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2015

Mechanics of Materials

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Articles 1 - 30 of 124

Full-Text Articles in Engineering Science and Materials

Process Development For Compression Molding Of Hybrid Continuous And Chopped Carbon Fiber Prepreg For Production Of Functionally Graded Composite Structures, Corinne Marie Warnock Dec 2015

Process Development For Compression Molding Of Hybrid Continuous And Chopped Carbon Fiber Prepreg For Production Of Functionally Graded Composite Structures, Corinne Marie Warnock

Master's Theses and Project Reports

Composite materials offer a high strength-to-weight ratio and directional load bearing capabilities. Compression molding of composite materials yields a superior surface finish and good dimensional stability between component lots with faster processing compared to traditional manufacturing methods. This experimental compression molding capability was developed for the ME composites lab using unidirectional carbon fiber prepreg composites. A direct comparison was drawn between autoclave and compression molding methods to validate compression molding as an alternative manufacturing method in that lab. A method of manufacturing chopped fiber from existing unidirectional prepreg materials was developed and evaluated using destructive testing methods. The results from ...


Failure Simulations At Multiple Length Scales In High Temperature Structural Alloys, Chao Pu Dec 2015

Failure Simulations At Multiple Length Scales In High Temperature Structural Alloys, Chao Pu

Doctoral Dissertations

A number of computational methodologies have been developed to investigate the deformation and damage mechanism of various structural materials at different length scale and under extreme loading conditions, and also to provide insights in the development of high-performance materials.

In microscopic material behavior and failure modes, polycrystalline metals of interest include heterogeneous deformation field due to crystalline anisotropy, inter/intra grain or phase and grain boundary interactions. Crystal plasticity model is utilized to simulate microstructure based polycrystalline materials, and micro-deformation information, such as lattice strain evolution, can be captured based on crystal plasticity finite element modeling (CPFEM) in ABAQUS. The ...


Pattern Formation Of Elastic Waves And Energy Localization Due To Elastic Gratings, A. Berezovski, J. Engelbrecht, Mihhail Berezovski Oct 2015

Pattern Formation Of Elastic Waves And Energy Localization Due To Elastic Gratings, A. Berezovski, J. Engelbrecht, Mihhail Berezovski

Publications

Elastic wave propagation through diffraction gratings is studied numerically in the plane strain setting. The interaction of the waves with periodically ordered elastic inclusions leads to a self-imaging Talbot effect for the wavelength equal or close to the grating size. The energy localization is observed at the vicinity of inclusions in the case of elastic gratings. Such a localization is absent in the case of rigid gratings.


Electromechanical Coupling Behavior Of Dielectric Elastomer Transducers, Jianyou Zhou Sep 2015

Electromechanical Coupling Behavior Of Dielectric Elastomer Transducers, Jianyou Zhou

Electronic Thesis and Dissertation Repository

Dielectric elastomer transducers with large deformation, high energy output, light weight and low cost have been drawing great interest from both the research and industry communities, and shown potential for versatile applications in biomimetics, dynamics, robotics and energy harvesting. However, in addition to multiple failure modes such as electrical breakdown, electromechanical instability, loss-of-tension and fatigue, the performance of dielectric elastomer transducers are also strongly influenced by the hyperelastic and viscoelastic properties of the material. Also, the interplay among these material properties and the failure modes is rather difficult to predict. Therefore, in order to provide guidelines for the optimal design ...


Effect Of Surface Omniphobicity On Drying By Forced Convection, Madani A. Khan, Jeffrey Alston, Andrew Guenthner Aug 2015

Effect Of Surface Omniphobicity On Drying By Forced Convection, Madani A. Khan, Jeffrey Alston, Andrew Guenthner

STAR (STEM Teacher and Researcher) Presentations

Low energy surfaces can strongly repel both oil and water. Recently these surfaces have been fabricated on various substrates including fabric, aluminum, stainless steel and many other materials. In this experiment we explore the use of low energy surface deposition on aluminum alloy, stainless steel and silicon substrates, to enhance the drying rate of liquids removed from the surface by forced convection. We control surface roughness by substrate abrasion and by the growth of Al2O3 nanograss to enhance liquid repellence by use of a hierarchical texture. Liquid repellence of the substrates is measured by contact angles of ...


