ARR - Annual Report

Executive Summary

groups, including carboxylates and amines, and other solvents.

crystals on the SAM surface, as well as exploration of other SAM surface functional

steps will include changing sample angle in order to increase the low number of observed

of yellow needles (YN), while methyl SAMs preferred red prisms (R). Next experimental

for selection of additional polymorphs. Besides Y, hydroxyl SAMs preferred the nucleation

surfaces. However, hydroxyl and methyl terminated SAMs showed a different tendency

that yellow crystal (Y) was the dominating polymorph on both -OH and -CH3 terminated

polymorph characterization of nucleated crystals. First experimental results demonstrated

jump at three different levels of supersaturation. Raman microscopy was applied for

solution and the nucleation was induced on the SAM surface by generating a temperature

project, control over the degree of supersaturation. SAMs were placed vertically in the

Crystallization by cooling experiments were conducted to allow, for the first time in this

[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) in toluene as solvent.

groups (-OH and -CH3) as nucleating surfaces for the organic model system 5-methyl-2-

based self-assembled monolayers (SAMs) with different terminal (omega) functional

number of industries. This project has moved to the formation of alkane-thiols on gold

as well as inorganic compounds are scientifically and technologically important to a

Understanding and control of crystallographic polymorphism and crystal habit of organic

EXECUTIVE SUMMARY

2 conditions for the first time, and address the main Aims.

Rheology (I). This will allow us to separately determine constitutive parameters and boundary data of the type collected here, we will soon be fully able to calculate the fluidity g(r) and the elucidate the nontrivial connection between these observations, which so far is confounding. Using techniques, are similarly affected by the roughness and compliance of the wall. Future work will of the flow, allowing us to observe that the pressure P and shear stress, measured by photoelastic of the flow most sensitive to nonlocal effects. Photoelastic techniques provide us full stress profile v(r) and shear rate profile _ (r), particularly as measured at the outer wall. This is also the region boundaries. We have observed that boundary roughness strongly controls both the flow profile both particle-dynamics and stress fields under controlled conditions for six different-roughness.

As Year 5 comes to a close, we have used fully-developed experimental protocols to measure properties.

On separating which flow properties are set by the particle properties, versus those set by the wall and (2) use these parameters to predict flows in other geometries. Thus, our current work focuses can we (1) make flow measurements in one geometry which determine the constitutive parameters and apply NLR to real granular systems. We aim to establish that, for a given set of particles, in Years 4-6 of this project, we aim to address current shortcomings in how to calibrate (A; b; s), but that we must know the amount of slip at the wall from geometry-dependent measurements.

Packing densities, particle sizes and shapes, and shear rates, using just 3 constitutive properties. In Years 1-3, we established that NLR successfully models granular flows across different both the particle properties, and the boundary conditions at the walls. The same particles). Doing this requires a quantitative understanding of which properties are set by and then determine the constitutive parameters for use in predicting flows in other geometries (for to be useful, the aim is to make a set of flow measurements for a set of particles in one geometry, large range of intermittent, creeping, quasi-static, and intermediate flows. In order for these models for a particular set of particles, which then can be used to predict flow fields and stresses over a models hold the promise of permitting the determination of a small number of empirical parameters been the development of various nonlocal rheologies [2, 4, 5, 11, 13, 15, 25]. These constitutive.

In the field of granular rheology, one of the most promising advances of the past decade has.

also presented into this report particularly in Annex 2.

scheduled as telecommuting was possible for these deliverables. Therefore, the first results of year 3 are

During the lockdown, the third year of the PhD work about modeling was started earlier than

reconstitution conditions in agitated vessels.

