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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 – [email protected] Lodz University of Technology, Faculty of Chemistry, Institute of Polymer and Dye Technology, Lodz, Poland – [email protected] 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