An Estimate Of The Second-Order In-Plane Acceleration Sensitivity Of A Y-Cut Quartz Thickness-Shear Resonator, Huijing He, Jiashi Yang, John A. Kosinski Aug 2015

An Estimate Of The Second-Order In-Plane Acceleration Sensitivity Of A Y-Cut Quartz Thickness-Shear Resonator, Huijing He, Jiashi Yang, John A. Kosinski

Mechanical & Materials Engineering Faculty Publications

We perform a theoretical analysis of the second-order in-plane acceleration sensitivity of a Y-cut quartz thick-ness-shear mode resonator. The second-order nonlinear theory of elasticity for anisotropic crystals is used to determine the biasing fields in the resonator under in-plane acceleration. The acceleration-induced frequency shift is determined from a per-turbation analysis based on the plate equations for small-amplitude vibrations superposed on a finite bias. We show that, whereas the first-order acceleration-induced frequency shift is zero for a structurally symmetric resonator under in-plane ac-celeration, the second-order frequency shift is nonzero and is quadratic in the acceleration. As the fourth-order nonlinear elastic constants ...


Biodegradable Medical Device Having An Adjustable Degradation Rate And Methods Of Making The Same, Yuebin Guo, Michael Sealy, Meisam Salahshoor Pirsoltan Jul 2015

Biodegradable Medical Device Having An Adjustable Degradation Rate And Methods Of Making The Same, Yuebin Guo, Michael Sealy, Meisam Salahshoor Pirsoltan

Mechanical & Materials Engineering Faculty Publications

Disclosed herein are biodegradable medical devices comprising biodegradable material (e.g., magnesium-calcium alloys) having an adjustable rate of degradation that can be used in various applications, including, but not limited to, drug delivery applications, cardiovascular applications, and orthopedic applications to make biodegradable and biocompatible devices. Also disclosed herein are methods of making biodegradable medical devices comprising biodegradable materials by using, for instance, hybrid dry cutting/hydrostatic burnishing.


Traction-Separation Relationships For Hydrogen-Induced Grain Boundary Embrittlement In Nickel Via Molecular Dynamics Simulations, Wesley Allen Barrows Jul 2015

Traction-Separation Relationships For Hydrogen-Induced Grain Boundary Embrittlement In Nickel Via Molecular Dynamics Simulations, Wesley Allen Barrows

Theses and Dissertations

The deleterious effects of atomic and molecular hydrogen on the mechanical properties of metals have long been observed. Although several theories exist describing the mechanisms by which hydrogen negatively influences the failure of materials, a consensus has yet to be reached regarding the exact mechanism or combination of mechanisms. Two mechanisms have gained support in explaining hydrogen’s degradative role in non-hydride forming metals: hydrogen-enhanced localized plasticity and hydrogen-enhanced decohesion. Yet, the interplay between these mechanisms and microstructure in metallic materials has not been explained. Accordingly, for this thesis, the three main objectives are: (i) to develop a numerical methodology ...


Optical Detection Of Acoustic Emission Signals, C Harvey Palmer, Robert E. Green Jr Jun 2015

Optical Detection Of Acoustic Emission Signals, C Harvey Palmer, Robert E. Green Jr

Robert A. Green

Piezoelectric transducers, long used in the generation and detection of ultrasonic waves, have more recently been the detector of choice for acoustic emission signals. Optical probing methods, however, have several important advantages for acoustic emission studies: (1) they have an inherent broad frequency response, free from mechanical resonances, (2) they do not interfere with the acoustic waves. (3) since the focused optical beam diameters are typically only a few hundredths of a millimeter, optical methods can probe very close to a crack or a twin, (4) they can probe internally in transparent media, and (5) they can be used over ...


Molecular Dynamics Investigation Of The Arabinan-Cellulose Interface For Cellulose Nanocomposite Applications, Luke Thornley Jun 2015

Molecular Dynamics Investigation Of The Arabinan-Cellulose Interface For Cellulose Nanocomposite Applications, Luke Thornley

Materials Engineering

Atom level computer simulations of the arabinan and cellulose interface were performed to better understand the mechanisms that give arabinan-cellulose composites (ArCCs) their strength with the goal to improve man-made ArCCs. The molecular dynamics (MD) software LAMMPS was used in conjunction with the ReaxFF/c force field to model the bond between cellulose and arabinan. A cellulose nanocrystal with dimensions 51 x 32 x 8 Å was minimized with various weight percent of water, 0%, 3%, 5%, 8%, 10%, and 12%. After the system was equilibrated for at least 100,000 femtoseconds, an arabinan molecule composed of 8 arabinose rings ...


