Structure of laponite-styrene precursor dispersions for production of advanced polymer-clay nanocomposites

One method for production of polymer-clay nanocomposites involves dispersal of surface-modified clay in a polymerisable monomeric solvent, followed by fast in situ polymerisation. In order to tailor the properties of the final material we aim to control the dispersion state of the clay in the precursor solvent. Here, we study dispersions of surface-modified Laponite, a synthetic clay, in styrene via large-scale Monte-Carlo simulations and experimentally, using small angle X-ray and static light scattering. By tuning the effective interaction between simulated laponite particles we are able to reproduce the experimental scattering intensity patterns for this system, with good accuracy over a wide range of length scales. However, this agreement could only be obtained by introducing a permanent electrostatic dipole moment into the plane of each Laponite particle, which we explain in terms of the distribution of substituted metal atoms within each Laponite particle. This suggests that Laponite dispersions, and perhaps other clay suspensions, should display some of the structural characteristics of dipolar fluids. Our simulated structures show aggregation regimes ranging from networks of long chains to dense clusters of Laponite particles, and we also obtain some intriguing ‘globular’ clusters, similar to capsids. We see no indication of any ‘house-of-cards’ structures. The simulation that most closely matches experimental results indicates that gel-like networks are obtained in Laponite dispersions, which however appear optically clear and non-sedimenting over extended periods of time. This suggests it could be difficult to obtain truly isotropic equilibrium dispersion as a starting point for synthesis of advanced polymer-clay nanocomposites with controlled structures

Irreversible Aging Dynamics and Generic Phase Behavior of Aqueous Suspensions of Laponite

In this work we study the aging behavior of aqueous suspension of Laponite having 2.8 weight % concentration using rheological tools. At various salt concentration all the samples demonstrate orientational order when observed using crossed polarizers. In rheological experiments we observe inherent irreversibility in the aging dynamics which forces the system not to rejuvenate to the same state in the shear melting experiment carried out at a later date since preparation. The extensive rheological experiments carried out as a function of time elapsed since preparation demonstrate the self similar trend in the aging behavior irrespective of the concentration of salt. We observe that the exploration of the low energy states as a function of aging time is only kinetically affected by the presence of salt. We estimate that the energy barrier to attain the low energy states decreases linearly with increase in the concentration of salt. The observed superposition of all the elapsed time and the salt concentration dependent data suggests that the aging that occurs in low salt concentration systems over a very long period is qualitatively similar to the aging behavior observed in systems with high salt concentration over a shorter period.Comment: 27 pages, 8 figures. Langmuir, in pres

Delayed solidification of soft glasses: New experiments, and a theoretical challenge

When subjected to large amplitude oscillatory shear stress, aqueous Laponite suspensions show an abrupt solidification transition after a long delay time tc. We measure the dependence of tc on stress amplitude, frequency, and on the age-dependent initial loss modulus. At first sight our observations appear quantitatively consistent with a simple soft-glassy rheology (SGR)-type model, in which barrier crossings by mesoscopic elements are purely strain-induced. For a given strain amplitude {\gamma}0 each element can be classified as fluid or solid according to whether its local yield strain exceeds {\gamma}0. Each cycle, the barrier heights E of yielded elements are reassigned according to a fixed prior distribution {\rho}(E): this fixes the per-cycle probability R({\gamma}0) of a fluid elements becoming solid. As the fraction of solid elements builds up, {\gamma}0 falls (at constant stress amplitude), so R({\gamma}0) increases. This positive feedback accounts for the sudden solidification after a long delay. The model thus appears to directly link macroscopic rheology with mesoscopic barrier height statistics: within its precepts, our data point towards a power law for {\rho}(E) rather than the exponential form usually assumed in SGR. However, despite this apparent success, closer investigation shows that the assumptions of the model cannot be reconciled with the extremely large strain amplitudes arising in our experiments. The quantitative explanation of delayed solidification in Laponite therefore remains an open theoretical challenge.Comment: 16 pages, 6 figures, to appear in Faraday Discussion

Is cultured meat a promising consumer alternative? Exploring key factors determining consumer's willingness to try, buy and pay a premium for cultured meat

Cultured meat is a relatively new product, enjoying consumer appreciation as a more sustainable meat option. The present study builds on a sample from a diverse set of countries and continents, including China, the US, the UK, France, Spain, Netherlands, New Zealand, Brazil, and the Dominican Republic and uses partial least square structural equation modelling. The proposed conceptual model identified key factors driving and inhibiting consumer willingness to try, buy, and pay a price premium for cultured meat. Results relate to the overall sample of 3091 respondents and two sub-sample comparisons based on gender and meat consumption behaviour. Food neophobia, having food allergies, being a locavore, and having concerns about food technology were found to be inhibiting factors towards willingness to try, buy, and pay a price premium for cultured meat. Food curiosity, meat importance, and a consumer's perception of cultured meat as a realistic alternative to regular meat were found to be important drivers that positively impacted consumers' willingness to try, buy and pay more. Best practice recommendations address issues facing marketing managers in food retail and gastronomy

