Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers

Abstract

In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, T switch. If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shapememory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly( -caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25°C resulted in temporary fixation of the mechanical deformation by 50 -60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f ‫؍‬ 258 kHz; H ‫؍‬ 30 kA⅐m ؊1 ). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature.nanocomposite ͉ shape-memory polymer ͉ stimuli-sensitive polymer S hape-memory polymers are able to recover their predefined original shape when exposed to an external stimulus. A prerequisite for the shape-memory effect is a preceding functionalization of the material to temporarily fix a mechanical deformation. Most shape-memory polymers are thermosensitive materials. The shape is actuated by exceeding a specific switching temperature, T switch (1). Thermoplastic shape-memory polymers have at least two separated phases, where the domains with the highest thermal transition (T perm ) stabilize the permanent shape by acting as physical netpoints. A second phase having another thermal transition T trans serves as switch. At temperatures above T trans the chain segments forming this phase are flexible and the material is highly elastic, whereas the flexibility of the chains below T trans is limited and enables the fixation of the temporary shape. T trans can either be a glass transition (T g ) or a melting temperature (T m ). Whereas T trans is the thermal transition of the switching segment phase, typically determined by differential scanning calorimetry (DSC), T switch is result of a thermomechanical test used to quantify the shape-memory effect.An important class of thermoplastic shape-memory polymers are polyurethanes. They often contain a hard segment from methylene bis(4-phenylisocyanate) (MDI) and 1,4-butanediol. Depending on the switching segment, T trans can be either a melting...

Shape-Memory Polymer Networks from Oligo[(ε-hydroxycaproate)-co-glycolate]dimethacrylates and Butyl Acrylate with Adjustable Hydrolytic Degradation Rate

“…26 Alternatively, in stresscontrolled experiments the straining of the test specimen with respect to the distance of the clamps is recorded while a defined stress is kept. 27 Stress-controlled, cyclic thermomechanical tests are performed using two different routines. First, programming and strain recovery are performed in air.…”

“…For the stress-controlled tests, values for R f are determined according to eq 1 in ref 27 and values for R r are determined according to eq 2 in ref 27. In strain-controlled cyclic thermomechanical tests, copolymer networks with a M n for the prepolymers of at least 4900 g‚mol -1 show R f above 94% and The chosen maximum elongation m in the strain-controlled tensile tests is 75%.…”

Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

“…The complementary use of different stimuli, such as the application of magnetic fields to reduce the temperature required for SMP relaxation [114], is a promising area, as is the potential of electrical or optical stimuli for remote, directional and modulated control.…”

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Radiation synthesis of magnetic sensitive ferrogels from poly(ethylene glycol) and methacrylic acid as drug delivery matrices for vitamin B12

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