Download or read book System of Measuring Mechanical Properties of Colloidal Gels with Optical Tweezers written by Na Wang and published by . This book was released on 2006 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: "We successfully assembled the main instrument, a time-sharing single beam optical tweezers, and calibrated the lateral stiffness of the optical trap. Our optical tweezers setup is used to study the polystyrene gel and it has many more applications in colloidal samples. The strong 3D optical trapping highlights the optical tweezers as a powerful technique suitable for further investigation of colloidal samples." --

Download or read book Microstructure and Microrheology of Colloidal Gels written by Myung Han Lee and published by ProQuest. This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal gels are of considerable interest for both research and industry, within ceramic coatings, pharmaceutical formulations, and mineral recovery. External forces and fields, including shear deformation and gravitational sedimentation, lead to microstructural transitions, which depend on the nature and strength of interparticle interactions and on the connectedness and topology of the gel. Characterizations of the microstructure and its response to such perturbations enable us to understand and control the rheology of gels. In this dissertation, we report direct measurements of microscopic structure and mechanical response of gels with the ultimate aim of establishing fundamental relationships between the microstructure and rheological properties. We achieve this through the combined use of confocal microscopy and optical tweezers. First, we study the microscopic mechanical response of colloidal gels by manipulating single probe particles within the network. For this work, we use a refractive index and density matched suspension of polymethylmethacrylate (PMMA) particles with non-adsorbing polymer. As polymer concentration increases, a dynamically arrested, space-filling network is formed, exhibiting structural transitions from a cluster-like to a more homogeneous string-like gel phase. In a gel, probe particles are oscillated with an optical trap, creating the local strain field in the network. We find that the micromechanics correlate strongly with the gel structure. At high polymer concentration, strain fields scale as 1/ r to a distance quite close to the probe particle, as expected for a purely elastic material. In contrast, at low polymer concentrations, gels exhibit anomalous strain fields in the near-field; the strain plateaus, indicating that many particles move together with the probe. By rescaling the probe size in the theoretical model, we obtain a micromechanical gel correlation length, which is consistent with the structural difference in terms of "cluster-like" and "string-like". Next, we observe the gel elasticity and particle rearrangements in the same system. The gel microelasticity from Stokes equation monotonically increases with polymer concentration, corresponding to the aggregate internal stiffness. Then, we correct for the structural heterogeneity based on the micromechanical correlation length in gels using a prefactor suggested by Schweizer and coworkers. The revised elasticity is non-monotonically dependent on polymer concentration and is in better agreement with the bulk measurements. We also examine local elastic and plastic deformations in gels with the probe oscillation. The rearrangements strongly depend on the strength of attraction. Finally, we investigate the coupled aggregation and sedimentation phenomena of colloidal particles as functions of the strength of attraction and initial volume fraction. For this work, we use a refractive index matched and density mismatched suspension of fluorescent core-shell silica particles with a non-adsorbing polymer, polystyrene. Silica particles with a fluorescent core and non-fluorescent shell are synthesized using a modified Stober method in the presence of sodium dodecyl sulfate (SDS). For high gravitational Peclet numbers (Pe g>1), we find that the strong coupling between aggregation and sedimentation determines the growth of clusters and evolution of the suspension. Early in the aggregation process, the suspension structure depends on the attractive well depth and initial volume fraction with the functional form that resembles thermally activated barrier hopping processes in colloidal systems, such as the delayed sedimentation of gels. The aggregation behavior prior to sedimentation determines the final structure of the suspension. Finally, we find that compaction and rearrangements in the sediment correlate strongly with the depth of attraction, but not with the sediment structure. The results from this work are expected to provide a better understanding of the role of the local structure and particle interactions in micromechanics and rheology of gels. Such an understanding will ultimately lead to more accurate predictions and a better control of gel processing and properties.

Download or read book Microrheology with Optical Tweezers written by Manlio Tassieri and published by CRC Press. This book was released on 2016-10-14 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thanks to the pioneering works of Ashkin and coworkers, optical tweezers (OTs) have become an invaluable tool for myriad studies throughout the natural sciences. Their success relies on the fact that they can be considered as exceptionally sensitive transducers that are able to resolve pN forces and nm displacements, with high temporal resolution, down to μs. Hence their application to study a wide range of biological phenomena such as measuring the compliance of bacterial tails, the forces exerted by a single motor protein, and the mechanical properties of human red blood cells and of individual biological molecules. The number of articles related to them totals to a whopping 58,000 (source Google Scholar)! Microrheology is a branch of rheology, but it works at micrometer length scales and with microliter sample volumes. Therefore, microrheology techniques have been revealed to be very useful tools for all those rheological/mechanical studies where rare or precious materials are employed, such as in biological and biomedical studies. The aim of this book is to provide a pedagogical introduction to the physics principles governing both the optical tweezers and their application in the field of microrheology of complex materials. This is achieved by following a linear path that starts from a narrative introduction of the "nature of light," followed by a rigorous description of the fundamental equations governing the propagation of light through matter. Moreover, some of the many possible instrumental configurations are presented, especially those that better adapt to perform microrheology measurements. In order to better appreciate the microrheological methods with optical tweezers explored in this book, informative introductions to the basic concepts of linear rheology, statistical mechanics, and the most popular microrheology techniques are also given. Furthermore, an enlightening prologue to the general applications of optical tweezers different from rheological purposes is provided at the end of the book.

