Restoration of Large Damage Volumes in Polymers White, S. R.; Moore, J. S.; Sottos, N. R. ...
Science (American Association for the Advancement of Science),
05/2014, Letnik:
344, Številka:
6184
Journal Article
Recenzirano
The regenerative power of tissues and organs in biology has no analog in synthetic materials. Although self-healing of microscopic defects has been demonstrated, the regrowth of material lost through ...catastrophic damage requires a regenerative-like approach. We demonstrate a vascular synthetic system that restores mechanical performance in response to large-scale damage. Gap-filling scaffolds are created through a two-stage polymer chemistry that initially forms a shape-conforming dynamic gel but later polymerizes to a solid structural polymer with robust mechanical properties. Through the control of reaction kinetics and vascular delivery rate, we filled impacted regions that exceed 35 mm in diameter within 20 min and restored mechanical function within 3 hours. After restoration of impact damage, 62% of the total absorbed energy was recovered in comparison with that in initial impact tests.
Self‐healing functionality is imparted to a poly(dimethyl siloxane) (PDMS) elastomer. This new material is produced by the incorporation of a microencapsulated PDMS resin and a microencapsulated ...crosslinker into the PDMS matrix. A protocol based on the recovery of tear strength is introduced to assess the healing efficiency for these compliant polymers. While most PDMS elastomers possess some ability to re‐mend through surface cohesion, the mechanism is generally insufficient to produce significant recovery of initial material strength under ambient conditions. Self‐healing PDMS specimens, however, routinely recover between 70–100 % of the original tear strength. Moreover, the addition of microcapsules increases the tear strength of the PDMS. The effect of microcapsule concentration on healing efficiency is also investigated.
A self‐healing poly(dimethyl siloxane) (PDMS) elastomer has been developed by the incorporation of a microencapsulated PDMS resin and a microencapsulated crosslinker into the PDMS matrix. Tear testing shows that this material is capable of routinely recovering over 70% of the original tear strength and is capable of producing healing efficiencies of 100%.
Successful arrest and retardation of fatigue cracks is achieved with an in situ self-healing epoxy matrix composite that incorporates microencapsulated dicyclopentadiene (DCPD) healing agent and ...Grubbs’ first generation Ru catalyst. Healing agent is released into the crack plane by the propagating crack, where it polymerizes to form a polymer wedge, generating a crack tip shielding mechanism. Due to the complex kinetics of healing a growing crack, the resulting in situ retardation and arrest of fatigue cracks exhibit a strong dependence on the applied range of cyclic stress intensity Δ
K
I. Significant crack arrest and life-extension result when the in situ healing rate is faster than the crack growth rate. In loading cases where the crack grows too rapidly (maximum applied stress intensity factor is a significant percentage of the mode-I fracture toughness value), a carefully timed rest period can be used to prolong fatigue life up to 118%. At moderate Δ
K
I, in situ healing extends fatigue life by as much as 213%. Further improvements in fatigue life-extension are achieved by employing a rest period, which leads to permanent arrest at this moderate Δ
K
I. At lower values of applied stress intensity factor, self-healing yields complete arrest of fatigue cracks providing infinite fatigue life-extension.
Microencapsulated dicyclopentadiene (DCPD) healing agent and Grubbs' Ru catalyst are incorporated into an epoxy matrix to produce a polymer composite capable of self-healing. The fracture toughness ...and healing efficiency of this composite are measured using a tapered double-cantilever beam (TDCB) specimen. Both the virgin and healed fracture toughness depend strongly on the size and concentration of microcapsules added to the epoxy. Fracture of the neat epoxy is brittle, exhibiting a mirror fracture surface. Addition of DCPD-filled urea-formaldehyde (UF) microcapsules yields up to 127% increase in fracture toughness and induces a change in the fracture plane morphology to hackle markings. The fracture toughness of epoxy with embedded microcapsules is much greater than epoxy samples with similar concentrations of silica microspheres or solid UF polymer particles. The increased toughening associated with fluid-filled microcapsules is attributed to increased hackle markings as well as subsurface microcracking not observed for solid particle fillers. Overall the embedded microcapsules provide two independent effects: the increase in virgin fracture toughness from general toughening and the ability to self-heal the virgin fracture event.
