Among the possible solutions for achieving low friction, polymer brushes that are grafted onto surfaces are good candidates. The tribological characterization of such layers becomes more difficult when the friction is lower: the signal-to-noise ratio of the friction force that is measured with conventional tribometers impedes the precise quantification. Therefore, we have applied a new technique that has been developed at the Laboratory of Tribology and System Dynamics (LTDS), called the ‘oscillating relaxation tribometer’. The advantage of this original technique is that it characterizes low friction with unequalled sensitivity. The lower the friction, the better the precision, and it permits obtaining the ‘friction law’ directly from robust and rapid experimental tests. In this study, the samples that have been used are the ionic liquid-type polymer brushes (ILPBs) with different thicknesses, which have been grafted onto silicon wafers and steel coupons. The counter-face is a mirror-polished steel ball. We show that (i) a thick ILPB layer on silicon is very resistant to high contact pressure, up to 555 MPa; (ii) the friction behavior that is obtained is close to that of a Newtonian viscous one, even under maximum normal loads; (iii) poorer results are obtained for the thinner sample; and (iv) the repetition, up to 5000 oscillations on the same surface, does not affect the friction damping of the contact, which demonstrates that this film provides a favorable resistance to friction under severe contact conditions. In addition, the feasibility of grafting onto steel surfaces is demonstrated. The results are then discussed, with respect to friction and dissipation.

Mesoporous silica is considered as promising host material for enzymes due to its uniform pore size of enzyme dimensions and tunable surface chemical properties. In this study, we applied nanoporous waveguide (NPWG) spectroscopy to observe adsorption dynamics of heme proteins with different molecular size within mesoporous silica film modified with different surface functional groups. Since NPWG spectroscopy provides kinetic information and rough quantification of adsorption amount, it is useful to study the adsorption process of enzymes within inorganic nanoporous materials.

Since human body joints have a gel-like structure with low friction that persists for several decades, hydrogels have attracted much interest for developing low-friction materials. However, such advantages can hardly be realized in industrial usage because water in the gel evaporates easily and the gel deswells. The substitution of water with an ionic liquid (IL) is one of the effective ways to overcome this problem. In this study, we substituted water in a double network (DN) hydrogel with 3-ethyl-1-methyl-imidazolium ethylsulfate (EMI-EtSulf), a hydrophilic IL, via a simple solvent exchange method to obtain a DN ion gel. A compressive test and thermogravimetric analysis showed that the DN ion gel has a high compression fracture stress and improved thermal properties, with the difference in 10% loss of temperature being ΔT₁₀ = 234 °C. A friction test conducted using a reciprocating tribometer showed that the friction of a glass ball/DN ion gel was relatively higher than that of a glass ball/DN hydrogel. Because the minimum coefficient of friction (COF) value increased after substitution, the increase in polymer adhesion caused by the electrostatic shielding of the surface moieties of glass and poly 2-acrylamidomethylpropanesulfonic acid (PAMPS) was considered the main contributor to the high friction. As the COF value decreased with increasing temperature, the DN ion gel can achieve low friction via the restriction of polymer adhesion at high temperatures, which is difficult in the DN hydrogel owing to drying.

Human joints support us to reduce the impact on our body and move them smoothly. As they are composed of gel-like structures, gel materials with soft and resilient properties are expected, as lubricants, to provide high efficiency and a long lifetime for mechanical parts. While double network gels including ionic liquids as swelling agents possess high mechanical strength and stable low friction under high temperature or vacuum, their fabrication process is complex and time-consuming. In this study, we applied one-pot synthesis to a double network ion gel (DNIG) to obtain a thin gel film by a simple coating method and examined its thermal, mechanical and tribological properties. The DNIG was obtained by one-pot synthesis (DNIG-1) combining polycondensation of tetraethoxysilane and radical polymerization of methyl methacrylate to form silica and poly(methyl methacrylate) as a 1st and 2nd network, respectively. Such obtained DNIG-1 was characterized and compared with DNIG obtained by a conventional two-step process (DNIG-2). Thermogravimetric analysis and the compressive stress–strain test showed high thermal stability and mechanical strength of DNIG-1. As friction at the glass/DNIG-1 interface showed high friction compared with that at glass/DNIG-2, various counterface materials were applied to examine their effect on the friction of DNIG-1. As SUS304/DNIG-1 showed much lower friction compared with glass/DNIG-1, the difference in the friction was presumably due to the different adsorption forces and compatibility between the materials.

In this paper, in situ surface-initiated atom-transfer radical polymerization (SI-ATRP) based on both an open and a coated system, without using volatile reagents, was developed to overcome the limited usage of ATRP due to the necessity of sealing. Nonvolatile ionic liquid (IL)-type components were used, specifically N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide as the polymerizable monomer and N,N-diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide as the polymerization solvent. In the experiment, the reversible-deactivation radical polymerization characteristics are properly ensured in nonvolatile ATRP solution coated on silicon wafer as thin liquid film, to form concentrated polymer brushes (CPBs). The average molecular weight and molecular-weight distribution of the polymer produced in the liquid film and formed on silicon wafer were measured by gel permeation chromatography, which confirms that the polymerization reaction occurred as designed. Furthermore, it is clarified that the surface of the polymer brush synthesized in situ swollen by IL also exhibited low friction characteristics, comparable to that synthesized in a typical immersion process. This paper is the first to establish the effectiveness of in situ preparation for CPBs by using the coating technique.