Download or read book Theory and Applications of Colloidal Suspension Rheology written by Norman J. Wagner and published by Cambridge University Press. This book was released on 2021-04-15 with total page 437 pages. Available in PDF, EPUB and Kindle. Book excerpt: Essential text on the practical application and theory of colloidal suspension rheology, written by an international coalition of experts.

Download or read book Optical Tweezers written by Miles J. Padgett and published by CRC Press. This book was released on 2010-06-02 with total page 510 pages. Available in PDF, EPUB and Kindle. Book excerpt: The technical development of optical tweezers, along with their application in the biological and physical sciences, has progressed significantly since the demonstration of an optical trap for micron-sized particles based on a single, tightly focused laser beam was first reported more than twenty years ago. Bringing together many landmark papers on

Download or read book Optical Tweezers written by Philip H. Jones and published by Cambridge University Press. This book was released on 2015-12-03 with total page 565 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive guide to the theory, practice and applications of optical tweezers, combining state-of-the-art research with a strong pedagogic approach.

Download or read book Assessment of Directions in Microgravity and Physical Sciences Research at NASA written by National Research Council and published by National Academies Press. This book was released on 2003-07-11 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt: For thirty years the NASA microgravity program has used space as a tool to study fundamental flow phenomena that are important to fields ranging from combustion science to biotechnology. This book assesses the past impact and current status of microgravity research programs in combustion, fluid dynamics, fundamental physics, and materials science and gives recommendations for promising topics of future research in each discipline. Guidance is given for setting priorities across disciplines by assessing each recommended topic in terms of the probability of its success and the magnitude of its potential impact on scientific knowledge and understanding; terrestrial applications and industry technology needs; and NASA technology needs. At NASA's request, the book also contains an examination of emerging research fields such as nanotechnology and biophysics, and makes recommendations regarding topics that might be suitable for integration into NASA's microgravity program.

Download or read book Oscillations Waves and Interactions written by Thomas Kurz and published by Universitätsverlag Göttingen. This book was released on 2007 with total page 485 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Measurement of Colloidal Dynamics Using Optical Tweezers written by Steven James Mitchell and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fluids Colloids and Soft Materials written by Alberto Fernandez-Nieves and published by John Wiley & Sons. This book was released on 2016-05-09 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents a compilation of self-contained chapters covering a wide range of topics within the broad field of soft condensed matter. Each chapter starts with basic definitions to bring the reader up-to-date on the topic at hand, describing how to use fluid flows to generate soft materials of high value either for applications or for basic research. Coverage includes topics related to colloidal suspensions and soft materials and how they differ in behavior, along with a roadmap for researchers on how to use soft materials to study relevant physics questions related to geometrical frustration.

