Surface Forces Characterization of Concentrated PMMA Brush Layers under Applied Load and Shear.

Concentrated polymer brushes (CPBs) are known to exhibit excellent lubrication properties. However, the frictional behaviors of CPBs vary, depending on their preparation and operating conditions. In order to understand such complicated properties, it is necessary to determine their structures and correlate them with their properties, during shear motion. In this study, we employed surface forces and resonance shear measurement (RSM) as well as refractive index measurement using fringes of equal chromatic order (FECO) for studying the structure of the CPBs of poly(methyl methacrylate) (PMMA) in toluene. The obtained elastic (ks) and viscous (bs) parameters based on the RSM for the PMMA-PMMA were higher than those obtained for PMMA-silica over the entire distance range. With the increasing shear amplitude on the PMMA-PMMA under an applied load, the bs value first increased and then decreased while the ks value monotonically decreased. These behaviors were consistent with those of the thicker CPBs reported in a previous paper (Soft Matter, 2019). Thus, the dynamics of the CPBs under the applied load and shear were not dependent on the thickness of the polymer brushes in this case. The density distribution of the swollen PMMA brushes along the distance in the thickness direction of the brush layer was estimated by using the measured refractive index values, showing that the fraction of the PMMA brushes in the outer region from the surface (20% in the thickness) was ca. 10%. This lower density region near the surface of the swollen CPBs enabled them to interpenetrate with each other. Changes in the refractive index value under shear were observed, indicating that the interpenetrated PMMA chains were pulled out with increasing shear amplitude. These results demonstrated that broader applications of CPBs are possible by regulating the friction between them under different operating conditions, even for usually lubricious CPBs.

Hypolipidemic and Anti-Inflammatory Effects of Curcuma longa-Derived Bisacurone in High-Fat Diet-Fed Mice.

Turmeric (Curcuma longa) contains various compounds that potentially improve health. Bisacurone is a turmeric-derived compound but has been less studied compared to other compounds, such as curcumin. In this study, we aimed to evaluate the anti-inflammatory and lipid-lowering effects of bisacurone in high-fat diet (HFD)-fed mice. Mice were fed HFD to induce lipidemia and orally administered bisacurone daily for two weeks. Bisacurone reduced liver weight, serum cholesterol and triglyceride levels, and blood viscosity in mice. Splenocytes from bisacurone-treated mice produced lower levels of the pro-inflammatory cytokines IL-6 and TNF-α upon stimulation with a toll-like receptor (TLR) 4 ligand, lipopolysaccharide (LPS), and TLR1/2 ligand, Pam3CSK4, than those from untreated mice. Bisacurone also inhibited LPS-induced IL-6 and TNF-α production in the murine macrophage cell line, RAW264.7. Western blot analysis revealed that bisacurone inhibited the phosphorylation of IKKα/ß and NF-κB p65 subunit, but not of the mitogen-activated protein kinases, p38 kinase and p42/44 kinases, and c-Jun N-terminal kinase in the cells. Collectively, these results suggest that bisacurone has the potential to reduce serum lipid levels and blood viscosity in mice with high-fat diet-induced lipidemia and modulate inflammation via inhibition of NF-κB-mediated pathways.

Viscosity of Nanoconfined Branched-Chain Fatty Acids Studied by Resonance Shear Measurements.

Lubricant performance can be improved using additives such as organic friction modifiers (OFMs) and is influenced by their conformation and properties in the space confined between the substrate surfaces, rendering the detailed property analysis of confined OFMs and lubricants a matter of high practical significance. To date, studies on fatty acids as confined OFMs have mainly focused on linear- and unsaturated-chain molecules, leaving branched-chain structures underexplored. To bridge this gap, we used resonance shear measurements in this study to probe the viscosity of two branched-chain C18 fatty acids (isostearic acid T and isostearic acid) confined between mica surfaces at different applied normal loads (L) and surface separation distances (D). The viscosity parameter (bs) of both acids significantly increased at D < ∼4 nm because of structuring and was lower for isostearic acid than that for isostearic acid T at L > ∼0.6 mN. This reversal of bulk viscosity order under nanoconfinement was ascribed to the ability of the bulky methyl-substituted side chain of isostearic acid to prevent ordering in the nanospace between the mica surfaces and thus preserve fluidlike properties. The obtained results provide fundamental insights into the lubricity of branched-chain fatty acids and are expected to promote the development of novel high-performance OFMs.