Effect Of Time Delay Between Etching And Adhesive Bonding (“Outlife” Time) On Lap-Shear Strength Of Aluminum Alloys Using Environmentally-Friendly P2 Etch, Josh Barkhimer, Matthew Erich, Gokul Nair Jun 2015

Effect Of Time Delay Between Etching And Adhesive Bonding (“Outlife” Time) On Lap-Shear Strength Of Aluminum Alloys Using Environmentally-Friendly P2 Etch, Josh Barkhimer, Matthew Erich, Gokul Nair

Materials Engineering

Raytheon Company currently uses a Forest Products Laboratory (FPL) paste etchant for preparing aluminum surfaces for adhesive bonding, and FPL is a source of hazardous hexavalent chromium. The goal of this study was to evaluate a less-toxic P2 paste etchant as a possible replacement. Coupons of 2024-T3, 6061-T6, and 7075-T6 grades of aluminum alloy were solvent-degreased, abrasively cleaned, and etched at room temperature using P2 paste following a strict protocol adopted from Raytheon. Coupons were then left exposed to air for assigned time intervals (or “outlife” times) of 0, 1, 4, 8, 16, and 63 or 72 hours. The aluminum ...


Analysis Of A Carbon Fiber Reinforced Polymer Impact Attenuator For A Formula Sae Vehicle Using Finite Element Analysis, John T. Rappolt Jun 2015

Analysis Of A Carbon Fiber Reinforced Polymer Impact Attenuator For A Formula Sae Vehicle Using Finite Element Analysis, John T. Rappolt

Master's Theses and Project Reports

The Hashin failure criteria and damage evolution model for laminated fiber reinforced polymers are explored. A series of tensile coupon finite element analyses are run to characterize the variables in the physical model as well as modeling techniques for using an explicit dynamic solver for a quasi-static problem. An attempt to validate the model on an axial tube crush is presented. It was found that fiber buckling was not occurring at the impactor-tube interface. Results and speculation as to why the failure initiation is incorrect are discussed. Lessons learned from the tube crush are applied successfully to the quasi-static Formula ...


Non-Wetting Surface-Driven High-Aspect-Ratio Crystalline Grain Growth For Efficient Hybrid Perovskite Solar Cells, Cheng Bi, Qi Wang, Yongbo Yuan, Zhengguo Xiao, Jinsong Huang Jun 2015

Non-Wetting Surface-Driven High-Aspect-Ratio Crystalline Grain Growth For Efficient Hybrid Perovskite Solar Cells, Cheng Bi, Qi Wang, Yongbo Yuan, Zhengguo Xiao, Jinsong Huang

Mechanical & Materials Engineering Faculty Publications

Large-aspect-ratio grains are needed in polycrystalline thin-film solar cells for reduced charge recombination at grain boundaries; however, the grain size in organolead trihalide perovskite (OTP) films is generally limited by the film thickness. Here we report the growth of OTP grains with high average aspect ratio of 2.3–7.9 on a wide range of non-wetting hole transport layers (HTLs), which increase nucleus spacing by suppressing heterogeneous nucleation and facilitate grain boundary migration in grain growth by imposing less drag force. The reduced grain boundary area and improved crystallinity dramatically reduce the charge recombination in OTP thin films to ...


Predictive Modeling Of Oxygen Transmission Through Micro-Perforations For Packaging Applications, Ayman Abdellatief, Bruce A. Welt, Jason Butler, Eric Mclamore, Arthur Teixeira, Sanjay Shukla May 2015

Predictive Modeling Of Oxygen Transmission Through Micro-Perforations For Packaging Applications, Ayman Abdellatief, Bruce A. Welt, Jason Butler, Eric Mclamore, Arthur Teixeira, Sanjay Shukla

Journal of Applied Packaging Research

Methods for creating precise perforations in respiring produce packaging are being increasingly adopted. Knowledge of oxygen transfer through perforated packaging and oxygen distribution in packages is necessary for successful packaging design of fresh produce. An approach to modeling perforated packaging performance was developed using a cylindrical chamber with precision perforations using Fick’s second law. The model was simulated using two techniques including Finite Element Method (FEM) using commercially available software and Finite Volume Method (FVM) through programming. Perforations were approximated as a source term in the second method. Both simulation techniques showed trends similar to experimental data.