(3) Definition of a reconstitutability index reflecting powder reconstitution behavior independently from

(2) Empirical models able to predict reconstitution times from powder physicochemical characteristics;

(1) Fitting of reconstitution kinetics followed by granulometric;

Deliverables of year 3 ((January 2021 – January 2022)

message in Figure 1).

wetting) and sugar nature, location, quantity, coating depth were thoroughly investigated (see take-home

transition temperature, hydrophilicity…Links between powder reconstitutability (more particularly

chosen to cover a whole range of physicochemical properties: solubility, chain length, structure, glass

agreement with IFPRI partners, five sugars (i.e. sucrose, lactose, glucose, fructose, and galactose) were

presenting a low wetting ability (i.e. whey protein powder) and coating was achieved with sugars. In

progress due to the lockdown caused by the CoViD-19 health crisis. The work was focused on a powder

The second year of the PhD work should meet these two stated deliverables which are still in

surface, minimal quantity necessary to improve wetting. etc.).

(2) Determine the effect of surface modifiers (quantities to cover the surface, distribution at the particle

reconstitutability.

(1) Surface chemical mapping and nanoindentation to establish correlations with powder

Deliverables of year 2 (January 2020 – January 2021)

related to year 1 deliverables (Annex 1).

Papers I and II, respectively submitted to Powder Technology and Journal of Food Engineering, are

ranking.

(3) First statistical correlations between the various powder characteristics and their reconstituability

(2) For selected powders: reconstitution kinetics in different conditions of temperature, stirring, etc.,

(1) Powder classification according to their reconstitution behavior,

2020 with the following deliverables:

and their classification according to their reconstitution ability. It was achieved at the end of January

The first year of the PhD work dealt with the systemic physicochemical analysis of powders

(PhD duration: 1st February 2019 –31th January 2022)

Executive summary until October 2020 – year 2

Executive Summary

detailed flow, and motivate further refinement in our modelling efforts.

experimental screw feeder assembly to test our model predictions, provide insight into the

constitutive model for the stress that accounts for dilatancy. We have recently built an

request of several IFPRI members at the GBM. For this, we are implementing a non-local

fluctuations in the inlet flow or spontaneous fluctuations within the screw – this was the

Our ongoing work is to model dynamical changes in the feed rate, due to

of gravity and friction at the screw surface.

volumetric discharge rate on the geometry of the feeder is not altered by the introduction

value of p/d at which the feed rate is maximum. Thus, the qualitative dependence of the

find that the discharge rate exhibits the same qualitative trend, in that there is an optimum

conditions of no friction at the screw surface and no gravity, employed in the model. We

frictionless screw in the absence of gravity. We then assess the effect of relaxing the

model to be in excellent agreement with the results of the DEM simulations for a

motion, in agreement with the assumption of the model. We find the prediction of the

simulations show that a significant fraction of the material does indeed exhibit solid body

by particle dynamics simulations using the discrete element method (DEM). Our

We then studied the detailed flow within the screw feeder for non-cohesive particles

yields a non-trivial result that could be useful in the design of screw feeders.

to a specific value. Thus, despite the assumptions that simplify the analysis, the model

discharge can be maximized by setting the ratio of the screw pitch p to barrel diameter d

the discharge rate for a given angular velocity and screw geometry. We show that the

and barrel, and neglecting the effects of gravity and friction on the screw surface, we obtain

that the granular medium moves as a rigid body that slips along the surfaces of the screw

and angular momentum on a suitably chosen continuum element. With the assumptions

We first constructed a mechanics-based model by enforcing the balances of linear

flow in a twin-screw feeder.

we have studied powder flow in a single-screw feeder, as the first step towards modelling

model. Such a model would assist in optimal design of screw feeders. In this investigation,

particulate materials, there has been no attempt to derive a detailed, mechanics-based

Despite the widespread use of screw feeders in industry for the transport of

In 2019, we started to investigate the microstructure and shear properties of capillary suspensions using confocal microscopy and rheology. The chosen model system was an index-matched mixture of Hexamoll DINCH/dodecane (oily bulk phase), aqueous glycerol (watery secondary liquid) and silica particles (Kromasil 100-7-SIL, average radius 3.21 m). Confocal measurements were performed on a Leica TCS SP8 inverted confocal microscope equipped with a linear shear cell (RheOptiCAD). Rheological measurements were performed on a stress-controlled MCR702 rheometer using an 8 mm parallel plate geometry. For the analysis of the confocal image stacks, a particle detection program based on Canny edge detection and Hough transform was written in IDL, which has an improved detection accuracy for concentrated and polydisperse suspensions compared to the classical Crocker and Grier algorithm [13].