Effect of vinylene carbonate on SEI formation on LiMn2O4 in carbonate-based electrolytes.

Spinel LiMn2O4 (LMO) is a well-known cathode material for lithium-ion batteries. In order to elucidate the molecular mechanism of the solid electrolyte interface (SEI) formation and the effect of an additive, vinylene carbonate (VC), we systematically studied the spontaneous and electrochemical reactions of solvents and a salt (LiPF6) in electrolytes with LMO in the absence and presence of VC. X-ray photoelectron spectroscopy (XPS) results of the LMO surfaces after soaking in the electrolyte solutions showed that the carbonate solvents as well as VC spontaneously decomposed on the LMO surfaces to form new compounds, such as alcohols, ethers, and carboxylates. The ratio of the produced LiF to MnF2 was similar for both with and without VC. Considering these spontaneously formed initial SEI components, we then investigated the variation of the SEI compositions during the initial electrochemical process until 3.8 V vs. Li+/Li. The role of the additive was studied and found that the electrochemical reaction of VC produced more organic compounds and led to an increase in the LiF/MnF2 ratio of the SEI layer. Based on the hard and soft acid and base theory, we proposed the mechanisms of the SEI formation via spontaneous and electrochemical reactions on the LMO thin film cathode with and without VC.

Structures of Nanoconfined Liquids Determined by Synchrotron X-ray Diffraction.

We have successfully performed X-ray diffraction measurements of the liquids octamethylcyclotetrasiloxane (OMCTS, a quasi-spherical-shaped molecule) and n-hexadecane (a normal alkane) confined between mica surfaces at surface separation distances (D's) from 500 nm to the hard-wall thickness (1.9 nm for OMCTS and 1.0 nm for hexadecane). At all of the studied D's, we observed diffraction peaks corresponding to their mean intermolecular spacing at q = 8.6 nm-1 (d = 0.73 nm) for OMCTS and q = 13.6 nm-1 (d = 0.45 nm) for n-hexadecane. The peak intensity increased at D < ca. 50 nm for OMCTS even with the decreasing distance and exhibited a local maximum at D = 17-13 nm, indicating the sharp increase in the molecular order in this distance range. The peak intensities normalized by the D and Inormalized values of OMCTS and n-hexadecane were nearly constant at D's greater than 100 nm, though they appeared to increase slightly. The increase then became more significant with decreasing D below 100 nm, and finally the Inormalized values became 120 (for OMCTS) and 160 (for n-hexadecane) at the hard wall. These results clearly demonstrated the significant increase in the structural order of OMCTS and n-hexadecane under nanoconfinement, especially below 100 nm. The fwhm values of the peaks of OMCTS and n-hexadecane showed no significant change until small distances when the confinement effect was significant. These results indicated that the increase in the structural order should be mainly ascribed to the ordering of the molecules in the parallel plane in the enhanced layered structure formed under the confinement. The viscous parameters (b2) of OMCTS and n-hexadecane obtained from the resonance shear measurement showed no increase at D's down to ca. 7 nm. This indicated that a certain ordering of the confined molecules was required for the observable increase in the viscosity.

Nano-confined electrochemical reaction studied by electrochemical surface forces apparatus.

Electrochemical reactions in a nano-space are different from those in bulk solutions due to structuring of the liquid molecules and peculiar ion behavior at the electric double layer and are important for applications involving sensors and energy devices. The electrochemical surface forces apparatus (EC-SFA) we developed enabled us to study the electrochemical reactions in a solution nano-confined between the electrodes with varying distance (D) at nm resolution. We recorded measurements of the current-distance profiles due to the electrochemical reaction of the redox couples in the electrolyte nano-confined between Pt electrodes using our EC-SFA. We observed a long-range feedback current due to redox cycling and the sudden current increase at a short distance, the latter for the first time. This sudden current increase was two orders greater than the conventional feedback current and was observed at D < 5 nm when the electrodes were approaching and D < 200 nm on separation. We simultaneously measured the electric double layer force and the current between the electrodes in the solution to study the mechanisms of this sudden current increase in the short distance range. The results revealed a molecular insight as to how the redox species affect the current between two electrodes under nano-confinement. This study demonstrated that EC-SFA is a powerful tool for obtaining fundamental knowledge about the nano-confined electrochemical reactions for nanoelectrodes which can be applied to sensors and energy devices.