Download or read book Microstructure and Mechanical Properties of Colloidal Particle Gels written by Iwan Schenker and published by . This book was released on 2009 with total page 187 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Micromechanics and Rheology of Colloidal Gels Via Dynamic Simulation written by Lilian Challingsworth Johnson and published by . This book was released on 2018 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal gels are soft solids comprising a viscoelastic, networked structure embedded in solvent. This network forms from microscopically small particles initially dispersed in a solvent which self-assemble into a hierarchical, space-spanning network of particles connected by physical bonds. When subjected to external forces, colloidal gels exhibit a solid-to-liquid transition yet regain elastic character when forcing is removed. Their tunable mechanical properties and ability to flow enable colloidal gels to serve as the foundation of a multitude of applications ranging from everyday products, like yogurt, to biomedical applications, such as injectable therapeutics. The nonlinear rheology of colloidal gels underlies their utility in nearly every application, for example, spreading, injecting, or pouring. The transition from rest to steady flow of colloidal gels is characterized by one or more stress overshoots indicative of gel yield. In strongly-bonded, dilute colloidal gels, yield is hypothesized to result from the catastrophic loss of the network structure. Solid-like fracture leading to fluidization of strongly bonded gels may not be relevant where particle strands are not single-particle thick chains but rather bicontinuous and time-evolving due to reversible bonds. The connections between gel yield and the structural evolution of dense, bicontinuous gels remains poorly understood due to the difficulty of imaging of the internal structure of dense particulate gels with sufficient time resolution in experiments and due to the large system size required in computational studies. Here we report large-scale dynamic simulation to study reversible colloidal gels to elucidate the micromechanical underpinnings of non-Newtonian behavior of soft materials and to understand ongoing phase separation. First, we show that the startup of a fixed strain rate reveals that colloidal gel yield, separating the short-time solid-like response from the long-time liquid-like response, can be framed as a transition in energy storage. Contrary to prior hypotheses connecting yield to loss of network connectivity, the network persists after flow startup and a predictive model connecting hierarchical structure to early-time stress growth is presented. We devised a novel approach to monitor bond stretching, compression, formation, and loss alongside macroscopic deformation. We find that changes in structure that underlie the stress growth and post-yield relaxation, as monitored by bond dynamics, indicate the switch from energy storage to release. After rheological yield, energy release continues if flow is sufficiently strong; however, when imposed flow is weak, energy release reverses after yield, and the gel densifies. This gives the important result that yield under weak flow can be viewed as a release from kinetic arrest, permitting the gel to evolve toward more complete phase separation. This supports our view that yield of weakly sheared gels is a `non-equilibrium phase transition'. Second, we compare our simulations to experimental measurements of colloidal gel rheology to study the influence of bond strength, volume fraction, and network morphology on the viscoelastic moduli. Strong agreement is found between linear viscoelasticity from sim...

Download or read book Probing the Mechanical Properties of Short Molecules with Optical Tweezers written by Benjamin Patrick Blake Downing and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Structural proteins play vital roles in many human tissues, roles to which their mechanical properties are of direct relevance. Optical tweezers give us the remarkable ability to quantitatively probe these properties at the single-molecule level, potentially revealing a wealth of information on how such proteins fulfil their physiological functions. I have worked toward applying this technique, in which micron-sized beads chemically linked to the protein are manipulated by focussed laser beams, to structural proteins, particularly elastin. I developed methods to eliminate or account for several experimental complications presented by the fact that these proteins are short compared to other molecules studied with optical tweezers. I proceeded to design and test multiple strategies for linking elastin to beads, discovering that its unusual biochemical properties raise significant additional challenges. Some of these I overcame, and an assay I developed for linking effectiveness may be of use in overcoming others.

Download or read book Physical Gels from Biological and Synthetic Polymers written by Madeleine Djabourov and published by Cambridge University Press. This book was released on 2013-05-16 with total page 367 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presenting a unique perspective on state-of-the-art physical gels, this interdisciplinary guide provides a complete, critical analysis of the field and highlights recent developments. It shows the interconnections between the key aspects of gels, from molecules and structure through to rheological and functional properties, with each chapter focusing on a different class of gel. There is also a final chapter covering innovative systems and applications, providing the information needed to understand current and future practical applications of gels in the pharmaceutical, agricultural, cosmetic, chemical and food industries. Many research teams are involved in the field of gels, including theoreticians, experimentalists and chemical engineers, but this interdisciplinary book collates and rationalises the many different points of view to provide a clear understanding of these complex systems for researchers and graduate students.

Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1968 with total page 1176 pages. Available in PDF, EPUB and Kindle. Book excerpt: NSA is a comprehensive collection of international nuclear science and technology literature for the period 1948 through 1976, pre-dating the prestigious INIS database, which began in 1970. NSA existed as a printed product (Volumes 1-33) initially, created by DOE's predecessor, the U.S. Atomic Energy Commission (AEC). NSA includes citations to scientific and technical reports from the AEC, the U.S. Energy Research and Development Administration and its contractors, plus other agencies and international organizations, universities, and industrial and research organizations. References to books, conference proceedings, papers, patents, dissertations, engineering drawings, and journal articles from worldwide sources are also included. Abstracts and full text are provided if available.

