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. 2023 Oct 12;15(20):4060.
doi: 10.3390/polym15204060.

Regulation Mechanism of Special Functional Groups Contained in Polymer Molecular Chains on the Tribological Properties of Modified Ti6Al4V

Mengmeng Liu  1 , Jing Ni  1 , Caixia Zhang  2 , Lihui Wang  2 , Yue Guo  1 , Zhifeng Liu  3
Affiliations

Regulation Mechanism of Special Functional Groups Contained in Polymer Molecular Chains on the Tribological Properties of Modified Ti6Al4V

Mengmeng Liu et al. Polymers (Basel). .

Abstract

Polymer coatings can effectively improve the surface tribological properties of human implant materials, thereby increasing their service life. In this study, poly(vinylsulfonic acid, sodium salt) (PVS), poly(acrylic acid) (PAA) and poly(vinylphosphonic acid) (PVPA) were used to modify Ti6Al4V surfaces. Experimental analyses were combined with molecular simulation to explore the regulation mechanism of special functional groups contained in polymer molecular chains on the tribological properties of modified surfaces. In addition, the bearing capacities and velocity dependence of different polymer modified surfaces during friction were also explored. The PVS coating, due to physical adsorption, can have an anti-friction effect under NaCl solution lubrication, but is not durable under long-term or repeated usage. Both PAA and PVPA molecular chains can form chemical bonds with Ti6Al4V. Phosphate acid groups can firmly bind to the substrate, and the adsorption of salt ions and water molecules can form a hydrated layer on the PVPA coating surface, achieving ultra-low friction and wear. The adsorption of salt ions would aggravate the surface wear of the PAA-modified Ti6Al4V due to the unfirm binding of carboxyl groups to the substrate, resulting in a high friction coefficient. This study can provide effective guidance for the design of modified polymer coatings on metals.

Keywords: Ti6Al4V; experimental analyses; functional groups of polymers; molecular simulation; surface modification; tribological properties.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Chemical structures of polymer molecular chains: (a) PVS; (b) PAA; (c) PVPA.
Figure 2
Figure 2
×PS scans of (I) bare Ti6Al4V and (II–IV) polymer-modified Ti6Al4V (II: PVS; Ⅲ: PAA; Ⅳ: PVPA).
Figure 3
Figure 3
The contact angles of the deionized water on surfaces: (a) Ti6Al4V; (b) PVS-modified Ti6Al4V; (c) PAA-modified Ti6Al4V and (d) PVPA-modified Ti6Al4V.
Figure 4
Figure 4
(a) Morphology of the soaked bare Ti6Al4V; (a1–a7) EDS mapping in the region of (a); (b) morphology of the soaked PVS-modified Ti6Al4V; (b1–b8) EDS mapping in the region of (b); (c) morphology of the soaked PAA-modified Ti6Al4V; (c1–c7) EDS mapping in the region of (c); (d) morphology of the soaked PVPA-modified Ti6Al4V; (d1–d8) EDS mapping in the region of (d).
Figure 5
Figure 5
(a) Heat−treated Ti6Al4V surface; (b) reaction of sulfonate groups with heat-treated Ti6Al4V surface; (c) reaction of carboxy groups with heat-treated Ti6Al4V surface; (d) reaction of phosphate groups with heat-treated Ti6Al4V surface.
Figure 6
Figure 6
Tribological properties of the bare and polymer-modified Ti6Al4V under NaCl solution lubrication: (a) the average friction coefficient; (b) the friction coefficient versus time; (c) wear morphologies of the bare Ti6Al4V and the PTFE ball; (d) wear morphologies of the PVS-modified Ti6Al4V and the PTFE ball; (e) wear morphologies of the PAA-modified Ti6Al4V and the PTFE ball; (f) wear morphologies of the PVPA-modified Ti6Al4V and the PTFE ball.
Figure 7
Figure 7
(a) Morphology of the bare Ti6Al4V wear area; (a1–a7) EDS mapping in the region of (a); (b) morphology of the soaked PVS-modified Ti6Al4V; (b1–b8) EDS mapping in the region of (b); (c) morphology of the soaked PAA-modified Ti6Al4V; (c1–c7) EDS mapping in the region of (c); (d) morphology of the soaked PVPA-modified Ti6Al4V; (d1–d8) EDS mapping in the region of (d).
Figure 8
Figure 8
Interaction energy calculation models of (a) PAA, (b) PVS and (c) PVPA.
Figure 9
Figure 9
Tribological properties of the bare and polymer-modified Ti6Al4V under dry friction: (a) the average friction coefficient; (b) the friction coefficient versus time; (c) wear morphologies of the bare Ti6Al4V and the PTFE ball; (d) wear morphologies of the PVS-modified Ti6Al4V and the PTFE ball; (e) wear morphologies of the PAA-modified Ti6Al4V and the PTFE ball; (f) wear morphologies of the PVPA-modified Ti6Al4V and the PTFE ball.
Figure 10
Figure 10
Tribological properties of the bare Ti6Al4V under different loads and at different velocities: (a1) the average friction coefficients under different loads; (a2) the friction coefficients versus time under different loads; (a3) wear morphologies of the bare Ti6Al4V and the PTFE ball under the load of 40 N; (b1) the average friction coefficients under different velocities; (b2) the friction coefficients versus time under different velocities; (b3) wear morphologies of the bare Ti6Al4V and the PTFE ball at the velocity of 24 mm/s.
Figure 11
Figure 11
Tribological properties of the PVS-modified Ti6Al4V under different loads and at different velocities: (a1) the average friction coefficients under different loads; (a2) the friction coefficients versus time under different loads; (a3) wear morphologies of the PVS-modified Ti6Al4V and the PTFE ball under the load of 40 N; (b1) the average friction coefficients under different velocities; (b2) the friction coefficients versus time under different velocities; (b3) wear morphologies of the PVS-modified Ti6Al4V and the PTFE ball at the velocity of 24 mm/s.
Figure 12
Figure 12
Tribological properties of the PAA-modified Ti6Al4V under different loads and at different velocities: (a1) the average friction coefficients under different loads; (a2) the friction coefficients versus time under different loads; (a3) wear morphologies of the PAA-modified Ti6Al4V and the PTFE ball under the load of 40 N; (b1) the average friction coefficients under different velocities; (b2) the friction coefficients versus time under different velocities; (b3) wear morphologies of the PAA-modified Ti6Al4V and the PTFE ball at the velocity of 24 mm/s.
Figure 13
Figure 13
Tribological properties of the PVPA-modified Ti6Al4V under different loads and at different velocities: (a1) the average friction coefficients under different loads; (a2) the friction coefficients versus time under different loads; (a3) wear morphologies of the PVPA-modified Ti6Al4V and the PTFE ball under the load of 40 N; (b1) the average friction coefficients under different velocities; (b2) the friction coefficients versus time under different velocities; (b3) wear morphologies of the PVPA-modified Ti6Al4V and the PTFE ball at the velocity of 24 mm/s.
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