The discovery of the depletion force.

This Editorial reports how the depletion force theory was originally developed by Sho Asakura and Fumio Oosawa and how their one-page paper was "rediscovered" about 20 years after the paper was published. The first part of this Editorial is mostly based on the lecture by Oosawa and his autobiographies, and the second part is written by one of two scientists who found the paper. The aim of this Editorial is to record the background of the discovery of the depletion force. We believe that this Editorial presents an interesting story showing how science develops. The story reminds us of the importance of basic education and continuous interests in unknown phenomena and interactions between people of different disciplines, although they are sometimes considered as separate elements of research.

Evaluation of Interfacial pH Using Surface Forces Apparatus Fluorescence Spectroscopy.

The fluorescence spectrum measurement of a fluorescence pH probe, C. SNARF-4F, was performed for monitoring the interfacial pH of aqueous electrolytes between mica or silica surfaces while varying the surface separation (D) using surface force apparatus (SFA) fluorescence spectroscopy. The pH of the aqueous CsCl between mica exponentially decreased with decreasing D. The order of the decay lengths of the interfacial pH obtained from the exponential fitting (L) at various electrolyte concentrations was L1mM > L0.1mM ≈ L0.4mM > L10mM. For studying the mechanisms of these changes, we performed the electric double layer (EDL) model calculation of the interfacial pH based on the surface potentials, which were evaluated from the EDL forces between the substrates in aqueous electrolytes using the same SFA. The calculated pH value for the 0.1 mM aqueous electrolyte corresponded to the values obtained from fluorescence spectroscopy, indicating that the interfacial pH was attributed to only the general EDL effect. On the other hand, the measured pH value for the higher concentrations of aqueous electrolytes (0.4-10 mM) decreased in the longer D ranges than the values calculated from the model, indicating that there was an additional factor affecting the interfacial pH for those concentrations. We also studied the effects of the cationic species of the electrolytes (Cs+, Na+, and Li+) and of the silica substrate on the interfacial pH. The systematic studies of the interfacial pH revealed that it depended on all three factors studied here, that is, the electrolyte concentration, electrolyte species, and the substrates. The results also suggested that the interfacial pH was not only due to the simple EDL theory but could also be affected by an additional factor due to the ion adsorption at the interface and chemical states of the substrates.

Effects of surface and shear forces on nano-confined smectic-A liquid crystals studied by X-ray diffraction.

The orientational behavior of a smectic-A liquid crystal (4-cyano-4'-octylbiphenyl, 8CB) confined between mica surfaces as well as between silica surfaces with a nanometer scale thickness was investigated by synchrotron X-ray diffraction measurement. The crystallographic axes of two confining mica sheets were adjusted parallel to each other to induce the preferential orientation of 8CB molecules along their crystallographic axis. The silica surfaces, which were hydrophilic and amorphous and had nanometer level smoothness, were prepared on mica surfaces using a sputtering technique. The X-ray diffraction measurement revealed that the 8CB molecules, confined between mica surfaces (DHW = 1.7 nm) and between silica surfaces (DHW = ca. 2 nm), took a planar orientation (oriented its long axis parallel to the surface) and formed a lamellar structure. However, the in-plane orientation of the confined 8CB changed depending on the confining surfaces. The lamellar axis of the 8CB confined between mica surfaces uniaxially oriented most probably due to the preferential alignment of its long axis along the principal crystallographic a-axis of the mica. On the other hand, 8CB between the silica surfaces formed lamellar domains in which the lamellar axis of 8CB omnidirectionally oriented in-plane. The effect of the shear on the orientation of the nano-confined 8CB was also investigated. The lamellar axis, corresponding to the long axis of the 8CB molecules confined between the mica surfaces, rotated only ca. 3 degrees within the plane parallel to the surface by perpendicularly applying shear to the axis. The lamellar axis of the 8CB molecules between the silica surfaces showed no noticeable change by applying the shear. These results indicated that the effect of shear to align the 8CB molecules was significantly suppressed due to the confinement effect which significantly reduces the mobility of molecules as well as the alignment effect along the crystallographic axis in the case of mica. We also observed a change in the orientation of nano-confined 8CB after shear treatment at large D (= 3.3 µm).

Ice premelting layer of ice-rubber friction studied using resonance shear measurement.