Energy Selective Neutron Imaging For The Characterization Of Polycrystalline Materials, Robin Woracek May 2015

Energy Selective Neutron Imaging For The Characterization Of Polycrystalline Materials, Robin Woracek

Doctoral Dissertations

This multipart dissertation focuses on the development and evaluation of advanced methods for material testing and characterization using neutron diffraction and imaging techniques. A major focus is on exploiting diffraction contrast in energy selective neutron imaging (often referred to as Bragg edge imaging) for strain and phase mapping of crystalline materials. The dissertation also evaluates the use of neutron diffraction to study the effect of multi-axial loading, in particular the role of applying directly shear strains from the application of torsion. A portable tension-torsion-tomography loading system has been developed for in-situ measurements and integrated at major user facilities around the ...


Development Of An Efficient Data Processing Procedure For The Prediction Of Cleavage Fracture In Reactor Pressure Vessel Steels Using The J-A2 Method, Phoebe E. Fogelman May 2015

Development Of An Efficient Data Processing Procedure For The Prediction Of Cleavage Fracture In Reactor Pressure Vessel Steels Using The J-A2 Method, Phoebe E. Fogelman

Chancellor’s Honors Program Projects

No abstract provided.


Effects Of Temperature Change On Interfacial Delamination In Thermal Barrier Coatings, Hossein Ebrahimi, Soheil Nakhodchi Apr 2015

Effects Of Temperature Change On Interfacial Delamination In Thermal Barrier Coatings, Hossein Ebrahimi, Soheil Nakhodchi

Hossein Ebrahimi

No abstract provided.


A Collocated C0 Finite Element Method: Reduced Quadrature Perspective, Cost Comparison With Standard Finite Elements, And Explicit Structural Dynamics, Dominik Schillinger, John A. Evans, Felix Frischmann, René R. Hiemstra, Ming-Chen Hsu, Thomas J.R. Hughes Apr 2015

A Collocated C0 Finite Element Method: Reduced Quadrature Perspective, Cost Comparison With Standard Finite Elements, And Explicit Structural Dynamics, Dominik Schillinger, John A. Evans, Felix Frischmann, René R. Hiemstra, Ming-Chen Hsu, Thomas J.R. Hughes

Mechanical Engineering Publications

We demonstrate the potential of collocation methods for efficient higher-order analysis on standard nodal finite element meshes. We focus on a collocation method that is variationally consistent and geometrically flexible, converges optimally, embraces concepts of reduced quadrature, and leads to symmetric stiffness and diagonal consistent mass matrices. At the same time, it minimizes the evaluation cost per quadrature point, thus reducing formation and assembly effort significantly with respect to standard Galerkin finite element methods. We provide a detailed review of all components of the technology in the context of elastodynamics, that is, weighted residual formulation, nodal basis functions on Gauss ...


Implications Of Heterogeneity In The Shock Wave Propagation Of Dynamically Shocked Materials, Jeffrey W. Lajeunesse Apr 2015

Implications Of Heterogeneity In The Shock Wave Propagation Of Dynamically Shocked Materials, Jeffrey W. Lajeunesse

Master's Theses (2009 -)

The field of shock physics as a whole has only recently begun to pay particular attention to modeling heterogeneous materials under shock loading. These materials are important because of their practicality in terms of creating stronger, more shock resistant materials. To understand why they absorb shock impact energy better than homogeneous materials means that the small-scale processes that occur during the shock loading of these heterogeneous materials needs to be understood. Recent computational experiments, called mesoscale simulations, have shown that explicitly incorporating small-scale heterogeneous features into hydrocode simulations allows the bulk shock response of the heterogeneous material to be observed ...


Methods And Systems For Handling Or Delivering Materials For Natural Orifice Surgery, Carl Nelson, Jeff Midday, Dimitry Oleynikov, Alan Goyzueta Mar 2015

Methods And Systems For Handling Or Delivering Materials For Natural Orifice Surgery, Carl Nelson, Jeff Midday, Dimitry Oleynikov, Alan Goyzueta

Mechanical & Materials Engineering Faculty Publications

The embodiments disclosed herein relate to various medical systems, including systems that can be used in conjunction with medical devices used in endoscopic surgery. Certain embodiments include various material handling devices that can transport materials between the inside and the outside of an endoscopic surgery patient.


