Bands from unsaturated carbon-carbon

chain: 993 cm-1, 909 cm-1

Mimicking the velcro system from nature for an alternative rubber/silica coupling system

Rafal Anyszka1,2, Wilma Dierkes1, Dariusz M. Bielinski2, Essi Sarlin3, Karolina Beton2, Anke Blume1

1 University of Twente, Faculty of Engineering Technology, Department of Mechanics of Solids, Surfaces & Systems (MS3),

Chair of Elastomer Technology & Engineering, Enschede, The Netherlands – r.p.anyszka@utwente.nl2 Lodz University of Technology, Faculty of Chemistry, Institute of Polymer and Dye Technology, Lodz, Poland – rafal.anyszka@p.lodz.pl3 Tampere University of Technology, Department of Materials Science, Tampere, Finland

Supramolecular velcro – an ability of molecular systems for full or partial

recovery of their cohesive (single-component system) or adhesive (two-component

system) strength at room temperature by means of supramolecular interactions.

Supramolecular velcro mechanism

Oligomer brushes/elastomer matrix entanglements2,3

1. Reaction between isocyanate silane and mono-functional

telechelic butadiene oligomer with high amount of vinyl groups 2. Grafting of the reaction product onto the silica

surface by silanol/alcoxyl groups condensation3. Branching the oligomer backbone with different thiols reactive towards

vinyl groups

4. Hydrogenation of the remaining unsaturated bonds4

References:

1. Van Krevelen D. W. (1997) Properties of Polymers 3rd Edition, Chapter 7: Cohesive Properties and Solubility:

189-225.

2. Gutsmann T., Hassenkam T., Cutroni J. A., Hansma P. K. (2005) Sacrificial Bonds in Polymer Brushes from Rat

Tail Tendon Functioning as Nanoscale Velcro, Biophysical Journal, 89(1): 536-542.

3. O’Connor K. P., McLeish T. C. B. (1993) „Molecular Velcro”: Dynamics of a Constrained Chain into an Elastomer

Network. Macromolecules, 26: 7322-7325.

4. Lin F., Wu C., Cui D. (2017) Synthesis and Characterization of Crystalline Styrene-b-(Ethylene-co-Butylene)-b-

Styrene Triblock Copolymers, Journal of Polymer Science, Part A: Polymer Chemistry, 55: 1243-1249.

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Figure 1: Scheme of the supramolecular velco mechanism on silica filler/elastomer matrix interphase. Long oligomer hooks attached to the silica surface form anchor-like connections with cross-linked

elastomer loops by good mutual miscibility, velcro entanglements and stearic hindrance (A). The interphase undergoes disconnection under external stress (B). After the stress relaxation (C) the

interphase is able to full recovery into original structure by re-entanglement of mutually miscible hooks-and-loops (D).

Chemical pathway of the oligomer brush (molecular hooks) synthesis on silica surface

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Beside carbon black, silica becomes the most important filler for high-performance rubber products. However,

unlike carbon black its surface properties are not favorable for providing satisfactory rubber/filler interactions. A

significant amount of silanol groups present on the silica surface results in a considerably polar character,

whereas most of rubbers exhibit a non-polar or relatively low-polar character. Because of this, various

approaches towards different surface treatments of silica were made.

The aim of this research is to introduce an alternative type of rubber/silica coupling inspired by the velcro system

existing in nature. The bio-mimicking mechanism is based on physical entanglements and steric hindrance

between mutually soluble (based on calculated solubility parameters1): cross-linked and entangled rubber

macromolecules – acting as molecular loops - and oligomer brushes grafted onto the silica surface – acting as

molecular hooks. This results in the formation of supramolecular hooks-and-loops, a rubber/silica interphase

fastener exhibiting reconnectable performance (Figure 1).

Introduction:

Branching efficiency – 42.7 %

Solubility parameter – 16.08 J1/2/cm3/2

Branching efficiency – 40.0 %

Solubility parameter – 16.52 J1/2/cm3/2Branching efficiency – 63.2 %

Solubility parameter – 16.22 J1/2/cm3/2

Solubility parameter – 16.42 J1/2/cm3/2 Solubility parameter – 17.00 J1/2/cm3/2Solubility parameter – 16.50 J1/2/cm3/2

isocyanate

urethane

Figure 2: Progress of the reaction between the

isocyanate silane and butadiene oligomer.

Figure 4: TGA analysis of the silicas modified with

the oligomer brushes.

Figure 3: FTIR spectra of the silica before and

after grafting the oligomer backbone.

Rubber type Solubility parameter(J1/2/cm3/2)

BR (100 % vinyl) 15.83

BR (100 % cis/trans) 15.67

IR 18.12

s-SBR (Buna SL 4525-0) 16.23

Table 1: Calculated solubility parameters1 for

various rubbers

Summary and conclusions: An alternative concept for coupling silica to polymer was presented. Mimicking the velcro

system from nature, a synthesis for supramolecular hooks was developed by grafting long

branched-oligomer molecules at the silica surface, which exhibit high chemical affinity to

commonly used non-polar rubber acting as a loops.

Application of this type of silica surface-treatment might allow in the future the

implementation of alternative filler/elastomer coupling featuring reconnectable interphase

interactions.

AB

C D

Oligomer brushes

(hooks)

Cross-linked elastomer matrix

(loops)

Cross-links

The differences and similarities between microscopic and supramolecular

velcro systems

Microscopic

velcro

Supramolecular

velcro

Superior fatigue resistence

Superior reconnectability performance

Good mechanical properties

Good ageing resistance

Hooks and loops materials chemical compatibility Not relevant Very relevant

Molecular mobility Not relevant Very relevant