We performed a resonance shear measurement (RSM) based on a low-temperature surface force apparatus to evaluate the frictional properties of the interface between butadiene rubber and ice at various temperatures below 0 °C. Friction between the rubber and ice was high and constant at temperatures below -5 °C, but sharply decreased when the temperature rose above -5 °C. We performed the same measurement by replacing the rubber with polystyrene and silica films which were rigid and exhibited practically minimal elastic deformation in comparison to the rubber. The friction decreased gradually with the increase in temperature from -20 °C to 0 °C at both the polystyrene-ice and the silica-ice interfaces. These results indicated that the elasticity of rubber was responsible for the differences in the rubber-ice interface and the other two samples. To understand the detailed mechanism of friction between the rubber and the ice, we analyzed the obtained RSM data using a physical model. The result indicated that the friction between ice and rubber was determined by the elastic deformation of the rubber film at temperatures below -5 °C, and by the viscosity of the ice premelting layer above -5 °C.

Ice Premelting Layer Studied by Resonance Shear Measurement (RSM).

The viscosity of the ice premelting layer in contact with silica in the temperature range of -18 to -1 °C was studied by resonance shear measurement (RSM). The viscosity of the ice premelting layer was determined to be ∼5 orders of magnitude greater than that of the bulk liquid water and continuously decreased with the increasing sliding speed between the two surfaces over the temperature range employed in this study, which was the same behavior as for the typical confined liquids including water. On the other hand, the normal load and the contact pressure did not influence the viscosity, indicating that the premelting layer behaved differently from the typical confined liquids.

Dynamics of lubricious, concentrated PMMA brush layers studied by surface forces and resonance shear measurements.

We employed surface forces and resonance shear measurement (RSM) for studying the structure and properties of typical concentrated polymer brushes (CPBs) of poly(methylmethacrylate) (PMMA) in toluene, which are known to show very low friction. The surface forces measured between the silica surfaces bearing PMMA brush layers showed a steric repulsive force at distances between the silica surfaces of less than ca. 1050 nm (Donset). Upon retraction after compression of the PMMA brush layers, no adhesive force was observed. This indicated that the interpenetration of the polymer chain was not induced by the normal load. Based on the resonance shear measurement, the elastic (k2) and damping (viscous) (b2) parameters, which represent the dynamic properties, of the PMMA brush layers were obtained by analyzing the resonance curves. At distances below the Donset, the b2 value significantly increased and slightly decreased at the higher normal loads, and the k2 value monotonically increased with increasing load. These k2 and b2 values were greater than those obtained for a PMMA brush layer and a bare silica surface (PMMA-silica). This indicated that the mobility of the polymer chains for the PMMA-PMMA brush layers was more suppressed compared to that for the PMMA-silica, due to the interpenetration of the polymer chains. The interpenetration of the polymer chains, commonly not observed for CPBs, could be most probably induced by the application of both the normal load and oscillating shear motion. With increasing shear amplitude on the compressed PMMA-PMMA brushes (at L = 0.84, 1.34 and 4.28 mN), the b2 value first increased then decreased whilst the k2 value monotonically decreased. These tendencies can be explained by the change from the sticking condition due to interpenetration (high k2), small sliding under interpenetration (increase in b2, decrease in k2), and then smooth sliding by pulling out of interpenetrated polymer chains (decrease in b2 and k2). The obtained results indicated that the operating conditions are quite important for using polymer brush layers as tribological materials because they can exhibit both a high and low friction depending on the conditions such as the load and shear amplitude.

Surface anchoring of nematic liquid crystal on swollen polymer brush studied by surface forces measurement.

Surface anchoring plays a fundamental role in controlling the molecular alignment of a bulk liquid crystal (LC). It has been previously shown that the pretilt angle of a nematic liquid crystal (NLC) can be controlled by changing the grafting density of a liquid crystalline polymer, poly(6-(4-methoxy-azobenzene-4'-oxy) hexyl methacrylate) (PMMAZO). In this study, the thickness of the swollen PMMAZO brush was measured by employing the surface forces apparatus (SFA). NLC 4-cyano-4'-pentylbiphenyl (5CB) and toluene were used as the solvents. It was shown that both 5CB and toluene were good solvents for PMMAZO. The repulsive force in 5CB appeared at D0 = 98.2 ±â€¯4.6 nm for high grafting density (HD) surfaces, and at 32.1 ±â€¯4.5 nm for the low grafting density (LD) surfaces. These results indicated that the PMMAZO molecules extended nearly perpendicular to the HD surfaces, while they laid on the substrate for the LD surfaces. The interaction between 5CB and the mesogenic group of PMMAZO was stronger than that for toluene. These results could support the expected surface anchoring mechanism of 5CB by the PMMAZO brush.