The rst experiments were designed to examine the in uence of compression and shear on the microstructure of capillary suspensions with varying solid volume fraction, while keeping the relative ratio of secondary liquid and particles constant. The confocal microscopy study revealed an increase in coordination number with increasing particle volume fraction, compression, and shear. The clustering coe - cient only exhibited only slight variation. The increase in coordination number was also re ected in a higher storage modulus for higher solid volume fraction samples. By compressing capillary suspensions in the shear cell and the rheometer, it appeared that a transition in the relative cluster compaction could be observed around an e ective solid volume of 30 % to 35 %. The increase in coordination number was signi cantly higher after compression for samples above this boundary and a normal force was measured on the rheometer when going to the gap.

Figure 1: Close-up micrographs of porous Kromasil particles wetted by a) lms and b) patches of secondary liquid might suggest a critical volume fraction determining the change from a oppy to a rigid network. In the work of Domenech and Velankar [18], a change towards a more heterogeneous microstructure was reported around a similar solid volume fraction. However, the change in structure did not a ect the scaling of the elastic modulus or yield stress in their study.

While the transition between a oppy and rigid network appears to be compelling, the porosity of the Kromasil particles induced large variations in the wetting behaviour. Porous particles were chosen due to the need for fully-dyed spheres in the Crocker-Grier-based particle detection program. After dyeing the particles, their porosity was reduced using a modi ed St ober synthesis to prevent secondary liquid imbibition in the pores. The poor reproducibility of this procedure was the reason for a multitude of observed bridge shapes, as shown in Figure 1. The desired toroidal bridge shape was not observed for the prepared capillary suspensions, which predominantly showed the liquid lm behaviour of Figure 1a. Hence, these experiments were repeated in 2020 using non-porous particles showing toroidal bridges, shown on Figure 2, which was now possible due to the new particle detection program.

Key updates

I was not able to recruit a dedicated PhD student, hence we are now on gap year. This issue was addressed in January 2020 and a PhD student Vishal Shinde was recruited. He graduated from Leicester in 2018 with an MSC with Distinction. He is expected to start in 2-3 months time after getting his visa.

Complementary to the project, I will be hosting a visiting PhD student from China (Ruochen Sun) from September 2020 for a period of 1 year, subject to approval of his China Scholarship Council application for funding. He will perform molecular dynamics simulations to analyse the interaction of mannitol and ibuprofen with iron. This is not related to the IFPRI project, but it could provide relevant insight.

A detailed planning for the following year will be prepared 1 month after the start of the PhD project. Also, I am planning an open workshop with participation of all academics and industrialists who are actively researching the problem of sticking at the present time of who have recently completed projects. This workshop will be planned 2-3 months after the start of the PhD project.

Proof of Concept

Reference: Sebastian Bindgen, Frank Bossler and Erin Koos “Defining structural transitions in capil- lary suspensions” Manuscript in Progress.

The structural properties of multiphase systems are essential to overall processability, functionality and acceptance among consumers. Therefore, it is crucial to understand the intrinsic connection between the microstructure of a material and the resulting rheological properties. Here, we demon- strate, how the transitions in the microstructural confirmations can be quantified and correlated to rheological measurements. We find methods from graph theory and thus from the mathematical study of networks, especially the clustering coefficient, to be a useful addition in accomplishing a link be- tween these two characterization methods. Our results, using capillary suspensions as a model system, show that the use of the clustering coefficient, in combination with the coordination number, is able to capture not only the agglomeration of particles, but also measures the formation of groups.

industry.

experimental results, and used to inform a `best practice' for the application of DEM in

number of benchmark systems are assessed and compared both to one another and to

(DEM) modelling to participate in a `round robin' in which their attempts to model a

This project brings together a cohort of companies who utilise discrete element method

1. Brief Summary of Project

Introduction to the Project

Executive Summary

For the year of 2019, an in-depth investigation was carried out into microstructural filter cake analysis. As planned comprehensive research involving of laboratory, modelling and simulation approaches were applied to characterize the filter cakes precisely. This was done for the case of hydrophobic and hydrophilic particles, forming hydrophobic and hydrophilic filter cakes.

