Fiber-matrix interface reinforcement using Atomic Layer Deposition
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Fiber-matrix interface reinforcement using Atomic Layer Deposition Sari Katz1, Yacov Carmiel2, Irina Gouzman1, Chaim N. Sukenik2, Hanoch D. Wagner3, Eitan Grossman1 1 Space Environment Department, Soreq NRC, Yavne 81800, Israel. 2 Department of Chemistry and Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel 3 Department of Materials and Interfaces, The Weizmann Institute of Science, Rehovot, 76100, Israel. ABSTRACT The interface between a matrix and its reinforcement is critical to the final composite properties. There are different ways to enhance bonding between the reinforcing fiber and the matrix, based mainly on surface plasma treatments which usually decrease the fiber tensile strength. In this research, atomic layer deposition (ALD) was tested as a possible way to enhance the chemical bonding between the fiber and matrix in the hope that it would not effect the fiber tensile strength. Microbond tests were carried out to measure the effect of an ALD aluminum oxide (Al2O3) coating on the fiber/matrix interfacial shear strength, and the fiber tensile strength was measured in order to assess whether this treatment harms the fiber strength. The ultrahigh molecular weight polyethylene (UHMWPE) fibers that were coated by ALD with aluminum oxide (Al2O3) showed a significant increase in the interfacial shear strength without reducing the fibers’ ultimate tensile strength. INTRODUCTION The interfacial adhesion between a fiber and matrix plays an important role in the final composite mechanical behavior. Ultrahigh molecular weight polyethylene (UHMWPE) fibers are highly crystalline fibers with very high tensile strength (3.9 GPa) [1]. The fibers are based on large numbers of fibrils with a high degree of chain alignment, which gives these fibers their unusual strength. However, these fibers are hard to bond to the matrix that they are intended to reinforce due to their non-polar surfaces that do not adhere well to polymeric matrices. In order to improve their interfacial adhesion, the surface of the fiber should be treated before they are embedded in the matrix. There are different surface treatments including: corona discharge [2], chemical treatment with chromic acid, potassium permanganate and hydrogen peroxide [3, 4], as well as different plasma treatments [5, 6], which are successful in enhancing the bonding between UHMWPE fibers and the epoxy matrix. These treatments increase the interfacial adhesion by removing any contaminants on the fiber surface as well as creating polar functional groups on the surface of the fiber and introducing roughness to the fiber surface. These common surface treatments degrade the UHMWPE fiber tensile strength by about 10% [3, 7]. This work suggests an alternative, new, method to improve fiber-matrix interfacial adhesion by adding a buffer layer using atomic layer deposition (ALD). ALD is a thin film deposition technique based on the sequential use of two chemically complementary precursors in a gas phase process. The substrate is sequen
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