Center for Composite Materials - University of Delaware

Research Summary

Study of the Interaction of Silica Glass Surface with Water and Silane Coupling Agent

Authors: Sanjib C. Chowdhury, Bazle Z. (Gama) Haque & John W. Gillespie Jr.

INTRODUCTION

Background & Motivation
• During the manufacturing process of glass fiber-polymer composites, interphase forms in between the fiber and the matrix.
• Load from the matrix to the fiber is transferred through this interphase.
• Strength if the interphase depends on the adhesion of glass fiber with silane coupling agent (w / wo water) and matrix.

Objectives
• Study interaction of silica glass with water and silane coupling agents using molecular dynamics (MD) simulations with reactive force field ReaxFF.
• Conduct MD simulations to determine the interphase traction separation relationships of silica-silane system.

SILICA MODEL

• Crystalline silica model is created by replicating the cristobalite silica unit cell in the X-, Y-, and Z-directions.
• Amorphous silica is created from the crystalline silica by annealing.
• Annealing process: (i) heating at 8000 K with NVT, (ii) cooling from 8000 K to 300 K with NVT, and (iii) relaxing at 300 K with NPT

SILICA-SILANE MODEL

• 150 Hydroxylated GPS molecules are randomly packed in 3D box.
• Silica and GPS models are put together with 0.2 nm gap and then relaxed.
• RDF indicates Si of Silica is making bond with O of GPS while O if silica is making bond with H of GPS.
• LAMMPS species analysis shows about 31 GPS molecules have been connected with the silica surface.

SILICA-WATER-SILANE MODEL

• Hydroxylated silica surface is created relaxing the amorphous silica in the presence of water.
• Water dissociates into OH- and H+
• OH- and H+ react with under-coordinated Si and O atoms of silica and form silanol on the silica surface.
• Excess water is removed from the silica surface
• GPS and hydroxylated silica models are put together and then relaxed.
• There is no direct bonding between GPS and silica due to the presence of water in between them

INTERPHASE LOADING & BOUNDARY CONDITIONS

• Displacement rate = 10 m/s, temp. = 300 K, NVT ensemble

INTERPHASE PROPERTIES

Interphase Traction Properties
• Atomistic traction-separation relationship resembles that of continuum analysis.
• Peak stresses found in the present simulation are significantly higher than those of the fiber-resin interphase obtained in conventional experiments.
• Interphase properties degrade when there is weakly bonded water in the interphase.

PATH FORWARD

• Epon and curing agent (CA) will be diffused into the GPS anchored silica system
• Cross-linking of CA with GPS will be conducted in the interphase region
• Cross-linking of CA with Epon will be conducted in the matrix region
• Mode-I & Mode-II loadings will be conducted to determine the interphase traction law of Silica-Cured Epon system

ACKNOWLEDGEMENTS

Research was sponsored by the Army Research Laboratory and was accomplished under Cooperative Agreement Number W911NF-12-2-0022. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein

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