Adhesion of soft materials based on polymers

Work in this area is carried out under the grant of the Russian Science Foundation 18-19-00645 “Adhesion of soft materials based on polymers: from liquid to solid” under the direction of Leonid Dorogin (Ph.D.).
The tribology of soft materials plays a crucial role in many natural, biological and technological systems. An understanding of the mechanisms of adhesive interaction is important for technological applications of soft polymer-based materials. In this area, systems based on rubber (elastomer) are being studied. Three main contributions to the adhesion of rubber acting on different length scales are viscoelasticity, surface roughness, and molecular mobility. To study adhesion, polydimethylsiloxane (PDMS) and composite materials based on it are used (see review [1]).
To date, a number of results have been obtained published in international peer-reviewed academic journals [1-6] (see list of publications below). Some selected results [2-6] are illustrated below.
Within the framework of the project, the conversion of PDMS material from an unbound liquid to a fully bound solid state was studied from the point of view of contact mechanics according to the classical Johnson-Kendall-Roberts (JKR) scheme [2]. It is shown that during the period of liquid to gel transformation, its viscosity increases by several orders of magnitude. The strength of the adhesive interaction as a function of time also shows a sharp increase when approaching the gelation point of PDMS. During the transition period, contact mechanics is characterized by the formation of strings and irreversible deformation, which are not observed either in the initial liquid state or in a fully bound state. Subsequently, the gel-like PDMS material hardens, which is accompanied by a change in the dynamic parameters of the contact interaction, as well as a decrease in the adhesive “wear” of the PDMS surface.








The PDMS thread adhered to the glass ball is close to the point where the attractive interaction of the ball with PDMS is maximum for the sample [2].








Samples of PDMS material with a layer of ZnO nanoparticles with photocatalytic activity deposited on the surface were also obtained [3]. PDMS was used as the carrier of the photocatalyst. PDMS is transparent to UV and visible light; therefore, PDMS / ZnO can be used as photocatalysts under both visible and ultraviolet light, regardless of the direction of incident light. To activate the photocatalytic reaction, light can enter both the surface coated with ZnO and the reverse side of the polymer.





Characteristics of the obtained PDMS-ZnO sample for photocatalytic applications, (a) light transmission, (b) wetting angle of PDMS, (c) wetting angle of PDMS-ZnO [3]




Samples of porous silicone were also prepared on the basis of PDMS [4]. The resulting sorbents demonstrated a high ability to sorb water.





Characteristics of the obtained samples of porous PDMS, (a) the effect of the amount of octanol-1 on water absorption, (b) the increase in the size of the porous PDMS containing 17% octanol-1 after saturation with water. [4]





A study was conducted of contact electrization (triboelectric effect) of a number of polymeric materials [5]:
• Ethylene octene copolymer
• Styrene-ethylene-butylene-styrene copolymer
• Polyethylene vinyl acetate copolymer.
• Polyhexadiol citrate
During experiments with the measurement of triboelectricity on various materials, a direct relationship was found between adhesion, roughness, and the magnitude of the triboelectric effect. The transfer of material that occurs during cyclic contact of the samples has also been demonstrated.

In parallel, experimental and theoretical studies of the mechanical properties of the silver and gold nanowires used during bending were carried out [6]. Understanding the behavior of nanowires during bending deformations is extremely important from a practical point of view, since silver nanowires can be used as fillers for PDMS to obtain flexible conductive materials in which the filler will be subjected to strain loads.





Fragments of visualization of simulation of deformation of a silver nanowire during bending. The simulation was performed by the molecular dynamics method [6].





Work is also underway in several other areas, in particular: (a) a study of the thermal conductivity of materials based on PDMS; (b) a study of the physicochemical properties of PDMS with metal filler; (c) numerical simulation of the contact mechanics of soft materials by the boundary element method (BEM).

List of publications

1. S. Vlassov, S. Oras, M. Antsov, I. Sosnin, B. Polyakov, A. Shutka, M. Yu. Krauchanka and L. M. Dorogin, "Adhesion and Mechanical Properties of PDMS-based materials probed with AFM: a Review", Reviews on Advanced Materials Science 56 (2018) 62-78.

2. L.M. Dorogin and I.M. Sosnin and E.G. Akimov and V.I. Agenkov, "Adhesion of polydimethylsiloxane during molecular cross-linking", Letters on Materials 9 (2019) 58-63, DOI: 10.22226/2410-3535-2019-1-58-63.

3. I. M. Sosnin, S. Vlassov, E. G. Akimov, V. I. Agenkov, L. M. Dorogin, "Transparent ZnO-coated polydimethylsiloxane-based material for photocatalytic purification applications", J. Coat. Technol. Res. [Q2, IF 1.584, SJR 0.415] (2020), DOI: 10.1007/s11998-019-00314-2.

4. I. M. Sosnin, S. Vlassov, E. G. Akimov, V. I. Agenkov, L. M. Dorogin, "Hydrophilic polydimethylsiloxane-based sponges for dewatering applications", Materials Letters [Q1, IF – 3.019], Volume 263, 15 March 2020, 127278, DOI: 10.1016/j.matlet.2019.127278.

5. L. Lapcinskis, K. Malnieks, J. Blums, M. Knite, S. Oras, T. Kaambre, S. Vlassov, M. Antsov, M. Timusk, A. Sutka, "The Adhesion Enhanced Contact Electrification and Efficiency of Triboelectric Nanogenerators", Macromol. Mater. Eng. [Q1, IF 3.038] 2019, 1900638, DOI: 10.1002/mame.201900638.

6. S. Vlassov, M. Mets, B. Polyakov, J. Bian, L. Dorogin and V. Zadin, "Abrupt elastic-to-plastic transition in pentagonal nanowires under bending", Beilstein J. Nanotechnol. [Q1, IF 2.27] 2019, 10, 2468–2476, DOI:10.3762/bjnano.10.237.