90 Colloid and Surface Science Symposium Harvard University

90th Colloid and Surface Science Symposium Harvard University June 5-8, 2016 ABSTRACTS CSSS 1 Entangled active matter: From ants to living cells Françoise Brochard-Wyart, [email protected]. Institut Curie, Paris, France We introduce the broad field of entangled active matter, a novel class of non-equilibrium materials composed of many interacting units that individually consume energy and collectively generate motion or mechanical stresses. Unlike swarms of fish and flocks of birds, both ants and cells can support static loads. This is because both cells and ants are also entangled, so that the individual units are bound by transient links. We explore and establish analogies between aggregates of both ants and cells in analogy with soft matter physics. We first describe the mechanical properties of this entangled active matter (surface tension, elastic modulus, viscosity). We use parallel-plate compression and pipette aspiration technique. Both aggregates of cells and ants exhibit a viscoelastic response. For cells, we observe aggregate reinforcement with pressure, which may results in pulsed contractions or “shivering”. We interpret this reinforcement as a mechano-sensitive active response of the acto-myosin cortex. We then describe the spreading of cellular aggregates on rigid and soft substrates, varying both intercellular and substrate adhesion. We find both partial and complete wetting, with a precursor film forming a cellular monolayer in a liquid or gas state. We show that the spreading of aggregates of ants is very similar, with a dense precursor film on water and a gas state on a solid substrate. We model the dynamics of spreading from a balance between active cellular driving forces and permeation of cells to enter into the film. On soft substrate, the precursor film is unstable, leading to a symmetry breaking and a global motion of the aggregate as a giant keratocytes. We describe the shapes of migrating aggregates, the flow and the force field responsible of the motion. We monitored the center of mass motion and we observe stick-slip. We extend our work to hybrid nanoparticles-cellular aggregates: we show that nanoparticles, within a limited size range, can be used as a glue “nanostickers” to enable the formation of self-assembled aggregates by promoting cell–cell interactions. We find that carboxylated polystyrene NPs are more efficient than the silica NPs of the same size, which were reported to induce fast wound healing and to glue soft tissue by Leibler et al. We hope that our models applied to active entangled matter will spur further investigations into ants and cells as active materials, and inspire the fabrication of synthetic analogs. CSSS 2 Estimating colloidal attachments onto fibrous substrates: From nanoparticle functionalization to pathogen detection Tanmay Bera1, [email protected], Patrick Sisco1, Hilal Goktas2,3, Aaron Bandremer3, Andrew Fong1, Sean Linder1, Karen Gleason2, Stephen Torosian3. (1) Food and Drug Administration, Orlando, Florida, United States (2) Dept. Chem Enging, MIT, Cambridge, Massachusetts, United States (3) Winchester Engineering and Analytical Center, Food and Drug Administration, Winchester, Massachusetts, United States Colloidal attachment to functional surfaces is a phenomenon that is encountered in various applications. Their correct estimation is often regarded as being critical since it is associated to the functionality and performance of the overall system. For example, the correct estimation of bacterial attachment to a biosensor surface reveals its sensitivity and detection limits. Similarly, the number (or density) of nanoparticles binding to functionalized substrates reveals the effectiveness of the functionalization process. Such colloidal attachments are usually characterized quantitatively using analytical tools such as spectroscopy, plate counts or oxidation utilization, all of which have limitations in precision. Imaging techniques such as electron microscopy are mostly used for qualitative visualization. While there have been some examples of the quantification of colloidal interactions, along with their size characterizations, done through electron microscopy, yet they have largely been restricted to planar substrates. However, non-planar substrates such as 3D fibrous matrixes are more often used as a functional surface due to their high surface area and resemblance to real-time systems such as textiles and water/air-filters. Thus an estimation technique that quantifies colloidal attachment on such systems using standard imaging tools like electron microscopy is needed. Herein, we present an estimation method that can quantify micron to nano size colloids on 3D fibrous matrices. In this method, electron microscopy images were processed using the NIH approved ImageJ platform to estimate both nanoparticle (nano size) and bacterial (micron size) attachment of functional surfaces. The method was optimized and compared with standard analytical tools to minimize errors to less than ±10 %, and was verified for 4 strains of bacteria and 4 different geometrical shaped for metal nanoparticles. Our results also indicate that selective estimation of individual bacterial species or nanoparticle types could also be possible using this method. The estimation methods also helped us to understand both specific and non-specific bacterial attachment. It further shed light on functionalization and conjugation of nanoparticles onto different substrates which ultimately helped us design a better pathogen sensor. We believe such estimation methods will also help improve other technologically relevant applications where colloidal attachments are prevalent. CSSS 3 Influence of surface roughness on colloid retention in impinging jet experiments Jacqueline A. Rasmuson, [email protected]. Geology and Geophysics, University of Utah, Salt Lake City, Utah, United States The failure of present transport models to accurately predict colloid attachment in column and field experiments is often explained by the absence of surface roughness in these models. The need to include roughness is obvious, as real collector surfaces are never as smooth as they are in a laboratory setting. However, there lacks a consensus on whether roughness serves to enhance or impede attachment under conditions favorable or unfavorable for attachment. In order to elucidate this issue, a series of impinging jet experiments were conducted for untreated (i.e. smooth glass slides) and treated (i.e. roughened glass slides) under favorable and unfavorable geochemical conditions for a range of colloid sizes (i.e. tens of nm to several µm). These experiments allowed direct observation of particle attachment, detachment, and average near- surface velocities. The results reveal that roughness can both increase and decrease particle attachment and detachment under a given set of conditions, and highlight the need to include both DLVO and hydrodynamic effects of surface roughness in future transport models. CSSS 4 Radioactivity-induced charging: Theory, measurements, and applications Yong-ha Kim1, [email protected], Sotira Yiacoumi1, Costas Tsouris1,2. (1) Georgia Institute of Technology, Atlanta, Georgia, United States (2) Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States Because radionuclides are ubiquitous on earth, it is necessary to more accurately understand radiological phenomena of radionuclides in the environment. One such radiological phenomenon is radioactivity-induced charging. Radionuclides undergo radioactive decay which results in chemical transformation of the radionuclides through emission of energetic particles, such as alpha and beta particles. Alpha and beta particles are inherently charged; thus, products generated by alpha and beta decay of radionuclides are intrinsically charged to maintain a charge balance. Energy of the emitted particles may be transferred to neighboring molecules on the trajectory of the particles. These molecules can be ionized and then captured by materials in the surrounding environment. Materials capturing ions also become charged or discharged. Since Becquerel's discovery of radioactivity, followed by the discovery of polonium and radium by P. and M. Curie, these phenomena have been extensively studied in various science and engineering fields. This study is aimed at reviewing the progress of theoretical and experimental investigations of radioactivity-induced charging, including our own recent work. Theoretical approaches reviewed in this study include charge and force balances that have been used since the mid-1950s. Charge balance equations consist of terms describing charging mechanisms, such as self and diffusion charging. Force balance equations generally include electrodynamic forces to consider radioactivity-induced charging. Various measurement techniques to quantify radioactivity-induced charge are introduced. Advantages and disadvantages of measurement techniques of radioactivity-induced charging are discussed. Application studies of radioactivity-induced charging are also examined. CSSS 5 Modeling diffusiophoresis during CO2 dissolution into aqueous suspensions Orest Shardt1, [email protected], Sangwoo Shin1, Patrick B. Warren2, Howard A. Stone1. (1) Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States (2) Unilever R&D Port Sunlight, Bebington, United Kingdom Diffusiophoresis is the motion of particles due to gradients in chemical potential. This phenomenon has

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