Tribo-system and method for reducing particle conglomeration therein
View Patent ↗A tribo-system includes a metal substrate having a surfactant layer chemisorbed to a side thereof, a lubricant established on the metal substrate, and a plurality of nanoparticles dispersed in the lubricant. Each of the nanoparticles includes i) an inorganic core having a predetermined size and shape, and ii) a surfactant shell chemisorbed to a surface of the inorganic core, where the surfactant shell has a predetermined thickness. The adhesive force and energy between the metal substrate surface and the nanoparticles is higher than the adhesive force and energy between individual particles of the nanoparticles.
1. A tribo-system, comprising:
a metal substrate;
a surfactant layer chemisorbed to and covering a surface of the metal substrate;
a lubricant established on the metal substrate; and
a plurality of nanoparticles dispersed in the lubricant, each of the plurality of nanoparticles including:
an inorganic core having a predetermined size and shape; and
a surfactant shell chemisorbed to a surface of the inorganic core, the surfactant shell having a predetermined thickness and being separate from the surfactant layer that is chemisorbed to the metal substrate surface;
wherein adhesive force and energy between the metal substrate surface and the plurality of nanoparticles is higher than adhesive force and energy between individual particles of the plurality of nanoparticles.
2. The tribo-system as defined in claim 1 wherein the inorganic core is an amorphous silica particle or a ceramic.
3. The tribo-system as defined in claim 1 wherein the surfactant shell is a silane, a hydrocarbon, a non-conductive carbon based surfactant, or a non-conductive phorphorus based surfactant.
4. The tribo-system as defined in claim 1 wherein a ratio of van der Waals forces between the individual particles of the plurality of nanoparticles to van der Waals forces between the metal substrate surface and the plurality of nanoparticles is equal to or greater than 1:3.
5. The tribo-system as defined in claim 1 wherein the lubricant is a water-based system or a non-polar liquid-based system.
6. The tribo-system as defined in claim 1 wherein Hamaker's constant (A) for interaction between nanoparticles is approximated by:
A
≈
3
(
n
1
2
-
n
2
2
)
2
hv
1
v
2
8
2
(
n
1
2
+
n
2
2
)
3
/
2
(
v
1
+
v
2
)
wherein n 1 is the refractive index of the nanoparticles, n 2 is the refractive index of the lubricant, h is Planck's constant, v 1 is an electronic absorption frequency of the nanoparticles, and v 2 is an electronic absorption frequency of the lubricant.
7. The tribo-system as defined in claim 6 wherein an adhesive energy E p-p between individual particles of the plurality of nanoparticles is determined by:
E p-p =−AR/ 12(2 T 2 )
wherein A is Hamaker's constant for interaction between nanoparticles, R is the predetermined radius of each individual nanoparticle, and T 2 is the predetermined thickness of the surfactant shell.
8. The tribo-system as defined in claim 1 wherein adhesive energy E p-s between the plurality of nanoparticles and the metal substrate surface is determined by:
E p-s =−A′R/ 6( T 2 +T 2 ′)
wherein R is a predetermined radius of each individual nanoparticle, T 2 is the predetermined thickness of the surfactant shell, and T 2 ′ is the thickness of the surfactant layer chemisorbed to the metal substrate surface, and A′ is a modified Hamaker's constant for nanoparticle-substrate interaction:
A
′
≈
3
h
8
2
(
n
1
2
-
n
2
2
)
2
hv
1
v
3
(
n
1
2
+
n
2
2
)
1
/
2
[
v
1
+
(
n
1
2
+
n
2
2
)
1
/
2
v
3
]
wherein n 1 is the refractive index of the inorganic core, n 2 is the refractive index of the lubricant, n 3 is the refractive index of the substrate, h is Planck's constant, ν 1 is an electronic absorption frequency of the inorganic core, and ν 2 is an electronic absorption frequency of the lubricant, and ν 3 is an electronic absorption frequency of the substrate.
9. The tribo-system as defined in claim 1 wherein the adhesive energy between the metal substrate surface and the plurality of nanoparticles is such that the plurality of nanoparticles at least one of i) roll, or ii) roll and slide along the metal substrate surface.
10. The tribo-system as defined in claim 1 wherein the surfactant shell prevents chemical bonding of the plurality of nanoparticles to the metal substrate surface.
11. The tribo-system as defined in claim 1 wherein the nanoparticles are spherical and wherein a diameter of the nanoparticles range from about 0.1 microns to about 100 microns.
12. The tribo-system as defined in claim 1 wherein:
the inorganic core is a silica core having a radius of 50 nm and a refractive index of 1.45;
the surfactant shell predetermined thickness is 1.5 nm; and
a thickness of the surfactant layer chemisorbed to and covering the metal substrate surface is 1.5 nm.
13. The tribo-system as defined in claim 1 wherein the metal substrate is selected from the group consisting of copper, aluminum, magnesium, titanium, iron, alloys of these metals, steel, and combinations thereof.