Mechanical model analysis for resonance shear measurement.

Resonance shear measurement (RSM), which we developed based on a surface force apparatus, can investigate the structuring, and rheological and tribological properties of confined liquids as a function of the surface separation distance (D) from several µm to zero with a nanometer resolution. Using RSM, we reported that the nanoconfined liquids, including commercial lubricants, exhibited properties quite different from the bulk phase. Mechanical modeling of the resonance system is necessary to quantitatively evaluate the properties of confined liquids and/or sheared interfaces. In this study, we improved the model for RSM as follows: (1) We directly measured the movements of the upper and lower surfaces in addition to the measurement on the movement of the vertical spring to confirm the model, which could be used to estimate the parameters used in the model; (2) we proposed a modified mechanical model which considers the effect of additional motion. This model could fit the resonance curves using a identical apparatus constant for the entire measurement range, while the characteristic values of the confined liquids are the same as those obtained using our previous model, and (3) we calculated the friction (shear) force using the improved model and obtained the characteristic values (viscous and elastic parameters) of the confined liquids. This study afforded the simplicity and reliability of a mechanical model analysis of resonance curves, and the friction force calculation employing the viscous and elastic terms can be useful for studying the mechanism of friction force.

Deformation of contacting interface between polymer hydrogel and silica sphere studied by resonance shear measurement.

The deformation of the interfaces between a soft material and hard material in contact plays an important role in the friction and lubrication between them. We recently reported that the elastic property of the contact interface dominated the friction of the interface between a flat polymer hydrogel [double network (DN) gel of 2-acrylamide-2-methylpropanesulfonic acid and N,N-dimethylacrylamide] and a silica sphere [Ren et al., Soft Matter 11, 6192-6200 (2015)]. In this study, in order to quantitatively describe the dependence of the elastic response on the geometrical parameters of the deformed interfaces, we employed the resonance shear measurement (RSM) and investigated the deformation of the interfaces between a flat DN gel and silica spheres by varying the curvature radius (R = 18.3, 13.8, 9.2, 6.9 mm). Resonance curves were analyzed using a mechanical model consisting of the elastic (k 2) and viscous (b 2) parameters of the contact interface. The obtained elastic parameter (k 2) increases at higher loads and for smaller silica spheres, while the viscous parameter (b 2) was negligibly low for all the conditions. The relations between the elastic parameter (k 2), geometric parameters of the deformed contact interface, and the applied normal load were investigated. The elastic parameter (k 2) was found to be proportional to the arc length (arc) (radius of contact area, r), i.e., k 2 ∝ arc or k 2 ∝ r. We introduced the term "elastic modulus of the contact interface, E contact" as a proportionality constant to describe the elastic parameter of the deformed interfaces (k 2): k 2 (N/m) = arc (m) × E contact (Pa). Thus, the friction (f) between the DN gel and the silica sphere can be described by the following equation: f = f elastic = arc (m) × E contact (N/m2) × Δx (m) (Δx: shear deformation of the contact interface between the DN gel and silica sphere). The E contact value determined from the slope k 2 vs arc was 493 ± 18 kPa. The RSM measurement and the analysis presented here can be a unique method for characterizing the specific properties of the deformed interfaces between soft and hard materials.

Viscosity measurement of Xanthan-Poly(vinyl alcohol) mixture and its effect on the mechanical properties of the hydrogel for 3D modeling.

Biomodels made of poly(vinyl alcohol) (PVA) are demanded because they can represent the geometries and mechanical properties of human tissues realistically. Injecting and molding, commonly used in three-dimensional (3D) modeling, help to represent the blood vessels accurately. However, these techniques sometimes require higher pressures than the upper pressure limit of the dispensers for pouring in high viscosity materials; the material viscosity should therefore be lower. Moreover, the mechanical properties of the biomodels should be reproduced. This study proposes a PVA solution through the addition of xanthan gum (XG) for 3D modeling, which lowers liquid viscosity while maintaining the mechanical properties of biomodels. XG is known to facilitate the achievement of non-Newtonian fluidity; however, the effects of XG on a PVA solution and PVA hydrogel (PVA-H) are not confirmed. The viscosity measurement using 15 wt% PVA with XG solution (PVA/XG) shows that it will provide easier pouring than 17 wt% PVA solution. The tensile test using the PVA-H of PVA(15 wt%)/XG(0.2 wt%) reveals that the gel is comparable in Young's modulus to 17 wt% PVA-H. X-ray diffraction shows the crystalline structures of the PVA/XG gel and PVA-H are identical. Thus, this PVA/XG would be useful for fabricating biomodels using injection molding techniques.