Coupled Mechanochemical Theories For Reacting Systems With Application To Nanovoid Nucleation And Li-Ion Batteries, Hamed Attariani Feb 2015

Coupled Mechanochemical Theories For Reacting Systems With Application To Nanovoid Nucleation And Li-Ion Batteries, Hamed Attariani

Hamed Attariani

Hollow nanoparticles (NPs) are produced by void nucleation and growth during chemical reactions. However, there is no proper understanding of nucleation and growth mechanisms, and their predictive modeling. Furthermore, models based on the Kirkendall effect predict the process time, which is larger by orders of magnitude than in the experiment. A continuum-mechanics approach for nucleation and growth of a nanovoid in reacting NPs based on the Kirkendall effect is developed, which quantitatively describes the experimental results for oxidation of copper NPs. The results show that the core is under compression (which eliminates fracture hypothesis) which promotes void nucleation by decreasing ...


Synthesis And Characterization Of A Novel Polyacetal & Design And Preparation Of Superhydrophobic Photocatalytic Surfaces, Yuanyuan Zhao Feb 2015

Synthesis And Characterization Of A Novel Polyacetal & Design And Preparation Of Superhydrophobic Photocatalytic Surfaces, Yuanyuan Zhao

All Dissertations, Theses, and Capstone Projects

Polyacetal polymers are thermoplastic resins that play an important role in industry because of numerous industrial applications including automobile; household appliance; etc. The first part of this thesis (Chapter 2) is about the synthesis of a new acetal copolymer that exhibits superior thermal stability. The second part of this thesis (Chapter 3) is about the preparation and applications of TiO2-based polymer nanocomposite films, where the reactive oxygen species (ROS) are generated on the solid surface. Catalytic nanocomposite films are an active area of research because of their potential uses for environmental remediation and chemical synthesis. Furthermore, to enhance ...


Highly-Selective Chemiresistive Sensing And Analysis Of Vapors Using Functionalized Nanotubes, Deon Hines Feb 2015

Highly-Selective Chemiresistive Sensing And Analysis Of Vapors Using Functionalized Nanotubes, Deon Hines

All Dissertations, Theses, and Capstone Projects

Specifically, the project involves the development of a diversified array of nanostructured gas-sensors comprised of selectively, novel surface-functionalized carbon nanotubes (for analyte selectivity by virtue of functionality). Harnessing carbon nanotubes with various electron withdrawing and donating groups help in determining their affinity toward certain prognostic gaseous markers thus increasing specificity of such created sensors. We have devised synthetic routes that have led to the facile production of covalently polyfunctionalized nanotubes in high yield. Seven carbon nanotube analogues were systematically considered and then chemically synthesized, from pristine single-walled nanotubes (SWNT's), for use as the main component of sensory units that ...


Computational Study Of Microstructure-Propertymechanism Relations In Ferroic Composites, Fengde D. Ma Jan 2015

Computational Study Of Microstructure-Propertymechanism Relations In Ferroic Composites, Fengde D. Ma

Dissertations, Master's Theses and Master's Reports - Open

Ferroic materials, as notable members of smart materials, have been widely used in applications that perform sensing, actuation and control. The macroscopic property change of ferroic materials may become remarkably large during ferroic phase transition, leading to the fact that the macroscopic properties can be tuned by carefully applying a suitable external field (electric, magnetic, stress). To obtain an enhancement in physical and/or mechanical properties, different kinds of ferroic composites have been fabricated. The properties of a ferroic composite are determined not only by the properties and relative amounts of the constituent phases, but also by the microstructure of ...


Discontinuous Element Insertion Algorithm, Timothy James Truster Jan 2015

Discontinuous Element Insertion Algorithm, Timothy James Truster

Faculty Publications and Other Works -- Civil & Environmental Engineering

An algorithm is presented for inserting zero-thickness interface elements, termed herein as “couplers”, into continuous finite element meshes in two and three dimensions. Insertion is governed solely by the mesh topology and is specified according to regions or subdomains within the overall analysis domain, a geometrically intuitive means to designate the coupler locations. The algorithm is self-contained and requires only nodal coordinates and element connectivity as input. A wide class of volume elements and interface couplers are treated within the framework. Since the algorithm is topologically-based, interfaces of arbitrary complexity are naturally accommodated. Separate treatment is given to inserting couplers ...


