Mechanical and Structural Properties of BaCrO₄ Nanorod Films under Confinement and Shear

Abstract

Using an X‐ray surface forces apparatus (X‐SFA) we have investigated the effects of normal load (stress) and shear on the ordering and tribological properties of 10 nm × 30 nm surfactant‐coated BaCrO4 nanorods in isooctane, confined within submicrometer films. The film structure and corresponding friction forces were monitored as a function of time and shearing distance at different gap sizes and loads. The X‐ray diffraction patterns indicate a cubic phase of nanorods coexisting with a surfactant phase that depends on the load, film thickness, shear rate, and shearing time. Atomic force microscopy and birefringence measurements performed on each surface after a shearing experiment showed ordered domains of nanorods over length scales of several tens of micrometers.

Frictional Properties of Confined Nanorods

“…This quantization is related to the oscillatory (normal) forces between any two smooth surfaces immersed in simple liquids, [7] and it often leads to undesirable stick-slip sliding. [18] Addition of the surfactant-coated nanorods to the liquid changed both the normal and friction forces, both quantitatively and qualitatively, depending on the nanorod concentration c. First, as previously found in nanorod solutions, [19] the normal forces were monotonically repulsive and, in dry liquid, roughly exponential, as previously also found with other trapped nanoparticles. Depending on the nanorod concentration c, steric 'hard walls' were encountered at separations ranging from n = 0 to approximately 10 nanorod diameters (layers), increasing in thickness with increasing c. The film thicknesses and refractive indices, r i of compressed nanorod films were typically D = 14.7 nm, r i = 2.5 ± 0.1, and D = 2.5 nm, r i = 2.2 ± 0.1 in the range of visible wavelengths.…”

Frictional Properties of Confined Nanorods

“…This quantization is related to the oscillatory (normal) forces between any two smooth surfaces immersed in simple liquids, [7] and it often leads to undesirable stick-slip sliding. [18] Addition of the surfactant-coated nanorods to the liquid changed both the normal and friction forces, both quantitatively and qualitatively, depending on the nanorod concentration c. First, as previously found in nanorod solutions, [19] the normal forces were monotonically repulsive and, in dry liquid, roughly exponential, as previously also found with other trapped nanoparticles. Depending on the nanorod concentration c, steric 'hard walls' were encountered at separations ranging from n = 0 to approximately 10 nanorod diameters (layers), increasing in thickness with increasing c. The film thicknesses and refractive indices, r i of compressed nanorod films were typically D = 14.7 nm, r i = 2.5 ± 0.1, and D = 2.5 nm, r i = 2.2 ± 0.1 in the range of visible wavelengths.…”

Adhesion and Stable Low Friction Provided by a Subnanometer-Thick Monolayer of a Natural Polysaccharide

“…To characterize the lubrication properties of the polysaccharide and to determine whether we could orient the polymer molecules (or its constituent monosaccharides) by different means, the polysaccharide was confined and sheared under various experimental conditions. This method has recently been found to be very effective for ordering alkane chains and nanoparticles between surfaces. It involves monitoring the thickness and lateral uniformity of the films during the shearing while the normal (compressive) pressure and lateral (friction) forces are also being measured.…”

Forces between Surfaces across Nanoparticle Solutions: Role of Size, Shape, and Concentration

“…Comparison with Similar Systems . Gourdon et al used an X-ray surface force apparatus to investigate the effects of normal load and shear on the ordering of 10 nm × 30 nm surfactant-coated BaCrO 4 nanorods in isooctane. They also observed roughly exponential forces as a function of surface separation and alignment of the rods with successive compressions and shear.…”

Frictional Properties of Confined Nanorods

“…This quantization is related to the oscillatory (normal) forces between any two smooth surfaces immersed in simple liquids, [7] and it often leads to undesirable stick-slip sliding. [18] Addition of the surfactant-coated nanorods to the liquid changed both the normal and friction forces, both quantitatively and qualitatively, depending on the nanorod concentration c. First, as previously found in nanorod solutions, [19] the normal forces were monotonically repulsive and, in dry liquid, roughly exponential, as previously also found with other trapped nanoparticles. Depending on the nanorod concentration c, steric 'hard walls' were encountered at separations ranging from n = 0 to approximately 10 nanorod diameters (layers), increasing in thickness with increasing c. The film thicknesses and refractive indices, r i of compressed nanorod films were typically D = 14.7 nm, r i = 2.5 ± 0.1, and D = 2.5 nm, r i = 2.2 ± 0.1 in the range of visible wavelengths.…”

Adhesion and Stable Low Friction Provided by a Subnanometer-Thick Monolayer of a Natural Polysaccharide

“…To characterize the lubrication properties of the polysaccharide and to determine whether we could orient the polymer molecules (or its constituent monosaccharides) by different means, the polysaccharide was confined and sheared under various experimental conditions. This method has recently been found to be very effective for ordering alkane chains and nanoparticles between surfaces. It involves monitoring the thickness and lateral uniformity of the films during the shearing while the normal (compressive) pressure and lateral (friction) forces are also being measured.…”

Forces between Surfaces across Nanoparticle Solutions: Role of Size, Shape, and Concentration

“…Comparison with Similar Systems . Gourdon et al used an X-ray surface force apparatus to investigate the effects of normal load and shear on the ordering of 10 nm × 30 nm surfactant-coated BaCrO 4 nanorods in isooctane. They also observed roughly exponential forces as a function of surface separation and alignment of the rods with successive compressions and shear.…”

Frictional Properties of Confined Nanorods

“…This quantization is related to the oscillatory (normal) forces between any two smooth surfaces immersed in simple liquids, [7] and it often leads to undesirable stick-slip sliding. [18] Addition of the surfactant-coated nanorods to the liquid changed both the normal and friction forces, both quantitatively and qualitatively, depending on the nanorod concentration c. First, as previously found in nanorod solutions, [19] the normal forces were monotonically repulsive and, in dry liquid, roughly exponential, as previously also found with other trapped nanoparticles. Depending on the nanorod concentration c, steric 'hard walls' were encountered at separations ranging from n = 0 to approximately 10 nanorod diameters (layers), increasing in thickness with increasing c. The film thicknesses and refractive indices, r i of compressed nanorod films were typically D = 14.7 nm, r i = 2.5 ± 0.1, and D = 2.5 nm, r i = 2.2 ± 0.1 in the range of visible wavelengths.…”

Adhesion and Stable Low Friction Provided by a Subnanometer-Thick Monolayer of a Natural Polysaccharide

“…To characterize the lubrication properties of the polysaccharide and to determine whether we could orient the polymer molecules (or its constituent monosaccharides) by different means, the polysaccharide was confined and sheared under various experimental conditions. This method has recently been found to be very effective for ordering alkane chains and nanoparticles between surfaces. It involves monitoring the thickness and lateral uniformity of the films during the shearing while the normal (compressive) pressure and lateral (friction) forces are also being measured.…”

Forces between Surfaces across Nanoparticle Solutions: Role of Size, Shape, and Concentration

“…Comparison with Similar Systems . Gourdon et al used an X-ray surface force apparatus to investigate the effects of normal load and shear on the ordering of 10 nm × 30 nm surfactant-coated BaCrO 4 nanorods in isooctane. They also observed roughly exponential forces as a function of surface separation and alignment of the rods with successive compressions and shear.…”