As applying the commercial software approach for micro-CT analysis for filter cakes, we were limited due to the predefined functionality. To implement a plug and play analysis was not satisfying us to trust the output data fully. For this reason, we validate the filter cake characteristics based on four methods. One method is the laboratory approach in which filtrations were carried out in a standard VDI nutsch filter to measure pore size distribution, porosity and capillary pressure curves. In parallel CT scans of the same filter cakes were done to study cake characteristics based on the 3D reconstructed volumes by modelling and simulation. This is the imaging analysis approach, which itself is divided into three approaches.

The first image-based approach uses commercially available software only. In our case the software VGSTUDIO MAX 3.3 (subsequently called VGSTUDIO) was used. This method is very fast but the results deviate significantly from the laboratory data. The second image-based approach uses customized algorithms applied on the raw images. This approach is called customized code within this report. Using customized code showed good agreement with laboratory data. Nevertheless, this approach is time-consuming and requires advanced knowledge in image analysis and programming. The third method is to generate a pore network of the filter cake using laboratory data such as pore size distributions. Based on the generated pore network, simulations can be run to make prediction on e.g. desaturation of the filter cake (pore network modelling). For pore network modelling the open-source tool open PNM was used. The methodology and validation of each method is discussed in the report.

Executive Summary

In our second phase of the project (year two) we build upon the serendipitous finding made in phase one (year one): The significance of the new Pèclet number Pe = γ˙ d/√T  extends beyond simply quantifying the relative importance of advection to diffusion,  Akin to the definition of the Inertial number (I) and viscous number (Iv), Pe also represents the ratio of microscopic kinetic rearrangement timescale d/√T to the macroscopic shearing timescale (1/γ˙ ).  Consequently, kinetic rearrangement—the fundamental driver of mixing—to the definition of the Inertial number (I) and viscous number (Iv), Pe also represents the ratio of microscopic kinetic rearrangement timescale d/√T to the macroscopic shearing is now controlled by the actual relative motion between particles, as opposed to assuming that the microscopic motion (so-called particle fall) is driven by pressure.

So building the new Pèclet-based rheology into a macroscopic-level process model of the rotating drum flow, could yield after suitable scaling, a dimensionless number that fully characterises the local mixing state of the granular assembly. And in terms of the IF- PRI project, the dimensionless number should facilitate robust scaling of the mixing state between different operating conditions.

However, before building the process model and dimensionless number upon a possible “house of cards” we embarked on an extensive testing process of the Pèclet-based rheology via simulation. Within the context of the DEM simulation framework, we treat the DEM outputs as “data” and apply coarse graining to yield the continuum-level stress and strain fields. Using > 200 simulation configurations spanning dry, wet, dense and dilute granular flows, we show that the Mohr-Coulomb friction coefficient µ = τ /σ, where τ is the shear stress and σ the pressure, varies linearly with √Pe for a variable yield stress ratio µs consistent with the different geometric configurations and flow regimes investigated.

µ = cµ√Pe,                                                              (1)

where the scaling parameter cµ is dependent on driving conditions, and hence the material contact friction coefficient µc.

The linear collapse of the data according to equation (1) spanned a wider range of the phase space than the µ (I)-rheology, viscoinertial rheology, non-local rheology and extended kinetic theory. We argue that cµ partly encodes the anisotropy of the tangential contact force network, and equation (1) relates this structure anisotropy to the stress ratio. Noting that these anisotropies are also signatures of the granular mixture state, we hypothesise that the most robust mixing rules will emerge from encoding the new Pèclet-based rheology into the formulation of the mixing rules.