Multiscale Simulations Of Dynamics Of Ferroelectric Domains, Shi Liu Jan 2015

Multiscale Simulations Of Dynamics Of Ferroelectric Domains, Shi Liu

Publicly Accessible Penn Dissertations

Ferroelectric materials exhibiting switchable polarization have been used as critical components in electronics, memory, actuators and acoustics, and electro-optics. The applications of ferroelectric materials heavily rely on the interactions between the polarization and external perturbations, such as electric field, stress, and temperature. It is therefore crucial to understand the dynamics of ferroelectric response at finite temperature. Despite the tremendous advance of computational power and the success of first-principles methods, large-scale simulations of dynamics in oxides at finite temperature can still only be performed using classical atomistic potential. We first develop a model potential based on principles of bond-valence and bond-valence ...


Improving The Signal-To-Noise Of Nanopore Sensors, Matthew Puster Jan 2015

Improving The Signal-To-Noise Of Nanopore Sensors, Matthew Puster

Publicly Accessible Penn Dissertations

Over the last five years, solid state nanopore technology advanced to rival biological pores as a platform for next generation DNA sequencing. Fabrication improvements led to a reduction in nanopore diameter and membrane thickness, offering high precision sensing. Custom electronics were developed concomitant with low capacitance membranes for low-noise, high-bandwidth measurements. These advances improved our ability to detect small differences between translocating molecules and to measure short molecules translocating at high speeds.

This work focuses specifically on the challenge of maximizing the signal magnitude generated by the solid state nanopore. One way that this can be achieved is by thinning ...


Surface Reconstructions Of Perovskite-Type Oxides: Their Exotic Structures And Modified Chemistry, John Mark Pinat Martirez Jan 2015

Surface Reconstructions Of Perovskite-Type Oxides: Their Exotic Structures And Modified Chemistry, John Mark Pinat Martirez

Publicly Accessible Penn Dissertations

The ability to manipulate the atomic and electronic structures and stoichiometry of surfaces is of utmost importance in optimizing heterogeneous catalysts. A critical requirement in this endeavor is a deep thermodynamic and kinetic understanding of surface reconstruction behavior, under various thermal and chemical constraints. We explore the reconstruction behaviors (structure and chemistry) of Ti-based perovskite type oxides: BaTiO3, PbTiO3 and SrTiO3. The former two exhibit ferroelectricity. We find that these oxides undergo surface reconstruction transformations that generally result in enrichment of their catalytically active component: Ti. These reconstructions show rich bonding and structural motifs that affect the ...


Engineering Novel Nanostructures Via Chemical And Morphological Transformations, Rahul Agarwal Jan 2015

Engineering Novel Nanostructures Via Chemical And Morphological Transformations, Rahul Agarwal

Publicly Accessible Penn Dissertations

Materials at the nanoscale have revolutionized the world around us by enabling the discovery of novel size dependent properties and experimental verification of untested theoretical concepts. However, most nanomaterials today are phases of matter that are well known and have been studied extensively at the bulk scale. For example, II-VI semiconductors, which are widely studied today at the nanoscale, were employed in photovoltaic applications at the microscale for nearly half a century. The question that arises is whether material processing at the nanoscale can allow us to go beyond the limitations of conventional synthesis techniques? We believe that the next ...


Dynamics In Polymer Nanocomposites Containing Fixed And Mobile Nanoparticles, Chia-Chun Lin Jan 2015

Dynamics In Polymer Nanocomposites Containing Fixed And Mobile Nanoparticles, Chia-Chun Lin

Publicly Accessible Penn Dissertations

This dissertation describes experimental studies on the dynamics of polymer nanocomposites (PNC), namely, center-of-mass (COM) polymer diffusion in PNCs, and COM nanoparticle (NP) diffusion in polymer melts. Elastic recoil detection (ERD) is used for polymer diffusion studies and Rutherford backscattering (RBS) is used for NP diffusion studies. Diffusion of the tracer polymer, deuterated poly(methyl methacrylate) (dPMMA) is slowed down in a PMMA matrix filled with hydroxyl-capped spherical silica nanoparticles. A confinement parameter, ID/2Rg, where ID is interparticle distance and 2Rg is probe size is defined to account for the NP crowding effect. For highly crowded region where ID ...