 K. A large increase in lateral force was observed for the 18-nonadecenyltrichlorosilane (NTS) after oxidation of vinyl end groups.

Mechanical nanofabrication of lignoceric acid monolayer with atomic force microscopy

Nanometer scale pits have been fabricated in a crystalline fatty acid monolayer by applying weak repulsive force exerted from the cantilever tip of an atomic force microscope. In this method, the shape of fabricated pits was controlled to be circular or rectangular. The minimum diameter of the pit was ∼20 nm. It was demonstrated that the pits could be artificially distributed with different size and surface area density in the organic monolayer.

Direct observation of defect-diminished fatty acid monolayers and their optical applications

Abstract The aggregation structure of fatty acid monolayers on the water surface have been classified with respect to thermal ( T sp , T αc , T m ) and chemical (the degree of ionic dissociation of hydrophilic group) factors. In the case of amphiphiles with a non-ionic hydrophilic group, at T sp below T m , the monolayer is in a crystalline phase which is designated “the crystalline monolayer”. The crystalline monolayer is further classified into “the fusing-oriented crystalline monolayer” and “the randomly assembled crystalline monolayer” at T sp below and above T αc , respectively. At T sp above T m , the monolayer is in an amorphous phase which is designated “the amorphous monolayer”. In the case of amphiphiles with an ionic hydrophilic group, at T sp below T m , amphiphile molecules form “the compressing crystallized monolayer”, and T sp above T m , the monolayer is not crystallized by compression. Molecular-resolution images of molecules in the monolayers were successfully observed with an atomic force microscope (AFM) for the first time. A high mechanical stability of the monolayer is inevitably required for the non-destructive AFM observation of the fatty acid monolayer. For the preparation of the mechanically stable monolayer, the continuous compression method up to a low surface pressure and the multi-step creep method were used. Further, the Langmuir-Blodgett (LB) films with a homogeneous surface morphology could be constructed by the mechanically stable monolayers, and the morphological homogeneity was necessary for the construction of low-propagation loss LB film optical waveguides.

Effect of end group chemistry on surface molecular motion of monodisperse polystyrene films

The surface molecular motion of monodisperse polystyrene (PS) with various chain end groups was investigated on the basis of temperature-dependent scanning viscoelasticity microscope (TDSVM). The surface glass transition temperatures, Tgss for the proton-terminated PS (PS-H) films with number-average molecular weight, Mn of 4.9k–1,450k measured by TDSVM measurement were smaller than those for the bulk one, with corresponding Mns, and the Tgss for Mn smaller than ca. 50k were lower than room temperature (293 K). In the case of Mn = ca. 50k, the Tgss for the α,ω-diamino-terminated PS (α,ω-PS(NH2)2) and α,ω-dicarboxy-terminated PS (α,ω-PS(COOH)2) films were higher than that of the PS-H film. On the other hand, the Tgs for the α,ω-perfluoroalkylsilyl-terminated PS (α,ω-PS(SiC2CF6)2) film with the same Mn was much lower than those for the PS films with all other chain ends. The change of Tgs for the PS film with various chain end groups can be explained in terms of the depth distribution of chain end groups at the surface region.

Melting behavior of thin polyethylene films

Melting behavior in thin films of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) was studied by local thermal analysis (µTA). Even in the films thinner than 100u2009nm, the melting temperature (Tm) was successfully observed by µTA. For LLDPE, Tm decreased as the thickness became thinner than 150u2009nm. For HDPE, Tm increased with decreasing thickness. Polarized infrared spectroscopy revealed that an edge-on lamellar structure formed in both cases, meaning that the crystallite orientation may not be a reason why the thickness dependence of Tm was not the same for both resins. A possible explanation is that for LLDPE the segmental mobility in the amorphous region predominates with decreasing thickness, and for HDPE the chain orientation in the region predominates with decreasing thickness.