Dynamic Rheological Behavior and Properties of Al2O3/Polyurethane Thermally Conductive Adhesives
Al2O3/Castor oil,Al2O3/polyurethane(PU)prepolymer suspensions,and Al2O3/PU thermally conductive adhesives with different loadings(w(Al2O3))and particle sizes of Al2O3 were prepared.The dynamic rheological behavior of the suspensions was characterized,and the linear viscoelastic data were fitted and quantitatively analyzed by using a two-phase model.At the same time,the effects of the loading and particle size of Al2O3 on the lap shear strength and thermal conductivity of the thermally conductive adhesives were investigated.The correlation among rheological property,structure and property was explored.Results show that when w(Al2O3)is more than 80%,the second plateau region appears in the storage modulus(G')versus frequency(ω)curve,which corresponds to the formation of the percolation network.The strain amplification factor and the viscoelastic contribution factor increase,while the gel point moves towards the low-frequency region with the increase of volume fraction of Al2O3(φ).With a fixed loading of 80%,the viscoelastic contribution to the suspension increases as the Al2O3 particle size decrease With a particle size of 70 μm and 80%loading of Al2O3,the lap shear strength of Al2O3/PU thermally conductive adhesives on aluminum alloy and stainless steel reaches 21.38 MPa and 25.85 MPa,respectively,and the thermal conductivity is the highest at 1.38 W/(m·K),which is related to the decreased Al2O3-PU phase interface and the formation of thermally conductive percolation network.
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