Low-Temperature Surface Forces Apparatus to Determine the Interactions between Ice and Silica Surfaces.

We have developed a low-temperature surface forces apparatus (SFA) using a thermoelectric Peltier module inserted below the bottom surface of the lower sample holder, giving easy access to the samples and allowing quick temperature changes. In air, the temperature can be decreased to ca. -20 °C. To demonstrate the performance of the apparatus, we measured the interactions between ice and a silica surface at -11.5 ± 0.5 °C. An exponentially decaying repulsion of the decay length, 11.2 ± 1.0 nm, was observed, and attributed to the electric double layer (EDL) repulsion. The surface potential of the ice was calculated to be -35 mV by fitting the data to the EDL model.

Engineering the anchoring behavior of nematic liquid crystals on a solid surface by varying the density of liquid crystalline polymer brushes.

Controlling the orientation of liquid crystal (LC) molecules towards contacting surfaces is a crucial requirement for the development of LC displays and passive electro-optical devices. Up to now, research has been focused on photo-responses of a LC azobenzene polymer system to obtain either planar or homeotropic orientation of LCs. It remains a challenge, however, to tune the polar angle of LC molecules on the solid surface and gain more insights about the polymer chain conformation extending in LC medium. Here, we deposit a liquid crystalline side chain polymer brush, poly(6-(4-methoxy-azobenzene-4'-oxy)hexyl methacrylate) (PMMAZO), onto the solid surface with film thickness varying between ∼3 nm and 13 nm; therefore, the grafting density of the brush layer ranges from 0.0219 to 0.0924 chains per nm2. When LCs are confined in hybrid cells with a top surface eliciting uniform homeotropic anchoring and a bottom surface covered by the PMMAZO brush, the out-of-plane polar angle of 4-pentyl-4'-cyanobiphenyl (5CB) on the brush layer gradually changes from ∼0° to ∼62° by simply increasing the grafting brush density. The surface forces apparatus (SFA) measurement is used to determine 5CB as a good solvent for the PMMAZO brush and understand the relationship between the chain conformation in 5CB and the anchoring behavior of LC molecules on the polymer brush layer. For high grafting density, the polymer chain in 5CB extends significantly away from the substrate, making the side chain mesogens on average almost parallel to the substrate; for the low-density case, the main chain extends in the narrow region around the surface for aligning the mesogens perpendicular to the substrate.

Selection of Diacrylate Monomers for Sub-15 nm Ultraviolet Nanoimprinting by Resonance Shear Measurement.

In UV nanoimprinting, the selection of monomers suitable for sub-15 nm patterning is difficult because the filling behavior of resin at this scale still remains scientifically unclear. We demonstrate sub-15 nm patterning by UV nanoimprinting using silica molds with 20, 15, and 7 nm diameter holes; however, the 7 nm diameter pillar patterns were not fabricated using hydroxy-containing monomers. The filling behavior into silica holes of around 10 nm depended on the chemical structure of the monomers. Resonance shear measurements revealed the following: (1) The viscosities of hydroxy-containing monomers confined between chlorodimethyl(3,3,3-trifluoropropyl)silane (FAS3-Cl)-modified surfaces began to increase at distances shorter than those of the monomers between unmodified surfaces. (2) The monomers confined between tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane-modified surfaces were squeezed out when the surface-surface distance decreased at less than 7 nm. The measured viscosities between the FAS3-Cl-modified silica surfaces were correlated with the insufficient filling behavior into the silica holes of around 10 nm in UV nanoimprinting. Contact angle measurements provided an additional insight that a higher wettability of the monomers onto the antisticking chemisorbed monolayers resulted in imprinted patterns with higher aspect ratios. Considering the increase in the monomer viscosity in the nanospace and the wettability of monomers onto chemisorbed monolayers, we concluded that the monomer showing low viscosity under confinement and high wettability onto the mold surface was suitable for single-digit nanometer UV nanoimprinting.