Self-healing structural composite materials Kessler, M.R; Sottos, N.R; White, S.R
Composites. Part A, Applied science and manufacturing,
08/2003, Letnik:
34, Številka:
8
Journal Article
Recenzirano
A self-healing fiber-reinforced structural polymer matrix composite material is demonstrated. In the composite, a microencapsulated healing agent and a solid chemical catalyst are dispersed within ...the polymer matrix phase. Healing is triggered by crack propagation through the microcapsules, which then release the healing agent into the crack plane. Subsequent exposure of the healing agent to the chemical catalyst initiates polymerization and bonding of the crack faces. Self-healing (autonomic healing) is demonstrated on width-tapered double cantilever beam fracture specimens in which a mid-plane delamination is introduced and then allowed to heal. Autonomic healing at room temperature yields as much as 45% recovery of virgin interlaminar fracture toughness, while healing at 80 °C increases the recovery to over 80%. The in situ kinetics of healing in structural composites is investigated in comparison to that of neat epoxy resin.
Microcapsules containing a solvent and reactive epoxy resin are a critical component for the development of cost-effective, low toxicity, and low flammability self-healing materials. We report a ...robust in situ encapsulation method for protection of a variety of oil soluble solvents and reactive epoxy resins surrounded by a thin, polymeric, urea–formaldehyde (UF) shell. Resin–solvent capsules are produced in high yield with diameters ranging from 10 to 300μm by controlling agitation rates. These capsules have a continuous inner shell wall and a rough exterior wall that promotes bonding to a polymer matrix. Capsules as small as 300nm in diameter are achieved through sonication and stabilization procedures. The presence of both the epoxy resin and solvent core components is confirmed by differential scanning calorimetry (DSC) measurements, and the relative amount of epoxy and solvent in the liquid core is determined by thermogravimetric analysis (TGA). The capsules are shown to satisfy the requirements for use in self-healing materials including processing survivability, thermal stability, and efficient in situ rupture for delivery of healing agent.
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We report an
in situ encapsulation method demonstrating over an order of magnitude size reduction for the preparation of urea–formaldehyde (UF) capsules filled with a healing agent, dicyclopentadiene ...(DCPD). Capsules with diameters as small as 220
nm are achieved using sonication techniques and an ultrahydrophobe to stabilize the DCPD droplets. The capsules possess a uniform UF shell wall (77 nm average thickness) and display good thermal stability. By controlling the
ζ-potential, the capsules are uniformly dispersed in an epoxy matrix and shown to cleave rather than debond upon fracture of the matrix. Mechanical properties of the epoxy/capsule composite, including mode-I fracture toughness, elastic modulus, and ultimate tensile strength are measured and compared to previous data for larger capsules (ca. 180
μm).
Microspheres of wax containing embedded Grubbs' catalyst are generated by congealing a molten aqueous suspension. Even with a ten‐fold reduction in catalyst concentration from previous systems, these ...microspheres produce unprecedented levels of toughness recovery in a polymeric self‐healing material (see Figure). Unlike the previously reported systems, samples healed with the wax microspheres show nonlinear fracture behavior. A protocol that addresses this nonlinearity is employed to measure healing efficiency.
Polydimethylsiloxane‐based self‐healing is achieved through the tin‐catalyzed polycondensation of phase‐separated droplets. The catalyst is released into the crack plane when microcapsules containing ...a tin compound are ruptured by the advancing crack (see figure). This system greatly extends the capability of self‐healing polymers by introducing a new, stable healing chemistry into a structural polymer matrix and may provide a route to self‐healing in harsh and corrosive environments.
As a first step towards a new crack healing methodology for cyclic loading, this paper examines two promising crack-tip shielding mechanisms during fatigue of a microcapsule toughened epoxy. ...Artificial crack closure is achieved by injecting precatalyzed monomer into the crack plane to form a polymer wedge at the crack tip. The effect of wedge geometry is also considered, as dictated by crack loading conditions during infiltration. Crack-tip shielding by a polymer wedge formed with the crack held open under the maximum cyclic loading condition (
K
max) yields temporary crack arrest and extends the fatigue life by more than 20 times. Hydrodynamic pressure and viscous damping as a mechanism of crack-tip shielding are also investigated by injecting mineral oil into the crack plane. Viscous fluid flow leads to retardation of crack growth independent of initial loading conditions. The success of these mechanisms for retarding fatigue crack growth demonstrates the potential for in situ self-healing of fatigue damage.
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