Download or read book On the Verge written by and published by . This book was released on 2019 with total page 249 pages. Available in PDF, EPUB and Kindle. Book excerpt: Material mechanics play a crucial role in a wide variety of scenarios and applications. Here we focused on two central material properties: stiffness and strength. Whereas stiffness characterizes the resistance to deformation for small strains, where the response remains linear, strength describes the resilience of a material to larger deformations and mechanical damage. For conventional materials strength and stiffness are readily described by established mechanical theories. However, many materials in nature, or engineering materials during processing, live in a state where stiffness and/or strength becomes so weak that classical mechanical theories no longer apply. This has been the focal point of this thesis. The exploration of such ultrasoft and/or ultraweak solids faces many challenges, some of which have been addressed in this thesis, including their structure-property relationships and the question howone characterizes these fragile materials where conventional mechanical methods are no longer viable. In chapter 2 we address the challenge of characterizing the mechanical response of solids at the verge of a mechanical instability, where classical approaches fail. We present a new method based on the propagation of infrasonic waves. These waves propagate at low Reynolds numbers, where dissipation is strong. We have not only shown an experimental approach to evaluate wave propagation properties, but also established a theoretical framework to interpret these data and extract quantitative mechanical properties with a unique resolution. In chapter 3 we detail the technical challenges associated with these measurements, performed with the help of optical tweezers to create travelling mechanical waves. When marginal networks are combined with secondary elastic matrices remarkable stiffening is observed. In chapter 4 we present a theoretical model to study the effect of bending rigidity to the mechanics in hybrid materials with simulations. We show how different mechanical regimes arise depending on the bending stiffness and the stiffness of the secondary network. Each of these regimes have different mechanisms that lead to mechanical enhancement of the composite network. Experimental access to these mechanisms is extremely challenging. In chapter 5 we take the first steps to studying these mechanisms experimentally. Here we propose a simple click-chemistry based surface modification method that can help to achieve the complex inter-particle interactions required for establishing hybrid colloidal networks. The second part of this thesis covers hyperweak solids and irreversible deformation. Chapters 6 to 8 deal with colloidal gels that are prototypical examples of hyper weak solids. In chapter 6 we address the structure to dynamics part of the structure-property relation in colloidal gels. We experimentally establish the connection between the intermittent dynamics of individual particles and their local connectivity. We interpret our experimental results with a model that describes single-particle dynamics based on highly cooperative thermal debonding. Our model is in quantitative agreement with experiments and provides a microscopic picture for the structural origin of dynamical heterogeneity and provides a new perspective of the link between structure and the complex mechanics of these heterogeneous solids. Chapter 7 focuses on the dynamics to mechanics part of the structure-property relation by studying fatigue in colloidal gels. Here we combine experiments and computer simulations to show how mechanical loading leads to irreversible strand stretching, which builds slack into the network that softens the solid at small strains and causes strain hardening at larger deformations. We thus find that microscopic plasticity governs fatigue at much larger scales. This sheds new light on fatigue in soft thermal solids and calls for new theoretical descriptions of soft gel mechanics in which local plasticity is taken into account. In chapter 8 we take first steps in investigating the overlooked role of inter-particle friction in colloidal gels. We present a colloidal system with a thermo-responsive trigger for systematically studying the effect of surface properties, grafting density and chain length, on the particle dynamics within colloidal gels. Microscopically, for colloids with a lower grafting density, we observe an increase in the thermal bond angle fluctuations of aggregated colloids. Macroscopically, we observe a clear increase of the linear elastic modulus for gels with increased grafting density and longer chain lengths. These effects are inversely proportional to the magnitude of local bond angle fluctuations. Our model system will allow for further study of the microscopic origins of the complex macroscopic mechanical behavior of hyperweak solids that include bending modes within the network. Fracture and mechanical failure are highly stochastic processes and predicting fracture is highly challenging with conventional theories but crucial to assessing the lifetimes of e.g. buildings, bridges and implants. In chapter 9 we explore new opportunities for predicting fracture in marginal fiber networks. Fracture is the ultimate form of irreversible deformation and, especially in soft materials, characterized with highly non-linear mechanics preempting the moment of failure. We show how machine learning methods can by employed to predict the critical fracture stress solely based on structural and topological input parameters. We show that neural networks, despite their black box behavior, can be used to study the physical mechanisms underlying fracture. By varying the input parameters for our fracture stress predictions we found three parameters for which we can achieve the same prediction quality as for all tested input parameters combined. In the last chapter, the general discussion, we discuss how our results relate to each other and how they fit in a broader context. Furthermore we suggest and describe experiments that can help advance our knowledge of hypersoft and hyperweak materials in the future.

Download or read book Biological Mechanisms of Tooth Movement written by Vinod Krishnan and published by John Wiley & Sons. This book was released on 2015-04-29 with total page 311 pages. Available in PDF, EPUB and Kindle. Book excerpt: Biological Mechanisms of Tooth Movement, Second Edition is an authoritative reference to the scientific foundations underpinning clinical orthodontics. Led by an expert editor team and with contributions from an international group of contributors, the book covers key topics including bone biology, the effects of mechanical loading on tissues and cells, genetics, inflammation, tissue remodeling and the effects of diet, drugs, and systemic diseases. Highly-illustrated throughout, this second edition has been fully revised, updated and expanded to new developments in genomics, rapid orthodontics and current controversies in tooth movement research. Trainees, qualified specialists and researchers in orthodontics can rely on this comprehensive text to inform them about the clinical and scientific implications of the biological mechanisms involved in the movement of teeth.