Enzymatic network for production of ether amines from alcohols

We constructed an enzymatic network composed of three different enzymes for the synthesis of valuable ether amines. The enzymatic reactions are interconnected to catalyze the oxidation and subsequent transamination of the substrate and to provide cofactor recycling. This allows production of the desired ether amines from the corresponding ether alcohols with inorganic ammonium as the only additional substrate. To examine conversion, individual and overall reaction equilibria were established. Using these data, it was found that the experimentally observed conversions of up to 60% observed for reactions containing 10mM alcohol and up to 280mM ammonia corresponded well to predicted conversions. The results indicate that efficient amination can be driven by high concentrations of ammonia and may require improving enzyme robustness for scale-up. (C) 2016 Wiley Periodicals, Inc

Understanding key factors influencing consumers’ willingness to try, buy, and pay a price premium for mycoproteins

Mycoprotein is a fungal-based meat alternative sold in food retail in various countries around the world. The present study builds on a multi-national sample and uses partial least square structural equation modeling. The proposed conceptual model identified key factors that are driving and inhibiting consumer willingness to try, buy, and pay a price premium for mycoprotein. The results relate to the overall sample of 4088 respondents and to two subsample comparisons based on gender and meat consumption behavior. The results show that the biggest drivers of willingness to consume mycoprotein were healthiness, followed by nutritional benefits, safe to eat, and sustainability. Affordability and taste had mixed results. Willingness to consume mycoprotein was inhibited if nutritional importance was placed on meat and, to a lesser extent, if the taste, texture, and smell of meat were deemed important. Best practice recommendations address issues facing marketing managers in the food industry

Structure et comportement rhéologique des suspensions aqueuses de Laponite en présence de plusieurs additifs

This study deals with aqueous Laponite suspensions. The origin ofgel formation has been determined by modifying interactionsbetween particles with added salt (NaCl) or sodium pyrophosphatewhich slows down the aggregation of particles and with an adsorbedpolymer layer (PEO). Different techniques (visual observations,static and dynamic light scattering, conventional and opticalrheology) has been used to determined the structure of thesesuspensions at equilibrium and under shear. A new phase diagram atlong time which respects the equilibrium kinetics of thesuspensions from very dilute concentrations and on a large rangeof ionic strenghts has been obtained. Thus, we concluded ongelation through an aggregation process rather than avitrification by repulsion of particles of Laponite suspensions.Adsorption and kinetics of adsorption of PEO on Laponite particleswere studied for a large range of concentrations and molar massesof PEO. We concluded that adsorbed polymer layer is insufficientto completely screen electrostatic interactions and protectparticles against aggregation. Furthermore, the high molecularweight of PEO bridge several particles and lead more resistantaggregates even under shear.Ce travail est centré sur l'étude des suspensions aqueuses deLaponite à l'équilibre mécanique et sous écoulement. Le premierobjectif de cette étude a été de préciser les conditions deformation du gel, en faisant varier les interactions, au traversde la force ionique (NaCl) et de la présence de différentsadditifs comme le pyrophosphate de sodium ou des couches depolymères adsorbées (POE) qui ralentissent l'agrégation desparticules. Nous avons associé pour cela différentes techniques(observations visuelles, diffusion de lumière statique etdynamique, rhéologie classique et optique). L'origine de lagélification, la structure des suspensions de Laponite àl'équilibre et sous cisaillement en présence ou non d'additifs ontégalement été déterminées. L'étude des suspensions, couvrant unelarge gamme de forces ioniques et s'étendant dans un régime trèsdilué, nous a permis de construire un diagramme de phase à tempslong qui tient mieux compte des cinétiques d'équilibre de laLaponite et de conclure à la formation d'un gel par agrégation (etnon vitrification par répulsion des particules) dans ces systèmes.L'adsorption du POE sur les particules puis la cinétiqued'agrégation des suspensions de Laponite en présence du POE ontété étudiées pour différentes concentrations et masses molaires dePOE. Nous concluons que la couche de polymère adsorbé ne suffitpas à écranter totalement l'influence des interactionsélectrostatiques. De plus, les POE de masses molaires élevéespontent plusieurs particules de Laponite formant des agrégatstenus entre eux, même sous écoulement, par l'intermédiaire du POE