Mechanical Properties of Layer-by-Layer Assembled Thin Film Nano-Composites Using Brillouin Light Scattering.

Layer-by-Layer;Brillouin Scattering;Elastic Constants;Mechanical Properties;Interface;Materials Science and Engineering;Engineering;Materials Science and Engineering

Sui, LangKotov, Nicholas ;

University of Michigan

关键词: Layer-by-Layer;    Brillouin Scattering;    Elastic Constants;    Mechanical Properties;    Interface;    Materials Science and Engineering;    Engineering;    Materials Science and Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/84601/lsui_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

This dissertation addresses how variations in the particle-matrix interface, particle size, geometry, and volume fraction affect the mechanical properties of layer-by-layer (LBL) assembled thin film materials.Films are primarily assembled using the linear-growth LBL method, which results in a layered structure with distinct interfaces.Particles with rod-like, sphere-like and plate-like geometries are incorporated in between polymer layers at various volume fractions.The volume fraction is adjusted by using different polymers and precursors with variable polymer concentration.In addition, one set of films is assembled using exponentially grown LBL, which results in the formation of diffuse interfaces, to study the role of interface definition.In these films, fumed silica aggregates are added during deposition to mark the location of the original interfaces. The relationship between structure and mechanical properties is studied using Brillouin light scattering.In LBL composites with rod-shaped nano-fillers, the in-plane elastic modulus increases continuously as a function of particle loading, whereas the out-of-plane modulus tails off or even reaches a maximum.The decrease in rigidity in this direction is due to the lack of continuous wetting of fibers by the polymer.Incorporation of spherical fillers results in a larger out-of-plane than in-plane modulus, which is due to the more effective particle-polymer-particle connections and load transfer as a direct consequence of the deposition process.Porosity in these films affects the in-plane Load transmission more prominently.For LBL nano-composites with plate-like particles, the beneficial effect of adding reinforcing particles tapers off because of the transmission of shear forces between particles becomes less efficient with thinner polymer layers.In the latter, structural relaxation occurs more rapidly and they respond more compliantly as a result.Diffuse interface between LBL layers result in the orientation of polymer chains in the film growth direction.As a result, the out-of-plane elastic modulus is higher than the in-plane modulus, and transport of small molecules across layers is facilitated.Addition of nano-particles neither improves nor deteriorates mechanical properties in these films.This work is the first of its kind to provide these new insights into the mechanics of layered thin films.